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

export interface AggregateWorkedDaysInput {
  assignmentIds: string[];
  startDate: Date;
  endDate: Date;
}

const MS_PER_DAY = 24 * 60 * 60 * 1000;

// UTC-midnight of a Date's calendar day, so the SQL range bounds are day-aligned regardless of
// any time-of-day component on the inputs (consistent with the UTC-day dedupe below).
function startOfUtcDay(d: Date): Date {
  return new Date(Date.UTC(d.getUTCFullYear(), d.getUTCMonth(), d.getUTCDate()));
}

/**
 * Function: aggregateWorkedDays
 * Description: Counts a worker's worked days over a date range, for
 * evaluating leave grant conditions (labour-law worked days). A worked day is a
 * distinct workDate on which any of the supplied Assignments has at least one
 * CalculatedTimeBlock — a day worked under any of the assignments counts once
 * (union across assignmentIds). Pure producer query (ADR-026 B1): the caller
 * resolves worker→assignments; this query does not depend on workforce.
 */
export async function run(db: ReadonlyDB<DB>, input: AggregateWorkedDaysInput) {
  if (Number.isNaN(input.startDate.getTime())) {
    return err(new InvalidSearchFilterError(`startDate=${String(input.startDate)}`));
  }
  if (Number.isNaN(input.endDate.getTime())) {
    return err(new InvalidSearchFilterError(`endDate=${String(input.endDate)}`));
  }
  if (input.endDate < input.startDate) {
    return err(
      new InvalidSearchFilterError(
        `${input.startDate.toISOString()}..${input.endDate.toISOString()}`,
      ),
    );
  }

  if (input.assignmentIds.length === 0) {
    return ok({ workedDays: 0 });
  }

  // Day-aligned window [winStart, winEndExclusive): covers every timestamp on the
  // startDate..endDate calendar days, so a non-midnight input cannot exclude a boundary day.
  const winStart = startOfUtcDay(input.startDate);
  const winEndExclusive = new Date(startOfUtcDay(input.endDate).getTime() + MS_PER_DAY);

  const blocks = await db
    .selectFrom("CalculatedTimeBlock")
    .select("workDate")
    .where("assignmentId", "in", input.assignmentIds)
    .where("workDate", ">=", winStart)
    .where("workDate", "<", winEndExclusive)
    .execute();

  // UTC calendar-date key ("YYYY-MM-DD"): workDates are UTC-midnight today, but keying on the
  // calendar date keeps the dedupe robust to time-of-day components and consistent with
  // leave-management's countDeemedAttendanceDays date keys.
  const distinctWorkDates = new Set(
    blocks.map((block) => block.workDate.toISOString().slice(0, 10)),
  );

  return ok({ workedDays: distinctWorkDates.size });
}