// NextSnap - Sync Engine
'use strict';

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

const Sync = {
    currentUsername: null,
    isOnline: navigator.onLine,
    isSyncing: false,
    MAX_RETRIES: 5,
    VERIFY_DELAY_MS: 800,

    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;
        });
    },

    // 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;

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

    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;
        }

        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;
            }

            await this.uploadPhoto(photo);
        }
    },

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

        try {
            console.log('[SYNC] Uploading:', photo.filename, '(attempt', retryCount + 1, 'of', this.MAX_RETRIES + ')');

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

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

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

            // Only check for duplicates on retries (skip on first attempt to reduce latency)
            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;
                }
            }

            // Resize if over 10MB
            let uploadBlob = photo.blob;
            if (uploadBlob.size > 10 * 1024 * 1024) {
                console.log('[SYNC] Photo too large (' + (uploadBlob.size / 1024 / 1024).toFixed(1) + 'MB), resizing...');
                uploadBlob = await this.resizeImage(uploadBlob, 10 * 1024 * 1024);
                console.log('[SYNC] Resized to ' + (uploadBlob.size / 1024 / 1024).toFixed(1) + 'MB');
            }

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

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

            const uploadResponse = await fetch(uploadUrl, {
                method: 'POST',
                body: formData
            });

            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);

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

    async resizeImage(blob, maxBytes) {
        return new Promise((resolve, reject) => {
            const img = new Image();
            const url = URL.createObjectURL(blob);

            img.onload = () => {
                URL.revokeObjectURL(url);
                let quality = 0.85;
                let scale = 1.0;

                const attempt = () => {
                    const canvas = document.createElement('canvas');
                    canvas.width = Math.round(img.width * scale);
                    canvas.height = Math.round(img.height * scale);
                    const ctx = canvas.getContext('2d');
                    ctx.drawImage(img, 0, 0, canvas.width, canvas.height);

                    canvas.toBlob((result) => {
                        if (!result) {
                            reject(new Error('Failed to resize image'));
                            return;
                        }
                        if (result.size <= maxBytes || (quality <= 0.4 && scale <= 0.3)) {
                            resolve(result);
                        } else {
                            // Reduce quality first, then scale down
                            if (quality > 0.5) {
                                quality -= 0.1;
                            } else {
                                scale *= 0.8;
                                quality = 0.7;
                            }
                            attempt();
                        }
                    }, 'image/jpeg', quality);
                };

                attempt();
            };

            img.onerror = () => {
                URL.revokeObjectURL(url);
                reject(new Error('Failed to load image for resize'));
            };

            img.src = url;
        });
    },

    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 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) {
            // If we can't check, assume it doesn't exist and proceed with upload
            return false;
        }
    },

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

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