/**
 * ZDDC Classifier — persistence for the Classify & Copy map.
 *
 * The assignment map and target trees, plus the picked source directory
 * HANDLE, are stored in IndexedDB (localStorage can't hold a
 * FileSystemDirectoryHandle; the handle is structured-cloneable, so IndexedDB
 * can). On reload we re-request permission on the stored handle — a single
 * click re-grants access, no re-navigation. If that fails (permission denied,
 * or a different machine), the caller falls back to a fresh pick and the map
 * re-attaches by relative path.
 *
 * NOTE: a stored handle is only valid in the same browser profile on the same
 * machine. The map keys on source-relative paths, so re-picking the same tree
 * elsewhere still re-attaches — that's the warning shown to the user on save.
 */
(function () {
    'use strict';

    var DB_NAME = 'zddc-classifier';
    var STORE = 'kv';
    var K_STATE = 'classify-state';
    var K_HANDLE = 'source-handle';

    var available = typeof indexedDB !== 'undefined';

    function openDB() {
        return new Promise(function (resolve, reject) {
            if (!available) { reject(new Error('IndexedDB unavailable')); return; }
            var req = indexedDB.open(DB_NAME, 1);
            req.onupgradeneeded = function () {
                var db = req.result;
                if (!db.objectStoreNames.contains(STORE)) db.createObjectStore(STORE);
            };
            req.onsuccess = function () { resolve(req.result); };
            req.onerror = function () { reject(req.error); };
        });
    }

    function tx(mode, fn) {
        return openDB().then(function (db) {
            return new Promise(function (resolve, reject) {
                var t = db.transaction(STORE, mode);
                var store = t.objectStore(STORE);
                var out = fn(store);
                t.oncomplete = function () { resolve(out && out.result !== undefined ? out.result : out); };
                t.onerror = function () { reject(t.error); };
                t.onabort = function () { reject(t.error); };
            });
        });
    }

    function put(key, value) { return tx('readwrite', function (s) { return s.put(value, key); }); }

    function getValue(key) {
        return openDB().then(function (db) {
            return new Promise(function (resolve, reject) {
                var t = db.transaction(STORE, 'readonly');
                var req = t.objectStore(STORE).get(key);
                req.onsuccess = function () { resolve(req.result); };
                req.onerror = function () { reject(req.error); };
            });
        });
    }

    // ── public API ─────────────────────────────────────────────────────────
    function saveState(obj) { return put(K_STATE, obj).catch(function (e) { console.warn('persist.saveState', e); }); }
    function loadState() { return getValue(K_STATE).catch(function () { return null; }); }

    function saveSourceHandle(handle) {
        // Real FileSystemDirectoryHandle only; the HTTP polyfill handle is not
        // worth persisting (server mode re-detects the root on load).
        if (!handle || handle.isHttp) return Promise.resolve();
        return put(K_HANDLE, handle).catch(function (e) { console.warn('persist.saveHandle', e); });
    }
    function loadSourceHandle() { return getValue(K_HANDLE).catch(function () { return null; }); }

    function clearAll() {
        return tx('readwrite', function (s) { s.delete(K_STATE); s.delete(K_HANDLE); })
            .catch(function (e) { console.warn('persist.clear', e); });
    }

    // Re-acquire read permission on a stored handle. Returns true if usable.
    function verifyPermission(handle) {
        if (!handle || typeof handle.queryPermission !== 'function') return Promise.resolve(false);
        var opts = { mode: 'read' };
        return handle.queryPermission(opts).then(function (p) {
            if (p === 'granted') return true;
            return handle.requestPermission(opts).then(function (p2) { return p2 === 'granted'; });
        }).catch(function () { return false; });
    }

    window.app.modules.persist = {
        available: available,
        saveState: saveState, loadState: loadState,
        saveSourceHandle: saveSourceHandle, loadSourceHandle: loadSourceHandle,
        verifyPermission: verifyPermission, clearAll: clearAll,
    };
})();