package service

import (
	"context"
	"crypto/sha256"
	"encoding/hex"
	"errors"
	"fmt"
	"net/http"
	"strings"
	"time"

	"git.umbrella.haus/ae/notatest/pkg/data"
	"github.com/go-chi/chi/v5"
	"github.com/golang-jwt/jwt/v5"
	"github.com/google/uuid"
)

const (
	accessTokenDuration  = 15 * time.Minute
	refreshTokenDuration = 7 * 24 * time.Hour
)

var (
	ErrInvalidToken      = errors.New("invalid token")
	ErrAuthHeaderInvalid = errors.New("token couldn't be parsed from authentication header")
)

type userClaims struct {
	Admin                bool   `json:"admin"`
	TokenType            string `json:"type"` // "access" or "refresh"
	jwt.RegisteredClaims        // User's UUID should be stored in the subject claim
}

type tokenPair struct {
	AccessToken  string `json:"access_token"`
	RefreshToken string `json:"refresh_token"`
}

// Mockable database operations interface
type TokenStore interface {
	CreateRefreshToken(ctx context.Context, arg data.CreateRefreshTokenParams) (data.RefreshToken, error)
	GetRefreshTokenByHash(ctx context.Context, tokenHash string) (data.RefreshToken, error)
	RevokeRefreshToken(ctx context.Context, tokenHash string) error
	RevokeAllUserRefreshTokens(ctx context.Context, id uuid.UUID) error
}

type tokensResource struct {
	JWTSecret string
	Tokens    TokenStore
}

func (rs tokensResource) Routes() chi.Router {
	r := chi.NewRouter()

	r.Group(func(r chi.Router) {
		r.Use(requireRefreshToken(rs.JWTSecret))
		r.Post("/refresh", rs.RefreshAccessToken) // POST /auth/refresh - convert refresh token to new token pair
	})

	return r
}

func (rs tokensResource) GenerateTokenPair(ctx context.Context, userID uuid.UUID, isAdmin bool) (*tokenPair, error) {
	tokenPair, err := generateTokenPair(userID.String(), isAdmin, rs.JWTSecret)
	if err != nil {
		return nil, err
	}

	hash := sha256.Sum256([]byte(tokenPair.RefreshToken))
	tokenHash := hex.EncodeToString(hash[:])

	// Store to DB with (almost) identical expiration timestamp
	expiresAt := time.Now().Add(refreshTokenDuration)
	_, err = rs.Tokens.CreateRefreshToken(ctx, data.CreateRefreshTokenParams{
		UserID:    userID,
		TokenHash: tokenHash,
		ExpiresAt: expiresAt,
	})
	if err != nil {
		return nil, err
	}

	return tokenPair, nil
}

func (rs tokensResource) RevokeRefreshToken(ctx context.Context, token string) error {
	hash := sha256.Sum256([]byte(token))
	tokenHash := hex.EncodeToString(hash[:])
	return rs.Tokens.RevokeRefreshToken(ctx, tokenHash)
}

func (rs tokensResource) ValidateRefreshToken(ctx context.Context, token string) (*data.RefreshToken, error) {
	hash := sha256.Sum256([]byte(token))
	tokenHash := hex.EncodeToString(hash[:])

	dbToken, err := rs.Tokens.GetRefreshTokenByHash(ctx, tokenHash)
	if err != nil {
		return nil, err
	}

	if dbToken.Revoked || time.Now().After(dbToken.ExpiresAt) {
		return nil, ErrInvalidToken
	}

	return &dbToken, nil
}

func (rs tokensResource) RefreshAccessToken(w http.ResponseWriter, r *http.Request) {
	// Get claims from context
	claims, ok := r.Context().Value(userCtxKey{}).(*userClaims)
	if !ok || claims.TokenType != "refresh" {
		respondError(w, http.StatusUnauthorized, "Invalid token")
		return
	}

	// Attempt to get the token from Authentication header ("Bearer <token>")
	refreshToken, err := getTokenFromRequest(r)
	if err != nil {
		respondError(w, http.StatusUnauthorized, fmt.Sprintf("Unauthorized: %s", err))
	}

	// Validate the refresh token in DB
	if _, err := rs.ValidateRefreshToken(r.Context(), refreshToken); err != nil {
		respondError(w, http.StatusUnauthorized, "Invalid refresh token")
		return
	}

	// Revoke the used refresh token
	if err := rs.RevokeRefreshToken(r.Context(), refreshToken); err != nil {
		respondError(w, http.StatusInternalServerError, "Failed to revoke token")
		return
	}

	// Generate a new pair (access & refresh tokens)
	userID, err := uuid.Parse(claims.Subject)
	if err != nil {
		respondError(w, http.StatusInternalServerError, "Invalid user ID")
		return
	}

	tokenPair, err := rs.GenerateTokenPair(r.Context(), userID, claims.Admin)
	if err != nil {
		respondError(w, http.StatusInternalServerError, "Failed to generate tokens")
		return
	}

	respondJSON(w, http.StatusOK, tokenPair)
}

func (rs tokensResource) HandleLogout(w http.ResponseWriter, r *http.Request) {
	claims, ok := r.Context().Value(userCtxKey{}).(*userClaims)
	if !ok {
		respondError(w, http.StatusUnauthorized, "Not authenticated")
		return
	}

	userID, err := uuid.Parse(claims.ID)
	if err != nil {
		respondError(w, http.StatusInternalServerError, "Invalid user ID")
		return
	}

	if err := rs.Tokens.RevokeAllUserRefreshTokens(r.Context(), userID); err != nil {
		respondError(w, http.StatusInternalServerError, "Failed to logout")
		return
	}

	respondJSON(w, http.StatusOK, map[string]string{"status": "logged out"})
}

func getTokenFromRequest(r *http.Request) (string, error) {
	bearerToken := r.Header.Get("Authorization")
	bearerFields := strings.Fields(bearerToken)
	if len(bearerFields) == 2 && strings.ToLower(bearerFields[0]) == "bearer" {
		return bearerFields[1], nil
	}
	return "", ErrAuthHeaderInvalid
}

func generateTokenPair(userID string, isAdmin bool, jwtSecret string) (*tokenPair, error) {
	atClaims := userClaims{
		Admin:     isAdmin,
		TokenType: "access",
		RegisteredClaims: jwt.RegisteredClaims{
			Subject:   userID,
			ExpiresAt: jwt.NewNumericDate(time.Now().Add(accessTokenDuration)),
			IssuedAt:  jwt.NewNumericDate(time.Now()),
			NotBefore: jwt.NewNumericDate(time.Now()),
		},
	}
	accessToken := jwt.NewWithClaims(jwt.SigningMethodHS256, atClaims)

	t, err := accessToken.SignedString([]byte(jwtSecret))
	if err != nil {
		return nil, err
	}

	rtClaims := userClaims{
		Admin:     isAdmin,
		TokenType: "refresh",
		RegisteredClaims: jwt.RegisteredClaims{
			Subject:   userID,
			ExpiresAt: jwt.NewNumericDate(time.Now().Add(refreshTokenDuration)),
			IssuedAt:  jwt.NewNumericDate(time.Now()),
			NotBefore: jwt.NewNumericDate(time.Now()),
		},
	}
	refreshToken := jwt.NewWithClaims(jwt.SigningMethodHS256, rtClaims)

	rt, err := refreshToken.SignedString([]byte(jwtSecret))
	if err != nil {
		return nil, err
	}

	return &tokenPair{AccessToken: t, RefreshToken: rt}, nil
}