/*
 * Copyright (C) 2023 Johnny Richard
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <https://www.gnu.org/licenses/>.
 */

#include "lexer.h"
#include <assert.h>
#include <ctype.h>
#include <errno.h>
#include <stdbool.h>
#include <stdio.h>
#include <string.h>

void
lexer_init(lexer_t *lexer, char *filepath)
{
  assert(lexer && "lexer must be defined");
  assert(filepath && "filepath must be defined");
  lexer->filepath = filepath;
  lexer->srclen = 0;
  lexer->cur = 0;
  lexer->row = 0;
  lexer->bol = 0;
  lexer_load_file_contents(lexer);
}

static void
lexer_define_literal_token_props(lexer_t *lexer, token_t *token, token_kind_t kind)
{
  token->kind = kind;
  token->value = string_view_new(lexer->src + lexer->cur, 1);
  token->filepath = lexer->filepath;
  token->row = lexer->row;
  token->col = lexer->cur - lexer->bol;
  token->bol = lexer->bol;
}

static void
lexer_drop_spaces(lexer_t *lexer)
{
  while (lexer_is_not_eof(lexer) && isspace(lexer_current_char(lexer))) {
    if (lexer_current_char(lexer) == '\n') {
      lexer_drop_char(lexer);
      lexer->row++;
      lexer->bol = lexer->cur;
      continue;
    }
    lexer_drop_char(lexer);
  }
}

static void
lexer_tokenize_from_given_position_to_cursor(lexer_t *lexer, token_t *token, size_t position, token_kind_t kind)
{
  token->kind = kind;
  token->value = string_view_new(lexer->src + position, lexer->cur - position);
  token->filepath = lexer->filepath;
  token->row = lexer->row;
  token->col = position - lexer->bol;
  token->bol = lexer->bol;
}

static void
lexer_tokenize_number(lexer_t *lexer, token_t *token)
{
  size_t begin = lexer->cur;

  while (lexer_is_not_eof(lexer) && isdigit(lexer_current_char(lexer))) {
    lexer_drop_char(lexer);
  }

  lexer_tokenize_from_given_position_to_cursor(lexer, token, begin, TOKEN_NUMBER);
}

static void
lexer_tokenize_name(lexer_t *lexer, token_t *token)
{
  size_t begin = lexer->cur;

  while (lexer_is_not_eof(lexer) && (isalnum(lexer_current_char(lexer)) || lexer_current_char(lexer) == '_')) {
    lexer_drop_char(lexer);
  }

  lexer_tokenize_from_given_position_to_cursor(lexer, token, begin, TOKEN_NAME);
}

static void
lexer_token_process_keyword(token_t *token)
{
  if (string_view_eq(string_view_from_str("let"), token->value)) {
    token->kind = TOKEN_KEYWORD_LET;
    return;
  }
  if (string_view_eq(string_view_from_str("return"), token->value)) {
    token->kind = TOKEN_KEYWORD_RETURN;
    return;
  }
  if (string_view_eq(string_view_from_str("fn"), token->value)) {
    token->kind = TOKEN_KEYWORD_FN;
    return;
  }
  if (string_view_eq(string_view_from_str("if"), token->value)) {
    token->kind = TOKEN_KEYWORD_IF;
    return;
  }
  if (string_view_eq(string_view_from_str("true"), token->value)) {
    token->kind = TOKEN_TRUE;
    return;
  }
  if (string_view_eq(string_view_from_str("false"), token->value)) {
    token->kind = TOKEN_FALSE;
    return;
  }
}

void
lexer_next_token(lexer_t *lexer, token_t *token)
{
  lexer_drop_spaces(lexer);

  if (lexer_is_eof(lexer)) {
    lexer_define_literal_token_props(lexer, token, TOKEN_EOF);
    lexer_drop_char(lexer);
    return;
  }

  if (isdigit(lexer_current_char(lexer))) {
    lexer_tokenize_number(lexer, token);
    return;
  }

  if (isalpha(lexer_current_char(lexer))) {
    lexer_tokenize_name(lexer, token);
    lexer_token_process_keyword(token);
    return;
  }

  if (lexer_current_char(lexer) == '(') {
    lexer_define_literal_token_props(lexer, token, TOKEN_OPAREN);
    lexer_drop_char(lexer);
    return;
  }

  if (lexer_current_char(lexer) == ')') {
    lexer_define_literal_token_props(lexer, token, TOKEN_CPAREN);
    lexer_drop_char(lexer);
    return;
  }

  if (lexer_current_char(lexer) == ':') {
    lexer_define_literal_token_props(lexer, token, TOKEN_COLON);
    lexer_drop_char(lexer);
    return;
  }

  if (lexer_current_char(lexer) == ',') {
    lexer_define_literal_token_props(lexer, token, TOKEN_COMMA);
    lexer_drop_char(lexer);
    return;
  }

  if (lexer_current_char(lexer) == ';') {
    lexer_define_literal_token_props(lexer, token, TOKEN_SEMICOLON);
    lexer_drop_char(lexer);
    return;
  }

  if (lexer_current_char(lexer) == '{') {
    lexer_define_literal_token_props(lexer, token, TOKEN_OCURLY);
    lexer_drop_char(lexer);
    return;
  }

  if (lexer_current_char(lexer) == '}') {
    lexer_define_literal_token_props(lexer, token, TOKEN_CCURLY);
    lexer_drop_char(lexer);
    return;
  }

  if (lexer_current_char(lexer) == '+') {
    lexer_define_literal_token_props(lexer, token, TOKEN_PLUS);
    lexer_drop_char(lexer);
    return;
  }

  if (lexer_current_char(lexer) == '-') {
    lexer_define_literal_token_props(lexer, token, TOKEN_MINUS);
    lexer_drop_char(lexer);
    return;
  }

  if (lexer_current_char(lexer) == '*') {
    lexer_define_literal_token_props(lexer, token, TOKEN_STAR);
    lexer_drop_char(lexer);
    return;
  }

  if (lexer_current_char(lexer) == '/') {
    lexer_define_literal_token_props(lexer, token, TOKEN_SLASH);
    lexer_drop_char(lexer);
    return;
  }

  if (lexer_current_char(lexer) == '=') {
    lexer_define_literal_token_props(lexer, token, TOKEN_ASSIGN);
    lexer_drop_char(lexer);

    if (lexer_current_char(lexer) == '=') {
      lexer_drop_char(lexer);
      lexer_tokenize_from_given_position_to_cursor(lexer, token, lexer->cur - 2, TOKEN_EQUAL);
      return;
    }

    return;
  }

  if (lexer_current_char(lexer) == '!') {
    lexer_define_literal_token_props(lexer, token, TOKEN_NOT);
    lexer_drop_char(lexer);

    if (lexer_current_char(lexer) == '=') {
      lexer_drop_char(lexer);
      lexer_tokenize_from_given_position_to_cursor(lexer, token, lexer->cur - 2, TOKEN_NOT_EQUAL);
      return;
    }

    return;
  }

  if (lexer_current_char(lexer) == '>') {
    lexer_define_literal_token_props(lexer, token, TOKEN_GT);
    lexer_drop_char(lexer);

    if (lexer_current_char(lexer) == '=') {
      lexer_drop_char(lexer);
      lexer_tokenize_from_given_position_to_cursor(lexer, token, lexer->cur - 2, TOKEN_GT_EQUAL);
      return;
    }

    if (lexer_current_char(lexer) == '>') {
      lexer_drop_char(lexer);
      lexer_tokenize_from_given_position_to_cursor(lexer, token, lexer->cur - 2, TOKEN_BITWISE_SHIFT_RIGHT);
      return;
    }
    return;
  }

  if (lexer_current_char(lexer) == '<') {
    lexer_define_literal_token_props(lexer, token, TOKEN_LT);
    lexer_drop_char(lexer);

    if (lexer_current_char(lexer) == '=') {
      lexer_drop_char(lexer);
      lexer_tokenize_from_given_position_to_cursor(lexer, token, lexer->cur - 2, TOKEN_LT_EQUAL);
      return;
    }

    if (lexer_current_char(lexer) == '<') {
      lexer_drop_char(lexer);
      lexer_tokenize_from_given_position_to_cursor(lexer, token, lexer->cur - 2, TOKEN_BITWISE_SHIFT_LEFT);
      return;
    }
    return;
  }

  if (lexer_current_char(lexer) == '&') {
    lexer_define_literal_token_props(lexer, token, TOKEN_BITWISE_AND);
    lexer_drop_char(lexer);

    if (lexer_current_char(lexer) == '&') {
      lexer_drop_char(lexer);
      lexer_tokenize_from_given_position_to_cursor(lexer, token, lexer->cur - 2, TOKEN_AND);
      return;
    }
    return;
  }

  if (lexer_current_char(lexer) == '|') {
    lexer_define_literal_token_props(lexer, token, TOKEN_BITWISE_OR);
    lexer_drop_char(lexer);

    if (lexer_current_char(lexer) == '|') {
      lexer_drop_char(lexer);
      lexer_tokenize_from_given_position_to_cursor(lexer, token, lexer->cur - 2, TOKEN_OR);
      return;
    }
    return;
  }

  if (lexer_current_char(lexer) == '^') {
    lexer_define_literal_token_props(lexer, token, TOKEN_BITWISE_XOR);
    lexer_drop_char(lexer);
    return;
  }

  if (lexer_current_char(lexer) == '~') {
    lexer_define_literal_token_props(lexer, token, TOKEN_BITWISE_NOT);
    lexer_drop_char(lexer);
    return;
  }

  lexer_define_literal_token_props(lexer, token, TOKEN_UNKNOWN);
  lexer_drop_char(lexer);
  return;
}

void
lexer_load_file_contents(lexer_t *lexer)
{
  assert(lexer && "lexer must be defined");

  FILE *file;
  file = fopen(lexer->filepath, "r");
  if (!file) {
    fprintf(stderr, "tried to open file '%s': %s\n", lexer->filepath, strerror(errno));
    exit(EXIT_FAILURE);
  }

  fseek(file, 0L, SEEK_END);
  lexer->srclen = ftell(file);
  rewind(file);

  lexer->src = calloc(1, lexer->srclen + 1);
  if (!lexer->src) {
    fclose(file);
    perror("lexer_load_file_contents -> calloc");
    exit(EXIT_FAILURE);
  }

  if (fread(lexer->src, lexer->srclen, 1, file) != 1) {
    fclose(file);
    free(lexer->src);
    // FIXME: distinguish error using ferror and feof functions
    fprintf(stderr, "could not read file '%s'\n", lexer->filepath);
    exit(EXIT_FAILURE);
  }
}

void
lexer_lookahead(lexer_t *lexer, token_t *token, size_t level)
{
  uint32_t cur = lexer->cur;
  uint32_t row = lexer->row;
  uint32_t bol = lexer->bol;

  while (level != 0) {
    lexer_next_token(lexer, token);
    level--;

    if (token->kind == TOKEN_EOF) {
      break;
    }
  }

  lexer->cur = cur;
  lexer->row = row;
  lexer->bol = bol;
}

void
lexer_peek_next_token(lexer_t *lexer, token_t *token)
{
  lexer_lookahead(lexer, token, 1);
}

void
lexer_drop_next_token(lexer_t *lexer)
{
  token_t token;
  lexer_next_token(lexer, &token);
}

void
lexer_drop_char(lexer_t *lexer)
{
  lexer->cur++;
}

bool
lexer_is_eof(lexer_t *lexer)
{
  return lexer->cur >= lexer->srclen;
}

bool
lexer_is_not_eof(lexer_t *lexer)
{
  return !lexer_is_eof(lexer);
}

char
lexer_current_char(lexer_t *lexer)
{
  return lexer->src[lexer->cur];
}

char *
token_kind_to_str(token_kind_t kind)
{
  switch (kind) {
    case TOKEN_NAME:
      return "TOKEN_NAME";
    case TOKEN_OPAREN:
      return "(";
    case TOKEN_CPAREN:
      return ")";
    case TOKEN_COLON:
      return ":";
    case TOKEN_COMMA:
      return ",";
    case TOKEN_SEMICOLON:
      return ";";
    case TOKEN_OCURLY:
      return "{";
    case TOKEN_CCURLY:
      return "}";
    case TOKEN_NUMBER:
      return "TOKEN_NUMBER";
    case TOKEN_PLUS:
      return "+";
    case TOKEN_MINUS:
      return "-";
    case TOKEN_STAR:
      return "*";
    case TOKEN_SLASH:
      return "/";
    case TOKEN_ASSIGN:
      return "=";
    case TOKEN_EQUAL:
      return "==";
    case TOKEN_NOT:
      return "!";
    case TOKEN_NOT_EQUAL:
      return "!=";
    case TOKEN_GT:
      return ">";
    case TOKEN_GT_EQUAL:
      return ">=";
    case TOKEN_LT:
      return "<";
    case TOKEN_LT_EQUAL:
      return "<=";
    case TOKEN_AND:
      return "&&";
    case TOKEN_OR:
      return "||";
    case TOKEN_BITWISE_AND:
      return "&";
    case TOKEN_BITWISE_OR:
      return "|";
    case TOKEN_BITWISE_SHIFT_LEFT:
      return "<<";
    case TOKEN_BITWISE_SHIFT_RIGHT:
      return ">>";
    case TOKEN_BITWISE_XOR:
      return "^";
    case TOKEN_BITWISE_NOT:
      return "~";
    case TOKEN_KEYWORD_RETURN:
      return "return";
    case TOKEN_KEYWORD_FN:
      return "fn";
    case TOKEN_KEYWORD_LET:
      return "let";
    case TOKEN_KEYWORD_IF:
      return "if";
    case TOKEN_TRUE:
      return "true";
    case TOKEN_FALSE:
      return "false";
    case TOKEN_EOF:
      return "TOKEN_EOF";
    case TOKEN_UNKNOWN:
      return "TOKEN_UNKNOWN";
  }
  assert(false && "unreachable");
}