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

export interface SetReferenceUnitInput {
  unitId: string;
  categoryId: string;
}

/**
 * Function: setReferenceUnit
 *
 * Changes the reference unit for a UoM category. All conversion factors
 * are recalculated relative to the new reference unit.
 */
export async function run(db: Transaction, input: SetReferenceUnitInput) {
  // 1. Find unit by ID
  const unit = await db
    .selectFrom("Unit")
    .selectAll()
    .where("id", "=", input.unitId)
    .forUpdate()
    .executeTakeFirst();

  if (!unit) {
    return err(new UnitNotFoundError(input.unitId));
  }

  // 2. Check unit belongs to specified category
  if (unit.categoryId !== input.categoryId) {
    return err(new UnitNotInCategoryError(`${input.unitId} in ${input.categoryId}`));
  }

  // 3. Get category
  const uoMCategory = await db
    .selectFrom("UoMCategory")
    .selectAll()
    .where("id", "=", input.categoryId)
    .forUpdate()
    .executeTakeFirst();

  // 4. If already reference unit, return (idempotent)
  if (uoMCategory?.referenceUnitId === input.unitId && uoMCategory) {
    return ok({ uoMCategory });
  }

  // 5. Get all units in category for recalculation
  const units = await db
    .selectFrom("Unit")
    .selectAll()
    .where("categoryId", "=", input.categoryId)
    .forUpdate()
    .execute();

  // 6. Recalculate all conversion factors
  // new_factor = old_factor / new_reference_old_factor
  const newReferenceFactor = unit.conversionFactor;
  for (const u of units) {
    const newFactor = u.conversionFactor / newReferenceFactor;
    await db
      .updateTable("Unit")
      .set({
        conversionFactor: newFactor,
      })
      .where("id", "=", u.id)
      .returningAll()
      .executeTakeFirst();
  }

  // 7. Update category reference unit
  const updatedCategory = await db
    .updateTable("UoMCategory")
    .set({
      referenceUnitId: input.unitId,
    })
    .where("id", "=", input.categoryId)
    .returningAll()
    .executeTakeFirstOrThrow();

  return ok({ uoMCategory: updatedCategory });
}