/*
 * Copyright (C) 2015 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#define LOG_TAG "Minikin"

#include "FontLanguage.h"

#include <algorithm>
#include <hb.h>
#include <string.h>
#include <unicode/uloc.h>

namespace minikin {

#define SCRIPT_TAG(c1, c2, c3, c4) \
        (((uint32_t)(c1)) << 24 | ((uint32_t)(c2)) << 16 | ((uint32_t)(c3)) <<  8 | \
         ((uint32_t)(c4)))

// Check if a language code supports emoji according to its subtag
static bool isEmojiSubtag(const char* buf, size_t bufLen, const char* subtag, size_t subtagLen) {
    if (bufLen < subtagLen) {
        return false;
    }
    if (strncmp(buf, subtag, subtagLen) != 0) {
        return false;  // no match between two strings
    }
    return (bufLen == subtagLen || buf[subtagLen] == '\0' ||
            buf[subtagLen] == '-' || buf[subtagLen] == '_');
}

// Pack the three letter code into 15 bits and stored to 16 bit integer. The highest bit is 0.
// For the region code, the letters must be all digits in three letter case, so the number of
// possible values are 10. For the language code, the letters must be all small alphabets, so the
// number of possible values are 26. Thus, 5 bits are sufficient for each case and we can pack the
// three letter language code or region code to 15 bits.
//
// In case of two letter code, use fullbit(0x1f) for the first letter instead.
static uint16_t packLanguageOrRegion(const char* c, size_t length, uint8_t twoLetterBase,
        uint8_t threeLetterBase) {
    if (length == 2) {
        return 0x7c00u |  // 0x1fu << 10
                (uint16_t)(c[0] - twoLetterBase) << 5 |
                (uint16_t)(c[1] - twoLetterBase);
    } else {
        return ((uint16_t)(c[0] - threeLetterBase) << 10) |
                (uint16_t)(c[1] - threeLetterBase) << 5 |
                (uint16_t)(c[2] - threeLetterBase);
    }
}

static size_t unpackLanguageOrRegion(uint16_t in, char* out, uint8_t twoLetterBase,
        uint8_t threeLetterBase) {
    uint8_t first = (in >> 10) & 0x1f;
    uint8_t second = (in >> 5) & 0x1f;
    uint8_t third = in & 0x1f;

    if (first == 0x1f) {
        out[0] = second + twoLetterBase;
        out[1] = third + twoLetterBase;
        return 2;
    } else {
        out[0] = first + threeLetterBase;
        out[1] = second + threeLetterBase;
        out[2] = third + threeLetterBase;
        return 3;
    }
}

// Find the next '-' or '_' index from startOffset position. If not found, returns bufferLength.
static size_t nextDelimiterIndex(const char* buffer, size_t bufferLength, size_t startOffset) {
    for (size_t i = startOffset; i < bufferLength; ++i) {
        if (buffer[i] == '-' || buffer[i] == '_') {
            return i;
        }
    }
    return bufferLength;
}

static inline bool isLowercase(char c) {
    return 'a' <= c && c <= 'z';
}

static inline bool isUppercase(char c) {
    return 'A' <= c && c <= 'Z';
}

static inline bool isDigit(char c) {
    return '0' <= c && c <= '9';
}

// Returns true if the buffer is valid for language code.
static inline bool isValidLanguageCode(const char* buffer, size_t length) {
    if (length != 2 && length != 3) return false;
    if (!isLowercase(buffer[0])) return false;
    if (!isLowercase(buffer[1])) return false;
    if (length == 3 && !isLowercase(buffer[2])) return false;
    return true;
}

// Returns true if buffer is valid for script code. The length of buffer must be 4.
static inline bool isValidScriptCode(const char* buffer) {
    return isUppercase(buffer[0]) && isLowercase(buffer[1]) && isLowercase(buffer[2]) &&
        isLowercase(buffer[3]);
}

// Returns true if the buffer is valid for region code.
static inline bool isValidRegionCode(const char* buffer, size_t length) {
    return (length == 2 && isUppercase(buffer[0]) && isUppercase(buffer[1])) ||
            (length == 3 && isDigit(buffer[0]) && isDigit(buffer[1]) && isDigit(buffer[2]));
}

// Parse BCP 47 language identifier into internal structure
FontLanguage::FontLanguage(const char* buf, size_t length) : FontLanguage() {
    size_t firstDelimiterPos = nextDelimiterIndex(buf, length, 0);
    if (isValidLanguageCode(buf, firstDelimiterPos)) {
        mLanguage = packLanguageOrRegion(buf, firstDelimiterPos, 'a', 'a');
    } else {
        // We don't understand anything other than two-letter or three-letter
        // language codes, so we skip parsing the rest of the string.
        return;
    }

    if (firstDelimiterPos == length) {
        mHbLanguage = hb_language_from_string(getString().c_str(), -1);
        return;  // Language code only.
    }

    size_t nextComponentStartPos = firstDelimiterPos + 1;
    size_t nextDelimiterPos = nextDelimiterIndex(buf, length, nextComponentStartPos);
    size_t componentLength = nextDelimiterPos - nextComponentStartPos;

    if (componentLength == 4) {
        // Possibly script code.
        const char* p = buf + nextComponentStartPos;
        if (isValidScriptCode(p)) {
            mScript = SCRIPT_TAG(p[0], p[1], p[2], p[3]);
            mSubScriptBits = scriptToSubScriptBits(mScript);
        }

        if (nextDelimiterPos == length) {
            mHbLanguage = hb_language_from_string(getString().c_str(), -1);
            mEmojiStyle = resolveEmojiStyle(buf, length, mScript);
            return;  // No region code.
        }

        nextComponentStartPos = nextDelimiterPos + 1;
        nextDelimiterPos = nextDelimiterIndex(buf, length, nextComponentStartPos);
        componentLength = nextDelimiterPos - nextComponentStartPos;
    }

    if (componentLength == 2 || componentLength == 3) {
        // Possibly region code.
        const char* p = buf + nextComponentStartPos;
        if (isValidRegionCode(p, componentLength)) {
            mRegion = packLanguageOrRegion(p, componentLength, 'A', '0');
        }
    }

    mHbLanguage = hb_language_from_string(getString().c_str(), -1);
    mEmojiStyle = resolveEmojiStyle(buf, length, mScript);
}

// static
FontLanguage::EmojiStyle FontLanguage::resolveEmojiStyle(const char* buf, size_t length,
        uint32_t script) {
    // First, lookup emoji subtag.
    // 10 is the length of "-u-em-text", which is the shortest emoji subtag,
    // unnecessary comparison can be avoided if total length is smaller than 10.
    const size_t kMinSubtagLength = 10;
    if (length >= kMinSubtagLength) {
        static const char kPrefix[] = "-u-em-";
        const char *pos = std::search(buf, buf + length, kPrefix, kPrefix + strlen(kPrefix));
        if (pos != buf + length) {  // found
            pos += strlen(kPrefix);
            const size_t remainingLength = length - (pos - buf);
            if (isEmojiSubtag(pos, remainingLength, "emoji", 5)){
                return EMSTYLE_EMOJI;
            } else if (isEmojiSubtag(pos, remainingLength, "text", 4)){
                return EMSTYLE_TEXT;
            } else if (isEmojiSubtag(pos, remainingLength, "default", 7)){
                return EMSTYLE_DEFAULT;
            }
        }
    }

    // If no emoji subtag was provided, resolve the emoji style from script code.
    if (script == SCRIPT_TAG('Z', 's', 'y', 'e')) {
        return EMSTYLE_EMOJI;
    } else if (script == SCRIPT_TAG('Z', 's', 'y', 'm')) {
        return EMSTYLE_TEXT;
    }

    return EMSTYLE_EMPTY;
}

//static
uint8_t FontLanguage::scriptToSubScriptBits(uint32_t script) {
    uint8_t subScriptBits = 0u;
    switch (script) {
        case SCRIPT_TAG('B', 'o', 'p', 'o'):
            subScriptBits = kBopomofoFlag;
            break;
        case SCRIPT_TAG('H', 'a', 'n', 'g'):
            subScriptBits = kHangulFlag;
            break;
        case SCRIPT_TAG('H', 'a', 'n', 'b'):
            // Bopomofo is almost exclusively used in Taiwan.
            subScriptBits = kHanFlag | kBopomofoFlag;
            break;
        case SCRIPT_TAG('H', 'a', 'n', 'i'):
            subScriptBits = kHanFlag;
            break;
        case SCRIPT_TAG('H', 'a', 'n', 's'):
            subScriptBits = kHanFlag | kSimplifiedChineseFlag;
            break;
        case SCRIPT_TAG('H', 'a', 'n', 't'):
            subScriptBits = kHanFlag | kTraditionalChineseFlag;
            break;
        case SCRIPT_TAG('H', 'i', 'r', 'a'):
            subScriptBits = kHiraganaFlag;
            break;
        case SCRIPT_TAG('H', 'r', 'k', 't'):
            subScriptBits = kKatakanaFlag | kHiraganaFlag;
            break;
        case SCRIPT_TAG('J', 'p', 'a', 'n'):
            subScriptBits = kHanFlag | kKatakanaFlag | kHiraganaFlag;
            break;
        case SCRIPT_TAG('K', 'a', 'n', 'a'):
            subScriptBits = kKatakanaFlag;
            break;
        case SCRIPT_TAG('K', 'o', 'r', 'e'):
            subScriptBits = kHanFlag | kHangulFlag;
            break;
    }
    return subScriptBits;
}

std::string FontLanguage::getString() const {
    if (isUnsupported()) {
        return "und";
    }
    char buf[16];
    size_t i = unpackLanguageOrRegion(mLanguage, buf, 'a', 'a');
    if (mScript != 0) {
        buf[i++] = '-';
        buf[i++] = (mScript >> 24) & 0xFFu;
        buf[i++] = (mScript >> 16) & 0xFFu;
        buf[i++] = (mScript >> 8) & 0xFFu;
        buf[i++] = mScript & 0xFFu;
    }
    if (mRegion != INVALID_CODE) {
        buf[i++] = '-';
        i += unpackLanguageOrRegion(mRegion, buf + i, 'A', '0');
    }
    return std::string(buf, i);
}

bool FontLanguage::isEqualScript(const FontLanguage& other) const {
    return other.mScript == mScript;
}

// static
bool FontLanguage::supportsScript(uint8_t providedBits, uint8_t requestedBits) {
    return requestedBits != 0 && (providedBits & requestedBits) == requestedBits;
}

bool FontLanguage::supportsHbScript(hb_script_t script) const {
    static_assert(SCRIPT_TAG('J', 'p', 'a', 'n') == HB_TAG('J', 'p', 'a', 'n'),
                  "The Minikin script and HarfBuzz hb_script_t have different encodings.");
    if (script == mScript) return true;
    return supportsScript(mSubScriptBits, scriptToSubScriptBits(script));
}

int FontLanguage::calcScoreFor(const FontLanguages& supported) const {
    bool languageScriptMatch = false;
    bool subtagMatch = false;
    bool scriptMatch = false;

    for (size_t i = 0; i < supported.size(); ++i) {
        if (mEmojiStyle != EMSTYLE_EMPTY &&
               mEmojiStyle == supported[i].mEmojiStyle) {
            subtagMatch = true;
            if (mLanguage == supported[i].mLanguage) {
                return 4;
            }
        }
        if (isEqualScript(supported[i]) ||
                supportsScript(supported[i].mSubScriptBits, mSubScriptBits)) {
            scriptMatch = true;
            if (mLanguage == supported[i].mLanguage) {
                languageScriptMatch = true;
            }
        }
    }

    if (supportsScript(supported.getUnionOfSubScriptBits(), mSubScriptBits)) {
        scriptMatch = true;
        if (mLanguage == supported[0].mLanguage && supported.isAllTheSameLanguage()) {
            return 3;
        }
    }

    if (languageScriptMatch) {
        return 3;
    } else if (subtagMatch) {
        return 2;
    } else if (scriptMatch) {
        return 1;
    }
    return 0;
}

FontLanguages::FontLanguages(std::vector<FontLanguage>&& languages)
    : mLanguages(std::move(languages)) {
    if (mLanguages.empty()) {
        return;
    }

    const FontLanguage& lang = mLanguages[0];

    mIsAllTheSameLanguage = true;
    mUnionOfSubScriptBits = lang.mSubScriptBits;
    for (size_t i = 1; i < mLanguages.size(); ++i) {
        mUnionOfSubScriptBits |= mLanguages[i].mSubScriptBits;
        if (mIsAllTheSameLanguage && lang.mLanguage != mLanguages[i].mLanguage) {
            mIsAllTheSameLanguage = false;
        }
    }
}

#undef SCRIPT_TAG
}  // namespace minikin