package signers

import (
	"bytes"
	"crypto/hmac"
	"crypto/sha1"
	"encoding/base64"
	"fmt"
	"io"
	"net/http"
	"net/url"
	"sort"
	"strings"
	"time"

	"github.com/minio-io/minio/pkg/utils/config"
)

func SignRequest(user config.User, req *http.Request) {
	if date := req.Header.Get("Date"); date == "" {
		req.Header.Set("Date", time.Now().UTC().Format(http.TimeFormat))
	}
	hm := hmac.New(sha1.New, []byte(user.SecretKey))
	ss := getStringToSign(req)
	io.WriteString(hm, ss)

	authHeader := new(bytes.Buffer)
	fmt.Fprintf(authHeader, "AWS %s:", user.AccessKey)
	encoder := base64.NewEncoder(base64.StdEncoding, authHeader)
	encoder.Write(hm.Sum(nil))
	encoder.Close()
	req.Header.Set("Authorization", authHeader.String())
}

// This package implements verification side of Object API Signature request
func ValidateRequest(user config.User, req *http.Request) (bool, error) {
	if date := req.Header.Get("Date"); date == "" {
		return false, fmt.Errorf("Date should be set")
	}
	hm := hmac.New(sha1.New, []byte(user.SecretKey))
	ss := getStringToSign(req)
	io.WriteString(hm, ss)

	authHeader := new(bytes.Buffer)
	fmt.Fprintf(authHeader, "AWS %s:", user.AccessKey)
	encoder := base64.NewEncoder(base64.StdEncoding, authHeader)
	encoder.Write(hm.Sum(nil))
	encoder.Close()

	if req.Header.Get("Authorization") != authHeader.String() {
		return false, fmt.Errorf("Authorization header mismatch")
	}
	return true, nil
}

// From the Amazon docs:
//
// StringToSign = HTTP-Verb + "\n" +
// 	 Content-MD5 + "\n" +
//	 Content-Type + "\n" +
//	 Date + "\n" +
//	 CanonicalizedAmzHeaders +
//	 CanonicalizedResource;
func getStringToSign(req *http.Request) string {
	buf := new(bytes.Buffer)
	buf.WriteString(req.Method)
	buf.WriteByte('\n')
	buf.WriteString(req.Header.Get("Content-MD5"))
	buf.WriteByte('\n')
	buf.WriteString(req.Header.Get("Content-Type"))
	buf.WriteByte('\n')
	if req.Header.Get("x-amz-date") == "" {
		buf.WriteString(req.Header.Get("Date"))
	}
	buf.WriteByte('\n')
	writeCanonicalizedAmzHeaders(buf, req)
	writeCanonicalizedResource(buf, req)
	return buf.String()
}

func hasPrefixCaseInsensitive(s, pfx string) bool {
	if len(pfx) > len(s) {
		return false
	}
	shead := s[:len(pfx)]
	if shead == pfx {
		return true
	}
	shead = strings.ToLower(shead)
	return shead == pfx || shead == strings.ToLower(pfx)
}

func writeCanonicalizedAmzHeaders(buf *bytes.Buffer, req *http.Request) {
	amzHeaders := make([]string, 0)
	vals := make(map[string][]string)
	for k, vv := range req.Header {
		if hasPrefixCaseInsensitive(k, "x-amz-") {
			lk := strings.ToLower(k)
			amzHeaders = append(amzHeaders, lk)
			vals[lk] = vv
		}
	}
	sort.Strings(amzHeaders)
	for _, k := range amzHeaders {
		buf.WriteString(k)
		buf.WriteByte(':')
		for idx, v := range vals[k] {
			if idx > 0 {
				buf.WriteByte(',')
			}
			if strings.Contains(v, "\n") {
				// TODO: "Unfold" long headers that
				// span multiple lines (as allowed by
				// RFC 2616, section 4.2) by replacing
				// the folding white-space (including
				// new-line) by a single space.
				buf.WriteString(v)
			} else {
				buf.WriteString(v)
			}
		}
		buf.WriteByte('\n')
	}
}

// Must be sorted:
var subResList = []string{"acl", "lifecycle", "location", "logging", "notification", "partNumber", "policy", "requestPayment", "torrent", "uploadId", "uploads", "versionId", "versioning", "versions", "website"}

// From the Amazon docs:
//
// CanonicalizedResource = [ "/" + Bucket ] +
// 	  <HTTP-Request-URI, from the protocol name up to the query string> +
// 	  [ sub-resource, if present. For example "?acl", "?location", "?logging", or "?torrent"];
func writeCanonicalizedResource(buf *bytes.Buffer, req *http.Request) {
	buf.WriteString(req.URL.Path)
	if req.URL.RawQuery != "" {
		n := 0
		vals, _ := url.ParseQuery(req.URL.RawQuery)
		for _, subres := range subResList {
			if vv, ok := vals[subres]; ok && len(vv) > 0 {
				n++
				if n == 1 {
					buf.WriteByte('?')
				} else {
					buf.WriteByte('&')
				}
				buf.WriteString(subres)
				if len(vv[0]) > 0 {
					buf.WriteByte('=')
					buf.WriteString(url.QueryEscape(vv[0]))
				}
			}
		}
	}
}