// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.

using System;
using System.Buffers;
using System.IO;
using System.Security.Cryptography;

namespace Microsoft.DotNet.Build.Tasks.FileCatalog;

/// <summary>
/// A single file (or in-memory blob) to include in a catalog. Only the SHA-1 and SHA-256
/// hashes of the content are recorded in the catalog, so an entry stores just those hashes
/// (never the raw content), keeping memory use bounded regardless of file size.
/// </summary>
public sealed class CatalogEntry
{
    /// <summary>
    /// Creates an entry whose hashes are computed by streaming <paramref name="filePath"/>.
    /// </summary>
    /// <param name="filePath">Path on disk to read for the file hashes.</param>
    /// <param name="name">
    /// Optional logical name for the entry. Defaults to <see cref="Path.GetFileName(string)"/>
    /// of <paramref name="filePath"/>. The name is not embedded in the catalog (makecat
    /// V2 catalogs do not carry per-member file names); it is retained only for diagnostics.
    /// </param>
    public static CatalogEntry FromFile(FileInfo filePath, string? name = null)
    {
        if (filePath is null)
        {
            throw new ArgumentNullException(nameof(filePath));
        }

        // Stream the file through both hash algorithms in a single pass so the full
        // content is never buffered in memory (catalog generation only needs the hashes).
        using IncrementalHash sha1 = IncrementalHash.CreateHash(HashAlgorithmName.SHA1);
        using IncrementalHash sha256 = IncrementalHash.CreateHash(HashAlgorithmName.SHA256);
        using (FileStream stream = File.OpenRead(filePath.FullName))
        {
            byte[] buffer = ArrayPool<byte>.Shared.Rent(81920);
            try
            {
                int read;
                while ((read = stream.Read(buffer, 0, buffer.Length)) > 0)
                {
                    sha1.AppendData(buffer, 0, read);
                    sha256.AppendData(buffer, 0, read);
                }
            }
            finally
            {
                ArrayPool<byte>.Shared.Return(buffer);
            }
        }

        return new CatalogEntry(name ?? filePath.Name, sha1.GetHashAndReset(), sha256.GetHashAndReset());
    }

    /// <summary>
    /// Creates an entry from in-memory content, computing its hashes immediately.
    /// </summary>
    public CatalogEntry(string name, ReadOnlyMemory<byte> content)
        : this(name, SHA1.HashData(content.Span), SHA256.HashData(content.Span))
    {
    }

    private CatalogEntry(string name, byte[] sha1, byte[] sha256)
    {
        if (string.IsNullOrEmpty(name))
        {
            throw new ArgumentException("Name must not be null or empty.", nameof(name));
        }

        Name = name;
        Sha1 = sha1;
        Sha256 = sha256;
    }

    /// <summary>Logical name for the entry (typically the file name). Not embedded in the catalog.</summary>
    public string Name { get; }

    /// <summary>The raw SHA-1 hash of the content, used as a legacy catalog lookup key.</summary>
    public byte[] Sha1 { get; }

    /// <summary>The raw SHA-256 hash of the content, recorded in the catalog.</summary>
    public byte[] Sha256 { get; }
}