/*
 * Copyright (c) 2018-2020, 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 <AK/JsonArray.h>
#include <AK/JsonObject.h>
#include <AK/JsonParser.h>
#include <AK/Memory.h>

namespace AK {

static inline bool is_whitespace(char ch)
{
    return ch == ' ' || ch == '\n' || ch == '\t' || ch == '\v' || ch == '\r';
}

char JsonParser::peek() const
{
    if (m_index < m_input.length())
        return m_input[m_index];
    return '\0';
}

char JsonParser::consume()
{
    if (m_index < m_input.length())
        return m_input[m_index++];
    return '\0';
}

template<typename C>
void JsonParser::consume_while(C condition)
{
    while (condition(peek()))
        consume();
}

void JsonParser::consume_whitespace()
{
    consume_while([](char ch) { return is_whitespace(ch); });
}

bool JsonParser::consume_specific(char expected_ch)
{
    char consumed_ch = consume();
    return consumed_ch == expected_ch;
}

String JsonParser::consume_quoted_string()
{
    if (!consume_specific('"'))
        return {};
    StringBuilder final_sb;

    for (;;) {
        size_t peek_index = m_index;
        char ch = 0;
        for (;;) {
            if (peek_index == m_input.length())
                break;
            ch = m_input[peek_index];
            if (ch == '"' || ch == '\\')
                break;
            ++peek_index;
        }

        if (peek_index != m_index) {
            while (peek_index != m_index) {
                final_sb.append(m_input.characters_without_null_termination()[m_index]);
                m_index++;
            }
        }

        if (m_index == m_input.length())
            break;
        if (ch == '"')
            break;
        if (ch != '\\') {
            final_sb.append(consume());
            continue;
        }
        consume();
        char escaped_ch = consume();
        switch (escaped_ch) {
        case 'n':
            final_sb.append('\n');
            break;
        case 'r':
            final_sb.append('\r');
            break;
        case 't':
            final_sb.append('\t');
            break;
        case 'b':
            final_sb.append('\b');
            break;
        case 'f':
            final_sb.append('\f');
            break;
        case 'u': {
            StringBuilder sb;
            sb.append(consume());
            sb.append(consume());
            sb.append(consume());
            sb.append(consume());

            auto codepoint = AK::StringUtils::convert_to_uint_from_hex(sb.to_string());
            if (codepoint.has_value()) {
                final_sb.append_codepoint(codepoint.value());
            } else {
                final_sb.append('?');
            }
        } break;
        default:
            final_sb.append(escaped_ch);
            break;
        }
    }
    if (!consume_specific('"'))
        return {};

    return final_sb.to_string();
}

Optional<JsonValue> JsonParser::parse_object()
{
    JsonObject object;
    if (!consume_specific('{'))
        return {};
    for (;;) {
        consume_whitespace();
        if (peek() == '}')
            break;
        consume_whitespace();
        auto name = consume_quoted_string();
        if (name.is_null())
            return {};
        consume_whitespace();
        if (!consume_specific(':'))
            return {};
        consume_whitespace();
        auto value = parse_helper();
        if (!value.has_value())
            return {};
        object.set(name, move(value.value()));
        consume_whitespace();
        if (peek() == '}')
            break;
        if (!consume_specific(','))
            return {};
        consume_whitespace();
        if (peek() == '}')
            return {};
    }
    if (!consume_specific('}'))
        return {};
    return object;
}

Optional<JsonValue> JsonParser::parse_array()
{
    JsonArray array;
    if (!consume_specific('['))
        return {};
    for (;;) {
        consume_whitespace();
        if (peek() == ']')
            break;
        auto element = parse_helper();
        if (!element.has_value())
            return {};
        array.append(element.value());
        consume_whitespace();
        if (peek() == ']')
            break;
        if (!consume_specific(','))
            return {};
        consume_whitespace();
        if (peek() == ']')
            return {};
    }
    consume_whitespace();
    if (!consume_specific(']'))
        return {};
    return array;
}

Optional<JsonValue> JsonParser::parse_string()
{
    auto result = consume_quoted_string();
    if (result.is_null())
        return {};
    return JsonValue(result);
}

Optional<JsonValue> JsonParser::parse_number()
{
    JsonValue value;
    Vector<char, 128> number_buffer;
    Vector<char, 128> fraction_buffer;

    bool is_double = false;
    for (;;) {
        char ch = peek();
        if (ch == '.') {
            is_double = true;
            ++m_index;
            continue;
        }
        if (ch == '-' || (ch >= '0' && ch <= '9')) {
            if (is_double)
                fraction_buffer.append(ch);
            else
                number_buffer.append(ch);
            ++m_index;
            continue;
        }
        break;
    }

    StringView number_string(number_buffer.data(), number_buffer.size());
    StringView fraction_string(fraction_buffer.data(), fraction_buffer.size());

#ifndef KERNEL
    if (is_double) {
        // FIXME: This logic looks shaky.
        int whole = 0;
        auto to_signed_result = number_string.to_uint();
        if (to_signed_result.has_value()) {
            whole = to_signed_result.value();
        } else {
            auto number = number_string.to_int();
            if (!number.has_value())
                return {};
            whole = number.value();
        }

        int fraction = fraction_string.to_uint().value();
        fraction *= (whole < 0) ? -1 : 1;

        auto divider = 1;
        for (size_t i = 0; i < fraction_buffer.size(); ++i) {
            divider *= 10;
        }
        value = JsonValue((double)whole + ((double)fraction / divider));
    } else {
#endif
        auto to_unsigned_result = number_string.to_uint();
        if (to_unsigned_result.has_value()) {
            value = JsonValue(to_unsigned_result.value());
        } else {
            auto number = number_string.to_int();
            if (!number.has_value())
                return {};
            value = JsonValue(number.value());
        }
#ifndef KERNEL
    }
#endif

    return value;
}

bool JsonParser::consume_string(const char* str)
{
    for (size_t i = 0, length = strlen(str); i < length; ++i) {
        if (!consume_specific(str[i]))
            return false;
    }
    return true;
}

Optional<JsonValue> JsonParser::parse_true()
{
    if (!consume_string("true"))
        return {};
    return JsonValue(true);
}

Optional<JsonValue> JsonParser::parse_false()
{
    if (!consume_string("false"))
        return {};
    return JsonValue(false);
}

Optional<JsonValue> JsonParser::parse_null()
{
    if (!consume_string("null"))
        return {};
    return JsonValue(JsonValue::Type::Null);
}

Optional<JsonValue> JsonParser::parse_helper()
{
    consume_whitespace();
    auto type_hint = peek();
    switch (type_hint) {
    case '{':
        return parse_object();
    case '[':
        return parse_array();
    case '"':
        return parse_string();
    case '-':
    case '0':
    case '1':
    case '2':
    case '3':
    case '4':
    case '5':
    case '6':
    case '7':
    case '8':
    case '9':
        return parse_number();
    case 'f':
        return parse_false();
    case 't':
        return parse_true();
    case 'n':
        return parse_null();
    }

    return {};
}

Optional<JsonValue> JsonParser::parse() {
    auto result = parse_helper();
    if (!result.has_value())
        return {};
    consume_whitespace();
    if (m_index != m_input.length())
        return {};
    return result;
}

}