refactor(ocr): extract extract_page_blocks() from both OCR engines

Enable per-page processing by extracting the inner loop body of
extract_blocks() into extract_page_blocks(image, page_idx, language).
The original extract_blocks() now delegates to the new function,
preserving backward compatibility for the batch path.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

ocr-service/test_engines.py

@@ -0,0 +1,132 @@
+"""Tests for per-page block extraction in OCR engines."""
+
+from unittest.mock import MagicMock, patch
+from PIL import Image
+
+from engines import surya, kraken
+
+
+# ─── Surya extract_page_blocks ───────────────────────────────────────────────
+
+
+def _make_surya_line(text, bbox, polygon=None, words=None):
+    """Create a mock Surya text line with the expected attributes."""
+    line = MagicMock()
+    line.text = text
+    line.bbox = bbox
+    line.polygon = polygon
+    line.words = words or []
+    if not words:
+        line.confidence = 0.95
+        # hasattr check needs words to be falsy
+        del line.words
+    return line
+
+
+def test_surya_extract_page_blocks_returns_blocks_for_single_image():
+    image = Image.new("RGB", (100, 200))
+
+    mock_line = _make_surya_line("Hallo Welt", [10, 20, 90, 40])
+    mock_pred = MagicMock()
+    mock_pred.text_lines = [mock_line]
+
+    with patch.object(surya, "_recognition_predictor") as mock_rec, \
+         patch.object(surya, "_loaded", True):
+        mock_rec.return_value = [mock_pred]
+
+        blocks = surya.extract_page_blocks(image, page_idx=2, language="de")
+
+    assert len(blocks) == 1
+    assert blocks[0]["pageNumber"] == 2
+    assert blocks[0]["text"] == "Hallo Welt"
+    assert blocks[0]["x"] == 10 / 100
+    assert blocks[0]["y"] == 20 / 200
+    assert blocks[0]["width"] == 80 / 100
+    assert blocks[0]["height"] == 20 / 200
+
+
+def test_surya_extract_blocks_delegates_to_extract_page_blocks():
+    """After refactoring, extract_blocks should produce the same output."""
+    image1 = Image.new("RGB", (100, 200))
+    image2 = Image.new("RGB", (100, 200))
+
+    mock_line = _make_surya_line("Test", [10, 20, 90, 40])
+    mock_pred = MagicMock()
+    mock_pred.text_lines = [mock_line]
+
+    with patch.object(surya, "_recognition_predictor") as mock_rec, \
+         patch.object(surya, "_loaded", True):
+        mock_rec.return_value = [mock_pred]
+
+        blocks = surya.extract_blocks([image1, image2])
+
+    assert len(blocks) == 2
+    assert blocks[0]["pageNumber"] == 0
+    assert blocks[1]["pageNumber"] == 1
+
+
+# ─── Kraken extract_page_blocks ──────────────────────────────────────────────
+
+
+def _make_kraken_record(text, cuts, confidences=None):
+    record = MagicMock()
+    record.prediction = text
+    record.cuts = cuts
+    record.line = cuts
+    record.confidences = confidences or [0.9] * len(text)
+    return record
+
+
+def _run_kraken_with_mocks(fn, *args):
+    """Run a kraken function with blla/rpred mocked via sys.modules."""
+    import sys
+    mock_blla = MagicMock()
+    mock_blla.segment.return_value = MagicMock()
+    mock_rpred = MagicMock()
+
+    mock_record = _make_kraken_record("Kurrent", [(10, 20), (90, 20), (90, 40), (10, 40)])
+    mock_rpred.rpred.return_value = [mock_record]
+
+    saved_kraken = sys.modules.get("kraken")
+    saved_blla = sys.modules.get("kraken.blla")
+    saved_rpred = sys.modules.get("kraken.rpred")
+
+    sys.modules["kraken"] = MagicMock(blla=mock_blla, rpred=mock_rpred)
+    sys.modules["kraken.blla"] = mock_blla
+    sys.modules["kraken.rpred"] = mock_rpred
+
+    try:
+        with patch.object(kraken, "_model", MagicMock()):
+            return fn(*args)
+    finally:
+        if saved_kraken is not None:
+            sys.modules["kraken"] = saved_kraken
+        else:
+            sys.modules.pop("kraken", None)
+        if saved_blla is not None:
+            sys.modules["kraken.blla"] = saved_blla
+        else:
+            sys.modules.pop("kraken.blla", None)
+        if saved_rpred is not None:
+            sys.modules["kraken.rpred"] = saved_rpred
+        else:
+            sys.modules.pop("kraken.rpred", None)
+
+
+def test_kraken_extract_page_blocks_returns_blocks_for_single_image():
+    image = Image.new("RGB", (100, 200))
+    blocks = _run_kraken_with_mocks(kraken.extract_page_blocks, image, 3, "de")
+
+    assert len(blocks) == 1
+    assert blocks[0]["pageNumber"] == 3
+    assert blocks[0]["text"] == "Kurrent"
+
+
+def test_kraken_extract_blocks_delegates_to_extract_page_blocks():
+    image1 = Image.new("RGB", (100, 200))
+    image2 = Image.new("RGB", (100, 200))
+    blocks = _run_kraken_with_mocks(kraken.extract_blocks, [image1, image2])
+
+    assert len(blocks) == 2
+    assert blocks[0]["pageNumber"] == 0
+    assert blocks[1]["pageNumber"] == 1