fix(generate_image): enhance image handling and output path resolution in generate_image script

skills/nano-banana-pro-openrouter/scripts/generate_image.py

@@ -15,6 +15,8 @@ import mimetypes
 import os
 from pathlib import Path
 
+from openai import OpenAI
+
 
 # Configuration
 MAX_INPUT_IMAGES = 3
@@ -56,7 +58,7 @@ def require_api_key():
 def encode_image_to_data_url(path: Path) -> str:
     if not path.exists():
         raise SystemExit(f"Input image not found: {path}")
-    mime, _ = mimetypes.guess_type(path.name)
+    mime, _ = mimetypes.guess_type(str(path))
     if not mime:
         mime = "image/png"
     data = path.read_bytes()
@@ -64,16 +66,17 @@ def encode_image_to_data_url(path: Path) -> str:
     return f"data:{mime};base64,{encoded}"
 
 
-def build_message_content(prompt: str, input_images):
-    content = [{"type": "text", "text": prompt}]
+def build_message_content(prompt: str, input_images: list[str]) -> list[dict]:
+    content: list[dict] = [{"type": "text", "text": prompt}]
     for image_path in input_images:
         data_url = encode_image_to_data_url(Path(image_path))
         content.append({"type": "image_url", "image_url": {"url": data_url}})
     return content
 
-def parse_data_url(data_url: str):
+
+def parse_data_url(data_url: str) -> tuple[str, bytes]:
     if not data_url.startswith("data:") or ";base64," not in data_url:
-        raise ValueError("Image URL is not a base64 data URL.")
+        raise SystemExit("Image URL is not a base64 data URL.")
     header, encoded = data_url.split(",", 1)
     mime = header[5:].split(";", 1)[0]
     try:
@@ -83,35 +86,27 @@ def parse_data_url(data_url: str):
     return mime, raw
 
 
-def resolve_output_paths(filename: str, image_count: int, mime: str):
-  output_path = Path(filename)
-  suffix = output_path.suffix
+def resolve_output_path(filename: str, image_index: int, total_count: int, mime: str) -> Path:
+    output_path = Path(filename)
+    suffix = output_path.suffix
 
-  # Validate/correct suffix matches MIME type
-  expected_suffix = MIME_TO_EXT.get(mime, ".png")
-  if suffix and suffix.lower() != expected_suffix.lower():
-    print(f"Warning: filename extension '{suffix}' doesn't match returned MIME type '{mime}'. Using '{expected_suffix}' instead.")
-    suffix = expected_suffix
-  elif not suffix:
-    suffix = expected_suffix
+    # Validate/correct suffix matches MIME type
+    expected_suffix = MIME_TO_EXT.get(mime, ".png")
+    if suffix and suffix.lower() != expected_suffix.lower():
+        print(f"Warning: filename extension '{suffix}' doesn't match returned MIME type '{mime}'. Using '{expected_suffix}' instead.")
+        suffix = expected_suffix
+    elif not suffix:
+        suffix = expected_suffix
 
-  output_path = output_path.with_suffix(suffix)
+    # Single image: use original stem + corrected suffix
+    if total_count <= 1:
+        return output_path.with_suffix(suffix)
 
-  # Create parent directory if it doesn't exist (for paths with parent directories, absolute or relative)
-  if output_path.parent and str(output_path.parent) != '.':
-    output_path.parent.mkdir(parents=True, exist_ok=True)
-
-  if image_count == 1:
-    return [output_path]
-
-  paths = []
-  for index in range(image_count):
-    numbered = output_path.with_name(f"{output_path.stem}-{index + 1}{suffix}")
-    paths.append(numbered)
-  return paths
+    # Multiple images: append numbering
+    return output_path.with_name(f"{output_path.stem}-{image_index + 1}{suffix}")
 
 
-def extract_image_url(image):
+def extract_image_url(image: dict | object) -> str | None:
     if isinstance(image, dict):
         return image.get("image_url", {}).get("url") or image.get("url")
     return None
@@ -123,7 +118,7 @@ def load_system_prompt():
     template_path = script_dir / "assets" / "SYSTEM_TEMPLATE"
 
     if template_path.exists():
-        content = template_path.read_text().strip()
+        content = template_path.read_text(encoding="utf-8").strip()
         if content:
             return content
     return None
@@ -135,9 +130,8 @@ def main():
     if len(args.input_image) > MAX_INPUT_IMAGES:
         raise SystemExit(f"Too many input images: {len(args.input_image)} (max {MAX_INPUT_IMAGES}).")
 
-    image_size = args.resolution or "1K"
+    image_size = args.resolution
 
-    from openai import OpenAI
     client = OpenAI(base_url="https://openrouter.ai/api/v1", api_key=require_api_key())
 
     # Build messages with optional system prompt
@@ -173,19 +167,18 @@ def main():
     if not images:
         raise SystemExit("No images returned by the API.")
 
-    first_url = extract_image_url(images[0])
-    if not first_url:
-        raise SystemExit("Image payload missing image_url.url.")
-    first_mime, _ = parse_data_url(first_url)
-    output_paths = resolve_output_paths(args.filename, len(images), first_mime)
+    # Create output directory once before processing images
+    output_base_path = Path(args.filename)
+    if output_base_path.parent and str(output_base_path.parent) != '.':
+        output_base_path.parent.mkdir(parents=True, exist_ok=True)
 
     saved_paths = []
     for idx, image in enumerate(images):
         image_url = extract_image_url(image)
         if not image_url:
             raise SystemExit("Image payload missing image_url.url.")
-        _, raw = parse_data_url(image_url)
-        output_path = output_paths[idx]
+        mime, raw = parse_data_url(image_url)
+        output_path = resolve_output_path(args.filename, idx, len(images), mime)
         output_path.write_bytes(raw)
         saved_paths.append(output_path.resolve())