#include <AK/Utf8View.h>

namespace AK {

Utf8View::Utf8View(const StringView& 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 (const unsigned char*)m_string.characters_without_null_termination() + m_string.length();
}

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

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

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

    return false;
}

bool Utf8View::validate() const
{
    for (auto ptr = begin_ptr(); ptr < end_ptr(); ptr++) {
        int codepoint_length_in_bytes;
        u32 value;
        bool first_byte_makes_sense = decode_first_byte(*ptr, codepoint_length_in_bytes, value);
        if (!first_byte_makes_sense)
            return false;

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

    return true;
}

Utf8CodepointIterator::Utf8CodepointIterator(const unsigned char* ptr, int 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++()
{
    do {
        ASSERT(m_length > 0);
        m_length--;
        m_ptr++;
    } while (m_ptr[0] >> 6 == 2);

    return *this;
}

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

    u32 codepoint_value_so_far;
    int codepoint_length_in_bytes;

    bool first_byte_makes_sense = decode_first_byte(m_ptr[0], codepoint_length_in_bytes, codepoint_value_so_far);
    ASSERT(first_byte_makes_sense);
    ASSERT(codepoint_length_in_bytes <= m_length);

    for (int offset = 1; offset < codepoint_length_in_bytes; offset++) {
        ASSERT(m_ptr[offset] >> 6 == 2);
        codepoint_value_so_far <<= 6;
        codepoint_value_so_far |= m_ptr[offset] & 63;
    }

    return codepoint_value_so_far;
}

}