// SPDX-FileCopyrightText: Copyright 2024 yuzu Emulator Project
// SPDX-License-Identifier: GPL-2.0-or-later

#pragma once

#include "common/assert.h"

namespace FileSys {

template <typename T>
constexpr int Strlen(const T* str) {
    ASSERT(str != nullptr);

    int length = 0;
    while (*str++) {
        ++length;
    }

    return length;
}

template <typename T>
constexpr int Strnlen(const T* str, int count) {
    ASSERT(str != nullptr);
    ASSERT(count >= 0);

    int length = 0;
    while (count-- && *str++) {
        ++length;
    }

    return length;
}

template <typename T>
constexpr int Strncmp(const T* lhs, const T* rhs, int count) {
    ASSERT(lhs != nullptr);
    ASSERT(rhs != nullptr);
    ASSERT(count >= 0);

    if (count == 0) {
        return 0;
    }

    T l, r;
    do {
        l = *(lhs++);
        r = *(rhs++);
    } while (l && (l == r) && (--count));

    return l - r;
}

template <typename T>
static constexpr int Strlcpy(T* dst, const T* src, int count) {
    ASSERT(dst != nullptr);
    ASSERT(src != nullptr);

    const T* cur = src;
    if (count > 0) {
        while ((--count) && *cur) {
            *(dst++) = *(cur++);
        }
        *dst = 0;
    }

    while (*cur) {
        cur++;
    }

    return static_cast<int>(cur - src);
}

enum CharacterEncodingResult {
    CharacterEncodingResult_Success = 0,
    CharacterEncodingResult_InsufficientLength = 1,
    CharacterEncodingResult_InvalidFormat = 2,
};

namespace impl {

class CharacterEncodingHelper {
public:
    static constexpr int8_t Utf8NBytesInnerTable[0x100 + 1] = {
        -1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
        1,  1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
        1,  1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
        1,  1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
        1,  1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
        0,  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
        0,  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
        2,  2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 3, 3, 3, 3, 3, 3, 3,
        3,  3, 3, 3, 3, 3, 3, 3, 3, 4, 4, 4, 4, 4, 4, 4, 4, 5, 5, 5, 5, 6, 6, 7, 8,
    };

    static constexpr char GetUtf8NBytes(size_t i) {
        return static_cast<char>(Utf8NBytesInnerTable[1 + i]);
    }
};

} // namespace impl

constexpr inline CharacterEncodingResult ConvertCharacterUtf8ToUtf32(u32* dst, const char* src) {
    // Check pre-conditions
    ASSERT(dst != nullptr);
    ASSERT(src != nullptr);

    // Perform the conversion
    const auto* p = src;
    switch (impl::CharacterEncodingHelper::GetUtf8NBytes(static_cast<unsigned char>(p[0]))) {
    case 1:
        *dst = static_cast<u32>(p[0]);
        return CharacterEncodingResult_Success;
    case 2:
        if ((static_cast<u32>(p[0]) & 0x1E) != 0) {
            if (impl::CharacterEncodingHelper::GetUtf8NBytes(static_cast<unsigned char>(p[1])) ==
                0) {
                *dst = (static_cast<u32>(p[0] & 0x1F) << 6) | (static_cast<u32>(p[1] & 0x3F) << 0);
                return CharacterEncodingResult_Success;
            }
        }
        break;
    case 3:
        if (impl::CharacterEncodingHelper::GetUtf8NBytes(static_cast<unsigned char>(p[1])) == 0 &&
            impl::CharacterEncodingHelper::GetUtf8NBytes(static_cast<unsigned char>(p[2])) == 0) {
            const u32 c = (static_cast<u32>(p[0] & 0xF) << 12) |
                          (static_cast<u32>(p[1] & 0x3F) << 6) |
                          (static_cast<u32>(p[2] & 0x3F) << 0);
            if ((c & 0xF800) != 0 && (c & 0xF800) != 0xD800) {
                *dst = c;
                return CharacterEncodingResult_Success;
            }
        }
        return CharacterEncodingResult_InvalidFormat;
    case 4:
        if (impl::CharacterEncodingHelper::GetUtf8NBytes(static_cast<unsigned char>(p[1])) == 0 &&
            impl::CharacterEncodingHelper::GetUtf8NBytes(static_cast<unsigned char>(p[2])) == 0 &&
            impl::CharacterEncodingHelper::GetUtf8NBytes(static_cast<unsigned char>(p[3])) == 0) {
            const u32 c =
                (static_cast<u32>(p[0] & 0x7) << 18) | (static_cast<u32>(p[1] & 0x3F) << 12) |
                (static_cast<u32>(p[2] & 0x3F) << 6) | (static_cast<u32>(p[3] & 0x3F) << 0);
            if (c >= 0x10000 && c < 0x110000) {
                *dst = c;
                return CharacterEncodingResult_Success;
            }
        }
        return CharacterEncodingResult_InvalidFormat;
    default:
        break;
    }

    // We failed to convert
    return CharacterEncodingResult_InvalidFormat;
}

constexpr inline CharacterEncodingResult PickOutCharacterFromUtf8String(char* dst,
                                                                        const char** str) {
    // Check pre-conditions
    ASSERT(dst != nullptr);
    ASSERT(str != nullptr);
    ASSERT(*str != nullptr);

    // Clear the output
    dst[0] = 0;
    dst[1] = 0;
    dst[2] = 0;
    dst[3] = 0;

    // Perform the conversion
    const auto* p = *str;
    u32 c = static_cast<u32>(*p);
    switch (impl::CharacterEncodingHelper::GetUtf8NBytes(c)) {
    case 1:
        dst[0] = (*str)[0];
        ++(*str);
        break;
    case 2:
        if ((p[0] & 0x1E) != 0) {
            if (impl::CharacterEncodingHelper::GetUtf8NBytes(static_cast<unsigned char>(p[1])) ==
                0) {
                c = (static_cast<u32>(p[0] & 0x1F) << 6) | (static_cast<u32>(p[1] & 0x3F) << 0);
                dst[0] = (*str)[0];
                dst[1] = (*str)[1];
                (*str) += 2;
                break;
            }
        }
        return CharacterEncodingResult_InvalidFormat;
    case 3:
        if (impl::CharacterEncodingHelper::GetUtf8NBytes(static_cast<unsigned char>(p[1])) == 0 &&
            impl::CharacterEncodingHelper::GetUtf8NBytes(static_cast<unsigned char>(p[2])) == 0) {
            c = (static_cast<u32>(p[0] & 0xF) << 12) | (static_cast<u32>(p[1] & 0x3F) << 6) |
                (static_cast<u32>(p[2] & 0x3F) << 0);
            if ((c & 0xF800) != 0 && (c & 0xF800) != 0xD800) {
                dst[0] = (*str)[0];
                dst[1] = (*str)[1];
                dst[2] = (*str)[2];
                (*str) += 3;
                break;
            }
        }
        return CharacterEncodingResult_InvalidFormat;
    case 4:
        if (impl::CharacterEncodingHelper::GetUtf8NBytes(static_cast<unsigned char>(p[1])) == 0 &&
            impl::CharacterEncodingHelper::GetUtf8NBytes(static_cast<unsigned char>(p[2])) == 0 &&
            impl::CharacterEncodingHelper::GetUtf8NBytes(static_cast<unsigned char>(p[3])) == 0) {
            c = (static_cast<u32>(p[0] & 0x7) << 18) | (static_cast<u32>(p[1] & 0x3F) << 12) |
                (static_cast<u32>(p[2] & 0x3F) << 6) | (static_cast<u32>(p[3] & 0x3F) << 0);
            if (c >= 0x10000 && c < 0x110000) {
                dst[0] = (*str)[0];
                dst[1] = (*str)[1];
                dst[2] = (*str)[2];
                dst[3] = (*str)[3];
                (*str) += 4;
                break;
            }
        }
        return CharacterEncodingResult_InvalidFormat;
    default:
        return CharacterEncodingResult_InvalidFormat;
    }

    return CharacterEncodingResult_Success;
}

} // namespace FileSys