package actor

const (
	defaultFixedCapacity = 64
	defaultBatchSize     = 64
)

type configuration[T any] struct {
	fixedCapacity int
	batchSize     int
	onPanic       func(T, any, []byte)
	dispatcher    Dispatcher
}

// Option configures an Actor during construction.
type Option[T any] func(*configuration[T])

// WithFixedCapacity sets the number of retained mailbox nodes. The default is
// 64. This is not a mailbox limit: further messages use dynamic nodes.
func WithFixedCapacity[T any](capacity int) Option[T] {
	return func(c *configuration[T]) { c.fixedCapacity = capacity }
}

// WithBatchSize sets how many messages are consumed between calls to
// runtime.Gosched. Long pending-batch reversals also yield at this interval.
// The default is 64, independent of the dispatcher.
func WithBatchSize[T any](size int) Option[T] {
	return func(c *configuration[T]) { c.batchSize = size }
}

// WithPanicHandler sets an optional callback for handler panics. It receives the
// message, the recovered value, and a stack trace. Its own panics are recovered.
// A nil callback disables panic reporting; messages still continue to drain.
func WithPanicHandler[T any](handler func(message T, value any, stack []byte)) Option[T] {
	return func(c *configuration[T]) { c.onPanic = handler }
}

// WithDispatcher chooses the construction-time scheduling policy. The default
// dispatcher runs inline. New rejects a nil interface or nil DispatcherFunc.
// Custom typed-nil implementations must themselves satisfy the Dispatcher
// contract; their validity is the caller's responsibility.
func WithDispatcher[T any](dispatcher Dispatcher) Option[T] {
	return func(c *configuration[T]) { c.dispatcher = dispatcher }
}

func configure[T any](opts []Option[T]) configuration[T] {
	c := configuration[T]{
		fixedCapacity: defaultFixedCapacity,
		batchSize:     defaultBatchSize,
		dispatcher:    inlineDispatcher{},
	}
	for _, opt := range opts {
		if opt == nil {
			panic("actor: nil option")
		}
		opt(&c)
	}
	if c.fixedCapacity <= 0 {
		panic("actor: fixed capacity must be positive")
	}
	if c.batchSize <= 0 {
		panic("actor: batch size must be positive")
	}
	if c.dispatcher == nil {
		panic("actor: nil dispatcher")
	}
	if f, ok := c.dispatcher.(DispatcherFunc); ok && f == nil {
		panic("actor: nil dispatcher function")
	}
	return c
}