package fsm

import (
	"context"
	"time"
)

type M2Hook[T any] func(ctx context.Context, event M2Event[T]) error

type M2State[T any] interface {
	Name() string
	SetAfterEnter([]M2Hook[T])
	AfterEnter() []M2Hook[T]
	SetBeforeLeave([]M2Hook[T])
	BeforeLeave() []M2Hook[T]
}

type M2Event[T any] interface {
	Name() string
	Data() T
}

type RetryableError interface {
	error
	RetryableError()
}

type M2Transition[T any] struct {
	guards, actions []M2Hook[T]
	next            State
}

func (mt *M2Transition[T]) SetGuards([]M2Hook[T])  {}
func (mt *M2Transition[T]) Guards() []M2Hook[T]    { return mt.guards }
func (mt *M2Transition[T]) SetActions([]M2Hook[T]) {}
func (mt *M2Transition[T]) Actions() []M2Hook[T]   { return mt.actions }
func (mt *M2Transition[T]) Next() State            { return mt.next }

type M2Matrix[T any] map[M2State[T]]map[M2Event[T]]M2Transition[T]

// M2BackoffFunc returning <0 means the retry limit has been reached.
type M2BackoffFunc func() time.Duration

type M2FSM[T any] interface {
	Name() string

	SetBackoff(fn M2BackoffFunc)

	SetMatrix(mx M2Matrix[T])
	Matrix() M2Matrix[T]

	StartState() M2State[T]
	EndState() M2State[T]
	ErrorState() M2State[T]
}

type M2PushMachine[T any] interface {
	M2FSM[T]
	Handle(context.Context, M2Event[T]) error // If ctx == nil, handling uses the machine context.
}

type M2PullMachine[T any] interface {
	M2FSM[T]
	Start(ctx context.Context, events chan<- M2Event[T]) M2State[T]
}

type M2VerifiableMachine[T any] interface {
	M2FSM[T]
	IsReachable(s1, s2 M2State[T]) bool
	IsStronglyConnected() bool // Minimal Complexity O(V+E) using DFS (Tarjan or Kosaraju)
}

var (
	m2BackoffInitialDelay    = time.Millisecond
	m2BackoffMaxAttempts     = 10
	m2DefaultBackoffAttempts = 0

	// M2YoloBackoff retries indefinitely without delay.
	M2YoloBackoff M2BackoffFunc = func() time.Duration {
		return 0
	}

	// M2NoBackoff retries immediately but only up to the maximum number of retries.
	M2NoBackoff M2BackoffFunc = func() time.Duration {
		m2DefaultBackoffAttempts++
		if m2DefaultBackoffAttempts > m2BackoffMaxAttempts {
			return -1
		}
		return M2YoloBackoff()
	}

	// M2ExponentialBackoff retries with an exponential delay and maximum number of retries.
	M2ExponentialBackoff M2BackoffFunc = func() time.Duration {
		d := M2NoBackoff()
		if d < 0 {
			return d
		}
		return (1 << m2DefaultBackoffAttempts) * m2BackoffInitialDelay
	}
)