module checkedint;

debug {
	import std.conv;
	import std.traits;
	
	class OverflowException : Exception {
		this( string msg, string file = __FILE__, uint line = __LINE__ ) {
			super( msg, file, line );
		}
	}
	
	struct Checked( T ) if ( isIntegral!T ) {
		T payload;
		
		alias payload this;
		
		pure
		this( U )( U value, string file = __FILE__, int line = __LINE__ ) if ( isIntegral!U ) {
			if ( value < T.min || value > T.max ) {
				debug throw new OverflowException( "Overflow!", file, line );
			}
			payload = cast( T )value;
		}
		
		pure
		Checked opUnary( string op, string file = __FILE__, int line = __LINE__ )( ) if ( !( op == "++" || op == "--" ) ) {
			Checked tmp = mixin( op ~ " payload" );
			debug asm {
				jo overflow;
			}
			return tmp;
		overflow:
			debug throw new OverflowException( "Overflow!", file, line );
		}
		
		pure
		ref Checked opUnary( string op, string file = __FILE__, int line = __LINE__ )( ) if ( op == "++" || op == "--" ) {
			payload = mixin( op ~ " payload" );
			debug asm {
				jo overflow;
			}
			return this;
		overflow:
			debug throw new OverflowException( "Overflow!", file, line );
		}
		
		const pure nothrow
		Checked opBinary( string op, string file = __FILE__, int line = __LINE__, U )( U other ) if ( isIntegral!U || is( U u == Checked!V, V ) ) {
			Checked tmp = mixin( "payload " ~ op ~ " other" );
			debug asm {
				jo overflow;
			}
			return tmp;
		overflow:
			debug throw new OverflowException( "Overflow!", file, line );
		}
		
		pure nothrow
		ref Checked opOpAssign( string op, string file = __FILE__, int line = __LINE__, U )( U other ) if ( isIntegral!U || is( U u == Checked!V, V ) ) {
			mixin( "payload " ~ op ~ "= other;" );
			debug asm {
				jo overflow;
			}
			return this;
		overflow:
			debug throw new OverflowException( "Overflow!", file, line );
		}
		
		pure
		ref Checked opAssign( string file = __FILE__, int line = __LINE__, U )( U value ) if ( isIntegral!U || is( U u == Checked!V, V ) ) {
			if ( value < T.min || value > T.max ) {
				debug throw new OverflowException( "Overflow!", file, line );
			}
			payload = cast( T )value;
			return this;
		}

		unittest {
			import core.exception;
			import std.exception;
			
			Checked a;
			a = 3;
			assertNotThrown!OverflowException( a + a, "Overflow on 3 + 3 for " ~ Checked.stringof );
			a = 3;
			assertNotThrown!OverflowException( a - a, "Overflow on 3 - 3 for " ~ Checked.stringof );
			a = 3;
			assertNotThrown!OverflowException( a * a, "Overflow on 3 * 3 for " ~ Checked.stringof );
			a = 3;
			assertNotThrown!OverflowException( a / a, "Overflow on 3 / 3 for " ~ Checked.stringof );
			static if( !is( T == uint ) && !is( T == ulong ) ) {
				a = Checked.max;
				assertThrown!OverflowException( a + 1, "No overflow on " ~ Checked.stringof ~ ".max(" ~ to!string( Checked.max ) ~ ") + 1 for " ~ Checked.stringof );
			}
			static if( !is( T == int ) && !is( T == long ) && !is( T == uint ) && !is( T == ulong ) ) {
				a = Checked.min;
				assertThrown!OverflowException( a - 1, "No overflow on " ~ Checked.stringof ~ ".min(" ~ to!string( Checked.min ) ~ ") - 1 for " ~ Checked.stringof );
			}
			static if( !is( T == uint ) && !is( T == long ) && !is( T == ulong ) ) {
				a = Checked.max;
				assertThrown!OverflowException( a << 1, "No overflow on " ~ Checked.stringof ~ ".max (" ~ to!string( Checked.max ) ~ ") << 1" );
			}
			static if ( !isUnsigned!T ) {
				static if( !is( T == int ) && !is( T == long ) ) {
					a = Checked.min;
					assertThrown!OverflowException( a << 1, "No overflow on " ~ Checked.stringof ~ ".min (" ~ to!string( Checked.min ) ~ ") << 1" );
				}
				a = Checked.min;
				assertThrown!OverflowException( --a,    "No overflow on --" ~ Checked.stringof ~ ".min(" ~ to!string( Checked.min ) ~ ") for " ~ Checked.stringof );
				a = Checked.min;
				assertThrown!OverflowException( a--,    "No overflow on "   ~ Checked.stringof ~ ".min(" ~ to!string( Checked.min ) ~ ")-- for " ~ Checked.stringof );
				a = Checked.min;
				assertThrown!OverflowException( -a,     "No overflow on -"  ~ Checked.stringof ~ ".min(" ~ to!string( Checked.min ) ~ ") for " ~ Checked.stringof );
				a = Checked.max;
				assertThrown!OverflowException( ++a,    "No overflow on ++" ~ Checked.stringof ~ ".max(" ~ to!string( Checked.max ) ~ ") for " ~ Checked.stringof );
				a = Checked.max;
				assertThrown!OverflowException( a++,    "No overflow on "   ~ Checked.stringof ~ ".max(" ~ to!string( Checked.max ) ~ ")++ for " ~ Checked.stringof );
				a = Checked.max;
				assertThrown!OverflowException( a += 1, "No overflow on "   ~ Checked.stringof ~ ".max(" ~ to!string( Checked.max ) ~ ") += 1 for " ~ Checked.stringof );
				static if( !is( T == int ) && !is( T == long ) ) {
					a = Checked.max;
					assertThrown!OverflowException( a *= 2, "No overflow on " ~ Checked.stringof ~ ".max(" ~ to!string( Checked.max ) ~ ") *= 2 for " ~ Checked.stringof );
				}
				a = Checked.min;
				assertThrown!OverflowException( a -= 1, "No overflow on " ~ Checked.stringof ~ ".min(" ~ to!string( Checked.min ) ~ ") -= -1 for " ~ Checked.stringof );
				a = Checked.min;
				assertThrown!OverflowException( a <<= 1, "No overflow on " ~ Checked.stringof ~ ".max (" ~ to!string( Checked.max ) ~ ") <<= 1" );
				a = Checked.max;
				assertThrown!OverflowException( a <<= 1, "No overflow on " ~ Checked.stringof ~ ".max (" ~ to!string( Checked.max ) ~ ") <<= 1" );
			}
		}
	}
} else {
	template Checked( T ) if ( isIntegral!T ) {
		alias T Checked;
	}
}

unittest {
	import std.typetuple;
	foreach ( e; TypeTuple!( byte, short, int, long ) ) {
		Checked!e a;
		Checked!(Unsigned!e) b;
	}
}

void main( ) {}