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

export interface GetWorkScheduleAsOfInput {
  assignmentId: string;
  asOf: Date;
}

/**
 * Function: getWorkScheduleAsOf
 * Description: Resolves which WorkSchedule generation was in force for an Assignment on a given
 * date. Effective-dated generations form a non-overlapping timeline (`effectiveStart` inclusive,
 * `effectiveEnd` inclusive, null = still current), so at most one generation covers `asOf`. This
 * effective-dated resolution is the workforce domain's rule and lives in the module rather than
 * being re-derived in the app layer (issue #38). Returns WORK_SCHEDULE_NOT_FOUND when no
 * generation covers the date.
 */
export async function run(db: ReadonlyDB<DB>, input: GetWorkScheduleAsOfInput) {
  if (Number.isNaN(input.asOf.getTime())) {
    return err(new InvalidDateError("asOf"));
  }

  const workSchedule = await db
    .selectFrom("WorkSchedule")
    .selectAll()
    .where("assignmentId", "=", input.assignmentId)
    .where("effectiveStart", "<=", input.asOf)
    .where((eb) => eb.or([eb("effectiveEnd", "is", null), eb("effectiveEnd", ">=", input.asOf)]))
    .executeTakeFirst();

  if (!workSchedule) {
    return err(new WorkScheduleNotFoundError(`${input.assignmentId}@${input.asOf.toISOString()}`));
  }

  return ok({ workSchedule });
}