cmkiss/js/cache.js

// Persistent cache for discovered articles, keyed by each article file's own
// path. Raw IndexedDB (no wrapper library — see
// .claude/nginx-sitemap-crawler-plan.md L4/L5 on the zero-dependency,
// long-stable-API requirement). If IndexedDB is unavailable (private
// browsing, old browser, blocked), every operation below silently becomes a
// no-op so discovery.js gets live-fetch behaviour for free without needing
// its own availability branching (plan doc R6).

// Bump this whenever discovery.js's derived article record shape changes.
// The version is baked into the DB name so a code deploy invalidates every
// cached entry immediately, instead of stale-shaped records lingering until
// each file's mtime happens to change — which, on a "deploy and forget"
// site, could be years.
const CACHE_SCHEMA_VERSION = 3;
const DB_NAME = `cmjs-cache-v${CACHE_SCHEMA_VERSION}`;
const STORE_NAME = 'articleFiles';

let cacheAvailable = true;
let dbPromise = null;

function openDb() {
    if (!dbPromise) {
        dbPromise = new Promise((resolve, reject) => {
            if (typeof indexedDB === 'undefined') { reject(new Error('IndexedDB unavailable')); return; }
            const request = indexedDB.open(DB_NAME, 1);
            request.onupgradeneeded = () => {
                request.result.createObjectStore(STORE_NAME, { keyPath: 'path' });
            };
            request.onsuccess = () => resolve(request.result);
            request.onerror = () => reject(request.error);
            request.onblocked = () => reject(new Error('IndexedDB open blocked'));
        }).catch(error => { cacheAvailable = false; throw error; });
    }
    return dbPromise;
}

// Opens a store and resolves/rejects with the given IDBRequest's own outcome
// — the standard pattern, so result timing never depends on transaction
// lifecycle details.
async function runRequest(mode, makeRequest) {
    if (!cacheAvailable) return undefined;
    let db;
    try {
        db = await openDb();
    } catch {
        return undefined; // openDb() itself already flipped cacheAvailable
    }
    try {
        const store = db.transaction(STORE_NAME, mode).objectStore(STORE_NAME);
        return await new Promise((resolve, reject) => {
            const request = makeRequest(store);
            request.onsuccess = () => resolve(request.result);
            request.onerror = () => reject(request.error);
        });
    } catch {
        // A single request/transaction failing (e.g. one write hitting a
        // storage quota) doesn't mean IndexedDB itself is gone — only
        // openDb() failing disables the cache wholesale. Leave
        // cacheAvailable as-is so later calls can still try.
        return undefined;
    }
}

export function isCacheAvailable() {
    return cacheAvailable;
}

// Returns every cached { path, mtime, article } record as a Map keyed by
// path — one bulk read instead of a separate IndexedDB round-trip per
// article file, which matters once there are hundreds of them: discovery.js
// reads this once up front rather than doing a point lookup per file during
// indexing. Empty Map on a miss or if the cache is unavailable.
export async function getAllCacheEntries() {
    const records = await runRequest('readonly', store => store.getAll());
    return new Map((records || []).map(record => [record.path, record]));
}

export async function setCacheEntry(path, entry) {
    await runRequest('readwrite', store => store.put({ ...entry, path }));
}

// Removes any cached entry whose path is no longer in the live directory
// listing (renamed/deleted slugs), so the cache doesn't grow unbounded.
export async function pruneCache(validPaths) {
    if (!cacheAvailable) return;
    const valid = new Set(validPaths);
    let db;
    try {
        db = await openDb();
    } catch {
        return; // openDb() itself already flipped cacheAvailable
    }
    try {
        const store = db.transaction(STORE_NAME, 'readwrite').objectStore(STORE_NAME);
        await new Promise((resolve, reject) => {
            const cursorRequest = store.openCursor();
            cursorRequest.onsuccess = event => {
                const cursor = event.target.result;
                if (!cursor) { resolve(); return; }
                if (!valid.has(cursor.value.path)) cursor.delete();
                cursor.continue();
            };
            cursorRequest.onerror = () => reject(cursorRequest.error);
        });
    } catch {
        // Same reasoning as runRequest() above — a failed prune pass doesn't
        // mean IndexedDB itself is unavailable.
    }
}