// text.cpp

/*    Copyright 2009 10gen Inc.
 *
 *    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.
 */

#include "../pch.h"
#include "text.h"

namespace mongo{
    inline int leadingOnes(unsigned char c){
        if (c < 0x80) return 0;
        static const char _leadingOnes[128] = {
            1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, // 0x80 - 0x8F
            1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, // 0x90 - 0x99
            1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, // 0xA0 - 0xA9
            1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, // 0xB0 - 0xB9
            2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, // 0xC0 - 0xC9
            2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, // 0xD0 - 0xD9
            3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, // 0xE0 - 0xE9
            4, 4, 4, 4, 4, 4, 4, 4,                         // 0xF0 - 0xF7
                                    5, 5, 5, 5,             // 0xF8 - 0xFB
                                                6, 6,       // 0xFC - 0xFD
                                                      7,    // 0xFE
                                                         8, // 0xFF
        };
        return _leadingOnes[c & 0x7f];

    }

    bool isValidUTF8(const char *s){
        int left = 0; // how many bytes are left in the current codepoint
        while (*s){
            const unsigned char c = (unsigned char) *(s++);
            const int ones = leadingOnes(c);
            if (left){
                if (ones != 1) return false; // should be a continuation byte
                left--;
            }else{
                if (ones == 0) continue; // ASCII byte
                if (ones == 1) return false; // unexpected continuation byte
                if (c > 0xF4) return false; // codepoint too large (< 0x10FFFF)
                if (c == 0xC0 || c == 0xC1) return false; // codepoints <= 0x7F shouldn't be 2 bytes

                // still valid
                left = ones-1;
            }
        }
        if (left!=0) return false; // string ended mid-codepoint
        return true;
    }
}