# 11 - Lot Suggestions (qt_vendor_partnumber_seen)

## Purpose

`qt_vendor_partnumber_seen` records vendor partnumbers encountered during import
that have no mapping in the active partnumber book. When a user manually maps
such a partnumber to one or more LOT names in the QuoteForge UI, those mappings
are written back to the server as **lot suggestions** — hints for the team that
maintains `qt_partnumber_book_items`.

## Schema Extension

Add one nullable column to `qt_vendor_partnumber_seen`:

```sql
ALTER TABLE `qt_vendor_partnumber_seen`
  ADD COLUMN `lot_suggestion` longtext DEFAULT NULL
    COMMENT 'JSON array [{lot_name, qty}] — user-entered LOT mappings from the UI';
```

### Updated table contract (relevant columns only)

| Column | Type | Notes |
|--------|------|-------|
| `partnumber` | varchar(255) UNIQUE NOT NULL | natural key |
| `lot_suggestion` | longtext (JSON) | nullable; set when user maps the PN manually |

`lot_suggestion` contains the same JSON shape as `qt_partnumber_book_items.lots_json`:

```json
[
  { "lot_name": "LOT_A", "qty": 1 },
  { "lot_name": "LOT_B", "qty": 2 }
]
```

Rules:
- `null` or absent means no suggestion has been entered yet;
- an empty array `[]` is not a valid value — use `null` instead;
- a single PN may map to multiple lots (`lot_name` entries), each with its own `qty`;
- the array is ordered — the order reflects the order of `lot_mappings[]` in the
  vendor spec row at the time of last user save;
- `qty` must be a positive integer (≥ 1).

## Write Contract (QuoteForge → MariaDB)

QuoteForge writes `lot_suggestion` when all of the following are true:

1. The user saves a vendor BOM via `PUT /api/configs/:uuid/vendor-spec`.
2. At least one `vendor_spec` row has a non-empty `lot_mappings[]` array (manually
   entered or confirmed by the user — not auto-resolved from a partnumber book).
3. The MariaDB connection is available at the time of save.

For each such row:

```sql
INSERT INTO qt_vendor_partnumber_seen
    (source_type, vendor, partnumber, description, is_ignored, last_seen_at, lot_suggestion)
VALUES
    ('manual', '', ?, ?, 0, NOW(3), ?)
ON DUPLICATE KEY UPDATE
    lot_suggestion = VALUES(lot_suggestion),
    last_seen_at   = IF(lot_suggestion IS NULL, last_seen_at, NOW(3))
```

- `lot_suggestion` value = JSON-marshalled `lot_mappings[]` from the vendor spec item,
  reusing the same `{lot_name, qty}` shape.
- If the PN row already exists and `lot_suggestion` is already set, it is **overwritten**
  with the latest user input (the user is assumed to have corrected it).
- If the user **clears** all lot_mappings for a PN (sets to empty), no update is sent —
  the existing `lot_suggestion` on the server is left untouched.
- Rows where `lot_mappings[]` is empty or nil are skipped entirely (no insert, no update).
- Writes are best-effort: a MariaDB error for one row is logged and skipped; remaining
  rows continue. A write failure does not fail the vendor-spec save.

## Read Contract (Partnumber-Book Creation Tool → MariaDB)

The tool that maintains `qt_partnumber_book_items` reads `qt_vendor_partnumber_seen`
to discover new partnumbers and their suggested mappings.

### Discovery query

```sql
SELECT
    s.id,
    s.partnumber,
    s.description,
    s.vendor,
    s.lot_suggestion,
    s.last_seen_at,
    b.lots_json AS book_lots_json
FROM qt_vendor_partnumber_seen s
LEFT JOIN qt_partnumber_book_items b ON b.partnumber = s.partnumber
WHERE s.is_ignored = 0
  AND s.lot_suggestion IS NOT NULL
ORDER BY s.last_seen_at DESC;
```

### Interpretation rules

| Condition | Meaning | Suggested action |
|-----------|---------|-----------------|
| `book_lots_json IS NULL` AND `lot_suggestion IS NOT NULL` | No book entry yet; user suggested mapping | Create new `qt_partnumber_book_items` row with `lots_json = lot_suggestion` |
| `book_lots_json IS NOT NULL` AND `lot_suggestion IS NOT NULL` AND they differ | User corrected or extended the existing mapping | Review diff and decide whether to update `qt_partnumber_book_items` |
| `book_lots_json IS NOT NULL` AND `lot_suggestion IS NOT NULL` AND they match | Suggestion already applied | No action needed |

### Suggestion format

`lot_suggestion` is valid JSON (or `null`). Parse it as an array of objects:

```json
[
  { "lot_name": "LOT_A", "qty": 1 },
  { "lot_name": "LOT_B", "qty": 2 }
]
```

Map directly to `qt_partnumber_book_items.lots_json` — the formats are identical.

### Multiple lots per PN

One PN may have multiple suggestion entries (e.g., a bundle). The array carries
all of them. The book-creation tool must preserve the full array when writing
`lots_json`, not just the first element.

### Qty semantics

`qty` in a lot suggestion means "how many of this LOT per one occurrence of the
vendor PN". This matches `qt_partnumber_book_items.lots_json` exactly. Example:
a server platform that comes with 4 PSUs would produce
`[{"lot_name": "PS_1300W_Titanium", "qty": 4}]`.

## Permissions

The existing `qfs_user` grant covers this column — no new permission is required:

```sql
GRANT SELECT, INSERT, UPDATE ON RFQ_LOG.qt_vendor_partnumber_seen TO 'qfs_user'@'%';
```

The book-creation tool connects with its own credentials and needs at minimum:

```sql
GRANT SELECT ON RFQ_LOG.qt_vendor_partnumber_seen TO '<book_tool_user>'@'%';
GRANT SELECT, INSERT, UPDATE ON RFQ_LOG.qt_partnumber_book_items TO '<book_tool_user>'@'%';
```

## Migration

Migration is applied outside this repo (server-side DDL):

```sql
ALTER TABLE `qt_vendor_partnumber_seen`
  ADD COLUMN IF NOT EXISTS `lot_suggestion` longtext DEFAULT NULL
    COMMENT 'JSON [{lot_name, qty}] — user LOT suggestions from QuoteForge UI';
```

QuoteForge handles a missing column gracefully: if the migration has not run yet,
the write with `lot_suggestion` fails with "Unknown column" (MariaDB 1054), a warning
is logged, and the row is re-inserted without the column. The app never crashes on
migration lag.