package interpreter

// environment represents the environment in which the interpreter operates.
type environment struct {
	values    map[string]any
	enclosing *environment
}

// newEnvironment creates a new environment.
// e is the enclosing environment and is nil for the global environment.
func newEnvironment(e *environment) *environment {
	return &environment{values: make(map[string]any), enclosing: e}
}

// define defines a new variable in the environment.
func (e *environment) define(name string, value any) {
	e.values[name] = value
}

// ancestor returns the environment at a given distance.
func (e *environment) ancestor(distance int) *environment {
	env := e
	for i := 0; i < distance; i++ {
		env = env.enclosing
	}

	return env
}

// getAt gets the value of a variable at a given distance.
func (e *environment) getAt(distance int, name string) any {
	return e.ancestor(distance).values[name]
}

// get gets the value of a variable in the environment.
func (e *environment) get(name string) any {
	value, ok := e.values[name]
	if !ok {
		if e.enclosing != nil {
			return e.enclosing.get(name)
		}

		panic("Undefined variable '" + name + "'.")
	}

	return value
}

// assignAt assigns a new value to a variable at a given distance.
func (e *environment) assignAt(distance int, name string, value any) {
	e.ancestor(distance).values[name] = value
}

// assign assigns a new value to a variable in the environment.
func (e *environment) assign(name string, value any) {
	_, ok := e.values[name]
	if !ok {
		if e.enclosing != nil {
			e.enclosing.assign(name, value)
			return
		}

		panic("Undefined variable '" + name + "'.")
	}

	e.values[name] = value
}