// Persistent cache for discovered articles (keyed by each article file's own
// path) and for per-search-query match results (keyed by the query text —
// see setSearchCacheEntry() below). 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/views.js get live-fetch/live-scan behaviour for free
// without needing their 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;
// Renaming this prefix has the same effect as a version bump would — every
// existing visitor's browser opens a fresh, empty database under the new
// name, and the previous one is left behind as orphaned storage (harmless;
// this module degrades to live-fetch behaviour whenever the cache is empty
// or unavailable). Do this deliberately, not casually.
const DB_NAME = `cmkiss-cache-v${CACHE_SCHEMA_VERSION}`;
const ARTICLE_STORE = 'articleFiles';
const SEARCH_STORE = 'searchQueries';
// IndexedDB's own upgrade counter — separate from CACHE_SCHEMA_VERSION,
// which only governs the *article* record shape (and busts the cache by
// renaming the whole database). Bump this instead whenever a store or index
// is added/changed; onupgradeneeded below creates only what's missing, so
// existing article-cache data survives the upgrade.
const DB_VERSION = 2;
// Caps how many distinct queries' match results stay cached — otherwise
// every unique term ever typed into search would keep its own per-article
// map forever, growing unbounded on a long-lived site. Evicted
// least-recently-searched-first — see setSearchCacheEntry().
const MAX_CACHED_SEARCHES = 30;

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, DB_VERSION);
            request.onupgradeneeded = () => {
                const db = request.result;
                if (!db.objectStoreNames.contains(ARTICLE_STORE)) db.createObjectStore(ARTICLE_STORE, { keyPath: 'path' });
                if (!db.objectStoreNames.contains(SEARCH_STORE)) {
                    db.createObjectStore(SEARCH_STORE, { keyPath: 'query' }).createIndex('lastUsed', 'lastUsed');
                }
            };
            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(storeName, 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(storeName, mode).objectStore(storeName);
        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;
    }
}

// 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(ARTICLE_STORE, 'readonly', store => store.getAll());
    return new Map((records || []).map(record => [record.path, record]));
}

export async function setCacheEntry(path, entry) {
    await runRequest(ARTICLE_STORE, '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(ARTICLE_STORE, 'readwrite').objectStore(ARTICLE_STORE);
        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.
    }
}

// Per-query search-match cache: `entries` is a { [articlePath]: { mtime,
// matched } } map — see loadSearch() in views.js, which trusts an entry
// (skipping a content re-fetch entirely) whenever its mtime still matches
// the live article, and only re-checks what's new or changed. Keyed by the
// exact (locale-lowercased) text matchesQuery() itself compares against, so
// "Linux" and "linux" share one cached entry.
export async function getSearchCacheEntry(query) {
    return runRequest(SEARCH_STORE, 'readonly', store => store.get(query));
}

export async function setSearchCacheEntry(query, entries) {
    await runRequest(SEARCH_STORE, 'readwrite', store => store.put({ query, entries, lastUsed: Date.now() }));
    await pruneSearchCache();
}

// Keeps the search-query cache bounded to MAX_CACHED_SEARCHES entries,
// dropping the least-recently-searched ones first — the same "don't grow
// unbounded" concern pruneCache() addresses for the article cache, just
// against searches instead of renamed/deleted files.
async function pruneSearchCache() {
    if (!cacheAvailable) return;
    let db;
    try {
        db = await openDb();
    } catch {
        return;
    }
    try {
        const store = db.transaction(SEARCH_STORE, 'readwrite').objectStore(SEARCH_STORE);
        let excess = await new Promise((resolve, reject) => {
            const request = store.count();
            request.onsuccess = () => resolve(request.result - MAX_CACHED_SEARCHES);
            request.onerror = () => reject(request.error);
        });
        if (excess <= 0) return;
        await new Promise((resolve, reject) => {
            const cursorRequest = store.index('lastUsed').openCursor();
            cursorRequest.onsuccess = event => {
                const cursor = event.target.result;
                if (!cursor || excess <= 0) { resolve(); return; }
                cursor.delete();
                excess -= 1;
                cursor.continue();
            };
            cursorRequest.onerror = () => reject(cursorRequest.error);
        });
    } catch {
        // Same reasoning as runRequest() above.
    }
}