From 3d83489819d1fa3bed1609a5100edd1458f189f1 Mon Sep 17 00:00:00 2001
From: Matthias Bisping <matthias.bisping@axbit.com>
Date: Tue, 10 Jan 2023 11:14:15 +0100
Subject: [PATCH] Refactoring: Make single pass rectangle merging stateless

---
 cv_analysis/layout_parsing.py  |  4 +--
 cv_analysis/utils/merging.py   | 47 ++++++++++++++++++++++++++--------
 cv_analysis/utils/rectangle.py |  3 +++
 cv_analysis/utils/spacial.py   |  2 +-
 4 files changed, 43 insertions(+), 13 deletions(-)

diff --git a/cv_analysis/layout_parsing.py b/cv_analysis/layout_parsing.py
index 85da4d4..2c92d84 100644
--- a/cv_analysis/layout_parsing.py
+++ b/cv_analysis/layout_parsing.py
@@ -14,7 +14,7 @@ from cv_analysis.utils.common import (
     fill_rectangles,
 )
 from cv_analysis.utils.conversion import contour_to_rectangle
-from cv_analysis.utils.merging import connect_related_rectangles
+from cv_analysis.utils.merging import merge_related_rectangles
 from cv_analysis.utils.postprocessing import remove_included, has_no_parent
 from cv_analysis.utils.rectangle import Rectangle
 
@@ -23,7 +23,7 @@ def parse_layout(image: np.array) -> List[Rectangle]:
     rectangles = rcompose(
         find_segments,
         remove_included,
-        connect_related_rectangles,
+        merge_related_rectangles,
         remove_included,
     )(image)
 
diff --git a/cv_analysis/utils/merging.py b/cv_analysis/utils/merging.py
index 15f84a6..d9c5067 100644
--- a/cv_analysis/utils/merging.py
+++ b/cv_analysis/utils/merging.py
@@ -1,25 +1,52 @@
+from functools import reduce
 from itertools import combinations
-from typing import List
+from typing import List, Tuple, Set
 
 from cv_analysis.utils import until, make_merger_sentinel
 from cv_analysis.utils.rectangle import Rectangle
-from cv_analysis.utils.spacial import is_related
+from cv_analysis.utils.spacial import related
 
 
-def connect_related_rectangles(rectangles: List[Rectangle]) -> List[Rectangle]:
+def merge_related_rectangles(rectangles: List[Rectangle]) -> List[Rectangle]:
+    """Merges rectangles that are related to each other, iterating on partial merge results until no more mergers are
+    possible."""
     assert isinstance(rectangles, list)
     no_new_merges = make_merger_sentinel()
     return until(no_new_merges, merge_rectangles_once, rectangles)
 
 
 def merge_rectangles_once(rectangles: List[Rectangle]) -> List[Rectangle]:
-    for alpha, beta in combinations(rectangles, 2):
-        if is_related(alpha, beta):
-            rectangles.remove(alpha)
-            rectangles.remove(beta)
-            rectangles.append(bounding_rect(alpha, beta))
-            return rectangles
-    return rectangles
+    """Merges rectangles that are related to each other, but does not iterate on the results."""
+
+    def merge_if_related(
+        acc: Tuple[Set[Rectangle], Set[Rectangle]],
+        pair: Tuple[Rectangle, Rectangle],
+    ) -> Tuple[Set[Rectangle], Set[Rectangle]]:
+        """Merges two rectangles if they are related, otherwise returns the accumulator unchanged."""
+        alpha, beta = pair
+        merged, used = acc
+
+        def unused(*args) -> bool:
+            return not used & {*args}
+
+        if unused(alpha) and unused(beta) and related(alpha, beta):
+            return merged | {bounding_rect(alpha, beta)}, used | {alpha, beta}
+
+        else:
+            return merged, used
+
+    rectangles = set(rectangles)
+    merged, used = reduce(merge_if_related, combinations(rectangles, 2), (set(), set()))
+
+    return list(merged | rectangles - used)
+
+    # for alpha, beta in combinations(rectangles, 2):
+    #     if related(alpha, beta):
+    #         rectangles.remove(alpha)
+    #         rectangles.remove(beta)
+    #         rectangles.append(bounding_rect(alpha, beta))
+    #         return rectangles
+    # return rectangles
 
 
 def bounding_rect(alpha: Rectangle, beta: Rectangle) -> Rectangle:
diff --git a/cv_analysis/utils/rectangle.py b/cv_analysis/utils/rectangle.py
index 8fa7f2c..b2d8834 100644
--- a/cv_analysis/utils/rectangle.py
+++ b/cv_analysis/utils/rectangle.py
@@ -20,6 +20,9 @@ class Rectangle:
         self.__x2 = nearest_valid(x2)
         self.__y2 = nearest_valid(y2)
 
+    def __repr__(self):
+        return f"Rectangle({self.x1}, {self.y1}, {self.x2}, {self.y2})"
+
     @property
     def x1(self):
         return self.__x1
diff --git a/cv_analysis/utils/spacial.py b/cv_analysis/utils/spacial.py
index 094db8a..b3a0835 100644
--- a/cv_analysis/utils/spacial.py
+++ b/cv_analysis/utils/spacial.py
@@ -273,7 +273,7 @@ def intersection_along_axis(alpha, beta, axis):
     return intersection
 
 
-def is_related(alpha: Rectangle, beta: Rectangle):
+def related(alpha: Rectangle, beta: Rectangle):
     return close(alpha, beta) or overlap(alpha, beta)