Use per-page annotation spacing with inferred margin fallback

copienator/annotation_layout.py

@@ -61,13 +61,26 @@ def move_answer_pdf(source, destination):
     metadata_path(source).unlink(missing_ok=True)
 
 
+def added_margin(margin_mm):
+    """Interpolate the configured (millimetres, pixels) points, clamping at ends."""
+    if margin_mm is None:
+        return configuration.ANNOTATION_MARGIN_LEFT
+    points = configuration.ANNOTATION_MARGIN_POINTS
+    if (not points or any(x < 0 or type(y) is not int or y < 0 for x, y in points)
+            or any(a[0] >= b[0] for a, b in zip(points, points[1:]))):
+        raise ValueError('Annotation margin points must have increasing mm and non-negative integer pixels')
+    if margin_mm <= points[0][0]:
+        return points[0][1]
+    for (x0, y0), (x1, y1) in zip(points, points[1:]):
+        if margin_mm <= x1:
+            return round(y0 + (y1 - y0) * (margin_mm - x0) / (x1 - x0))
+    return points[-1][1]
+
+
 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}
+    margins = [added_margin(part.get('margin_mm')) for part in answer_parts(pdf)]
+    return {'version': 2, 'margin_left': max(margins, default=added_margin(None)),
+            'page_margins': margins, 'narrow_left_pad_limit': 0}
 
 
 def legacy_layout():