WFDASH-WEBAPP/src/lib/server/pos-service.test.ts

import { describe, it, expect, beforeEach, vi } from "vitest";
import { checkoutSale, type PosPb } from "./pos-service";

/**
 * Pure-logic tests for the discount math. Mocks out the PB
 * instance so we can pin down: gross total, applied discount, the
 * post-discount subtotal/vat/total, the fields written to the
 * pos_sales row, and the edge cases (cap, fat-finger, no
 * discount).
 */

function fakePb(): PosPb & {
  _salesCalls: Array<Record<string, unknown>>;
  _stockItem: Record<string, unknown>;
} {
  const stockItem = { id: "si-1", sku: "WID-1", cost_price: 50, current_qty: 100 };
  const _salesCalls: Array<Record<string, unknown>> = [];

  // Each collection gets its own create fn that pushes to a
  // shared _salesCalls array. The PB SDK calls `create(data)`,
  // not `create(collectionName, data)`, so we identify the
  // collection by the data shape (sale items have a `sale`
  // field, sales don't, etc).
  const salesCreate = async (data: Record<string, unknown>) => {
    _salesCalls.push(data);
    return { id: "sale-1", ...data };
  };
  const itemCreate = async (data: Record<string, unknown>) => {
    return { id: "pos-item-1", ...data };
  };
  const ledgerCreate = async () => ({ id: "ledger-1" });

  const pb = {
    collection: (name: string) => {
      if (name === "stock_items") {
        return {
          getFullList: async () => [stockItem],
          getList: async () => ({ items: [stockItem] }),
          getOne: async () => stockItem,
          create: salesCreate, // unused; placeholder
          update: async () => stockItem,
        };
      }
      if (name === "pos_sales") {
        return {
          getFullList: async () => [],
          getList: async () => ({ items: [] }),
          getOne: async () => ({ id: "sale-1" }),
          create: salesCreate,
          update: async () => ({}),
        };
      }
      if (name === "pos_sale_items") {
        return {
          getFullList: async () => [],
          getList: async () => ({ items: [] }),
          getOne: async () => ({ id: "pos-item-1" }),
          create: itemCreate,
          update: async () => ({}),
        };
      }
      if (name === "stock_ledger") {
        return {
          getFullList: async () => [],
          getList: async () => ({ items: [] }),
          getOne: async () => ({ id: "ledger-1" }),
          create: ledgerCreate,
          update: async () => ({}),
        };
      }
      return {
        getFullList: async () => [],
        getList: async () => ({ items: [] }),
        getOne: async () => {
          throw new Error("404");
        },
        create: salesCreate, // fallback
        update: async () => ({}),
      };
    },
  };
  return Object.assign(pb as PosPb, { _salesCalls, _stockItem: stockItem });
}

describe("checkoutSale — discount math", () => {
  let pb: ReturnType<typeof fakePb>;

  beforeEach(() => {
    pb = fakePb();
  });

  function lastSale(pb: ReturnType<typeof fakePb>) {
    const calls = pb._salesCalls;
    return calls[calls.length - 1] as Record<string, unknown>;
  }

  it("records no discount by default (kind=none, amount=0, input=0)", async () => {
    const result = await checkoutSale(pb, {
      items: [{ stock_item_id: "si-1", qty: 1, unit_price: 115 }],
      payment_method: "cash",
    });
    expect(result.ok).toBe(true);
    if (!result.ok) return;
    const saleData = lastSale(pb);
    expect(saleData.discount_kind).toBe("none");
    expect(saleData.discount_amount).toBe(0);
    expect(saleData.discount_input).toBe(0);
    expect(saleData.gross_total).toBe(115);
    expect(saleData.total).toBe(115);
  });

  it("applies an R-amount discount to the post-VAT total and splits VAT proportionally", async () => {
    // 1 × R115 = R115 gross. R15 off → R100 net.
    //   sub = 100 / 1.15 ≈ 86.96
    //   vat = 100 - 86.96 ≈ 13.04
    const result = await checkoutSale(pb, {
      items: [{ stock_item_id: "si-1", qty: 1, unit_price: 115 }],
      payment_method: "cash",
      discount_kind: "amount",
      discount_input: 15,
    });
    expect(result.ok).toBe(true);
    if (!result.ok) return;
    const saleData = lastSale(pb);
    expect(saleData.gross_total).toBe(115);
    expect(saleData.discount_kind).toBe("amount");
    expect(saleData.discount_input).toBe(15);
    expect(saleData.discount_amount).toBe(15);
    expect(saleData.total).toBe(100);
    expect(saleData.subtotal).toBeCloseTo(86.9565, 3);
    expect(saleData.vat).toBeCloseTo(13.0435, 3);
  });

  it("applies a percentage discount", async () => {
    // 1 × R200 = R200 gross. 10% off → R180 net.
    const result = await checkoutSale(pb, {
      items: [{ stock_item_id: "si-1", qty: 1, unit_price: 200 }],
      payment_method: "cash",
      discount_kind: "percent",
      discount_input: 10,
    });
    expect(result.ok).toBe(true);
    if (!result.ok) return;
    const saleData = lastSale(pb);
    expect(saleData.gross_total).toBe(200);
    expect(saleData.discount_amount).toBe(20);
    expect(saleData.discount_input).toBe(10);
    expect(saleData.total).toBe(180);
  });

  it("caps a fat-finger percentage at the gross total (no negative total)", async () => {
    // 1 × R100, 200% off — should be capped at R100 off, not -R100.
    const result = await checkoutSale(pb, {
      items: [{ stock_item_id: "si-1", qty: 1, unit_price: 100 }],
      payment_method: "cash",
      discount_kind: "percent",
      discount_input: 200,
    });
    expect(result.ok).toBe(true);
    if (!result.ok) return;
    const saleData = lastSale(pb);
    expect(saleData.discount_amount).toBe(100);
    expect(saleData.total).toBe(0);
  });

  it("caps a fat-finger amount at the gross total", async () => {
    // 1 × R50, R999 off — should be capped at R50 off.
    const result = await checkoutSale(pb, {
      items: [{ stock_item_id: "si-1", qty: 1, unit_price: 50 }],
      payment_method: "cash",
      discount_kind: "amount",
      discount_input: 999,
    });
    expect(result.ok).toBe(true);
    if (!result.ok) return;
    const saleData = lastSale(pb);
    expect(saleData.discount_amount).toBe(50);
    expect(saleData.total).toBe(0);
  });

  it("ignores a discount of 0 (no change to totals, no row-level discount state)", async () => {
    const result = await checkoutSale(pb, {
      items: [{ stock_item_id: "si-1", qty: 1, unit_price: 115 }],
      payment_method: "cash",
      discount_kind: "amount",
      discount_input: 0,
    });
    expect(result.ok).toBe(true);
    if (!result.ok) return;
    const saleData = lastSale(pb);
    expect(saleData.discount_amount).toBe(0);
    expect(saleData.total).toBe(115);
  });

  it("gross_subtotal and gross_vat are recorded alongside the post-discount values", async () => {
    // The accountant needs both views on the audit row.
    const result = await checkoutSale(pb, {
      items: [{ stock_item_id: "si-1", qty: 1, unit_price: 115 }],
      payment_method: "cash",
      discount_kind: "amount",
      discount_input: 15,
    });
    expect(result.ok).toBe(true);
    if (!result.ok) return;
    const saleData = lastSale(pb);
    expect(saleData.gross_total).toBe(115);
    expect(saleData.gross_subtotal).toBeCloseTo(100, 2);
    expect(saleData.gross_vat).toBeCloseTo(15, 2);
    expect(saleData.total).toBe(100);
  });

  it("adjusts cash change against the post-discount total", async () => {
    // R200 - 10% = R180. Cash given R200 → change R20.
    const result = await checkoutSale(pb, {
      items: [{ stock_item_id: "si-1", qty: 1, unit_price: 200 }],
      payment_method: "cash",
      cash_given: 200,
      discount_kind: "percent",
      discount_input: 10,
    });
    expect(result.ok).toBe(true);
    if (!result.ok) return;
    const saleData = lastSale(pb);
    expect(saleData.change_given).toBe(20);
    expect(saleData.total).toBe(180);
  });
});