From 2057c69585b058de1c218c9b64d47a9dd0f3094c Mon Sep 17 00:00:00 2001
From: Josh Holtrop <jholtrop@gmail.com>
Date: Wed, 11 Jan 2017 22:18:02 -0500
Subject: [PATCH] add Buffer::{undo,redo}()

---
 src/core/Buffer.cc | 31 +++++++++++++++++++++++++++++++
 src/core/Buffer.h  |  2 ++
 2 files changed, 33 insertions(+)

diff --git a/src/core/Buffer.cc b/src/core/Buffer.cc
index 64a65d8..a6e18b0 100644
--- a/src/core/Buffer.cc
+++ b/src/core/Buffer.cc
@@ -386,3 +386,34 @@ void Buffer::apply_change_unit(const ChangeUnit & change_unit, bool forward)
         erase_data(change_unit.buffer_position, change_unit.length);
     }
 }
+
+void Buffer::undo()
+{
+    if (m_current_change_operation_index != INVALID_CHANGE_OPERATION_INDEX)
+    {
+        apply_change_operation(*m_change_operations[m_current_change_operation_index], false);
+        m_current_change_operation_index = m_change_operations[m_current_change_operation_index]->parent;
+    }
+}
+
+void Buffer::redo()
+{
+    size_t child_index = INVALID_CHANGE_OPERATION_INDEX;
+    if (m_current_change_operation_index == INVALID_CHANGE_OPERATION_INDEX)
+    {
+        if (m_change_operations.size() > 0u)
+        {
+            child_index = 0u;
+        }
+    }
+    else
+    {
+        child_index = *m_change_operations[m_current_change_operation_index]->children.begin();
+    }
+
+    if (child_index != INVALID_CHANGE_OPERATION_INDEX)
+    {
+        apply_change_operation(*m_change_operations[child_index], true);
+        m_current_change_operation_index = child_index;
+    }
+}
diff --git a/src/core/Buffer.h b/src/core/Buffer.h
index e58bfb0..68b41e7 100644
--- a/src/core/Buffer.h
+++ b/src/core/Buffer.h
@@ -134,6 +134,8 @@ public:
     Iterator end() const { return *m_eof_iterator; }
     void push_operation() { m_operation_level++; }
     void pop_operation();
+    void undo();
+    void redo();
 
 protected:
     bool m_eol_at_eof;