package game

import (
	"errors"
	"fmt"
)

// ErrNotFound reports that a game record was requested but does not exist
// in the store.
var ErrNotFound = errors.New("game not found")

// ErrConflict reports that a game mutation could not be applied because the
// record changed concurrently or failed a compare-and-swap guard.
var ErrConflict = errors.New("game conflict")

// ErrInvalidTransition is the sentinel returned when Transition rejects a
// `(from, to, trigger)` triplet.
var ErrInvalidTransition = errors.New("invalid game status transition")

// InvalidTransitionError stores the rejected `(from, to, trigger)` triplet
// and wraps ErrInvalidTransition so callers can match it with errors.Is.
type InvalidTransitionError struct {
	// From stores the source status that was attempted to leave.
	From Status

	// To stores the destination status that was attempted to enter.
	To Status

	// Trigger stores the transition trigger that was attempted.
	Trigger Trigger
}

// Error reports a human-readable summary of the rejected triplet.
func (err *InvalidTransitionError) Error() string {
	return fmt.Sprintf(
		"invalid game status transition from %q to %q with trigger %q",
		err.From, err.To, err.Trigger,
	)
}

// Unwrap returns ErrInvalidTransition so errors.Is recognizes the sentinel.
func (err *InvalidTransitionError) Unwrap() error {
	return ErrInvalidTransition
}