// SPDX-License-Identifier: MIT
// SPDX-FileCopyrightText: © 2015 LabStack LLC and Echo contributors

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

package middleware

import (
	"errors"
	"fmt"
	"net/http"
	"reflect"

	"github.com/golang-jwt/jwt"
	"github.com/labstack/echo/v4"
)

// JWTConfig defines the config for JWT middleware.
type 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.
type JWTSuccessHandler func(c echo.Context)

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

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

// Algorithms
const (
	AlgorithmHS256 = "HS256"
)

// ErrJWTMissing is error that is returned when no JWToken was extracted from the request.
var ErrJWTMissing = echo.NewHTTPError(http.StatusBadRequest, "missing or malformed jwt")

// ErrJWTInvalid is error that is returned when middleware could not parse JWT correctly.
var ErrJWTInvalid = echo.NewHTTPError(http.StatusUnauthorized, "invalid or expired jwt")

// DefaultJWTConfig is the default JWT auth middleware config.
var 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`
//
// Deprecated: Please use https://github.com/labstack/echo-jwt instead
func JWT(key interface{}) echo.MiddlewareFunc {
	c := DefaultJWTConfig
	c.SigningKey = key
	return JWTWithConfig(c)
}

// JWTWithConfig returns a JWT auth middleware with config.
// See: `JWT()`.
//
// Deprecated: Please use https://github.com/labstack/echo-jwt instead
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, cErr := createExtractors(config.TokenLookup, config.AuthScheme)
	if cErr != nil {
		panic(cErr)
	}
	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
}
