package saltyim

import (
	"bytes"
	"context"
	"crypto/sha256"
	"encoding/json"
	"errors"
	"fmt"
	"net/http"
	"net/url"
	"os"
	"path"
	"strings"
	"time"

	"git.mills.io/prologic/msgbus"
	msgbus_client "git.mills.io/prologic/msgbus/client"
	"github.com/avast/retry-go"
	"github.com/keys-pub/keys"
	log "github.com/sirupsen/logrus"

	"go.mills.io/salty"
	"go.mills.io/saltyim/internal/exec"
)

const (
	DefaultEnvPath = "/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"
	ServiceUser    = "salty"
)

var (
	ErrNoMessages      = errors.New("error: no messages found")
	ErrNotConnected    = errors.New("error: client not connected")
	ErrMissingIdentity = errors.New("error: missing identity")
)

type addrCache map[string]*Addr

type Message struct {
	Text string
	Key  *keys.EdX25519PublicKey
}

// TODO: Support shell quoting and escapes?
func parseExtraEnvs(extraenvs string) map[string]string {
	env := make(map[string]string)
	for _, extraenv := range strings.Split(extraenvs, " ") {
		tokens := strings.SplitN(extraenv, "=", 2)
		switch len(tokens) {
		case 1:
			env[tokens[0]] = ""
		case 2:
			env[tokens[0]] = tokens[1]
		}
	}
	return env
}

// PackMessage formts an outoing message in the Message Format
// <timestamp>\t(<sender>) <message>
func PackMessage(me *Addr, msg string) []byte {
	log.Debug("pack: ", me.Formatted(), msg)
	return []byte(
		fmt.Sprint(
			time.Now().UTC().Format(time.RFC3339), "\t",
			me.Formatted(), "\t",
			strings.TrimSpace(msg), "\n",
		),
	)
}

// Client is a Salty IM client that handles talking to a Salty IM Broker
// and Sedngina and Receiving messages to/from Salty IM Users.
type Client struct {
	me    *Addr
	id    *Identity
	key   *keys.EdX25519Key
	cache addrCache
	state *State

	lookup Lookuper
	send   Sender
}

// ClientOption is a function that configures a client
type ClientOption func(cli *Client) error

// NewClient reeturns a new Salty IM client for sending and receiving
// encrypted messages to other Salty IM users as well as decrypting
// and displaying messages of the user's own inbox.
func NewClient(me *Addr, options ...ClientOption) (*Client, error) {
	cli := &Client{
		me:     me,
		cache:  make(addrCache),
		lookup: &DirectLookup{},
		send:   &DirectSend{},
	}

	for _, option := range options {
		if err := option(cli); err != nil {
			return nil, fmt.Errorf("error configuring client: %w", err)
		}
	}

	if cli.state == nil {
		log.Debugf("no state loaded, using an empty state")
		cli.state = NewState()
	}

	if cli.id == nil || cli.id.key == nil {
		return nil, ErrMissingIdentity
	}

	if me == nil || me.IsZero() {
		me = cli.id.addr
	}

	if me == nil || me.IsZero() {
		return nil, fmt.Errorf("unable to find your user addressn in %s", cli.id.Source())
	}

	if err := me.Refresh(); err != nil {
		log.WithError(err).Warn("error looking up user endpoint")
	}

	log.Debugf("Using identity %s with public key %s", cli.id.Source(), cli.id.key)
	log.Debugf("Salty Addr is %s", cli.me)
	log.Debugf("Endpoint is %s", cli.me.Endpoint())

	return cli, nil
}

func (cli *Client) getAddr(user string) (*Addr, error) {
	addr, ok := cli.cache[user]
	if ok {
		return addr, nil
	}

	addr, err := cli.lookup.LookupAddr(user)
	if err != nil {
		return nil, fmt.Errorf("error: failed to lookup user %s: %w", user, err)
	}

	cli.cache[user] = addr

	return addr, nil
}

func (cli *Client) processMessage(msg *msgbus.Message, extraenvs, prehook, posthook string) (Message, error) {
	var data []byte

	defer func() {
		if posthook != "" {
			out, err := exec.RunCmd(exec.DefaultRunCmdTimeout, cli.Env(extraenvs), posthook, bytes.NewBuffer(data))
			if err != nil {
				log.WithError(err).Debugf("error running post-hook %s", posthook)
			}
			log.Debugf("post-hook: %q", out)
		}
	}()

	if prehook != "" {
		out, err := exec.RunCmd(exec.DefaultRunCmdTimeout, cli.Env(extraenvs), prehook, bytes.NewBuffer(msg.Payload))
		if err != nil {
			log.WithError(err).Debugf("error running pre-hook %s", prehook)
		}
		log.Debugf("pre-hook: %q", out)
	}

	unencrypted, senderKey, err := salty.Decrypt(cli.key, msg.Payload)
	if err != nil {
		return Message{}, fmt.Errorf("error decrypting message: %w", err)
	}
	data = unencrypted[:]

	return Message{Text: string(data), Key: senderKey}, nil
}

func (cli *Client) messageHandler(extraenvs, prehook, posthook string, msgs chan Message) msgbus.HandlerFunc {
	return func(msg *msgbus.Message) error {
		message, err := cli.processMessage(msg, extraenvs, prehook, posthook)
		if err != nil {
			return fmt.Errorf("error processing message: %w", err)
		}
		cli.state.SetIndex(msg.Topic.Name, msg.ID)

		msgs <- message

		return nil
	}
}

func (cli *Client) Me() *Addr                    { return cli.me }
func (cli *Client) Key() *keys.EdX25519PublicKey { return cli.key.PublicKey() }
func (cli *Client) State() *State                { return cli.state }

func (cli *Client) Env(extraenvs string) []string {
	Path := DefaultEnvPath
	GoPath := os.Getenv("GOPATH")
	if GoPath != "" {
		Path = fmt.Sprintf("%s/bin:%s", GoPath, Path)
	}

	env := []string{
		fmt.Sprintf("PATH=%s", Path),
		fmt.Sprintf("PWD=%s", os.Getenv("PWD")),
		fmt.Sprintf("HOME=%s", os.Getenv("HOME")),

		fmt.Sprintf("SALTY_USER=%s", cli.me.String()),
		fmt.Sprintf("SALTY_IDENTITY=%s", cli.id.Source()),
	}

	for key, val := range parseExtraEnvs(extraenvs) {
		log.Debugf("key: %q", key)
		log.Debugf("val: %q", val)
		val = os.ExpandEnv(val)
		if val == "" {
			val = os.Getenv(key)
		}
		if val != "" {
			env = append(env, fmt.Sprintf("%s=%s", key, val))
		}
	}

	log.Debugf("env: #%v", env)

	return env
}

func (cli *Client) Outbox() *url.URL {
	ep := cli.me.Endpoint()
	ep.Path = path.Join(
		path.Dir(ep.Path),
		fmt.Sprintf("%x", sha256.Sum256(cli.me.key.Private())),
	)
	return ep
}

func (cli *Client) OutboxAddr(to *Addr) *Addr {
	return &Addr{
		User:   to.User,
		Domain: to.Domain,

		endpoint:     cli.Outbox(),
		key:          cli.me.key,
		capabilities: cli.me.capabilities,
	}
}

func (cli *Client) OutboxClient(to *Addr) *Client {
	if to == nil {
		to = cli.me
	}

	return &Client{
		me: &Addr{
			User:             to.User,
			Domain:           to.Domain,
			key:              cli.me.key,
			endpoint:         cli.Outbox(),
			discoveredDomain: cli.me.discoveredDomain,
			avatar:           cli.me.avatar,
			capabilities:     cli.me.capabilities,
			checkedAvatar:    cli.me.checkedAvatar,
		},
		id: &Identity{
			addr: &Addr{
				User:             to.User,
				Domain:           to.Domain,
				key:              cli.me.key,
				endpoint:         cli.Outbox(),
				discoveredDomain: cli.me.discoveredDomain,
				avatar:           cli.me.avatar,
				capabilities:     cli.me.capabilities,
				checkedAvatar:    cli.me.checkedAvatar,
			},
			key: cli.key,
		},
		key:    cli.key,
		cache:  cli.cache,
		state:  NewState(),
		lookup: cli.lookup,
		send:   cli.send,
	}
}

func (cli *Client) String() string {
	b := &bytes.Buffer{}
	fmt.Fprintln(b, "Me:        ", cli.me)
	fmt.Fprintln(b, "Endpoint:  ", cli.me.Endpoint())
	fmt.Fprintln(b, "Outbox:    ", cli.Outbox())
	fmt.Fprintln(b, "Key:       ", cli.key)
	return b.String()
}

// SetLookup sets the internal lookup interface to use (Lookuper) for looking
// up Salty Addresses. By default the DirectLookup implementation is used.
func (cli *Client) SetLookup(lookup Lookuper) {
	cli.lookup = lookup
}

// SetSend sets the internal send interface to use (Sender) for sending
// messages to endpoints. By default the DirectSend implementation is used.
func (cli *Client) SetSend(send Sender) {
	cli.send = send
}

// Read reads a single message from this user's inbox
func (cli *Client) Read(extraenvs, prehook, posthook string) (Message, error) {
	if cli.me.Endpoint() == nil {
		return Message{}, ErrNotConnected
	}

	uri, inbox := SplitInbox(cli.me.Endpoint().String())
	bus := msgbus_client.NewClient(uri, nil)

	msg, err := bus.Pull(inbox)
	if err != nil {
		return Message{}, fmt.Errorf("error reading inbox: %w", err)
	}
	if msg == nil {
		return Message{}, ErrNoMessages
	}

	return cli.processMessage(msg, extraenvs, prehook, posthook)
}

// Subscribe subscribers to this user's inbox for new messages
func (cli *Client) Subscribe(ctx context.Context, extraenvs, prehook, posthook string) chan Message {
	if cli.me.Endpoint() == nil {
		return nil
	}

	uri, inbox := SplitInbox(cli.me.Endpoint().String())
	bus := msgbus_client.NewClient(uri, nil)

	msgs := make(chan Message)
	index := cli.state.GetIndex("inbox/"+inbox) + 1 // +1 to skip over the last seen message
	log.Debugf("streaming inbox %s from %d ...", inbox, index)
	s := bus.Subscribe(inbox, index, cli.messageHandler(extraenvs, prehook, posthook, msgs))
	s.Start()

	log.Debugf("Connected to %s/%s", uri, inbox)

	go func() {
		<-ctx.Done()
		s.Stop()
		close(msgs)
	}()

	return msgs
}

// Lookup performs a lookup for a user's address and config
// If the user has an address already cached, the cached addr
// is returned, otherwise a full lookup is done.
func (cli *Client) Lookup(user string) (*Addr, error) {
	return cli.getAddr(user)
}

// Send sends an encrypted message to the specified user
func (cli *Client) Send(user, msg string) error {
	addr, err := cli.getAddr(user)
	if err != nil {
		return fmt.Errorf("error looking up user %s: %w", user, err)
	}

	err = cli.SendToAddr(addr, msg)
	if err != nil {
		return err
	}

	return cli.OutboxClient(addr).SendToAddr(cli.OutboxAddr(addr), msg)
}

func (cli *Client) SendToAddr(addr *Addr, msg string) error {
	b, err := salty.Encrypt(cli.key, PackMessage(cli.me, msg), []string{addr.key.ID().String()})
	if err != nil {
		return fmt.Errorf("error encrypting message to %s: %w", addr, err)
	}

	if err := cli.send.Send(cli.key, addr.Endpoint().String(), string(b), addr.Cap()); err != nil {
		return fmt.Errorf("error sending message to %s: %w", addr, err)
	}

	return nil
}

// Register sends a registration request to the service user of a Salty Broker
func (cli *Client) Register() error {
	svc, err := cli.lookup.LookupAddr(fmt.Sprintf("%s@%s", ServiceUser, cli.Me().Domain))
	if err != nil {
		return fmt.Errorf("error looking up service user on %s: %w", cli.Me().Domain, err)
	}

	if err := cli.SendToAddr(svc, "REGISTER"); err != nil {
		return fmt.Errorf("error sending REGISTER to %s: %w", svc, err)
	}

	if err := retry.Do(
		func() error {
			return cli.Me().Refresh()
		},
	); err != nil {
		return fmt.Errorf("error registrating account: %w", err)
	}

	return nil
}

// SetAvatar creates or updates an avatar for a user with a broker
func (cli *Client) SetAvatar(content []byte) error {
	// TODO: Verify cli.Me().Domain has valid SRV records

	req := AvatarRequest{Addr: cli.Me(), Content: content}
	data, err := json.Marshal(req)
	if err != nil {
		return fmt.Errorf("error serializing avatar request: %w", err)
	}
	signed, err := salty.Sign(cli.key, data)
	if err != nil {
		return fmt.Errorf("error signing avatar request: %w", err)
	}

	// TODO: Automatically work out the URI based on SRV lookups of the user's address
	u := cli.Me().Endpoint()
	u.Path = "/api/v1/avatar"

	_, err = Request(http.MethodPost, u.String(), nil, bytes.NewBuffer(signed))
	if err != nil {
		return fmt.Errorf("error updating avatar: %w", err)
	}

	return nil
}