// SPDX-License-Identifier: MIT OR MPL-2.0 OR LGPL-2.1-or-later OR GPL-2.0-or-later
// Copyright 2010, SIL International, All rights reserved.

#pragma once

#include <cstdlib>
#include "graphite2/Types.h"

typedef gr_uint8        uint8;
typedef gr_uint8        byte;
typedef gr_uint16       uint16;
typedef gr_uint32       uint32;
typedef gr_int8         int8;
typedef gr_int16        int16;
typedef gr_int32        int32;

namespace graphite2 {

typedef uint32 	uchar_t;

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

	static void 	put(codeunit_t * cp, const uchar_t , int8 & len) throw();
	static uchar_t	get(const codeunit_t * cp, int8 & len) throw();
};


template <>
struct _utf_codec<32>
{
private:
	static const uchar_t	limit = 0x110000;
public:
	typedef	uint32	codeunit_t;

	inline
	static void put(codeunit_t * cp, const uchar_t usv, int8 & l) throw()
	{
		*cp = usv; l = 1;
	}

	inline
	static uchar_t get(const codeunit_t * cp, int8 & l) throw()
	{
		if (cp[0] < limit)	{ l = 1;  return cp[0]; }
		else				{ l = -1; return 0xFFFD; }
	}
};


template <>
struct _utf_codec<16>
{
private:
	static const int32	lead_offset		 = 0xD800 - (0x10000 >> 10);
	static const int32	surrogate_offset = 0x10000 - (0xD800 << 10) - 0xDC00;
public:
	typedef	uint16	codeunit_t;

	inline
	static void put(codeunit_t * cp, const uchar_t usv, int8 & 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 & l) throw()
	{
		const uint32	uh = cp[0];
		l = 1;

		if (0xD800 > uh || uh > 0xDFFF)	{ return uh; }
		const uint32 ul = cp[1];
		if (uh > 0xDBFF || 0xDC00 > ul || ul > 0xDFFF) { l = -1; return 0xFFFD; }
		++l;
		return (uh<<10) + ul + surrogate_offset;
	}
};


template <>
struct _utf_codec<8>
{
private:
	static const int8 sz_lut[16];
	static const byte mask_lut[5];


public:
	typedef	uint8	codeunit_t;

	inline
	static void put(codeunit_t * cp, const uchar_t usv, int8 & 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 & l) throw()
	{
		const int8 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)
		{
			l = -l;
			return 0xFFFD;
		}
		return u;
	}
};


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

	C 	  		  * cp;
	mutable int8	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;
};


typedef utf<uint32>	utf32;
typedef utf<uint16>	utf16;
typedef utf<uint8>	utf8;

} // namespace graphite2
