import { ok, type ReadonlyDB } from "@tailor-platform/erp-kit/core";
import type { DB } from "../generated/kysely-tailordb";

export interface GetAnnualLeaveRegisterInput {
  workerId: string;
  /** Optional: restrict the register to one balance-backed leave type; omitted = all STATUTORY grants. */
  leaveTypeKey?: string;
}

// Article 39 ⑦: a worker granted 10+ days of annual leave in a grant year must actually take at
// least 5 of them within the year following that grant.
const FIVE_DAY_DUTY_THRESHOLD_DAYS = 10;
const FIVE_DAY_DUTY_REQUIRED_DAYS = 5;

// Only actually-taken leave counts toward the register and the 5-day obligation: an APPROVED
// LeaveRequest. PENDING/CANCEL_PENDING reservations are not yet "taken", and REJECTED/CANCELLED
// never happened.
const TAKEN_STATUS = "APPROVED";

function oneYearAfter(date: Date): Date {
  const deadline = new Date(date);
  deadline.setUTCFullYear(deadline.getUTCFullYear() + 1);
  return deadline;
}

/**
 * Function: getAnnualLeaveRegister
 * Description: The annual paid-leave compliance register for one worker (ADR-009), derived entirely
 * from the ledger — there is no stored register. One row per STATUTORY LeaveGrant: the grant's date,
 * amount, expiration, the days actually taken against it, the derived remaining, and — for a grant of
 * 10+ days — the 5-day mandatory-acquisition obligation (Labor Standards Act Article 39 ⑦): its
 * grant-year deadline (grantedDate + 1 year), how many paid-leave days were taken in that window, and
 * whether the duty is satisfied or the worker is at risk. "Taken" means an APPROVED LeaveRequest.
 */
export async function run(db: ReadonlyDB<DB>, input: GetAnnualLeaveRegisterInput) {
  let grantsQuery = db
    .selectFrom("LeaveGrant")
    .selectAll()
    .where("workerId", "=", input.workerId)
    .where("grantType", "=", "STATUTORY");
  if (input.leaveTypeKey != null) {
    grantsQuery = grantsQuery.where("leaveTypeKey", "=", input.leaveTypeKey);
  }
  const grants = await grantsQuery.orderBy("grantedDate", "asc").execute();

  // Every APPROVED taking for this worker's grants, with the taking's start date, so both the
  // per-grant taken total and the per-grant-year 5-day count can be reconstructed from the ledger.
  const grantIds = grants.map((grant) => grant.id);
  const takings = grantIds.length
    ? await db
        .selectFrom("LeaveConsumption")
        .innerJoin("LeaveRequest", "LeaveRequest.id", "LeaveConsumption.leaveRequestId")
        .select([
          "LeaveConsumption.leaveGrantId",
          "LeaveConsumption.daysConsumed",
          "LeaveRequest.startDate",
        ])
        .where("LeaveConsumption.leaveGrantId", "in", grantIds)
        .where("LeaveRequest.status", "=", TAKEN_STATUS)
        .execute()
    : [];

  const takenByGrant = new Map<string, number>();
  for (const taking of takings) {
    takenByGrant.set(
      taking.leaveGrantId,
      (takenByGrant.get(taking.leaveGrantId) ?? 0) + Number(taking.daysConsumed),
    );
  }

  const register = grants.map((grant) => {
    const grantedDays = Number(grant.grantedDays);
    const takenDays = takenByGrant.get(grant.id) ?? 0;
    const subjectToFiveDayDuty = grantedDays >= FIVE_DAY_DUTY_THRESHOLD_DAYS;
    const fiveDayDeadline = subjectToFiveDayDuty ? oneYearAfter(grant.grantedDate) : null;

    // The 5-day obligation counts paid leave taken anywhere in the grant year, not only what drew
    // from this specific grant.
    let fiveDayTakenDays = 0;
    if (fiveDayDeadline) {
      for (const taking of takings) {
        if (
          taking.startDate.getTime() >= grant.grantedDate.getTime() &&
          taking.startDate.getTime() <= fiveDayDeadline.getTime()
        ) {
          fiveDayTakenDays += Number(taking.daysConsumed);
        }
      }
    }
    const fiveDayDutyMet = subjectToFiveDayDuty
      ? fiveDayTakenDays >= FIVE_DAY_DUTY_REQUIRED_DAYS
      : false;

    return {
      leaveGrantId: grant.id,
      leaveTypeKey: grant.leaveTypeKey,
      grantedDate: grant.grantedDate,
      grantedDays,
      expirationDate: grant.expirationDate,
      takenDays,
      remainingDays: grantedDays - takenDays,
      subjectToFiveDayDuty,
      fiveDayDeadline,
      fiveDayTakenDays,
      fiveDayDutyMet,
      fiveDayAtRisk: subjectToFiveDayDuty && !fiveDayDutyMet,
    };
  });

  return ok({ register });
}