When no margin detected, reserve a bit more space for comments

copienator/annotation_layout.py

@@ -0,0 +1,75 @@
+"""Answer provenance and reproducible annotation spacing (200 dpi pixels)."""
+from hashlib import sha256
+from pathlib import Path
+import shutil
+
+import pymupdf
+
+from copienator import configuration
+from copienator.json_io import atomic_write_json, read_json
+
+
+def fingerprint(path):
+    return sha256(Path(path).read_bytes()).hexdigest()
+
+
+def metadata_path(pdf):
+    return Path(pdf).with_suffix('.layout.json')
+
+
+def answer_parts(pdf):
+    """Ignore stale sidecars after a PDF is replaced or manually edited."""
+    if pdf is None or not Path(pdf).is_file():
+        return []
+    try:
+        data = read_json(metadata_path(pdf), default={})
+        if data.get('sha256') == fingerprint(pdf):
+            parts = data.get('parts', [])
+            if isinstance(parts, list) and all(isinstance(part, dict) for part in parts):
+                return parts
+    except (OSError, ValueError, TypeError, AttributeError):
+        pass
+    return []
+
+
+def save_parts(pdf, parts):
+    atomic_write_json(metadata_path(pdf), {
+        'version': 1, 'sha256': fingerprint(pdf), 'parts': parts,
+    })
+
+
+def page_parts(pdf):
+    parts = answer_parts(pdf)
+    if not Path(pdf).is_file():
+        return []
+    with pymupdf.open(pdf) as document:
+        if len(parts) == len(document):
+            return parts
+        return [{'margin_status': 'unknown'} for _ in document]
+
+
+def copy_answer_pdf(source, destination):
+    parts = answer_parts(source)
+    shutil.copy(source, destination)
+    save_parts(destination, parts)
+
+
+def move_answer_pdf(source, destination):
+    parts = answer_parts(source)
+    shutil.move(str(source), str(destination))
+    save_parts(destination, parts)
+    metadata_path(source).unlink(missing_ok=True)
+
+
+def layout_for(pdf):
+    low = any(part.get('margin_status') == 'low' for part in answer_parts(pdf))
+    margin = (configuration.ANNOTATION_LOW_MARGIN_LEFT if low
+              else configuration.ANNOTATION_MARGIN_LEFT)
+    if type(margin) is not int or margin < 0:
+        raise ValueError('Annotation left margins must be non-negative integers')
+    return {'version': 1, 'margin_left': margin, 'narrow_left_pad_limit': 300}
+
+
+def legacy_layout():
+    # Old annotation scans were produced with these literal constants.
+    return {'version': 1, 'margin_left': 300, 'narrow_left_pad_limit': 300}