/*
 * InkNote — Client Sync Engine
 * ─────────────────────────────
 * Handles offline-first sync with conflict resolution.
 * Works in React Native, Flutter (via JS bridge), Electron, and web.
 *
 * Usage:
 *   import { SyncEngine } from './sync-client';
 *   const sync = new SyncEngine('https://your-server.com', deviceId);
 *   await sync.authenticate(email, password);
 *   sync.start();    // begins periodic sync + WebSocket listener
 *   sync.stop();     // stops sync
 */

class SyncEngine {
  constructor(serverUrl, deviceId) {
    this.serverUrl = serverUrl.replace(/\/$/, "");
    this.deviceId = deviceId;
    this.token = null;
    this.ws = null;
    this.syncInterval = null;
    this.pendingChanges = [];
    this.lastSyncTimestamp = null;
    this.listeners = new Map();
    this.isOnline = true;
    this.isSyncing = false;
  }

  /* ─── Authentication ─── */
  async authenticate(email, password) {
    const res = await fetch(`${this.serverUrl}/api/auth/login`, {
      method: "POST",
      headers: { "Content-Type": "application/json" },
      body: JSON.stringify({ email, password }),
    });
    if (!res.ok) throw new Error("Authentication failed");
    const data = await res.json();
    this.token = data.token;
    return data.user;
  }

  async register(email, password, displayName) {
    const res = await fetch(`${this.serverUrl}/api/auth/register`, {
      method: "POST",
      headers: { "Content-Type": "application/json" },
      body: JSON.stringify({ email, password, displayName }),
    });
    if (!res.ok) throw new Error("Registration failed");
    const data = await res.json();
    this.token = data.token;
    return data.user;
  }

  /* ─── Event system ─── */
  on(event, callback) {
    if (!this.listeners.has(event)) this.listeners.set(event, []);
    this.listeners.get(event).push(callback);
    return () => {
      const cbs = this.listeners.get(event);
      const idx = cbs.indexOf(callback);
      if (idx > -1) cbs.splice(idx, 1);
    };
  }

  emit(event, data) {
    const cbs = this.listeners.get(event) || [];
    cbs.forEach((cb) => cb(data));
  }

  /* ─── Start / Stop ─── */
  start(intervalMs = 30000) {
    this.connectWebSocket();
    this.syncInterval = setInterval(() => this.sync(), intervalMs);
    this.sync(); // immediate first sync

    // Listen for online/offline
    if (typeof window !== "undefined") {
      window.addEventListener("online", () => {
        this.isOnline = true;
        this.emit("status", "online");
        this.sync();
      });
      window.addEventListener("offline", () => {
        this.isOnline = false;
        this.emit("status", "offline");
      });
    }
  }

  stop() {
    if (this.syncInterval) clearInterval(this.syncInterval);
    if (this.ws) this.ws.close();
    this.ws = null;
  }

  /* ─── WebSocket ─── */
  connectWebSocket() {
    const wsUrl = this.serverUrl.replace(/^http/, "ws") + "/ws";
    this.ws = new WebSocket(wsUrl);

    this.ws.onopen = () => {
      this.ws.send(JSON.stringify({
        type: "auth",
        token: this.token,
        deviceId: this.deviceId,
      }));
    };

    this.ws.onmessage = (event) => {
      try {
        const msg = JSON.parse(event.data);
        if (msg.type === "auth_ok") {
          this.emit("status", "connected");
        } else if (msg.type.endsWith("_created") || msg.type.endsWith("_updated") || msg.type.endsWith("_deleted")) {
          this.emit("remote_change", msg);
          this.sync(); // re-sync on remote change
        }
      } catch { /* ignore parse errors */ }
    };

    this.ws.onclose = () => {
      this.emit("status", "disconnected");
      // Auto-reconnect after 5s
      setTimeout(() => {
        if (this.token) this.connectWebSocket();
      }, 5000);
    };

    this.ws.onerror = () => {
      this.emit("status", "error");
    };
  }

  /* ─── Queue changes for sync ─── */
  queueChange(entityType, entityId, action, data) {
    const change = {
      entityType,
      entityId,
      action,
      data: { ...data, id: entityId },
      timestamp: new Date().toISOString(),
      deviceId: this.deviceId,
    };
    this.pendingChanges.push(change);

    // Persist to local storage for crash recovery
    this.savePendingChanges();

    // Try immediate sync if online
    if (this.isOnline && !this.isSyncing) {
      this.sync();
    }
  }

  /* ─── Full sync cycle ─── */
  async sync() {
    if (!this.token || !this.isOnline || this.isSyncing) return;
    this.isSyncing = true;
    this.emit("status", "syncing");

    try {
      const res = await fetch(`${this.serverUrl}/api/sync`, {
        method: "POST",
        headers: {
          "Content-Type": "application/json",
          "Authorization": `Bearer ${this.token}`,
          "X-Device-Id": this.deviceId,
        },
        body: JSON.stringify({
          lastSyncTimestamp: this.lastSyncTimestamp,
          deviceId: this.deviceId,
          changes: this.pendingChanges,
        }),
      });

      if (!res.ok) throw new Error(`Sync failed: ${res.status}`);
      const result = await res.json();

      // Process results
      for (const pushed of result.pushed) {
        if (pushed.status === "ok") {
          this.pendingChanges = this.pendingChanges.filter((c) => c.data?.id !== pushed.id);
        }
      }

      // Handle conflicts
      for (const conflict of result.conflicts) {
        this.emit("conflict", conflict);
      }

      // Apply pulled changes from server
      for (const change of result.pulled) {
        this.emit("remote_change", change);
      }

      this.lastSyncTimestamp = result.syncTimestamp;
      this.savePendingChanges();
      this.emit("status", "synced");
    } catch (err) {
      this.emit("status", "error");
      console.error("Sync error:", err);
    } finally {
      this.isSyncing = false;
    }
  }

  /* ─── Local persistence for pending changes ─── */
  savePendingChanges() {
    try {
      if (typeof localStorage !== "undefined") {
        localStorage.setItem(`inknote_pending_${this.deviceId}`, JSON.stringify(this.pendingChanges));
        localStorage.setItem(`inknote_last_sync_${this.deviceId}`, this.lastSyncTimestamp || "");
      }
    } catch { /* ignore storage errors */ }
  }

  loadPendingChanges() {
    try {
      if (typeof localStorage !== "undefined") {
        const pending = localStorage.getItem(`inknote_pending_${this.deviceId}`);
        if (pending) this.pendingChanges = JSON.parse(pending);
        this.lastSyncTimestamp = localStorage.getItem(`inknote_last_sync_${this.deviceId}`) || null;
      }
    } catch { /* ignore storage errors */ }
  }

  /* ─── API helpers ─── */
  async fetchNotes() {
    const res = await fetch(`${this.serverUrl}/api/notes`, {
      headers: { Authorization: `Bearer ${this.token}`, "X-Device-Id": this.deviceId },
    });
    return res.json();
  }

  async fetchNote(id) {
    const res = await fetch(`${this.serverUrl}/api/notes/${id}`, {
      headers: { Authorization: `Bearer ${this.token}`, "X-Device-Id": this.deviceId },
    });
    return res.json();
  }

  async createNote(note) {
    const res = await fetch(`${this.serverUrl}/api/notes`, {
      method: "POST",
      headers: {
        "Content-Type": "application/json",
        Authorization: `Bearer ${this.token}`,
        "X-Device-Id": this.deviceId,
      },
      body: JSON.stringify(note),
    });
    const data = await res.json();
    this.queueChange("note", data.id, "create", note);
    return data;
  }

  async updateNote(id, updates) {
    const res = await fetch(`${this.serverUrl}/api/notes/${id}`, {
      method: "PUT",
      headers: {
        "Content-Type": "application/json",
        Authorization: `Bearer ${this.token}`,
        "X-Device-Id": this.deviceId,
      },
      body: JSON.stringify(updates),
    });
    if (res.status === 409) {
      const conflict = await res.json();
      this.emit("conflict", conflict);
      return conflict;
    }
    this.queueChange("note", id, "update", updates);
    return res.json();
  }

  async deleteNote(id) {
    await fetch(`${this.serverUrl}/api/notes/${id}`, {
      method: "DELETE",
      headers: { Authorization: `Bearer ${this.token}`, "X-Device-Id": this.deviceId },
    });
    this.queueChange("note", id, "delete", { id });
  }

  async uploadPDF(file) {
    const formData = new FormData();
    formData.append("pdf", file);
    const res = await fetch(`${this.serverUrl}/api/notes/pdf`, {
      method: "POST",
      headers: {
        Authorization: `Bearer ${this.token}`,
        "X-Device-Id": this.deviceId,
      },
      body: formData,
    });
    return res.json();
  }

  async saveDrawing(noteId, drawingDataUrl) {
    await fetch(`${this.serverUrl}/api/notes/${noteId}/drawing`, {
      method: "PUT",
      headers: {
        "Content-Type": "application/json",
        Authorization: `Bearer ${this.token}`,
        "X-Device-Id": this.deviceId,
      },
      body: JSON.stringify({ drawingData: drawingDataUrl }),
    });
  }
}

export { SyncEngine };