import { BATCH_TIMEZONE } from './booking-batch.constants';

/** EAT intake boundaries — cron runs at these hours; each window spans to the next. */
export const BATCH_WINDOW_START_HOURS = [7, 10, 13, 16, 19, 22] as const;

export interface BatchWindow {
  key: string;
  label: string;
  start: Date;
  end: Date;
}

type EatDateParts = {
  year: number;
  month: number;
  day: number;
  hour: number;
  minute: number;
};

const dateFmt = new Intl.DateTimeFormat('en-GB', {
  day: '2-digit',
  month: 'short',
  year: 'numeric',
  timeZone: BATCH_TIMEZONE,
});

const timeFmt = new Intl.DateTimeFormat('en-GB', {
  hour: '2-digit',
  minute: '2-digit',
  hour12: false,
  timeZone: BATCH_TIMEZONE,
});

function eatParts(date: Date): EatDateParts {
  const parts = new Intl.DateTimeFormat('en-US', {
    timeZone: BATCH_TIMEZONE,
    year: 'numeric',
    month: '2-digit',
    day: '2-digit',
    hour: '2-digit',
    minute: '2-digit',
    hour12: false,
  }).formatToParts(date);

  const get = (type: Intl.DateTimeFormatPartTypes) =>
    Number(parts.find((p) => p.type === type)?.value ?? 0);

  return {
    year: get('year'),
    month: get('month'),
    day: get('day'),
    hour: get('hour'),
    minute: get('minute'),
  };
}

/**
 * The EAT calendar day a timestamp falls on, as `yyyy-MM-dd`. This is the day
 * key for day-level booking pools — it must match the day the portal calendar
 * renders, so always derive day keys through this (never `toISOString().slice`).
 */
export function eatDay(date: Date): string {
  const { year, month, day } = eatParts(date);
  return `${year}-${String(month).padStart(2, '0')}-${String(day).padStart(2, '0')}`;
}

/** Build a UTC Date for a given EAT local wall-clock time on a calendar day. */
function eatToUtc(
  year: number,
  month: number,
  day: number,
  hour: number,
  minute = 0,
): Date {
  // EAT is UTC+3 year-round (no DST). Binary search would be safer across DST zones;
  // for Africa/Addis_Ababa the offset is fixed.
  const utcMs = Date.UTC(year, month - 1, day, hour - 3, minute, 0, 0);
  return new Date(utcMs);
}

function formatWindowLabel(start: Date, end: Date, endHourLabel?: string): string {
  const endTime = endHourLabel ?? timeFmt.format(new Date(end.getTime() - 60_000));
  return `${dateFmt.format(start)} · ${timeFmt.format(start)} – ${endTime} EAT`;
}

function windowFromEatStart(
  year: number,
  month: number,
  day: number,
  startHour: number,
): BatchWindow {
  const start = eatToUtc(year, month, day, startHour);
  let endYear = year;
  let endMonth = month;
  let endDay = day;
  let endHour: number;
  let endHourLabel: string;

  const idx = BATCH_WINDOW_START_HOURS.indexOf(startHour as (typeof BATCH_WINDOW_START_HOURS)[number]);
  if (idx === BATCH_WINDOW_START_HOURS.length - 1) {
    endHour = 7;
    endHourLabel = '07:00';
    const next = new Date(eatToUtc(year, month, day, 0));
    next.setUTCDate(next.getUTCDate() + 1);
    const nextParts = eatParts(next);
    endYear = nextParts.year;
    endMonth = nextParts.month;
    endDay = nextParts.day;
  } else {
    endHour = BATCH_WINDOW_START_HOURS[idx + 1];
    endHourLabel = `${String(endHour).padStart(2, '0')}:00`;
  }

  const end = eatToUtc(endYear, endMonth, endDay, endHour);
  return {
    key: start.toISOString(),
    start,
    end,
    label: formatWindowLabel(start, end, endHourLabel),
  };
}

/** Build a UTC Date for an EAT wall-clock time on a `yyyy-MM-dd` EAT calendar day. */
export function eatDayToUtc(day: string, hour: number, minute = 0): Date {
  const [year, month, dayOfMonth] = day.split('-').map(Number);
  return eatToUtc(year, month, dayOfMonth, hour, minute);
}

/** Shift a `yyyy-MM-dd` EAT day key by whole days. */
export function shiftEatDay(day: string, deltaDays: number): string {
  // Noon UTC keeps the +3h EAT offset from crossing a day boundary.
  const [year, month, dayOfMonth] = day.split('-').map(Number);
  const shifted = new Date(Date.UTC(year, month - 1, dayOfMonth + deltaDays, 12));
  return `${shifted.getUTCFullYear()}-${String(shifted.getUTCMonth() + 1).padStart(2, '0')}-${String(
    shifted.getUTCDate(),
  ).padStart(2, '0')}`;
}

export interface InitialWindowTimes {
  windowOpensAt: Date;
  windowClosesAt: Date;
}

/**
 * Import booking-day window: opens at `windowOpenHour` EAT on departure-day minus
 * `importWindowLeadDays`, for `windowDurationHours`. A schedule created after its
 * computed window has fully passed gets a same-day window starting now instead,
 * capped at departure.
 */
export function computeImportWindowTimes(
  departure: Date,
  cfg: {
    importWindowLeadDays: number;
    windowOpenHour: number;
    windowDurationHours: number;
  },
  now: Date,
): InitialWindowTimes {
  const windowDay = shiftEatDay(eatDay(departure), -cfg.importWindowLeadDays);
  let opensAt = eatDayToUtc(windowDay, cfg.windowOpenHour);
  let closesAt = new Date(opensAt.getTime() + cfg.windowDurationHours * 3_600_000);
  if (closesAt.getTime() <= now.getTime()) {
    opensAt = now;
    closesAt = new Date(now.getTime() + cfg.windowDurationHours * 3_600_000);
  }
  if (closesAt.getTime() > departure.getTime()) {
    closesAt = departure;
  }
  return { windowOpensAt: opensAt, windowClosesAt: closesAt };
}

/** Export booking window: FCFS from `exportBookingLeadHours` before departure until departure. */
export function computeExportWindowTimes(
  departure: Date,
  cfg: { exportBookingLeadHours: number },
): InitialWindowTimes {
  return {
    windowOpensAt: new Date(departure.getTime() - cfg.exportBookingLeadHours * 3_600_000),
    windowClosesAt: departure,
  };
}

/**
 * Earliest departure a train may be scheduled for — staff cannot schedule inside
 * the lead window. IMPORT/DOMESTIC lead is in whole EAT days: with lead 3 and
 * today the 11th, the 12th and 13th are blocked and the 14th is the first
 * allowed departure day (00:00 EAT). EXPORT lead is in hours: earliest departure
 * is `now + exportBookingLeadHours` (24h = 1 day). Mirrors the booking-window
 * math so a schedulable date always has a real booking window before it.
 */
export function earliestSchedulableDeparture(
  direction: string | null | undefined,
  cfg: { importWindowLeadDays: number; exportBookingLeadHours: number },
  now: Date,
): Date {
  if (direction === 'EXPORT') {
    return new Date(now.getTime() + cfg.exportBookingLeadHours * 3_600_000);
  }
  const earliestDay = shiftEatDay(eatDay(now), cfg.importWindowLeadDays);
  return eatDayToUtc(earliestDay, 0);
}

/** Which 3h EAT intake window a timestamp (e.g. fullyExecutedAt) belongs to. */
export function getBatchWindowForTimestamp(date: Date): BatchWindow {
  const { year, month, day, hour } = eatParts(date);

  if (hour < 7) {
    const prev = new Date(eatToUtc(year, month, day, 0));
    prev.setUTCDate(prev.getUTCDate() - 1);
    const prevParts = eatParts(prev);
    return windowFromEatStart(prevParts.year, prevParts.month, prevParts.day, 22);
  }

  let startHour: (typeof BATCH_WINDOW_START_HOURS)[number] = 7;
  for (const h of BATCH_WINDOW_START_HOURS) {
    if (hour >= h) startHour = h;
  }

  return windowFromEatStart(year, month, day, startHour);
}

/** All six intake windows for an EAT calendar day (includes overnight 22:00–07:00). */
export function listBatchWindowsForDate(reference: Date): BatchWindow[] {
  const { year, month, day } = eatParts(reference);
  return BATCH_WINDOW_START_HOURS.map((startHour) =>
    windowFromEatStart(year, month, day, startHour),
  );
}

export function compareBatchWindows(a: BatchWindow, b: BatchWindow): number {
  return a.start.getTime() - b.start.getTime();
}

/** Schedule-day windows plus any extra windows that contain booking timestamps (cross-day). */
export function listBatchWindowsForBookings(
  timestamps: Array<Date | null | undefined>,
  referenceDate: Date,
): BatchWindow[] {
  const byKey = new Map<string, BatchWindow>();
  for (const w of listBatchWindowsForDate(referenceDate)) {
    byKey.set(w.key, w);
  }
  for (const ts of timestamps) {
    if (!ts) continue;
    const w = getBatchWindowForTimestamp(ts);
    byKey.set(w.key, w);
  }
  return [...byKey.values()].sort(compareBatchWindows);
}

// ---------------------------------------------------------------------------
// Board-display windows: the REAL booking-window cycles derived from the
// train_scheduling_global_rules config (window open hour, lead days, duration,
// reopen delay) — NOT a fixed clock grid. Import shows each booking-window cycle
// (opens at windowOpenHour EAT, lasts windowDurationHours, reopens after
// reopenDelayMinutes until departure). Export shows the single FCFS lead window.
// ---------------------------------------------------------------------------

/** A board window carries an EAT calendar date in addition to the slot times. */
export interface BoardWindow extends BatchWindow {
  /** EAT calendar day as ISO `YYYY-MM-DD`. */
  date: string;
  /** Human label for the day, e.g. `Thu, 05 Jun`. */
  dateLabel: string;
}

/** Config fields the board needs to reconstruct booking-window cycles. */
export interface BoardWindowConfig {
  importWindowLeadDays: number;
  windowOpenHour: number;
  windowDurationHours: number;
  reopenDelayMinutes: number;
  exportBookingLeadHours: number;
}

const dayLabelFmt = new Intl.DateTimeFormat('en-GB', {
  weekday: 'short',
  day: '2-digit',
  month: 'short',
  timeZone: BATCH_TIMEZONE,
});

function pad2(n: number): string {
  return String(n).padStart(2, '0');
}

/** Wrap a [start, end] interval as a labelled BoardWindow keyed on its EAT day. */
function boardWindowFromInterval(start: Date, end: Date): BoardWindow {
  const { year, month, day } = eatParts(start);
  return {
    key: start.toISOString(),
    start,
    end,
    label: formatWindowLabel(start, end),
    date: `${year}-${pad2(month)}-${pad2(day)}`,
    dateLabel: dayLabelFmt.format(start),
  };
}

/**
 * The real booking-window cycles for a schedule, straight from config.
 *
 * IMPORT: first window opens at `windowOpenHour` EAT on `departure − importWindowLeadDays`
 * for `windowDurationHours`; if the train isn't full it reopens `reopenDelayMinutes`
 * after each close, on the same booking day, until departure. This mirrors
 * `computeImportWindowTimes` + `concludeCycle`'s reopen math so the board shows the
 * exact windows the engine runs.
 * EXPORT: a single FCFS window from `departure − exportBookingLeadHours` to departure.
 *
 * `anchorOpensAt` pins the FIRST window's open time to the schedule's stored
 * `windowOpensAt` instead of recomputing it from config. Pass it so the board
 * shows the real frozen window (and reopen cycles projected from it) even after
 * the global rule changed — the recomputed open time would otherwise drift.
 */
export function listConfigBookingWindows(
  direction: string | null | undefined,
  departure: Date,
  cfg: BoardWindowConfig,
  anchorOpensAt?: Date | null,
): BoardWindow[] {
  if (direction === 'EXPORT') {
    const start =
      anchorOpensAt ??
      new Date(departure.getTime() - cfg.exportBookingLeadHours * 3_600_000);
    return [boardWindowFromInterval(start, departure)];
  }

  const windows: BoardWindow[] = [];
  const durationMs = cfg.windowDurationHours * 3_600_000;
  const reopenMs = cfg.reopenDelayMinutes * 60_000;
  const windowDay = shiftEatDay(eatDay(departure), -cfg.importWindowLeadDays);

  let opensAt = anchorOpensAt ?? eatDayToUtc(windowDay, cfg.windowOpenHour);
  // Reopen stays on the same EAT booking day and before departure; cap at 12 cycles.
  for (let cycle = 0; cycle < 12; cycle += 1) {
    if (opensAt.getTime() >= departure.getTime()) break;
    let closesAt = new Date(opensAt.getTime() + durationMs);
    if (closesAt.getTime() > departure.getTime()) closesAt = departure;
    windows.push(boardWindowFromInterval(opensAt, closesAt));

    const nextOpensAt = new Date(closesAt.getTime() + reopenMs);
    if (
      nextOpensAt.getTime() >= departure.getTime() ||
      eatDay(nextOpensAt) !== eatDay(opensAt)
    ) {
      break;
    }
    opensAt = nextOpensAt;
  }

  // Degenerate config (no window before departure) — surface a single window
  // clamped to departure so the board still renders something meaningful.
  if (windows.length === 0) {
    windows.push(boardWindowFromInterval(new Date(departure.getTime() - durationMs), departure));
  }
  return windows;
}

/** Which config booking-window a timestamp falls in; null if before/after all of them. */
function configWindowForTimestamp(
  windows: BoardWindow[],
  date: Date,
): BoardWindow | null {
  const ms = date.getTime();
  for (const w of windows) {
    if (ms >= w.start.getTime() && ms < w.end.getTime()) return w;
  }
  return null;
}

/**
 * Group items into the real config booking-window cycles for a schedule. Empty
 * windows are kept so the UI shows every cycle. Items whose timestamp falls
 * outside every window (e.g. a booking created before the window opened) are
 * attached to the nearest window by start time so nothing is hidden. Items
 * without a timestamp go to `pendingKey`.
 */
export function groupBookingsIntoBoardWindows<T>(
  items: T[],
  getTimestamp: (item: T) => Date | null | undefined,
  direction: string | null | undefined,
  departure: Date,
  cfg: BoardWindowConfig,
  pendingKey = 'pending-contract',
  anchorOpensAt?: Date | null,
): Map<string, { window: BoardWindow | null; items: T[] }> {
  const windows = listConfigBookingWindows(direction, departure, cfg, anchorOpensAt);
  const map = new Map<string, { window: BoardWindow | null; items: T[] }>();
  for (const w of windows) {
    map.set(w.key, { window: w, items: [] });
  }
  map.set(pendingKey, { window: null, items: [] });

  const firstWindow = windows[0] ?? null;
  const lastWindow = windows[windows.length - 1] ?? null;

  for (const item of items) {
    const ts = getTimestamp(item);
    if (!ts) {
      map.get(pendingKey)!.items.push(item);
      continue;
    }
    let w = configWindowForTimestamp(windows, ts);
    if (!w) {
      // Booked before the window opened → first cycle; after it closed → last cycle.
      w =
        firstWindow && ts.getTime() < firstWindow.start.getTime()
          ? firstWindow
          : lastWindow;
    }
    if (!w) {
      map.get(pendingKey)!.items.push(item);
      continue;
    }
    map.get(w.key)!.items.push(item);
  }

  return map;
}

/** Group items by batch window key; items without a timestamp go to `pendingKey`. */
export function groupByBatchWindow<T>(
  items: T[],
  getTimestamp: (item: T) => Date | null | undefined,
  referenceDate: Date,
  pendingKey = 'pending-contract',
): Map<string, { window: BatchWindow | null; items: T[] }> {
  const timestamps = items.map(getTimestamp);
  const windows = listBatchWindowsForBookings(timestamps, referenceDate);
  const map = new Map<string, { window: BatchWindow | null; items: T[] }>();

  for (const w of windows) {
    map.set(w.key, { window: w, items: [] });
  }
  map.set(pendingKey, { window: null, items: [] });

  for (const item of items) {
    const ts = getTimestamp(item);
    if (!ts) {
      map.get(pendingKey)!.items.push(item);
      continue;
    }
    const w = getBatchWindowForTimestamp(ts);
    if (!map.has(w.key)) {
      map.set(w.key, { window: w, items: [] });
    }
    map.get(w.key)!.items.push(item);
  }

  return map;
}