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app/services/figure_export.py

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+"""Publication figure export helpers.
+
+BioNexus composes figures as SVG first, then derives distribution formats from
+that single source so panel layout and labels do not diverge between formats.
+Exports are content-addressed and return metadata suitable for figure
+provenance records.
+"""
+from __future__ import annotations
+
+import hashlib
+import io
+from dataclasses import dataclass
+from typing import Literal
+
+FigureFormat = Literal["svg", "png", "pdf", "tiff"]
+
+
+@dataclass(frozen=True)
+class FigureArtifact:
+    payload: bytes
+    format: FigureFormat
+    content_type: str
+    dpi: int | None
+    sha256: str
+    width_px: int | None = None
+    height_px: int | None = None
+
+    def metadata(self) -> dict:
+        return {
+            "format": self.format,
+            "content_type": self.content_type,
+            "dpi": self.dpi,
+            "sha256": self.sha256,
+            "bytes": len(self.payload),
+            "width_px": self.width_px,
+            "height_px": self.height_px,
+        }
+
+
+def _sha(data: bytes) -> str:
+    return hashlib.sha256(data).hexdigest()
+
+
+def _raster_size(data: bytes) -> tuple[int | None, int | None]:
+    try:
+        from PIL import Image
+        with Image.open(io.BytesIO(data)) as image:
+            return image.size
+    except Exception:
+        return None, None
+
+
+def export_figure(svg: str, fmt: FigureFormat = "svg", dpi: int = 300) -> FigureArtifact:
+    """Convert the canonical SVG into a requested publication format.
+
+    PNG/TIFF are rendered at 300-600 DPI. PDF remains vector. Conversion
+    failures are raised to the caller; an endpoint must never return SVG bytes
+    while labelling them as a raster/PDF artifact.
+    """
+    if fmt not in {"svg", "png", "pdf", "tiff"}:
+        raise ValueError(f"unsupported figure format: {fmt}")
+    if dpi < 300 or dpi > 600:
+        raise ValueError("publication raster DPI must be between 300 and 600")
+
+    svg_bytes = svg.encode("utf-8")
+    if fmt == "svg":
+        return FigureArtifact(svg_bytes, "svg", "image/svg+xml", None, _sha(svg_bytes))
+
+    try:
+        import cairosvg
+    except ImportError as exc:
+        raise RuntimeError("CairoSVG is required for PNG/PDF/TIFF figure export") from exc
+
+    if fmt == "pdf":
+        payload = cairosvg.svg2pdf(bytestring=svg_bytes)
+        return FigureArtifact(payload, "pdf", "application/pdf", None, _sha(payload))
+
+    # CairoSVG interprets output_width/height in pixels; scale from CSS 96 DPI.
+    scale = dpi / 96.0
+    png = cairosvg.svg2png(bytestring=svg_bytes, scale=scale)
+    if fmt == "png":
+        width, height = _raster_size(png)
+        return FigureArtifact(png, "png", "image/png", dpi, _sha(png), width, height)
+
+    try:
+        from PIL import Image
+    except ImportError as exc:
+        raise RuntimeError("Pillow is required for TIFF figure export") from exc
+    source = Image.open(io.BytesIO(png)).convert("RGB")
+    out = io.BytesIO()
+    source.save(out, format="TIFF", dpi=(dpi, dpi), compression="tiff_lzw")
+    payload = out.getvalue()
+    width, height = source.size
+    return FigureArtifact(payload, "tiff", "image/tiff", dpi, _sha(payload), width, height)