/**
 * Browser Notification helper. Pure-ish wrapper around the Web
 * Notification API plus a localStorage flag for the operator's
 * opt-in preference. We use this for surfaced, in-tab notifications
 * — when a tab is open, fire a notification on:
 *
 *   - reminder.fired (status=success / partial)
 *   - send_test.done (ok=true)
 *
 * For background push (closed app) we'd need a service-worker
 * subscription + VAPID, which is a bigger lift. This module is the
 * foundation that swap-in lands on later.
 */

const STORAGE_KEY = "cmbot.notifications.optedIn";

export type NotificationPermission = "default" | "granted" | "denied";
export type NotificationCapability = "supported" | "unsupported";

/** Detect whether the browser exposes the Notification API at all. */
export function notificationSupport(): NotificationCapability {
  if (typeof window === "undefined") return "unsupported";
  if (typeof window.Notification === "undefined") return "unsupported";
  return "supported";
}

/** Read the current permission state, treating unsupported browsers
 *  as "denied" so callers don't have to handle a third state. */
export function getPermission(): NotificationPermission {
  if (notificationSupport() === "unsupported") return "denied";
  return window.Notification.permission as NotificationPermission;
}

/** Has the operator opted in (saved in localStorage)? */
export function isOptedIn(): boolean {
  if (typeof window === "undefined") return false;
  try {
    return window.localStorage.getItem(STORAGE_KEY) === "1";
  } catch {
    return false;
  }
}

export function setOptedIn(value: boolean): void {
  if (typeof window === "undefined") return;
  try {
    if (value) {
      window.localStorage.setItem(STORAGE_KEY, "1");
    } else {
      window.localStorage.removeItem(STORAGE_KEY);
    }
  } catch {
    // localStorage can throw in private mode / quota — non-fatal.
  }
}

/**
 * Ask the browser for permission. Resolves with the resulting
 * permission state. Idempotent if already granted/denied.
 */
export async function requestPermission(): Promise<NotificationPermission> {
  if (notificationSupport() === "unsupported") return "denied";
  const result = await window.Notification.requestPermission();
  return result as NotificationPermission;
}

export interface ShowNotificationOptions {
  title: string;
  body?: string;
  /** Stable identifier so repeats of the same event coalesce. */
  tag?: string;
  /** Path the click handler should navigate to (page reuses or
   *  opens a new tab). Optional. */
  href?: string;
  /** Override the default icon; defaults to `/icon-192.png`. */
  icon?: string;
}

export type NotificationDispatch =
  | { ok: true; tag: string | undefined }
  | { ok: false; reason: "unsupported" | "permission" | "opted-out" | "error"; error?: string };

/**
 * Show a notification if everything's lined up:
 *   - browser supports it
 *   - operator has opted in
 *   - permission is granted
 *
 * Returns a discriminated result so callers can decide whether to
 * fall back to a UI toast.
 */
export function showNotification(opts: ShowNotificationOptions): NotificationDispatch {
  if (notificationSupport() === "unsupported") {
    return { ok: false, reason: "unsupported" };
  }
  if (!isOptedIn()) {
    return { ok: false, reason: "opted-out" };
  }
  if (getPermission() !== "granted") {
    return { ok: false, reason: "permission" };
  }
  try {
    const n = new window.Notification(opts.title, {
      body: opts.body,
      tag: opts.tag,
      icon: opts.icon ?? "/icon-192.png",
      badge: "/icon-192.png",
    });
    if (opts.href) {
      n.onclick = () => {
        try {
          window.focus();
          window.location.href = opts.href!;
        } catch {
          // ignore — focus can fail under iframe sandboxing
        }
      };
    }
    return { ok: true, tag: opts.tag };
  } catch (err) {
    return { ok: false, reason: "error", error: (err as Error).message };
  }
}

// ---------------------------------------------------------------------------
// Event → notification mapping
// ---------------------------------------------------------------------------

/**
 * Map a `reminder.fired` SSE event into the notification arguments
 * the manager component should call `showNotification` with.
 *
 * Returns null when the run isn't worth notifying about (e.g.
 * `skipped` runs are bookkeeping noise, not user-facing events).
 */
export function reminderFiredToNotification(event: {
  type: "reminder.fired";
  reminderId: string;
  runId: string;
  status: string;
  sent?: number;
  total?: number;
}): ShowNotificationOptions | null {
  if (event.status === "skipped") return null;
  const headline =
    event.status === "success"
      ? "Reminder sent"
      : event.status === "paused"
        ? "Reminder paused"
        : event.status === "partial"
          ? "Reminder partly sent"
          : "Reminder failed";
  let body =
    event.status === "success"
      ? "All groups received the message."
      : event.status === "paused"
        ? "Delivery window closed before all groups got the message."
        : event.status === "partial"
          ? "Some groups received the message; others failed. See activity."
          : "No groups received the message. See activity.";
  if (event.status === "paused" && event.sent !== undefined && event.total !== undefined) {
    body = `${event.sent} of ${event.total} groups delivered. Tap to resume or cancel.`;
  } else if (
    event.status === "partial" &&
    event.sent !== undefined &&
    event.total !== undefined
  ) {
    body = `${event.sent} of ${event.total} groups delivered. See activity for details.`;
  }
  return {
    title: headline,
    body,
    // Coalesce repeat fires of the same reminder on the same tab —
    // only the most recent one stays visible.
    tag: `reminder:${event.reminderId}`,
    href: `/reminders/${event.reminderId}`,
  };
}

/**
 * Map a `send_test.done` SSE event into notification arguments.
 * Returns null on the failure case so the in-page toast (which
 * shows the error verbatim) stays the source of truth.
 */
export function sendTestDoneToNotification(event: {
  type: "send_test.done";
  groupId: string;
  ok: boolean;
}): ShowNotificationOptions | null {
  if (!event.ok) return null;
  return {
    title: "Test message sent",
    body: "WhatsApp delivered the test message.",
    tag: `send-test:${event.groupId}`,
    href: `/groups/${event.groupId}`,
  };
}