/*
 * Copyright (c) 2020, Andreas Kling <kling@serenityos.org>
 *
 * SPDX-License-Identifier: BSD-2-Clause
 */

#include "Lexer.h"
#include <AK/CharacterTypes.h>
#include <AK/Vector.h>

namespace GUI::GML {

Lexer::Lexer(StringView input)
    : m_input(input)
{
}

char Lexer::peek(size_t offset) const
{
    if ((m_index + offset) >= m_input.length())
        return 0;
    return m_input[m_index + offset];
}

char Lexer::consume()
{
    VERIFY(m_index < m_input.length());
    char ch = m_input[m_index++];
    if (ch == '\n') {
        m_position.line++;
        m_position.column = 0;
    } else {
        m_position.column++;
    }
    return ch;
}

constexpr bool is_valid_identifier_start(char ch)
{
    return is_ascii_alpha(ch) || ch == '_';
}

constexpr bool is_valid_identifier_character(char ch)
{
    return is_ascii_alphanumeric(ch) || ch == '_';
}

constexpr bool is_valid_class_character(char ch)
{
    return is_ascii_alphanumeric(ch) || ch == '_' || ch == ':';
}

Vector<Token> Lexer::lex()
{
    Vector<Token> tokens;

    size_t token_start_index = 0;
    Position token_start_position;

    auto begin_token = [&] {
        token_start_index = m_index;
        token_start_position = m_position;
    };

    auto commit_token = [&](auto type) {
        Token token;
        token.m_view = m_input.substring_view(token_start_index, m_index - token_start_index);
        token.m_type = type;
        token.m_start = token_start_position;
        token.m_end = m_position;
        tokens.append(token);
    };

    auto consume_class = [&] {
        begin_token();
        consume();
        commit_token(Token::Type::ClassMarker);
        begin_token();
        while (is_valid_class_character(peek()))
            consume();
        commit_token(Token::Type::ClassName);
    };

    while (m_index < m_input.length()) {
        if (is_ascii_space(peek(0))) {
            begin_token();
            while (is_ascii_space(peek()))
                consume();
            continue;
        }

        // C++ style comments
        if (peek(0) && peek(0) == '/' && peek(1) == '/') {
            begin_token();
            while (peek() && peek() != '\n')
                consume();
            commit_token(Token::Type::Comment);
            continue;
        }

        if (peek(0) == '{') {
            begin_token();
            consume();
            commit_token(Token::Type::LeftCurly);
            continue;
        }

        if (peek(0) == '}') {
            begin_token();
            consume();
            commit_token(Token::Type::RightCurly);
            continue;
        }

        if (peek(0) == '@') {
            consume_class();
            continue;
        }

        if (is_valid_identifier_start(peek(0))) {
            begin_token();
            consume();
            while (is_valid_identifier_character(peek(0)))
                consume();
            commit_token(Token::Type::Identifier);
            continue;
        }

        if (peek(0) == ':') {
            begin_token();
            consume();
            commit_token(Token::Type::Colon);

            while (is_ascii_space(peek()))
                consume();

            if (peek(0) == '@') {
                consume_class();
            } else {
                begin_token();
                while (peek() && peek() != '\n')
                    consume();
                commit_token(Token::Type::JsonValue);
            }
            continue;
        }

        consume();
        commit_token(Token::Type::Unknown);
    }
    return tokens;
}

}