// Internal (non-generated) shared validation for Shift segments — used by both createShift and
// createShifts so the two commands can never drift on what makes a shift valid.

export const SHIFT_TYPES = ["NORMAL", "SPLIT", "THROUGH", "ON_CALL", "SUPPORT"] as const;
export type ShiftType = (typeof SHIFT_TYPES)[number];

export interface ShiftSegmentInput {
  plannedStartAt: Date;
  plannedEndAt: Date;
  breakMinutes: number;
}

export interface ResolvedSegment {
  plannedStartAt: Date;
  plannedEndAt: Date;
  breakMinutes: number;
}

const MINUTE_MS = 60_000;

export function resolvePatternSegment(
  date: Date,
  seg: {
    startTime: number;
    endTime: number;
    spansMidnight: boolean;
    breakMinutes: number;
  },
): ResolvedSegment {
  const dayStart = new Date(Date.UTC(date.getUTCFullYear(), date.getUTCMonth(), date.getUTCDate()));
  const plannedStartAt = new Date(dayStart.getTime() + seg.startTime * MINUTE_MS);
  const endDayStart = seg.spansMidnight
    ? new Date(dayStart.getTime() + 24 * 60 * MINUTE_MS)
    : dayStart;
  const plannedEndAt = new Date(endDayStart.getTime() + seg.endTime * MINUTE_MS);
  return { plannedStartAt, plannedEndAt, breakMinutes: seg.breakMinutes };
}

export function validateSegments(
  segments: ResolvedSegment[],
): { ok: true } | { ok: false; error: "GAP" | "BREAK" } {
  const sorted = [...segments].sort(
    (a, b) => a.plannedStartAt.getTime() - b.plannedStartAt.getTime(),
  );
  for (const seg of sorted) {
    const grossSpanMinutes =
      (seg.plannedEndAt.getTime() - seg.plannedStartAt.getTime()) / MINUTE_MS;
    if (seg.breakMinutes < 0 || seg.breakMinutes >= grossSpanMinutes) {
      return { ok: false, error: "BREAK" };
    }
  }
  for (let i = 1; i < sorted.length; i++) {
    if (sorted[i].plannedStartAt.getTime() <= sorted[i - 1].plannedEndAt.getTime()) {
      return { ok: false, error: "GAP" };
    }
  }
  return { ok: true };
}

export function isShiftTypeConsistent(shiftType: ShiftType, segmentCount: number): boolean {
  switch (shiftType) {
    case "SPLIT":
      return segmentCount >= 2;
    case "SUPPORT":
      return segmentCount >= 1;
    case "NORMAL":
    case "THROUGH":
    case "ON_CALL":
      return segmentCount === 1;
    default:
      return false;
  }
}

export function sortSegments(segments: ResolvedSegment[]): ResolvedSegment[] {
  return [...segments].sort((a, b) => a.plannedStartAt.getTime() - b.plannedStartAt.getTime());
}