package middleware

import (
	"github.com/labstack/echo/v4"
	"github.com/labstack/echo/v4/middleware"
	"net/http"
)

type CORSConfig struct {
	// Skipper defines a function to skip middleware.
	Skipper func(c echo.Context) bool

	// AllowOrigins determines the value of the Access-Control-Allow-Origin
	// response header.  This header defines a list of origins that may access the
	// resource.  The wildcard characters '*' and '?' are supported and are
	// converted to regex fragments '.*' and '.' accordingly.
	//
	// Security: use extreme caution when handling the origin, and carefully
	// validate any logic. Remember that attackers may register hostile domain names.
	// See https://blog.portswigger.net/2016/10/exploiting-cors-misconfigurations-for.html
	//
	// Optional. Default value []string{"*"}.
	//
	// See also: https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Access-Control-Allow-Origin
	AllowOrigins []string

	// AllowOriginFunc is a custom function to validate the origin. It takes the
	// origin as an argument and returns true if allowed or false otherwise. If
	// an error is returned, it is returned by the handler. If this option is
	// set, AllowOrigins is ignored.
	//
	// Security: use extreme caution when handling the origin, and carefully
	// validate any logic. Remember that attackers may register hostile domain names.
	// See https://blog.portswigger.net/2016/10/exploiting-cors-misconfigurations-for.html
	//
	// Optional.
	AllowOriginFunc func(origin string) (bool, error)

	// AllowMethods determines the value of the Access-Control-Allow-Methods
	// response header.  This header specified the list of methods allowed when
	// accessing the resource.  This is used in response to a preflight request.
	//
	// Optional. Default value DefaultCORSConfig.AllowMethods.
	// If `allowMethods` is left empty, this middleware will fill for preflight
	// request `Access-Control-Allow-Methods` header value
	// from `Allow` header that echo.Router set into context.
	//
	// See also: https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Access-Control-Allow-Methods
	AllowMethods []string

	// AllowHeaders determines the value of the Access-Control-Allow-Headers
	// response header.  This header is used in response to a preflight request to
	// indicate which HTTP headers can be used when making the actual request.
	//
	// Optional. Default value []string{}.
	//
	// See also: https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Access-Control-Allow-Headers
	AllowHeaders []string

	// AllowCredentials determines the value of the
	// Access-Control-Allow-Credentials response header.  This header indicates
	// whether the response to the request can be exposed when the
	// credentials mode (Request.credentials) is true. When used as part of a
	// response to a preflight request, this indicates whether or not the actual
	// request can be made using credentials.  See also
	// [MDN: Access-Control-Allow-Credentials].
	//
	// Optional. Default value false, in which case the header is not set.
	//
	// Security: avoid using `AllowCredentials = true` with `AllowOrigins = *`.
	// See "Exploiting CORS misconfigurations for Bitcoins and bounties",
	// https://blog.portswigger.net/2016/10/exploiting-cors-misconfigurations-for.html
	//
	// See also: https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Access-Control-Allow-Credentials
	AllowCredentials bool

	// UnsafeWildcardOriginWithAllowCredentials UNSAFE/INSECURE: allows wildcard '*' origin to be used with AllowCredentials
	// flag. In that case we consider any origin allowed and send it back to the client with `Access-Control-Allow-Origin` header.
	//
	// This is INSECURE and potentially leads to [cross-origin](https://portswigger.net/research/exploiting-cors-misconfigurations-for-bitcoins-and-bounties)
	// attacks. See: https://github.com/labstack/echo/issues/2400 for discussion on the subject.
	//
	// Optional. Default value is false.
	UnsafeWildcardOriginWithAllowCredentials bool

	// ExposeHeaders determines the value of Access-Control-Expose-Headers, which
	// defines a list of headers that clients are allowed to access.
	//
	// Optional. Default value []string{}, in which case the header is not set.
	//
	// See also: https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Access-Control-Expose-Header
	ExposeHeaders []string

	// MaxAge determines the value of the Access-Control-Max-Age response header.
	// This header indicates how long (in seconds) the results of a preflight
	// request can be cached.
	//
	// Optional. Default value 0.  The header is set only if MaxAge > 0.
	//
	// See also: https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Access-Control-Max-Age
	MaxAge int
}

// DefaultCORSConfig is the default CORS middleware config.
var DefaultCORSConfig = CORSConfig{
	Skipper: func(c echo.Context) bool {
		return false
	},
	AllowOrigins: []string{"*"},
	AllowMethods: []string{
		http.MethodGet,
		http.MethodHead,
		http.MethodPut,
		http.MethodPatch,
		http.MethodPost,
		http.MethodDelete,
	},
}

func (c *CORSConfig) ToMiddleware() echo.MiddlewareFunc {
	return middleware.CORSWithConfig(middleware.CORSConfig{
		Skipper:                                  c.Skipper,
		AllowOrigins:                             c.AllowOrigins,
		AllowOriginFunc:                          c.AllowOriginFunc,
		AllowMethods:                             c.AllowMethods,
		AllowHeaders:                             c.AllowHeaders,
		AllowCredentials:                         c.AllowCredentials,
		UnsafeWildcardOriginWithAllowCredentials: c.UnsafeWildcardOriginWithAllowCredentials,
		ExposeHeaders:                            c.ExposeHeaders,
		MaxAge:                                   c.MaxAge,
	})
}

func CORS() echo.MiddlewareFunc {
	return DefaultCORSConfig.ToMiddleware()
}