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comic/mock_backend.py

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+"""Offline mock backends — no GPU, no Modal, no cost.
+
+They honour the same contracts as the real backends so the whole flow (idea ->
+bible -> panels -> images -> reader) can be built and tested locally. The mock
+writer returns valid JSON for BOTH prompt kinds (bible vs panel batch), detected by
+a marker in the system prompt; the mock artist draws a clearly-placeholder panel.
+"""
+
+from __future__ import annotations
+
+import io
+import json
+import re
+
+from PIL import Image, ImageDraw
+
+from .backends import WriterBackend, ArtistBackend
+from .schema import PAGES, PANELS_PER_PAGE
+
+
+def _is_panel_request(messages: list) -> bool:
+    sys = next((m["content"] for m in messages if m["role"] == "system"), "")
+    return "scripting individual panels" in sys
+
+
+def _user_text(messages: list) -> str:
+    return next((m["content"] for m in reversed(messages)
+                 if m["role"] == "user"), "")
+
+
+# Refuse the mock only on an obvious red flag, so the offline path still exercises
+# the refusal branch when asked.
+_BLOCK_RE = re.compile(r"\b(child porn|csam|sexual.*(child|minor))\b", re.IGNORECASE)
+
+
+class MockWriter(WriterBackend):
+    """Deterministic JSON for the bible call and the panel-batch calls."""
+
+    def chat(self, messages: list) -> str:
+        user = _user_text(messages)
+        if _is_panel_request(messages):
+            return self._panels(user)
+        return self._bible(user)
+
+    # call #1
+    def _bible(self, user: str) -> str:
+        if _BLOCK_RE.search(user):
+            return json.dumps({
+                "approved": False,
+                "refusal_reason": "That request isn't something I can make a comic about.",
+            })
+        # Pull the reader's request out of the prompt for a touch of flavor.
+        m = re.search(r'"""\s*(.+?)\s*"""', user, re.DOTALL)
+        idea = (m.group(1).strip() if m else "an adventure")[:80]
+        pages = [
+            {"page": i, "synopsis": f"Page {i}: the tale of {idea} advances toward its end."}
+            for i in range(1, PAGES + 1)
+        ]
+        return json.dumps({
+            "approved": True,
+            "refusal_reason": "",
+            "title": f"The Saga of {idea.title()}"[:60],
+            "logline": f"A mock comic about {idea}.",
+            "art_style": ("modern western comic book art, bold black ink linework, "
+                          "dynamic cel shading"),
+            "palette": "warm saturated comic palette",
+            "characters": [
+                {"name": "Mara", "appearance": ("a determined young woman, late 20s, short "
+                 "auburn hair, green travel cloak over leather armor, a brass compass at her belt")},
+                {"name": "Finn", "appearance": ("a wiry teenage boy, freckles, messy black hair, "
+                 "patched blue tunic, always carrying a worn satchel")},
+            ],
+            "pages": pages,
+        })
+
+    # calls #2..N
+    def _panels(self, user: str) -> str:
+        # The batch's pages are the "Page N:" lines AFTER the "NOW WRITE" marker
+        # (the bible brief above it lists the full synopsis, which we must ignore).
+        tail = user.split("NOW WRITE")[-1]
+        nums = [int(n) for n in re.findall(r"Page (\d+):", tail)]
+        seen, req = set(), []
+        for n in nums:
+            if n not in seen:
+                seen.add(n)
+                req.append(n)
+        panels = []
+        for pg in req:
+            for pn in range(1, PANELS_PER_PAGE + 1):
+                panels.append({
+                    "page": pg,
+                    "panel": pn,
+                    "scene": (f"wide shot, Mara and Finn on page {pg} panel {pn}, "
+                              "dramatic lighting, a tense moment in their journey"),
+                    "caption": f"Page {pg}, panel {pn}: the journey continues. "
+                               f"\"We're close now,\" Mara says.",
+                    "characters": ["Mara", "Finn"],
+                })
+        return json.dumps({"panels": panels})
+
+
+class MockArtist(ArtistBackend):
+    """A placeholder landscape panel — a tinted gradient with abstract blocks."""
+
+    W, H = 1024, 768
+
+    def render(self, prompt: str, seed: int = 0) -> bytes:
+        h = (abs(hash((prompt, seed))) & 0xFFFFFFFF)
+        base = _tint(prompt)
+        img = Image.new("RGB", (self.W, self.H), base)
+        d = ImageDraw.Draw(img)
+        for y in range(self.H):
+            f = y / self.H
+            d.line([(0, y), (self.W, y)],
+                   fill=tuple(int(c * (1 - 0.4 * f)) for c in base))
+        rnd = h
+        for _ in range(16):
+            rnd = (rnd * 1103515245 + 12345) & 0x7FFFFFFF
+            x = rnd % self.W
+            rnd = (rnd * 1103515245 + 12345) & 0x7FFFFFFF
+            y = self.H // 2 + rnd % (self.H // 2)
+            rnd = (rnd * 1103515245 + 12345) & 0x7FFFFFFF
+            w = 40 + rnd % 160
+            shade = tuple(max(0, c - 60) for c in base)
+            d.rectangle([x, y, x + w, y + 50 + rnd % 90], fill=shade)
+        buf = io.BytesIO()
+        img.save(buf, format="JPEG", quality=88)
+        return buf.getvalue()
+
+
+def _tint(prompt: str) -> tuple:
+    p = prompt.lower()
+    if "noir" in p or "dark" in p:
+        return (70, 74, 86)
+    if "warm" in p or "sunset" in p:
+        return (150, 110, 80)
+    if "forest" in p or "green" in p:
+        return (80, 120, 90)
+    return (95, 100, 120)