//go:build go1.15
// +build go1.15

package middleware

import (
	"errors"
	"fmt"
	"github.com/golang-jwt/jwt"
	"github.com/labstack/echo/v4"
	"net/http"
	"reflect"
)

type (
	// JWTConfig defines the config for JWT middleware.
	JWTConfig struct {
		// Skipper defines a function to skip middleware.
		Skipper Skipper

		// BeforeFunc defines a function which is executed just before the middleware.
		BeforeFunc BeforeFunc

		// SuccessHandler defines a function which is executed for a valid token before middleware chain continues with next
		// middleware or handler.
		SuccessHandler JWTSuccessHandler

		// ErrorHandler defines a function which is executed for an invalid token.
		// It may be used to define a custom JWT error.
		ErrorHandler JWTErrorHandler

		// ErrorHandlerWithContext is almost identical to ErrorHandler, but it's passed the current context.
		ErrorHandlerWithContext JWTErrorHandlerWithContext

		// ContinueOnIgnoredError allows the next middleware/handler to be called when ErrorHandlerWithContext decides to
		// ignore the error (by returning `nil`).
		// This is useful when parts of your site/api allow public access and some authorized routes provide extra functionality.
		// In that case you can use ErrorHandlerWithContext to set a default public JWT token value in the request context
		// and continue. Some logic down the remaining execution chain needs to check that (public) token value then.
		ContinueOnIgnoredError bool

		// Signing key to validate token.
		// This is one of the three options to provide a token validation key.
		// The order of precedence is a user-defined KeyFunc, SigningKeys and SigningKey.
		// Required if neither user-defined KeyFunc nor SigningKeys is provided.
		SigningKey interface{}

		// Map of signing keys to validate token with kid field usage.
		// This is one of the three options to provide a token validation key.
		// The order of precedence is a user-defined KeyFunc, SigningKeys and SigningKey.
		// Required if neither user-defined KeyFunc nor SigningKey is provided.
		SigningKeys map[string]interface{}

		// Signing method used to check the token's signing algorithm.
		// Optional. Default value HS256.
		SigningMethod string

		// Context key to store user information from the token into context.
		// Optional. Default value "user".
		ContextKey string

		// Claims are extendable claims data defining token content. Used by default ParseTokenFunc implementation.
		// Not used if custom ParseTokenFunc is set.
		// Optional. Default value jwt.MapClaims
		Claims jwt.Claims

		// TokenLookup is a string in the form of "<source>:<name>" or "<source>:<name>,<source>:<name>" that is used
		// to extract token from the request.
		// Optional. Default value "header:Authorization".
		// Possible values:
		// - "header:<name>" or "header:<name>:<cut-prefix>"
		// 			`<cut-prefix>` is argument value to cut/trim prefix of the extracted value. This is useful if header
		//			value has static prefix like `Authorization: <auth-scheme> <authorisation-parameters>` where part that we
		//			want to cut is `<auth-scheme> ` note the space at the end.
		//			In case of JWT tokens `Authorization: Bearer <token>` prefix we cut is `Bearer `.
		// If prefix is left empty the whole value is returned.
		// - "query:<name>"
		// - "param:<name>"
		// - "cookie:<name>"
		// - "form:<name>"
		// Multiple sources example:
		// - "header:Authorization,cookie:myowncookie"
		TokenLookup string

		// TokenLookupFuncs defines a list of user-defined functions that extract JWT token from the given context.
		// This is one of the two options to provide a token extractor.
		// The order of precedence is user-defined TokenLookupFuncs, and TokenLookup.
		// You can also provide both if you want.
		TokenLookupFuncs []ValuesExtractor

		// AuthScheme to be used in the Authorization header.
		// Optional. Default value "Bearer".
		AuthScheme string

		// KeyFunc defines a user-defined function that supplies the public key for a token validation.
		// The function shall take care of verifying the signing algorithm and selecting the proper key.
		// A user-defined KeyFunc can be useful if tokens are issued by an external party.
		// Used by default ParseTokenFunc implementation.
		//
		// When a user-defined KeyFunc is provided, SigningKey, SigningKeys, and SigningMethod are ignored.
		// This is one of the three options to provide a token validation key.
		// The order of precedence is a user-defined KeyFunc, SigningKeys and SigningKey.
		// Required if neither SigningKeys nor SigningKey is provided.
		// Not used if custom ParseTokenFunc is set.
		// Default to an internal implementation verifying the signing algorithm and selecting the proper key.
		KeyFunc jwt.Keyfunc

		// ParseTokenFunc defines a user-defined function that parses token from given auth. Returns an error when token
		// parsing fails or parsed token is invalid.
		// Defaults to implementation using `github.com/golang-jwt/jwt` as JWT implementation library
		ParseTokenFunc func(auth string, c echo.Context) (interface{}, error)
	}

	// JWTSuccessHandler defines a function which is executed for a valid token.
	JWTSuccessHandler func(c echo.Context)

	// JWTErrorHandler defines a function which is executed for an invalid token.
	JWTErrorHandler func(err error) error

	// JWTErrorHandlerWithContext is almost identical to JWTErrorHandler, but it's passed the current context.
	JWTErrorHandlerWithContext func(err error, c echo.Context) error
)

// Algorithms
const (
	AlgorithmHS256 = "HS256"
)

// Errors
var (
	ErrJWTMissing = echo.NewHTTPError(http.StatusBadRequest, "missing or malformed jwt")
	ErrJWTInvalid = echo.NewHTTPError(http.StatusUnauthorized, "invalid or expired jwt")
)

var (
	// DefaultJWTConfig is the default JWT auth middleware config.
	DefaultJWTConfig = JWTConfig{
		Skipper:          DefaultSkipper,
		SigningMethod:    AlgorithmHS256,
		ContextKey:       "user",
		TokenLookup:      "header:" + echo.HeaderAuthorization,
		TokenLookupFuncs: nil,
		AuthScheme:       "Bearer",
		Claims:           jwt.MapClaims{},
		KeyFunc:          nil,
	}
)

// JWT returns a JSON Web Token (JWT) auth middleware.
//
// For valid token, it sets the user in context and calls next handler.
// For invalid token, it returns "401 - Unauthorized" error.
// For missing token, it returns "400 - Bad Request" error.
//
// See: https://jwt.io/introduction
// See `JWTConfig.TokenLookup`
func JWT(key interface{}) echo.MiddlewareFunc {
	c := DefaultJWTConfig
	c.SigningKey = key
	return JWTWithConfig(c)
}

// JWTWithConfig returns a JWT auth middleware with config.
// See: `JWT()`.
func JWTWithConfig(config JWTConfig) echo.MiddlewareFunc {
	// Defaults
	if config.Skipper == nil {
		config.Skipper = DefaultJWTConfig.Skipper
	}
	if config.SigningKey == nil && len(config.SigningKeys) == 0 && config.KeyFunc == nil && config.ParseTokenFunc == nil {
		panic("echo: jwt middleware requires signing key")
	}
	if config.SigningMethod == "" {
		config.SigningMethod = DefaultJWTConfig.SigningMethod
	}
	if config.ContextKey == "" {
		config.ContextKey = DefaultJWTConfig.ContextKey
	}
	if config.Claims == nil {
		config.Claims = DefaultJWTConfig.Claims
	}
	if config.TokenLookup == "" && len(config.TokenLookupFuncs) == 0 {
		config.TokenLookup = DefaultJWTConfig.TokenLookup
	}
	if config.AuthScheme == "" {
		config.AuthScheme = DefaultJWTConfig.AuthScheme
	}
	if config.KeyFunc == nil {
		config.KeyFunc = config.defaultKeyFunc
	}
	if config.ParseTokenFunc == nil {
		config.ParseTokenFunc = config.defaultParseToken
	}

	extractors, err := createExtractors(config.TokenLookup, config.AuthScheme)
	if err != nil {
		panic(err)
	}
	if len(config.TokenLookupFuncs) > 0 {
		extractors = append(config.TokenLookupFuncs, extractors...)
	}

	return func(next echo.HandlerFunc) echo.HandlerFunc {
		return func(c echo.Context) error {
			if config.Skipper(c) {
				return next(c)
			}

			if config.BeforeFunc != nil {
				config.BeforeFunc(c)
			}

			var lastExtractorErr error
			var lastTokenErr error
			for _, extractor := range extractors {
				auths, err := extractor(c)
				if err != nil {
					lastExtractorErr = ErrJWTMissing // backwards compatibility: all extraction errors are same (unlike KeyAuth)
					continue
				}
				for _, auth := range auths {
					token, err := config.ParseTokenFunc(auth, c)
					if err != nil {
						lastTokenErr = err
						continue
					}
					// Store user information from token into context.
					c.Set(config.ContextKey, token)
					if config.SuccessHandler != nil {
						config.SuccessHandler(c)
					}
					return next(c)
				}
			}
			// we are here only when we did not successfully extract or parse any of the tokens
			err := lastTokenErr
			if err == nil { // prioritize token errors over extracting errors
				err = lastExtractorErr
			}
			if config.ErrorHandler != nil {
				return config.ErrorHandler(err)
			}
			if config.ErrorHandlerWithContext != nil {
				tmpErr := config.ErrorHandlerWithContext(err, c)
				if config.ContinueOnIgnoredError && tmpErr == nil {
					return next(c)
				}
				return tmpErr
			}

			// backwards compatible errors codes
			if lastTokenErr != nil {
				return &echo.HTTPError{
					Code:     ErrJWTInvalid.Code,
					Message:  ErrJWTInvalid.Message,
					Internal: err,
				}
			}
			return err // this is lastExtractorErr value
		}
	}
}

func (config *JWTConfig) defaultParseToken(auth string, c echo.Context) (interface{}, error) {
	var token *jwt.Token
	var err error
	// Issue #647, #656
	if _, ok := config.Claims.(jwt.MapClaims); ok {
		token, err = jwt.Parse(auth, config.KeyFunc)
	} else {
		t := reflect.ValueOf(config.Claims).Type().Elem()
		claims := reflect.New(t).Interface().(jwt.Claims)
		token, err = jwt.ParseWithClaims(auth, claims, config.KeyFunc)
	}
	if err != nil {
		return nil, err
	}
	if !token.Valid {
		return nil, errors.New("invalid token")
	}
	return token, nil
}

// defaultKeyFunc returns a signing key of the given token.
func (config *JWTConfig) defaultKeyFunc(t *jwt.Token) (interface{}, error) {
	// Check the signing method
	if t.Method.Alg() != config.SigningMethod {
		return nil, fmt.Errorf("unexpected jwt signing method=%v", t.Header["alg"])
	}
	if len(config.SigningKeys) > 0 {
		if kid, ok := t.Header["kid"].(string); ok {
			if key, ok := config.SigningKeys[kid]; ok {
				return key, nil
			}
		}
		return nil, fmt.Errorf("unexpected jwt key id=%v", t.Header["kid"])
	}

	return config.SigningKey, nil
}