// Package statemachine holds the pure runtime and commitment transition
// functions. No I/O, no shared state.
package statemachine

import (
	"fmt"

	"keel/internal/mode/focus/domain"
)

// RuntimeAction enumerates runtime transitions. Activate's policy acceptance
// and admin-override exit targets are flattened into distinct actions so the
// action type stays a simple value.
type RuntimeAction string

const (
	EnterPlanning               RuntimeAction = "enter_planning"
	CancelOrTimeout             RuntimeAction = "cancel_or_timeout"
	ActivateAccepted            RuntimeAction = "activate_accepted"
	ActivateRejected            RuntimeAction = "activate_rejected"
	StartTransition             RuntimeAction = "start_transition"
	CompleteForReview           RuntimeAction = "complete_for_review"
	SevereViolation             RuntimeAction = "severe_violation"
	ReturnToActive              RuntimeAction = "return_to_active"
	SwitchTask                  RuntimeAction = "switch_task"
	EndTransitionForReview      RuntimeAction = "end_transition_for_review"
	ContinuePlanning            RuntimeAction = "continue_planning"
	EndWorkPeriod               RuntimeAction = "end_work_period"
	EnterAdminOverride          RuntimeAction = "enter_admin_override"
	ExitAdminOverrideToLocked   RuntimeAction = "exit_admin_override_to_locked"
	ExitAdminOverrideToPlanning RuntimeAction = "exit_admin_override_to_planning"
)

type CommitmentAction string

const (
	CommitmentActivate CommitmentAction = "activate"
	PauseForTransition CommitmentAction = "pause_for_transition"
	ReturnFromPause    CommitmentAction = "return_from_pause"
	Complete           CommitmentAction = "complete"
	Abandon            CommitmentAction = "abandon"
	Violate            CommitmentAction = "violate"
	RecoverExplicitly  CommitmentAction = "recover_explicitly"
)

// IllegalTransitionError reports a rejected transition.
type IllegalTransitionError struct {
	From   string
	Action string
}

func (e IllegalTransitionError) Error() string {
	return fmt.Sprintf("illegal transition from %s via %s", e.From, e.Action)
}

// PolicyRejectedError reports an activation attempted with an unaccepted policy.
type PolicyRejectedError struct{}

func (PolicyRejectedError) Error() string { return "policy was rejected" }

func TransitionRuntime(current domain.RuntimeState, action RuntimeAction) (domain.RuntimeState, error) {
	type key struct {
		s domain.RuntimeState
		a RuntimeAction
	}
	table := map[key]domain.RuntimeState{
		{domain.RuntimeLocked, EnterPlanning}:                      domain.RuntimePlanning,
		{domain.RuntimePlanning, ActivateAccepted}:                 domain.RuntimeActive,
		{domain.RuntimePlanning, CancelOrTimeout}:                  domain.RuntimeLocked,
		{domain.RuntimeActive, StartTransition}:                    domain.RuntimeTransition,
		{domain.RuntimeActive, CompleteForReview}:                  domain.RuntimeReview,
		{domain.RuntimeActive, SevereViolation}:                    domain.RuntimeLocked,
		{domain.RuntimeTransition, ReturnToActive}:                 domain.RuntimeActive,
		{domain.RuntimeTransition, SwitchTask}:                     domain.RuntimePlanning,
		{domain.RuntimeTransition, EndTransitionForReview}:         domain.RuntimeReview,
		{domain.RuntimeTransition, CancelOrTimeout}:                domain.RuntimeLocked,
		{domain.RuntimeReview, ContinuePlanning}:                   domain.RuntimePlanning,
		{domain.RuntimeReview, EndWorkPeriod}:                      domain.RuntimeLocked,
		{domain.RuntimeAdminOverride, ExitAdminOverrideToLocked}:   domain.RuntimeLocked,
		{domain.RuntimeAdminOverride, ExitAdminOverrideToPlanning}: domain.RuntimePlanning,
	}

	if action == ActivateRejected && current == domain.RuntimePlanning {
		return current, PolicyRejectedError{}
	}
	if action == EnterAdminOverride {
		return domain.RuntimeAdminOverride, nil
	}
	if next, ok := table[key{current, action}]; ok {
		return next, nil
	}
	return current, IllegalTransitionError{From: string(current), Action: string(action)}
}

func TransitionCommitment(current domain.CommitmentState, action CommitmentAction) (domain.CommitmentState, error) {
	type key struct {
		s domain.CommitmentState
		a CommitmentAction
	}
	table := map[key]domain.CommitmentState{
		{domain.CommitmentDraft, CommitmentActivate}:   domain.CommitmentActive,
		{domain.CommitmentActive, PauseForTransition}:  domain.CommitmentPaused,
		{domain.CommitmentPaused, ReturnFromPause}:     domain.CommitmentActive,
		{domain.CommitmentActive, Complete}:            domain.CommitmentCompleted,
		{domain.CommitmentActive, Abandon}:             domain.CommitmentAbandoned,
		{domain.CommitmentActive, Violate}:             domain.CommitmentViolated,
		{domain.CommitmentPaused, Abandon}:             domain.CommitmentAbandoned,
		{domain.CommitmentViolated, RecoverExplicitly}: domain.CommitmentActive,
		{domain.CommitmentViolated, Abandon}:           domain.CommitmentAbandoned,
	}
	if next, ok := table[key{current, action}]; ok {
		return next, nil
	}
	return current, IllegalTransitionError{From: string(current), Action: string(action)}
}