package github

import (
	"context"
	"encoding/json"
	"fmt"
	"io/ioutil"
	"math/rand"
	"net/http"
	"net/url"
	"regexp"
	"sort"
	"strconv"
	"strings"
	"time"

	"github.com/pkg/errors"

	"github.com/MichaelMure/git-bug/bridge/core"
	"github.com/MichaelMure/git-bug/bridge/core/auth"
	"github.com/MichaelMure/git-bug/cache"
	"github.com/MichaelMure/git-bug/input"
	"github.com/MichaelMure/git-bug/repository"
)

const githubClientID = "ce3600aa56c2e69f18a5" // git-bug org

var (
	ErrBadProjectURL = errors.New("bad project url")
)

func (g *Github) ValidParams() map[string]interface{} {
	return map[string]interface{}{
		"URL":        nil,
		"Login":      nil,
		"CredPrefix": nil,
		"TokenRaw":   nil,
		"Owner":      nil,
		"Project":    nil,
	}
}

func (g *Github) Configure(repo *cache.RepoCache, params core.BridgeParams) (core.Configuration, error) {
	var err error
	var owner string
	var project string
	var ok bool

	// getting owner and project name
	switch {
	case params.Owner != "" && params.Project != "":
		// first try to use params if both or project and owner are provided
		owner = params.Owner
		project = params.Project
	case params.URL != "":
		// try to parse params URL and extract owner and project
		owner, project, err = splitURL(params.URL)
		if err != nil {
			return nil, err
		}
	default:
		// terminal prompt
		owner, project, err = promptURL(repo)
		if err != nil {
			return nil, err
		}
	}

	// validate project owner and override with the correct case
	ok, owner, err = validateUsername(owner)
	if err != nil {
		return nil, err
	}
	if !ok {
		return nil, fmt.Errorf("invalid parameter owner: %v", owner)
	}

	var login string
	var cred auth.Credential

	switch {
	case params.CredPrefix != "":
		cred, err = auth.LoadWithPrefix(repo, params.CredPrefix)
		if err != nil {
			return nil, err
		}
		l, ok := cred.GetMetadata(auth.MetaKeyLogin)
		if !ok {
			return nil, fmt.Errorf("credential doesn't have a login")
		}
		login = l
	case params.TokenRaw != "":
		token := auth.NewToken(target, params.TokenRaw)
		login, err = getLoginFromToken(token)
		if err != nil {
			return nil, err
		}
		token.SetMetadata(auth.MetaKeyLogin, login)
		cred = token
	default:
		if params.Login == "" {
			login, err = promptLogin()
		} else {
			// validate login and override with the correct case
			ok, login, err = validateUsername(params.Login)
			if !ok {
				return nil, fmt.Errorf("invalid parameter login: %v", params.Login)
			}
		}
		if err != nil {
			return nil, err
		}
		cred, err = promptTokenOptions(repo, login, owner, project)
		if err != nil {
			return nil, err
		}
	}

	token, ok := cred.(*auth.Token)
	if !ok {
		return nil, fmt.Errorf("the Github bridge only handle token credentials")
	}

	// verify access to the repository with token
	ok, err = validateProject(owner, project, token)
	if err != nil {
		return nil, err
	}
	if !ok {
		return nil, fmt.Errorf("project doesn't exist or authentication token has an incorrect scope")
	}

	conf := make(core.Configuration)
	conf[core.ConfigKeyTarget] = target
	conf[confKeyOwner] = owner
	conf[confKeyProject] = project
	conf[confKeyDefaultLogin] = login

	err = g.ValidateConfig(conf)
	if err != nil {
		return nil, err
	}

	// don't forget to store the now known valid token
	if !auth.IdExist(repo, cred.ID()) {
		err = auth.Store(repo, cred)
		if err != nil {
			return nil, err
		}
	}

	return conf, core.FinishConfig(repo, metaKeyGithubLogin, login)
}

func (*Github) ValidateConfig(conf core.Configuration) error {
	if v, ok := conf[core.ConfigKeyTarget]; !ok {
		return fmt.Errorf("missing %s key", core.ConfigKeyTarget)
	} else if v != target {
		return fmt.Errorf("unexpected target name: %v", v)
	}
	if _, ok := conf[confKeyOwner]; !ok {
		return fmt.Errorf("missing %s key", confKeyOwner)
	}
	if _, ok := conf[confKeyProject]; !ok {
		return fmt.Errorf("missing %s key", confKeyProject)
	}
	if _, ok := conf[confKeyDefaultLogin]; !ok {
		return fmt.Errorf("missing %s key", confKeyDefaultLogin)
	}

	return nil
}

func requestToken() (string, error) {
	scope, err := promptUserForProjectVisibility()
	if err != nil {
		return "", errors.WithStack(err)
	}
	resp, err := requestUserVerificationCode(scope)
	if err != nil {
		return "", err
	}
	promptUserToGoToBrowser(resp.uri, resp.userCode)
	return pollGithubForAuthorization(resp.deviceCode, resp.interval)
}

func promptUserForProjectVisibility() (string, error) {
	fmt.Println("git-bug will now generate an access token in your Github profile. The token is stored in the global git config.")
	fmt.Println()
	fmt.Println("The access scope depend on the type of repository.")
	fmt.Println("Public:")
	fmt.Println("  - 'public_repo': to be able to read public repositories")
	fmt.Println("Private:")
	fmt.Println("  - 'repo'       : to be able to read private repositories")
	fmt.Println()
	index, err := input.PromptChoice("repository visibility", []string{"public", "private"})
	if err != nil {
		return "", err
	}
	return []string{"public_repo", "repo"}[index], nil
}

type githRespT struct {
	uri        string
	userCode   string
	deviceCode string
	interval   int64
}

func requestUserVerificationCode(scope string) (*githRespT, error) {
	params := url.Values{}
	params.Set("client_id", githubClientID)
	params.Set("scope", scope)
	client := &http.Client{
		Timeout: defaultTimeout,
	}

	resp, err := client.PostForm("https://github.com/login/device/code", params)
	if err != nil {
		return nil, errors.Wrap(err, "error requesting user verification code")
	}
	defer resp.Body.Close()
	if resp.StatusCode != http.StatusOK {
		return nil, fmt.Errorf("unexpected response status code %d from Github API", resp.StatusCode)
	}

	data, err := ioutil.ReadAll(resp.Body)
	if err != nil {
		return nil, errors.Wrap(err, "error requesting user verification code")
	}

	vals, err := url.ParseQuery(string(data))
	if err != nil {
		return nil, errors.Wrap(err, "error decoding Github API response")
	}

	interval, err := strconv.ParseInt(vals.Get("interval"), 10, 64) // base 10, bitSize 64
	if err != nil {
		return nil, errors.Wrap(err, "Error parsing integer received from Github API")
	}

	return &githRespT{
		uri:        vals.Get("verification_uri"),
		userCode:   vals.Get("user_code"),
		deviceCode: vals.Get("device_code"),
		interval:   interval,
	}, nil
}

func promptUserToGoToBrowser(url, userCode string) {
	fmt.Println("Please visit the following Github URL in a browser and enter your user authentication code.")
	fmt.Println()
	fmt.Println("  URL:", url)
	fmt.Println("  user authentiation code:", userCode)
	fmt.Println()
}

func pollGithubForAuthorization(deviceCode string, intervalSec int64) (string, error) {
	params := url.Values{}
	params.Set("client_id", githubClientID)
	params.Set("device_code", deviceCode)
	params.Set("grant_type", "urn:ietf:params:oauth:grant-type:device_code") // fixed by RFC 8628
	client := &http.Client{
		Timeout: defaultTimeout,
	}
	interval := time.Duration(intervalSec * 1100) // milliseconds, add 10% margin

	for {
		resp, err := client.PostForm("https://github.com/login/oauth/access_token", params)
		if err != nil {
			return "", errors.Wrap(err, "error polling the Github API")
		}
		if resp.StatusCode != http.StatusOK {
			_ = resp.Body.Close()
			return "", fmt.Errorf("unexpected response status code %d from Github API", resp.StatusCode)
		}

		data, err := ioutil.ReadAll(resp.Body)
		if err != nil {
			_ = resp.Body.Close()
			return "", errors.Wrap(err, "error polling the Github API")
		}
		_ = resp.Body.Close()

		values, err := url.ParseQuery(string(data))
		if err != nil {
			return "", errors.Wrap(err, "error decoding Github API response")
		}

		if token := values.Get("access_token"); token != "" {
			return token, nil
		}

		switch apiError := values.Get("error"); apiError {
		case "slow_down":
			interval += 5500 // add 5 seconds (RFC 8628), plus some margin
			time.Sleep(interval * time.Millisecond)
			continue
		case "authorization_pending":
			time.Sleep(interval * time.Millisecond)
			continue
		case "":
			return "", errors.New("unexpected response from Github API")
		default:
			// apiError should equal one of: "expired_token", "unsupported_grant_type",
			// "incorrect_client_credentials", "incorrect_device_code", or "access_denied"
			return "", fmt.Errorf("error creating token: %v, %v", apiError, values.Get("error_description"))
		}
	}
}

func randomFingerprint() string {
	// Doesn't have to be crypto secure, it's just to avoid token collision
	rand.Seed(time.Now().UnixNano())
	var letterRunes = []rune("abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ")
	b := make([]rune, 32)
	for i := range b {
		b[i] = letterRunes[rand.Intn(len(letterRunes))]
	}
	return string(b)
}

func promptTokenOptions(repo repository.RepoKeyring, login, owner, project string) (auth.Credential, error) {
	creds, err := auth.List(repo,
		auth.WithTarget(target),
		auth.WithKind(auth.KindToken),
		auth.WithMeta(auth.MetaKeyLogin, login),
	)
	if err != nil {
		return nil, err
	}

	cred, index, err := input.PromptCredential(target, "token", creds, []string{
		"enter my token",
		"interactive token creation",
	})
	switch {
	case err != nil:
		return nil, err
	case cred != nil:
		return cred, nil
	case index == 0:
		return promptToken()
	case index == 1:
		value, err := requestToken()
		if err != nil {
			return nil, err
		}
		token := auth.NewToken(target, value)
		token.SetMetadata(auth.MetaKeyLogin, login)
		return token, nil
	default:
		panic("missed case")
	}
}

func promptToken() (*auth.Token, error) {
	fmt.Println("You can generate a new token by visiting https://github.com/settings/tokens.")
	fmt.Println("Choose 'Generate new token' and set the necessary access scope for your repository.")
	fmt.Println()
	fmt.Println("The access scope depend on the type of repository.")
	fmt.Println("Public:")
	fmt.Println("  - 'public_repo': to be able to read public repositories")
	fmt.Println("Private:")
	fmt.Println("  - 'repo'       : to be able to read private repositories")
	fmt.Println()

	re := regexp.MustCompile(`^[a-zA-Z0-9]{40}$`)

	var login string

	validator := func(name string, value string) (complaint string, err error) {
		if !re.MatchString(value) {
			return "token has incorrect format", nil
		}
		login, err = getLoginFromToken(auth.NewToken(target, value))
		if err != nil {
			return fmt.Sprintf("token is invalid: %v", err), nil
		}
		return "", nil
	}

	rawToken, err := input.Prompt("Enter token", "token", input.Required, validator)
	if err != nil {
		return nil, err
	}

	token := auth.NewToken(target, rawToken)
	token.SetMetadata(auth.MetaKeyLogin, login)

	return token, nil
}

func promptURL(repo repository.RepoCommon) (string, string, error) {
	validRemotes, err := getValidGithubRemoteURLs(repo)
	if err != nil {
		return "", "", err
	}

	validator := func(name, value string) (string, error) {
		_, _, err := splitURL(value)
		if err != nil {
			return err.Error(), nil
		}
		return "", nil
	}

	url, err := input.PromptURLWithRemote("Github project URL", "URL", validRemotes, input.Required, validator)
	if err != nil {
		return "", "", err
	}

	return splitURL(url)
}

// splitURL extract the owner and project from a github repository URL. It will remove the
// '.git' extension from the URL before parsing it.
// Note that Github removes the '.git' extension from projects names at their creation
func splitURL(url string) (owner string, project string, err error) {
	cleanURL := strings.TrimSuffix(url, ".git")

	re := regexp.MustCompile(`github\.com[/:]([a-zA-Z0-9\-_]+)/([a-zA-Z0-9\-_.]+)`)

	res := re.FindStringSubmatch(cleanURL)
	if res == nil {
		return "", "", ErrBadProjectURL
	}

	owner = res[1]
	project = res[2]
	return
}

func getValidGithubRemoteURLs(repo repository.RepoCommon) ([]string, error) {
	remotes, err := repo.GetRemotes()
	if err != nil {
		return nil, err
	}

	urls := make([]string, 0, len(remotes))
	for _, url := range remotes {
		// split url can work again with shortURL
		owner, project, err := splitURL(url)
		if err == nil {
			shortURL := fmt.Sprintf("%s/%s/%s", "github.com", owner, project)
			urls = append(urls, shortURL)
		}
	}

	sort.Strings(urls)

	return urls, nil
}

func promptLogin() (string, error) {
	var login string

	validator := func(_ string, value string) (string, error) {
		ok, fixed, err := validateUsername(value)
		if err != nil {
			return "", err
		}
		if !ok {
			return "invalid login", nil
		}
		login = fixed
		return "", nil
	}

	_, err := input.Prompt("Github login", "login", input.Required, validator)
	if err != nil {
		return "", err
	}

	return login, nil
}

func validateUsername(username string) (bool, string, error) {
	url := fmt.Sprintf("%s/users/%s", githubV3Url, username)

	client := &http.Client{
		Timeout: defaultTimeout,
	}

	resp, err := client.Get(url)
	if err != nil {
		return false, "", err
	}

	if resp.StatusCode != http.StatusOK {
		return false, "", nil
	}

	data, err := ioutil.ReadAll(resp.Body)
	if err != nil {
		return false, "", err
	}

	err = resp.Body.Close()
	if err != nil {
		return false, "", err
	}

	var decoded struct {
		Login string `json:"login"`
	}
	err = json.Unmarshal(data, &decoded)
	if err != nil {
		return false, "", err
	}

	if decoded.Login == "" {
		return false, "", fmt.Errorf("validateUsername: missing login in the response")
	}

	return true, decoded.Login, nil
}

func validateProject(owner, project string, token *auth.Token) (bool, error) {
	url := fmt.Sprintf("%s/repos/%s/%s", githubV3Url, owner, project)

	req, err := http.NewRequest("GET", url, nil)
	if err != nil {
		return false, err
	}

	// need the token for private repositories
	req.Header.Set("Authorization", fmt.Sprintf("token %s", token.Value))

	client := &http.Client{
		Timeout: defaultTimeout,
	}

	resp, err := client.Do(req)
	if err != nil {
		return false, err
	}

	err = resp.Body.Close()
	if err != nil {
		return false, err
	}

	return resp.StatusCode == http.StatusOK, nil
}

func getLoginFromToken(token *auth.Token) (string, error) {
	ctx, cancel := context.WithTimeout(context.Background(), defaultTimeout)
	defer cancel()

	client := buildClient(token)

	var q loginQuery

	err := client.Query(ctx, &q, nil)
	if err != nil {
		return "", err
	}
	if q.Viewer.Login == "" {
		return "", fmt.Errorf("github say username is empty")
	}

	return q.Viewer.Login, nil
}