/**
 * Builds the frozen screen payload from resolved schedule data.
 *
 * Every string the panel will show is computed here, server-side and in both
 * languages. The renderer downstream draws and nothing else: it has no access
 * to the schedule, so it cannot disagree with this file about what the shop's
 * hours are. That separation is what lets the whole display be tested without
 * a device attached.
 */

import {
  addCivilDays,
  civilDayOfWeek,
  startOfCivilWeek,
  toCivilDate,
  toIsoWithOffset,
} from '@/lib/schedule/civil';
import {
  formatDateEn,
  formatDateFr,
  formatHoursText,
  formatNextChangeEn,
  formatNextChangeFr,
  shortDayLabelEn,
  shortDayLabelFr,
  type NextChange,
} from '@/lib/schedule/format';
import { detectDivergence, getCurrentStatus, resolveCivilDay } from '@/lib/schedule/resolver';
import type { ScheduleContext } from '@/lib/schedule/types';

import {
  AUTO_BANNERS,
  MESSAGE_MAX_CHARS,
  SCREEN_SCHEMA_VERSION,
  type ScreenBanner,
  type ScreenPayload,
  type ScreenWeekDay,
} from './contract';

export type MessageCandidate = {
  textFr: string;
  /** `null` while the translation is pending, or if it failed. */
  textEn: string | null;
  startsAt: Date | null;
  endsAt: Date | null;
  priority: number;
  isActive: boolean;
};

export type ScreenInput = {
  now: Date;
  ctx: ScheduleContext;
  shopName: string;
  logoUrl: string;
  messages: MessageCandidate[];
};

/** The highest-priority message that is active and inside its validity window. */
export function selectActiveMessage(
  messages: MessageCandidate[],
  now: Date,
): MessageCandidate | null {
  const instant = now.getTime();
  const live = messages.filter(
    (message) =>
      message.isActive &&
      (message.startsAt === null || message.startsAt.getTime() <= instant) &&
      (message.endsAt === null || message.endsAt.getTime() >= instant),
  );
  if (live.length === 0) {
    return null;
  }
  return live.reduce((best, candidate) => (candidate.priority > best.priority ? candidate : best));
}

export function buildScreenPayload({
  now,
  ctx,
  shopName,
  logoUrl,
  messages,
}: ScreenInput): ScreenPayload {
  const today = toCivilDate(now, ctx.timezone);
  const status = getCurrentStatus(now, ctx);

  // Closing soon is still open, and opening soon is still closed: the large
  // word states the fact, the line under it carries the nuance.
  const isOpenNow = status.status === 'OPEN' || status.status === 'CLOSING_SOON';

  const nextChange: NextChange | null = status.nextChangeAt
    ? {
        kind: isOpenNow ? 'CLOSES' : 'OPENS',
        date: status.nextChangeAt.date,
        time: status.nextChangeAt.time,
      }
    : null;

  return {
    schema: SCREEN_SCHEMA_VERSION,
    generated_at: toIsoWithOffset(now, ctx.timezone),
    shop_name: shopName,
    logo_url: logoUrl,
    today: {
      date_fr: formatDateFr(today),
      date_en: formatDateEn(today),
      status: status.status,
      status_fr: isOpenNow ? 'OUVERT' : 'FERMÉ',
      status_en: isOpenNow ? 'OPEN' : 'CLOSED',
      hours_text: formatHoursText(status.today.slots),
      next_change_fr: formatNextChangeFr(nextChange, today),
      next_change_en: formatNextChangeEn(nextChange, today),
      is_exception: status.today.isException,
    },
    week: buildWeek(today, ctx),
    banner: buildBanner(now, ctx, messages),
  };
}

/** Monday through Sunday of the week containing `today`. */
function buildWeek(today: string, ctx: ScheduleContext): ScreenWeekDay[] {
  const monday = startOfCivilWeek(today);
  return Array.from({ length: 7 }, (_, offset) => {
    const date = addCivilDays(monday, offset);
    const day = resolveCivilDay(date, ctx);
    const dayOfWeek = civilDayOfWeek(date);
    return {
      label_fr: shortDayLabelFr(dayOfWeek),
      label_en: shortDayLabelEn(dayOfWeek),
      hours_text: formatHoursText(day.slots),
      is_today: date === today,
      is_closed: !day.isOpen,
      is_exception: day.isException,
    };
  });
}

function buildBanner(
  now: Date,
  ctx: ScheduleContext,
  messages: MessageCandidate[],
): ScreenBanner | null {
  // A message someone took the trouble to write always wins the space.
  const message = selectActiveMessage(messages, now);
  if (message) {
    return {
      kind: 'MESSAGE',
      text_fr: clamp(message.textFr),
      text_en: clamp(message.textEn ?? ''),
    };
  }

  const divergence = detectDivergence(now, ctx);
  if (divergence === 'NONE') {
    return null;
  }

  const kind = divergence === 'TODAY' ? 'SCHEDULE_TODAY' : 'SCHEDULE_WEEK';
  const wording = AUTO_BANNERS[kind];
  return { kind, text_fr: wording.fr, text_en: wording.en };
}

/**
 * The editor warns before anyone can save something this long, so reaching
 * here means the limit changed after the fact. Cut rather than let the text
 * spill off a panel nobody can scroll.
 */
function clamp(text: string): string {
  if (text.length <= MESSAGE_MAX_CHARS) {
    return text;
  }
  return `${text.slice(0, MESSAGE_MAX_CHARS - 1).trimEnd()}…`;
}