package main

import "fmt"

// A wire is modeled as a channel of booleans.
// You can feed it a single value without blocking.
// Reading a value blocks until a value is available.
type Wire chan bool

func MkWire() Wire {
	return make(Wire, 1)
}

// A source for zero values.
func Zero() (r Wire) {
	r = MkWire()
	go func() {
		for {
			r <- false
		}
	}()
	return
}

// And gate.
func And(a, b Wire) (r Wire) {
	r = MkWire()
	go func() {
		for {
			r <- (<-a && <-b)
		}
	}()
	return
}

// Or gate.
func Or(a, b Wire) (r Wire) {
	r = MkWire()
	go func() {
		for {
			r <- (<-a || <-b)
		}
	}()
	return
}

// Not gate.
func Not(a Wire) (r Wire) {
	r = MkWire()
	go func() {
		for {
			r <- !(<-a)
		}
	}()
	return
}

// Split a wire in two.
func Split(a Wire) (Wire, Wire) {
	r1 := MkWire()
	r2 := MkWire()
	go func() {
		for {
			x := <-a
			r1 <- x
			r2 <- x
		}
	}()
	return r1, r2
}

// Xor gate, composed of Or, And and Not gates.
func Xor(a, b Wire) Wire {
	a1, a2 := Split(a)
	b1, b2 := Split(b)
	return Or(And(Not(a1), b1), And(a2, Not(b2)))
}

// A half adder, composed of two splits and an And and Xor gate.
func HalfAdder(a, b Wire) (sum, carry Wire) {
	a1, a2 := Split(a)
	b1, b2 := Split(b)
	carry = And(a1, b1)
	sum = Xor(a2, b2)
	return
}

// A full adder, composed of two half adders, and an Or gate.
func FullAdder(a, b, carryIn Wire) (result, carryOut Wire) {
	s1, c1 := HalfAdder(carryIn, a)
	result, c2 := HalfAdder(b, s1)
	carryOut = Or(c1, c2)
	return
}

// A four bit adder, composed of a zero source, and four full adders.
func FourBitAdder(a1, a2, a3, a4 Wire, b1, b2, b3, b4 Wire) (r1, r2, r3, r4 Wire, carry Wire) {
	carry = Zero()
	r1, carry = FullAdder(a1, b1, carry)
	r2, carry = FullAdder(a2, b2, carry)
	r3, carry = FullAdder(a3, b3, carry)
	r4, carry = FullAdder(a4, b4, carry)
	return
}

func main() {
	// Create wires
	a1, a2, a3, a4 := MakeWire(), MakeWire(), MakeWire(), MakeWire()
	b1, b2, b3, b4 := MakeWire(), MakeWire(), MakeWire(), MakeWire()
	// Construct circuit
	r1, r2, r3, r4, carry := FourBitAdder(a1, a2, a3, a4, b1, b2, b3, b4)
	// Feed it some values
	a4 <- false
	a3 <- false
	a2 <- true
	a1 <- false // 0010
	b4 <- true
	b3 <- true
	b2 <- true
	b1 <- false // 1110
	B := map[bool]int{false: 0, true: 1}
	// Read the result
	fmt.Printf("0010 + 1110 = %d%d%d%d (carry = %d)\n",
		B[<-r4], B[<-r3], B[<-r2], B[<-r1], B[<-carry])
}