package csrf

import (
	"errors"
	"fmt"
	"net/url"
	"slices"
	"strings"
	"time"

	"github.com/gofiber/utils/v2"
	utilsstrings "github.com/gofiber/utils/v2/strings"

	"github.com/gofiber/fiber/v3"
	"github.com/gofiber/fiber/v3/extractors"
)

var (
	ErrTokenNotFound    = errors.New("csrf: token not found")
	ErrTokenInvalid     = errors.New("csrf: token invalid")
	ErrFetchSiteInvalid = errors.New("csrf: sec-fetch-site header invalid")
	ErrRefererNotFound  = errors.New("csrf: referer header missing")
	ErrRefererInvalid   = errors.New("csrf: referer header invalid")
	ErrRefererNoMatch   = errors.New("csrf: referer does not match host or trusted origins")
	ErrOriginInvalid    = errors.New("csrf: origin header invalid")
	ErrOriginNoMatch    = errors.New("csrf: origin does not match host or trusted origins")
	errOriginNotFound   = errors.New("origin not supplied or is null") // internal error, will not be returned to the user
	dummyValue          = []byte{'+'}                                  // dummyValue is a placeholder value stored in token storage. The actual token validation relies on the key, not this value.

)

// Handler for CSRF middleware
type Handler struct {
	sessionManager *sessionManager
	storageManager *storageManager
	config         Config
}

// The contextKey type is unexported to prevent collisions with context keys defined in
// other packages.
type contextKey int

// The keys for the values in context
const (
	tokenKey contextKey = iota
	handlerKey
)

// New creates a new middleware handler
func New(config ...Config) fiber.Handler {
	// Set default config
	cfg := configDefault(config...)

	redactKeys := !cfg.DisableValueRedaction

	maskValue := func(value string) string {
		if redactKeys {
			return redactedKey
		}
		return value
	}

	// Create manager to simplify storage operations ( see *_manager.go )
	var sessionManager *sessionManager
	var storageManager *storageManager
	if cfg.Session != nil {
		sessionManager = newSessionManager(cfg.Session)
	} else {
		storageManager = newStorageManager(cfg.Storage, redactKeys)
	}

	// Pre-parse trusted origins
	trustedOrigins := []string{}
	trustedSubOrigins := []subdomain{}

	for _, origin := range cfg.TrustedOrigins {
		trimmedOrigin := utils.TrimSpace(origin)
		if i := strings.Index(trimmedOrigin, "://*."); i != -1 {
			withoutWildcard := trimmedOrigin[:i+len("://")] + trimmedOrigin[i+len("://*."):]
			isValid, normalizedOrigin := normalizeOrigin(withoutWildcard)
			if !isValid {
				panic("[CSRF] Invalid origin format in configuration:" + maskValue(origin))
			}
			schemeSep := strings.Index(normalizedOrigin, "://") + len("://")
			sd := subdomain{prefix: normalizedOrigin[:schemeSep], suffix: normalizedOrigin[schemeSep:]}
			trustedSubOrigins = append(trustedSubOrigins, sd)
		} else {
			isValid, normalizedOrigin := normalizeOrigin(trimmedOrigin)
			if !isValid {
				panic("[CSRF] Invalid origin format in configuration:" + maskValue(origin))
			}
			trustedOrigins = append(trustedOrigins, normalizedOrigin)
		}
	}

	// Create the handler outside of the returned function
	handler := &Handler{
		config:         cfg,
		sessionManager: sessionManager,
		storageManager: storageManager,
	}

	// Return new handler
	return func(c fiber.Ctx) error {
		// Don't execute middleware if Next returns true
		if cfg.Next != nil && cfg.Next(c) {
			return c.Next()
		}

		// Store the CSRF handler in the context
		fiber.StoreInContext(c, handlerKey, handler)

		var token string

		// Action depends on the HTTP method
		switch c.Method() {
		case fiber.MethodGet, fiber.MethodHead, fiber.MethodOptions, fiber.MethodTrace:
			cookieToken := c.Cookies(cfg.CookieName)

			if cookieToken != "" {
				raw, err := getRawFromStorage(c, cookieToken, &cfg, sessionManager, storageManager)
				if err != nil {
					return cfg.ErrorHandler(c, err)
				}

				if raw != nil {
					token = cookieToken // Token is valid, safe to set it
				}
			}
		default:
			// Assume that anything not defined as 'safe' by RFC7231 needs protection

			// Evaluate Sec-Fetch-Site to reject cross-site requests earlier when available.
			if err := validateSecFetchSite(c); err != nil {
				return cfg.ErrorHandler(c, err)
			}

			// Enforce an origin check for unsafe requests.
			err := originMatchesHost(c, trustedOrigins, trustedSubOrigins)

			// If there's no origin, enforce a referer check for HTTPS connections.
			if errors.Is(err, errOriginNotFound) {
				if c.Scheme() == schemeHTTPS {
					err = refererMatchesHost(c, trustedOrigins, trustedSubOrigins)
				} else {
					// If it's not HTTPS, clear the error to allow the request to proceed.
					err = nil
				}
			}

			// If there's an error (either from origin check or referer check), handle it.
			if err != nil {
				return cfg.ErrorHandler(c, err)
			}

			// Extract token from client request i.e. header, query, param, form
			extractedToken, err := cfg.Extractor.Extract(c)
			if err != nil {
				if errors.Is(err, extractors.ErrNotFound) {
					return cfg.ErrorHandler(c, ErrTokenNotFound)
				}
				// If there's an error during extraction (other than not found), handle it.
				return cfg.ErrorHandler(c, err)
			}

			if extractedToken == "" {
				return cfg.ErrorHandler(c, ErrTokenNotFound)
			}

			// Double Submit Cookie validation: ensure the extracted token matches the cookie value
			// This prevents CSRF attacks by requiring attackers to know both the cookie AND submit
			// the same token through a different channel (header, form, etc.)
			// WARNING: If using a custom extractor that reads from the same cookie, this provides no protection
			if !compareStrings(extractedToken, c.Cookies(cfg.CookieName)) {
				return cfg.ErrorHandler(c, ErrTokenInvalid)
			}

			raw, err := getRawFromStorage(c, extractedToken, &cfg, sessionManager, storageManager)
			if err != nil {
				return cfg.ErrorHandler(c, err)
			}

			if raw == nil {
				// If token is not in storage, expire the cookie
				expireCSRFCookie(c, &cfg)
				// and return an error
				return cfg.ErrorHandler(c, ErrTokenNotFound)
			}
			if cfg.SingleUseToken {
				// If token is single use, delete it from storage
				if err := deleteTokenFromStorage(c, extractedToken, &cfg, sessionManager, storageManager); err != nil {
					return cfg.ErrorHandler(c, err)
				}
			} else {
				token = extractedToken // Token is valid, safe to set it
			}
		}

		// Generate CSRF token if not exist
		if token == "" {
			// And generate a new token
			token = cfg.KeyGenerator()
		}

		// Create or extend the token in the storage
		if err := createOrExtendTokenInStorage(c, token, &cfg, sessionManager, storageManager); err != nil {
			return cfg.ErrorHandler(c, err)
		}

		// Update the CSRF cookie
		updateCSRFCookie(c, &cfg, token)

		// Tell the browser that a new header value is generated
		c.Vary(fiber.HeaderCookie)

		// Store the token in the context
		fiber.StoreInContext(c, tokenKey, token)

		// Continue stack
		return c.Next()
	}
}

// TokenFromContext returns the token found in the context.
// It accepts fiber.CustomCtx, fiber.Ctx, *fasthttp.RequestCtx, and context.Context.
// It returns an empty string if the token does not exist.
func TokenFromContext(ctx any) string {
	if token, ok := fiber.ValueFromContext[string](ctx, tokenKey); ok {
		return token
	}

	return ""
}

// HandlerFromContext returns the Handler found in the context.
// It accepts fiber.CustomCtx, fiber.Ctx, *fasthttp.RequestCtx, and context.Context.
// It returns nil if the handler does not exist.
func HandlerFromContext(ctx any) *Handler {
	if handler, ok := fiber.ValueFromContext[*Handler](ctx, handlerKey); ok {
		return handler
	}

	return nil
}

// getRawFromStorage returns the raw value from the storage for the given token
// returns nil if the token does not exist, is expired or is invalid
func getRawFromStorage(c fiber.Ctx, token string, cfg *Config, sessionManager *sessionManager, storageManager *storageManager) ([]byte, error) {
	if cfg.Session != nil {
		return sessionManager.getRaw(c, token, dummyValue), nil
	}
	raw, err := storageManager.getRaw(c, token)
	if err != nil {
		return nil, fmt.Errorf("csrf: failed to fetch token from storage: %w", err)
	}
	return raw, nil
}

// createOrExtendTokenInStorage creates or extends the token in the storage
func createOrExtendTokenInStorage(c fiber.Ctx, token string, cfg *Config, sessionManager *sessionManager, storageManager *storageManager) error {
	if cfg.Session != nil {
		sessionManager.setRaw(c, token, dummyValue, cfg.IdleTimeout)
		return nil
	}
	if err := storageManager.setRaw(c, token, dummyValue, cfg.IdleTimeout); err != nil {
		return fmt.Errorf("csrf: failed to store token in storage: %w", err)
	}
	return nil
}

func deleteTokenFromStorage(c fiber.Ctx, token string, cfg *Config, sessionManager *sessionManager, storageManager *storageManager) error {
	if cfg.Session != nil {
		sessionManager.delRaw(c)
		return nil
	}
	if err := storageManager.delRaw(c, token); err != nil {
		return fmt.Errorf("csrf: failed to delete token from storage: %w", err)
	}
	return nil
}

// Update CSRF cookie
// if expireCookie is true, the cookie will expire immediately
func updateCSRFCookie(c fiber.Ctx, cfg *Config, token string) {
	setCSRFCookie(c, cfg, token, cfg.IdleTimeout)
}

func expireCSRFCookie(c fiber.Ctx, cfg *Config) {
	setCSRFCookie(c, cfg, "", -time.Hour)
}

func setCSRFCookie(c fiber.Ctx, cfg *Config, token string, expiry time.Duration) {
	cookie := &fiber.Cookie{
		Name:        cfg.CookieName,
		Value:       token,
		Domain:      cfg.CookieDomain,
		Path:        cfg.CookiePath,
		Secure:      cfg.CookieSecure,
		HTTPOnly:    cfg.CookieHTTPOnly,
		SameSite:    cfg.CookieSameSite,
		SessionOnly: cfg.CookieSessionOnly,
		Expires:     time.Now().Add(expiry),
	}

	// Set the CSRF cookie to the response
	c.Cookie(cookie)
}

// DeleteToken removes the token found in the context from the storage
// and expires the CSRF cookie
func (handler *Handler) DeleteToken(c fiber.Ctx) error {
	// Extract token from the client request cookie
	cookieToken := c.Cookies(handler.config.CookieName)
	if cookieToken == "" {
		return handler.config.ErrorHandler(c, ErrTokenNotFound)
	}
	// Remove the token from storage
	if err := deleteTokenFromStorage(c, cookieToken, &handler.config, handler.sessionManager, handler.storageManager); err != nil {
		return handler.config.ErrorHandler(c, err)
	}
	// Expire the cookie
	expireCSRFCookie(c, &handler.config)
	return nil
}

func validateSecFetchSite(c fiber.Ctx) error {
	secFetchSite := utils.Trim(c.Get(fiber.HeaderSecFetchSite), ' ')

	if secFetchSite == "" {
		return nil
	}

	switch utilsstrings.ToLower(secFetchSite) {
	case "same-origin", "none", "cross-site", "same-site":
		return nil
	default:
		return ErrFetchSiteInvalid
	}
}

// originMatchesHost checks that the origin header matches the host header
// returns an error if the origin header is not present or is invalid
// returns nil if the origin header is valid
func originMatchesHost(c fiber.Ctx, trustedOrigins []string, trustedSubOrigins []subdomain) error {
	origin := utilsstrings.ToLower(c.Get(fiber.HeaderOrigin))
	if origin == "" || origin == "null" { // "null" is set by some browsers when the origin is a secure context https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Origin#description
		return errOriginNotFound
	}

	originURL, err := url.Parse(origin)
	if err != nil {
		return ErrOriginInvalid
	}

	if schemeAndHostMatch(originURL.Scheme, originURL.Host, c.Scheme(), c.Host()) {
		return nil
	}

	if slices.Contains(trustedOrigins, origin) {
		return nil
	}

	for _, trustedSubOrigin := range trustedSubOrigins {
		if trustedSubOrigin.match(origin) {
			return nil
		}
	}

	return ErrOriginNoMatch
}

// refererMatchesHost checks that the referer header matches the host header
// returns an error if the referer header is not present or is invalid
// returns nil if the referer header is valid
func refererMatchesHost(c fiber.Ctx, trustedOrigins []string, trustedSubOrigins []subdomain) error {
	referer := utilsstrings.ToLower(c.Get(fiber.HeaderReferer))
	if referer == "" {
		return ErrRefererNotFound
	}

	refererURL, err := url.Parse(referer)
	if err != nil {
		return ErrRefererInvalid
	}

	if schemeAndHostMatch(refererURL.Scheme, refererURL.Host, c.Scheme(), c.Host()) {
		return nil
	}

	refererOrigin := refererURL.Scheme + "://" + refererURL.Host

	if slices.Contains(trustedOrigins, refererOrigin) {
		return nil
	}

	for _, trustedSubOrigin := range trustedSubOrigins {
		if trustedSubOrigin.match(refererOrigin) {
			return nil
		}
	}

	return ErrRefererNoMatch
}
