using System;
using System.Collections.Generic;
using Paca.Mobile.Core;
using Xunit;

namespace Paca.Tests.Core;

public class StorageQuotaEvictionPlannerGateTests
{
    [Fact]
    public void Gate437_StorageQuotaEvictionPlanner_CalculatesRequiredSpace_Correctly()
    {
        // 5GB free, 8GB requested, 1GB headroom -> 4GB deficit
        long deficit = StorageQuotaEvictionPlanner.CalculateDeficit(
            freeSpaceBytes: 5L * 1024 * 1024 * 1024,
            requestedBytes: 8L * 1024 * 1024 * 1024,
            headroomBytes: 1L * 1024 * 1024 * 1024
        );
        Assert.Equal(4L * 1024 * 1024 * 1024, deficit);

        // 10GB free, 8GB requested, 1GB headroom -> 0 deficit
        long noDeficit = StorageQuotaEvictionPlanner.CalculateDeficit(
            freeSpaceBytes: 10L * 1024 * 1024 * 1024,
            requestedBytes: 8L * 1024 * 1024 * 1024,
            headroomBytes: 1L * 1024 * 1024 * 1024
        );
        Assert.Equal(0, noDeficit);
    }

    [Fact]
    public void Gate438_StorageQuotaEvictionPlanner_EvictsByLru_WhilePreservingPinned()
    {
        var now = DateTime.UtcNow;
        var candidates = new List<EvictionCandidate>
        {
            new("file1.mp4", 1000, now.AddDays(-10), IsPinned: true), // pinned!
            new("file2.mp4", 1000, now.AddDays(-5), IsPinned: false),
            new("file3.mp4", 1000, now.AddDays(-20), IsPinned: false), // oldest unpinned!
            new("file4.mp4", 1000, now.AddDays(-1), IsPinned: false)
        };

        var plan = StorageQuotaEvictionPlanner.PlanEviction(candidates, deficitBytes: 1500, EvictionStrategy.LRU);

        Assert.True(plan.IsSatisfiable);
        Assert.Equal(2, plan.FilesToEvict.Count);
        Assert.Equal("file3.mp4", plan.FilesToEvict[0].FilePath); // oldest
        Assert.Equal("file2.mp4", plan.FilesToEvict[1].FilePath); // second oldest
        Assert.DoesNotContain(plan.FilesToEvict, f => f.FilePath == "file1.mp4"); // preserved!
    }

    [Fact]
    public void Gate439_StorageQuotaEvictionPlanner_EvictsByLargestFirst()
    {
        var now = DateTime.UtcNow;
        var candidates = new List<EvictionCandidate>
        {
            new("small.mp4", 500, now, false),
            new("huge.mp4", 3000, now, false),
            new("medium.mp4", 1000, now, false)
        };

        var plan = StorageQuotaEvictionPlanner.PlanEviction(candidates, deficitBytes: 2500, EvictionStrategy.LargestFirst);

        Assert.True(plan.IsSatisfiable);
        Assert.Single(plan.FilesToEvict);
        Assert.Equal("huge.mp4", plan.FilesToEvict[0].FilePath);
        Assert.Equal(3000, plan.TotalFreedBytes);
    }

    [Fact]
    public void Gate440_StorageQuotaEvictionPlanner_DeterminesFeasibility()
    {
        var now = DateTime.UtcNow;
        var candidates = new List<EvictionCandidate>
        {
            new("file1.mp4", 1000, now, false)
        };

        var plan = StorageQuotaEvictionPlanner.PlanEviction(candidates, deficitBytes: 5000, EvictionStrategy.LRU);

        Assert.False(plan.IsSatisfiable);
        Assert.Equal(1000, plan.TotalFreedBytes);
    }
}