package middleware

import (
	"context"
	"crypto/subtle"
	"io"
	"net/http"
	"os"
	"strings"

	"emperror.dev/errors"
	"github.com/apex/log"
	"github.com/gin-gonic/gin"
	"github.com/google/uuid"
	"github.com/pterodactyl/wings/config"
	"github.com/pterodactyl/wings/server"
	"github.com/pterodactyl/wings/server/filesystem"
)

// RequestError is a custom error type returned when something goes wrong with
// any of the HTTP endpoints.
type RequestError struct {
	err    error
	status int
	msg    string
}

// NewError returns a new RequestError for the provided error.
func NewError(err error) *RequestError {
	return &RequestError{
		// Attach a stacktrace to the error if it is missing at this point and mark it
		// as originating from the location where NewError was called, rather than this
		// specific point in the code.
		err: errors.WithStackDepthIf(err, 1),
	}
}

// SetMessage allows for a custom error message to be set on an existing
// RequestError instance.
func (re *RequestError) SetMessage(m string) {
	re.msg = m
}

// SetStatus sets the HTTP status code for the error response. By default this
// is a HTTP-500 error.
func (re *RequestError) SetStatus(s int) {
	re.status = s
}

// Abort aborts the given HTTP request with the specified status code and then
// logs the event into the logs. The error that is output will include the unique
// request ID if it is present.
func (re *RequestError) Abort(c *gin.Context, status int) {
	reqId := c.Writer.Header().Get("X-Request-Id")

	// Generate the base logger instance, attaching the unique request ID and
	// the URL that was requested.
	event := log.WithField("request_id", reqId).WithField("url", c.Request.URL.String())
	// If there is a server present in the gin.Context stack go ahead and pull it
	// and attach that server UUID to the logs as well so that we can see what specific
	// server triggered this error.
	if s, ok := c.Get("server"); ok {
		if s, ok := s.(*server.Server); ok {
			event = event.WithField("server_id", s.Id())
		}
	}

	if c.Writer.Status() == 200 {
		// Handle context deadlines being exceeded a little differently since we want
		// to report a more user-friendly error and a proper error code. The "context
		// canceled" error is generally when a request is terminated before all of the
		// logic is finished running.
		if errors.Is(re.err, context.DeadlineExceeded) {
			re.SetStatus(http.StatusGatewayTimeout)
			re.SetMessage("The server could not process this request in time, please try again.")
		} else if strings.Contains(re.Cause().Error(), "context canceled") {
			re.SetStatus(http.StatusBadRequest)
			re.SetMessage("Request aborted by client.")
		}
	}

	// c.Writer.Status() will be a non-200 value if the headers have already been sent
	// to the requester but an error is encountered. This can happen if there is an issue
	// marshaling a struct placed into a c.JSON() call (or c.AbortWithJSON() call).
	if status >= 500 || c.Writer.Status() != 200 {
		event.WithField("status", status).WithField("error", re.err).Error("error while handling HTTP request")
	} else {
		event.WithField("status", status).WithField("error", re.err).Debug("error handling HTTP request (not a server error)")
	}
	if re.msg == "" {
		re.msg = "An unexpected error was encountered while processing this request"
	}
	// Now abort the request with the error message and include the unique request
	// ID that was present to make things super easy on people who don't know how
	// or cannot view the response headers (where X-Request-Id would be present).
	c.AbortWithStatusJSON(status, gin.H{"error": re.msg, "request_id": reqId})
}

// Cause returns the underlying error.
func (re *RequestError) Cause() error {
	return re.err
}

// Error returns the underlying error message for this request.
func (re *RequestError) Error() string {
	return re.err.Error()
}

// Looks at the given RequestError and determines if it is a specific filesystem
// error that we can process and return differently for the user.
//
// Some external things end up calling fmt.Errorf() on our filesystem errors
// which ends up just unleashing chaos on the system. For the sake of this,
// fallback to using text checks.
//
// If the error passed into this call is nil or does not match empty values will
// be returned to the caller.
func (re *RequestError) asFilesystemError() (int, string) {
	err := re.Cause()
	if err == nil {
		return 0, ""
	}
	if filesystem.IsErrorCode(err, filesystem.ErrCodeDenylistFile) || strings.Contains(err.Error(), "filesystem: file access prohibited") {
		return http.StatusForbidden, "This file cannot be modified: present in egg denylist."
	}
	if filesystem.IsErrorCode(err, filesystem.ErrCodePathResolution) || strings.Contains(err.Error(), "resolves to a location outside the server root") {
		return http.StatusNotFound, "The requested resource was not found on the system."
	}
	if filesystem.IsErrorCode(err, filesystem.ErrCodeIsDirectory) || strings.Contains(err.Error(), "filesystem: is a directory") {
		return http.StatusBadRequest, "Cannot perform that action: file is a directory."
	}
	if filesystem.IsErrorCode(err, filesystem.ErrCodeDiskSpace) || strings.Contains(err.Error(), "filesystem: not enough disk space") {
		return http.StatusBadRequest, "There is not enough disk space available to perform that action."
	}
	if strings.HasSuffix(err.Error(), "file name too long") {
		return http.StatusBadRequest, "Cannot perform that action: file name is too long."
	}
	if e, ok := err.(*os.SyscallError); ok && e.Syscall == "readdirent" {
		return http.StatusNotFound, "The requested directory does not exist."
	}
	return 0, ""
}

// AttachRequestID attaches a unique ID to the incoming HTTP request so that any
// errors that are generated or returned to the client will include this reference
// allowing for an easier time identifying the specific request that failed for
// the user.
//
// If you are using a tool such as Sentry or Bugsnag for error reporting this is
// a great location to also attach this request ID to your error handling logic
// so that you can easily cross-reference the errors.
func AttachRequestID() gin.HandlerFunc {
	return func(c *gin.Context) {
		id := uuid.New().String()
		c.Set("request_id", id)
		c.Set("logger", log.WithField("request_id", id))
		c.Header("X-Request-Id", id)
		c.Next()
	}
}

// CaptureAndAbort aborts the request and attaches the provided error to the gin
// context so it can be reported properly. If the error is missing a stacktrace
// at the time it is called the stack will be attached.
func CaptureAndAbort(c *gin.Context, err error) {
	c.Abort()
	c.Error(errors.WithStackDepthIf(err, 1))
}

// CaptureErrors is custom handler function allowing for errors bubbled up by
// c.Error() to be returned in a standardized format with tracking UUIDs on them
// for easier log searching.
func CaptureErrors() gin.HandlerFunc {
	return func(c *gin.Context) {
		c.Next()
		err := c.Errors.Last()
		if err == nil || err.Err == nil {
			return
		}

		status := http.StatusInternalServerError
		if c.Writer.Status() != 200 {
			status = c.Writer.Status()
		}
		if err.Error() == io.EOF.Error() {
			c.AbortWithStatusJSON(http.StatusBadRequest, gin.H{"error": "The data passed in the request was not in a parsable format. Please try again."})
			return
		}
		captured := NewError(err.Err)
		if status, msg := captured.asFilesystemError(); msg != "" {
			c.AbortWithStatusJSON(status, gin.H{"error": msg, "request_id": c.Writer.Header().Get("X-Request-Id")})
			return
		}
		captured.Abort(c, status)
	}
}

// SetAccessControlHeaders sets the access request control headers on all of
// the requests.
func SetAccessControlHeaders() gin.HandlerFunc {
	origins := config.Get().AllowedOrigins
	location := config.Get().PanelLocation

	return func(c *gin.Context) {
		c.Header("Access-Control-Allow-Credentials", "true")
		c.Header("Access-Control-Allow-Methods", "GET, POST, PATCH, PUT, DELETE, OPTIONS")
		// Maximum age allowable under Chromium v76 is 2 hours, so just use that since
		// anything higher will be ignored (even if other browsers do allow higher values).
		//
		// @see https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Access-Control-Max-Age#Directives
		c.Header("Access-Control-Max-Age", "7200")
		c.Header("Access-Control-Allow-Origin", location)
		c.Header("Access-Control-Allow-Headers", "Accept, Accept-Encoding, Authorization, Cache-Control, Content-Type, Content-Length, Origin, X-Real-IP, X-CSRF-Token")
		// Validate that the request origin is coming from an allowed origin. Because you
		// cannot set multiple values here we need to see if the origin is one of the ones
		// that we allow, and if so return it explicitly. Otherwise, just return the default
		// origin which is the same URL that the Panel is located at.
		origin := c.GetHeader("Origin")
		if origin != location {
			for _, o := range origins {
				if o != "*" && o != origin {
					continue
				}
				c.Header("Access-Control-Allow-Origin", o)
				break
			}
		}
		if c.Request.Method == http.MethodOptions {
			c.AbortWithStatus(http.StatusNoContent)
			return
		}
		c.Next()
	}
}

// ServerExists will ensure that the requested server exists in this setup.
// Returns a 404 if we cannot locate it. If the server is found it is set into
// the request context, and the logger for the context is also updated to include
// the server ID in the fields list.
func ServerExists() gin.HandlerFunc {
	return func(c *gin.Context) {
		s := server.GetServers().Find(func(s *server.Server) bool {
			return c.Param("server") == s.Id()
		})
		if s == nil {
			c.AbortWithStatusJSON(http.StatusNotFound, gin.H{"error": "The requested resource does not exist on this instance."})
			return
		}
		c.Set("logger", ExtractLogger(c).WithField("server_id", s.Id()))
		c.Set("server", s)
		c.Next()
	}
}

// RequireAuthorization authenticates the request token against the given
// permission string, ensuring that if it is a server permission, the token has
// control over that server. If it is a global token, this will ensure that the
// request is using a properly signed global token.
func RequireAuthorization() gin.HandlerFunc {
	return func(c *gin.Context) {
		// We don't put this value outside this function since the node's authentication
		// token can be changed on the fly and the config.Get() call returns a copy, so
		// if it is rotated this value will never properly get updated.
		token := config.Get().AuthenticationToken
		auth := strings.SplitN(c.GetHeader("Authorization"), " ", 2)
		if len(auth) != 2 || auth[0] != "Bearer" {
			c.Header("WWW-Authenticate", "Bearer")
			c.AbortWithStatusJSON(http.StatusUnauthorized, gin.H{"error": "The required authorization heads were not present in the request."})
			return
		}

		// All requests to Wings must be authorized with the authentication token present in
		// the Wings configuration file. Remeber, all requests to Wings come from the Panel
		// backend, or using a signed JWT for temporary authentication.
		if subtle.ConstantTimeCompare([]byte(auth[1]), []byte(token)) != 1 {
			c.AbortWithStatusJSON(http.StatusForbidden, gin.H{"error": "You are not authorized to access this endpoint."})
			return
		}
		c.Next()
	}
}

// RemoteDownloadEnabled checks if remote downloads are enabled for this instance
// and if not aborts the request.
func RemoteDownloadEnabled() gin.HandlerFunc {
	disabled := config.Get().Api.DisableRemoteDownload
	return func(c *gin.Context) {
		if disabled {
			c.AbortWithStatusJSON(http.StatusBadRequest, gin.H{"error": "This functionality is not currently enabled on this instance."})
			return
		}
		c.Next()
	}
}

// ExtractLogger pulls the logger out of the request context and returns it. By
// default this will include the request ID, but may also include the server ID
// if that middleware has been used in the chain by the time it is called.
func ExtractLogger(c *gin.Context) *log.Entry {
	v, ok := c.Get("logger")
	if !ok {
		panic("middleware/middleware: cannot extract logger: not present in request context")
	}
	return v.(*log.Entry)
}

// ExtractServer will return the server from the gin.Context or panic if it is
// not present.
func ExtractServer(c *gin.Context) *server.Server {
	v, ok := c.Get("server")
	if !ok {
		panic("middleware/middleware: cannot extract server: not present in request context")
	}
	return v.(*server.Server)
}