// Copyright (c) 2015-2021 MinIO, Inc.
//
// This file is part of MinIO Object Storage stack
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU Affero General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU Affero General Public License for more details.
//
// You should have received a copy of the GNU Affero General Public License
// along with this program.  If not, see <http://www.gnu.org/licenses/>.

package cmd

import (
	"bytes"
	"github.com/minio/minio/internal/config"
	"net/http"
	"os"
	"strings"
	"text/template"
)

// Standard cross domain policy information located at https://s3.amazonaws.com/crossdomain.xml
const crossDomainXML = `<?xml version="1.0"?><!DOCTYPE cross-domain-policy SYSTEM "http://www.adobe.com/xml/dtds/cross-domain-policy.dtd"><cross-domain-policy><allow-access-from domain="*" secure="false" /></cross-domain-policy>`

// 自定义crossdomain.xml
const crossDomainXMLPrefix = `<?xml version="1.0"?><!DOCTYPE cross-domain-policy SYSTEM "http://www.adobe.com/xml/dtds/cross-domain-policy.dtd"><cross-domain-policy>`
const crossDomainXMLSuffix = `</cross-domain-policy>`
const allowAccessFromTemplate = `<allow-access-from domain="{{.Domain}}" secure="false" />`

// Standard path where an app would find cross domain policy information.
const crossDomainXMLEntity = "/crossdomain.xml"

// A cross-domain policy file is an XML document that grants a web client, such as Adobe Flash Player
// or Adobe Acrobat (though not necessarily limited to these), permission to handle data across domains.
// When clients request content hosted on a particular source domain and that content make requests
// directed towards a domain other than its own, the remote domain needs to host a cross-domain
// policy file that grants access to the source domain, allowing the client to continue the transaction.
func setCrossDomainPolicyMiddleware(h http.Handler) http.Handler {
	// get env MINIO_ALLOW_ACCESS_FROM_DOMAIN
	allowAccessFromDomain := os.Getenv(config.EnvMinIOAllowAccessFromDomain)
	if allowAccessFromDomain == "" {
		allowAccessFromDomain = "*"
	}
	// logger.Info("MINIO_ALLOW_ACCESS_FROM_DOMAIN=%s", allowAccessFromDomain)

	// 如果配置了多个就需要解析一下
	domains := strings.Split(allowAccessFromDomain, ",")
	allowAccessFrom := crossDomainXMLPrefix
	for _, domain := range domains {
		// fill string template
		buffer := &bytes.Buffer{}
		tmpl, _ := template.New("tmp").Parse(allowAccessFromTemplate)
		data := struct{ Domain string }{Domain: domain}
		_ = tmpl.Execute(buffer, data)
		allowAccessFrom += buffer.String()
	}
	allowAccessFrom += crossDomainXMLSuffix

	// Write to ServeHTTP
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		// Look for 'crossdomain.xml' in the incoming request.
		if r.URL.Path == crossDomainXMLEntity {
			// Write the standard cross domain policy xml.
			w.Write([]byte(allowAccessFrom))
			// Request completed, no need to serve to other handlers.
			return
		}
		h.ServeHTTP(w, r)
	})
}