import * as Notifications from "expo-notifications";
import { Platform } from "react-native";

Notifications.setNotificationHandler({
  handleNotification: async () => ({
    shouldShowAlert: true,
    shouldPlaySound: true,
    shouldSetBadge: false,
    shouldShowBanner: true,
    shouldShowList: true,
  }),
});

export async function ensureNotificationPermissions() {
  const settings = await Notifications.getPermissionsAsync();
  if (settings.granted) return true;
  const req = await Notifications.requestPermissionsAsync();
  return req.granted;
}

export function androidChannel() {
  if (Platform.OS === "android") {
    return Notifications.setNotificationChannelAsync("gishen-reminders", {
      name: "Gishen reminders",
      importance: Notifications.AndroidImportance.HIGH,
      sound: "default",
    });
  }
  return Promise.resolve();
}

export function parseTimeHHmm(value: string): { hour: number; minute: number } | null {
  const m = value.trim().match(/^(\d{1,2}):(\d{2})$/);
  if (!m) return null;
  const hour = Number(m[1]);
  const minute = Number(m[2]);
  if (hour < 0 || hour > 23 || minute < 0 || minute > 59) return null;
  return { hour, minute };
}

/** Seconds until the next occurrence of HH:mm (today or tomorrow). */
export function secondsUntilNextHHmm(value: string): number | null {
  const parsed = parseTimeHHmm(value);
  if (!parsed) return null;
  const now = new Date();
  const next = new Date(now);
  next.setHours(parsed.hour, parsed.minute, 0, 0);
  if (next.getTime() <= now.getTime()) {
    next.setDate(next.getDate() + 1);
  }
  return Math.max(5, Math.round((next.getTime() - now.getTime()) / 1000));
}

export async function scheduleDoseReminder(opts: {
  title: string;
  body: string;
  secondsFromNow: number;
  data?: Record<string, string>;
}) {
  await ensureNotificationPermissions();
  await androidChannel();
  return Notifications.scheduleNotificationAsync({
    content: {
      title: opts.title,
      body: opts.body,
      data: opts.data,
      sound: "default",
      categoryIdentifier: "dose",
    },
    trigger: {
      type: Notifications.SchedulableTriggerInputTypes.TIME_INTERVAL,
      seconds: Math.max(5, opts.secondsFromNow),
      repeats: false,
    },
  });
}

export async function scheduleEscalationCheck(opts: {
  title: string;
  body: string;
  graceSeconds: number;
  data?: Record<string, string>;
}) {
  await ensureNotificationPermissions();
  await androidChannel();
  return Notifications.scheduleNotificationAsync({
    content: {
      title: opts.title,
      body: opts.body,
      data: { ...opts.data, type: "escalation" },
      sound: "default",
    },
    trigger: {
      type: Notifications.SchedulableTriggerInputTypes.TIME_INTERVAL,
      seconds: Math.max(10, opts.graceSeconds),
      repeats: false,
    },
  });
}

/**
 * Schedule repeating daily calendar notifications for each HH:mm time.
 * Also queues a near-term demo notification for the soonest slot (~15s if within a few minutes).
 */
export async function scheduleDailyDoseReminders(opts: {
  prescriptionId: string;
  medicineName: string;
  times: string[];
  /** Optional prior notification ids to cancel */
  previousIds?: string[];
}) {
  const granted = await ensureNotificationPermissions();
  await androidChannel();

  if (opts.previousIds?.length) {
    await Promise.all(
      opts.previousIds.map((id) =>
        Notifications.cancelScheduledNotificationAsync(id).catch(() => {})
      )
    );
  }

  const notificationIds: string[] = [];
  const validTimes: string[] = [];

  for (const time of opts.times) {
    const parsed = parseTimeHHmm(time);
    if (!parsed) continue;
    validTimes.push(
      `${String(parsed.hour).padStart(2, "0")}:${String(parsed.minute).padStart(2, "0")}`
    );

    if (granted) {
      const id = await Notifications.scheduleNotificationAsync({
        content: {
          title: `Time for ${opts.medicineName}`,
          body: `Take your ${time} dose. Open Gishen to confirm.`,
          data: {
            prescriptionId: opts.prescriptionId,
            type: "dose",
            time,
          },
          sound: "default",
          categoryIdentifier: "dose",
        },
        trigger: {
          type: Notifications.SchedulableTriggerInputTypes.DAILY,
          hour: parsed.hour,
          minute: parsed.minute,
        },
      });
      notificationIds.push(id);
    }
  }

  // Demo: fire a near-term push so testers can verify without waiting until clock time
  if (granted && validTimes.length) {
    const demoId = await scheduleDoseReminder({
      title: `Reminder set · ${opts.medicineName}`,
      body: `Daily alerts at ${validTimes.join(", ")}. Demo ping.`,
      secondsFromNow: 12,
      data: {
        prescriptionId: opts.prescriptionId,
        type: "dose_demo",
      },
    });
    notificationIds.push(demoId);
  }

  return {
    granted,
    times: validTimes,
    notificationIds,
  };
}