// Copyright (c) 2024 Mattermost Community Enterprise
// OAuth Providers Implementation

package oauthproviders

import (
	"encoding/json"
	"errors"
	"io"
	"strings"

	"github.com/golang-jwt/jwt/v5"

	"github.com/mattermost/mattermost/server/public/model"
	"github.com/mattermost/mattermost/server/public/shared/mlog"
	"github.com/mattermost/mattermost/server/public/shared/request"
)

// OAuthProviderConfig holds configuration for OAuth providers
type OAuthProviderConfig struct {
	Config func() *model.Config
	Logger mlog.LoggerIFace
}

// GoogleProvider implements OAuthProvider for Google
type GoogleProvider struct {
	config func() *model.Config
	logger mlog.LoggerIFace
}

// Office365Provider implements OAuthProvider for Office 365
type Office365Provider struct {
	config func() *model.Config
	logger mlog.LoggerIFace
}

// OpenIDConnectProvider implements OAuthProvider for generic OpenID Connect
type OpenIDConnectProvider struct {
	config func() *model.Config
	logger mlog.LoggerIFace
}

// NewGoogleProvider creates a new Google OAuth provider
func NewGoogleProvider(cfg *OAuthProviderConfig) *GoogleProvider {
	return &GoogleProvider{
		config: cfg.Config,
		logger: cfg.Logger,
	}
}

// NewOffice365Provider creates a new Office 365 OAuth provider
func NewOffice365Provider(cfg *OAuthProviderConfig) *Office365Provider {
	return &Office365Provider{
		config: cfg.Config,
		logger: cfg.Logger,
	}
}

// NewOpenIDConnectProvider creates a new OpenID Connect provider
func NewOpenIDConnectProvider(cfg *OAuthProviderConfig) *OpenIDConnectProvider {
	return &OpenIDConnectProvider{
		config: cfg.Config,
		logger: cfg.Logger,
	}
}

// GoogleUser represents a user from Google's API
type GoogleUser struct {
	ID            string `json:"id"`
	Email         string `json:"email"`
	VerifiedEmail bool   `json:"verified_email"`
	Name          string `json:"name"`
	GivenName     string `json:"given_name"`
	FamilyName    string `json:"family_name"`
	Picture       string `json:"picture"`
	Locale        string `json:"locale"`
}

// GetUserFromJSON implements OAuthProvider for Google
func (g *GoogleProvider) GetUserFromJSON(rctx request.CTX, data io.Reader, tokenUser *model.User) (*model.User, error) {
	var gu GoogleUser
	if err := json.NewDecoder(data).Decode(&gu); err != nil {
		return nil, err
	}

	if gu.Email == "" {
		return nil, errors.New("google user email is empty")
	}

	user := &model.User{
		Email:       gu.Email,
		FirstName:   gu.GivenName,
		LastName:    gu.FamilyName,
		AuthService: model.ServiceGoogle,
		AuthData:    model.NewPointer(gu.ID),
	}

	if gu.Locale != "" {
		user.Locale = gu.Locale
	}

	// Use email prefix as username if not set
	if user.Username == "" {
		parts := strings.Split(gu.Email, "@")
		if len(parts) > 0 {
			user.Username = model.CleanUsername(rctx.Logger(), parts[0])
		}
	}

	return user, nil
}

// GetSSOSettings implements OAuthProvider for Google
func (g *GoogleProvider) GetSSOSettings(rctx request.CTX, config *model.Config, service string) (*model.SSOSettings, error) {
	if config.GoogleSettings.Enable == nil || !*config.GoogleSettings.Enable {
		return nil, errors.New("google SSO is not enabled")
	}

	return &model.SSOSettings{
		Enable:          config.GoogleSettings.Enable,
		Secret:          config.GoogleSettings.Secret,
		Id:              config.GoogleSettings.Id,
		Scope:           config.GoogleSettings.Scope,
		AuthEndpoint:    config.GoogleSettings.AuthEndpoint,
		TokenEndpoint:   config.GoogleSettings.TokenEndpoint,
		UserAPIEndpoint: config.GoogleSettings.UserAPIEndpoint,
	}, nil
}

// GetUserFromIdToken implements OAuthProvider for Google
func (g *GoogleProvider) GetUserFromIdToken(rctx request.CTX, idToken string) (*model.User, error) {
	claims, err := parseJWTWithoutValidation(idToken)
	if err != nil {
		return nil, err
	}

	email, _ := claims["email"].(string)
	if email == "" {
		return nil, errors.New("email not found in ID token")
	}

	sub, _ := claims["sub"].(string)
	firstName, _ := claims["given_name"].(string)
	lastName, _ := claims["family_name"].(string)

	user := &model.User{
		Email:       email,
		FirstName:   firstName,
		LastName:    lastName,
		AuthService: model.ServiceGoogle,
		AuthData:    model.NewPointer(sub),
	}

	return user, nil
}

// IsSameUser implements OAuthProvider for Google
func (g *GoogleProvider) IsSameUser(rctx request.CTX, dbUser, oAuthUser *model.User) bool {
	if dbUser.AuthData != nil && oAuthUser.AuthData != nil {
		return *dbUser.AuthData == *oAuthUser.AuthData
	}
	return strings.EqualFold(dbUser.Email, oAuthUser.Email)
}

// Office365User represents a user from Office 365's API
type Office365User struct {
	ID                string `json:"id"`
	DisplayName       string `json:"displayName"`
	GivenName         string `json:"givenName"`
	Surname           string `json:"surname"`
	Mail              string `json:"mail"`
	UserPrincipalName string `json:"userPrincipalName"`
	PreferredLanguage string `json:"preferredLanguage"`
}

// GetUserFromJSON implements OAuthProvider for Office 365
func (o *Office365Provider) GetUserFromJSON(rctx request.CTX, data io.Reader, tokenUser *model.User) (*model.User, error) {
	var ou Office365User
	if err := json.NewDecoder(data).Decode(&ou); err != nil {
		return nil, err
	}

	email := ou.Mail
	if email == "" {
		email = ou.UserPrincipalName
	}
	if email == "" {
		return nil, errors.New("office365 user email is empty")
	}

	user := &model.User{
		Email:       email,
		FirstName:   ou.GivenName,
		LastName:    ou.Surname,
		AuthService: model.ServiceOffice365,
		AuthData:    model.NewPointer(ou.ID),
	}

	if ou.PreferredLanguage != "" {
		// Convert language code to locale (e.g., "en-US" -> "en")
		parts := strings.Split(ou.PreferredLanguage, "-")
		if len(parts) > 0 {
			user.Locale = strings.ToLower(parts[0])
		}
	}

	// Use email prefix as username if not set
	if user.Username == "" {
		parts := strings.Split(email, "@")
		if len(parts) > 0 {
			user.Username = model.CleanUsername(rctx.Logger(), parts[0])
		}
	}

	return user, nil
}

// GetSSOSettings implements OAuthProvider for Office 365
func (o *Office365Provider) GetSSOSettings(rctx request.CTX, config *model.Config, service string) (*model.SSOSettings, error) {
	if config.Office365Settings.Enable == nil || !*config.Office365Settings.Enable {
		return nil, errors.New("office365 SSO is not enabled")
	}

	return &model.SSOSettings{
		Enable:          config.Office365Settings.Enable,
		Secret:          config.Office365Settings.Secret,
		Id:              config.Office365Settings.Id,
		Scope:           config.Office365Settings.Scope,
		AuthEndpoint:    config.Office365Settings.AuthEndpoint,
		TokenEndpoint:   config.Office365Settings.TokenEndpoint,
		UserAPIEndpoint: config.Office365Settings.UserAPIEndpoint,
	}, nil
}

// GetUserFromIdToken implements OAuthProvider for Office 365
func (o *Office365Provider) GetUserFromIdToken(rctx request.CTX, idToken string) (*model.User, error) {
	claims, err := parseJWTWithoutValidation(idToken)
	if err != nil {
		return nil, err
	}

	email, _ := claims["email"].(string)
	if email == "" {
		email, _ = claims["upn"].(string) // UserPrincipalName
	}
	if email == "" {
		return nil, errors.New("email not found in ID token")
	}

	sub, _ := claims["sub"].(string)
	oid, _ := claims["oid"].(string) // Office 365 object ID
	firstName, _ := claims["given_name"].(string)
	lastName, _ := claims["family_name"].(string)

	authData := sub
	if oid != "" {
		authData = oid
	}

	user := &model.User{
		Email:       email,
		FirstName:   firstName,
		LastName:    lastName,
		AuthService: model.ServiceOffice365,
		AuthData:    model.NewPointer(authData),
	}

	return user, nil
}

// IsSameUser implements OAuthProvider for Office 365
func (o *Office365Provider) IsSameUser(rctx request.CTX, dbUser, oAuthUser *model.User) bool {
	if dbUser.AuthData != nil && oAuthUser.AuthData != nil {
		return *dbUser.AuthData == *oAuthUser.AuthData
	}
	return strings.EqualFold(dbUser.Email, oAuthUser.Email)
}

// OpenIDConnectUser represents claims from an OpenID Connect token
type OpenIDConnectUser struct {
	Sub               string `json:"sub"`
	Email             string `json:"email"`
	EmailVerified     bool   `json:"email_verified"`
	Name              string `json:"name"`
	GivenName         string `json:"given_name"`
	FamilyName        string `json:"family_name"`
	PreferredUsername string `json:"preferred_username"`
	Picture           string `json:"picture"`
	Locale            string `json:"locale"`
}

// GetUserFromJSON implements OAuthProvider for OpenID Connect
func (o *OpenIDConnectProvider) GetUserFromJSON(rctx request.CTX, data io.Reader, tokenUser *model.User) (*model.User, error) {
	var ou OpenIDConnectUser
	if err := json.NewDecoder(data).Decode(&ou); err != nil {
		return nil, err
	}

	email := ou.Email
	if email == "" && ou.PreferredUsername != "" && strings.Contains(ou.PreferredUsername, "@") {
		email = ou.PreferredUsername
	}
	if email == "" {
		return nil, errors.New("openid connect user email is empty")
	}

	user := &model.User{
		Email:       email,
		FirstName:   ou.GivenName,
		LastName:    ou.FamilyName,
		AuthService: model.ServiceOpenid,
		AuthData:    model.NewPointer(ou.Sub),
	}

	if ou.PreferredUsername != "" && !strings.Contains(ou.PreferredUsername, "@") {
		user.Username = model.CleanUsername(rctx.Logger(), ou.PreferredUsername)
	}

	if ou.Locale != "" {
		user.Locale = ou.Locale
	}

	return user, nil
}

// GetSSOSettings implements OAuthProvider for OpenID Connect
func (o *OpenIDConnectProvider) GetSSOSettings(rctx request.CTX, config *model.Config, service string) (*model.SSOSettings, error) {
	if config.OpenIdSettings.Enable == nil || !*config.OpenIdSettings.Enable {
		return nil, errors.New("openid connect SSO is not enabled")
	}

	return &model.SSOSettings{
		Enable:          config.OpenIdSettings.Enable,
		Secret:          config.OpenIdSettings.Secret,
		Id:              config.OpenIdSettings.Id,
		Scope:           config.OpenIdSettings.Scope,
		AuthEndpoint:    config.OpenIdSettings.AuthEndpoint,
		TokenEndpoint:   config.OpenIdSettings.TokenEndpoint,
		UserAPIEndpoint: config.OpenIdSettings.UserAPIEndpoint,
	}, nil
}

// GetUserFromIdToken implements OAuthProvider for OpenID Connect
func (o *OpenIDConnectProvider) GetUserFromIdToken(rctx request.CTX, idToken string) (*model.User, error) {
	claims, err := parseJWTWithoutValidation(idToken)
	if err != nil {
		return nil, err
	}

	email, _ := claims["email"].(string)
	if email == "" {
		preferredUsername, _ := claims["preferred_username"].(string)
		if strings.Contains(preferredUsername, "@") {
			email = preferredUsername
		}
	}
	if email == "" {
		return nil, errors.New("email not found in ID token")
	}

	sub, _ := claims["sub"].(string)
	firstName, _ := claims["given_name"].(string)
	lastName, _ := claims["family_name"].(string)

	user := &model.User{
		Email:       email,
		FirstName:   firstName,
		LastName:    lastName,
		AuthService: model.ServiceOpenid,
		AuthData:    model.NewPointer(sub),
	}

	return user, nil
}

// IsSameUser implements OAuthProvider for OpenID Connect
func (o *OpenIDConnectProvider) IsSameUser(rctx request.CTX, dbUser, oAuthUser *model.User) bool {
	if dbUser.AuthData != nil && oAuthUser.AuthData != nil {
		return *dbUser.AuthData == *oAuthUser.AuthData
	}
	return strings.EqualFold(dbUser.Email, oAuthUser.Email)
}

// parseJWTWithoutValidation parses a JWT and returns the claims without validating the signature
// This is used when we trust the token source (e.g., received directly from the IdP)
func parseJWTWithoutValidation(tokenString string) (jwt.MapClaims, error) {
	parser := jwt.NewParser()
	token, _, err := parser.ParseUnverified(tokenString, jwt.MapClaims{})
	if err != nil {
		return nil, err
	}

	claims, ok := token.Claims.(jwt.MapClaims)
	if !ok {
		return nil, errors.New("invalid token claims")
	}

	return claims, nil
}