/*
 * Ricochet - A minimalist CLI web browser for fast, distraction-free navigation.
 * Copyright (C) 2026  Richard Qin
 *
 * 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 "ricochet/parser/html_lexer.hh"

#include <cstdint>
#include <string_view>

namespace ricochet::parser {

namespace {
enum class LexerState : std::uint8_t
{
  Data,             // Reading plain text
  TagOpen,          // Just encountered '<'
  TagName,          // Reading the name of an opening tag (e.g., "div")
  ClosingTagName,   // Reading the name of a closing tag (e.g., "/div")
  SwallowAttributes // Ignore attributes mode (ignore until encountering '>')
};

void emit_text( std::string& buffer, std::vector<HtmlToken>& tokens )
{
  if ( buffer.empty() ) {
    return; // 提前返回，减少 if 嵌套层级
  }

  bool all_whitespace = true;
  for ( const char c : buffer ) {
    if ( !std::isspace( static_cast<unsigned char>( c ) ) ) {
      all_whitespace = false;
      break;
    }
  }

  if ( !all_whitespace ) {
    tokens.emplace_back( TextToken { buffer } );
  }
  buffer.clear();
}

} // namespace

std::vector<HtmlToken> HtmlLexer::tokenize( // NOLINT(readability-convert-member-functions-to-static)
  std::string_view html ) const
{
  std::vector<HtmlToken> tokens;

  LexerState state = LexerState::Data;
  std::string buffer {};

  for ( const char c : html ) {
    switch ( state ) {
      case LexerState::Data:
        if ( c == '<' ) {
          emit_text( buffer, tokens );
          state = LexerState::TagOpen;
        } else {
          buffer += c;
        }
        break;
      case LexerState::TagOpen:
        if ( c == '/' ) {
          state = LexerState::ClosingTagName;
        } else if ( std::isalpha( static_cast<unsigned char>( c ) ) ) {
          buffer.push_back( c );
          state = LexerState::TagName;
        } else {
          buffer.push_back( '<' );
          buffer.push_back( c );
          state = LexerState::Data;
        }
        break;
      case LexerState::TagName:
        if ( c == '>' ) {
          tokens.emplace_back( TagOpenToken { buffer } );
          buffer.clear();
          state = LexerState::Data;
        } else if ( std::isspace( static_cast<unsigned char>( c ) ) ) {
          tokens.emplace_back( TagOpenToken { buffer } );
          buffer.clear();
          state = LexerState::SwallowAttributes;
        } else {
          buffer += static_cast<char>( std::tolower( static_cast<unsigned char>( c ) ) );
        }
        break;
      case LexerState::ClosingTagName:
        if ( c == '>' ) {
          tokens.emplace_back( TagCloseToken { buffer } );
          buffer.clear();
          state = LexerState::Data;
        } else {
          buffer += static_cast<char>( std::tolower( static_cast<unsigned char>( c ) ) );
        }
        break;
      case LexerState::SwallowAttributes:
        if ( c == '>' ) {
          state = LexerState::Data;
        }
        break;
    }
  }

  emit_text( buffer, tokens );

  return tokens;
}

} // namespace ricochet::parser