/*
 * Copyright (c) 2019-2020, Sergey Bugaev <bugaevc@serenityos.org>
 * Copyright (c) 2021, Max Wipfli <mail@maxwipfli.ch>
 *
 * SPDX-License-Identifier: BSD-2-Clause
 */

#include <AK/Assertions.h>
#include <AK/Format.h>
#include <AK/Utf8View.h>

namespace AK {

Utf8View::Utf8View(const String& string)
    : m_string(string)
{
}

Utf8View::Utf8View(const StringView& string)
    : m_string(string)
{
}

Utf8View::Utf8View(const char* string)
    : m_string(string)
{
}

const unsigned char* Utf8View::begin_ptr() const
{
    return (const unsigned char*)m_string.characters_without_null_termination();
}

const unsigned char* Utf8View::end_ptr() const
{
    return begin_ptr() + m_string.length();
}

Utf8CodepointIterator Utf8View::begin() const
{
    return { begin_ptr(), m_string.length() };
}

Utf8CodepointIterator Utf8View::end() const
{
    return { end_ptr(), 0 };
}

Utf8CodepointIterator Utf8View::iterator_at_byte_offset(size_t byte_offset) const
{
    size_t current_offset = 0;
    for (auto iterator = begin(); !iterator.done(); ++iterator) {
        if (current_offset >= byte_offset)
            return iterator;
        current_offset += iterator.code_point_length_in_bytes();
    }
    return end();
}

size_t Utf8View::byte_offset_of(const Utf8CodepointIterator& it) const
{
    VERIFY(it.m_ptr >= begin_ptr());
    VERIFY(it.m_ptr <= end_ptr());

    return it.m_ptr - begin_ptr();
}

Utf8View Utf8View::substring_view(size_t byte_offset, size_t byte_length) const
{
    StringView string = m_string.substring_view(byte_offset, byte_length);
    return Utf8View { string };
}

Utf8View Utf8View::unicode_substring_view(size_t codepoint_offset, size_t codepoint_length) const
{
    if (codepoint_length == 0)
        return {};

    size_t codepoint_index = 0, offset_in_bytes = 0;
    for (auto iterator = begin(); !iterator.done(); ++iterator) {
        if (codepoint_index == codepoint_offset)
            offset_in_bytes = byte_offset_of(iterator);
        if (codepoint_index == codepoint_offset + codepoint_length - 1) {
            size_t length_in_bytes = byte_offset_of(++iterator) - offset_in_bytes;
            return substring_view(offset_in_bytes, length_in_bytes);
        }
        ++codepoint_index;
    }

    VERIFY_NOT_REACHED();
}

static inline bool decode_first_byte(
    unsigned char byte,
    size_t& out_code_point_length_in_bytes,
    u32& out_value)
{
    if ((byte & 128) == 0) {
        out_value = byte;
        out_code_point_length_in_bytes = 1;
        return true;
    }
    if ((byte & 64) == 0) {
        return false;
    }
    if ((byte & 32) == 0) {
        out_value = byte & 31;
        out_code_point_length_in_bytes = 2;
        return true;
    }
    if ((byte & 16) == 0) {
        out_value = byte & 15;
        out_code_point_length_in_bytes = 3;
        return true;
    }
    if ((byte & 8) == 0) {
        out_value = byte & 7;
        out_code_point_length_in_bytes = 4;
        return true;
    }

    return false;
}

bool Utf8View::validate(size_t& valid_bytes) const
{
    valid_bytes = 0;
    for (auto ptr = begin_ptr(); ptr < end_ptr(); ptr++) {
        size_t code_point_length_in_bytes;
        u32 value;
        bool first_byte_makes_sense = decode_first_byte(*ptr, code_point_length_in_bytes, value);
        if (!first_byte_makes_sense)
            return false;

        for (size_t i = 1; i < code_point_length_in_bytes; i++) {
            ptr++;
            if (ptr >= end_ptr())
                return false;
            if (*ptr >> 6 != 2)
                return false;
        }

        valid_bytes += code_point_length_in_bytes;
    }

    return true;
}

size_t Utf8View::calculate_length() const
{
    size_t length = 0;
    for ([[maybe_unused]] auto code_point : *this) {
        ++length;
    }
    return length;
}

bool Utf8View::starts_with(const Utf8View& start) const
{
    if (start.is_empty())
        return true;
    if (is_empty())
        return false;
    if (start.length() > length())
        return false;
    if (begin_ptr() == start.begin_ptr())
        return true;

    for (auto k = begin(), l = start.begin(); l != start.end(); ++k, ++l) {
        if (*k != *l)
            return false;
    }
    return true;
}

Utf8CodepointIterator::Utf8CodepointIterator(const unsigned char* ptr, size_t length)
    : m_ptr(ptr)
    , m_length(length)
{
}

bool Utf8CodepointIterator::operator==(const Utf8CodepointIterator& other) const
{
    return m_ptr == other.m_ptr && m_length == other.m_length;
}

bool Utf8CodepointIterator::operator!=(const Utf8CodepointIterator& other) const
{
    return !(*this == other);
}

Utf8CodepointIterator& Utf8CodepointIterator::operator++()
{
    VERIFY(m_length > 0);

    size_t code_point_length_in_bytes = 0;
    u32 value;
    bool first_byte_makes_sense = decode_first_byte(*m_ptr, code_point_length_in_bytes, value);

    VERIFY(first_byte_makes_sense);

    VERIFY(code_point_length_in_bytes <= m_length);
    m_ptr += code_point_length_in_bytes;
    m_length -= code_point_length_in_bytes;

    return *this;
}

size_t Utf8CodepointIterator::code_point_length_in_bytes() const
{
    VERIFY(m_length > 0);
    size_t code_point_length_in_bytes = 0;
    u32 value;
    bool first_byte_makes_sense = decode_first_byte(*m_ptr, code_point_length_in_bytes, value);
    VERIFY(first_byte_makes_sense);
    return code_point_length_in_bytes;
}

u32 Utf8CodepointIterator::operator*() const
{
    VERIFY(m_length > 0);

    u32 code_point_value_so_far = 0;
    size_t code_point_length_in_bytes = 0;

    bool first_byte_makes_sense = decode_first_byte(m_ptr[0], code_point_length_in_bytes, code_point_value_so_far);
    if (!first_byte_makes_sense)
        dbgln("First byte doesn't make sense, bytes: {}", StringView { (const char*)m_ptr, m_length });
    VERIFY(first_byte_makes_sense);
    if (code_point_length_in_bytes > m_length)
        dbgln("Not enough bytes (need {}, have {}), first byte is: {:#02x}, '{}'", code_point_length_in_bytes, m_length, m_ptr[0], (const char*)m_ptr);
    VERIFY(code_point_length_in_bytes <= m_length);

    for (size_t offset = 1; offset < code_point_length_in_bytes; offset++) {
        VERIFY(m_ptr[offset] >> 6 == 2);
        code_point_value_so_far <<= 6;
        code_point_value_so_far |= m_ptr[offset] & 63;
    }

    return code_point_value_so_far;
}

}