/*
 * Copyright (c) 2007 Alexey Vatchenko <av@bsdua.org>
 *
 * Permission to use, copy, modify, and/or distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */
#include "config.h"  // IWYU pragma: keep

#include <stdint.h>  // IWYU pragma: keep
#include <sys/types.h>
#include <limits>
#include <string>

#include "utf8.h"

#define _NXT 0x80
#define _SEQ2 0xc0
#define _SEQ3 0xe0
#define _SEQ4 0xf0

#define _BOM 0xfeff

// We can tweak the following typedef to allow us to simulate Windows-style 16 bit wchar's on Unix.
typedef wchar_t utf8_wchar_t;
#define UTF8_WCHAR_MAX (wchar_t) std::numeric_limits<utf8_wchar_t>::max()

typedef std::basic_string<utf8_wchar_t> utf8_wstring_t;

static size_t utf8_to_wchar_internal(const char *in, size_t insize, utf8_wstring_t *result,
                                     int flags);
static size_t wchar_to_utf8_internal(const utf8_wchar_t *in, size_t insize, char *out,
                                     size_t outsize, int flags);

static bool safe_copy_wchar_to_utf8_wchar(const wchar_t *in, utf8_wchar_t *out, size_t count) {
    bool result = true;
    for (size_t i = 0; i < count; i++) {
        wchar_t c = in[i];
        if (c > UTF8_WCHAR_MAX) {
            result = false;
            break;
        }
        out[i] = c;
    }
    return result;
}

bool wchar_to_utf8_string(const std::wstring &str, std::string *result) {
    result->clear();
    const size_t inlen = str.size();
    if (inlen == 0) {
        return true;
    }

    bool success = false;
    const wchar_t *input = str.c_str();
    size_t outlen = wchar_to_utf8(input, inlen, NULL, 0, 0);
    if (outlen > 0) {
        char *tmp = new char[outlen];
        size_t outlen2 = wchar_to_utf8(input, inlen, tmp, outlen, 0);
        if (outlen2 > 0) {
            result->assign(tmp, outlen2);
            success = true;
        }
        delete[] tmp;
    }
    return success;
}

size_t utf8_to_wchar(const char *in, size_t insize, std::wstring *out, int flags) {
    if (in == NULL || insize == 0) {
        return 0;
    }

    size_t result;
    if (sizeof(wchar_t) == sizeof(utf8_wchar_t)) {
        result = utf8_to_wchar_internal(in, insize, reinterpret_cast<utf8_wstring_t *>(out), flags);
    } else if (out == NULL) {
        result = utf8_to_wchar_internal(in, insize, NULL, flags);
    } else {
        // Allocate a temporary buffer to hold the output, invoke the conversion with the temporary,
        // and then copy it back.
        utf8_wstring_t tmp_output;
        result = utf8_to_wchar_internal(in, insize, &tmp_output, flags);
        out->insert(out->end(), tmp_output.begin(), tmp_output.end());
    }
    return result;
}

size_t wchar_to_utf8(const wchar_t *in, size_t insize, char *out, size_t outsize, int flags) {
    if (in == NULL || insize == 0 || (outsize == 0 && out != NULL)) {
        return 0;
    }

    size_t result;
    if (sizeof(wchar_t) == sizeof(utf8_wchar_t)) {
        result = wchar_to_utf8_internal(reinterpret_cast<const utf8_wchar_t *>(in), insize, out,
                                        outsize, flags);
    } else {
        // Allocate a temporary buffer to hold the input the std::copy performs the size conversion.
        // Note: insize may be 0.
        utf8_wchar_t *tmp_input = new utf8_wchar_t[insize];
        if (!safe_copy_wchar_to_utf8_wchar(in, tmp_input, insize)) {
            // Our utf8_wchar_t is UCS-16 and there was an astral character.
            result = 0;
        } else {
            // Invoke the conversion with the temporary, then clean up the input.
            result = wchar_to_utf8_internal(tmp_input, insize, out, outsize, flags);
        }
        delete[] tmp_input;
    }
    return result;
}

static int __wchar_forbitten(utf8_wchar_t sym);
static int __utf8_forbitten(unsigned char octet);

static int __wchar_forbitten(utf8_wchar_t sym) {
    // Surrogate pairs.
    if (sym >= 0xd800 && sym <= 0xdfff) return -1;
    return 0;
}

static int __utf8_forbitten(unsigned char octet) {
    switch (octet) {
        case 0xc0:
        case 0xc1:
        case 0xf5:
        case 0xff: {
            return -1;
        }
    }

    return 0;
}

/// This function translates UTF-8 string into UCS-2 or UCS-4 string (all symbols will be in local
/// machine byte order). It takes the following arguments:
///
/// in	- input UTF-8 string. It can be null-terminated.
/// insize	- size of input string in bytes.
/// out_string	- result buffer for UCS-2/4 string.
///
/// RETURN VALUES
/// The function returns size of result buffer (in wide characters).
/// Zero is returned in case of error.
///
/// CAVEATS
/// 1. If UTF-8 string contains zero symbols, they will be translated
/// as regular symbols.
///
/// 2. If UTF8_IGNORE_ERROR or UTF8_SKIP_BOM flag is set, sizes may vary when `out' is NULL and not
/// NULL. It's because of special UTF-8 sequences which may result in forbitten (by RFC3629) UNICODE
/// characters.  So, the caller must check return value every time and not prepare buffer in advance
/// (\0 terminate) but after calling this function.
static size_t utf8_to_wchar_internal(const char *in, size_t insize, utf8_wstring_t *out_string,
                                     int flags) {
    unsigned char *p, *lim;
    utf8_wchar_t high;
    size_t n, total, i, n_bits;

    if (in == NULL || insize == 0) return 0;

    if (out_string != NULL) out_string->clear();

    total = 0;
    p = (unsigned char *)in;
    lim = p + insize;

    for (; p < lim; p += n) {
        if (__utf8_forbitten(*p) != 0 && (flags & UTF8_IGNORE_ERROR) == 0) return 0;

        // Get number of bytes for one wide character.
        n = 1;  // default: 1 byte. Used when skipping bytes
        if ((*p & 0x80) == 0)
            high = (utf8_wchar_t)*p;
        else if ((*p & 0xe0) == _SEQ2) {
            n = 2;
            high = (utf8_wchar_t)(*p & 0x1f);
        } else if ((*p & 0xf0) == _SEQ3) {
            n = 3;
            high = (utf8_wchar_t)(*p & 0x0f);
        } else if ((*p & 0xf8) == _SEQ4) {
            n = 4;
            high = (utf8_wchar_t)(*p & 0x07);
        } else {
            if ((flags & UTF8_IGNORE_ERROR) == 0) return 0;
            continue;
        }

        // Does the sequence header tell us truth about length?
        if ((size_t)(lim - p) <= n - 1) {
            if ((flags & UTF8_IGNORE_ERROR) == 0) return 0;
            n = 1;
            continue;  // skip
        }

        // Validate sequence. All symbols must have higher bits set to 10xxxxxx.
        if (n > 1) {
            for (i = 1; i < n; i++) {
                if ((p[i] & 0xc0) != _NXT) break;
            }
            if (i != n) {
                if ((flags & UTF8_IGNORE_ERROR) == 0) return 0;
                n = 1;
                continue;  // skip
            }
        }

        total++;
        if (out_string == NULL) continue;

        uint32_t out_val = 0;
        n_bits = 0;
        for (i = 1; i < n; i++) {
            out_val |= (utf8_wchar_t)(p[n - i] & 0x3f) << n_bits;
            n_bits += 6;  // 6 low bits in every byte
        }
        out_val |= high << n_bits;

        bool skip = false;
        if (__wchar_forbitten(out_val) != 0) {
            if ((flags & UTF8_IGNORE_ERROR) == 0) {
                return 0;  // forbidden character
            }
            skip = true;
        } else if (out_val == _BOM && (flags & UTF8_SKIP_BOM) != 0) {
            skip = true;
        }

        if (skip) {
            total--;
        } else if (out_val > (uint32_t)UTF8_WCHAR_MAX) {
            // wchar_t is UCS-2, but the UTF-8 specified an astral character.
            return 0;
        } else {
            out_string->push_back(out_val);
        }
    }

    return total;
}

/// This function translates UCS-2/4 symbols (given in local machine byte order) into UTF-8 string.
/// It takes the following arguments:
///
/// in	- input unicode string. It can be null-terminated.
/// insize	- size of input string in wide characters.
/// out	- result buffer for utf8 string. If out is NULL, function returns size of result buffer.
/// outsize - size of result buffer.
///
/// RETURN VALUES
/// The function returns size of result buffer (in bytes). Zero is returned in case of error.
///
/// CAVEATS
/// If UCS-4 string contains zero symbols, they will be translated as regular symbols.
static size_t wchar_to_utf8_internal(const utf8_wchar_t *in, size_t insize, char *out,
                                     size_t outsize, int flags) {
    const utf8_wchar_t *w, *wlim;
    unsigned char *p, *lim;
    size_t total, n;

    if (in == NULL || insize == 0 || (outsize == 0 && out != NULL)) return 0;

    w = in;
    wlim = w + insize;
    p = (unsigned char *)out;
    lim = p + outsize;
    total = 0;
    for (; w < wlim; w++) {
        if (__wchar_forbitten(*w) != 0) {
            if ((flags & UTF8_IGNORE_ERROR) == 0) return 0;
            continue;
        }

        if (*w == _BOM && (flags & UTF8_SKIP_BOM) != 0) continue;

        const int32_t w_wide = *w;
        if (w_wide < 0) {
            if ((flags & UTF8_IGNORE_ERROR) == 0) return 0;
            continue;
        }
        if (w_wide <= 0x0000007f)
            n = 1;
        else if (w_wide <= 0x000007ff)
            n = 2;
        else if (w_wide <= 0x0000ffff)
            n = 3;
        else if (w_wide <= 0x001fffff)
            n = 4;
        else if (w_wide <= 0x03ffffff)
            n = 5;
        else
            n = 6;  /// if (w_wide <= 0x7fffffff)

        total += n;

        if (out == NULL) continue;
        if (size_t(lim - p) <= n - 1) return 0;  // no space left

        // Extract the wchar_t as big-endian. If wchar_t is UCS-16, the first two bytes will be 0.
        unsigned char oc[4];
        uint32_t w_tmp = *w;
        oc[3] = w_tmp & 0xFF;
        w_tmp >>= 8;
        oc[2] = w_tmp & 0xFF;
        w_tmp >>= 8;
        oc[1] = w_tmp & 0xFF;
        w_tmp >>= 8;
        oc[0] = w_tmp & 0xFF;

        switch (n) {
            case 1: {
                p[0] = oc[3];
                break;
            }
            case 2: {
                p[1] = _NXT | (oc[3] & 0x3f);
                p[0] = _SEQ2 | (oc[3] >> 6) | ((oc[2] & 0x07) << 2);
                break;
            }
            case 3: {
                p[2] = _NXT | (oc[3] & 0x3f);
                p[1] = _NXT | (oc[3] >> 6) | ((oc[2] & 0x0f) << 2);
                p[0] = _SEQ3 | ((oc[2] & 0xf0) >> 4);
                break;
            }
            case 4: {
                p[3] = _NXT | (oc[3] & 0x3f);
                p[2] = _NXT | (oc[3] >> 6) | ((oc[2] & 0x0f) << 2);
                p[1] = _NXT | ((oc[2] & 0xf0) >> 4) | ((oc[1] & 0x03) << 4);
                p[0] = _SEQ4 | ((oc[1] & 0x1f) >> 2);
                break;
            }
        }

        // NOTE: do not check here for forbitten UTF-8 characters. They cannot appear here because
        // we do proper convertion.
        p += n;
    }

    return total;
}