/*  GRAPHITE2 LICENSING

    Copyright 2011, SIL International
    All rights reserved.

    This library is free software; you can redistribute it and/or modify
    it under the terms of the GNU Lesser General Public License as published
    by the Free Software Foundation; either version 2.1 of 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
    Lesser General Public License for more details.

    You should also have received a copy of the GNU Lesser General Public
    License along with this library in the file named "LICENSE".
    If not, write to the Free Software Foundation, 51 Franklin Street,
    Suite 500, Boston, MA 02110-1335, USA or visit their web page on the
    internet at http://www.fsf.org/licenses/lgpl.html.

Alternatively, the contents of this file may be used under the terms of the
Mozilla Public License (http://mozilla.org/MPL) or the GNU General Public
License, as published by the Free Software Foundation, either version 2
of the License or (at your option) any later version.
*/
#pragma once

#include <cstddef>
#include <cstdlib>
#include <cstdint>

using std::int8_t;
using std::uint8_t;
using std::ptrdiff_t;

typedef uint32_t  uchar_t;

template <int N>
struct _utf_codec
{
    typedef uchar_t codeunit_t;

    static void     put(codeunit_t * cp, const uchar_t , int8_t & len) throw();
    static uchar_t  get(const codeunit_t * cp, int8_t & len) throw();
    static bool     validate(const codeunit_t * s, const codeunit_t * e) throw();
};


template <>
struct _utf_codec<32>
{
private:
    static const uchar_t    limit = 0x110000;
public:
    typedef uint32_t  codeunit_t;

    inline
    static void put(codeunit_t * cp, const uchar_t usv, int8_t & l) throw()
    {
        *cp = usv; l = 1;
    }

    inline
    static uchar_t get(const codeunit_t * cp, int8_t & l) throw()
    {
        if (cp[0] < limit)  { l = 1;  return cp[0]; }
        else                { l = -1; return 0xFFFD; }
    }

    inline
    static bool validate(codeunit_t * s, codeunit_t * e) throw()
    {
        return e > s;
    }
};


template <>
struct _utf_codec<16>
{
private:
    static const int32_t  lead_offset      = 0xD800 - (0x10000 >> 10);
    static const int32_t  surrogate_offset = 0x10000 - (0xD800 << 10) - 0xDC00;
public:
    typedef uint16_t  codeunit_t;

    inline
    static void put(codeunit_t * cp, const uchar_t usv, int8_t & l) throw()
    {
        if (usv < 0x10000)  { l = 1; cp[0] = codeunit_t(usv); }
        else
        {
            cp[0] = codeunit_t(lead_offset + (usv >> 10));
            cp[1] = codeunit_t(0xDC00 + (usv & 0x3FF));
            l = 2;
        }
    }

    inline
    static uchar_t get(const codeunit_t * cp, int8_t & l) throw()
    {
        const uint32_t    uh = cp[0];
        l = 1;

        if (uh < 0xD800|| uh > 0xDFFF) { return uh; }
        const uint32_t ul = cp[1];
        if (uh > 0xDBFF || ul < 0xDC00 || ul > 0xDFFF) { l = -1; return 0xFFFD; }
        ++l;
        return (uh<<10) + ul + surrogate_offset;
    }

    inline
    static bool validate(codeunit_t * s, codeunit_t * e) throw()
    {
        const ptrdiff_t n = e-s;
        if (n <= 0) return n == 0;
        const uint32_t u = *(s+(n-1)); // Get the last codepoint
        return (u < 0xD800 || u > 0xDBFF);
    }
};


template <>
struct _utf_codec<8>
{
private:
    static const uchar_t    limit = 0x110000;
    static const int8_t sz_lut[16];
    static const uint8_t mask_lut[5];


public:
    typedef uint8_t   codeunit_t;

    inline
    static void put(codeunit_t * cp, const uchar_t usv, int8_t & l) throw()
    {
        if (usv < 0x80)     {l = 1; cp[0] = usv; return; }
        if (usv < 0x0800)   {l = 2; cp[0] = 0xC0 + (usv >> 6);  cp[1] = 0x80 + (usv & 0x3F); return; }
        if (usv < 0x10000)  {l = 3; cp[0] = 0xE0 + (usv >> 12); cp[1] = 0x80 + ((usv >> 6) & 0x3F);  cp[2] = 0x80 + (usv & 0x3F); return; }
        else                {l = 4; cp[0] = 0xF0 + (usv >> 18); cp[1] = 0x80 + ((usv >> 12) & 0x3F); cp[2] = 0x80 + ((usv >> 6) & 0x3F); cp[3] = 0x80 + (usv & 0x3F); return; }
    }

    inline
    static uchar_t get(const codeunit_t * cp, int8_t & l) throw()
    {
        const int8_t seq_sz = sz_lut[*cp >> 4];
        uchar_t u = *cp & mask_lut[seq_sz];
        l = 1;
        bool toolong = false;

        switch(seq_sz) {
            case 4:     u <<= 6; u |= *++cp & 0x3F; if (*cp >> 6 != 2) break; ++l; toolong  = (u < 0x10);
                // no break
            case 3:     u <<= 6; u |= *++cp & 0x3F; if (*cp >> 6 != 2) break; ++l; toolong |= (u < 0x20);
                // no break
            case 2:     u <<= 6; u |= *++cp & 0x3F; if (*cp >> 6 != 2) break; ++l; toolong |= (u < 0x80);
                // no break
            case 1:     break;
            case 0:     l = -1; return 0xFFFD;
        }

        if (l != seq_sz || toolong || u >= limit)
        {
            l = -l;
            return 0xFFFD;
        }
        return u;
    }

    inline
    static bool validate(codeunit_t * s, codeunit_t * e) throw()
    {
        const ptrdiff_t n = e-s;
        if (n <= 0) return n == 0;
        s += (n-1);
        if (*s < 0x80) return true;
        if (*s >= 0xC0) return false;
        if (n == 1) return true;
        if (*--s < 0x80) return true;
        if (*s >= 0xe0) return false;
        if (n == 2 || *s >= 0xC0) return true;
        if (*--s < 0x80) return true;
        if (*s >= 0xF0) return false;
        return true;
    }

};


template <typename C>
class _utf_iterator
{
    typedef _utf_codec<sizeof(C)*8> codec;

    C             * cp;
    mutable int8_t    sl;

public:
    typedef C           codeunit_type;
    typedef uchar_t     value_type;
    typedef uchar_t   * pointer;

    class reference
    {
        const _utf_iterator & _i;

        reference(const _utf_iterator & i): _i(i) {}
    public:
        operator value_type () const throw ()                   { return codec::get(_i.cp, _i.sl); }
        reference & operator = (const value_type usv) throw()   { codec::put(_i.cp, usv, _i.sl); return *this; }

        friend class _utf_iterator;
    };


    _utf_iterator(const void * us=0)    : cp(reinterpret_cast<C *>(const_cast<void *>(us))), sl(1) { }

    _utf_iterator   & operator ++ ()    { cp += abs(sl); return *this; }
    _utf_iterator   operator ++ (int)   { _utf_iterator tmp(*this); operator++(); return tmp; }

    bool operator == (const _utf_iterator & rhs) const throw() { return cp >= rhs.cp; }
    bool operator != (const _utf_iterator & rhs) const throw() { return !operator==(rhs); }

    reference   operator * () const throw() { return *this; }
    pointer     operator ->() const throw() { return &operator *(); }

    operator codeunit_type * () const throw() { return cp; }

    bool error() const throw()  { return sl < 1; }
};

template <typename C>
struct utf
{
    typedef typename _utf_codec<sizeof(C)*8>::codeunit_t codeunit_t;

    typedef _utf_iterator<C>        iterator;
    typedef _utf_iterator<const C>  const_iterator;

    inline
    static bool validate(codeunit_t * s, codeunit_t * e) throw() {
        return _utf_codec<sizeof(C)*8>::validate(s,e);
    }
};


typedef utf<uint32_t> utf32;
typedef utf<uint16_t> utf16;
typedef utf<uint8_t>  utf8;