using TheLivingWorld.Api.Simulation;
using TheLivingWorld.Core.Contracts;
using TheLivingWorld.Core.Simulation;

namespace TheLivingWorld.Tests;

public sealed class WorldSimulationTests
{
    [Fact]
    public void Create_starts_at_default_morning_and_ticks_at_x1()
    {
        using var simulation = WorldSimulation.Create(ReadySummary(), catchUp: false);

        var before = simulation.SnapshotClock();
        Assert.Equal(GameTime.DefaultStart, before.GameTime);
        Assert.Equal(1, before.TimeScale);
        Assert.False(before.Paused);

        simulation.Tick(TimeSpan.FromSeconds(2));

        var after = simulation.SnapshotClock();
        Assert.Equal(GameTime.DefaultStart.AddMinutes(10), after.GameTime);
        Assert.True(simulation.IsDirty);
    }

    [Fact]
    public void Tick_does_not_advance_while_paused()
    {
        var summary = ReadySummary() with
        {
            Clock = WorldSimulation.DefaultClock() with { Paused = true },
        };
        using var simulation = WorldSimulation.Create(summary, catchUp: false);

        simulation.Tick(TimeSpan.FromSeconds(5));

        Assert.Equal(GameTime.DefaultStart, simulation.SnapshotClock().GameTime);
        Assert.False(simulation.IsDirty);
    }

    [Fact]
    public void Update_bakes_elapsed_time_before_changing_scale()
    {
        using var simulation = WorldSimulation.Create(ReadySummary(), catchUp: false);

        simulation.Tick(TimeSpan.FromSeconds(1));
        var clock = simulation.Update(new UpdateClockRequest { TimeScale = 2 });

        Assert.Equal(2, clock.TimeScale);
        // Tick advanced 5 game minutes; Update may bake a few extra wall-clock milliseconds.
        Assert.InRange(
            clock.GameTime,
            GameTime.DefaultStart.AddMinutes(5),
            GameTime.DefaultStart.AddMinutes(5).AddSeconds(30));
        Assert.True(simulation.IsDirty);
    }

    [Fact]
    public void Update_rejects_invalid_time_scale()
    {
        using var simulation = WorldSimulation.Create(ReadySummary(), catchUp: false);

        Assert.Throws<ArgumentOutOfRangeException>(() =>
            simulation.Update(new UpdateClockRequest { TimeScale = 5 }));
    }

    [Fact]
    public void Catch_up_advances_from_last_ticked_at()
    {
        var lastTickedAt = DateTimeOffset.UtcNow - TimeSpan.FromSeconds(3);
        var summary = ReadySummary() with { LastTickedAt = lastTickedAt };

        using var simulation = WorldSimulation.Create(summary, catchUp: true);

        // ~3 real seconds at x1 → ~15 game minutes (allow a little wall-clock drift).
        var actual = simulation.SnapshotClock().GameTime;
        Assert.InRange(
            actual,
            GameTime.DefaultStart.AddMinutes(14),
            GameTime.DefaultStart.AddMinutes(17));
    }

    [Fact]
    public void Catch_up_skips_a_world_that_was_paused_when_the_host_went_down()
    {
        var summary = ReadySummary() with
        {
            Clock = WorldSimulation.DefaultClock() with { Paused = true },
            LastTickedAt = DateTimeOffset.UtcNow - TimeSpan.FromHours(6),
        };

        using var simulation = WorldSimulation.Create(summary, catchUp: true);

        Assert.Equal(GameTime.DefaultStart, simulation.SnapshotClock().GameTime);

        // Unpausing must not replay the six hours spent paused offline either.
        var resumed = simulation.Update(new UpdateClockRequest { Paused = false });
        Assert.False(resumed.Paused);
        Assert.InRange(resumed.GameTime, GameTime.DefaultStart, GameTime.DefaultStart.AddMinutes(5));
    }

    [Fact]
    public void OverlayForApi_projects_the_stored_world_and_adds_live_weather()
    {
        using var simulation = WorldSimulation.Create(ReadySummary(), catchUp: false);
        var overlaid = simulation.OverlayForApi(ReadySummary());

        Assert.NotNull(overlaid.Clock);
        Assert.Equal(ClimateKind.CentralEuropean, overlaid.Climate);
        Assert.NotNull(overlaid.Weather);
        Assert.InRange(overlaid.Weather.Humidity, 0, 1);
        Assert.InRange(overlaid.Weather.CloudCover, 0, 1);
        Assert.InRange(overlaid.Weather.WindDirectionDeg, 0, 360);
    }

    [Fact]
    public void Climate_defaults_to_the_latitude_when_the_world_never_picked_one()
    {
        var summary = ReadySummary() with { Latitude = 78.22, Climate = null };
        using var simulation = WorldSimulation.Create(summary, catchUp: false);

        Assert.Equal(ClimateKind.Tundra, simulation.Climate);
    }

    [Fact]
    public void ApplyTo_persists_the_climate_and_the_drifting_pressure_systems()
    {
        using var simulation = WorldSimulation.Create(ReadySummary(), catchUp: false);
        simulation.Tick(TimeSpan.FromSeconds(30));

        var stored = simulation.ApplyTo(ReadySummary());

        Assert.Equal(ClimateKind.CentralEuropean, stored.Climate);
        Assert.NotNull(stored.WeatherState);
        Assert.NotEmpty(stored.WeatherState.Systems);
        Assert.NotEqual(0ul, stored.WeatherState.RngState);
    }

    /// <summary>
    /// The projection is one-way on purpose: the storage type carries the bookkeeping, the wire type has no
    /// field that could hold it, and derived weather never reaches the file.
    /// </summary>
    [Fact]
    public void The_stored_shape_and_the_wire_shape_carry_different_things()
    {
        var storedFields = typeof(StoredWorldDto).GetProperties().Select(static p => p.Name).ToHashSet();
        var wireFields = typeof(WorldSummaryDto).GetProperties().Select(static p => p.Name).ToHashSet();

        Assert.Contains("LastTickedAt", storedFields);
        Assert.Contains("WeatherState", storedFields);
        Assert.DoesNotContain("LastTickedAt", wireFields);
        Assert.DoesNotContain("WeatherState", wireFields);

        Assert.Contains("Weather", wireFields);
        Assert.DoesNotContain("Weather", storedFields);
    }

    [Fact]
    public void A_restart_resumes_the_sky_it_had_rather_than_rolling_a_new_one()
    {
        using var before = WorldSimulation.Create(ReadySummary(), catchUp: false);
        before.Tick(TimeSpan.FromSeconds(45));

        var persisted = before.ApplyTo(ReadySummary());
        var weatherBefore = before.SnapshotWeather();

        using var after = WorldSimulation.Create(persisted with { LastTickedAt = null }, catchUp: false);
        var weatherAfter = after.SnapshotWeather();

        Assert.Equal(weatherBefore.PressureHpa, weatherAfter.PressureHpa, 1);
        Assert.Equal(weatherBefore.Condition, weatherAfter.Condition);
    }

    [Fact]
    public void A_week_of_downtime_only_costs_the_world_the_capped_amount_of_game_time()
    {
        var summary = ReadySummary() with { LastTickedAt = DateTimeOffset.UtcNow - TimeSpan.FromDays(7) };
        var options = new SimulationOptions { MaxCatchUpGameHours = 24 };

        using var simulation = WorldSimulation.Create(summary, catchUp: true, options);

        // Uncapped this would be about six game years; the world wakes up one day older instead.
        var advanced = simulation.SnapshotClock().GameTime - GameTime.DefaultStart;
        Assert.InRange(advanced, TimeSpan.FromHours(24), TimeSpan.FromHours(24.2));
    }

    [Fact]
    public void A_zero_cap_means_the_world_replays_everything_it_missed()
    {
        var summary = ReadySummary() with { LastTickedAt = DateTimeOffset.UtcNow - TimeSpan.FromHours(1) };
        var options = new SimulationOptions { MaxCatchUpGameHours = 0 };

        using var simulation = WorldSimulation.Create(summary, catchUp: true, options);

        // One real hour at x1 is 12.5 game days, and nothing trims it.
        var advanced = simulation.SnapshotClock().GameTime - GameTime.DefaultStart;
        Assert.InRange(advanced, TimeSpan.FromDays(12), TimeSpan.FromDays(13));
    }

    [Fact]
    public void A_world_is_watched_when_it_attaches_and_goes_idle_once_nobody_asks()
    {
        using var simulation = WorldSimulation.Create(ReadySummary(), catchUp: false);
        var now = DateTimeOffset.UtcNow;

        Assert.False(simulation.IsIdle(now, TimeSpan.FromSeconds(20)));
        Assert.True(simulation.IsIdle(now + TimeSpan.FromMinutes(5), TimeSpan.FromSeconds(20)));

        simulation.Touch();
        Assert.False(simulation.IsIdle(DateTimeOffset.UtcNow, TimeSpan.FromSeconds(20)));

        // A zero threshold turns the whole idea off: everything stays watched.
        Assert.False(simulation.IsIdle(now + TimeSpan.FromDays(1), TimeSpan.Zero));
    }

    [Fact]
    public void Ticking_lazily_lands_on_the_same_game_time_as_ticking_often()
    {
        using var lazy = WorldSimulation.Create(ReadySummary(), catchUp: false);
        using var eager = WorldSimulation.Create(ReadySummary(), catchUp: false);

        lazy.Tick(TimeSpan.FromSeconds(5));
        for (var i = 0; i < 50; i++) eager.Tick(TimeSpan.FromMilliseconds(100));

        // The tick rate is a cost decision, not a correctness one: a step is driven by elapsed wall time.
        Assert.Equal(lazy.SnapshotClock().GameTime, eager.SnapshotClock().GameTime);
    }

    [Fact]
    public void A_long_absence_rolls_a_fresh_sky_instead_of_stepping_through_it()
    {
        // Six real hours is roughly two and a half game months - the systems that were drifting are long gone.
        var summary = ReadySummary() with { LastTickedAt = DateTimeOffset.UtcNow - TimeSpan.FromHours(6) };

        using var simulation = WorldSimulation.Create(summary, catchUp: true);
        var stored = simulation.ApplyTo(summary);

        Assert.NotNull(stored.WeatherState);
        Assert.Equal(ClimateCatalog.CentralEuropean.Storminess, stored.WeatherState.Systems.Count);

        // A reseeded pool is caught mid-life over the map, not parked at age zero off the edge.
        Assert.Contains(stored.WeatherState.Systems, static system => system.AgeHours > 0f);
    }

    /// <summary>
    /// The weather has to actually move. The pressure systems drift, so a world sampled hours apart must not
    /// keep reporting the same sky - that was the failure that hid behind a field which never varied.
    /// </summary>
    [Fact]
    public void The_weather_changes_as_the_systems_drift_over()
    {
        var summary = ReadySummary() with { Climate = ClimateKind.Oceanic, Latitude = 51.51 };
        using var simulation = WorldSimulation.Create(summary, catchUp: false);

        var readings = new List<double>();
        for (var step = 0; step < 8; step++)
        {
            // Two game hours a step, which is a few real seconds of play at x1.
            simulation.Tick(TimeSpan.FromSeconds(24));
            readings.Add(simulation.SnapshotWeather().PressureHpa);
        }

        Assert.True(
            readings.Max() - readings.Min() > 0.5,
            $"Pressure barely moved over sixteen game hours: {string.Join(", ", readings)}");
    }

    private static StoredWorldDto ReadySummary() => new()
    {
        Id = "town-aaaaaaaa",
        Name = "Town",
        Latitude = 31.9,
        Longitude = -100.5,
        SizeMeters = 10_000,
        Status = WorldStatus.Ready,
        CreatedAt = DateTimeOffset.UtcNow,
        Clock = WorldSimulation.DefaultClock(),
        Climate = ClimateKind.CentralEuropean,
        LastTickedAt = DateTimeOffset.UtcNow,
    };
}