package saltyim

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

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

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

const (
	// DefaultEnvPath is the default PATH for pre and post hooks that are shelled out to
	DefaultEnvPath = "/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"
)

var (
	// ErrNoMessages is an error returned when there are no further messages found for an inbox from the broker
	ErrNoMessages = errors.New("error: no messages found")

	// ErrNoSender is an error returned when the client is not properly configured with a valid sender
	ErrNoSender = errors.New("error: no sender configured")

	// ErrMissingIdentity is an error returned when the client is not properly configured with a valid identity
	ErrMissingIdentity = errors.New("error: missing identity")
)

type addrCache map[string]Addr

// Message contains the plaintext (decrypted) message and the sender's public key
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
}

// 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

	cache addrCache
	state *State

	lookup Lookuper
	send   Sender
}

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

// NewClient returns 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(options ...ClientOption) (*Client, error) {
	cli := &Client{
		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 cli.me == nil || cli.me.IsZero() {
		cli.me = cli.id.addr
	}

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

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

	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, opts *ReadOptions) (Message, error) {
	var data []byte

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

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

	unencrypted, senderKey, err := salty.Decrypt(cli.id.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(ctx context.Context, opts *ReadOptions, msgs chan Message) msgbus.HandlerFunc {
	return func(msg *msgbus.Message) error {
		message, err := cli.processMessage(msg, opts)
		if err != nil {
			return fmt.Errorf("error processing message: %w", err)
		}
		cli.state.SetIndex(msg.Topic.Name, msg.ID)

		select {
		case <-ctx.Done():
			close(msgs)
			return nil
		case msgs <- message:
		}

		return nil
	}
}

// Me returns our (self) address
func (cli *Client) Me() Addr { return cli.me }

// Key returns our (self) public key
func (cli *Client) Key() *keys.EdX25519PublicKey { return cli.id.key.PublicKey() }

// State returns the current state of the client
func (cli *Client) State() *State { return cli.state }

// Env sets up a sensible (and hopefully secure) environment for running pre and post hooks
// Extra environment variables are parsed from extraenvs and some default variables injected
// into the new environment such as PATH, PWD and HOME as well as the current user's Salty address
// (SALTY_USER) and their public key (SALTY_IDENTITY).
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
}

// Outbox returns the URL of our (self) outbox for sending copies of our outgoing messages to
// which is later used by the client as a way to track messages sent.
func (cli *Client) Outbox() *url.URL {
	// use url struct copy to avoid modifying cli.me.Endpoint().Path
	// https://github.com/golang/go/issues/38351
	ep := *cli.me.Endpoint()
	ep.Path = path.Join(
		path.Dir(ep.Path),
		fmt.Sprintf("%x", sha256.Sum256(cli.id.key.Private())),
	)
	return &ep
}

// OutboxAddr returns the address of our (self) outbox
func (cli *Client) OutboxAddr(to Addr) Addr {
	return cli.me.WithEndpoint(cli.Outbox())
}

// OutboxClient returns a modified client for our (self) outbox
func (cli *Client) OutboxClient(to Addr) *Client {
	if to == nil {
		to = cli.me
	}

	me := to.WithEndpoint(cli.Outbox())

	return &Client{
		me: me,
		id: &Identity{
			addr: me,
			key:  cli.id.key,
		},
		cache:  cli.cache,
		state:  cli.state,
		lookup: cli.lookup,
		send:   cli.send,
	}
}

// String implements the fmt.Stringer interface and outputs who we (self) are,
// what our endpoint is we're connected to (broker), our outbox and our public key.
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.id.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
}

// ReadOptions allows a client to read from its inbox and provide additional options for processing
// messages such as extra environment variables for pre/post hooks.
type ReadOptions struct {
	ExtraEnvs string
	PreHook   string
	PostHook  string
}

// ReadOption is a function that configures a client
type ReadOption func(opts *ReadOptions) error

// WithExtraEnvs sets extra environment variables for use by pre/post hooks
func WithExtraEnvs(extraenvs string) ReadOption {
	return func(opts *ReadOptions) error {
		opts.ExtraEnvs = extraenvs
		return nil
	}
}

// WithPreHook sets the prehook used for processing incoming messages which is the path to a
// script that is passed the encrypted message payload as its standard input.
func WithPreHook(prehook string) ReadOption {
	return func(opts *ReadOptions) error {
		opts.PreHook = prehook
		return nil
	}
}

// WithPostHook sets the posthook used for processing incoming messages which is the path to a
// script that is passed the decrypted message as its standard input.
func WithPostHook(posthook string) ReadOption {
	return func(opts *ReadOptions) error {
		opts.PostHook = posthook
		return nil
	}
}

// Read reads a single message from this user's inbox
func (cli *Client) Read(options ...ReadOption) (Message, error) {
	if cli.me.Endpoint() == nil {
		if err := cli.me.Refresh(); err != nil {
			return Message{}, fmt.Errorf("unable to find your endpoint for %s: %w", cli.me.String(), err)
		}
	}

	opts := &ReadOptions{}
	for _, option := range options {
		if err := option(opts); err != nil {
			return Message{}, fmt.Errorf("error configuring read options: %w", err)
		}
	}

	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, opts)
}

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

	opts := &ReadOptions{}
	for _, option := range options {
		if err := option(opts); err != nil {
			log.WithError(err).Errorf("error configuring read options")
			return nil
		}
	}

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

	msgs := make(chan Message, 1)
	index := cli.state.GetIndex(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(ctx, opts, msgs))
	go s.Run(ctx)

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

	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 {
	if cli.me.Endpoint() == nil {
		if err := cli.me.Refresh(); err != nil {
			return fmt.Errorf("unable to find your endpoint for %s: %w", cli.me.String(), err)
		}
	}

	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)
}

// SendToAddr encrypts and sends the message to a specified address
func (cli *Client) SendToAddr(addr Addr, msg string) error {
	if cli.me == nil || cli.me.IsZero() {
		return ErrNoSender
	}

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

	endpoint := addr.Endpoint().String()
	log.Debugf("sending message to %s", endpoint)
	if err := cli.send.Send(cli.id.key, endpoint, 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(brokerURI string) error {
	if brokerURI == "" {
		log.Debugf("Looking up SRV record for _salty._tcp.%s", cli.Me().Domain())
		target, err := DefaultResolver.LookupSRV("salty", "tcp", cli.Me().Domain())
		if err != nil {
			return fmt.Errorf("unable to find broker for %s: %w", cli.Me(), err)
		}
		brokerURI = fmt.Sprintf("https://%s", target)
	}
	u, err := url.Parse(brokerURI)
	if err != nil {
		return fmt.Errorf("error parsing broker uri %s: %w", brokerURI, err)
	}
	u.Path = "/api/v1/register"

	req := RegisterRequest{Hash: cli.Me().Hash(), Key: cli.Key().ID().String()}
	data, err := json.Marshal(req)
	if err != nil {
		return fmt.Errorf("error serializing register request: %w", err)
	}
	signed, err := salty.Sign(cli.id.key, data)
	if err != nil {
		return fmt.Errorf("error signing register request: %w", err)
	}

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

// Request makes a signed request to a broker's API.
func (cli *Client) Request(method, endpoint string, body []byte) ([]byte, error) {
	u, err := url.Parse(endpoint)
	if err != nil {
		return nil, fmt.Errorf("error parsing endpoint address %s: %w", endpoint, err)
	}

	res, err := SignedRequest(cli.id.key, method, u.String(), nil, bytes.NewBuffer(body))
	if err != nil {
		return nil, fmt.Errorf("error making %s request to %s: %w", method, u, err)
	}
	defer res.Body.Close()

	return io.ReadAll(res.Body)
}