lazy/Var.go

package pixelMenu

import (
	"github.com/pkg/errors"
	"gitlab.com/Pixdigit/uniqueID"
)

var ErrCircularDependency = errors.New("circular dependency while resolving")

var VarIDSpace = uniqueID.IDSpace{}

type Var struct {
	id           uniqueID.ID
	isResolving  bool
	IsResolved   bool
	Value        float64
	evaluator    func() float64
	dependencies []Var
}

func Invariant(value float64) Var {
	return Var{
		VarIDSpace.NewID(),
		false,
		true,
		value,
		func() float64 { return value },
		make([]Var, 0),
	}
}

func NewVar() Var {
	return Var{
		VarIDSpace.NewID(),
		false,
		false,
		0,
		func() float64 { return 0 },
		make([]Var, 0),
	}
}

func Combine(p1, p2 Var, combinator func(float64, float64) float64) Var {
	return Var{
		VarIDSpace.NewID(),
		false,
		false,
		0,
		func() float64 { return combinator(p1.evaluator(), p2.evaluator()) },
		[]Var{p1, p2},
	}
}

func Add(p1, p2 Var) Var {
	return Combine(p1, p2, func(arg1 float64, arg2 float64) float64 {
		return arg1 + arg2
	})
}
func Sub(p1, p2 Var) Var {
	return Combine(p1, p2, func(arg1 float64, arg2 float64) float64 {
		return arg1 - arg2
	})
}
func Mul(p1, p2 Var) Var {
	return Combine(p1, p2, func(arg1 float64, arg2 float64) float64 {
		return arg1 * arg2
	})
}
func Div(p1, p2 Var) Var {
	return Combine(p1, p2, func(arg1 float64, arg2 float64) float64 {
		return arg1 / arg2
	})
}

func (p *Var) HasDependency(p2 Var) bool {
	for _, dep := range p.dependencies {
		if dep.id == p2.id {
			return true
		}
		if dep.HasDependency(p2) {
			return true
		}
	}
	return false
}

func (p *Var) Resolve() error {
	p.isResolving = true
	defer func() { p.isResolving = false }()
	//Assume user has done dependency check
	for _, dep := range p.dependencies {
		if !dep.IsResolved {
			dep.Resolve()
		}
	}

	p.Value = p.evaluator()

	p.IsResolved = true
	return nil
}