/*

 * Copyright (c) 2019-2020, Sergey Bugaev <bugaevc@serenityos.org>

 * Copyright (c) 2021, Max Wipfli <mail@maxwipfli.ch>

 *

 * SPDX-License-Identifier: BSD-2-Clause

 */

#pragma once

#include <AK/Format.h>

#include <AK/Function.h>

#include <AK/StringView.h>

#include <AK/Types.h>

#ifndef KERNEL

#    include <AK/ByteString.h>

#endif

namespace AK {

class Utf8View;

class Utf8CodePointIterator {

    friend class Utf8View;

public:

    Utf8CodePointIterator() = default;

    ~Utf8CodePointIterator() = default;

    bool operator==(Utf8CodePointIterator const&) const = default;

    bool operator!=(Utf8CodePointIterator const&) const = default;

    Utf8CodePointIterator& operator++();

    u32 operator*() const;

    // NOTE: This returns {} if the peek is at or past EOF.

    Optional<u32> peek(size_t offset = 0) const;

    ssize_t operator-(Utf8CodePointIterator const& other) const

    {

        return m_ptr - other.m_ptr;

    }

    u8 const* ptr() const { return m_ptr; }

    // Note : These methods return the information about the underlying UTF-8 bytes.

    // If the UTF-8 string encoding is not valid at the iterator's position, then the underlying bytes might be different from the

    // decoded character's re-encoded bytes (which will be an `0xFFFD REPLACEMENT CHARACTER` with an UTF-8 length of three bytes).

    // If your code relies on the decoded character being equivalent to the re-encoded character, use the `UTF8View::validate()`

    // method on the view prior to using its iterator.

    size_t underlying_code_point_length_in_bytes() const;

    ReadonlyBytes underlying_code_point_bytes() const;

    bool done() const { return m_length == 0; }

private:

    Utf8CodePointIterator(u8 const* ptr, size_t length)

        : m_ptr(ptr)

        , m_length(length)

    {

    }

    u8 const* m_ptr { nullptr };

    size_t m_length { 0 };

};

class Utf8View {

public:

    using Iterator = Utf8CodePointIterator;

    Utf8View() = default;

    explicit constexpr Utf8View(StringView string)

        : m_string(string)

    {

    }

#ifndef KERNEL

    explicit Utf8View(ByteString& string)

        : m_string(string.view())

    {

    }

    explicit Utf8View(ByteString&&) = delete;

#endif

    enum class AllowSurrogates {

        Yes,

        No,

    };

    ~Utf8View() = default;

    StringView as_string() const { return m_string; }

    Utf8CodePointIterator begin() const { return { begin_ptr(), m_string.length() }; }

    Utf8CodePointIterator end() const { return { end_ptr(), 0 }; }

    Utf8CodePointIterator iterator_at_byte_offset(size_t) const;

    Utf8CodePointIterator iterator_at_byte_offset_without_validation(size_t) const;

    unsigned char const* bytes() const { return begin_ptr(); }

    size_t byte_length() const { return m_string.length(); }

    size_t byte_offset_of(Utf8CodePointIterator const&) const;

    size_t byte_offset_of(size_t code_point_offset) const;

    Utf8View substring_view(size_t byte_offset, size_t byte_length) const { return Utf8View { m_string.substring_view(byte_offset, byte_length) }; }

    Utf8View substring_view(size_t byte_offset) const { return substring_view(byte_offset, byte_length() - byte_offset); }

    Utf8View unicode_substring_view(size_t code_point_offset, size_t code_point_length) const;

    Utf8View unicode_substring_view(size_t code_point_offset) const { return unicode_substring_view(code_point_offset, length() - code_point_offset); }

    bool is_empty() const { return m_string.is_empty(); }

    bool is_null() const { return m_string.is_null(); }

    bool starts_with(Utf8View const&) const;

    bool contains(u32) const;

    Utf8View trim(Utf8View const& characters, TrimMode mode = TrimMode::Both) const;

    size_t iterator_offset(Utf8CodePointIterator const& it) const

    {

        return byte_offset_of(it);

    }

    size_t length() const

    {

        if (!m_have_length) {

            m_length = calculate_length();

            m_have_length = true;

        }

        return m_length;

    }

    constexpr bool validate(AllowSurrogates surrogates = AllowSurrogates::Yes) const

    {

        size_t valid_bytes = 0;

        return validate(valid_bytes, surrogates);

    }

    constexpr bool validate(size_t& valid_bytes, AllowSurrogates surrogates = AllowSurrogates::Yes) const

    {

        valid_bytes = 0;

        for (auto it = m_string.begin(); it != m_string.end(); ++it) {

            auto [byte_length, code_point, is_valid] = decode_leading_byte(static_cast<u8>(*it));

            if (!is_valid)

                return false;

            for (size_t i = 1; i < byte_length; ++i) {

                if (++it == m_string.end())

                    return false;

                auto [code_point_bits, is_valid] = decode_continuation_byte(static_cast<u8>(*it));

                if (!is_valid)

                    return false;

                code_point <<= 6;

                code_point |= code_point_bits;

            }

            if (!is_valid_code_point(code_point, byte_length, surrogates))

                return false;

            valid_bytes += byte_length;

        }

        return true;

    }

    template<typename Callback>

    auto for_each_split_view(Function<bool(u32)> splitter, SplitBehavior split_behavior, Callback callback) const

    {

        bool keep_empty = has_flag(split_behavior, SplitBehavior::KeepEmpty);

        bool keep_trailing_separator = has_flag(split_behavior, SplitBehavior::KeepTrailingSeparator);

        auto start_offset = 0u;

        auto offset = 0u;

        auto run_callback = [&]() {

            auto length = offset - start_offset;

            if (length == 0 && !keep_empty)

                return;

            auto substring = unicode_substring_view(start_offset, length);

            // Reject splitter-only entries if we're not keeping empty results

            if (keep_trailing_separator && !keep_empty && length == 1 && splitter(*substring.begin()))

                return;

            callback(substring);

        };

        auto iterator = begin();

        while (iterator != end()) {

            if (splitter(*iterator)) {

                if (keep_trailing_separator)

                    ++offset;

                run_callback();

                if (!keep_trailing_separator)

                    ++offset;

                start_offset = offset;

                ++iterator;

                continue;

            }

            ++offset;

            ++iterator;

        }

        run_callback();

    }

private:

    friend class Utf8CodePointIterator;

    u8 const* begin_ptr() const { return reinterpret_cast<u8 const*>(m_string.characters_without_null_termination()); }

    u8 const* end_ptr() const { return begin_ptr() + m_string.length(); }

    size_t calculate_length() const;

    struct Utf8EncodedByteData {

        size_t byte_length { 0 };

        u8 encoding_bits { 0 };

        u8 encoding_mask { 0 };

        u32 first_code_point { 0 };

        u32 last_code_point { 0 };

    };

    static constexpr Array<Utf8EncodedByteData, 4> utf8_encoded_byte_data { {

        { 1, 0b0000'0000, 0b1000'0000, 0x0000, 0x007F },

        { 2, 0b1100'0000, 0b1110'0000, 0x0080, 0x07FF },

        { 3, 0b1110'0000, 0b1111'0000, 0x0800, 0xFFFF },

        { 4, 0b1111'0000, 0b1111'1000, 0x10000, 0x10FFFF },

    } };

    struct LeadingByte {

        size_t byte_length { 0 };

        u32 code_point_bits { 0 };

        bool is_valid { false };

    };

    static constexpr LeadingByte decode_leading_byte(u8 byte)

    {

        for (auto const& data : utf8_encoded_byte_data) {

            if ((byte & data.encoding_mask) != data.encoding_bits)

                continue;

            byte &= ~data.encoding_mask;

            return { data.byte_length, byte, true };

        }

        return { .is_valid = false };

    }

    struct ContinuationByte {

        u32 code_point_bits { 0 };

        bool is_valid { false };

    };

    static constexpr ContinuationByte decode_continuation_byte(u8 byte)

    {

        constexpr u8 continuation_byte_encoding_bits = 0b1000'0000;

        constexpr u8 continuation_byte_encoding_mask = 0b1100'0000;

        if ((byte & continuation_byte_encoding_mask) == continuation_byte_encoding_bits) {

            byte &= ~continuation_byte_encoding_mask;

            return { byte, true };

        }

        return { .is_valid = false };

    }

    static constexpr bool is_valid_code_point(u32 code_point, size_t byte_length, AllowSurrogates surrogates = AllowSurrogates::Yes)

    {

        if (surrogates == AllowSurrogates::No && byte_length == 3 && code_point >= 0xD800 && code_point <= 0xDFFF)

            return false;

        for (auto const& data : utf8_encoded_byte_data) {

            if (code_point >= data.first_code_point && code_point <= data.last_code_point)

                return byte_length == data.byte_length;

        }

        return false;

    }

    StringView m_string;

    mutable size_t m_length { 0 };

    mutable bool m_have_length { false };

};

#ifndef KERNEL

class DeprecatedStringCodePointIterator {

public:

    Optional<u32> next()

    {

        if (m_it.done())

            return {};

        auto value = *m_it;

        ++m_it;

        return value;

    }

    [[nodiscard]] Optional<u32> peek() const

    {

        if (m_it.done())

            return {};

        return *m_it;

    }

    [[nodiscard]] size_t byte_offset() const

    {

        return Utf8View(m_string).byte_offset_of(m_it);

    }

    DeprecatedStringCodePointIterator(ByteString string)

        : m_string(move(string))

        , m_it(Utf8View(m_string).begin())

    {

    }

private:

    ByteString m_string;

    Utf8CodePointIterator m_it;

};

#endif

template<>

struct Formatter<Utf8View> : Formatter<StringView> {

    ErrorOr<void> format(FormatBuilder&, Utf8View const&);

};

}

#if USING_AK_GLOBALLY

#    ifndef KERNEL

using AK::DeprecatedStringCodePointIterator;

#    endif

using AK::Utf8CodePointIterator;

using AK::Utf8View;

#endif