/* input.c */
#include <stdio.h>
#include <stdlib.h>
#include "input.h"
/* Input Data */
#define CHUNK_SIZE 128
static char buffer[CHUNK_SIZE];
static int buffer_pos = 0;
static int buffer_size = 0;
static char unget_buffer_stack[8];
static int unget_buffer_stack_pos = 0;

static FILE *file = NULL;

/* Input Initialization */
void input_init(const char *filename) {
  file = fopen(filename, "r");
  if (file == NULL) {
    fprintf(stderr, "Error: Cannot open file %s\n", filename);
    exit(1);
  }
}

/* Input Get Character */
int input_getc(void) {
  if (unget_buffer_stack_pos > 0) {
    return unget_buffer_stack[--unget_buffer_stack_pos];
  }
  if (buffer_pos == buffer_size) {
    buffer_size = fread(buffer, 1, CHUNK_SIZE, file);
    buffer_pos = 0;
  }
  if (buffer_size == 0) {
    return EOF;
  }
  char c = buffer[buffer_pos++];
  return c;
}

/* Input Unget Character */
void input_ungetc(int c) {
  unget_buffer_stack[unget_buffer_stack_pos++] = c;
}

/* Input Destroy */
void input_destroy(void) {
  fclose(file);
}