3787cc4dd0
Approved design: percentage per line item, reduces net (VAT on discounted net), conditional PDF column, offers + issued invoices only. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
99 lines
4.0 KiB
Markdown
99 lines
4.0 KiB
Markdown
# Per-item Sleva (% discount) — Offers + Invoices
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**Date:** 2026-06-13
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**Status:** Approved → implementing
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**Scope:** Add a per-line-item percentage discount ("Sleva") to **offers**
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(nabídky) and **issued invoices** (Faktury), on both the detail-page item
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editor and the PDF. Received invoices, issued orders and orders are NOT
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touched.
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## Decisions (from brainstorming)
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- **Type:** percentage per item (0–100), not an absolute amount.
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- **Totals/VAT:** the discount reduces the line **net**; on invoices VAT is
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computed on the **discounted** net. `net = qty × unit_price × (1 − discount/100)`.
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- **PDF column is conditional:** render the Sleva column only when at least one
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(included) item has `discount > 0`; otherwise the table is identical to today.
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- **Detail-page column is always visible** (it's the input).
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## Data model
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Add to `quotation_items` and `invoice_items`:
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```
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discount Decimal? @default(0.00) @db.Decimal(5, 2) // percent, 0–100
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```
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Nullable with default `0`, matching the existing money columns. "No sleva" =
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`0` or null. One tracked migration; apply to dev `app` and `app_test`, then
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`prisma generate`.
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## Line math (single rule)
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`lineNet = qty × unit_price × (1 − clamp(discount,0,100)/100)`
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Add a shared backend helper so every site is identical:
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```ts
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// src/utils/money.ts (new)
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export const lineNet = (qty: number, unitPrice: number, discountPct: number) =>
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qty * unitPrice * (1 - (discountPct || 0) / 100);
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```
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## Backend
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- **Schemas (Zod):** add `discount` to the offer-item and invoice-item schemas
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via `numberInRange(0, 100)` (shared coercer in `common.ts`), optional, default
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`0`.
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- **offers.service** (`enrichQuotation`): line total uses `lineNet`; document
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net ("Celkem bez DPH") sums discounted included lines. Persist `discount` on
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item create/update.
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- **invoices.service**: every `computeMoney` `getBase` callback
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(`computeInvoiceTotals`, monthly-stats `invoiceMonthlyAmount`, per-rate
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`vatMap`) returns `lineNet(...)` so subtotal **and** VAT use the discounted
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net. Persist `discount` on item create/update.
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- **DocumentItemsEditor's `documentItemsTotal`** (frontend) mirrors the same
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discounted net.
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## Frontend (Section 1 — detail-page editor)
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- **Offers** → shared `src/admin/components/document/DocumentItemsEditor.tsx`:
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`DocumentItem` gains `discount`; add a **"Sleva %"** numeric column (0–100);
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per-line total and the footer net total apply it. Mobile card layout gets the
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field. `emptyDocumentItem` defaults `discount: 0`. Hydration + save payloads
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carry `discount`.
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- **Invoices** → `src/admin/pages/InvoiceDetail.tsx` own editor
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(`SortableInvoiceRow` + create/edit rows): `InvoiceItem` gains `discount`;
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same column; net/VAT/gross totals apply it. Mobile layout too.
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## PDF (Section 2 — conditional column)
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`src/routes/admin/offers-pdf.ts` and `src/routes/admin/invoices-pdf.ts`:
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- `const hasDiscount = items.some(i => includedInTotal(i) && Number(i.discount) > 0)`.
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- When `hasDiscount`: add a column — header **"Sleva"** (cs) / **"Discount"**
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(en, from the document's `language`), cell renders `"<n> %"` (escaped); adjust
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colspans of any full-width rows accordingly.
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- Line net / document total / VAT always use the discounted net regardless of
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`hasDiscount`.
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- `escapeHtml` every interpolation (string-built PDF templates).
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## Tests
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- `offer-invoice-totals` / invoice totals: net, VAT and gross with discounts
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(incl. a 100% line = 0, and VAT-on-discounted-net).
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- Schema: `discount` rejects <0 and >100, coerces form strings, defaults 0.
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- PDF: column present when an item has a discount; absent when none; values
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escaped.
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## Non-goals (YAGNI)
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- No separate "total discount" summary line, no document-level discount.
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- No changes to received invoices, issued orders, or orders.
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## Migration etiquette
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DB change → user stops the dev server first; create the migration via the
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non-interactive `prisma migrate diff` recipe, `migrate deploy` + `generate` on
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dev and `app_test`, commit schema + migration folder together.
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