feat(platform): images port — decode, resolution bar (Q-3), WebP renditions (SD-0002 §6.2)

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
2026-06-12 00:09:58 -07:00
parent 385df8d728
commit f27a24353d
3 changed files with 133 additions and 0 deletions
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+"""platform/images — pure image processing (SD-0002 §6.2).
+
+Model-free, deterministic, no I/O of its own: decode bytes, enforce the
+resolution bar (INV-18 / Q-3), and emit downscale-only WebP renditions. The
+caller (the image-fetch phase) owns fetching, storage, and status.
+"""
+from __future__ import annotations
+
+import io
+from dataclasses import dataclass
+
+from PIL import Image, UnidentifiedImageError
+
+# Q-3 (SD-0002 §13): the minimum shorter-side dimension; below it an image is
+# rejected_low_res. Rejects icons/thumbnails, accepts normal product photos.
+MIN_IMAGE_SHORT_SIDE = 500
+
+# Rendition longest-side caps (px); downscale-only — a smaller source is kept
+# at its own size, never upscaled. Encoded WebP.
+RENDITIONS = {"thumb": 160, "card": 480, "detail": 1600}
+
+# Source formats we accept (Pillow format names).
+_ACCEPTED = {"JPEG", "PNG", "WEBP"}
+
+_WEBP_QUALITY = 82
+
+
+@dataclass(frozen=True)
+class Processed:
+    source_format: str
+    width: int
+    height: int
+    renditions: dict[str, bytes]  # name -> WebP bytes
+
+
+@dataclass(frozen=True)
+class Rejected:
+    reason: str  # "rejected_low_res" | "rejected_not_image"
+
+
+def process(data: bytes) -> Processed | Rejected:
+    """Decode + bar-check + renditions, or a typed rejection. Never raises on
+    bad input — undecodable/unsupported bytes are Rejected('rejected_not_image')."""
+    try:
+        with Image.open(io.BytesIO(data)) as im:
+            im.load()
+            source_format = im.format or ""
+            if source_format not in _ACCEPTED:
+                return Rejected(reason="rejected_not_image")
+            rgb = im.convert("RGB")
+            width, height = rgb.size
+            if min(width, height) < MIN_IMAGE_SHORT_SIDE:
+                return Rejected(reason="rejected_low_res")
+            renditions = {
+                name: _rendition(rgb, cap) for name, cap in RENDITIONS.items()
+            }
+            return Processed(
+                source_format=source_format,
+                width=width,
+                height=height,
+                renditions=renditions,
+            )
+    except (UnidentifiedImageError, OSError, ValueError):
+        return Rejected(reason="rejected_not_image")
+
+
+def _rendition(rgb: Image.Image, cap: int) -> bytes:
+    longest = max(rgb.size)
+    if longest > cap:
+        scale = cap / longest
+        size = (max(1, round(rgb.width * scale)), max(1, round(rgb.height * scale)))
+        resized = rgb.resize(size, Image.LANCZOS)
+    else:
+        resized = rgb
+    buf = io.BytesIO()
+    resized.save(buf, format="WEBP", quality=_WEBP_QUALITY, method=6)
+    return buf.getvalue()