import { ok } from "@tailor-platform/erp-kit/core";
import { Decimal } from "decimal.js";
import type { Selectable, Transaction } from "../../../generated/kysely-tailordb";

// Average costing never restates history: the consumed share of an invoice
// price variance is expensed to the consumed price variance account, and only the
// on-hand share folds into the moving average. The split is by quantity alone,
// so unlike FIFO no consumption classification is needed.
export async function restateAverageLayer(
  db: Transaction,
  args: { layer: Selectable<"CostLayer">; delta: Decimal },
) {
  const { layer, delta } = args;
  const received = new Decimal(layer.quantity);
  const consumed = received.minus(layer.remainingQuantity);
  const consumedShare = delta.mul(consumed).div(received);
  const onHandShare = delta.minus(consumedShare);

  if (!onHandShare.isZero()) {
    // On-hand quantity from a costed receipt guarantees the moving-average pool exists.
    const current = await db
      .selectFrom("AverageCost")
      .selectAll()
      .where("itemId", "=", layer.itemId)
      .where("companyId", "=", layer.companyId)
      .orderBy("sequence", "desc")
      .limit(1)
      .executeTakeFirstOrThrow();
    // Value moves without quantity: the pool quantity is unchanged and the
    // average shifts by the on-hand share over the pool.
    const quantityBefore = new Decimal(current.quantityAfter);
    const unitCostBefore = new Decimal(current.unitCostAfter);
    const unitCostAfter = quantityBefore.mul(unitCostBefore).plus(onHandShare).div(quantityBefore);
    await db
      .insertInto("AverageCost")
      .values({
        itemId: layer.itemId,
        companyId: layer.companyId,
        sequence: current.sequence + 1,
        eventType: "COST_ADJUSTMENT",
        quantityBefore: quantityBefore.toString(),
        unitCostBefore: unitCostBefore.toString(),
        quantity: "0",
        unitCost: null,
        quantityAfter: quantityBefore.toString(),
        unitCostAfter: unitCostAfter.toString(),
      })
      .execute();
  }

  const contributions = [
    ...(onHandShare.isZero() ? [] : [{ role: "INVENTORY" as const, amount: onHandShare }]),
    ...(consumedShare.isZero()
      ? []
      : [{ role: "CONSUMED_PRICE_VARIANCE" as const, amount: consumedShare }]),
  ];
  return ok(contributions);
}