package hamlet

import "reflect"

type Assertion struct {
	truth bool
}

func (a Assertion) Assert() bool {
	return a.truth
}

func Present(v any) Assertion {
	return Assertion{!reflect.ValueOf(v).IsZero()}
}

func Absent(v any) Assertion {
	return Assertion{reflect.ValueOf(v).IsZero()}
}

// Not computes ~a, given assertion a.
func Not(a Assertion) Assertion {
	negation := !a.truth

	return Assertion{negation}
}

// Or computes a v b, given assertions a and b.
func Or(a Assertion, b Assertion) Assertion {
	av := a.truth
	bv := b.truth

	return Assertion{av || bv}
}

// And computes a ^ b, given assertions a and b.
func And(a Assertion, b Assertion) Assertion {
	av := a.truth
	bv := b.truth

	return Assertion{av && bv}
}

// If computes a → b, given assertions a and b.
func If(a Assertion, b Assertion) Assertion {
	return Or(Not(a), b)
}

// If computes a ↔ b, given assertions a and b.
func Iff(a Assertion, b Assertion) Assertion {
	return And(If(a, b), If(b, a))
}

// Xor computes a ⊻ b, given assertions a and b.
func Xor(a Assertion, b Assertion) Assertion {
	return Not(Iff(a, b))
}