#include "core/buffer.h"

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define INITIAL_CAPACITY 1024

static size_t gap_size(const Buffer *buffer) {
  return buffer->gap_end - buffer->gap_start;
}

static size_t physical_index(const Buffer *buffer, size_t logical) {
  if (logical < buffer->gap_start) {
    return logical;
  }
  return logical + gap_size(buffer);
}

static bool ensure_gap(Buffer *buffer, size_t needed) {
  if (gap_size(buffer) >= needed) {
    return true;
  }

  size_t old_gap = gap_size(buffer);
  size_t old_capacity = buffer->capacity;
  size_t new_capacity = old_capacity;
  while ((new_capacity - buffer->gap_start - (old_capacity - buffer->gap_end)) < needed) {
    new_capacity *= 2;
  }

  char *new_data = (char *)malloc(new_capacity);
  if (!new_data) {
    return false;
  }

  memcpy(new_data, buffer->data, buffer->gap_start);
  size_t tail_size = old_capacity - buffer->gap_end;
  size_t new_gap_end = new_capacity - tail_size;
  memcpy(new_data + new_gap_end, buffer->data + buffer->gap_end, tail_size);

  free(buffer->data);
  buffer->data = new_data;
  buffer->capacity = new_capacity;
  buffer->gap_end = new_gap_end;

  (void)old_gap;
  return true;
}

static void move_gap(Buffer *buffer, size_t target) {
  if (target == buffer->gap_start) {
    return;
  }

  if (target < buffer->gap_start) {
    size_t move = buffer->gap_start - target;
    memmove(buffer->data + buffer->gap_end - move, buffer->data + target, move);
    buffer->gap_start = target;
    buffer->gap_end -= move;
    return;
  }

  size_t move = target - buffer->gap_start;
  memmove(buffer->data + buffer->gap_start, buffer->data + buffer->gap_end, move);
  buffer->gap_start += move;
  buffer->gap_end += move;
}

bool buffer_init(Buffer *buffer) {
  buffer->data = (char *)malloc(INITIAL_CAPACITY);
  if (!buffer->data) {
    return false;
  }
  buffer->capacity = INITIAL_CAPACITY;
  buffer->gap_start = 0;
  buffer->gap_end = INITIAL_CAPACITY;
  buffer->path[0] = '\0';
  buffer->modified = false;
  return true;
}

void buffer_free(Buffer *buffer) {
  free(buffer->data);
  buffer->data = NULL;
  buffer->capacity = 0;
  buffer->gap_start = 0;
  buffer->gap_end = 0;
}

size_t buffer_length(const Buffer *buffer) {
  return buffer->capacity - gap_size(buffer);
}

size_t buffer_point(const Buffer *buffer) {
  return buffer->gap_start;
}

void buffer_set_point(Buffer *buffer, size_t point) {
  size_t len = buffer_length(buffer);
  if (point > len) {
    point = len;
  }
  move_gap(buffer, point);
}

bool buffer_insert_char(Buffer *buffer, char c) {
  if (!ensure_gap(buffer, 1)) {
    return false;
  }
  buffer->data[buffer->gap_start++] = c;
  buffer->modified = true;
  return true;
}

bool buffer_insert_cstr(Buffer *buffer, const char *text) {
  size_t len = strlen(text);
  if (!ensure_gap(buffer, len)) {
    return false;
  }
  memcpy(buffer->data + buffer->gap_start, text, len);
  buffer->gap_start += len;
  if (len > 0) {
    buffer->modified = true;
  }
  return true;
}

bool buffer_backspace(Buffer *buffer) {
  if (buffer->gap_start == 0) {
    return false;
  }
  buffer->gap_start--;
  buffer->modified = true;
  return true;
}

bool buffer_delete_forward(Buffer *buffer) {
  if (buffer->gap_end >= buffer->capacity) {
    return false;
  }
  buffer->gap_end++;
  buffer->modified = true;
  return true;
}

char buffer_char_at(const Buffer *buffer, size_t index) {
  size_t len = buffer_length(buffer);
  if (index >= len) {
    return '\0';
  }
  return buffer->data[physical_index(buffer, index)];
}

bool buffer_load_file(Buffer *buffer, const char *path) {
  FILE *fp = fopen(path, "rb");
  if (!fp) {
    return false;
  }

  if (fseek(fp, 0, SEEK_END) != 0) {
    fclose(fp);
    return false;
  }

  long file_size = ftell(fp);
  if (file_size < 0) {
    fclose(fp);
    return false;
  }
  rewind(fp);

  buffer->gap_start = 0;
  buffer->gap_end = buffer->capacity;

  if (!ensure_gap(buffer, (size_t)file_size + 1)) {
    fclose(fp);
    return false;
  }

  size_t read = fread(buffer->data, 1, (size_t)file_size, fp);
  fclose(fp);
  if (read != (size_t)file_size) {
    return false;
  }

  buffer->gap_start = (size_t)file_size;
  buffer->gap_end = buffer->capacity;

  strncpy(buffer->path, path, sizeof(buffer->path) - 1);
  buffer->path[sizeof(buffer->path) - 1] = '\0';
  buffer->modified = false;
  return true;
}

bool buffer_save_file(Buffer *buffer, const char *path) {
  const char *out_path = path;
  if (!out_path || out_path[0] == '\0') {
    out_path = buffer->path;
  }

  if (!out_path || out_path[0] == '\0') {
    return false;
  }

  FILE *fp = fopen(out_path, "wb");
  if (!fp) {
    return false;
  }

  size_t before = buffer->gap_start;
  size_t after = buffer->capacity - buffer->gap_end;

  if (before > 0 && fwrite(buffer->data, 1, before, fp) != before) {
    fclose(fp);
    return false;
  }

  if (after > 0 && fwrite(buffer->data + buffer->gap_end, 1, after, fp) != after) {
    fclose(fp);
    return false;
  }

  fclose(fp);

  if (path && path[0] != '\0') {
    strncpy(buffer->path, path, sizeof(buffer->path) - 1);
    buffer->path[sizeof(buffer->path) - 1] = '\0';
  }

  buffer->modified = false;

  return true;
}

const char *buffer_path(const Buffer *buffer) {
  return buffer->path;
}

bool buffer_modified(const Buffer *buffer) {
  return buffer->modified;
}

void buffer_index_to_line_col(const Buffer *buffer, size_t index, int *line, int *col) {
  size_t len = buffer_length(buffer);
  if (index > len) {
    index = len;
  }

  int l = 0;
  int c = 0;
  for (size_t i = 0; i < index; ++i) {
    char ch = buffer_char_at(buffer, i);
    if (ch == '\n') {
      l++;
      c = 0;
    } else {
      c++;
    }
  }

  *line = l;
  *col = c;
}

size_t buffer_line_col_to_index(const Buffer *buffer, int target_line, int target_col) {
  if (target_line < 0) {
    target_line = 0;
  }
  if (target_col < 0) {
    target_col = 0;
  }

  size_t len = buffer_length(buffer);
  int line = 0;
  int col = 0;

  for (size_t i = 0; i < len; ++i) {
    if (line == target_line && col == target_col) {
      return i;
    }

    char ch = buffer_char_at(buffer, i);
    if (ch == '\n') {
      if (line == target_line) {
        return i;
      }
      line++;
      col = 0;
    } else {
      col++;
    }
  }

  return len;
}