backend/app/domains/products/diff.py

@@ -0,0 +1,207 @@
+"""Diff engine — catalog × canonical products → preview records (SD-0002 §6.5.2).
+
+Classifies each canonical product against the storefront's current catalog as
+add / update / unchanged / error, producing JSON-ready preview records (stored
+as draft JSONB, served verbatim to the SPA) plus a summary and a deterministic
+fingerprint that detects catalog drift between preview and confirm (INV-11).
+
+Deliberately DB-free: the catalog snapshot dataclasses are defined here and the
+repo layer builds them. Only fields present in the file's canonical fields{}
+participate in a comparison — an absent column is untouched, never a change
+(§6.5.1); a present-but-empty cell resolves to the field's CLEAR_DEFAULTS entry.
+Catalog variants/images absent from the file are likewise untouched (INV-10).
+"""
+from __future__ import annotations
+
+import hashlib
+import json
+from dataclasses import dataclass
+from decimal import Decimal
+
+from .models import CLEAR_DEFAULTS, CanonicalProduct, CanonicalVariant
+
+
+@dataclass
+class CatalogVariant:
+    id: int
+    options: tuple[str | None, str | None, str | None]
+    position: int
+    # sku, barcode, price (Decimal|None), cost, weight, weight_unit, volume,
+    # volume_unit, tax_id_1, tax_id_2, inventory_tracker, inventory_qty,
+    # variant_image (linked image source_url or None)
+    fields: dict[str, object]
+
+
+@dataclass
+class CatalogImage:
+    id: int
+    source_url: str
+    position: int
+    alt_text: str | None
+
+
+@dataclass
+class CatalogProduct:
+    id: int
+    handle: str
+    title: str
+    option_names: tuple[str | None, str | None, str | None]
+    # title, description_html, vendor, product_type, google_product_category,
+    # tags (list[str]), status, published (bool)
+    fields: dict[str, object]
+    variants: list[CatalogVariant]
+    images: list[CatalogImage]
+
+
+@dataclass(frozen=True)
+class DiffResult:
+    records: list[dict]
+    summary: dict
+    fingerprint: str
+
+
+# Option-name presence markers in fields{} (see validate.py); the values are
+# compared via the option_names attribute, not through the generic field loop.
+_OPTION_NAME_FIELDS = ("option1_name", "option2_name", "option3_name")
+_SUMMARY_KEY = {"add": "adds", "update": "updates", "unchanged": "unchanged", "error": "errors"}
+
+
+def compute_diff(catalog: dict[str, CatalogProduct], products: list[CanonicalProduct]) -> DiffResult:
+    records: list[dict] = []
+    summary = {"adds": 0, "updates": 0, "unchanged": 0, "errors": 0}
+    for product in products:
+        current = catalog.get(product.handle)
+        if product.errors:
+            kind, detail = "error", {"errors": [e.as_json() for e in product.errors]}
+        elif current is None:
+            kind, detail = "add", _add_detail(product)
+        else:
+            detail = _update_detail(product, current)
+            kind = "update" if detail else "unchanged"
+        records.append(
+            {
+                "handle": product.handle,
+                "title": product.title or (current.title if current else ""),
+                "kind": kind,
+                "variant_count": len(current.variants) if kind == "unchanged" else len(product.variants),
+                "detail": detail,
+            }
+        )
+        summary[_SUMMARY_KEY[kind]] += 1
+    fingerprint = hashlib.sha256(
+        json.dumps(records, sort_keys=True, separators=(",", ":"), default=str).encode()
+    ).hexdigest()
+    return DiffResult(records=records, summary=summary, fingerprint=fingerprint)
+
+
+def _add_detail(product: CanonicalProduct) -> dict:
+    # On add, absent fields fall back to their defaults for display where one
+    # exists — the detail shows what will actually be set.
+    set_fields = _resolved_product_fields(product)
+    for field_name, default in CLEAR_DEFAULTS.items():
+        set_fields.setdefault(field_name, default)
+    return {
+        "set": {f: _json_safe(v) for f, v in set_fields.items()},
+        "option_names": list(product.option_names),
+        "variants": [
+            {"options": list(v.options), "set": _resolved_variant_fields(v)}
+            for v in product.variants
+        ],
+        "images": [
+            {"src": i.source_url, "position": i.position, "alt_text": i.alt_text}
+            for i in product.images
+        ],
+    }
+
+
+def _update_detail(product: CanonicalProduct, current: CatalogProduct) -> dict:
+    changes: list[dict] = []
+    # Title is always file-present (required header column); "" means the block
+    # already carries an error and never reaches here.
+    if product.title and product.title != current.title:
+        changes.append(_change("title", current.title, product.title))
+    for field_name, resolved in _resolved_product_fields(product).items():
+        before = current.fields.get(field_name)
+        if resolved != before:
+            changes.append(_change(field_name, before, resolved))
+    for slot in (1, 2, 3):
+        if f"option{slot}_name" not in product.fields:
+            continue
+        before, after = current.option_names[slot - 1], product.option_names[slot - 1]
+        if after != before:
+            changes.append(_change(f"option{slot}_name", before, after))
+
+    variant_entries: list[dict] = []
+    by_options = {v.options: v for v in current.variants}
+    for variant in product.variants:
+        match = by_options.get(variant.options)
+        if match is None:
+            variant_entries.append(
+                {"options": list(variant.options), "kind": "add", "set": _resolved_variant_fields(variant)}
+            )
+            continue
+        variant_changes = [
+            _change(f, match.fields.get(f), resolved)
+            for f, resolved in _resolved_fields(variant.fields).items()
+            if resolved != match.fields.get(f)
+        ]
+        if variant_changes:
+            variant_entries.append(
+                {"options": list(variant.options), "kind": "update", "changes": variant_changes}
+            )
+
+    image_entries: list[dict] = []
+    by_src = {i.source_url: i for i in current.images}
+    for image in product.images:
+        match = by_src.get(image.source_url)
+        if match is None:
+            image_entries.append(
+                {"src": image.source_url, "kind": "add", "position": image.position, "alt_text": image.alt_text}
+            )
+            continue
+        image_changes = [
+            _change(f, before, after)
+            for f, before, after in (
+                ("position", match.position, image.position),
+                ("alt_text", match.alt_text, image.alt_text),
+            )
+            if after != before
+        ]
+        if image_changes:
+            image_entries.append({"src": image.source_url, "kind": "update", "changes": image_changes})
+
+    detail: dict = {}
+    if changes:
+        detail["changes"] = changes
+    if variant_entries:
+        detail["variants"] = variant_entries
+    if image_entries:
+        detail["images"] = image_entries
+    return detail
+
+
+def _resolved_fields(fields: dict[str, object]) -> dict[str, object]:
+    """File-present fields with None (an explicit clear) resolved to the default."""
+    return {f: (v if v is not None else CLEAR_DEFAULTS.get(f)) for f, v in fields.items()}
+
+
+def _resolved_product_fields(product: CanonicalProduct) -> dict[str, object]:
+    return {
+        f: v for f, v in _resolved_fields(product.fields).items() if f not in _OPTION_NAME_FIELDS
+    }
+
+
+def _resolved_variant_fields(variant: CanonicalVariant) -> dict[str, object]:
+    return {f: _json_safe(v) for f, v in _resolved_fields(variant.fields).items()}
+
+
+def _change(field_name: str, before: object, after: object) -> dict:
+    return {"field": field_name, "before": _json_safe(before), "after": _json_safe(after)}
+
+
+def _json_safe(value: object) -> object:
+    if isinstance(value, Decimal):
+        return str(value)
+    if isinstance(value, (tuple, list)):
+        return [_json_safe(v) for v in value]
+    return value

backend/app/domains/products/validate.py

@@ -31,8 +31,10 @@ from .models import (
 
 _HANDLE_RE = re.compile(r"^[a-z0-9-]+$")
 _STATUSES = {"draft", "active", "archived"}
-# Product columns handled as attributes (title, option_names), not via fields{}.
-_ATTRIBUTE_COLUMNS = {"Title", "Option1 Name", "Option2 Name", "Option3 Name"}
+# Title is handled as an attribute, not via fields{}. Option names live in BOTH
+# .option_names (the values) and fields{} (the file-presence signal the diff
+# needs: absent column == untouched, never a clear).
+_ATTRIBUTE_COLUMNS = {"Title"}
 # Sentinel: the cell failed normalization (the error is already recorded).
 _INVALID = object()
 

backend/tests/test_products_diff.py

@@ -0,0 +1,110 @@
+"""Diff engine — classification, blank-vs-absent, option matching, fingerprint (§6.8)."""
+from decimal import Decimal
+
+from app.domains.products.codec import parse_csv
+from app.domains.products.diff import (
+    CatalogImage, CatalogProduct, CatalogVariant, compute_diff,
+)
+from app.domains.products.validate import build_products
+
+
+def _canon(*lines: str):
+    return build_products(parse_csv(("\n".join(lines) + "\n").encode()))
+
+
+def _catalog_mug(**overrides):
+    fields = {
+        "title": "Moon Mug", "description_html": None, "vendor": "Acme",
+        "product_type": "standalone", "google_product_category": None,
+        "tags": ["kitchen"], "status": "active", "published": True,
+    } | overrides
+    return {
+        "moon-mug": CatalogProduct(
+            id=1, handle="moon-mug", title=fields["title"],
+            option_names=(None, None, None), fields=fields,
+            variants=[CatalogVariant(id=10, options=(None, None, None), position=1,
+                                     fields={"sku": "SKU-1", "barcode": None, "price": Decimal("18.00"),
+                                             "cost": None, "weight": None, "weight_unit": None,
+                                             "volume": None, "volume_unit": None, "tax_id_1": None,
+                                             "tax_id_2": None, "inventory_tracker": None,
+                                             "inventory_qty": 40, "variant_image": None})],
+            images=[CatalogImage(id=100, source_url="https://x/a.jpg", position=1, alt_text=None)],
+        )
+    }
+
+
+HEADER = "Handle,Title,Vendor,Tags,Status,Variant SKU,Variant Price,Variant Inventory Qty,Image Src"
+MUG_ROW = 'moon-mug,Moon Mug,Acme,kitchen,active,SKU-1,18.00,40,https://x/a.jpg'
+
+
+def test_new_handle_classifies_add():
+    diff = compute_diff({}, _canon(HEADER, MUG_ROW))
+    [rec] = diff.records
+    assert rec["kind"] == "add" and rec["handle"] == "moon-mug" and rec["variant_count"] == 1
+    assert diff.summary == {"adds": 1, "updates": 0, "unchanged": 0, "errors": 0}
+    assert rec["detail"]["set"]["status"] == "active"
+
+
+def test_identical_file_classifies_unchanged():
+    diff = compute_diff(_catalog_mug(), _canon(HEADER, MUG_ROW))
+    assert diff.records[0]["kind"] == "unchanged"
+    assert diff.summary["unchanged"] == 1
+
+
+def test_changed_price_classifies_update_with_before_after():
+    row = MUG_ROW.replace("18.00", "21.00")
+    diff = compute_diff(_catalog_mug(), _canon(HEADER, row))
+    [rec] = diff.records
+    assert rec["kind"] == "update"
+    [vchange] = rec["detail"]["variants"]
+    assert {"field": "price", "before": "18.00", "after": "21.00"} in vchange["changes"]
+
+
+def test_absent_column_untouched_empty_cell_clears():
+    # Vendor column absent: vendor stays Acme. Status present-but-empty: clears to default 'active' (already active -> no change).
+    diff = compute_diff(
+        _catalog_mug(),
+        _canon("Handle,Title,Status,Variant SKU,Variant Price,Variant Inventory Qty,Image Src",
+               "moon-mug,Moon Mug,,SKU-1,18.00,40,https://x/a.jpg"),
+    )
+    assert diff.records[0]["kind"] == "unchanged"
+
+
+def test_empty_cell_clear_shows_in_diff():
+    # Vendor present-but-empty clears Acme -> None: an explicit, previewable change (§6.5.1).
+    diff = compute_diff(
+        _catalog_mug(),
+        _canon("Handle,Title,Vendor,Variant SKU,Variant Price,Variant Inventory Qty,Image Src",
+               "moon-mug,Moon Mug,,SKU-1,18.00,40,https://x/a.jpg"),
+    )
+    [rec] = diff.records
+    assert rec["kind"] == "update"
+    assert {"field": "vendor", "before": "Acme", "after": None} in rec["detail"]["changes"]
+
+
+def test_new_option_combo_is_variant_add_existing_untouched():
+    catalog = _catalog_mug()
+    diff = compute_diff(
+        catalog,
+        _canon("Handle,Title,Option1 Name,Option1 Value,Variant Price",
+               "moon-mug,Moon Mug,Size,Large,25.00"),
+    )
+    [rec] = diff.records
+    assert rec["kind"] == "update"
+    kinds = [v.get("kind") for v in rec["detail"]["variants"]]
+    assert "add" in kinds
+
+
+def test_error_product_classifies_error():
+    diff = compute_diff({}, _canon("Handle,Title,Variant Price", "mug,Mug,nope"))
+    [rec] = diff.records
+    assert rec["kind"] == "error"
+    assert rec["detail"]["errors"][0]["column"] == "Variant Price"
+
+
+def test_fingerprint_stable_and_drift_sensitive():
+    d1 = compute_diff(_catalog_mug(), _canon(HEADER, MUG_ROW))
+    d2 = compute_diff(_catalog_mug(), _canon(HEADER, MUG_ROW))
+    d3 = compute_diff(_catalog_mug(title="Renamed"), _canon(HEADER, MUG_ROW))
+    assert d1.fingerprint == d2.fingerprint
+    assert d1.fingerprint != d3.fingerprint