package main

const (
	unknownVarType string = `unknown` // placeholder
	mixedVarType   string = `mixed`   // when setting an incompatible type
)

type LocalVar struct {
	Name string
	Type string
}

type Scope struct {
	parent *Scope
	locals []LocalVar
}

func NewScope() *Scope {
	return &Scope{}
}

func (this *Scope) NewScope() *Scope {
	return &Scope{
		parent: this,
	}
}

func (this *Scope) Has(varName string) *LocalVar {
	for idx := range this.locals {
		if this.locals[idx].Name == varName {
			return &this.locals[idx] // Mutable
		}
	}

	if this.parent != nil {
		return this.parent.Has(varName)
	}

	return nil // not found
}

func (this *Scope) Set(Name, Type string) *LocalVar {

	if lv := this.Has(Name); lv != nil {
		// Update known type for existing variable
		if lv.Type == unknownVarType {
			lv.Type = Type
		} else if lv.Type == Type {
			// no-op, more evidence for the same type
		} else if lv.Type != Type {
			// conflicting type information
			lv.Type = mixedVarType
		}
		return lv
	}

	// Insert new
	this.locals = append(this.locals, LocalVar{Name: Name, Type: Type})
	return &this.locals[len(this.locals)-1]
}