import type { Schedule } from 'fhir/r4';
import type { BookabilityBlocker } from './bookabilityReasons';
import type { BandResult } from './scheduleUsable';
import { calendarDateInZone, viewerTimeZone } from '../practiceTimezone';

// BAND 3 of bookability: does this block actually produce open times?
//
// This is where "the provider is selectable but there are no times" lives - the most common real-world
// complaint, and the one no existing check can see, because it was buried inline in handleScheduleChange
// rather than being asked as a question.
//
// MIRROR, NEVER A GATE - see bookabilityReasons.ts.

/** The minimum shape getScheduleAvailabilityEvents returns; kept structural so this imports no services. */
export interface AvailabilityEventLike {
  extendedProps?: { type?: string };
}

export interface YieldsTimesAccessors {
  availabilityEvents: (s: Schedule) => AvailabilityEventLike[];
}

// getScheduleAvailabilityEvents also returns 'not-available' (time-off) BACKGROUND events, which must never
// count as bookable. This one filter is SHARED with the patient flow's handleScheduleChange so the two cannot
// diverge - that shared use is the whole reason it is exported rather than inlined below.
//
// Generic so a caller holding a richer event type gets that same type back and needs no cast.
export const availabilityWindowsFor = <T extends AvailabilityEventLike>(events: T[]): T[] =>
  events.filter((event) => event.extendedProps?.type === 'availability');

// A date-only end is a calendar day and stays open through it, as the slot generator reads it; parsed
// as UTC midnight, a block read as ended on its own last day.
const horizonEnded = (end: string, now: Date): boolean =>
  /^\d{4}-\d{2}-\d{2}$/.test(end)
    ? end < calendarDateInZone(now, viewerTimeZone())
    : new Date(end).getTime() < now.getTime();

export function evaluateScheduleYieldsTimes(
  schedule: Schedule,
  accessors: YieldsTimesAccessors,
  now: Date,
): BandResult {
  const blockers: BookabilityBlocker[] = [];

  if (availabilityWindowsFor(accessors.availabilityEvents(schedule)).length === 0) {
    blockers.push('BLOCK_NO_HOURS');
  }

  const start = schedule.planningHorizon?.start;
  const end = schedule.planningHorizon?.end;
  if (!start || !end) {
    // A half-set horizon is reported as MISSING, not expired - "expired" would send someone off to extend a
    // date that was never set in the first place.
    blockers.push('BLOCK_NO_PLANNING_HORIZON');
  } else if (horizonEnded(end, now)) {
    blockers.push('BLOCK_HORIZON_EXPIRED');
  }

  return { ok: blockers.length === 0, blockers };
}