begin working on Cursor movement routines

src/core/GapBuffer.cc

@@ -8,6 +8,7 @@ GapBuffer::GapBuffer(Encoding::Type encoding)
     m_size = 0u;
     m_gap_position = 0u;
     m_encoding = encoding;
+    tabstop = 4u;
 }
 
 GapBuffer::GapBuffer(uint8_t * buffer, size_t buffer_size, size_t size, Encoding::Type encoding)
@@ -17,6 +18,7 @@ GapBuffer::GapBuffer(uint8_t * buffer, size_t buffer_size, size_t size, Encoding
     m_size = size;
     m_gap_position = size;
     m_encoding = encoding;
+    tabstop = 4u;
 }
 
 GapBuffer::~GapBuffer()
@@ -86,3 +88,81 @@ bool GapBuffer::Iterator::check_back()
     }
     return false;
 }
+
+
+bool GapBuffer::Cursor::is_start_of_line()
+{
+    Iterator i2 = m_iterator;
+    if (!i2.check_back())
+    {
+        /* Iterator cannot go backwards so it is at beginning of buffer. */
+        return true;
+    }
+    return *i2 == '\n';
+}
+
+bool GapBuffer::Cursor::go_start_of_line()
+{
+    /* TODO */
+}
+
+bool GapBuffer::Cursor::go_end_of_line()
+{
+    /* TODO */
+}
+
+bool GapBuffer::Cursor::go_left()
+{
+    if (!is_start_of_line())
+    {
+        uint32_t chr = *m_iterator;
+        if (m_iterator.check_back())
+        {
+            if (chr == '\t')
+            {
+                calculate_column();
+            }
+            else
+            {
+                /* TODO: handle multi-column characters */
+                m_column--;
+            }
+            return true;
+        }
+    }
+    return false;
+}
+
+bool GapBuffer::Cursor::go_right()
+{
+    if (!is_end_of_line())
+    {
+        if (m_iterator.check_forward())
+        {
+            uint32_t chr = *m_iterator;
+            if (chr == '\t')
+            {
+                uint8_t tabstop = m_iterator.gap_buffer()->tabstop;
+                m_column += tabstop - (m_column + 1u) % tabstop;
+            }
+            else
+            {
+                /* TODO: handle multi-column characters */
+                m_column++;
+            }
+            return true;
+        }
+    }
+    return false;
+}
+
+void GapBuffer::Cursor::calculate_column()
+{
+    Cursor tmp_cursor = *this;
+    tmp_cursor.go_start_of_line();
+    while (tmp_cursor < *this)
+    {
+        tmp_cursor.go_right();
+    }
+    m_column = tmp_cursor.m_column;
+}

src/core/GapBuffer.h

@@ -41,6 +41,11 @@ public:
                 return 0xFFFFFFFFu;
             }
         }
+        GapBuffer * gap_buffer() { return m_gap_buffer; }
+        bool operator<(const Iterator & other)
+        {
+            return m_offset < other.m_offset;
+        }
 
     protected:
         GapBuffer * m_gap_buffer;
@@ -56,13 +61,30 @@ public:
             m_line = 0u;
             m_column = 0u;
         }
+        bool is_start_of_line();
+        bool is_end_of_line()
+        {
+            return *m_iterator == '\n';
+        }
+        bool go_start_of_line();
+        bool go_end_of_line();
+        bool go_left();
+        bool go_right();
+        bool operator<(const Cursor & other)
+        {
+            return m_iterator < other.m_iterator;
+        }
 
     protected:
         Iterator m_iterator;
         size_t m_line;
         size_t m_column;
+
+        void calculate_column();
     };
 
+    uint8_t tabstop;
+
     GapBuffer(Encoding::Type encoding);
     GapBuffer(uint8_t * buffer, size_t buffer_size, size_t size, Encoding::Type encoding);
     ~GapBuffer();