using System;
using System.IO;
using System.Linq;
using Developpez.Dotnet.Collections;
using Developpez.Dotnet.IO;
using NUnit.Framework;

namespace Developpez.Dotnet.Tests.Collections
{
    [TestFixture]
    public class VirtualizingCollectionBaseTests
    {
        class TestCollection : VirtualizingCollectionBase<string>
        {
            private readonly string _dicoFileName;

            public TestCollection(string dicoFileName)
                : base(50)
            {
                _dicoFileName = dicoFileName;
            }

            #region Overrides of VirtualizingCollectionBase<string>

            protected override string[] FetchItems(int start, int count)
            {
                using (var reader = File.OpenText(_dicoFileName))
                {
                    var res = reader.AsLineEnumerable().Skip(start).Take(count).ToArray();
                    if (PageFetched != null)
                        PageFetched(start, count);
                    return res;
                }
            }

            protected override int FetchCount()
            {
                using (var reader = File.OpenText(_dicoFileName))
                {
                    int count = reader.AsLineEnumerable().Count();
                    if (CountFetched != null)
                        CountFetched();
                    return count;
                }
            }

            #endregion

            public event Action<int, int> PageFetched;
            public event Action CountFetched;
        }

        [Test]
        public void Test_CountIsFetchedOnlyOnce()
        {
            var collection = new TestCollection(@"Collections\dico.txt");
            bool countFetched = false;
            collection.CountFetched += () => countFetched = true;

            int count = collection.Count;
            Assert.IsTrue(countFetched);
            countFetched = false;
            count = collection.Count;
            Assert.IsFalse(countFetched);
        }

        [Test]
        public void Test_PageAreLoadedAndUnloadedAsNecessary()
        {
            var collection = new TestCollection(@"Collections\dico.txt");
            int fetchStart = -1;
            collection.PageFetched += (start, count) => fetchStart = start;

            // Should load first page
            string s = collection[0];
            Assert.AreEqual(0, fetchStart);

            // Still on the same page, shouldn't fetch
            fetchStart = -1;
            s = collection[49];
            Assert.AreEqual(-1, fetchStart);

            // Should load second page
            s = collection[50];
            Assert.AreEqual(50, fetchStart);

            // First page should still be there, no fetch necessary
            fetchStart = -1;
            s = collection[25];
            Assert.AreEqual(-1, fetchStart);

            // Should load third page
            s = collection[123];
            Assert.AreEqual(100, fetchStart);

            // Second page should still be there, no fetch necessary
            fetchStart = -1;
            s = collection[70];
            Assert.AreEqual(-1, fetchStart);

            // First page has been unloaded and should be fetched again
            s = collection[42];
            Assert.AreEqual(0, fetchStart);

            // Second page should still be there, no fetch necessary
            fetchStart = -1;
            s = collection[70];
            Assert.AreEqual(-1, fetchStart);

            // Third page has been unloaded and should be fetched again
            s = collection[140];
            Assert.AreEqual(100, fetchStart);
        }

        [Test]
        public void Test_InvalidateForcesReload()
        {
            var collection = new TestCollection(@"Collections\dico.txt");
            int fetchStart = -1;
            bool countFetched = false;
            collection.PageFetched += (start, count) => fetchStart = start;
            collection.CountFetched += () => countFetched = true;

            // Should load first page
            string s = collection[0];
            Assert.AreEqual(0, fetchStart);
            Assert.IsTrue(countFetched);

            // Data still there, shouldn't fetch
            fetchStart = -1;
            countFetched = false;
            s = collection[49];
            Assert.AreEqual(-1, fetchStart);
            Assert.IsFalse(countFetched);

            collection.Invalidate();

            // Data should be reloaded
            s = collection[0];
            Assert.AreEqual(0, fetchStart);
            Assert.IsTrue(countFetched);
        }
    }
}