package signer

import (
	"crypto/ecdsa"
	"crypto/rand"
	"crypto/sha256"
	"encoding/hex"
	"fmt"
	"net/url"
	"strconv"
	"strings"
	"time"

	"gitlink.org.cn/cloudream/common/utils/sort2"
)

var ErrSignatureMismatch = fmt.Errorf("signature mismatch")

var ErrExpired = fmt.Errorf("signature expired")

const (
	DateQueryKey        = "x-jcs-date"
	ExpiresQueryKey     = "x-jcs-expires"
	SignatureQueryKey   = "x-jcs-signature"
	AccessKeyIDQueryKey = "x-jcs-access-key-id"
	AlgorithmQueryKey   = "x-jcs-algorithm"
	AlgorithmValue      = "ECDSA256"
	DateFormat          = "20060102T150405Z"
)

type SignKey struct {
	privateKey  *ecdsa.PrivateKey
	accessKeyID string
}

func PresignURL(key *SignKey, method string, u *url.URL, signingTime time.Time, expiresSeconds int) error {
	date := signingTime.Format(DateFormat)

	queries := u.Query()
	queries.Set(DateQueryKey, date)
	queries.Set(ExpiresQueryKey, fmt.Sprintf("%v", expiresSeconds))
	queries.Set(AccessKeyIDQueryKey, key.accessKeyID)
	queries.Set(AlgorithmQueryKey, AlgorithmValue)

	ss := makeStringToSign(method, u.Host, u.Path, queries)
	ssHash := sha256.Sum256([]byte(ss))

	sign, err := ecdsa.SignASN1(rand.Reader, key.privateKey, ssHash[:])
	if err != nil {
		return err
	}

	queries.Set(SignatureQueryKey, hex.EncodeToString(sign))
	u.RawQuery = queries.Encode()
	return nil
}

type VerifyKey struct {
	publicKey *ecdsa.PublicKey
}

func NewVerifyKey(publicKey *ecdsa.PublicKey) *VerifyKey {
	return &VerifyKey{publicKey: publicKey}
}

func GetAccessKeyID(u *url.URL) string {
	return u.Query().Get(AccessKeyIDQueryKey)
}

func VerifyPresigned(key *VerifyKey, method string, u *url.URL) error {
	queries := u.Query()

	dateStr := queries.Get(DateQueryKey)
	if dateStr == "" {
		return fmt.Errorf("missing date in query string")
	}

	date, err := time.Parse(DateFormat, dateStr)
	if err != nil {
		return fmt.Errorf("invalid date format: %v", err)
	}

	expiresStr := queries.Get(ExpiresQueryKey)
	if expiresStr == "" {
		return fmt.Errorf("missing expires in query string")
	}

	expires, err := strconv.Atoi(expiresStr)
	if err != nil {
		return fmt.Errorf("invalid expires format: %v", err)
	}

	if time.Now().After(date.Add(time.Duration(expires) * time.Second)) {
		return ErrExpired
	}

	signatureStr := queries.Get(SignatureQueryKey)
	signature, err := hex.DecodeString(signatureStr)
	if err != nil {
		return fmt.Errorf("invalid signature format: %v", err)
	}

	queries.Del(SignatureQueryKey)
	ss := makeStringToSign(method, u.Host, u.Path, queries)
	ssHash := sha256.Sum256([]byte(ss))

	if !ecdsa.VerifyASN1(key.publicKey, ssHash[:], signature) {
		return ErrSignatureMismatch
	}

	return nil
}

func makeStringToSign(method string, host string, path string, queries url.Values) string {
	type queryKv struct {
		Key    string
		Values []string
	}

	var queryKvs []queryKv
	for k, vs := range queries {
		vs = sort2.SortAsc(vs)
		queryKvs = append(queryKvs, queryKv{Key: k, Values: vs})
	}

	queryKvs = sort2.Sort(queryKvs, func(left, right queryKv) int {
		return strings.Compare(left.Key, right.Key)
	})

	var str strings.Builder
	str.WriteString(method)
	str.WriteByte('\n')
	str.WriteString(host)
	str.WriteByte('\n')
	str.WriteString(path)
	str.WriteByte('\n')
	for _, kv := range queryKvs {
		str.WriteString(kv.Key)
		str.WriteByte('=')

		for i, v := range kv.Values {
			if i > 0 {
				str.WriteByte(',')
			}
			str.WriteString(v)
		}
		str.WriteByte('\n')
	}
	return str.String()
}