// Copyright (c) .NET Foundation. All rights reserved.
// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.

using System;
using System.Threading;
using System.Threading.Tasks;
using NuGet.Common;
using System.Collections.Generic;
using System.IO;
using System.Security.Cryptography;
using System.Security.Cryptography.Pkcs;
using System.Security.Cryptography.X509Certificates;

namespace NuGet.Packaging.Signing
{
    /// <summary>
    /// Utility methods for signing.
    /// </summary>
    public static class SigningUtility
    {
        public static void Verify(SignPackageRequest request, ILogger logger)
        {
            if (request == null)
            {
                throw new ArgumentNullException(nameof(request));
            }

            if (logger == null)
            {
                throw new ArgumentNullException(nameof(logger));
            }

            if (!CertificateUtility.IsSignatureAlgorithmSupported(request.Certificate))
            {
                throw new SignatureException(NuGetLogCode.NU3013, Strings.SigningError_CertificateHasUnsupportedSignatureAlgorithm);
            }

            if (!CertificateUtility.IsCertificatePublicKeyValid(request.Certificate))
            {
                throw new SignatureException(NuGetLogCode.NU3014, Strings.SigningError_CertificateFailsPublicKeyLengthRequirement);
            }

            if (CertificateUtility.HasExtendedKeyUsage(request.Certificate, Oids.LifetimeSigningEku))
            {
                throw new SignatureException(NuGetLogCode.NU3015, Strings.SigningError_CertificateHasLifetimeSigningEKU);
            }

            if (CertificateUtility.IsCertificateValidityPeriodInTheFuture(request.Certificate))
            {
                throw new SignatureException(NuGetLogCode.NU3017, Strings.SigningError_NotYetValid);
            }

            request.BuildSigningCertificateChainOnce(logger);
        }

        public static CryptographicAttributeObjectCollection CreateSignedAttributes(
            SignPackageRequest request,
            IReadOnlyList<X509Certificate2> chainList)
        {
            if (request == null)
            {
                throw new ArgumentNullException(nameof(request));
            }

            if (chainList == null || chainList.Count == 0)
            {
                throw new ArgumentException(Strings.ArgumentCannotBeNullOrEmpty, nameof(chainList));
            }

            var attributes = new CryptographicAttributeObjectCollection
            {
                new Pkcs9SigningTime()
            };

            if (request.SignatureType != SignatureType.Unknown)
            {
                // Add signature type if set.
                attributes.Add(AttributeUtility.CreateCommitmentTypeIndication(request.SignatureType));
            }

            attributes.Add(AttributeUtility.CreateSigningCertificateV2(chainList[0], request.SignatureHashAlgorithm));

            return attributes;
        }

        public static CryptographicAttributeObjectCollection CreateSignedAttributes(
            RepositorySignPackageRequest request,
            IReadOnlyList<X509Certificate2> chainList)
        {
            if (request == null)
            {
                throw new ArgumentNullException(nameof(request));
            }

            if (chainList == null || chainList.Count == 0)
            {
                throw new ArgumentException(Strings.ArgumentCannotBeNullOrEmpty, nameof(chainList));
            }

            var attributes = CreateSignedAttributes((SignPackageRequest)request, chainList);

            attributes.Add(AttributeUtility.CreateNuGetV3ServiceIndexUrl(request.V3ServiceIndexUrl));

            if (request.PackageOwners?.Count > 0)
            {
                attributes.Add(AttributeUtility.CreateNuGetPackageOwners(request.PackageOwners));
            }

            return attributes;
        }

        public static CmsSigner CreateCmsSigner(SignPackageRequest request, ILogger logger)
        {
            if (request == null)
            {
                throw new ArgumentNullException(nameof(request));
            }

            if (logger == null)
            {
                throw new ArgumentNullException(nameof(logger));
            }

            // Subject Key Identifier (SKI) is smaller and less prone to accidental matching than issuer and serial
            // number.  However, to ensure cross-platform verification, SKI should only be used if the certificate
            // has the SKI extension attribute.
            CmsSigner signer;

            if (request.Certificate.Extensions[Oids.SubjectKeyIdentifier] == null)
            {
                signer = new CmsSigner(SubjectIdentifierType.IssuerAndSerialNumber, request.Certificate);
            }
            else
            {
                signer = new CmsSigner(SubjectIdentifierType.SubjectKeyIdentifier, request.Certificate);
            }

            request.BuildSigningCertificateChainOnce(logger);

            var chain = request.Chain;

            foreach (var certificate in chain)
            {
                signer.Certificates.Add(certificate);
            }

            CryptographicAttributeObjectCollection attributes;

            if (request.SignatureType == SignatureType.Repository)
            {
                attributes = CreateSignedAttributes((RepositorySignPackageRequest)request, chain);
            }
            else
            {
                attributes = CreateSignedAttributes(request, chain);
            }

            foreach (var attribute in attributes)
            {
                signer.SignedAttributes.Add(attribute);
            }

            // We built the chain ourselves and added certificates.
            // Passing any other value here would trigger another chain build
            // and possibly add duplicate certs to the collection.
            signer.IncludeOption = X509IncludeOption.None;
            signer.DigestAlgorithm = request.SignatureHashAlgorithm.ConvertToOid();

            return signer;
        }

        /// <summary>
        /// Add a signature to a package.
        /// </summary>
        public static async Task SignAsync(SigningOptions options, SignPackageRequest signRequest, CancellationToken token)
        {
            token.ThrowIfCancellationRequested();

            Verify(signRequest, options.Logger);

            var tempPackageFile = new FileInfo(Path.GetTempFileName());
            Stream? unsignedPackageStream = null;
            var signaturePlacement = SignaturePlacement.PrimarySignature;

            try
            {
                PrimarySignature? primarySignature;
                var isSigned = false;

                using (var package = new SignedPackageArchive(options.InputPackageStream, Stream.Null))
                {
                    if (await package.IsZip64Async(token))
                    {
                        throw new SignatureException(NuGetLogCode.NU3006, Strings.ErrorZip64NotSupported);
                    }

                    // The maximum number of entries in a 32-bit ZIP file is 0xFFFE, as 0xFFFF indicates
                    // that the archive is 64-bit ZIP.  The signature file itself adds one entry, so the
                    // maximum number of entries in a package before we sign it is 0xFFFD.
                    if (package.GetPackageEntryCount() >= ZipConstants.Mask16Bit - 1)
                    {
                        throw new SignatureException(NuGetLogCode.NU3039, Strings.SigningWouldRequireZip64);
                    }

                    primarySignature = await package.GetPrimarySignatureAsync(token);
                    isSigned = primarySignature != null;

                    if (signRequest.SignatureType == SignatureType.Repository && primarySignature != null)
                    {
                        if (primarySignature.Type == SignatureType.Repository)
                        {
                            throw new SignatureException(NuGetLogCode.NU3033, Strings.Error_RepositorySignatureMustNotHaveARepositoryCountersignature);
                        }

                        if (SignatureUtility.HasRepositoryCountersignature(primarySignature))
                        {
                            throw new SignatureException(NuGetLogCode.NU3032, Strings.SignedPackagePackageAlreadyCountersigned);
                        }

                        signaturePlacement = SignaturePlacement.Countersignature;
                    }

                    if (isSigned && !options.Overwrite && signaturePlacement != SignaturePlacement.Countersignature)
                    {
                        throw new SignatureException(NuGetLogCode.NU3001, Strings.SignedPackageAlreadySigned);
                    }
                }

                var inputPackageStream = options.InputPackageStream;
                if (isSigned)
                {
                    unsignedPackageStream = tempPackageFile.Open(FileMode.OpenOrCreate, FileAccess.ReadWrite);

                    using (var package = new SignedPackageArchive(options.InputPackageStream, unsignedPackageStream))
                    {
                        await package.RemoveSignatureAsync(token);
                    }

                    inputPackageStream = unsignedPackageStream;
                }

                using (var package = new SignedPackageArchive(inputPackageStream, options.OutputPackageStream))
                {
                    PrimarySignature signature;
                    if (signaturePlacement == SignaturePlacement.Countersignature)
                    {
                        signature = await options.SignatureProvider.CreateRepositoryCountersignatureAsync(
                            (RepositorySignPackageRequest)signRequest,
                            primarySignature!,
                            options.Logger,
                            token);
                    }
                    else
                    {
                        var hashAlgorithm = signRequest.SignatureHashAlgorithm;
                        var zipArchiveHash = await package.GetArchiveHashAsync(hashAlgorithm, token);
                        var signatureContent = GenerateSignatureContent(hashAlgorithm, zipArchiveHash);
                        signature = await options.SignatureProvider.CreatePrimarySignatureAsync(signRequest, signatureContent, options.Logger, token);
                    }

                    using (var stream = new MemoryStream(signature.GetBytes()))
                    {
                        await package.AddSignatureAsync(stream, token);
                    }
                }
            }
            finally
            {
                if (unsignedPackageStream != null && !ReferenceEquals(unsignedPackageStream, options.InputPackageStream))
                {
                    unsignedPackageStream.Dispose();
                }

                FileUtility.Delete(tempPackageFile.FullName);
            }
        }

        private static SignatureContent GenerateSignatureContent(Common.HashAlgorithmName hashAlgorithmName, byte[] zipArchiveHash)
        {
            var base64ZipArchiveHash = Convert.ToBase64String(zipArchiveHash);

            return new SignatureContent(SigningSpecifications.V1, hashAlgorithmName, base64ZipArchiveHash);
        }
    }
}