// NextSnap - Sync Engine
'use strict';

console.log('[SYNC] Loading sync.js...');

const Sync = {
    currentUsername: null,
    isOnline: navigator.onLine,
    isSyncing: false,
    MAX_RETRIES: 15,
    VERIFY_DELAY_MS: 800,
    UPLOAD_TIMEOUT_MS: 120000,
    _retryTimerId: null,

    init(username) {
        this.currentUsername = username;
        this.setupEventListeners();
        console.log('[SYNC] Initialized for:', username);

        if (this.isOnline) {
            this.triggerSync();
        }
    },

    setupEventListeners() {
        window.addEventListener('online', () => {
            console.log('[SYNC] Network online');
            this.isOnline = true;
            this.triggerSync();
        });

        window.addEventListener('offline', () => {
            console.log('[SYNC] Network offline');
            this.isOnline = false;
            this.isSyncing = false;
            if (this._retryTimerId) {
                clearTimeout(this._retryTimerId);
                this._retryTimerId = null;
            }
        });
    },

    // Prevent page navigation during active upload
    _setUploading(active) {
        if (active) {
            this._beforeUnloadHandler = (e) => {
                e.preventDefault();
                e.returnValue = 'Upload in progress - leaving will cancel it.';
                return e.returnValue;
            };
            window.addEventListener('beforeunload', this._beforeUnloadHandler);
        } else {
            if (this._beforeUnloadHandler) {
                window.removeEventListener('beforeunload', this._beforeUnloadHandler);
                this._beforeUnloadHandler = null;
            }
        }
    },

    async triggerSync() {
        if (!this.isOnline || this.isSyncing) {
            console.log('[SYNC] Skip sync - online:', this.isOnline, 'syncing:', this.isSyncing);
            return;
        }

        console.log('[SYNC] Starting sync...');
        this.isSyncing = true;

        let hadFailures = false;
        try {
            hadFailures = await this.processQueue();
        } catch (error) {
            console.error('[SYNC] Error:', error);
            hadFailures = true;
        } finally {
            this.isSyncing = false;
            this._setUploading(false);
        }

        // If there were failures, schedule a retry cycle after a delay
        // so it doesn't block the current page load
        if (hadFailures && this.isOnline) {
            console.log('[SYNC] Scheduling retry in 15s...');
            this._retryTimerId = setTimeout(() => {
                this._retryTimerId = null;
                this.triggerSync();
            }, 15000);
        }
    },

    async processQueue() {
        const pendingPhotos = await Storage.db.photos
            .where('username').equals(this.currentUsername)
            .and(photo => photo.status === 'pending' || photo.status === 'uploading')
            .sortBy('timestamp');

        console.log('[SYNC] Found', pendingPhotos.length, 'photos to process');

        if (pendingPhotos.length === 0) {
            return false;
        }

        let hadFailures = false;

        for (const photo of pendingPhotos) {
            if (!this.isOnline) {
                console.log('[SYNC] Lost connection, stopping');
                break;
            }

            // Skip photos that have exceeded max retries
            const retryCount = photo.retryCount || 0;
            if (retryCount >= this.MAX_RETRIES) {
                console.warn('[SYNC] Skipping photo (max retries reached):', photo.filename, 'retries:', retryCount);
                await Storage.updatePhoto(photo.id, { status: 'failed' });
                continue;
            }

            // No delay — upload immediately. Retries are handled by
            // scheduling a new triggerSync() after the full queue pass.
            const success = await this.uploadPhoto(photo);
            if (!success) hadFailures = true;
        }

        return hadFailures;
    },

    async uploadPhoto(photo) {
        const retryCount = photo.retryCount || 0;

        try {
            // Re-read photo from IndexedDB to get a fresh blob reference
            // (iOS Safari can invalidate blob references between reads)
            const freshPhoto = await Storage.db.photos.get(photo.id);
            if (!freshPhoto || (freshPhoto.status !== 'pending' && freshPhoto.status !== 'uploading')) {
                console.log('[SYNC] Photo no longer pending, skipping:', photo.id);
                return true;
            }

            const blob = freshPhoto.blob;

            console.log('[SYNC] Uploading:', photo.filename,
                '(' + (blob ? (blob.size / 1024 / 1024).toFixed(1) + 'MB' : 'no blob') + ')',
                'attempt', retryCount + 1, 'of', this.MAX_RETRIES);

            // Validate blob reference exists
            if (!blob || !(blob instanceof Blob) || blob.size === 0) {
                throw new Error('Photo data is missing or corrupted - please delete and re-capture');
            }

            // Actually try to read the blob to verify data is accessible
            // (iOS Safari can evict blob data from IndexedDB while keeping the reference)
            const readable = await this.validateBlobReadable(blob);
            if (!readable) {
                // Blob data is gone — no amount of retrying will fix this
                console.error('[SYNC] Blob data is no longer readable:', photo.filename);
                await Storage.updatePhoto(photo.id, {
                    status: 'failed',
                    lastError: 'Photo data was lost by the browser - please re-capture',
                    error: 'Photo data was lost by the browser - please re-capture'
                });
                return false;
            }

            await Storage.updatePhoto(photo.id, { status: 'uploading' });

            // Prevent page navigation during upload
            this._setUploading(true);

            // On retries, first check if a previous attempt actually succeeded
            // (the upload may have completed but the verify/status update was interrupted)
            if (retryCount > 0) {
                const fullPath = photo.targetPath.replace(/\/$/, '') + '/' + photo.filename;
                const alreadyExists = await this.checkFileExists(fullPath);

                if (alreadyExists) {
                    console.log('[SYNC] File already exists on server, skipping upload:', fullPath);
                    await Storage.updatePhoto(photo.id, {
                        status: 'verified',
                        blob: null,
                        completedAt: Date.now()
                    });
                    await this.pruneHistory();
                    this._setUploading(false);
                    return true;
                }
            }

            const formData = new FormData();
            formData.append('file', blob, photo.filename);

            const uploadUrl = '/api/files/upload?path=' + encodeURIComponent(photo.targetPath);

            // Upload with timeout via AbortController
            const controller = new AbortController();
            const timeoutId = setTimeout(() => controller.abort(), this.UPLOAD_TIMEOUT_MS);

            let uploadResponse;
            try {
                uploadResponse = await fetch(uploadUrl, {
                    method: 'POST',
                    body: formData,
                    signal: controller.signal
                });
            } catch (fetchErr) {
                clearTimeout(timeoutId);
                if (fetchErr.name === 'AbortError') {
                    throw new Error('Upload timed out (' + (this.UPLOAD_TIMEOUT_MS / 1000) + 's)');
                }
                // Capture detailed error info for debugging
                const errDetail = fetchErr.name + ': ' + fetchErr.message;
                console.error('[SYNC] Fetch threw:', errDetail);
                throw new Error('Network error: ' + errDetail);
            }
            clearTimeout(timeoutId);

            if (!uploadResponse.ok) {
                let errorMsg = 'Upload failed';
                try {
                    const errData = await uploadResponse.json();
                    errorMsg = errData.error || errorMsg;
                } catch (e) {
                    errorMsg = 'Upload failed (HTTP ' + uploadResponse.status + ')';
                }
                throw new Error(errorMsg);
            }

            const uploadResult = await uploadResponse.json();
            console.log('[SYNC] Upload successful:', uploadResult.path);

            await Storage.updatePhoto(photo.id, { status: 'uploaded' });

            // Wait before verifying to allow server-side processing
            await this.delay(this.VERIFY_DELAY_MS);

            const verifyUrl = '/api/files/verify?path=' + encodeURIComponent(uploadResult.path);
            const verifyResponse = await fetch(verifyUrl);

            if (!verifyResponse.ok) {
                throw new Error('Verification failed');
            }

            const verifyResult = await verifyResponse.json();

            if (!verifyResult.exists) {
                throw new Error('File not found on server');
            }

            console.log('[SYNC] Verified:', uploadResult.path);

            // Keep record but strip blob to save storage
            await Storage.updatePhoto(photo.id, {
                status: 'verified',
                blob: null,
                completedAt: Date.now()
            });

            console.log('[SYNC] Upload complete:', photo.id);

            // Prune old completed entries beyond 20
            await this.pruneHistory();

            // Clear navigation guard after successful upload
            this._setUploading(false);
            return true;

        } catch (error) {
            this._setUploading(false);
            const errMsg = (error.name || 'Error') + ': ' + error.message;
            console.error('[SYNC] Upload failed:', errMsg, '(attempt', retryCount + 1 + ')');
            await Storage.updatePhoto(photo.id, {
                status: 'pending',
                retryCount: retryCount + 1,
                lastError: errMsg,
                error: errMsg
            });
            return false;
        }
    },

    async pruneHistory() {
        // Keep only the last 20 completed (verified/failed) entries per user
        const completed = await Storage.db.photos
            .where('username').equals(this.currentUsername)
            .and(p => p.status === 'verified' || p.status === 'failed')
            .sortBy('timestamp');

        if (completed.length > 20) {
            const toDelete = completed.slice(0, completed.length - 20);
            for (const photo of toDelete) {
                await Storage.deletePhoto(photo.id);
            }
            console.log('[SYNC] Pruned', toDelete.length, 'old history entries');
        }
    },

    async validateBlobReadable(blob) {
        try {
            // Try to read the first byte — if iOS has evicted the data,
            // this will throw even though the Blob reference looks valid
            const slice = blob.slice(0, 1);
            const buf = await slice.arrayBuffer();
            return buf.byteLength > 0;
        } catch (e) {
            console.error('[SYNC] Blob readability check failed:', e.message);
            return false;
        }
    },

    async checkFileExists(path) {
        try {
            const verifyUrl = '/api/files/verify?path=' + encodeURIComponent(path);
            const response = await fetch(verifyUrl);
            if (!response.ok) return false;
            const result = await response.json();
            return result.exists === true;
        } catch (e) {
            return false;
        }
    },

    delay(ms) {
        return new Promise(resolve => setTimeout(resolve, ms));
    }
};

window.SyncEngine = Sync;
console.log('[SYNC] SyncEngine exported successfully');