window.BrowserCache = (function () {
    var PREFIX = 'ying-cache:';
    var DEBUG_KEY = PREFIX + 'debug';
    var DEBUG = detectDebug();

    function detectDebug() {
        try {
            if (typeof window === 'undefined' || !window.location) return false;
            var loc = window.location;
            var host = loc.hostname || '';
            var protocol = loc.protocol || '';
            var search = loc.search || '';

            // Explicit URL override wins over everything.
            if (/(^|[?&])debug-cache=1(&|$)/.test(search)) return true;
            if (/(^|[?&])debug-cache=0(&|$)/.test(search)) return false;

            // Persisted toggle (set via setDebug) wins over auto-detection.
            try {
                var stored = localStorage.getItem(DEBUG_KEY);
                if (stored === '1') return true;
                if (stored === '0') return false;
            } catch (e) {}

            // Auto-enable on local dev origins.
            if (protocol === 'file:') return true;
            if (host === 'localhost' || host === '127.0.0.1' || host === '0.0.0.0') return true;
        } catch (e) {}
        return false;
    }

    function setDebug(enabled) {
        DEBUG = !!enabled;
        try {
            localStorage.setItem(DEBUG_KEY, DEBUG ? '1' : '0');
        } catch (e) {}
        return DEBUG;
    }

    function isDebug() {
        return DEBUG;
    }

    function isStorageAvailable() {
        try {
            var key = PREFIX + '__test__';
            localStorage.setItem(key, '1');
            localStorage.removeItem(key);
            return true;
        } catch (e) {
            return false;
        }
    }

    function buildKey(key) {
        return PREFIX + key;
    }

    function log(tagOrEvent, payload) {
        if (!DEBUG || typeof console === 'undefined' || !console.info) return;
        var label = tagOrEvent && tagOrEvent.charAt(0) === '[' ? tagOrEvent : '[BrowserCache][' + tagOrEvent + ']';
        console.info(label, payload || {});
    }

    function formatDuration(ms) {
        if (!ms || ms <= 0) return '0s';
        var totalSeconds = Math.floor(ms / 1000);
        var hours = Math.floor(totalSeconds / 3600);
        var minutes = Math.floor((totalSeconds % 3600) / 60);
        var seconds = totalSeconds % 60;
        if (hours > 0) return hours + 'h ' + minutes + 'm';
        if (minutes > 0) return minutes + 'm ' + seconds + 's';
        return seconds + 's';
    }

    function remove(key) {
        if (!isStorageAvailable()) return;
        try {
            localStorage.removeItem(buildKey(key));
            log('remove', { key: buildKey(key) });
        } catch (e) {}
    }

    function read(key, options) {
        options = options || {};
        if (!isStorageAvailable()) {
            log('storage-unavailable', { key: buildKey(key) });
            return null;
        }

        var fullKey = buildKey(key);

        try {
            var raw = localStorage.getItem(fullKey);
            if (!raw) {
                log('miss', { key: fullKey });
                return null;
            }

            var payload = JSON.parse(raw);
            if (!payload || typeof payload !== 'object') {
                remove(key);
                log('invalid-payload', { key: fullKey });
                return null;
            }

            if (payload.version !== options.version) {
                remove(key);
                log('version-mismatch', { key: fullKey, expected: options.version, actual: payload.version });
                return null;
            }

            if (typeof payload.cachedAt !== 'number' || !('data' in payload)) {
                remove(key);
                log('invalid-shape', { key: fullKey });
                return null;
            }

            if (typeof options.validate === 'function' && !options.validate(payload.data)) {
                remove(key);
                log('validate-failed', { key: fullKey });
                return null;
            }

            var now = Date.now();
            var age = now - payload.cachedAt;
            var softTtl = options.softTtl || 0;
            var hardTtl = options.hardTtl || softTtl;

            if (hardTtl > 0 && age > hardTtl) {
                remove(key);
                log('expired', { key: fullKey, age: formatDuration(age), hardTtl: formatDuration(hardTtl) });
                return null;
            }

            var result = {
                key: fullKey,
                data: payload.data,
                cachedAt: payload.cachedAt,
                age: age,
                ageText: formatDuration(age),
                softTtl: softTtl,
                softTtlText: formatDuration(softTtl),
                hardTtl: hardTtl,
                hardTtlText: formatDuration(hardTtl),
                isFresh: softTtl <= 0 || age <= softTtl,
                isStale: softTtl > 0 && age > softTtl
            };

            log(result.isFresh ? 'hit-fresh' : 'hit-stale', {
                key: fullKey,
                age: result.ageText,
                softTtl: result.softTtlText,
                hardTtl: result.hardTtlText
            });

            return result;
        } catch (e) {
            remove(key);
            log('parse-failed', { key: fullKey, message: e && e.message ? e.message : e });
            return null;
        }
    }

    function write(key, options, data) {
        options = options || {};
        if (!isStorageAvailable()) {
            log('storage-unavailable', { key: buildKey(key) });
            return;
        }

        var fullKey = buildKey(key);

        try {
            localStorage.setItem(fullKey, JSON.stringify({
                version: options.version,
                cachedAt: Date.now(),
                data: data
            }));
            log('write', {
                key: fullKey,
                softTtl: formatDuration(options.softTtl || 0),
                hardTtl: formatDuration(options.hardTtl || options.softTtl || 0)
            });
        } catch (e) {
            if (DEBUG && typeof console !== 'undefined' && console.warn) {
                console.warn('BrowserCache write failed:', e);
            }
        }
    }

    return {
        read: read,
        write: write,
        remove: remove,
        buildKey: buildKey,
        formatDuration: formatDuration,
        log: log,
        setDebug: setDebug,
        isDebug: isDebug
    };
})();