/* tokenizer.c */

#include <ctype.h>
#include <string.h>

#include "ring.h"
#include "tokenizer.h"

DEFINE_RING(token, struct token)

static const char *SEPARATORS = " \t\n";
static const int NUM_TOKENS = 6;
static const char *TOKENS[] = {
    [TOK_PLUS]  = "+", 
    [TOK_MINUS] = "-", 
    [TOK_MUL]   = "*", 
    [TOK_DIV]   = "/", 
    [TOK_OPEN]  ="(", 
    [TOK_CLOSE] = ")", 
    [TOK_LIT]   = "",
    [TOK_NEG]   = "-" 
};

const char *TOKENS_STR[] = {
    [TOK_PLUS] = "PLUS", 
    [TOK_MINUS] = "MINUS", 
    [TOK_MUL] = "MUL", 
    [TOK_DIV] = "DIV", 
    [TOK_OPEN]  ="OPEN", 
    [TOK_CLOSE] = "CLOSE", 
    [TOK_LIT] = "LIT", 
    [TOK_NEG] = "NEG", 
    [TOK_END] = "END", 
    [TOK_ERROR] = "ERROR"
    };

char *skip_separators(char *str)
{
  while (*str != '\0' && strchr(SEPARATORS, *str) != NULL)
    str++;
  return str;
}

struct token next_token(char **str)
{
  int i;
  char *buf = skip_separators(*str);

  if (*buf == '\0')
  {
    return (struct token){TOK_END, 0};
  }

  /* Serarch for an operation */
  for (i = 0; i < NUM_TOKENS; i++)
    if (strncmp(buf, TOKENS[i], strlen(TOKENS[i])) == 0)
    {
      *str = buf + strlen(TOKENS[i]);
      return (struct token){i, 0};
    }

  /* Serach for literals */
  if (isdigit(*buf))
  {
    char *str_end;
    int64_t tmp = strtoll(buf, &str_end, 10);
    *str = str_end;
    return (struct token){TOK_LIT, tmp};
  }

  return (struct token){TOK_ERROR, 0};
}

int is_binop(struct token token)
{
  return token.type == TOK_PLUS || token.type == TOK_MINUS ||
         token.type == TOK_MUL || token.type == TOK_DIV;
}

struct ring_token *tokenize(char *str)
{
  struct token token, prev = {TOK_ERROR, 0};
  struct ring_token *tokens = NULL;
  while ((token = next_token(&str)).type != TOK_END)
  {
    if (token.type == TOK_ERROR)
    {
      ring_token_free(&tokens);
      return NULL;
    }
    if (token.type == TOK_MINUS && 
        (tokens == NULL || prev.type == TOK_OPEN || is_binop(prev)))
      token.type = TOK_NEG;
    ring_token_push(&tokens, token);
    prev = token;
  }

  return tokens;
}