using System;
using System.IO;
using System.Linq;
using System.Threading.Tasks;
using MongoDB.Bson;
using MongoDB.Driver;
using MongoDB.Driver.GridFS;
using NUnit.Framework;

namespace GridFSTests
{
    [TestFixture]
    public class GridTest
    {
        [Test]
        public void CanDoIOInParallel()
        {
            const int fileCount = 1000;

            var server = MongoServer.Create();
            var db = server.GetDatabase("test");
            var grid = db.GridFS;

            // Clean existing files
            foreach (var n in Enumerable.Range(0, fileCount))
            {
                var filename = String.Format("/tmp/parallel/file{0}", n);
                grid.Delete(filename);
            }
            
            // Create 10,000 files in parallel and see if we break
            var writeResult =
            Parallel.ForEach(Enumerable.Range(0, fileCount), new ParallelOptions() { MaxDegreeOfParallelism = 20 }, (n) =>
            {
                MongoGridFSFileInfo fileInfo;
                // In my system I cannot guarantee that Touch and Write happen in the same thread. But it
                // should be easy to guarantee that a write cannot happen during a touch.
                using (var request = db.RequestStart())
                {
                    var filename = String.Format("/tmp/parallel/file{0}", n);
                    fileInfo = TouchFile(grid, filename);
                    Assert.IsFalse(server.GetLastError().HasLastErrorMessage);
                // Comment next three lines to do touch and write in same requeststart.
                }
                using (var request = db.RequestStart())
                {
                    using (var stream = fileInfo.OpenWrite())
                    {
                        stream.Write((from b in Enumerable.Range(0, 50) select (byte) b).ToArray(), 0, 50);
                    }
                    Assert.IsFalse(server.GetLastError().HasLastErrorMessage);
                }
            });
            Assert.IsTrue(writeResult.IsCompleted);

            // Ensure the files have the correct data.
            var readResult =
            Parallel.ForEach(Enumerable.Range(0, fileCount), new ParallelOptions() { MaxDegreeOfParallelism = 1 }, (n) =>
            {
                var filename = String.Format("/tmp/parallel/file{0}", n);
                var fileInfo = TouchFile(grid, filename);
                using (var stream = fileInfo.OpenRead())
                {
                    var buffer = new byte[50];
                    stream.Read(buffer, 0, 50);
                    for (var b = 0; b < 50; ++b)
                        Assert.AreEqual((byte)b, buffer[b]);
                }
            });
            Assert.IsTrue(readResult.IsCompleted);
        }

        private static MongoGridFSFileInfo TouchFile(MongoGridFS grid, string path)
        {
            var dir = Path.GetDirectoryName(path);
            // Uploads an empty file into the system marked as 
            // a 'directory'
            var info = grid.Upload(
                new System.IO.MemoryStream(new byte[0]), path,
                new MongoGridFSCreateOptions()
                {
                    Metadata = new BsonDocument()
                        {{ "dirpath", BsonValue.Create(dir) }}
                });
            return info;
        }
    }
}