package github

import (
	"bufio"
	"bytes"
	"encoding/json"
	"fmt"
	"io"
	"io/ioutil"
	"math/rand"
	"net/http"
	"os"
	"regexp"
	"strconv"
	"strings"
	"syscall"
	"time"

	"github.com/pkg/errors"
	"golang.org/x/crypto/ssh/terminal"

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

const (
	target      = "github"
	githubV3Url = "https://api.github.com"
	keyOwner    = "owner"
	keyProject  = "project"
	keyToken    = "token"

	defaultTimeout = 60 * time.Second
)

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

func (g *Github) Configure(repo repository.RepoCommon, params core.BridgeParams) (core.Configuration, error) {
	conf := make(core.Configuration)
	var err error
	var token string
	var owner string
	var project string

	if params.Token != "" &&
		!(params.URL != "" || (params.Project != "" && params.Owner != "")) {
		return nil, fmt.Errorf("you must provide a project URL or Owner/Name to configure this bridge with a token")
	}

	// getting owner and project name
	if params.Owner != "" && params.Project != "" {
		// first try to use params if both or project and owner are provided
		owner = params.Owner
		project = params.Project

	} else if params.URL != "" {
		// try to parse params URL and extract owner and project
		owner, project, err = splitURL(params.URL)
		if err != nil {
			return nil, err
		}

	} else {
		// remote suggestions
		remotes, err := repo.GetRemotes()
		if err != nil {
			return nil, err
		}

		// terminal prompt
		owner, project, err = promptURL(remotes)
		if err != nil {
			return nil, err
		}
	}

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

	// try to get token from params if provided, else use terminal prompt to either
	// enter a token or login and generate a new one
	if params.Token != "" {
		token = params.Token

	} else {
		token, err = promptTokenOptions(owner, project)
		if err != nil {
			return nil, err
		}
	}

	// 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[core.KeyTarget] = target
	conf[keyToken] = token
	conf[keyOwner] = owner
	conf[keyProject] = project

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

	return conf, nil
}

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

	if _, ok := conf[keyToken]; !ok {
		return fmt.Errorf("missing %s key", keyToken)
	}

	if _, ok := conf[keyOwner]; !ok {
		return fmt.Errorf("missing %s key", keyOwner)
	}

	if _, ok := conf[keyProject]; !ok {
		return fmt.Errorf("missing %s key", keyProject)
	}

	return nil
}

func requestToken(note, username, password string, scope string) (*http.Response, error) {
	return requestTokenWith2FA(note, username, password, "", scope)
}

func requestTokenWith2FA(note, username, password, otpCode string, scope string) (*http.Response, error) {
	url := fmt.Sprintf("%s/authorizations", githubV3Url)
	params := struct {
		Scopes      []string `json:"scopes"`
		Note        string   `json:"note"`
		Fingerprint string   `json:"fingerprint"`
	}{
		Scopes:      []string{scope},
		Note:        note,
		Fingerprint: randomFingerprint(),
	}

	data, err := json.Marshal(params)
	if err != nil {
		return nil, err
	}

	req, err := http.NewRequest("POST", url, bytes.NewBuffer(data))
	if err != nil {
		return nil, err
	}

	req.SetBasicAuth(username, password)
	req.Header.Set("Content-Type", "application/json")

	if otpCode != "" {
		req.Header.Set("X-GitHub-OTP", otpCode)
	}

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

	return client.Do(req)
}

func decodeBody(body io.ReadCloser) (string, error) {
	data, _ := ioutil.ReadAll(body)

	aux := struct {
		Token string `json:"token"`
	}{}

	err := json.Unmarshal(data, &aux)
	if err != nil {
		return "", err
	}

	if aux.Token == "" {
		return "", fmt.Errorf("no token found in response: %s", string(data))
	}

	return aux.Token, nil
}

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(owner, project string) (string, error) {
	for {
		fmt.Println()
		fmt.Println("[1]: user provided token")
		fmt.Println("[2]: interactive token creation")
		fmt.Print("Select option: ")

		line, err := bufio.NewReader(os.Stdin).ReadString('\n')
		fmt.Println()
		if err != nil {
			return "", err
		}

		line = strings.TrimRight(line, "\n")

		index, err := strconv.Atoi(line)
		if err != nil || (index != 1 && index != 2) {
			fmt.Println("invalid input")
			continue
		}

		if index == 1 {
			return promptToken()
		}

		return loginAndRequestToken(owner, project)
	}
}

func promptToken() (string, 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, err := regexp.Compile(`^[a-zA-Z0-9]{40}`)
	if err != nil {
		panic("regexp compile:" + err.Error())
	}

	for {
		fmt.Print("Enter token: ")

		line, err := bufio.NewReader(os.Stdin).ReadString('\n')
		if err != nil {
			return "", err
		}

		token := strings.TrimRight(line, "\n")
		if re.MatchString(token) {
			return token, nil
		}

		fmt.Println("token is invalid")
	}
}

func loginAndRequestToken(owner, project string) (string, error) {
	fmt.Println("git-bug will now generate an access token in your Github profile. Your credential are not stored and are only used to generate the token. The token is stored in the repository 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()

	// prompt project visibility to know the token scope needed for the repository
	isPublic, err := promptProjectVisibility()
	if err != nil {
		return "", err
	}

	username, err := promptUsername()
	if err != nil {
		return "", err
	}

	password, err := promptPassword()
	if err != nil {
		return "", err
	}

	var scope string
	if isPublic {
		// public_repo is requested to be able to read public repositories
		scope = "public_repo"
	} else {
		// 'repo' is request to be able to read private repositories
		// /!\ token will have read/write rights on every private repository you have access to
		scope = "repo"
	}

	// Attempt to authenticate and create a token

	note := fmt.Sprintf("git-bug - %s/%s", owner, project)

	resp, err := requestToken(note, username, password, scope)
	if err != nil {
		return "", err
	}

	defer resp.Body.Close()

	// Handle 2FA is needed
	OTPHeader := resp.Header.Get("X-GitHub-OTP")
	if resp.StatusCode == http.StatusUnauthorized && OTPHeader != "" {
		otpCode, err := prompt2FA()
		if err != nil {
			return "", err
		}

		resp, err = requestTokenWith2FA(note, username, password, otpCode, scope)
		if err != nil {
			return "", err
		}

		defer resp.Body.Close()
	}

	if resp.StatusCode == http.StatusCreated {
		return decodeBody(resp.Body)
	}

	b, _ := ioutil.ReadAll(resp.Body)
	return "", fmt.Errorf("error creating token %v: %v", resp.StatusCode, string(b))
}

func promptUsername() (string, error) {
	for {
		fmt.Print("username: ")

		line, err := bufio.NewReader(os.Stdin).ReadString('\n')
		if err != nil {
			return "", err
		}

		line = strings.TrimRight(line, "\n")

		ok, err := validateUsername(line)
		if err != nil {
			return "", err
		}
		if ok {
			return line, nil
		}

		fmt.Println("invalid username")
	}
}

func promptURL(remotes map[string]string) (string, string, error) {
	validRemotes := getValidGithubRemoteURLs(remotes)
	if len(validRemotes) > 0 {
		for {
			fmt.Println("\nDetected projects:")

			// print valid remote github urls
			for i, remote := range validRemotes {
				fmt.Printf("[%d]: %v\n", i+1, remote)
			}

			fmt.Printf("\n[0]: Another project\n\n")
			fmt.Printf("Select option: ")

			line, err := bufio.NewReader(os.Stdin).ReadString('\n')
			if err != nil {
				return "", "", err
			}

			line = strings.TrimRight(line, "\n")

			index, err := strconv.Atoi(line)
			if err != nil || index < 0 || index > len(validRemotes) {
				fmt.Println("invalid input")
				continue
			}

			// if user want to enter another project url break this loop
			if index == 0 {
				break
			}

			// get owner and project with index
			owner, project, _ := splitURL(validRemotes[index-1])
			return owner, project, nil
		}
	}

	// manually enter github url
	for {
		fmt.Print("Github project URL: ")

		line, err := bufio.NewReader(os.Stdin).ReadString('\n')
		if err != nil {
			return "", "", err
		}

		line = strings.TrimRight(line, "\n")
		if line == "" {
			fmt.Println("URL is empty")
			continue
		}

		// get owner and project from url
		owner, project, err := splitURL(line)
		if err != nil {
			fmt.Println(err)
			continue
		}

		return owner, project, nil
	}
}

// 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, err := regexp.Compile(`github\.com[/:]([a-zA-Z0-9\-_]+)/([a-zA-Z0-9\-_.]+)`)
	if err != nil {
		panic("regexp compile:" + err.Error())
	}

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

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

func getValidGithubRemoteURLs(remotes map[string]string) []string {
	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)
		}
	}

	return urls
}

func validateUsername(username string) (bool, 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
	}

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

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

func validateProject(owner, project, token string) (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))

	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 promptPassword() (string, error) {
	for {
		fmt.Print("password: ")

		bytePassword, err := terminal.ReadPassword(int(syscall.Stdin))
		// new line for coherent formatting, ReadPassword clip the normal new line
		// entered by the user
		fmt.Println()

		if err != nil {
			return "", err
		}

		if len(bytePassword) > 0 {
			return string(bytePassword), nil
		}

		fmt.Println("password is empty")
	}
}

func prompt2FA() (string, error) {
	for {
		fmt.Print("two-factor authentication code: ")

		byte2fa, err := terminal.ReadPassword(int(syscall.Stdin))
		fmt.Println()
		if err != nil {
			return "", err
		}

		if len(byte2fa) > 0 {
			return string(byte2fa), nil
		}

		fmt.Println("code is empty")
	}
}

func promptProjectVisibility() (bool, error) {
	for {
		fmt.Println("[1]: public")
		fmt.Println("[2]: private")
		fmt.Print("repository visibility: ")

		line, err := bufio.NewReader(os.Stdin).ReadString('\n')
		fmt.Println()
		if err != nil {
			return false, err
		}

		line = strings.TrimRight(line, "\n")

		index, err := strconv.Atoi(line)
		if err != nil || (index != 1 && index != 2) {
			fmt.Println("invalid input")
			continue
		}

		// return true for public repositories, false for private
		return index == 1, nil
	}
}