using FluentAssertions;
using Xunit;

namespace BucketChain.Test;

public sealed class BucketTests
{
    private const double BucketSize = 1.2D;
    
    [Fact]
    public void Construction()
    {
        var bucket = new Bucket(BucketSize);

        bucket.IsEmpty.Should().BeTrue();
    }

    [Fact]
    public void Fill_Simple()
    {
        var bucket = new Bucket(BucketSize);

        bucket.Fill(BucketSize)
            .Should().Be(BucketSize, "full amount used");
        bucket.IsEmpty.Should().BeFalse();
    }
    
    [Fact]
    public void Fill_NotEnough()
    {
        const double Available = BucketSize / 2;
        
        var bucket = new Bucket(BucketSize);

        bucket.Fill(Available)
            .Should().Be(Available, "everything available used");
        bucket.IsEmpty.Should().BeFalse("not completely full, but not empty either");
    }
    
    [Fact]
    public void Fill_MoreThanNeeded()
    {
        const double Available = BucketSize * 3;
        
        var bucket = new Bucket(BucketSize);

        bucket.Fill(Available)
            .Should().Be(BucketSize, "can't take more than fits into bucket");
        bucket.IsEmpty.Should().BeFalse();
    }
    
    [Fact]
    public void Fill_InvalidAmount()
    {
        const double Available = -3;
        
        var bucket = new Bucket(BucketSize);

        bucket.Fill(Available)
            .Should().Be(0, "cannot take anything");
        bucket.IsEmpty.Should().BeTrue("bucket is still empty");
    }

    [Fact]
    public void Empty_Simple()
    {
        var bucket = new Bucket(BucketSize);
        bucket.Fill(BucketSize * 2);

        bucket.Empty()
            .Should().Be(BucketSize, "bucket was full and gets emptied completely");
        bucket.IsEmpty.Should().BeTrue("has been emptied");
    }
    
    [Fact]
    public void Empty_PartiallyFull()
    {
        var bucket = new Bucket(BucketSize);
        bucket.Fill(BucketSize / 2);

        bucket.Empty()
            .Should().BeApproximately(BucketSize / 2, 
                double.Epsilon, "bucket was only partially full and gets emptied completely");
        bucket.IsEmpty.Should().BeTrue("has been emptied");
    }
    
    [Fact]
    public void Empty_Empty()
    {
        var bucket = new Bucket(BucketSize);

        bucket.Empty()
            .Should().Be(0, "bucket was empty");
        bucket.IsEmpty.Should().BeTrue("bucket is still empty");
    }
}