feat: add download target type for fetching files from URLs

hokusai/builder.py

@@ -9,7 +9,9 @@ from collections.abc import Callable
 from dataclasses import dataclass, field
 from pathlib import Path
 
-from hokusai.config import ProjectConfig
+import httpx
+
+from hokusai.config import DownloadTargetConfig, GenerateTargetConfig, ProjectConfig
 from hokusai.graph import build_graph, get_build_order, get_subgraph_for_target
 from hokusai.providers import Provider
 from hokusai.providers.blackforest import BlackForestProvider
@@ -73,6 +75,8 @@ def _collect_dep_files(
 ) -> list[Path]:
     """Collect all dependency file paths for a target."""
     target_cfg = config.targets[target_name]
+    if not isinstance(target_cfg, GenerateTargetConfig):
+        return []
     deps: list[str] = list(target_cfg.inputs)
     deps.extend(target_cfg.reference_images)
     deps.extend(target_cfg.control_images)
@@ -82,6 +86,8 @@ def _collect_dep_files(
 def _collect_extra_params(target_name: str, config: ProjectConfig) -> dict[str, object]:
     """Collect extra parameters that affect rebuild decisions."""
     target_cfg = config.targets[target_name]
+    if not isinstance(target_cfg, GenerateTargetConfig):
+        return {}
     params: dict[str, object] = {}
     if target_cfg.width is not None:
         params["width"] = target_cfg.width
@@ -97,6 +103,8 @@ def _collect_extra_params(target_name: str, config: ProjectConfig) -> dict[str,
 def _collect_all_deps(target_name: str, config: ProjectConfig) -> list[str]:
     """Collect all dependency names (inputs + reference_images + control_images)."""
     target_cfg = config.targets[target_name]
+    if not isinstance(target_cfg, GenerateTargetConfig):
+        return []
     deps: list[str] = list(target_cfg.inputs)
     deps.extend(target_cfg.reference_images)
     deps.extend(target_cfg.control_images)
@@ -128,6 +136,18 @@ def _build_provider_index(providers: list[Provider]) -> dict[str, Provider]:
     return index
 
 
+async def _download_target(
+    target_name: str,
+    target_cfg: DownloadTargetConfig,
+    project_dir: Path,
+) -> None:
+    """Download a file from a URL and write it to *project_dir / target_name*."""
+    async with httpx.AsyncClient(headers={"User-Agent": "hokusai"}) as client:
+        response = await client.get(target_cfg.download, follow_redirects=True)
+        _ = response.raise_for_status()
+    _ = (project_dir / target_name).write_bytes(response.content)
+
+
 async def _build_single_target(
     target_name: str,
     config: ProjectConfig,
@@ -136,6 +156,11 @@ async def _build_single_target(
 ) -> None:
     """Build a single target by dispatching to the appropriate provider."""
     target_cfg = config.targets[target_name]
+
+    if isinstance(target_cfg, DownloadTargetConfig):
+        await _download_target(target_name, target_cfg, project_dir)
+        return
+
     model_info = resolve_model(target_name, target_cfg, config.defaults)
     resolved_prompt = _resolve_prompt(target_cfg.prompt, project_dir)
 
@@ -227,6 +252,9 @@ def _should_skip_failed_dep(
     return any(d in result.failed for d in _collect_all_deps(target_name, config))
 
 
+_DOWNLOAD_MODEL_SENTINEL = "__download__"
+
+
 def _is_dirty(
     target_name: str,
     config: ProjectConfig,
@@ -235,6 +263,18 @@ def _is_dirty(
 ) -> bool:
     """Check if a target needs rebuilding."""
     target_cfg = config.targets[target_name]
+
+    if isinstance(target_cfg, DownloadTargetConfig):
+        return is_target_dirty(
+            target_name,
+            resolved_prompt=target_cfg.download,
+            model=_DOWNLOAD_MODEL_SENTINEL,
+            dep_files=[],
+            extra_params={},
+            state=state,
+            project_dir=project_dir,
+        )
+
     model_info = resolve_model(target_name, target_cfg, config.defaults)
     resolved_prompt = _resolve_prompt(target_cfg.prompt, project_dir)
     dep_files = _collect_dep_files(target_name, config, project_dir)
@@ -260,6 +300,8 @@ def _has_provider(
 ) -> bool:
     """Check that the required provider is available; record failure if not."""
     target_cfg = config.targets[target_name]
+    if isinstance(target_cfg, DownloadTargetConfig):
+        return True
     model_info = resolve_model(target_name, target_cfg, config.defaults)
     if model_info.name not in provider_index:
         msg = f"No provider available for model '{model_info.name}' (provider: {model_info.provider}) — check API key environment variables"
@@ -302,15 +344,22 @@ def _process_outcomes(
             on_progress(BuildEvent.TARGET_FAILED, name, str(error))
         else:
             target_cfg = config.targets[name]
-            model_info = resolve_model(name, target_cfg, config.defaults)
-            resolved_prompt = _resolve_prompt(target_cfg.prompt, project_dir)
+
+            if isinstance(target_cfg, DownloadTargetConfig):
+                resolved_prompt = target_cfg.download
+                model_name = _DOWNLOAD_MODEL_SENTINEL
+            else:
+                model_info = resolve_model(name, target_cfg, config.defaults)
+                resolved_prompt = _resolve_prompt(target_cfg.prompt, project_dir)
+                model_name = model_info.name
+
             dep_files = _collect_dep_files(name, config, project_dir)
             extra = _collect_extra_params(name, config)
 
             record_target_state(
                 name,
                 resolved_prompt=resolved_prompt,
-                model=model_info.name,
+                model=model_name,
                 dep_files=dep_files,
                 extra_params=extra,
                 state=state,