mop3/ce/gapbuffer.c

#include "gapbuffer.h"
#include "arena_alloc.h"
#include <liballoc.h>
#include <stddef.h>
#include <string.h>

void gapbuffer_init (struct gapbuffer* gb, size_t capacity) {
  gb->buffer = arena_malloc (&arena, capacity);

  if (gb->buffer == NULL)
    return;

  memset (gb->buffer, 0, capacity);
  gb->size = capacity;
  gb->gap_start = 0;
  gb->gap_end = capacity;
}

void gapbuffer_fini (struct gapbuffer* gb) { memset (gb, 0, sizeof (*gb)); }

void gapbuffer_grow (struct gapbuffer* gb) {
  size_t old_size = gb->size;
  size_t new_size = gb->size * 2;

  char* new = arena_realloc (&arena, gb->buffer, old_size, new_size);

  if (new == NULL)
    return;

  gb->buffer = new;

  size_t post_gap_size = old_size - gb->gap_end;
  size_t new_gap_end = new_size - post_gap_size;

  memmove (gb->buffer + new_gap_end, gb->buffer + gb->gap_end, post_gap_size);

  gb->gap_end = new_gap_end;
  gb->size = new_size;
}

void gapbuffer_move (struct gapbuffer* gb, size_t pos) {
  if (pos > (gb->size - (gb->gap_end - gb->gap_start)))
    pos = (gb->size - (gb->gap_end - gb->gap_start));

  while (gb->gap_start > pos) {
    gb->gap_start--;
    gb->gap_end--;
    gb->buffer[gb->gap_end] = gb->buffer[gb->gap_start];
  }

  while (gb->gap_start < pos) {
    gb->buffer[gb->gap_start] = gb->buffer[gb->gap_end];
    gb->gap_start++;
    gb->gap_end++;
  }
}

void gapbuffer_insert (struct gapbuffer* gb, char c) {
  if (gb->gap_start == gb->gap_end)
    gapbuffer_grow (gb);

  gb->buffer[gb->gap_start] = c;
  gb->gap_start++;
}

void gapbuffer_backspace (struct gapbuffer* gb) {
  if (gb->gap_start > 0)
    gb->gap_start--;
}

char* gapbuffer_get_string (struct gapbuffer* gb) {
  size_t size = gb->size - (gb->gap_end - gb->gap_start);

  char* str = arena_malloc (&arena, size + 1);

  if (str == NULL)
    return NULL;

  memcpy (str, gb->buffer, gb->gap_start);

  memcpy (str + gb->gap_start, gb->buffer + gb->gap_end, gb->size - gb->gap_end);

  str[size] = '\0';
  return str;
}

size_t gapbuffer_length (struct gapbuffer* gb) { return gb->size - (gb->gap_end - gb->gap_start); }

char* gapbuffer_string_at (struct gapbuffer* gb, size_t pos) {
  size_t total_size = gapbuffer_length (gb);

  if (pos >= total_size)
    return "";

  size_t tail_size = total_size - pos;

  char* res = arena_malloc (&arena, tail_size + 1);

  if (res == NULL)
    return NULL;

  size_t written = 0;

  if (pos < gb->gap_start) {
    size_t copy = gb->gap_start - pos;

    if (copy > tail_size)
      copy = tail_size;

    memcpy (res, &gb->buffer[pos], copy);
    written += copy;
    pos += copy;
  }

  if (written < tail_size) {
    size_t gap_size = gb->gap_end - gb->gap_start;
    size_t phys_pos = pos + gap_size;

    size_t copy = tail_size - written;
    memcpy (&res[written], &gb->buffer[phys_pos], copy);
    written += copy;
  }

  res[written] = '\0';
  return res;
}