// Package twitch implements the OAuth2 protocol for authenticating users through Twitch.
// This package can be used as a reference implementation of an OAuth2 provider for Twitch.
package twitch

import (
	"encoding/json"
	"io"
	"net/http"
	"strconv"

	"github.com/markbates/goth"
	"golang.org/x/oauth2"
	"fmt"
)

const (
	authURL      string = "https://api.twitch.tv/kraken/oauth2/authorize"
	tokenURL     string = "https://api.twitch.tv/kraken/oauth2/token"
	userEndpoint string = "https://api.twitch.tv/kraken/user"
)

const (
	// ScopeUserRead provides read access to non-public user information, such
	// as their email address.
	ScopeUserRead string = "user_read"
	// ScopeUserBlocksEdit provides the ability to ignore or unignore on
	// behalf of a user.
	ScopeUserBlocksEdit string = "user_blocks_edit"
	// ScopeUserBlocksRead provides read access to a user's list of ignored
	// users.
	ScopeUserBlocksRead string = "user_blocks_read"
	// ScopeUserFollowsEdit provides access to manage a user's followed
	// channels.
	ScopeUserFollowsEdit string = "user_follows_edit"
	// ScopeChannelRead provides read access to non-public channel information,
	// including email address and stream key.
	ScopeChannelRead string = "channel_read"
	// ScopeChannelEditor provides write access to channel metadata (game,
	// status, etc).
	ScopeChannelEditor string = "channel_editor"
	// ScopeChannelCommercial provides access to trigger commercials on
	// channel.
	ScopeChannelCommercial string = "channel_commercial"
	// ScopeChannelStream provides the ability to reset a channel's stream key.
	ScopeChannelStream string = "channel_stream"
	// ScopeChannelSubscriptions provides read access to all subscribers to
	// your channel.
	ScopeChannelSubscriptions string = "channel_subscriptions"
	// ScopeUserSubscriptions provides read access to subscriptions of a user.
	ScopeUserSubscriptions string = "user_subscriptions"
	// ScopeChannelCheckSubscription provides read access to check if a user is
	// subscribed to your channel.
	ScopeChannelCheckSubscription string = "channel_check_subscription"
	// ScopeChatLogin provides the ability to log into chat and send messages.
	ScopeChatLogin string = "chat_login"
)

// New creates a new Twitch provider, and sets up important connection details.
// You should always call `twitch.New` to get a new Provider. Never try to create
// one manually.
func New(clientKey string, secret string, callbackURL string, scopes ...string) *Provider {
	p := &Provider{
		ClientKey:           clientKey,
		Secret:              secret,
		CallbackURL:         callbackURL,
		providerName:        "twitch",
	}
	p.config = newConfig(p, scopes)
	return p
}

// Provider is the implementation of `goth.Provider` for accessing Twitch
type Provider struct {
	ClientKey    string
	Secret       string
	CallbackURL  string
	HTTPClient   *http.Client
	config       *oauth2.Config
	providerName string
}

// Name gets the name used to retrieve this provider.
func (p *Provider) Name() string {
	return p.providerName
}

// SetName is to update the name of the provider (needed in case of multiple providers of 1 type)
func (p *Provider) SetName(name string) {
	p.providerName = name
}

func (p *Provider) Client() *http.Client {
	return goth.HTTPClientWithFallBack(p.HTTPClient)
}

// Debug is no-op for the Twitch package.
func (p *Provider) Debug(debug bool) {}

// BeginAuth asks Twitch for an authentication end-point.
func (p *Provider) BeginAuth(state string) (goth.Session, error) {
	url := p.config.AuthCodeURL(state)
	s := &Session{
		AuthURL: url,
	}
	return s, nil
}

// FetchUser will go to Twitch and access basic info about the user.
func (p *Provider) FetchUser(session goth.Session) (goth.User, error) {

	s := session.(*Session)

	user := goth.User{
		AccessToken:  s.AccessToken,
		Provider:     p.Name(),
		RefreshToken: s.RefreshToken,
		ExpiresAt:    s.ExpiresAt,
	}

	if user.AccessToken == "" {
		// data is not yet retrieved since accessToken is still empty
		return user, fmt.Errorf("%s cannot get user information without accessToken", p.providerName)
	}

	req, err := http.NewRequest("GET", userEndpoint, nil)
	if err != nil {
		return user, err
	}
	req.Header.Set("Accept", "application/vnd.twitchtv.v3+json")
	req.Header.Set("Authorization", "OAuth "+s.AccessToken)
	resp, err := p.Client().Do(req)
	if err != nil {
		return user, err
	}
	defer resp.Body.Close()

	if resp.StatusCode != http.StatusOK {
		return user, fmt.Errorf("%s responded with a %d trying to fetch user information", p.providerName, resp.StatusCode)
	}

	err = userFromReader(resp.Body, &user)
	return user, err
}

func userFromReader(r io.Reader, user *goth.User) error {
	u := struct {
		Name        string `json:"name"`
		Email       string `json:"email"`
		Nickname    string `json:"display_name"`
		AvatarURL   string `json:"logo"`
		Description string `json:"bio"`
		ID          int    `json:"_id"`
	}{}

	err := json.NewDecoder(r).Decode(&u)
	if err != nil {
		return err
	}

	user.Name = u.Name
	user.Email = u.Email
	user.NickName = u.Nickname
	user.Location = "No location is provided by the Twitch API"
	user.AvatarURL = u.AvatarURL
	user.Description = u.Description
	user.UserID = strconv.Itoa(u.ID)

	return nil
}

func newConfig(p *Provider, scopes []string) *oauth2.Config {
	c := &oauth2.Config{
		ClientID:     p.ClientKey,
		ClientSecret: p.Secret,
		RedirectURL:  p.CallbackURL,
		Endpoint: oauth2.Endpoint{
			AuthURL:  authURL,
			TokenURL: tokenURL,
		},
		Scopes: []string{},
	}

	if len(scopes) > 0 {
		for _, scope := range scopes {
			c.Scopes = append(c.Scopes, scope)
		}
	} else {
		c.Scopes = []string{ScopeUserRead}
	}

	return c
}

//RefreshTokenAvailable refresh token is provided by auth provider or not
func (p *Provider) RefreshTokenAvailable() bool {
	return true
}

//RefreshToken get new access token based on the refresh token
func (p *Provider) RefreshToken(refreshToken string) (*oauth2.Token, error) {
	token := &oauth2.Token{RefreshToken: refreshToken}
	ts := p.config.TokenSource(goth.ContextForClient(p.Client()), token)
	newToken, err := ts.Token()
	if err != nil {
		return nil, err
	}
	return newToken, err
}