Factor out the notion of the line

Makefile

@@ -2,4 +2,4 @@ CFLAGS=-Wall -Wextra -std=c11 -pedantic -ggdb `pkg-config --cflags sdl2`
 LIBS=`pkg-config --libs sdl2` -lm
 
 te: main.c
-	$(CC) $(CFLAGS) -o te main.c la.c $(LIBS)
+	$(CC) $(CFLAGS) -o te main.c la.c buffer.c $(LIBS)

buffer.c

@@ -0,0 +1,56 @@
+#include <assert.h>
+#include <string.h>
+#include "./buffer.h"
+
+#define LINE_INIT_CAPACITY 1024
+
+static void line_grow(Line *line, size_t n)
+{
+    size_t new_capacity = line->capacity;
+
+    assert(new_capacity >= line->size);
+    while (new_capacity - line->size < n) {
+        if (new_capacity == 0) {
+            new_capacity = LINE_INIT_CAPACITY;
+        } else {
+            new_capacity *= 2;
+        }
+    }
+
+    if (new_capacity != line->capacity) {
+        line->chars = realloc(line->chars, new_capacity);
+        line->capacity = new_capacity;
+    }
+}
+
+void line_insert_text_before(Line *line, const char *text, size_t col)
+{
+    const size_t text_size = strlen(text);
+    line_grow(line, text_size);
+
+    memmove(line->chars + col + text_size,
+            line->chars + col,
+            line->size - col);
+    memcpy(line->chars + col, text, text_size);
+    line->size += text_size;
+}
+
+void line_backspace(Line *line, size_t col)
+{
+    if (col > 0 && line->size > 0) {
+        memmove(line->chars + col - 1,
+                line->chars + col,
+                line->size - col);
+        line->size -= 1;
+    }
+}
+
+void line_delete(Line *line, size_t col)
+{
+    if (col < line->size && line->size > 0) {
+        memmove(line->chars + col,
+                line->chars + col + 1,
+                line->size - col);
+        line->size -= 1;
+    }
+}

buffer.h

@@ -0,0 +1,16 @@
+#ifndef BUFFER_H_
+#define BUFFER_H_
+
+#include <stdlib.h>
+
+typedef struct {
+    size_t capacity;
+    size_t size;
+    char *chars;
+} Line;
+
+void line_insert_text_before(Line *line, const char *text, size_t col);
+void line_backspace(Line *line, size_t col);
+void line_delete(Line *line, size_t col);
+
+#endif // BUFFER_H_

main.c

@@ -9,6 +9,8 @@
 #define STB_IMAGE_IMPLEMENTATION
 #include "./stb_image.h"
 
+#include "./buffer.h"
+
 #define FONT_WIDTH 128
 #define FONT_HEIGHT 64
 #define FONT_COLS 18
@@ -136,47 +138,8 @@ void render_text_sized(SDL_Renderer *renderer, Font *font, const char *text, siz
     }
 }
 
-#define BUFFER_CAPACITY 1024
-
-char buffer[BUFFER_CAPACITY];
-size_t buffer_cursor = 0;
-size_t buffer_size = 0;
-
-void buffer_insert_text_before_cursor(const char *text)
-{
-    size_t text_size = strlen(text);
-    const size_t free_space = BUFFER_CAPACITY - buffer_size;
-    if (text_size > free_space) {
-        text_size = free_space;
-    }
-    memmove(buffer + buffer_cursor + text_size,
-            buffer + buffer_cursor,
-            buffer_size - buffer_cursor);
-    memcpy(buffer + buffer_cursor, text, text_size);
-    buffer_size += text_size;
-    buffer_cursor += text_size;
-}
-
-void buffer_backspace(void)
-{
-    if (buffer_cursor > 0 && buffer_size > 0) {
-        memmove(buffer + buffer_cursor - 1,
-                buffer + buffer_cursor,
-                buffer_size - buffer_cursor);
-        buffer_size -= 1;
-        buffer_cursor -= 1;
-    }
-}
-
-void buffer_delete(void)
-{
-    if (buffer_cursor < buffer_size && buffer_size > 0) {
-        memmove(buffer + buffer_cursor,
-                buffer + buffer_cursor + 1,
-                buffer_size - buffer_cursor);
-        buffer_size -= 1;
-    }
-}
+Line line = {0};
+size_t cursor = 0;
 
 #define UNHEX(color) \
     ((color) >> (8 * 0)) & 0xFF, \
@@ -186,7 +149,7 @@ void buffer_delete(void)
 
 void render_cursor(SDL_Renderer *renderer, const Font *font)
 {
-    const Vec2f pos = vec2f((float) buffer_cursor * FONT_CHAR_WIDTH * FONT_SCALE, 0.0f);
+    const Vec2f pos = vec2f((float) cursor * FONT_CHAR_WIDTH * FONT_SCALE, 0.0f);
 
     const SDL_Rect rect = {
         .x = (int) floorf(pos.x),
@@ -199,25 +162,22 @@ void render_cursor(SDL_Renderer *renderer, const Font *font)
     scc(SDL_RenderFillRect(renderer, &rect));
 
     set_texture_color(font->spritesheet, 0xFF000000);
-    if (buffer_cursor < buffer_size) {
-        render_char(renderer, font, buffer[buffer_cursor], pos, FONT_SCALE);
+    if (cursor < line.size) {
+        render_char(renderer, font, line.chars[cursor], pos, FONT_SCALE);
     }
 }
 
-
+// TODO: Multiple lines
+// TODO: Save/Load file
 // TODO: Jump forward/backward by a word
 // TODO: Delete a word
 // TODO: Blinking cursor
-// TODO: Multiple lines
-// TODO: Save/Load file
 
 int main(int argc, char **argv)
 {
     (void) argc;
     (void) argv;
 
-    buffer_insert_text_before_cursor("Hello, World");
-
     scc(SDL_Init(SDL_INIT_VIDEO));
 
     SDL_Window *window =
@@ -243,24 +203,27 @@ int main(int argc, char **argv)
             case SDL_KEYDOWN: {
                 switch (event.key.keysym.sym) {
                 case SDLK_BACKSPACE: {
-                    buffer_backspace();
+                    line_backspace(&line, cursor);
+                    if (cursor > 0) {
+                        cursor -= 1;
+                    }
                 }
                 break;
 
                 case SDLK_DELETE: {
-                    buffer_delete();
+                    line_delete(&line, cursor);
                 } break;
 
                 case SDLK_LEFT: {
-                    if (buffer_cursor > 0) {
-                        buffer_cursor -= 1;
+                    if (cursor > 0) {
+                        cursor -= 1;
                     }
                 }
                 break;
 
                 case SDLK_RIGHT: {
-                    if (buffer_cursor < buffer_size) {
-                        buffer_cursor += 1;
+                    if (cursor < line.size) {
+                        cursor += 1;
                     }
                 }
                 break;
@@ -269,7 +232,8 @@ int main(int argc, char **argv)
             break;
 
             case SDL_TEXTINPUT: {
-                buffer_insert_text_before_cursor(event.text.text);
+                line_insert_text_before(&line, event.text.text, cursor);
+                cursor += strlen(event.text.text);
             }
             break;
             }
@@ -278,7 +242,7 @@ int main(int argc, char **argv)
         scc(SDL_SetRenderDrawColor(renderer, 0, 0, 0, 0));
         scc(SDL_RenderClear(renderer));
 
-        render_text_sized(renderer, &font, buffer, buffer_size, vec2f(0.0, 0.0), 0xFFFFFFFF, FONT_SCALE);
+        render_text_sized(renderer, &font, line.chars, line.size, vec2f(0.0, 0.0), 0xFFFFFFFF, FONT_SCALE);
         render_cursor(renderer, &font);
 
         SDL_RenderPresent(renderer);