/*
 * This file was automatically generated by sel-utils and
 * released under the MIT License.
 * 
 * License: https://github.com/sel-project/sel-utils/blob/master/LICENSE
 * Repository: https://github.com/sel-project/sel-utils
 */

module sul.utils.var;

import std.traits : isNumeric, isIntegral, isSigned, isUnsigned, Unsigned;

struct var(T) if(isNumeric!T && isIntegral!T && T.sizeof > 1) {
	
	alias U = Unsigned!T;
	
	public static immutable U MASK = U.max - 0x7F;
	public static immutable size_t MAX_BYTES = T.sizeof * 8 / 7 + (T.sizeof * 8 % 7 == 0 ? 0 : 1);
	public static immutable size_t RIGHT_SHIFT = (T.sizeof * 8) - 1;
	
	public static pure nothrow @safe ubyte[] encode(T value) {
		ubyte[] buffer;
		static if(isUnsigned!T) {
			U unsigned = value;
		} else {
			U unsigned;
			if(value >= 0) {
				unsigned = cast(U)(value << 1);
			} else if(value < 0) {
				unsigned = cast(U)((-value << 1) - 1);
			}
		}
		while((unsigned & MASK) != 0) {
			buffer ~= unsigned & 0x7F | 0x80;
			unsigned >>>= 7;
		}
		buffer ~= unsigned & 0xFF;
		return buffer;
	}

	public static pure nothrow @trusted T decode(ubyte[] buffer, size_t index=0) {
		return decode(buffer, &index);
	}
	
	public static pure nothrow @safe T decode(ubyte[] buffer, size_t* index) {
		if(buffer.length <= *index) return T.init;
		U unsigned = 0;
		size_t j, k;
		do {
			k = buffer[*index];
			unsigned |= cast(U)(k & 0x7F) << (j++ * 7);
		} while(++*index < buffer.length && j < MAX_BYTES && (k & 0x80) != 0);
		static if(isUnsigned!T) {
			return unsigned;
		} else {
			T value = unsigned >> 1;
			if(unsigned & 1) {
				value++;
				return -value;
			} else {
				return value;
			}
		}
	}

	public static pure nothrow @trusted T fromBuffer(ref ubyte[] buffer) {
		size_t index = 0;
		auto ret = decode(buffer, &index);
		buffer = buffer[index..$];
		return ret;
	}
	
	public enum stringof = "var" ~ T.stringof;
	
}

alias varshort = var!short;

alias varushort = var!ushort;

alias varint = var!int;

alias varuint = var!uint;

alias varlong = var!long;

alias varulong = var!ulong;