//
// aegis - project change supervisor
// Copyright (C) 2014 Peter Miller
//
// This program is free software; you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation; either version 3 of the License, or (at
// your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
// General Public License for more details.
//
// You should have received a copy of the GNU General Public License along
// with this program. If not, see <http://www.gnu.org/licenses/>.
//

#include <common/nstring.h>


bool
nstring::looks_like_utf8(void)
    const
{
    const char *cp = c_str();
    const char *end = cp + size();
    unsigned octets_remaining = 0;
    while (cp < end)
    {
        unsigned char c = *cp++;
        if (octets_remaining == 0)
        {
            if ((c & 0x80) == 0)
            {
                // make sure we like the character
                switch (c)
                {
                case '\b':
                case '\t':
                case '\n':
                case '\v':
                case '\f':
                case '\r':
                case ' ':
                case '!':
                case '"':
                case '#':
                case '$':
                case '%':
                case '&':
                case '\'':
                case '(':
                case ')':
                case '*':
                case '+':
                case ',':
                case '-':
                case '.':
                case '/':
                case '0':
                case '1':
                case '2':
                case '3':
                case '4':
                case '5':
                case '6':
                case '7':
                case '8':
                case '9':
                case ':':
                case ';':
                case '<':
                case '=':
                case '>':
                case '?':
                case '@':
                case 'A':
                case 'B':
                case 'C':
                case 'D':
                case 'E':
                case 'F':
                case 'G':
                case 'H':
                case 'I':
                case 'J':
                case 'K':
                case 'L':
                case 'M':
                case 'N':
                case 'O':
                case 'P':
                case 'Q':
                case 'R':
                case 'S':
                case 'T':
                case 'U':
                case 'V':
                case 'W':
                case 'X':
                case 'Y':
                case 'Z':
                case '[':
                case '\\':
                case ']':
                case '^':
                case '_':
                case '`':
                case 'a':
                case 'b':
                case 'c':
                case 'd':
                case 'e':
                case 'f':
                case 'g':
                case 'h':
                case 'i':
                case 'j':
                case 'k':
                case 'l':
                case 'm':
                case 'n':
                case 'o':
                case 'p':
                case 'q':
                case 'r':
                case 's':
                case 't':
                case 'u':
                case 'v':
                case 'w':
                case 'x':
                case 'y':
                case 'z':
                case '{':
                case '|':
                case '}':
                case '~':
                    break;

                default:
                    // not a valid utf-8 encoding
                    not_a_valid_encoding:
                    return false;
                }
                continue;
            }
            if ((c & 0xC0) == 0x80)
            {
               // unexpected continuation byte
               goto not_a_valid_encoding;
            }
            if ((c & 0xE0) == 0xC0)
            {
                octets_remaining = 1;
                continue;
            }
            if ((c & 0xF0) == 0xE0)
            {
                octets_remaining = 2;
                continue;
            }
            if ((c & 0xF8) == 0xF0)
            {
                octets_remaining = 3;
                continue;
            }
        }
        else
        {
            if ((c & 0xC0) == 0x80)
            {
                // continuation byte
                --octets_remaining;
                continue;
            }
        }
        goto not_a_valid_encoding;
    }
    return true;
}


// vim: set ts=8 sw=4 et :