/*
 * Copyright (c) 2020, Andreas Kling <kling@serenityos.org>
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice, this
 *    list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright notice,
 *    this list of conditions and the following disclaimer in the documentation
 *    and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
 * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include <LibWeb/Parser/HTMLToken.h>
#include <LibWeb/Parser/HTMLTokenizer.h>
#include <ctype.h>

#pragma GCC diagnostic ignored "-Wunused-label"

//#define TOKENIZER_TRACE

#define TODO()                                                                                              \
    do {                                                                                                    \
        dbg() << "[TODO: " << state_name(m_state) << "] '" << (char)current_input_character.value() << "'"; \
        ASSERT_NOT_REACHED();                                                                               \
    } while (0)

#define SWITCH_TO(new_state)                    \
    will_switch_to(State::new_state);           \
    m_state = State::new_state;                 \
    current_input_character = next_codepoint(); \
    goto new_state;

#define RECONSUME_IN(new_state)          \
    will_reconsume_in(State::new_state); \
    m_state = State::new_state;          \
    goto new_state;

#define SWITCH_TO_AND_EMIT_CURRENT_TOKEN(new_state) \
    will_switch_to(State::new_state);               \
    m_state = State::new_state;                     \
    return m_current_token;

#define DONT_CONSUME_NEXT_INPUT_CHARACTER --m_cursor;

#define ON(codepoint) \
    if (current_input_character.has_value() && current_input_character.value() == codepoint)

#define ON_EOF \
    if (!current_input_character.has_value())

#define ON_ASCII_ALPHA \
    if (current_input_character.has_value() && isalpha(current_input_character.value()))

#define ON_ASCII_UPPER_ALPHA \
    if (current_input_character.has_value() && current_input_character.value() >= 'A' && current_input_character.value() <= 'Z')

#define ON_WHITESPACE \
    if (current_input_character.has_value() && (current_input_character.value() == '\t' || current_input_character.value() == '\n' || current_input_character.value() == '\f' || current_input_character.value() == ' '))

#define ANYTHING_ELSE if (1)

#define EMIT_EOF                                  \
    if (m_has_emitted_eof)                        \
        return {};                                \
    m_has_emitted_eof = true;                     \
    create_new_token(HTMLToken::Type::EndOfFile); \
    return m_current_token;

#define EMIT_CURRENT_TOKEN \
    return m_current_token;

#define BEGIN_STATE(state) \
    state:                 \
    case State::state: {   \
        {                  \
            {

#define END_STATE         \
    ASSERT_NOT_REACHED(); \
    break;                \
    }                     \
    }                     \
    }

namespace Web {

Optional<u32> HTMLTokenizer::next_codepoint()
{
    if (m_cursor >= m_input.length())
        return {};
    return m_input[m_cursor++];
}

Optional<u32> HTMLTokenizer::peek_codepoint(size_t offset) const
{
    if ((m_cursor + offset) >= m_input.length())
        return {};
    return m_input[m_cursor + offset];
}

Optional<HTMLToken> HTMLTokenizer::next_token()
{
    for (;;) {
        auto current_input_character = next_codepoint();
        switch (m_state) {
            BEGIN_STATE(Data)
            {
                ON('&')
                {
                    m_return_state = State::Data;
                    SWITCH_TO(CharacterReference);
                }
                ON('<')
                {
                    SWITCH_TO(TagOpen);
                }
                ON_EOF
                {
                    EMIT_EOF;
                }
                ANYTHING_ELSE
                {
                    create_new_token(HTMLToken::Type::Character);
                    m_current_token.m_comment_or_character.data.append(current_input_character.value());
                    return m_current_token;
                }
            }
            END_STATE

            BEGIN_STATE(TagOpen)
            {
                ON('!')
                {
                    SWITCH_TO(MarkupDeclarationOpen);
                }
                ON('/')
                {
                    SWITCH_TO(EndTagOpen);
                }
                ON_ASCII_ALPHA
                {
                    create_new_token(HTMLToken::Type::StartTag);
                    RECONSUME_IN(TagName);
                }
                ON('?')
                {
                    TODO();
                }
                ANYTHING_ELSE
                {
                    TODO();
                }
            }
            END_STATE

            BEGIN_STATE(TagName)
            {
                ON_WHITESPACE
                {
                    SWITCH_TO(BeforeAttributeName);
                }
                ON('/')
                {
                    SWITCH_TO(SelfClosingStartTag);
                }
                ON('>')
                {
                    SWITCH_TO_AND_EMIT_CURRENT_TOKEN(Data);
                }
                ANYTHING_ELSE
                {
                    m_current_token.m_tag.tag_name.append(current_input_character.value());
                    continue;
                }
            }
            END_STATE

            BEGIN_STATE(EndTagOpen)
            {
                ON_ASCII_ALPHA
                {
                    create_new_token(HTMLToken::Type::EndTag);
                    RECONSUME_IN(TagName);
                }
            }
            END_STATE

            BEGIN_STATE(MarkupDeclarationOpen)
            {
                DONT_CONSUME_NEXT_INPUT_CHARACTER;
                if (next_few_characters_are("--")) {
                    consume("--");
                    create_new_token(HTMLToken::Type::Comment);
                    SWITCH_TO(CommentStart);
                }
                if (next_few_characters_are("DOCTYPE")) {
                    consume("DOCTYPE");
                    SWITCH_TO(DOCTYPE);
                }
            }
            END_STATE

            BEGIN_STATE(DOCTYPE)
            {
                ON_WHITESPACE
                {
                    SWITCH_TO(BeforeDOCTYPEName);
                }
                ON('>')
                {
                    RECONSUME_IN(BeforeDOCTYPEName);
                }
                ON_EOF
                {
                    TODO();
                }
                ANYTHING_ELSE
                {
                    TODO();
                }
            }
            END_STATE

            BEGIN_STATE(BeforeDOCTYPEName)
            {
                ON_WHITESPACE
                {
                    continue;
                }
                ON_ASCII_UPPER_ALPHA
                {
                    create_new_token(HTMLToken::Type::DOCTYPE);
                    m_current_token.m_doctype.name.append(tolower(current_input_character.value()));
                    SWITCH_TO(DOCTYPEName);
                }
                ON(0)
                {
                    TODO();
                }
                ON('>')
                {
                    TODO();
                }
                ON_EOF
                {
                    TODO();
                }
                ANYTHING_ELSE
                {
                    create_new_token(HTMLToken::Type::DOCTYPE);
                    m_current_token.m_doctype.name.append(current_input_character.value());
                    SWITCH_TO(DOCTYPEName);
                }
            }
            END_STATE

            BEGIN_STATE(DOCTYPEName)
            {
                ON_WHITESPACE
                {
                    SWITCH_TO(AfterDOCTYPEName);
                }
                ON('>')
                {
                    SWITCH_TO_AND_EMIT_CURRENT_TOKEN(Data);
                }
                ON_ASCII_UPPER_ALPHA
                {
                    m_current_token.m_doctype.name.append(tolower(current_input_character.value()));
                }
                ON(0)
                {
                    TODO();
                }
                ON_EOF
                {
                    TODO();
                }
                ANYTHING_ELSE
                {
                    m_current_token.m_doctype.name.append(current_input_character.value());
                    continue;
                }
            }
            END_STATE

            BEGIN_STATE(AfterDOCTYPEName)
            {
                ON_WHITESPACE
                {
                    continue;
                }
                ON('>')
                {
                    SWITCH_TO_AND_EMIT_CURRENT_TOKEN(Data);
                }
                ON_EOF
                {
                    TODO();
                }
                ANYTHING_ELSE
                {
                    TODO();
                }
            }
            END_STATE

            BEGIN_STATE(BeforeAttributeName)
            {
                ON_WHITESPACE
                {
                    continue;
                }
                ON('/')
                {
                    RECONSUME_IN(AfterAttributeName);
                }
                ON('>')
                {
                    RECONSUME_IN(AfterAttributeName);
                }
                ON_EOF
                {
                    RECONSUME_IN(AfterAttributeName);
                }
                ON('=')
                {
                    TODO();
                }
                ANYTHING_ELSE
                {
                    m_current_token.m_tag.attributes.append(HTMLToken::AttributeBuilder());
                    RECONSUME_IN(AttributeName);
                }
            }
            END_STATE

            BEGIN_STATE(SelfClosingStartTag)
            {
            }
            END_STATE

            BEGIN_STATE(AttributeName)
            {
                ON_WHITESPACE
                {
                    RECONSUME_IN(AfterAttributeName);
                }
                ON('/')
                {
                    RECONSUME_IN(AfterAttributeName);
                }
                ON('>')
                {
                    RECONSUME_IN(AfterAttributeName);
                }
                ON_EOF
                {
                    RECONSUME_IN(AfterAttributeName);
                }
                ON('=')
                {
                    SWITCH_TO(BeforeAttributeValue);
                }
                ANYTHING_ELSE
                {
                    m_current_token.m_tag.attributes.last().name_builder.append(current_input_character.value());
                    continue;
                }
            }
            END_STATE

            BEGIN_STATE(AfterAttributeName)
            {
            }
            END_STATE

            BEGIN_STATE(BeforeAttributeValue)
            {
                ON_WHITESPACE
                {
                    continue;
                }
                ON('"')
                {
                    SWITCH_TO(AttributeValueDoubleQuoted);
                }
                ON('\'')
                {
                    SWITCH_TO(AttributeValueSingleQuoted);
                }
                ON('>')
                {
                    TODO();
                }
                ANYTHING_ELSE
                {
                    RECONSUME_IN(AttributeValueUnquoted);
                }
            }
            END_STATE

            BEGIN_STATE(AttributeValueDoubleQuoted)
            {
                ON('"')
                {
                    SWITCH_TO(AfterAttributeValueQuoted);
                }
                ON('&')
                {
                    m_return_state = State::AttributeValueDoubleQuoted;
                    SWITCH_TO(CharacterReference);
                }
                ON(0)
                {
                    TODO();
                }
                ON_EOF
                {
                    TODO();
                }
                ANYTHING_ELSE
                {
                    m_current_token.m_tag.attributes.last().value_builder.append(current_input_character.value());
                    continue;
                }
            }
            END_STATE

            BEGIN_STATE(AttributeValueSingleQuoted)
            {
                ON('\'')
                {
                    SWITCH_TO(AfterAttributeValueQuoted);
                }
                ON('&')
                {
                    m_return_state = State::AttributeValueSingleQuoted;
                    SWITCH_TO(CharacterReference);
                }
                ON(0)
                {
                    TODO();
                }
                ON_EOF
                {
                    TODO();
                }
                ANYTHING_ELSE
                {
                    m_current_token.m_tag.attributes.last().value_builder.append(current_input_character.value());
                    continue;
                }
            }
            END_STATE

            BEGIN_STATE(AttributeValueUnquoted)
            {
                ON_WHITESPACE
                {
                    SWITCH_TO(BeforeAttributeName);
                }
                ON('&')
                {
                    m_return_state = State::AttributeValueUnquoted;
                    SWITCH_TO(CharacterReference);
                }
                ON('>')
                {
                    SWITCH_TO_AND_EMIT_CURRENT_TOKEN(Data);
                }
                ON(0)
                {
                    TODO();
                }
                ON_EOF
                {
                    TODO();
                }
                ANYTHING_ELSE
                {
                    m_current_token.m_tag.attributes.last().value_builder.append(current_input_character.value());
                    continue;
                }
            }
            END_STATE

            BEGIN_STATE(AfterAttributeValueQuoted)
            {
                ON_WHITESPACE
                {
                    SWITCH_TO(BeforeAttributeName);
                }
                ON('/')
                {
                    SWITCH_TO(SelfClosingStartTag);
                }
                ON('>')
                {
                    SWITCH_TO_AND_EMIT_CURRENT_TOKEN(Data);
                }
                ON_EOF
                {
                    TODO();
                }
                ANYTHING_ELSE
                {
                    TODO();
                }
            }
            END_STATE

            BEGIN_STATE(CommentStart)
            {
                ON('-')
                {
                    SWITCH_TO(CommentStartDash);
                }
                ON('>')
                {
                    TODO();
                }
                ANYTHING_ELSE
                {
                    RECONSUME_IN(Comment);
                }
            }
            END_STATE

            BEGIN_STATE(CommentStartDash)
            {
                ON('-')
                {
                    SWITCH_TO(CommentEnd);
                }
                ON('>')
                {
                    TODO();
                }
                ON_EOF
                {
                    TODO();
                }
                ANYTHING_ELSE
                {
                    m_current_token.m_comment_or_character.data.append('-');
                    RECONSUME_IN(Comment);
                }
            }
            END_STATE

            BEGIN_STATE(Comment)
            {
                ON('<')
                {
                    m_current_token.m_comment_or_character.data.append(current_input_character.value());
                    SWITCH_TO(CommentLessThanSign);
                }
                ON('-')
                {
                    SWITCH_TO(CommentEndDash);
                }
                ON(0)
                {
                    TODO();
                }
                ON_EOF
                {
                    TODO();
                }
                ANYTHING_ELSE
                {
                    m_current_token.m_comment_or_character.data.append(current_input_character.value());
                    continue;
                }
            }
            END_STATE

            BEGIN_STATE(CommentEnd)
            {
                ON('>')
                {
                    SWITCH_TO_AND_EMIT_CURRENT_TOKEN(Data);
                }
                ON('!')
                {
                    SWITCH_TO(CommentEndBang);
                }
                ON('-')
                {
                    m_current_token.m_comment_or_character.data.append('-');
                    continue;
                }
                ON_EOF
                {
                    TODO();
                }
                ANYTHING_ELSE
                {
                    m_current_token.m_comment_or_character.data.append('-');
                    RECONSUME_IN(Comment);
                }
            }
            END_STATE

            BEGIN_STATE(CommentEndBang)
            {
                ON('-')
                {
                    m_current_token.m_comment_or_character.data.append("--!");
                    SWITCH_TO(CommentEndDash);
                }
                ON('>')
                {
                    TODO();
                }
                ON_EOF
                {
                    TODO();
                }
                ANYTHING_ELSE
                {
                    m_current_token.m_comment_or_character.data.append("--!");
                    RECONSUME_IN(Comment);
                }
            }
            END_STATE

            BEGIN_STATE(CommentEndDash)
            {
                ON('-')
                {
                    SWITCH_TO(CommentEnd);
                }
                ON_EOF
                {
                    TODO();
                }
                ANYTHING_ELSE
                {
                    m_current_token.m_comment_or_character.data.append('-');
                    RECONSUME_IN(Comment);
                }
            }
            END_STATE

            BEGIN_STATE(CommentLessThanSign)
            {
                ON('!')
                {
                    m_current_token.m_comment_or_character.data.append(current_input_character.value());
                    SWITCH_TO(CommentLessThanSignBang);
                }
                ON('<')
                {
                    m_current_token.m_comment_or_character.data.append(current_input_character.value());
                    continue;
                }
                ANYTHING_ELSE
                {
                    RECONSUME_IN(Comment);
                }
            }
            END_STATE

            BEGIN_STATE(CommentLessThanSignBang)
            {
                ON('-')
                {
                    SWITCH_TO(CommentLessThanSignBangDash);
                }
                ANYTHING_ELSE
                {
                    RECONSUME_IN(Comment);
                }
            }
            END_STATE

            BEGIN_STATE(CommentLessThanSignBangDash)
            {
                ON('-')
                {
                    SWITCH_TO(CommentLessThanSignBangDashDash);
                }
                ANYTHING_ELSE
                {
                    RECONSUME_IN(Comment);
                }
            }
            END_STATE

            BEGIN_STATE(CommentLessThanSignBangDashDash)
            {
                ON('>')
                {
                    SWITCH_TO(CommentEnd);
                }
                ANYTHING_ELSE
                {
                    TODO();
                }
            }
            END_STATE

            BEGIN_STATE(CharacterReference)
            {
            }
            END_STATE

        default:
            ASSERT_NOT_REACHED();
        }
    }
}

void HTMLTokenizer::consume(const StringView& string)
{
    ASSERT(next_few_characters_are(string));
    m_cursor += string.length();
}

bool HTMLTokenizer::next_few_characters_are(const StringView& string) const
{
    for (size_t i = 0; i < string.length(); ++i) {
        auto codepoint = peek_codepoint(i);
        if (!codepoint.has_value())
            return false;
        // FIXME: This should be more Unicode-aware.
        if (codepoint.value() != (u32)string[i])
            return false;
    }
    return true;
}

void HTMLTokenizer::create_new_token(HTMLToken::Type type)
{
    m_current_token = {};
    m_current_token.m_type = type;
}

HTMLTokenizer::HTMLTokenizer(const StringView& input)
    : m_input(input)
{
}

void HTMLTokenizer::will_switch_to([[maybe_unused]] State new_state)
{
#ifdef TOKENIZER_TRACE
    dbg() << "[" << state_name(m_state) << "] Switch to " << state_name(new_state);
#endif
}

void HTMLTokenizer::will_reconsume_in([[maybe_unused]] State new_state)
{
#ifdef TOKENIZER_TRACE
    dbg() << "[" << state_name(m_state) << "] Reconsume in " << state_name(new_state);
#endif
}

}