Vocaluxe/VocaluxeLib/Songs/CSongFiles.cs

#region license
// This file is part of Vocaluxe.
//
// Vocaluxe is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// Vocaluxe is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with Vocaluxe. If not, see <http://www.gnu.org/licenses/>.
#endregion

using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Threading.Tasks;

namespace VocaluxeLib.Songs
{
    /// <summary>
    ///     Access to the files of a song (audio, video, cover, backgrounds).
    ///     Songs from a song server exist locally only as their text file at first; their other files are
    ///     downloaded on demand. Everything that opens a song file should check <see cref="IsLocal" /> and
    ///     call <see cref="RequestAsync" /> (or <see cref="EnsureLocal" /> on background threads) first.
    /// </summary>
    public interface ISongFileProvider
    {
        /// <summary>True if the file exists locally or can be downloaded.</summary>
        bool Exists(string path);

        /// <summary>True if the file can be opened now (exists locally and is complete).</summary>
        bool IsLocal(string path);

        /// <summary>Downloads the files that are not local yet. The task completes when all are local (or failed).</summary>
        Task RequestAsync(IEnumerable<string> paths);

        /// <summary>Progress of the downloads of these files in [0..1], 1 if all are local.</summary>
        float GetProgress(IEnumerable<string> paths);
    }

    /// <summary>The default provider: plain local files.</summary>
    public class CLocalSongFileProvider : ISongFileProvider
    {
        public bool Exists(string path)
        {
            return File.Exists(path);
        }

        public bool IsLocal(string path)
        {
            return File.Exists(path);
        }

        public Task RequestAsync(IEnumerable<string> paths)
        {
            return Task.CompletedTask;
        }

        public float GetProgress(IEnumerable<string> paths)
        {
            return 1f;
        }
    }

    public static class CSongFiles
    {
        public static ISongFileProvider Provider { get; set; } = new CLocalSongFileProvider();

        public static bool Exists(string path)
        {
            return !string.IsNullOrEmpty(path) && Provider.Exists(path);
        }

        public static bool IsLocal(string path)
        {
            return !string.IsNullOrEmpty(path) && Provider.IsLocal(path);
        }

        public static bool AreLocal(IEnumerable<string> paths)
        {
            return paths.All(IsLocal);
        }

        public static Task RequestAsync(IEnumerable<string> paths)
        {
            var missing = paths.Where(p => !string.IsNullOrEmpty(p) && !Provider.IsLocal(p)).Distinct().ToList();
            return missing.Count == 0 ? Task.CompletedTask : Provider.RequestAsync(missing);
        }

        /// <summary>Blocks until the file is local. Only for background threads (e.g. cover loading).</summary>
        public static bool EnsureLocal(string path)
        {
            if (IsLocal(path))
            {
                return true;
            }

            if (!Exists(path))
            {
                return false;
            }

            try
            {
                RequestAsync(new[] { path }).Wait();
            }
            catch
            {
                // A failed download is reported by the provider; the caller handles the missing file.
            }

            return IsLocal(path);
        }

        public static float GetProgress(IEnumerable<string> paths)
        {
            return Provider.GetProgress(paths.Where(p => !string.IsNullOrEmpty(p)));
        }
    }
}