package saltyim

import (
	"bytes"
	"context"
	"fmt"
	"strings"
	"sync"

	"github.com/avast/retry-go"
	"github.com/keys-pub/keys"
	log "github.com/sirupsen/logrus"

	"go.yarn.social/lextwt"
)

// Service is an object that implements an async responder (bot) that responds to
// textual callbacks (commands) or events. This can be used to implement automated
// users, bots or services.
type Service struct {
	mu sync.RWMutex

	me    Addr
	id    *Identity
	cli   *Client
	state string

	textFns  map[string]MessageTextHandlerFunc
	eventFns map[string]MessageEventHandlerFunc
}

// MessageTextHandlerFunc defines a function type to handle an inbound message to a service
type MessageTextHandlerFunc func(context.Context, *Service, *keys.EdX25519PublicKey, *lextwt.SaltyText) error

// MessageEventHandlerFunc defines a function type to handle an inbound event to a service
type MessageEventHandlerFunc func(context.Context, *Service, *keys.EdX25519PublicKey, *lextwt.SaltyEvent) error

// NewService constructs a new service with the provided address, identity and state
func NewService(me Addr, id *Identity, state string) (*Service, error) {
	svc := &Service{
		me:       me,
		id:       id,
		state:    state,
		textFns:  make(map[string]MessageTextHandlerFunc),
		eventFns: make(map[string]MessageEventHandlerFunc),
	}
	svc.TextFunc("ping", func(ctx context.Context, svc *Service, key *keys.EdX25519PublicKey, msg *lextwt.SaltyText) error {
		return svc.Respond(msg.User.String(), "pong")
	})

	return svc, nil
}

// SetClient sets the client instance to used for this service
func (svc *Service) SetClient(cli *Client) {
	svc.mu.Lock()
	defer svc.mu.Unlock()

	svc.cli = cli
}

func (svc *Service) String() string {
	svc.mu.RLock()
	defer svc.mu.RUnlock()

	buf := &bytes.Buffer{}
	fmt.Fprintln(buf, "Bot: ", svc.me)
	for k := range svc.textFns {
		fmt.Fprintln(buf, " - TextCmd: ", k)
	}
	for k := range svc.eventFns {
		fmt.Fprintln(buf, " - EventCmd: ", k)
	}
	return buf.String()
}

// Respond is a convenitne method to respond to a user with the provided message
func (svc *Service) Respond(user, msg string) error {
	if svc.cli == nil {
		return fmt.Errorf("service not connected")
	}
	return svc.cli.Send(user, msg)
}

// Run runs the service tunil the context is done, if an error occurred at any point
// an error is returned.
func (svc *Service) Run(ctx context.Context) error {
	// create the service user's client in a loop until successful
	// TODO: Should this timeout? Use a context?
	if err := retry.Do(func() error {
		cli, err := NewClient(
			WithAddr(svc.me),
			WithIdentity(svc.id),
			WithStateFromFile(svc.state),
		)
		if err != nil {
			return err
		}
		if err := cli.me.Refresh(); err != nil {
			return err
		}
		svc.SetClient(cli)
		return nil
	},
		retry.LastErrorOnly(true),
		retry.OnRetry(func(n uint, err error) {
			log.Debugf("retrying service user setup (try #%d): %s", n, err)
		}),
	); err != nil {
		return fmt.Errorf("error setting up service user %s: %w", svc.me, err)
	}
	defer func() {
		if err := svc.cli.State().Save(svc.state); err != nil {
			log.WithError(err).Warnf("error saving state: %s", svc.state)
		}
	}()

	log.Debugf("listening for service requests as %s", svc.me)

	msgch := svc.cli.Subscribe(ctx)

	for {
		select {
		case <-ctx.Done():
			return nil
		case msg := <-msgch:
			if err := svc.handle(ctx, msg); err != nil {
				log.WithError(err).Println("failed to handle message")
			}
		}
	}
}

func (svc *Service) handle(ctx context.Context, msg Message) error {
	decoded, err := lextwt.ParseSalty(msg.Text)
	if err != nil {
		return err
	}

	switch m := decoded.(type) {
	case *lextwt.SaltyText:
		fields := strings.Fields(m.LiteralText())
		svc.mu.RLock()
		defer svc.mu.RUnlock()

		if fn, ok := svc.textFns[strings.ToUpper(fields[0])]; ok {
			err = fn(ctx, svc, msg.Key, m)
		}
	case *lextwt.SaltyEvent:
		svc.mu.RLock()
		defer svc.mu.RUnlock()

		if fn, ok := svc.eventFns[strings.ToUpper(m.Command)]; ok {
			err = fn(ctx, svc, msg.Key, m)
		}
	}

	return err
}

// TextFunc registers a handler for processing textual callbacks (commands)
func (svc *Service) TextFunc(name string, fn MessageTextHandlerFunc) {
	svc.mu.Lock()
	defer svc.mu.Unlock()

	svc.textFns[strings.ToUpper(name)] = fn
}

// EventFunc registers a handler for processing event callbacks (events)
func (svc *Service) EventFunc(name string, fn MessageEventHandlerFunc) {
	svc.mu.Lock()
	defer svc.mu.Unlock()

	svc.eventFns[strings.ToUpper(name)] = fn
}