package api

import (
	"crypto/sha256"
	"database/sql"
	"encoding/base64"
	"encoding/json"
	"fmt"
	"io"
	"log"
	"net/http"
	"strings"
	"time"

	"git.hatecomputers.club/hatecomputers/hatecomputers.club/database"
	"git.hatecomputers.club/hatecomputers/hatecomputers.club/utils"
	"golang.org/x/oauth2"
)

func StartSessionContinuation(context *RequestContext, req *http.Request, resp http.ResponseWriter) ContinuationChain {
	return func(success Continuation, failure Continuation) ContinuationChain {
		verifier := utils.RandomId() + utils.RandomId()

		sha2 := sha256.New()
		io.WriteString(sha2, verifier)
		codeChallenge := base64.RawURLEncoding.EncodeToString(sha2.Sum(nil))

		state := utils.RandomId()
		url := context.Args.OauthConfig.AuthCodeURL(state, oauth2.SetAuthURLParam("code_challenge_method", "S256"), oauth2.SetAuthURLParam("code_challenge", codeChallenge))

		http.SetCookie(resp, &http.Cookie{
			Name:     "verifier",
			Value:    verifier,
			Path:     "/",
			Secure:   true,
			SameSite: http.SameSiteLaxMode,
			MaxAge:   60,
		})
		http.SetCookie(resp, &http.Cookie{
			Name:     "state",
			Value:    state,
			Path:     "/",
			Secure:   true,
			SameSite: http.SameSiteLaxMode,
			MaxAge:   60,
		})

		http.Redirect(resp, req, url, http.StatusFound)
		return success(context, req, resp)
	}
}

func InterceptCodeContinuation(context *RequestContext, req *http.Request, resp http.ResponseWriter) ContinuationChain {
	return func(success Continuation, failure Continuation) ContinuationChain {
		state := req.URL.Query().Get("state")
		code := req.URL.Query().Get("code")

		if code == "" || state == "" {
			resp.WriteHeader(http.StatusBadRequest)
			return failure(context, req, resp)
		}

		if !verifyState(req, "state", state) {
			resp.WriteHeader(http.StatusBadRequest)
			return failure(context, req, resp)
		}
		verifierCookie, err := req.Cookie("verifier")
		if err != nil {
			resp.WriteHeader(http.StatusBadRequest)
			return failure(context, req, resp)
		}

		reqContext := req.Context()
		token, err := context.Args.OauthConfig.Exchange(reqContext, code, oauth2.SetAuthURLParam("code_verifier", verifierCookie.Value))
		if err != nil {
			log.Println(err)
			resp.WriteHeader(http.StatusInternalServerError)
			return failure(context, req, resp)
		}

		client := context.Args.OauthConfig.Client(reqContext, token)
		user, err := getOauthUser(context.DBConn, client, context.Args.OauthUserInfoURI)
		if err != nil {
			log.Println(err)
			resp.WriteHeader(http.StatusInternalServerError)

			return failure(context, req, resp)
		}

		session, err := database.MakeUserSessionFor(context.DBConn, user)
		if err != nil {
			log.Println(err)
			resp.WriteHeader(http.StatusInternalServerError)
			return failure(context, req, resp)
		}

		http.SetCookie(resp, &http.Cookie{
			Name:     "session",
			Value:    session.ID,
			Path:     "/",
			SameSite: http.SameSiteLaxMode,
			Secure:   true,
		})

		redirect := "/"
		redirectCookie, err := req.Cookie("redirect")
		if err == nil && redirectCookie.Value != "" {
			redirect = redirectCookie.Value
			http.SetCookie(resp, &http.Cookie{
				Name:   "redirect",
				MaxAge: 0,
			})
		}

		http.Redirect(resp, req, redirect, http.StatusFound)
		return success(context, req, resp)
	}
}

func getUserFromAuthHeader(dbConn *sql.DB, bearerToken string) (*database.User, error) {
	if bearerToken == "" {
		return nil, nil
	}

	parts := strings.Split(bearerToken, " ")
	if len(parts) != 2 || parts[0] != "Bearer" {
		return nil, nil
	}

	apiKey, err := database.GetAPIKey(dbConn, parts[1])
	if err != nil {
		return nil, err
	}
	if apiKey == nil {
		return nil, nil
	}

	user, err := database.GetUser(dbConn, apiKey.UserID)
	if err != nil {
		return nil, err
	}

	return user, nil
}

func getUserFromSession(dbConn *sql.DB, sessionId string) (*database.User, error) {
	session, err := database.GetSession(dbConn, sessionId)
	if err != nil {
		return nil, err
	}

	if session.ExpireAt.Before(time.Now()) {
		session = nil
		database.DeleteSession(dbConn, sessionId)
		return nil, fmt.Errorf("session expired")
	}

	user, err := database.GetUser(dbConn, session.UserID)
	if err != nil {
		return nil, err
	}

	return user, nil
}

func VerifySessionContinuation(context *RequestContext, req *http.Request, resp http.ResponseWriter) ContinuationChain {
	return func(success Continuation, failure Continuation) ContinuationChain {
		authHeader := req.Header.Get("Authorization")
		user, userErr := getUserFromAuthHeader(context.DBConn, authHeader)

		sessionCookie, err := req.Cookie("session")
		if err == nil {
			user, userErr = getUserFromSession(context.DBConn, sessionCookie.Value)
		}

		if userErr != nil || user == nil {
			log.Println(userErr, user)

			http.SetCookie(resp, &http.Cookie{
				Name:   "session",
				MaxAge: 0, // reset session cookie in case
			})
			return failure(context, req, resp)
		}

		context.User = user
		return success(context, req, resp)
	}
}

func GoLoginContinuation(context *RequestContext, req *http.Request, resp http.ResponseWriter) ContinuationChain {
	return func(success Continuation, failure Continuation) ContinuationChain {
		http.SetCookie(resp, &http.Cookie{
			Name:     "redirect",
			Value:    req.URL.Path,
			Path:     "/",
			Secure:   true,
			SameSite: http.SameSiteLaxMode,
		})

		http.Redirect(resp, req, "/login", http.StatusFound)
		return failure(context, req, resp)
	}
}

func RefreshSessionContinuation(context *RequestContext, req *http.Request, resp http.ResponseWriter) ContinuationChain {
	return func(success Continuation, failure Continuation) ContinuationChain {
		sessionCookie, err := req.Cookie("session")
		if err != nil {
			resp.WriteHeader(http.StatusUnauthorized)
			return failure(context, req, resp)
		}

		_, err = database.RefreshSession(context.DBConn, sessionCookie.Value)
		if err != nil {
			resp.WriteHeader(http.StatusUnauthorized)
			return failure(context, req, resp)
		}

		return success(context, req, resp)
	}
}

func LogoutContinuation(context *RequestContext, req *http.Request, resp http.ResponseWriter) ContinuationChain {
	return func(success Continuation, failure Continuation) ContinuationChain {
		sessionCookie, err := req.Cookie("session")
		if err == nil && sessionCookie.Value != "" {
			_ = database.DeleteSession(context.DBConn, sessionCookie.Value)
		}

		http.Redirect(resp, req, "/", http.StatusFound)
		http.SetCookie(resp, &http.Cookie{
			Name:   "session",
			MaxAge: 0,
		})
		return success(context, req, resp)
	}
}

func getOauthUser(dbConn *sql.DB, client *http.Client, uri string) (*database.User, error) {
	userResponse, err := client.Get(uri)
	if err != nil {
		return nil, err
	}

	userStruct, err := createUserFromResponse(userResponse)
	if err != nil {
		return nil, err
	}

	user, err := database.FindOrSaveUser(dbConn, userStruct)
	if err != nil {
		return nil, err
	}

	return user, nil
}

func createUserFromResponse(response *http.Response) (*database.User, error) {
	defer response.Body.Close()
	user := &database.User{
		CreatedAt: time.Now(),
	}
	err := json.NewDecoder(response.Body).Decode(user)
	if err != nil {
		log.Println(err)
		return nil, err
	}

	user.Username = strings.ToLower(user.Username)
	user.Username = strings.Split(user.Username, "@")[0]

	return user, nil
}

func verifyState(req *http.Request, stateCookieName string, expectedState string) bool {
	cookie, err := req.Cookie(stateCookieName)
	if err != nil || cookie.Value != expectedState {
		return false
	}

	return true
}