using System;
using System.Collections.Generic;
using AcDream.App.Streaming;
using AcDream.Core.Terrain;
using AcDream.Core.World;
using DatReaderWriter.DBObjs;
using Xunit;

namespace AcDream.Core.Tests.Streaming;

public class StreamingControllerPriorityApplyTests
{
    private static LandblockStreamResult.Loaded LoadedOf(uint canonicalId)
        => new(canonicalId, LandblockStreamTier.Near,
               new LoadedLandblock(canonicalId, new LandBlock(), Array.Empty<WorldEntity>()),
               new LandblockMeshData(Array.Empty<TerrainVertex>(), Array.Empty<uint>()));

    [Fact]
    public void PriorityLandblock_isApplied_evenWhenBeyondPerFrameCap()
    {
        uint priority = StreamingRegion.EncodeLandblockIdForTest(169, 180);
        var outbox = new Queue<LandblockStreamResult>(new LandblockStreamResult[]
        {
            LoadedOf(StreamingRegion.EncodeLandblockIdForTest(0, 0)),
            LoadedOf(StreamingRegion.EncodeLandblockIdForTest(0, 1)),
            LoadedOf(StreamingRegion.EncodeLandblockIdForTest(0, 2)),
            LoadedOf(StreamingRegion.EncodeLandblockIdForTest(0, 3)),
            LoadedOf(priority),
        });

        var applied = new List<uint>();
        var state = new GpuWorldState();
        var ctrl = new StreamingController(
            enqueueLoad: (_, _) => { },
            enqueueUnload: _ => { },
            drainCompletions: max =>
            {
                var batch = new List<LandblockStreamResult>();
                while (batch.Count < max && outbox.Count > 0) batch.Add(outbox.Dequeue());
                return batch;
            },
            applyTerrain: (lb, _) => applied.Add(lb.LandblockId),
            state: state, nearRadius: 4, farRadius: 12)
        { MaxCompletionsPerFrame = 4 };

        ctrl.PriorityLandblockId = priority;
        ctrl.Tick(169, 180);

        Assert.Contains(priority, applied);   // priority applied THIS tick
        Assert.True(applied.Count <= 5);       // did not blindly flush the whole outbox
    }

    [Fact]
    public void Deferred_nonPriority_completions_applyOnLaterFrames_withoutLoss()
    {
        // After the priority is found, the non-priority items drained past it must
        // still be applied (over subsequent ticks), never dropped.
        uint priority = StreamingRegion.EncodeLandblockIdForTest(169, 180);
        var outbox = new Queue<LandblockStreamResult>(new LandblockStreamResult[]
        {
            LoadedOf(StreamingRegion.EncodeLandblockIdForTest(0, 0)),
            LoadedOf(StreamingRegion.EncodeLandblockIdForTest(0, 1)),
            LoadedOf(StreamingRegion.EncodeLandblockIdForTest(0, 2)),
            LoadedOf(StreamingRegion.EncodeLandblockIdForTest(0, 3)),
            LoadedOf(StreamingRegion.EncodeLandblockIdForTest(0, 4)),
            LoadedOf(priority),
        });
        var applied = new List<uint>();
        var state = new GpuWorldState();
        var ctrl = new StreamingController(
            enqueueLoad:       (_, _) => { },
            enqueueUnload:     _ => { },
            drainCompletions:  max =>
            {
                var batch = new List<LandblockStreamResult>();
                while (batch.Count < max && outbox.Count > 0) batch.Add(outbox.Dequeue());
                return batch;
            },
            applyTerrain:      (lb, _) => applied.Add(lb.LandblockId),
            state:             state,
            nearRadius:        4,
            farRadius:         12)
        { MaxCompletionsPerFrame = 4 };
        ctrl.PriorityLandblockId = priority;

        ctrl.Tick(169, 180);  // priority + some others
        ctrl.PriorityLandblockId = 0u;
        ctrl.Tick(169, 180);  // drains the deferred remainder
        ctrl.Tick(169, 180);

        Assert.Contains(priority, applied);
        Assert.Equal(6, applied.Count);  // all six applied, none lost
    }

    [Fact]
    public void PriorityNeverArrives_noThrow_noLoss_noDoubleApply()
    {
        // While a PriorityLandblockId is set but the matching completion never
        // arrives (e.g. the load failed), the hunt moves outbox completions into
        // _deferredApply and they drain at the per-frame budget — same backpressure
        // as the normal throttle, just relocated — until the caller clears
        // PriorityLandblockId (the TAS MaxContinue safety net does this on timeout).
        uint priority  = StreamingRegion.EncodeLandblockIdForTest(169, 180);
        uint otherId0  = StreamingRegion.EncodeLandblockIdForTest(1, 0);
        uint otherId1  = StreamingRegion.EncodeLandblockIdForTest(1, 1);
        uint otherId2  = StreamingRegion.EncodeLandblockIdForTest(1, 2);

        var outbox = new Queue<LandblockStreamResult>(new LandblockStreamResult[]
        {
            LoadedOf(otherId0),
            LoadedOf(otherId1),
            LoadedOf(otherId2),
        });

        var applied = new List<uint>();
        var state = new GpuWorldState();
        var ctrl = new StreamingController(
            enqueueLoad:      (_, _) => { },
            enqueueUnload:    _ => { },
            drainCompletions: max =>
            {
                var batch = new List<LandblockStreamResult>();
                while (batch.Count < max && outbox.Count > 0) batch.Add(outbox.Dequeue());
                return batch;
            },
            applyTerrain:     (lb, _) => applied.Add(lb.LandblockId),
            state:            state,
            nearRadius:       4,
            farRadius:        12)
        { MaxCompletionsPerFrame = 4 };

        // Set a priority id that will NEVER appear in the outbox.
        ctrl.PriorityLandblockId = priority;

        // Tick several times — should not throw and every non-priority completion
        // must still be applied without duplication.
        ctrl.Tick(169, 180);
        ctrl.Tick(169, 180);
        ctrl.Tick(169, 180);

        // (a) no throw — covered by reaching here without exception
        // (b) every non-priority completion is applied (no loss)
        Assert.Contains(otherId0, applied);
        Assert.Contains(otherId1, applied);
        Assert.Contains(otherId2, applied);
        // (c) no double-apply: applied count matches completions enqueued
        Assert.Equal(3, applied.Count);
    }
}