From b9313ad60658af95f4cd93cc22517ef257910b24 Mon Sep 17 00:00:00 2001
From: Josh Holtrop <jholtrop@gmail.com>
Date: Mon, 9 Jan 2017 22:05:43 -0500
Subject: [PATCH] add GapBuffer::copy_to()

---
 src/core/GapBuffer.h       | 34 ++++++++++++++++++++++++++++++++++
 test/src/test_GapBuffer.cc | 13 +++++++++++++
 2 files changed, 47 insertions(+)

diff --git a/src/core/GapBuffer.h b/src/core/GapBuffer.h
index 41fb50d..4d9e4cd 100644
--- a/src/core/GapBuffer.h
+++ b/src/core/GapBuffer.h
@@ -99,6 +99,40 @@ public:
         move_gap(m_size);
     }
 
+    /**
+     * Copy a range of data from this GapBuffer to another.
+     *
+     * @param source_position
+     *   Position in the gap buffer containing the data to copy.
+     * @param length
+     *   Length of the data to copy.
+     * @param other
+     *   Destination GapBuffer to copy the data into.
+     * @param destination_position
+     *   Position in the destination GapBuffer to copy the data to.
+     */
+    void copy_to(size_t source_position, size_t length, GapBuffer & other, size_t destination_position)
+    {
+        if ((source_position < m_size) &&
+                (length > 0u) &&
+                ((source_position + length) <= m_size))
+        {
+            if ((m_gap_position <= source_position) ||
+                    (m_gap_position >= (source_position + length)))
+            {
+                /* The gap is before or after the range of data to copy. */
+                other.insert(destination_position, address(source_position), length);
+            }
+            else
+            {
+                /* The gap is in the middle of the range of data to copy. */
+                size_t pre_gap_size = m_gap_position - source_position;
+                other.insert(destination_position, address(source_position), pre_gap_size);
+                other.insert(destination_position + pre_gap_size, address(source_position + pre_gap_size), length - pre_gap_size);
+            }
+        }
+    }
+
 protected:
     /** Address of the allocated memory buffer. */
     uint8_t * m_buffer;
diff --git a/test/src/test_GapBuffer.cc b/test/src/test_GapBuffer.cc
index 9232f76..27f8bce 100644
--- a/test/src/test_GapBuffer.cc
+++ b/test/src/test_GapBuffer.cc
@@ -86,3 +86,16 @@ TEST(GapBufferTest, allocates_more_memory_and_copies_buffer_contents_when_needed
     s += "EFGH";
     EXPECT_EQ(s, gp.get_string());
 }
+
+TEST(GapBufferTest, allows_copying_data_range_from_one_gap_buffer_to_another)
+{
+    GapBuffer gp1, gp2;
+    gp1.insert(0u, (const uint8_t *)"ABCDEFGH", 8u);
+    gp1.copy_to(0u, 4u, gp2, 0u);
+    EXPECT_EQ("ABCD", gp2.get_string());
+    gp1.insert(0u, (const uint8_t *)"IJKL", 4u);
+    gp1.copy_to(8u, 2u, gp2, 0u);
+    EXPECT_EQ("EFABCD", gp2.get_string());
+    gp1.copy_to(2u, 4u, gp2, 3u);
+    EXPECT_EQ("EFAKLABBCD", gp2.get_string());
+}