add: persistant storage of elo ranking

scripts/lib/rankings-state.js

@@ -0,0 +1,241 @@
+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 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,
+    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 syncStoredState(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,
+    elo: {
+      defaultRating: seedData.elo.defaultRating,
+      kFactor: seedData.elo.kFactor,
+      entries,
+    },
+  };
+}
+
+function createPairKey(leftId, rightId) {
+  return [leftId, rightId].sort().join(":");
+}
+
+function applyVote(seedData, state, winnerId, loserId, pairKey) {
+  const entryById = new Map(state.elo.entries.map((entry) => [entry.id, cloneEntry(entry)]));
+  const winner = entryById.get(winnerId);
+  const loser = entryById.get(loserId);
+
+  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: pairKey || createPairKey(winnerId, loserId),
+    updatedAt: new Date().toISOString(),
+    elo: {
+      ...state.elo,
+      entries: seedData.meals.map((meal) => entryById.get(meal.id)),
+    },
+  };
+}
+
+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 = `${statePath}.tmp`;
+
+  fs.writeFileSync(tempPath, nextState);
+  fs.renameSync(tempPath, statePath);
+}
+
+function loadRankingsState(options = {}) {
+  const statePath = resolveStatePath(options.statePath);
+  const seedData = loadSeedData();
+  const storedState = readPersistedState(statePath);
+
+  return syncStoredState(seedData, storedState);
+}
+
+function saveRankingsState(state, options = {}) {
+  const statePath = resolveStatePath(options.statePath);
+  const seedData = loadSeedData();
+  const nextState = syncStoredState(seedData, state);
+
+  writePersistedState(statePath, nextState);
+
+  return nextState;
+}
+
+function recordVote(vote, options = {}) {
+  if (!vote || typeof vote !== "object" || Array.isArray(vote)) {
+    throw new Error("Vote payload must be an object");
+  }
+
+  const { winnerId, loserId, pairKey } = vote;
+
+  if (typeof winnerId !== "string" || !/^\d+$/.test(winnerId)) {
+    throw new Error("Vote payload is missing a valid winnerId");
+  }
+
+  if (typeof loserId !== "string" || !/^\d+$/.test(loserId)) {
+    throw new Error("Vote payload is missing a valid loserId");
+  }
+
+  if (winnerId === loserId) {
+    throw new Error("winnerId and loserId must be different");
+  }
+
+  const statePath = resolveStatePath(options.statePath);
+  const seedData = loadSeedData();
+  const storedState = syncStoredState(seedData, readPersistedState(statePath));
+  const nextState = applyVote(seedData, storedState, winnerId, loserId, pairKey);
+
+  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,
+};