package state

import (
	"fmt"
	"strings"
	"time"
)

const PendingRegionCandidatesMetadataKey = "pending_region_candidates"

type Machine struct {
	session ConversationSession
}

func NewMachine(initial ConversationSession) *Machine {
	now := time.Now().UTC()
	if initial.StartedAt.IsZero() {
		initial.StartedAt = now
	}
	if initial.UpdatedAt.IsZero() {
		initial.UpdatedAt = initial.StartedAt
	}
	if initial.State == "" {
		initial.State = StateCallStarted
	}
	if initial.Region.Status == "" {
		initial.Region.Status = RegionUnknown
	}
	if initial.Metadata == nil {
		initial.Metadata = map[string]string{}
	}
	return &Machine{session: initial}
}

func (m *Machine) Session() ConversationSession    { return cloneSession(m.session) }
func (m *Machine) CurrentState() ConversationState { return m.session.State }

func (m *Machine) CanTransition(event ConversationEvent) bool {
	_, err := m.next(event)
	return err == nil
}

func (m *Machine) Apply(event ConversationEvent) (TransitionResult, error) {
	from := m.session.State
	to, err := m.next(event)
	if err != nil {
		m.recordDenied(string(event.Type), err.Error())
		return TransitionResult{From: from, To: from, Changed: false, MessageKey: "error.invalid_transition", RequiredNextAction: requiredActionForState(from)}, err
	}
	if event.At.IsZero() {
		event.At = time.Now().UTC()
	}
	if from == StateEnded {
		return TransitionResult{From: from, To: from, Changed: false, MessageKey: "error.invalid_transition", RequiredNextAction: "none"}, fmt.Errorf("ended state is immutable")
	}
	m.session.State = to
	switch event.Type {
	case EventLanguageSelected:
		m.session.Language = event.Language
	case EventRegionSelected:
		m.session.Region = event.Region
		m.ClearPendingRegion()
	case EventCallEnded:
		t := event.At
		m.session.EndedAt = &t
	}
	m.session.UpdatedAt = event.At
	m.session.TransitionHistory = append(m.session.TransitionHistory, TransitionRecord{From: from, To: to, Event: event.Type, Reason: event.Reason, At: event.At})
	return TransitionResult{From: from, To: to, Changed: from != to, MessageKey: messageKeyForState(to), RequiredNextAction: requiredActionForState(to)}, nil
}

func (m *Machine) AddDenied(action, reason string) {
	m.recordDenied(action, reason)
}

func (m *Machine) SetRegionPending(codes []string) {
	if m.session.Metadata == nil {
		m.session.Metadata = map[string]string{}
	}
	m.session.Region = RegionSelection{Status: RegionPendingClarification, Source: "resolver"}
	m.session.Metadata[PendingRegionCandidatesMetadataKey] = strings.Join(codes, ",")
	m.session.UpdatedAt = time.Now().UTC()
}

func (m *Machine) PendingRegionCandidates() []string {
	v := strings.TrimSpace(m.session.Metadata[PendingRegionCandidatesMetadataKey])
	if v == "" {
		return nil
	}
	parts := strings.Split(v, ",")
	out := make([]string, 0, len(parts))
	for _, p := range parts {
		p = strings.TrimSpace(p)
		if p != "" {
			out = append(out, p)
		}
	}
	return out
}

func (m *Machine) ClearPendingRegion() {
	if m.session.Metadata != nil {
		delete(m.session.Metadata, PendingRegionCandidatesMetadataKey)
	}
}

func (m *Machine) recordDenied(action, reason string) {
	m.session.DeniedActions = append(m.session.DeniedActions, DeniedActionRecord{Action: action, State: m.session.State, ReasonCode: reason, At: time.Now().UTC()})
	m.session.UpdatedAt = time.Now().UTC()
}

func (m *Machine) next(event ConversationEvent) (ConversationState, error) {
	if m.session.State == StateEnded {
		return StateEnded, fmt.Errorf("ended_state")
	}
	switch event.Type {
	case EventCallStarted:
		if m.session.State == StateCallStarted {
			return StateGreeting, nil
		}
	case EventGreetingPlayed, EventLanguageRequested:
		if m.session.State == StateGreeting {
			return StateReadyToHelp, nil
		}
	case EventLanguageSelected:
		if event.Language != LanguageRU && event.Language != LanguageKK {
			return m.session.State, fmt.Errorf("invalid_language")
		}
		switch m.session.State {
		case StateLanguageSelection:
			return StateRegionSelection, nil
		case StateRegionSelection, StateReadyToHelp, StateQuestionAnswering:
			return m.session.State, nil
		}
	case EventRegionSelected:
		if event.Region.Code == "" || event.Region.Status != RegionSelected {
			return m.session.State, fmt.Errorf("invalid_region")
		}
		switch m.session.State {
		case StateRegionSelection, StateReadyToHelp, StateQuestionAnswering:
			return StateReadyToHelp, nil
		}
	case EventQuestionReceived:
		if m.session.State == StateReadyToHelp {
			return StateQuestionAnswering, nil
		}
		return m.session.State, fmt.Errorf("state_not_ready")
	case EventAnswerCompleted:
		if m.session.State == StateQuestionAnswering {
			return StateReadyToHelp, nil
		}
	case EventHandoffRequested:
		return StateHandoff, nil
	case EventClosingRequested:
		return StateClosing, nil
	case EventCallEnded:
		return StateEnded, nil
	}
	return m.session.State, fmt.Errorf("invalid_transition")
}

func messageKeyForState(s ConversationState) string {
	switch s {
	case StateGreeting:
		return "greeting.initial"
	case StateLanguageSelection:
		return "language.ask"
	case StateRegionSelection:
		return "region.ask"
	case StateReadyToHelp:
		return "ready.to_help"
	case StateQuestionAnswering:
		return "answer.allowed"
	case StateHandoff:
		return "handoff.started"
	case StateClosing:
		return "closing.started"
	default:
		return ""
	}
}

func requiredActionForState(s ConversationState) string {
	switch s {
	case StateGreeting:
		return "play_greeting"
	case StateLanguageSelection:
		return "ask_language"
	case StateRegionSelection:
		return "ask_region"
	case StateReadyToHelp:
		return "wait_for_question"
	case StateQuestionAnswering:
		return "answer_question"
	case StateHandoff:
		return "handoff"
	case StateClosing, StateEnded:
		return "close_call"
	default:
		return "none"
	}
}

func cloneSession(s ConversationSession) ConversationSession {
	s.TransitionHistory = append([]TransitionRecord(nil), s.TransitionHistory...)
	s.DeniedActions = append([]DeniedActionRecord(nil), s.DeniedActions...)
	if s.Metadata != nil {
		cp := make(map[string]string, len(s.Metadata))
		for k, v := range s.Metadata {
			cp[k] = v
		}
		s.Metadata = cp
	}
	return s
}