// Copyright 2023 Versity Software
// This file is licensed under the Apache License, Version 2.0
// (the "License"); you may not use this file except in compliance
// with the License.  You may obtain a copy of the License at
//
//   http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing,
// software distributed under the License is distributed on an
// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
// KIND, either express or implied.  See the License for the
// specific language governing permissions and limitations
// under the License.

package utils

import (
	"fmt"
	"net/url"
	"os"
	"strconv"
	"strings"
	"time"

	"github.com/aws/aws-sdk-go-v2/aws"
	"github.com/aws/smithy-go/logging"
	"github.com/gofiber/fiber/v3"
	v4 "github.com/versity/versitygw/aws/signer/v4"
	"github.com/versity/versitygw/debuglogger"
	"github.com/versity/versitygw/s3err"
)

const (
	unsignedPayload string = "UNSIGNED-PAYLOAD"

	algoHMAC  string = "AWS4-HMAC-SHA256"
	algoECDSA string = "AWS4-ECDSA-P256-SHA256"
)

// CheckPresignedSignature validates presigned request signature
func CheckPresignedSignature(ctx fiber.Ctx, auth AuthData, secret string) error {
	signedHdrs := strings.Split(auth.SignedHeaders, ";")

	var contentLength int64
	var err error
	contentLengthStr := ctx.Get("Content-Length")
	if contentLengthStr != "" {
		contentLength, err = strconv.ParseInt(contentLengthStr, 10, 64)
		if err != nil {
			return s3err.GetAPIError(s3err.ErrInvalidRequest)
		}
	}

	// Create a new http request instance from fasthttp request
	req, err := createPresignedHttpRequestFromCtx(ctx, signedHdrs, contentLength)
	if err != nil {
		return err
	}

	date, _ := time.Parse(iso8601Format, auth.Date)

	signer := v4.NewSigner()
	uri, _, signMeta, signErr := signer.PresignHTTP(ctx.RequestCtx(), aws.Credentials{
		AccessKeyID:     auth.Access,
		SecretAccessKey: secret,
	}, req, unsignedPayload, service, auth.Region, date, signedHdrs, func(options *v4.SignerOptions) {
		options.DisableURIPathEscaping = true
		if debuglogger.IsDebugEnabled() {
			options.LogSigning = true
			options.Logger = logging.NewStandardLogger(os.Stderr)
		}
	})
	if signErr != nil {
		return fmt.Errorf("presign generated http request: %w", err)
	}

	urlParts, err := url.Parse(uri)
	if err != nil {
		return fmt.Errorf("parse presigned url: %w", err)
	}

	signature := urlParts.Query().Get("X-Amz-Signature")
	if signature != auth.Signature {
		return s3err.GetSignatureDoesNotMatchErr(
			auth.Access,
			signMeta.StringToSign,
			auth.Signature,
			HexBytes(signMeta.StringToSign),
			signMeta.CanonicalString,
			HexBytes(signMeta.CanonicalString),
		)
	}

	return nil
}

// https://docs.aws.amazon.com/AmazonS3/latest/API/sigv4-query-string-auth.html
//
// # ParsePresignedURIParts parses and validates request URL query parameters
//
// ?X-Amz-Algorithm=AWS4-HMAC-SHA256
// &X-Amz-Credential=access-key-id/20130721/us-east-1/s3/aws4_request
// &X-Amz-Date=20130721T201207Z
// &X-Amz-Expires=86400
// &X-Amz-SignedHeaders=host
// &X-Amz-Signature=1e68ad45c1db540284a4a1eca3884c293ba1a0ff63ab9db9a15b5b29dfa02cd8
func ParsePresignedURIParts(ctx fiber.Ctx, region string) (AuthData, error) {
	a := AuthData{}

	// Get and verify algorithm query parameter
	algo := ctx.Query("X-Amz-Algorithm")
	err := validateAlgorithm(algo)
	if err != nil {
		return a, err
	}

	// Parse and validate credentials query parameter
	credsQuery := ctx.Query("X-Amz-Credential")
	if credsQuery == "" {
		return a, s3err.QueryAuthErrors.MissingRequiredParams()
	}

	creds, err := ParseCredentials(credsQuery, s3err.QueryAuthErrors)
	if err != nil {
		return a, err
	}

	// validate the region
	if creds.Region != region {
		return a, s3err.QueryAuthErrors.IncorrectRegion(region, creds.Region)
	}

	// Parse and validate Date query param
	date := ctx.Query("X-Amz-Date")
	if date == "" {
		return a, s3err.QueryAuthErrors.MissingRequiredParams()
	}

	tdate, err := time.Parse(iso8601Format, date)
	if err != nil {
		return a, s3err.QueryAuthErrors.InvalidXAmzDateFormat()
	}

	if date[:8] != creds.Date {
		return a, s3err.QueryAuthErrors.DateMismatch(creds.Date, date[:8])
	}

	signature := ctx.Query("X-Amz-Signature")
	if signature == "" {
		return a, s3err.QueryAuthErrors.MissingRequiredParams()
	}

	signedHdrs := ctx.Query("X-Amz-SignedHeaders")
	if signedHdrs == "" {
		return a, s3err.QueryAuthErrors.MissingRequiredParams()
	}

	// Validate X-Amz-Expires query param and check if request is expired
	err = validateExpiration(ctx.Query("X-Amz-Expires"), tdate)
	if err != nil {
		return a, err
	}

	a.Signature = signature
	a.Access = creds.Access
	a.Algorithm = algo
	a.Region = creds.Region
	a.SignedHeaders = signedHdrs
	a.Date = date

	return a, nil
}

func validateExpiration(str string, date time.Time) error {
	if str == "" {
		return s3err.QueryAuthErrors.MissingRequiredParams()
	}

	exp, err := strconv.Atoi(str)
	if err != nil {
		return s3err.QueryAuthErrors.ExpiresNumber()
	}

	if exp < 0 {
		return s3err.QueryAuthErrors.ExpiresNegative()
	}

	if exp > 604800 {
		return s3err.QueryAuthErrors.ExpiresTooLarge()
	}

	now := time.Now().UTC()
	expiresAt := date.Add(time.Duration(exp) * time.Second)

	if expiresAt.Before(now) {
		return s3err.GetExpiredPresignedURLError(exp, expiresAt.Format(time.RFC3339), now.Format(time.RFC3339))
	}

	return nil
}

// validateAlgorithm validates the algorithm
// for AWS4-ECDSA-P256-SHA256 it returns a custom non AWS error
// currently only AWS4-HMAC-SHA256 algorithm is supported
func validateAlgorithm(algo string) error {
	switch algo {
	case "":
		return s3err.QueryAuthErrors.MissingRequiredParams()
	case algoHMAC:
		return nil
	case algoECDSA:
		return s3err.QueryAuthErrors.OnlyHMACSupported()
	default:
		// all other algorithms are considered as invalid
		return s3err.QueryAuthErrors.UnsupportedAlgorithm()
	}
}

// IsPresignedURLAuth determines if the request is presigned:
// which is authorization with query params
func IsPresignedURLAuth(ctx fiber.Ctx) bool {
	algo := ctx.Query("X-Amz-Algorithm")
	creds := ctx.Query("X-Amz-Credential")
	signature := ctx.Query("X-Amz-Signature")
	signedHeaders := ctx.Query("X-Amz-SignedHeaders")
	expires := ctx.Query("X-Amz-Expires")

	return !allEmpty(algo, creds, signature, signedHeaders, expires) || IsPresignedURLAuthV2(ctx)
}

// IsPresignedURLAuthV2 determines if the request is
// query-string signed with aws v2 signer
func IsPresignedURLAuthV2(ctx fiber.Ctx) bool {
	expires := ctx.Query("Expires")
	access := ctx.Query("AWSAccessKeyId")
	signature := ctx.Query("Signature")

	return anyNonEmpty(expires, access, signature)
}

// allEmpty reports whether every given string is empty.
func allEmpty(args ...string) bool {
	for _, a := range args {
		if a != "" {
			return false
		}
	}

	return true
}

// anyNonEmpty reports whether at least one given string is non-empty.
func anyNonEmpty(args ...string) bool {
	for _, a := range args {
		if a != "" {
			return true
		}
	}

	return false
}