add: go back button in rankings

.dockerignore

@@ -0,0 +1,4 @@
+.DS_Store
+.git
+.runtime
+node_modules

.gitignore

@@ -1,2 +1,3 @@
 .DS_Store
 node_modules/
+.runtime/

Dockerfile

@@ -0,0 +1,15 @@
+FROM node:22-bookworm-slim
+
+WORKDIR /app
+
+COPY package.json package-lock.json ./
+RUN npm ci --omit=dev
+
+COPY . .
+
+ENV HOST=0.0.0.0
+ENV PORT=80
+
+EXPOSE 80
+
+CMD ["npm", "start"]

README.md

@@ -2,7 +2,7 @@
 
 Static photo gallery for logging meals and food memories.
 
-The site is based on the HTML5 UP Lens template and currently ships as a plain static site: HTML, CSS, JavaScript, and local image assets.
+The site is based on the HTML5 UP Lens template. The front-end remains a mostly static HTML/CSS/JavaScript site, and the local Node server now also exposes a tiny rankings sync API for shared Elo persistence.
 
 ## Repo Layout
 
@@ -19,8 +19,9 @@ The site is based on the HTML5 UP Lens template and currently ships as a plain s
 - `scripts/check.js`: validates data, image assets, and generated pages
 - `scripts/generate-thumbnails.js`: regenerates thumbnails from the full-size images
 - `scripts/ingest-meal.js`: ingests a new meal image and metadata in one command
-- `scripts/serve.js`: serves the generated site locally with a small static file server
+- `scripts/serve.js`: serves the generated site and the rankings sync API
 - `scripts/lib/elo.js`: validates and syncs Elo data against the meal list
+- `scripts/lib/rankings-state.js`: normalizes and persists the shared rankings state
 - `package.json`: minimal Node build entrypoint
 
 ## Run Locally
@@ -45,6 +46,9 @@ npm run serve
 
 Then open `http://127.0.0.1:4321`.
 
+By default, rankings sync state is written to `.runtime/rankings-state.json`.
+Override that path with `RANKINGS_STATE_PATH=/absolute/path/to/rankings-state.json`.
+
 If you want a single command that builds and serves, run:
 
 ```sh
@@ -97,9 +101,58 @@ npm run build:thumbs:force
 `data/elo.json` stores the seed rating, Elo `kFactor`, and a win-loss record for each meal.
 The page build keeps this file aligned with `data/meals.json`, so new meals automatically appear in `rankings.html` with the default seed rating.
 
-The interactive voting flow on `rankings.html` uses browser `localStorage` for persistence.
+The interactive voting flow on `rankings.html` now prefers the same-origin API exposed by `scripts/serve.js`:
-That means Elo votes persist across reloads on the same browser and device, but they do not sync automatically across devices.
+
-Use the reset button on the rankings page if you want to clear the local vote history and go back to the seeded board.
+- `GET /api/rankings`: load the shared rankings state
+- `POST /api/rankings/vote`: apply one head-to-head result on the server
+- `POST /api/rankings/reset`: reset the shared board back to the seeded state
+
+The server persists the shared board to `.runtime/rankings-state.json` by default, or to `RANKINGS_STATE_PATH` if you set it.
+That makes rankings persist across reloads, sessions, browsers, and devices as long as they are hitting the same deployed site.
+
+If the API is unavailable, the page falls back to browser `localStorage`.
+In that fallback mode, votes still persist across reloads in the same browser profile, but they do not sync across browsers or devices.
+Use the reset button on the rankings page if you want to clear the current saved board and go back to the seeded state.
+
+## Deployment Notes
+
+For Docker/VPS deployment, mount a persistent volume and point `RANKINGS_STATE_PATH` at it so rankings survive container rebuilds and restarts.
+
+Example:
+
+```sh
+RANKINGS_STATE_PATH=/data/rankings-state.json npm start
+```
+
+In a containerized setup, mount `/data` as a named volume or bind mount.
+If you reverse-proxy the app through Caddy on the same domain, the rankings page will use the shared API automatically with no extra CORS setup.
+
+The current server deployment lives one directory up from this repo in `~/docker/websites/docker-compose.yml` and uses this `gallery` service definition:
+
+```yaml
+services:
+  gallery:
+    build:
+      context: ./gallery-src
+    container_name: gallery
+    environment:
+      HOST: 0.0.0.0
+      PORT: 80
+      RANKINGS_STATE_PATH: /data/rankings-state.json
+    volumes:
+      - gallery-rankings:/data
+    restart: unless-stopped
+    networks:
+      - web
+
+networks:
+  web:
+    external: true
+    name: web
+
+volumes:
+  gallery-rankings:
+```
 
 ## Image Conventions
 
@@ -131,7 +184,3 @@ For images that should crop away from the center, add optional thumbnail focus m
 ```
 
 The `x` and `y` values are normalized from `0` to `1`, where `0.5, 0.5` is the center of the image.
-
-## Planned Features
-
-1. Optional shared sync or export/import for rankings if browser-local persistence becomes too limiting.

assets/js/rankings.js

@@ -3,6 +3,10 @@
   const STORAGE_TEST_KEY = `${STORAGE_KEY}.probe`;
   const STATE_VERSION = 1;
   const CLOSE_MATCH_COUNT = 6;
+  const REMOTE_RANKINGS_URL = "/api/rankings";
+  const REMOTE_RANKINGS_VOTE_URL = "/api/rankings/vote";
+  const REMOTE_RANKINGS_RESET_URL = "/api/rankings/reset";
+  const REMOTE_RANKINGS_UNDO_URL = "/api/rankings/undo";
 
   function $(id) {
     return document.getElementById(id);
@@ -30,6 +34,10 @@
     return [leftId, rightId].sort().join(":");
   }
 
+  function isValidMealId(id) {
+    return typeof id === "string" && /^\d+$/.test(id);
+  }
+
   function createDefaultEntry(id, defaultRating) {
     return {
       id,
@@ -72,7 +80,24 @@
     return seedData;
   }
 
-  function createPersistence() {
+  async function requestJson(url, options) {
+    const response = await fetch(url, {
+      cache: "no-store",
+      headers: {
+        Accept: "application/json",
+        ...(options && options.body ? { "Content-Type": "application/json" } : {}),
+      },
+      ...options,
+    });
+
+    if (!response.ok) {
+      throw new Error(`Request failed with status ${response.status}`);
+    }
+
+    return response.json();
+  }
+
+  function createLocalPersistence() {
     let available = false;
 
     try {
@@ -124,6 +149,155 @@
     };
   }
 
+  function createPersistence() {
+    const local = createLocalPersistence();
+    let mode = "memory";
+    let pendingNotice = null;
+
+    function setMode(nextMode, nextNotice) {
+      if (mode !== nextMode && nextNotice) {
+        pendingNotice = nextNotice;
+      }
+
+      mode = nextMode;
+    }
+
+    function getFallbackMode() {
+      return local.available ? "local" : "memory";
+    }
+
+    return {
+      get mode() {
+        return mode;
+      },
+      async load(seedData) {
+        if (typeof fetch === "function") {
+          try {
+            const remoteState = await requestJson(REMOTE_RANKINGS_URL, { method: "GET" });
+
+            setMode("server");
+
+            return syncStoredState(seedData, remoteState);
+          } catch (error) {
+            setMode(getFallbackMode());
+          }
+        } else {
+          setMode(getFallbackMode());
+        }
+
+        return syncStoredState(seedData, local.load());
+      },
+      async save(state) {
+        if (mode === "local") {
+          local.save(state);
+        }
+
+        return state;
+      },
+      async submitVote(seedData, state, winnerId, loserId, pairKey, leftId, rightId) {
+        if (mode === "server" && typeof fetch === "function") {
+          try {
+            const remoteState = await requestJson(REMOTE_RANKINGS_VOTE_URL, {
+              method: "POST",
+              body: JSON.stringify({
+                winnerId,
+                loserId,
+                pairKey,
+                leftId,
+                rightId,
+              }),
+            });
+
+            return syncStoredState(seedData, remoteState);
+          } catch (error) {
+            setMode(
+              getFallbackMode(),
+              local.available
+                ? "Server sync failed, so votes are now saved only in this browser."
+                : "Server sync failed, so votes will reset when you reload."
+            );
+          }
+        }
+
+        const nextState = applyVote(
+          seedData,
+          state,
+          winnerId,
+          loserId,
+          pairKey,
+          leftId,
+          rightId
+        );
+
+        if (mode === "local") {
+          local.save(nextState);
+        }
+
+        return nextState;
+      },
+      async undo(seedData, state) {
+        if (mode === "server" && typeof fetch === "function") {
+          try {
+            const remoteState = await requestJson(REMOTE_RANKINGS_UNDO_URL, {
+              method: "POST",
+            });
+
+            return syncStoredState(seedData, remoteState);
+          } catch (error) {
+            setMode(
+              getFallbackMode(),
+              local.available
+                ? "Server sync failed, so go back now applies only in this browser."
+                : "Server sync failed, so go back lasts only until you reload."
+            );
+          }
+        }
+
+        const nextState = undoLastVote(seedData, state);
+
+        if (mode === "local") {
+          local.save(nextState);
+        }
+
+        return nextState;
+      },
+      async reset(seedData) {
+        if (mode === "server" && typeof fetch === "function") {
+          try {
+            const remoteState = await requestJson(REMOTE_RANKINGS_RESET_URL, {
+              method: "POST",
+            });
+
+            return syncStoredState(seedData, remoteState);
+          } catch (error) {
+            setMode(
+              getFallbackMode(),
+              local.available
+                ? "Server sync failed, so resets now apply only in this browser."
+                : "Server sync failed, so resets last only until you reload."
+            );
+          }
+        }
+
+        const nextState = createSeedState(seedData);
+
+        if (mode === "local") {
+          local.clear();
+          local.save(nextState);
+        }
+
+        return nextState;
+      },
+      consumeNotice() {
+        const notice = pendingNotice;
+
+        pendingNotice = null;
+
+        return notice;
+      },
+    };
+  }
+
   function isValidStoredEntry(entry) {
     if (!entry || typeof entry !== "object" || Array.isArray(entry)) {
       return false;
@@ -148,6 +322,7 @@
       voteCount: 0,
       lastPairKey: null,
       updatedAt: null,
+      undo: null,
       elo: {
         defaultRating: seedData.elo.defaultRating,
         kFactor: seedData.elo.kFactor,
@@ -162,7 +337,7 @@
     };
   }
 
-  function syncStoredState(seedData, storedState) {
+  function syncStateCore(seedData, storedState) {
     if (!storedState || typeof storedState !== "object" || Array.isArray(storedState)) {
       return createSeedState(seedData);
     }
@@ -194,6 +369,7 @@
           : derivedVoteCount,
       lastPairKey: typeof storedState.lastPairKey === "string" ? storedState.lastPairKey : null,
       updatedAt: typeof storedState.updatedAt === "string" ? storedState.updatedAt : null,
+      undo: null,
       elo: {
         defaultRating: seedData.elo.defaultRating,
         kFactor: seedData.elo.kFactor,
@@ -202,6 +378,89 @@
     };
   }
 
+  function createUndoSnapshot(state) {
+    return {
+      voteCount: state.voteCount,
+      lastPairKey: state.lastPairKey,
+      updatedAt: state.updatedAt,
+      elo: {
+        defaultRating: state.elo.defaultRating,
+        kFactor: state.elo.kFactor,
+        entries: state.elo.entries.map(cloneEntry),
+      },
+    };
+  }
+
+  function resolveUndoPairIds(winnerId, loserId, leftId, rightId) {
+    const validPair =
+      isValidMealId(leftId) &&
+      isValidMealId(rightId) &&
+      leftId !== rightId &&
+      [leftId, rightId].includes(winnerId) &&
+      [leftId, rightId].includes(loserId);
+
+    if (validPair) {
+      return { leftId, rightId };
+    }
+
+    return { leftId: winnerId, rightId: loserId };
+  }
+
+  function syncUndo(seedData, storedUndo) {
+    if (!storedUndo || typeof storedUndo !== "object" || Array.isArray(storedUndo)) {
+      return null;
+    }
+
+    const { leftId, rightId, winnerId, loserId, snapshot } = storedUndo;
+
+    if (
+      !isValidMealId(leftId) ||
+      !isValidMealId(rightId) ||
+      !isValidMealId(winnerId) ||
+      !isValidMealId(loserId) ||
+      leftId === rightId ||
+      winnerId === loserId
+    ) {
+      return null;
+    }
+
+    const pairIds = new Set([leftId, rightId]);
+    const mealIds = new Set(seedData.meals.map((meal) => meal.id));
+
+    if (
+      !pairIds.has(winnerId) ||
+      !pairIds.has(loserId) ||
+      ![leftId, rightId, winnerId, loserId].every((id) => mealIds.has(id))
+    ) {
+      return null;
+    }
+
+    return {
+      pairKey: createPairKey(leftId, rightId),
+      leftId,
+      rightId,
+      winnerId,
+      loserId,
+      snapshot: createUndoSnapshot(syncStateCore(seedData, snapshot)),
+    };
+  }
+
+  function syncStoredState(seedData, storedState) {
+    const nextState = syncStateCore(seedData, storedState);
+
+    return {
+      ...nextState,
+      undo: syncUndo(seedData, storedState?.undo),
+    };
+  }
+
+  function restoreUndoSnapshot(seedData, snapshot) {
+    return {
+      ...syncStateCore(seedData, snapshot),
+      undo: null,
+    };
+  }
+
   function compareRankedMeals(left, right) {
     const leftMatches = left.wins + left.losses;
     const rightMatches = right.wins + right.losses;
@@ -252,12 +511,17 @@
     return 1 / (1 + Math.pow(10, (opponentRating - rating) / 400));
   }
 
-  function applyVote(seedData, state, winnerId, loserId, pairKey) {
+  function applyVote(seedData, state, winnerId, loserId, pairKey, leftId, rightId) {
     const entryById = new Map(
       state.elo.entries.map((entry) => [entry.id, cloneEntry(entry)])
     );
     const winner = entryById.get(winnerId);
     const loser = entryById.get(loserId);
+    const undoPair = resolveUndoPairIds(winnerId, loserId, leftId, rightId);
+    const resolvedPairKey =
+      typeof pairKey === "string" && pairKey.length > 0
+        ? pairKey
+        : createPairKey(undoPair.leftId, undoPair.rightId);
 
     if (!winner || !loser) {
       return state;
@@ -274,8 +538,16 @@
     return {
       ...state,
       voteCount: state.voteCount + 1,
-      lastPairKey: pairKey,
+      lastPairKey: resolvedPairKey,
       updatedAt: new Date().toISOString(),
+      undo: {
+        pairKey: createPairKey(undoPair.leftId, undoPair.rightId),
+        leftId: undoPair.leftId,
+        rightId: undoPair.rightId,
+        winnerId,
+        loserId,
+        snapshot: createUndoSnapshot(state),
+      },
       elo: {
         ...state.elo,
         entries: seedData.meals.map((meal) => entryById.get(meal.id)),
@@ -283,6 +555,14 @@
     };
   }
 
+  function undoLastVote(seedData, state) {
+    if (!state.undo) {
+      return state;
+    }
+
+    return restoreUndoSnapshot(seedData, state.undo.snapshot);
+  }
+
   function choosePair(rankedMeals, avoidedPairKeys) {
     if (rankedMeals.length < 2) {
       return null;
@@ -333,9 +613,11 @@
     };
   }
 
-  function renderDuelCard(meal, sideLabel) {
+  function renderDuelCard(meal, sideLabel, disabled) {
+    const disabledAttributes = disabled ? ' disabled aria-disabled="true"' : "";
+
     return `<article class="duel-card">
-      <button class="duel-card__button" type="button" data-meal-id="${meal.id}">
+      <button class="duel-card__button" type="button" data-meal-id="${meal.id}"${disabledAttributes}>
         <div class="duel-card__media">
           <img src="images/fulls/${meal.id}.jpg" alt="${escapeHtml(`${meal.title} photo`)}" />
         </div>
@@ -368,22 +650,30 @@
   function getSummaryText(seedData, state, persistence) {
     const voteText = `${state.voteCount} ${pluralize(state.voteCount, "vote", "votes")}`;
 
-    if (persistence.available) {
+    if (persistence.mode === "server") {
-      return `${seedData.meals.length} meals ranked. ${voteText} saved in this browser.`;
+      return `${seedData.meals.length} meals ranked. ${voteText} saved on the server.`;
+    }
+
+    if (persistence.mode === "local") {
+      return `${seedData.meals.length} meals ranked. ${voteText} saved only in this browser.`;
     }
 
     return `${seedData.meals.length} meals ranked. ${voteText} active for this session only.`;
   }
 
   function getStatusText(persistence) {
-    if (persistence.available) {
+    if (persistence.mode === "server") {
-      return "Votes are saved in this browser on this device.";
+      return "Votes are saved on the server and shared across browsers.";
+    }
+
+    if (persistence.mode === "local") {
+      return "Server sync is unavailable, so votes are saved only in this browser.";
     }
 
     return "Browser storage is unavailable, so votes reset when you reload.";
   }
 
-  function init() {
+  async function init() {
     let seedData;
 
     try {
@@ -400,6 +690,7 @@
       voteStatus: $("vote-status"),
       voteMessage: $("vote-message"),
       skipPair: $("skip-pair"),
+      undoVote: $("undo-vote"),
       resetRankings: $("reset-rankings"),
     };
 
@@ -410,20 +701,40 @@
       !elements.voteStatus ||
       !elements.voteMessage ||
       !elements.skipPair ||
+      !elements.undoVote ||
       !elements.resetRankings
     ) {
       return;
     }
 
+    elements.voteMessage.textContent = "Loading saved rankings...";
+
     const persistence = createPersistence();
-    let state = syncStoredState(seedData, persistence.load());
+    const mealById = new Map(seedData.meals.map((meal) => [meal.id, meal]));
+    let state = await persistence.load(seedData);
     let currentPair = null;
     let currentPairKey = null;
+    let pendingPairIds = null;
     let lastMessage = "Choose the better meal to start ranking.";
+    let busy = false;
 
-    persistence.save(state);
+    await persistence.save(state);
 
     function queueNextPair(rankedMeals) {
+      if (pendingPairIds) {
+        const rankedMealById = new Map(rankedMeals.map((meal) => [meal.id, meal]));
+        const left = rankedMealById.get(pendingPairIds.leftId);
+        const right = rankedMealById.get(pendingPairIds.rightId);
+
+        pendingPairIds = null;
+
+        if (left && right && left.id !== right.id) {
+          currentPair = { left, right };
+          currentPairKey = createPairKey(left.id, right.id);
+          return;
+        }
+      }
+
       currentPair = choosePair(rankedMeals, [currentPairKey, state.lastPairKey]);
       currentPairKey = currentPair
         ? createPairKey(currentPair.left.id, currentPair.right.id)
@@ -448,6 +759,8 @@
       elements.voteStatus.textContent = getStatusText(persistence);
       elements.voteMessage.textContent = lastMessage;
       elements.rankingSummary.textContent = getSummaryText(seedData, state, persistence);
+      elements.undoVote.disabled = busy || !state.undo;
+      elements.resetRankings.disabled = busy;
       elements.rankings.innerHTML = rankedMeals
         .map((meal, index) => renderRankingCard(meal, index + 1))
         .join("");
@@ -459,15 +772,15 @@
         return;
       }
 
-      elements.skipPair.disabled = false;
+      elements.skipPair.disabled = busy;
       elements.duelCards.innerHTML = [
-        renderDuelCard(currentPair.left, "Left Pick"),
+        renderDuelCard(currentPair.left, "Left Pick", busy),
-        renderDuelCard(currentPair.right, "Right Pick"),
+        renderDuelCard(currentPair.right, "Right Pick", busy),
       ].join("");
     }
 
-    function handleVote(winnerId) {
+    async function handleVote(winnerId) {
-      if (!currentPair) {
+      if (!currentPair || busy) {
         return;
       }
 
@@ -476,44 +789,132 @@
         currentPair.left.id === winnerId ? currentPair.left.title : currentPair.right.title;
       const loserTitle =
         currentPair.left.id === winnerId ? currentPair.right.title : currentPair.left.title;
+      let nextMessage = `Picked ${winnerTitle} over ${loserTitle}.`;
 
-      state = applyVote(seedData, state, winnerId, loserId, currentPairKey);
+      busy = true;
-      persistence.save(state);
+      render(`Saving ${winnerTitle} over ${loserTitle}...`);
-      currentPair = null;
+
-      render(`Picked ${winnerTitle} over ${loserTitle}.`);
+      try {
+        state = await persistence.submitVote(
+          seedData,
+          state,
+          winnerId,
+          loserId,
+          currentPairKey,
+          currentPair.left.id,
+          currentPair.right.id
+        );
+        currentPair = null;
+
+        const notice = persistence.consumeNotice();
+
+        if (notice) {
+          nextMessage = `${nextMessage} ${notice}`;
+        }
+      } catch (error) {
+        console.error(error);
+        nextMessage = "Failed to save that vote.";
+      } finally {
+        busy = false;
+        render(nextMessage);
+      }
     }
 
-    elements.duelCards.addEventListener("click", (event) => {
+    async function handleUndo() {
+      if (!state.undo || busy) {
+        return;
+      }
+
+      const undoInfo = state.undo;
+      const winnerTitle = mealById.get(undoInfo.winnerId)?.title || "that meal";
+      const loserTitle = mealById.get(undoInfo.loserId)?.title || "the other meal";
+      let nextMessage = `Went back before ${winnerTitle} over ${loserTitle}. Pick again.`;
+
+      busy = true;
+      render(`Going back before ${winnerTitle} over ${loserTitle}...`);
+
+      try {
+        state = await persistence.undo(seedData, state);
+        currentPair = null;
+        currentPairKey = null;
+        pendingPairIds = {
+          leftId: undoInfo.leftId,
+          rightId: undoInfo.rightId,
+        };
+
+        const notice = persistence.consumeNotice();
+
+        if (notice) {
+          nextMessage = `${nextMessage} ${notice}`;
+        }
+      } catch (error) {
+        console.error(error);
+        nextMessage = "Failed to go back to the previous vote.";
+      } finally {
+        busy = false;
+        render(nextMessage);
+      }
+    }
+
+    elements.duelCards.addEventListener("click", async (event) => {
       const button = event.target.closest("[data-meal-id]");
 
       if (!button) {
         return;
       }
 
-      handleVote(button.getAttribute("data-meal-id"));
+      await handleVote(button.getAttribute("data-meal-id"));
     });
 
     elements.skipPair.addEventListener("click", () => {
+      if (busy) {
+        return;
+      }
+
       const rankedMeals = getRankedMeals(seedData.meals, state.elo);
 
       queueNextPair(rankedMeals);
       render("Skipped that pair.");
     });
 
-    elements.resetRankings.addEventListener("click", () => {
+    elements.undoVote.addEventListener("click", async () => {
-      if (!window.confirm("Reset the local Elo votes saved in this browser?")) {
+      await handleUndo();
+    });
+
+    elements.resetRankings.addEventListener("click", async () => {
+      if (busy) {
         return;
       }
 
-      state = createSeedState(seedData);
+      if (!window.confirm("Reset the saved rankings back to the seeded board?")) {
-      persistence.clear();
+        return;
-      persistence.save(state);
+      }
-      currentPair = null;
+
-      currentPairKey = null;
+      let nextMessage = "Saved rankings cleared. Back to the seeded board.";
-      render("Local votes cleared. Back to the seeded board.");
+
+      busy = true;
+      render("Resetting saved rankings...");
+
+      try {
+        state = await persistence.reset(seedData);
+        currentPair = null;
+        currentPairKey = null;
+
+        const notice = persistence.consumeNotice();
+
+        if (notice) {
+          nextMessage = `${nextMessage} ${notice}`;
+        }
+      } catch (error) {
+        console.error(error);
+        nextMessage = "Failed to reset rankings.";
+      } finally {
+        busy = false;
+        render(nextMessage);
+      }
     });
 
-    document.addEventListener("keydown", (event) => {
+    document.addEventListener("keydown", async (event) => {
       const target = event.target;
 
       if (
@@ -523,21 +924,33 @@
         return;
       }
 
+      if (busy) {
+        return;
+      }
+
+      if (event.key.toLowerCase() === "z" && state.undo) {
+        event.preventDefault();
+        await handleUndo();
+        return;
+      }
+
       if (!currentPair) {
         return;
       }
 
       if (event.key === "ArrowLeft") {
         event.preventDefault();
-        handleVote(currentPair.left.id);
+        await handleVote(currentPair.left.id);
       } else if (event.key === "ArrowRight") {
         event.preventDefault();
-        handleVote(currentPair.right.id);
+        await handleVote(currentPair.right.id);
       }
     });
 
     render();
   }
 
-  init();
+  init().catch((error) => {
+    console.error(error);
+  });
 })();

images/thumbs/.thumbs-manifest.json

@@ -4,7 +4,7 @@
     "width": 240,
     "height": 320,
     "quality": 82,
-    "mtimeMs": 1770500129000,
+    "mtimeMs": 1774257676921.0168,
     "size": 1052830,
     "focus": {
       "x": 0.35,
@@ -16,7 +16,7 @@
     "width": 240,
     "height": 320,
     "quality": 82,
-    "mtimeMs": 1770500128000,
+    "mtimeMs": 1774257676923.4688,
     "size": 835360,
     "focus": null
   },
@@ -25,7 +25,7 @@
     "width": 240,
     "height": 320,
     "quality": 82,
-    "mtimeMs": 1770500128000,
+    "mtimeMs": 1774257676926.1216,
     "size": 1034158,
     "focus": {
       "x": 0.5,
@@ -37,7 +37,7 @@
     "width": 240,
     "height": 320,
     "quality": 82,
-    "mtimeMs": 1770500128000,
+    "mtimeMs": 1774257676928.9744,
     "size": 1090215,
     "focus": null
   },
@@ -46,7 +46,7 @@
     "width": 240,
     "height": 320,
     "quality": 82,
-    "mtimeMs": 1770500128000,
+    "mtimeMs": 1774257676931.93,
     "size": 1122236,
     "focus": {
       "x": 0.5,
@@ -58,7 +58,7 @@
     "width": 240,
     "height": 320,
     "quality": 82,
-    "mtimeMs": 1770444049000,
+    "mtimeMs": 1774257676932.7878,
     "size": 676787,
     "focus": null
   },
@@ -67,7 +67,7 @@
     "width": 240,
     "height": 320,
     "quality": 82,
-    "mtimeMs": 1770500128000,
+    "mtimeMs": 1774257676935.0764,
     "size": 872024,
     "focus": null
   },
@@ -76,7 +76,7 @@
     "width": 240,
     "height": 320,
     "quality": 82,
-    "mtimeMs": 1770500128000,
+    "mtimeMs": 1774257676936.637,
     "size": 618276,
     "focus": null
   },
@@ -85,7 +85,7 @@
     "width": 240,
     "height": 320,
     "quality": 82,
-    "mtimeMs": 1770500127000,
+    "mtimeMs": 1774257676938.8577,
     "size": 1349804,
     "focus": null
   },
@@ -94,7 +94,7 @@
     "width": 240,
     "height": 320,
     "quality": 82,
-    "mtimeMs": 1770500128000,
+    "mtimeMs": 1774257676940.0383,
     "size": 1071870,
     "focus": null
   },
@@ -103,7 +103,7 @@
     "width": 240,
     "height": 320,
     "quality": 82,
-    "mtimeMs": 1770500128000,
+    "mtimeMs": 1774257676941.5466,
     "size": 764329,
     "focus": null
   },
@@ -112,7 +112,7 @@
     "width": 240,
     "height": 320,
     "quality": 82,
-    "mtimeMs": 1770500128000,
+    "mtimeMs": 1774257676943.8735,
     "size": 1172905,
     "focus": null
   },
@@ -121,7 +121,7 @@
     "width": 240,
     "height": 320,
     "quality": 82,
-    "mtimeMs": 1770500129000,
+    "mtimeMs": 1774257676945.2588,
     "size": 1099540,
     "focus": null
   },
@@ -130,7 +130,7 @@
     "width": 240,
     "height": 320,
     "quality": 82,
-    "mtimeMs": 1770500128000,
+    "mtimeMs": 1774257676946.2732,
     "size": 1052362,
     "focus": null
   },
@@ -139,7 +139,7 @@
     "width": 240,
     "height": 320,
     "quality": 82,
-    "mtimeMs": 1770500128000,
+    "mtimeMs": 1774257676947.5552,
     "size": 1227608,
     "focus": null
   },
@@ -148,7 +148,7 @@
     "width": 240,
     "height": 320,
     "quality": 82,
-    "mtimeMs": 1770500127000,
+    "mtimeMs": 1774257676949.5437,
     "size": 840466,
     "focus": null
   },
@@ -157,7 +157,7 @@
     "width": 240,
     "height": 320,
     "quality": 82,
-    "mtimeMs": 1770500128000,
+    "mtimeMs": 1774257676951.916,
     "size": 1136990,
     "focus": null
   },
@@ -166,7 +166,7 @@
     "width": 240,
     "height": 320,
     "quality": 82,
-    "mtimeMs": 1770500127000,
+    "mtimeMs": 1774257676954.4558,
     "size": 1261294,
     "focus": null
   },
@@ -175,7 +175,7 @@
     "width": 240,
     "height": 320,
     "quality": 82,
-    "mtimeMs": 1770500128000,
+    "mtimeMs": 1774257676956.7886,
     "size": 1119498,
     "focus": null
   },
@@ -184,7 +184,7 @@
     "width": 240,
     "height": 320,
     "quality": 82,
-    "mtimeMs": 1770500128000,
+    "mtimeMs": 1774257676958.691,
     "size": 868085,
     "focus": null
   },
@@ -193,7 +193,7 @@
     "width": 240,
     "height": 320,
     "quality": 82,
-    "mtimeMs": 1770500128000,
+    "mtimeMs": 1774257676961.0393,
     "size": 1057896,
     "focus": null
   },
@@ -202,7 +202,7 @@
     "width": 240,
     "height": 320,
     "quality": 82,
-    "mtimeMs": 1770500128000,
+    "mtimeMs": 1774257676963.4336,
     "size": 1088795,
     "focus": null
   },
@@ -211,7 +211,7 @@
     "width": 240,
     "height": 320,
     "quality": 82,
-    "mtimeMs": 1770500129000,
+    "mtimeMs": 1774257676965.364,
     "size": 852307,
     "focus": null
   },
@@ -220,7 +220,7 @@
     "width": 240,
     "height": 320,
     "quality": 82,
-    "mtimeMs": 1770500129000,
+    "mtimeMs": 1774257676967.8005,
     "size": 1149955,
     "focus": null
   },
@@ -229,7 +229,7 @@
     "width": 240,
     "height": 320,
     "quality": 82,
-    "mtimeMs": 1770500129000,
+    "mtimeMs": 1774257676970.2761,
     "size": 1242099,
     "focus": null
   },
@@ -238,7 +238,7 @@
     "width": 240,
     "height": 320,
     "quality": 82,
-    "mtimeMs": 1770500128000,
+    "mtimeMs": 1774257676971.9075,
     "size": 1414024,
     "focus": null
   },
@@ -247,7 +247,7 @@
     "width": 240,
     "height": 320,
     "quality": 82,
-    "mtimeMs": 1770500128000,
+    "mtimeMs": 1774257676973.2812,
     "size": 1022877,
     "focus": null
   },
@@ -256,7 +256,7 @@
     "width": 240,
     "height": 320,
     "quality": 82,
-    "mtimeMs": 1770500129000,
+    "mtimeMs": 1774257676974.2112,
     "size": 1018868,
     "focus": null
   },
@@ -265,7 +265,7 @@
     "width": 240,
     "height": 320,
     "quality": 82,
-    "mtimeMs": 1770500128000,
+    "mtimeMs": 1774257676975.1504,
     "size": 1233602,
     "focus": null
   },
@@ -274,7 +274,7 @@
     "width": 240,
     "height": 320,
     "quality": 82,
-    "mtimeMs": 1770500129000,
+    "mtimeMs": 1774257676976.6533,
     "size": 739786,
     "focus": null
   },
@@ -283,7 +283,7 @@
     "width": 240,
     "height": 320,
     "quality": 82,
-    "mtimeMs": 1771126436000,
+    "mtimeMs": 1774257676977.1958,
     "size": 1069693,
     "focus": null
   },
@@ -292,7 +292,7 @@
     "width": 240,
     "height": 320,
     "quality": 82,
-    "mtimeMs": 1771226059000,
+    "mtimeMs": 1774257676979.063,
     "size": 995282,
     "focus": null
   },
@@ -301,7 +301,7 @@
     "width": 240,
     "height": 320,
     "quality": 82,
-    "mtimeMs": 1771226144000,
+    "mtimeMs": 1774257676980.472,
     "size": 729224,
     "focus": null
   }

index.html

@@ -30,9 +30,9 @@
 				<h1>for vham :3</h1>
 				<p id="haiku">Please enable javascript >.<</p>
 				<p class="page-links">
-					<a href="index.html" aria-current="page">gallery</a>
+					<a href="./" aria-current="page">gallery</a>
 					<span class="page-links__separator">/</span>
-					<a href="rankings.html">rankings</a>
+					<a href="rankings">rankings</a>
 				</p>
 			</header>
 

rankings.html

@@ -30,9 +30,9 @@
 				<h1>food power rankings</h1>
 				<p>pick the better meal, one pair at a time, and the board updates live in this browser.</p>
 				<p class="page-links">
-					<a href="index.html">gallery</a>
+					<a href="./">gallery</a>
 					<span class="page-links__separator">/</span>
-					<a href="rankings.html" aria-current="page">rankings</a>
+					<a href="rankings" aria-current="page">rankings</a>
 				</p>
 			</header>
 
@@ -42,17 +42,18 @@
 					<div class="voting-panel__intro">
 						<p class="voting-panel__eyebrow">Head-To-Head Voting</p>
 						<h2>Pick the winner.</h2>
-						<p class="vote-status" id="vote-status" aria-live="polite">Enable JavaScript to save votes in this browser.</p>
+						<p class="vote-status" id="vote-status" aria-live="polite">Enable JavaScript to load saved rankings.</p>
 					</div>
 					<div class="voting-panel__actions">
 						<button class="button small" id="skip-pair" type="button">skip pair</button>
-						<button class="button small" id="reset-rankings" type="button">reset local votes</button>
+						<button class="button small" id="undo-vote" type="button">go back</button>
+						<button class="button small" id="reset-rankings" type="button">reset saved rankings</button>
 					</div>
-					<p class="vote-message" id="vote-message" aria-live="polite">Enable JavaScript to start head-to-head voting.</p>
+					<p class="vote-message" id="vote-message" aria-live="polite">Enable JavaScript to load head-to-head voting.</p>
 					<div class="duel-grid" id="duel-cards">
 						<p class="duel-placeholder">Enable JavaScript to compare meals here.</p>
 					</div>
-					<p class="vote-hint">Tip: use the left and right arrow keys to vote faster.</p>
+					<p class="vote-hint">Tip: use the left and right arrow keys to vote faster, or press Z to go back.</p>
 				</div>
 			</section>
 

scripts/lib/rankings-state.js

@@ -0,0 +1,380 @@
+const fs = require("fs");
+const path = require("path");
+
+const { loadEloData } = require("./elo");
+const { loadMeals, repoRoot } = require("./meals");
+
+const STATE_VERSION = 1;
+const defaultStatePath = path.join(repoRoot, ".runtime", "rankings-state.json");
+
+function isValidMealId(id) {
+  return typeof id === "string" && /^\d+$/.test(id);
+}
+
+function createDefaultEntry(id, defaultRating) {
+  return {
+    id,
+    rating: defaultRating,
+    wins: 0,
+    losses: 0,
+  };
+}
+
+function cloneEntry(entry) {
+  return {
+    id: entry.id,
+    rating: entry.rating,
+    wins: entry.wins,
+    losses: entry.losses,
+  };
+}
+
+function roundRating(rating) {
+  return Math.round(rating * 1000) / 1000;
+}
+
+function expectedScore(rating, opponentRating) {
+  return 1 / (1 + Math.pow(10, (opponentRating - rating) / 400));
+}
+
+function isValidStoredEntry(entry) {
+  if (!entry || typeof entry !== "object" || Array.isArray(entry)) {
+    return false;
+  }
+
+  if (typeof entry.id !== "string" || !/^\d+$/.test(entry.id)) {
+    return false;
+  }
+
+  if (typeof entry.rating !== "number" || !Number.isFinite(entry.rating) || entry.rating <= 0) {
+    return false;
+  }
+
+  return ["wins", "losses"].every(
+    (field) => Number.isInteger(entry[field]) && entry[field] >= 0
+  );
+}
+
+function createSeedState(seedData) {
+  return {
+    version: STATE_VERSION,
+    voteCount: 0,
+    lastPairKey: null,
+    updatedAt: null,
+    undo: null,
+    elo: {
+      defaultRating: seedData.elo.defaultRating,
+      kFactor: seedData.elo.kFactor,
+      entries: seedData.meals.map((meal) => {
+        const seedEntry =
+          seedData.elo.entries.find((entry) => entry.id === meal.id) ||
+          createDefaultEntry(meal.id, seedData.elo.defaultRating);
+
+        return cloneEntry(seedEntry);
+      }),
+    },
+  };
+}
+
+function syncStateCore(seedData, storedState) {
+  if (!storedState || typeof storedState !== "object" || Array.isArray(storedState)) {
+    return createSeedState(seedData);
+  }
+
+  const storedEntries = Array.isArray(storedState.elo?.entries)
+    ? storedState.elo.entries.filter(isValidStoredEntry)
+    : [];
+  const storedEntryById = new Map(storedEntries.map((entry) => [entry.id, entry]));
+  const seedEntryById = new Map(seedData.elo.entries.map((entry) => [entry.id, entry]));
+  const entries = seedData.meals.map((meal) => {
+    const storedEntry = storedEntryById.get(meal.id);
+
+    if (storedEntry) {
+      return cloneEntry(storedEntry);
+    }
+
+    const seedEntry =
+      seedEntryById.get(meal.id) || createDefaultEntry(meal.id, seedData.elo.defaultRating);
+
+    return cloneEntry(seedEntry);
+  });
+  const derivedVoteCount = entries.reduce((sum, entry) => sum + entry.wins, 0);
+
+  return {
+    version: STATE_VERSION,
+    voteCount:
+      Number.isInteger(storedState.voteCount) && storedState.voteCount >= derivedVoteCount
+        ? storedState.voteCount
+        : derivedVoteCount,
+    lastPairKey: typeof storedState.lastPairKey === "string" ? storedState.lastPairKey : null,
+    updatedAt: typeof storedState.updatedAt === "string" ? storedState.updatedAt : null,
+    undo: null,
+    elo: {
+      defaultRating: seedData.elo.defaultRating,
+      kFactor: seedData.elo.kFactor,
+      entries,
+    },
+  };
+}
+
+function createPairKey(leftId, rightId) {
+  return [leftId, rightId].sort().join(":");
+}
+
+function createUndoSnapshot(state) {
+  return {
+    voteCount: state.voteCount,
+    lastPairKey: state.lastPairKey,
+    updatedAt: state.updatedAt,
+    elo: {
+      defaultRating: state.elo.defaultRating,
+      kFactor: state.elo.kFactor,
+      entries: state.elo.entries.map(cloneEntry),
+    },
+  };
+}
+
+function resolveUndoPairIds(winnerId, loserId, leftId, rightId) {
+  const validPair =
+    isValidMealId(leftId) &&
+    isValidMealId(rightId) &&
+    leftId !== rightId &&
+    [leftId, rightId].includes(winnerId) &&
+    [leftId, rightId].includes(loserId);
+
+  if (validPair) {
+    return { leftId, rightId };
+  }
+
+  return { leftId: winnerId, rightId: loserId };
+}
+
+function syncUndo(seedData, storedUndo) {
+  if (!storedUndo || typeof storedUndo !== "object" || Array.isArray(storedUndo)) {
+    return null;
+  }
+
+  const { leftId, rightId, winnerId, loserId, snapshot } = storedUndo;
+
+  if (
+    !isValidMealId(leftId) ||
+    !isValidMealId(rightId) ||
+    !isValidMealId(winnerId) ||
+    !isValidMealId(loserId) ||
+    leftId === rightId ||
+    winnerId === loserId
+  ) {
+    return null;
+  }
+
+  const pairIds = new Set([leftId, rightId]);
+  const mealIds = new Set(seedData.meals.map((meal) => meal.id));
+
+  if (
+    !pairIds.has(winnerId) ||
+    !pairIds.has(loserId) ||
+    ![leftId, rightId, winnerId, loserId].every((id) => mealIds.has(id))
+  ) {
+    return null;
+  }
+
+  return {
+    pairKey: createPairKey(leftId, rightId),
+    leftId,
+    rightId,
+    winnerId,
+    loserId,
+    snapshot: createUndoSnapshot(syncStateCore(seedData, snapshot)),
+  };
+}
+
+function syncStoredState(seedData, storedState) {
+  const nextState = syncStateCore(seedData, storedState);
+
+  return {
+    ...nextState,
+    undo: syncUndo(seedData, storedState?.undo),
+  };
+}
+
+function restoreUndoSnapshot(seedData, snapshot) {
+  return {
+    ...syncStateCore(seedData, snapshot),
+    undo: null,
+  };
+}
+
+function applyVote(seedData, state, vote) {
+  const { winnerId, loserId, pairKey, leftId, rightId } = vote;
+  const entryById = new Map(state.elo.entries.map((entry) => [entry.id, cloneEntry(entry)]));
+  const winner = entryById.get(winnerId);
+  const loser = entryById.get(loserId);
+  const undoPair = resolveUndoPairIds(winnerId, loserId, leftId, rightId);
+  const resolvedPairKey =
+    typeof pairKey === "string" && pairKey.length > 0
+      ? pairKey
+      : createPairKey(undoPair.leftId, undoPair.rightId);
+
+  if (!winner || !loser) {
+    throw new Error("Vote referenced an unknown meal id");
+  }
+
+  const winnerExpected = expectedScore(winner.rating, loser.rating);
+  const loserExpected = expectedScore(loser.rating, winner.rating);
+
+  winner.rating = roundRating(winner.rating + state.elo.kFactor * (1 - winnerExpected));
+  loser.rating = roundRating(loser.rating + state.elo.kFactor * (0 - loserExpected));
+  winner.wins += 1;
+  loser.losses += 1;
+
+  return {
+    ...state,
+    voteCount: state.voteCount + 1,
+    lastPairKey: resolvedPairKey,
+    updatedAt: new Date().toISOString(),
+    undo: {
+      pairKey: createPairKey(undoPair.leftId, undoPair.rightId),
+      leftId: undoPair.leftId,
+      rightId: undoPair.rightId,
+      winnerId,
+      loserId,
+      snapshot: createUndoSnapshot(state),
+    },
+    elo: {
+      ...state.elo,
+      entries: seedData.meals.map((meal) => entryById.get(meal.id)),
+    },
+  };
+}
+
+function undoVote(seedData, state) {
+  if (!state.undo) {
+    return state;
+  }
+
+  return restoreUndoSnapshot(seedData, state.undo.snapshot);
+}
+
+function resolveStatePath(statePath) {
+  return statePath ? path.resolve(statePath) : defaultStatePath;
+}
+
+function loadSeedData() {
+  return {
+    meals: loadMeals(),
+    elo: loadEloData(),
+  };
+}
+
+function readPersistedState(statePath) {
+  if (!fs.existsSync(statePath)) {
+    return null;
+  }
+
+  return JSON.parse(fs.readFileSync(statePath, "utf8"));
+}
+
+function writePersistedState(statePath, state) {
+  fs.mkdirSync(path.dirname(statePath), { recursive: true });
+
+  const nextState = `${JSON.stringify(state, null, 2)}\n`;
+  const tempPath = `${statePath}.tmp`;
+
+  fs.writeFileSync(tempPath, nextState);
+  fs.renameSync(tempPath, statePath);
+}
+
+function loadRankingsState(options = {}) {
+  const statePath = resolveStatePath(options.statePath);
+  const seedData = loadSeedData();
+  const storedState = readPersistedState(statePath);
+
+  return syncStoredState(seedData, storedState);
+}
+
+function saveRankingsState(state, options = {}) {
+  const statePath = resolveStatePath(options.statePath);
+  const seedData = loadSeedData();
+  const nextState = syncStoredState(seedData, state);
+
+  writePersistedState(statePath, nextState);
+
+  return nextState;
+}
+
+function recordVote(vote, options = {}) {
+  if (!vote || typeof vote !== "object" || Array.isArray(vote)) {
+    throw new Error("Vote payload must be an object");
+  }
+
+  const { winnerId, loserId, pairKey, leftId, rightId } = vote;
+
+  if (!isValidMealId(winnerId)) {
+    throw new Error("Vote payload is missing a valid winnerId");
+  }
+
+  if (!isValidMealId(loserId)) {
+    throw new Error("Vote payload is missing a valid loserId");
+  }
+
+  if (winnerId === loserId) {
+    throw new Error("winnerId and loserId must be different");
+  }
+
+  if (leftId !== undefined || rightId !== undefined) {
+    if (!isValidMealId(leftId) || !isValidMealId(rightId) || leftId === rightId) {
+      throw new Error("Vote payload is missing a valid left/right pair");
+    }
+
+    if (![leftId, rightId].includes(winnerId) || ![leftId, rightId].includes(loserId)) {
+      throw new Error("Vote payload leftId/rightId must match winnerId/loserId");
+    }
+  }
+
+  const statePath = resolveStatePath(options.statePath);
+  const seedData = loadSeedData();
+  const storedState = syncStoredState(seedData, readPersistedState(statePath));
+  const nextState = applyVote(seedData, storedState, {
+    winnerId,
+    loserId,
+    pairKey,
+    leftId,
+    rightId,
+  });
+
+  writePersistedState(statePath, nextState);
+
+  return nextState;
+}
+
+function undoLastRankingsVote(options = {}) {
+  const statePath = resolveStatePath(options.statePath);
+  const seedData = loadSeedData();
+  const storedState = syncStoredState(seedData, readPersistedState(statePath));
+  const nextState = undoVote(seedData, storedState);
+
+  writePersistedState(statePath, nextState);
+
+  return nextState;
+}
+
+function resetRankingsState(options = {}) {
+  const statePath = resolveStatePath(options.statePath);
+  const seedData = loadSeedData();
+  const nextState = createSeedState(seedData);
+
+  writePersistedState(statePath, nextState);
+
+  return nextState;
+}
+
+module.exports = {
+  createSeedState,
+  defaultStatePath,
+  loadRankingsState,
+  recordVote,
+  resetRankingsState,
+  saveRankingsState,
+  syncStoredState,
+  undoLastRankingsVote,
+};

scripts/serve.js

@@ -3,9 +3,17 @@ const http = require("http");
 const path = require("path");
 
 const { repoRoot } = require("./lib/meals");
+const {
+  defaultStatePath,
+  loadRankingsState,
+  recordVote,
+  resetRankingsState,
+  undoLastRankingsVote,
+} = require("./lib/rankings-state");
 
 const DEFAULT_HOST = "127.0.0.1";
 const DEFAULT_PORT = 4321;
+const MAX_REQUEST_BODY_BYTES = 16 * 1024;
 const MIME_TYPES = {
   ".css": "text/css; charset=utf-8",
   ".gif": "image/gif",
@@ -29,6 +37,7 @@ function parseArgs(argv) {
   const options = {
     host: process.env.HOST || DEFAULT_HOST,
     port: Number.parseInt(process.env.PORT || String(DEFAULT_PORT), 10),
+    rankingsStatePath: path.resolve(process.env.RANKINGS_STATE_PATH || defaultStatePath),
   };
 
   for (let index = 0; index < argv.length; index += 1) {
@@ -44,6 +53,12 @@ function parseArgs(argv) {
     if (arg === "--port" && value) {
       options.port = Number.parseInt(value, 10);
       index += 1;
+      continue;
+    }
+
+    if (arg === "--rankings-state-path" && value) {
+      options.rankingsStatePath = path.resolve(value);
+      index += 1;
     }
   }
 
@@ -58,9 +73,15 @@ function getContentType(filePath) {
   return MIME_TYPES[path.extname(filePath).toLowerCase()] || "application/octet-stream";
 }
 
-function resolveRequestPath(requestUrl) {
+function hasHiddenSegment(pathname) {
-  const url = new URL(requestUrl, "http://localhost");
+  return pathname.split("/").some((segment) => segment.startsWith(".") && segment.length > 1);
-  const pathname = decodeURIComponent(url.pathname);
+}
+
+function resolveRequestPath(pathname) {
+  if (hasHiddenSegment(pathname)) {
+    return null;
+  }
+
   const requestedPath = pathname === "/" ? "/index.html" : pathname;
   const absolutePath = path.resolve(repoRoot, `.${requestedPath}`);
   const withinRepo =
@@ -74,9 +95,76 @@ function resolveRequestPath(requestUrl) {
     return path.join(absolutePath, "index.html");
   }
 
+  if (
+    path.extname(absolutePath) === "" &&
+    !fs.existsSync(absolutePath) &&
+    fs.existsSync(`${absolutePath}.html`) &&
+    fs.statSync(`${absolutePath}.html`).isFile()
+  ) {
+    return `${absolutePath}.html`;
+  }
+
   return absolutePath;
 }
 
+function sendJson(response, statusCode, payload) {
+  response.writeHead(statusCode, {
+    "Cache-Control": "no-store",
+    "Content-Type": "application/json; charset=utf-8",
+  });
+  response.end(`${JSON.stringify(payload, null, 2)}\n`);
+}
+
+function sendText(response, statusCode, body) {
+  response.writeHead(statusCode, {
+    "Cache-Control": "no-store",
+    "Content-Type": "text/plain; charset=utf-8",
+  });
+  response.end(body);
+}
+
+function sendRedirect(response, location) {
+  response.writeHead(301, {
+    Location: location,
+    "Cache-Control": "no-store",
+  });
+  response.end();
+}
+
+function parseJsonBody(request) {
+  return new Promise((resolve, reject) => {
+    const chunks = [];
+    let totalBytes = 0;
+
+    request.on("data", (chunk) => {
+      totalBytes += chunk.length;
+
+      if (totalBytes > MAX_REQUEST_BODY_BYTES) {
+        reject(new Error("Request body is too large"));
+        request.destroy();
+        return;
+      }
+
+      chunks.push(chunk);
+    });
+
+    request.on("end", () => {
+      if (chunks.length === 0) {
+        resolve({});
+        return;
+      }
+
+      try {
+        resolve(JSON.parse(Buffer.concat(chunks).toString("utf8")));
+      } catch (error) {
+        reject(new Error("Request body must be valid JSON"));
+      }
+    });
+
+    request.on("error", reject);
+  });
+}
+
 function sendFile(response, filePath) {
   const stream = fs.createReadStream(filePath);
 
@@ -87,24 +175,106 @@ function sendFile(response, filePath) {
 
   stream.pipe(response);
   stream.on("error", () => {
-    response.writeHead(500, { "Content-Type": "text/plain; charset=utf-8" });
+    sendText(response, 500, "Failed to read file");
-    response.end("Failed to read file");
   });
 }
 
-function createServer() {
+async function handleApiRequest(request, response, pathname, options) {
-  return http.createServer((request, response) => {
+  if (pathname === "/api/rankings" && request.method === "GET") {
-    const filePath = resolveRequestPath(request.url || "/");
+    sendJson(response, 200, loadRankingsState({ statePath: options.rankingsStatePath }));
+    return true;
+  }
+
+  if (pathname === "/api/rankings/vote" && request.method === "POST") {
+    const body = await parseJsonBody(request);
+    sendJson(response, 200, recordVote(body, { statePath: options.rankingsStatePath }));
+    return true;
+  }
+
+  if (pathname === "/api/rankings/reset" && request.method === "POST") {
+    sendJson(response, 200, resetRankingsState({ statePath: options.rankingsStatePath }));
+    return true;
+  }
+
+  if (pathname === "/api/rankings/undo" && request.method === "POST") {
+    sendJson(response, 200, undoLastRankingsVote({ statePath: options.rankingsStatePath }));
+    return true;
+  }
+
+  if (
+    pathname === "/api/rankings" ||
+    pathname === "/api/rankings/vote" ||
+    pathname === "/api/rankings/reset" ||
+    pathname === "/api/rankings/undo"
+  ) {
+    sendText(response, 405, "Method not allowed");
+    return true;
+  }
+
+  if (pathname.startsWith("/api/")) {
+    sendText(response, 404, "Not found");
+    return true;
+  }
+
+  return false;
+}
+
+function createServer(options) {
+  return http.createServer(async (request, response) => {
+    let pathname;
+    let search;
+
+    try {
+      const requestUrl = new URL(request.url || "/", "http://localhost");
+      pathname = decodeURIComponent(requestUrl.pathname);
+      search = requestUrl.search;
+    } catch (error) {
+      sendText(response, 400, "Bad request");
+      return;
+    }
+
+    if (request.method === "GET" || request.method === "HEAD") {
+      if (pathname === "/index.html") {
+        sendRedirect(response, `/${search}`);
+        return;
+      }
+
+      if (pathname.endsWith(".html") && pathname !== "/index.html") {
+        sendRedirect(response, `${pathname.slice(0, -5)}${search}`);
+        return;
+      }
+    }
+
+    try {
+      if (await handleApiRequest(request, response, pathname, options)) {
+        return;
+      }
+    } catch (error) {
+      const statusCode =
+        error.message === "Request body must be valid JSON" ||
+        error.message === "Request body is too large" ||
+        error.message.startsWith("Vote payload") ||
+        error.message === "winnerId and loserId must be different"
+          ? 400
+          : 500;
+
+      if (statusCode >= 500) {
+        console.error(error);
+      }
+
+      sendJson(response, statusCode, { error: error.message });
+      return;
+    }
+
+    const filePath = resolveRequestPath(pathname);
 
     if (!filePath) {
-      response.writeHead(403, { "Content-Type": "text/plain; charset=utf-8" });
+      sendText(response, 403, "Forbidden");
-      response.end("Forbidden");
       return;
     }
 
     if (!fs.existsSync(filePath) || !fs.statSync(filePath).isFile()) {
-      response.writeHead(404, { "Content-Type": "text/plain; charset=utf-8" });
+      sendText(response, 404, "Not found");
-      response.end("Not found");
       return;
     }
 
@@ -114,10 +284,11 @@ function createServer() {
 
 function main() {
   const options = parseArgs(process.argv.slice(2));
-  const server = createServer();
+  const server = createServer(options);
 
   server.listen(options.port, options.host, () => {
     console.log(`Serving ${repoRoot} at http://${options.host}:${options.port}`);
+    console.log(`Rankings state path: ${options.rankingsStatePath}`);
   });
 }
 

templates/index.html

@@ -30,9 +30,9 @@
 				<h1>for vham :3</h1>
 				<p id="haiku">Please enable javascript >.<</p>
 				<p class="page-links">
-					<a href="index.html" aria-current="page">gallery</a>
+					<a href="./" aria-current="page">gallery</a>
 					<span class="page-links__separator">/</span>
-					<a href="rankings.html">rankings</a>
+					<a href="rankings">rankings</a>
 				</p>
 			</header>
 

templates/rankings.html

@@ -30,9 +30,9 @@
 				<h1>food power rankings</h1>
 				<p>pick the better meal, one pair at a time, and the board updates live in this browser.</p>
 				<p class="page-links">
-					<a href="index.html">gallery</a>
+					<a href="./">gallery</a>
 					<span class="page-links__separator">/</span>
-					<a href="rankings.html" aria-current="page">rankings</a>
+					<a href="rankings" aria-current="page">rankings</a>
 				</p>
 			</header>
 
@@ -42,17 +42,18 @@
 					<div class="voting-panel__intro">
 						<p class="voting-panel__eyebrow">Head-To-Head Voting</p>
 						<h2>Pick the winner.</h2>
-						<p class="vote-status" id="vote-status" aria-live="polite">Enable JavaScript to save votes in this browser.</p>
+						<p class="vote-status" id="vote-status" aria-live="polite">Enable JavaScript to load saved rankings.</p>
 					</div>
 					<div class="voting-panel__actions">
 						<button class="button small" id="skip-pair" type="button">skip pair</button>
-						<button class="button small" id="reset-rankings" type="button">reset local votes</button>
+						<button class="button small" id="undo-vote" type="button">go back</button>
+						<button class="button small" id="reset-rankings" type="button">reset saved rankings</button>
 					</div>
-					<p class="vote-message" id="vote-message" aria-live="polite">Enable JavaScript to start head-to-head voting.</p>
+					<p class="vote-message" id="vote-message" aria-live="polite">Enable JavaScript to load head-to-head voting.</p>
 					<div class="duel-grid" id="duel-cards">
 						<p class="duel-placeholder">Enable JavaScript to compare meals here.</p>
 					</div>
-					<p class="vote-hint">Tip: use the left and right arrow keys to vote faster.</p>
+					<p class="vote-hint">Tip: use the left and right arrow keys to vote faster, or press Z to go back.</p>
 				</div>
 			</section>