From 9849c62d80cbd1fefb49a36b10f87d2bd90ee8dc Mon Sep 17 00:00:00 2001
From: Nathan Sobo <nathan@github.com>
Date: Wed, 8 May 2013 16:16:26 -0600
Subject: [PATCH] Properly handle regions that straddle existing regions

When we're creating folds that contain other folds, we'll need the
region based on the new fold's row mapping to overwrite the regions
from the old folds. This commit ensures that the new region cleanly
slots in, replacing any regions it completely contains and splitting
regions that it only partially overlaps.
---
 spec/app/row-map-spec.coffee | 15 +++++++++++++
 src/app/row-map.coffee       | 43 ++++++++++++++++++++++--------------
 2 files changed, 41 insertions(+), 17 deletions(-)

diff --git a/spec/app/row-map-spec.coffee b/spec/app/row-map-spec.coffee
index 2872d0372..48f9a723f 100644
--- a/spec/app/row-map-spec.coffee
+++ b/spec/app/row-map-spec.coffee
@@ -171,6 +171,21 @@ describe "RowMap", ->
         expect(map.bufferRowRangeForScreenRow(7)).toEqual [21, 22]
         expect(map.bufferRowRangeForScreenRow(8)).toEqual [22, 27]
 
+    describe "when the row range straddles existing regions", ->
+      it "splits the straddled regions and places the new region between them", ->
+                                         # filler region 0
+        map.mapBufferRowRange(4, 7, 1)   # region 1
+                                         # filler region 2
+        map.mapBufferRowRange(13, 15, 1) # region 3
+
+        # create region straddling region 0 and region 2
+        map.mapBufferRowRange(2, 10, 1)
+
+        expect(map.regions[0]).toEqual(bufferRows: 2, screenRows: 2)
+        expect(map.regions[1]).toEqual(bufferRows: 8, screenRows: 1)
+        expect(map.regions[2]).toEqual(bufferRows: 3, screenRows: 8)
+        expect(map.regions[3]).toEqual(bufferRows: 2, screenRows: 1)
+
   describe ".applyScreenDelta(startScreenRow, delta)", ->
     describe "when applying a positive delta", ->
       it "can enlarge the screen side of existing regions", ->
diff --git a/src/app/row-map.coffee b/src/app/row-map.coffee
index e3132462c..3efeadc79 100644
--- a/src/app/row-map.coffee
+++ b/src/app/row-map.coffee
@@ -29,30 +29,39 @@ class RowMap
   mapBufferRowRange: (startBufferRow, endBufferRow, screenRows) ->
     { index, bufferRow, screenRow } = @traverseToBufferRow(startBufferRow)
 
+    overlapStartIndex = index
+    overlapStartBufferRow = bufferRow
+    overlapEndIndex = index
+    overlapEndBufferRow = bufferRow
+    overlapEndScreenRow = screenRow
+
+    # determine regions that the new region overlaps. they will need replacement.
+    while overlapEndIndex < @regions.length
+      region = @regions[overlapEndIndex]
+      overlapEndBufferRow += region.bufferRows
+      overlapEndScreenRow += region.screenRows
+      break if overlapEndBufferRow >= endBufferRow
+      overlapEndIndex++
+
+    # we will replace overlapStartIndex..overlapEndIndex with these regions
     newRegions = []
 
-    preRows = startBufferRow - bufferRow
+    # if we straddle the first overlapping region, push a smaller region representing
+    # the portion before the new region
+    preRows = startBufferRow - overlapStartBufferRow
     if preRows > 0
       newRegions.push(bufferRows: preRows, screenRows: preRows)
 
-    bufferRows = endBufferRow - startBufferRow
-    newRegions.push({bufferRows, screenRows})
+    # push the new region
+    newRegions.push(bufferRows: endBufferRow - startBufferRow, screenRows: screenRows)
 
-    startIndex = index
-    endIndex = index
-    while bufferRows > 0 and endIndex < @regions.length
-      region = @regions[endIndex]
-      if region.bufferRows < bufferRows
-        bufferRows -= region.bufferRows
-        endIndex++
-      else
-        postBufferRows = region.bufferRows - preRows - bufferRows
-        postScreenRows = region.screenRows - preRows - screenRows
-        if postBufferRows > 0 or postScreenRows > 0
-          newRegions.push(bufferRows: postBufferRows, screenRows: postScreenRows)
-        bufferRows = 0
+    # if we straddle the last overlapping region, push a smaller region representing
+    # the portion after the new region
+    if overlapEndBufferRow > endBufferRow
+      endScreenRow = screenRow + preRows + screenRows
+      newRegions.push(bufferRows: overlapEndBufferRow - endBufferRow, screenRows: overlapEndScreenRow - endScreenRow)
 
-    @regions[startIndex..endIndex] = newRegions
+    @regions[overlapStartIndex..overlapEndIndex] = newRegions
 
   applyBufferDelta: (startBufferRow, delta) ->
     { region } = @traverseToBufferRow(startBufferRow)