using System.Collections.Generic;
using System.Text.Json;
using System.Threading.Tasks;
using Godot;
using Age.Engine.Hosting;
using Age.Engine.Model;
using Age.Engine.Sys4;
using Age.Engine.Vm;
using Script = Age.Engine.Model.Script;   // disambiguate from Godot.Script

public partial class Main : Godot.Control
{
    private TextureRect _screenView = null!;              // shows the composited screen backbuffer
    private Image _screen = null!;                        // 800x600 immediate-mode canvas
    private ImageTexture _screenTex = null!;
    private Label _text = null!;
    private Label _status = null!;
    private AudioStreamPlayer _bgm = null!;                // looping background music
    private AudioStreamPlayer _voice = null!;              // interrupt-on-new voice
    private VirtualMachine _vm = null!;
    private GodotAdvHost _host = null!;
    private readonly Age.Engine.Hosting.FrameClock _clock = new();
    private GodotTraceSink _trace = null!;
    private Age.Engine.Diagnostics.HistogramTraceSink? _hist;   // --trace-histogram: profile the real run
    private string? _histFile;
    private Age.Engine.Model.OpcodeTable? _table;
    private bool _histDumped;
    private volatile bool _done;
    private bool _ended;
    private bool _selftest;
    private string? _shotPath;                 // --shot <png>: capture a page then quit (dev tool)
    private int _shotPage = 1;                  // --shot-page <n>: which page to capture (default 1)
    private volatile int _pageCount;
    private int _shotSettle;
    private int _shotSettleTarget = 3;          // --shot-settle <frames>: settle N frames before grabbing (to
                                                // capture mid-tween — the anim clock keeps running while parked)
    private bool _shotDone;
    private string? _seqDir;                    // --shot-sequence <dir>: dump one PNG per frame (verify paced anim)
    private int _seqFrames = 180;               // --frames <n>: how many frames to dump (default ~3s @60fps)
    private int _seqIdx;

    public override void _Ready()
    {
        // Screen backbuffer: one 800x600 canvas that draw-texture blits into, shown behind the dialogue.
        _screen = Image.CreateEmpty(800, 600, false, Image.Format.Rgba8);
        _screenTex = ImageTexture.CreateFromImage(_screen);
        _screenView = new TextureRect
        {
            Texture = _screenTex,
            ExpandMode = TextureRect.ExpandModeEnum.IgnoreSize,
            StretchMode = TextureRect.StretchModeEnum.Scale,
            MouseFilter = MouseFilterEnum.Ignore,
        };
        _screenView.SetAnchorsAndOffsetsPreset(LayoutPreset.FullRect);
        AddChild(_screenView);   // added first -> draws behind the text/status labels

        _text = new Label { AutowrapMode = TextServer.AutowrapMode.WordSmart };
        _text.SetAnchorsAndOffsetsPreset(LayoutPreset.FullRect);
        _text.OffsetLeft = 40; _text.OffsetTop = 40; _text.OffsetRight = -40; _text.OffsetBottom = -80;
        AddChild(_text);
        _status = new Label();
        _status.SetAnchorsAndOffsetsPreset(LayoutPreset.BottomWide);
        _status.OffsetLeft = 40; _status.OffsetTop = -60;
        AddChild(_status);

        // Best-effort CJK font so the visual isn't tofu (headless self-test doesn't depend on it).
        foreach (var fp in new[] { "C:/Windows/Fonts/YuGothM.ttc", "C:/Windows/Fonts/YuGothR.ttc",
                                   "C:/Windows/Fonts/msgothic.ttc", "C:/Windows/Fonts/meiryo.ttc" })
        {
            if (!System.IO.File.Exists(fp)) continue;
            try
            {
                var ff = new FontFile { Data = System.IO.File.ReadAllBytes(fp) };
                _text.AddThemeFontOverride("font", ff);
                _status.AddThemeFontOverride("font", ff);
                _text.AddThemeFontSizeOverride("font_size", 22);
                break;
            }
            catch { /* fall back to the default font */ }
        }

        _bgm = new AudioStreamPlayer();
        _voice = new AudioStreamPlayer();
        AddChild(_bgm);
        AddChild(_voice);

        var userArgs = OS.GetCmdlineUserArgs();
        _selftest = System.Array.IndexOf(userArgs, "--selftest") >= 0;
        bool boot = System.Array.IndexOf(userArgs, "--boot") >= 0;   // run SYSTEM4's state prefix first
        string scene = "SC0000";                        // --scene <NAME>: which scene to play (default SC0000)
        var seeds = new List<(int Addr, long Val)>();   // --seed 0xADDR=VAL (repeatable) — initial global state
        double sleepScale = 1.0;                         // --sleep-scale <f>: slow/speed the paced opening for inspection
        string? histFile = null;                         // --trace-histogram <file>: op/call-site execution counts of the REAL run
        for (int i = 0; i < userArgs.Length; i++)
        {
            if (userArgs[i] == "--scene" && i + 1 < userArgs.Length) scene = userArgs[i + 1];
            if (userArgs[i] == "--shot" && i + 1 < userArgs.Length) _shotPath = userArgs[i + 1];
            if (userArgs[i] == "--shot-page" && i + 1 < userArgs.Length) int.TryParse(userArgs[i + 1], out _shotPage);
            if (userArgs[i] == "--shot-settle" && i + 1 < userArgs.Length) int.TryParse(userArgs[i + 1], out _shotSettleTarget);
            if (userArgs[i] == "--shot-sequence" && i + 1 < userArgs.Length) _seqDir = userArgs[i + 1];
            if (userArgs[i] == "--frames" && i + 1 < userArgs.Length) int.TryParse(userArgs[i + 1], out _seqFrames);
            if (userArgs[i] == "--sleep-scale" && i + 1 < userArgs.Length) double.TryParse(userArgs[i + 1], out sleepScale);
            if (userArgs[i] == "--trace-histogram" && i + 1 < userArgs.Length) histFile = userArgs[i + 1];
            if (userArgs[i] == "--seed" && i + 1 < userArgs.Length)
            {
                var kv = userArgs[i + 1].Split('=');
                if (kv.Length == 2)
                {
                    int k = kv[0].StartsWith("0x") ? System.Convert.ToInt32(kv[0], 16) : int.Parse(kv[0]);
                    long v = kv[1].StartsWith("0x") ? System.Convert.ToInt64(kv[1], 16) : long.Parse(kv[1]);
                    seeds.Add((k, v));
                }
            }
        }

        var table = OpcodeTableJson.Load(Paths.OpcodesJson);
        // Full op handling everywhere: the provider lets call-script load & run subroutines. Selftest
        // runs a SYNTHESIZED scene (not a real scene in a crippled mode) so its output is deterministic.
        Script script;
        IScriptProvider provider;
        if (_selftest) (script, provider) = BuildSelfTestScene(table);
        else { script = Sys4Loader.Load(Paths.Scripts()[scene.ToUpperInvariant() + ".BIN"], table); provider = Sys4ScriptProvider.Load(table); }
        _host = new GodotAdvHost(this, ResourceMap.Load(), scene, _clock) { SleepScale = sleepScale };
        _trace = new GodotTraceSink();
        // --trace-histogram: aggregate op/call-site execution counts of the REAL Godot run (headless flow
        // diverges — wait-for-input is a no-op there — so this is the only way to profile the live path).
        _table = table;
        _histFile = histFile;
        Age.Engine.Diagnostics.ITraceSink sink = _trace;
        if (histFile != null) { _hist = new Age.Engine.Diagnostics.HistogramTraceSink();
                                 sink = new Age.Engine.Diagnostics.CompositeTraceSink(_trace, _hist); }
        _vm = new VirtualMachine(script, table, _host, new VmOptions(MaxSteps: 20_000_000), provider, sink);
        // --boot: run SYSTEM4's state prefix (INITCONFIG/INIT2/INIT) so the scene sees boot state — chiefly
        // INIT2's gfx handle array 0x62455.. (skips the UI scripts LOGO/OP/TITLE). State carries via globals.
        if (boot && !_selftest)
        {
            var session = new GameSession();
            foreach (var b in new[] { "INITCONFIG.BIN", "INIT2.BIN", "INIT.BIN" })
                session.RunScene(Sys4Loader.Load(Paths.Scripts()[b], table), table, new CaptureHost(), null, provider);
            foreach (var kv in session.Globals) _vm.Globals[kv.Key] = kv.Value;
            foreach (var kv in session.GlobalStrings) _vm.GlobalStrings[kv.Key] = kv.Value;
            GD.Print($"[boot] system boot done: {session.Globals.Count} globals seeded");
        }
        foreach (var (addr, val) in seeds) _vm.Globals[addr] = val;   // --seed overrides boot state
        _ = Task.Run(() => { _vm.Run(); _done = true; });

        if (_selftest)
            _ = Task.Run(async () => { while (!_done) { if (_host.IsWaiting) _host.SignalInput(); await Task.Delay(1); } });
        // --shot: auto-advance up to (but not past) the target page, then _Process captures + quits.
        if (_shotPath != null)
            _ = Task.Run(async () => { while (!_done) { if (_host.IsWaiting && _host.Pages < _shotPage) _host.SignalInput(); await Task.Delay(1); } });
        // --shot-sequence: auto-advance past every input wait so the paced burst isn't blocked on a click.
        if (_seqDir != null)
            _ = Task.Run(async () => { while (!_done) { if (_host.IsWaiting) _host.SignalInput(); await Task.Delay(1); } });
    }

    public override void _Process(double delta)
    {
        _lastDelta = delta;
        _clock.Advance(delta);
        _host?.PulseFrame();
        if (!_selftest && _vm != null) Recomposite();   // retained per-frame compositor (surface+object model)
        // --shot-sequence: dump one PNG per frame across the opening so a time-based (paced) effect can be
        // verified as distinct frames, not just the final state. Captures after Recomposite; quits when full.
        if (_seqDir != null && _seqIdx < _seqFrames && !_done)
        {
            System.IO.Directory.CreateDirectory(_seqDir);
            // Headless has no rendered viewport texture (GetImage() is null). Still advance/count/quit so the
            // real-run trace-histogram can profile the live path without a display; only the PNG grab is skipped.
            var fimg = GetViewport().GetTexture()?.GetImage();
            fimg?.SavePng($"{_seqDir}/frame_{_seqIdx:0000}.png");
            _seqIdx++;
            if (_seqIdx >= _seqFrames) { GD.Print($"SEQ saved {_seqIdx} frames -> {_seqDir}"); GetTree().Quit(0); }
            return;
        }
        // --shot: once the target page is composed and parked at wait-for-input, settle a few frames then grab it.
        if (_shotPath != null && !_shotDone && (_host.Pages >= _shotPage && _host.IsWaiting || _done))
        {
            if (++_shotSettle >= _shotSettleTarget)
            {
                _shotDone = true;
                var img = GetViewport().GetTexture().GetImage();
                img.SavePng(_shotPath);
                GD.Print($"SHOT saved page {_pageCount} -> {_shotPath}");
                ReportSubroutines();
                GetTree().Quit(0);
            }
            return;
        }
        if (_done && !_ended)
        {
            _ended = true;
            DumpHistogram();
            ReportSubroutines();
            ShowEnd();
            if (_selftest) RunSelfTest();
        }
    }

    // _Input (not _UnhandledInput): the root Control consumes mouse clicks as GUI input before they
    // reach _UnhandledInput, so clicks were swallowed while keyboard ui_accept still got through.
    public override void _Input(InputEvent e)
    {
        if (_selftest) return;
        if (e.IsActionPressed("ui_accept") ||
            (e is InputEventMouseButton mb && mb.Pressed && mb.ButtonIndex == MouseButton.Left))
            _host.SignalInput();
    }

    public override void _ExitTree() { DumpHistogram(); _host?.SignalInput(); }

    // Write the real-run op/call-site histogram to --trace-histogram <file>. Idempotent; called when the
    // scene ends or the window closes (the opening parks at wait-for-input, so closing is the usual trigger).
    private void DumpHistogram()
    {
        if (_histDumped || _hist == null || _histFile == null) return;
        _histDumped = true;
        try
        {
            var dir = System.IO.Path.GetDirectoryName(_histFile);
            if (!string.IsNullOrEmpty(dir)) System.IO.Directory.CreateDirectory(dir);
            using var w = new System.IO.StreamWriter(_histFile);
            _hist.WriteReport(w, _table);
            GD.Print($"[trace-histogram] wrote {_hist.TotalSteps} steps -> {_histFile}");
        }
        catch (System.Exception e) { GD.Print($"[trace-histogram] write failed: {e.Message}"); }
    }

    // ---- retained per-frame compositor (main thread, from _Process) ----
    // Clear the screen and composite the VM's current VISIBLE gfx objects in ascending-handle order (= the
    // engine's z-order), each blitting its live surface's rect at its position. Surfaces are cached by BMP
    // path (this runs every frame). Animated objects tween over the global anim-clock (0x238); their opacity
    // is applied by the alpha-aware BlitLayer. See docs/engine-re.md "sprite transform / ANIMATION cluster".
    private readonly System.Collections.Generic.Dictionary<(string Path, long Key), Image?> _imgCache = new();

    // Per-handle wall-clock tween of the animation channel. The engine's clock (op 0x238) is a GLOBAL,
    // non-blocking clock; the host advances it here while the VM is parked at wait-for-input. Opacity comes
    // from the 3rd anim vec component (TZ), data-driven from the opening (100=full, 0=clear).
    private sealed class TweenState
    {
        public long Generation = long.MinValue;
        public bool Initialized;
        public double Elapsed, Duration;
        public double StartA, TargetA, CurrentA = 1.0;
    }
    private readonly System.Collections.Generic.Dictionary<long, TweenState> _tweens = new();
    private long _lastClockGen = long.MinValue;
    private double _lastDelta;
    private const double GameTickSeconds = 1.0 / 60.0;   // anim-clock ticks -> seconds (game runs ~60fps)

    private void Recomposite()
    {
        _screen.Fill(new Color(0, 0, 0, 0));
        long clockGen = _vm.Gfx.AnimClockGeneration;
        double clockDur = System.Math.Max(1, _vm.Gfx.AnimClockDurationTicks) * GameTickSeconds;
        bool clockReset = clockGen != _lastClockGen;
        _lastClockGen = clockGen;
        foreach (var v in _vm.Gfx.SnapshotVisibleObjects())   // already ascending-handle = z-order
        {
            float a = AlphaFor(v, clockReset, clockDur) * (v.Alpha / 255f);
            if (v.SurfaceResId == 0)
            {
                // A colored object with no bound surface = a fade/flash fill (e.g. fade-to-black). Fill its
                // rect (full-screen when it has no size, the opening's case) with the tint at alpha. Uncolored
                // surfaceless objects are render targets — still skipped (slice C).
                if (v.Blend != Age.Engine.Model.BlendKind.Opaque)
                {
                    int fw = v.W > 0 ? v.W : 800, fh = v.H > 0 ? v.H : 600;
                    FillQuad(v.DstX, v.DstY, fw, fh, v.Tint, a);
                }
                continue;
            }
            var bmp = _host.ResolveResIdTexture(v.SurfaceResId);
            if (bmp == null) continue;
            BlitLayer(bmp, v.ColorKey, v.Tint, v.SrcX, v.SrcY, v.W, v.H, v.DstX, v.DstY, a);
        }
        _screenTex.Update(_screen);
    }

    // Current opacity for a visible object: 1.0 unless it has an active anim channel, in which case tween the
    // 3rd vec component (TZ, ~percent) over the global clock. Start opaque on first sight so a CG never
    // begins invisible (the safe direction); re-arm whenever the object's or the clock's generation bumps.
    private float AlphaFor(Age.Engine.Model.RenderObject v, bool clockReset, double clockDur)
    {
        if (!v.Anim.Enabled) return 1f;
        var tw = _tweens.TryGetValue(v.Handle, out var t) ? t : (_tweens[v.Handle] = new TweenState());
        double targetA = System.Math.Clamp(v.Anim.TZ / 100.0, 0, 1);
        if (clockReset || tw.Generation != v.Anim.Generation)
        {
            tw.Generation = v.Anim.Generation;
            tw.Elapsed = 0; tw.Duration = clockDur;
            tw.StartA = tw.Initialized ? tw.CurrentA : 1.0;   // hold previous on-screen alpha; first sight opaque
            tw.TargetA = targetA;
            tw.Initialized = true;
        }
        tw.Elapsed += _lastDelta * _clock.Speed;   // Speed==1 now => identical; future Ctrl scales the tween
        double p = tw.Duration > 0 ? System.Math.Clamp(tw.Elapsed / tw.Duration, 0, 1) : 1;
        tw.CurrentA = tw.StartA + (tw.TargetA - tw.StartA) * p;
        return (float)tw.CurrentA;
    }

    // Blit one object's surface rect. The source Image is cached per (path, colorKey): on first load, texels
    // matching the surface colorkey are made transparent (native bakes the key at load — engine-re.md §Blend).
    // tint (0xRRGGBB) modulates the texel RGB (fade-to-black uses tint=black); alpha is the object's opacity.
    private void BlitLayer(string bmpPath, long colorKey, long tint, int srcX, int srcY, int w, int h,
                           int dstX, int dstY, float alpha = 1f)
    {
        var cacheKey = (bmpPath, colorKey);
        if (!_imgCache.TryGetValue(cacheKey, out var src))
        {
            src = new Image();
            if (src.LoadBmpFromBuffer(System.IO.File.ReadAllBytes(bmpPath)) != Error.Ok)
            { GD.Print($"BMP load failed {bmpPath}"); src = null; }
            else
            {
                if (src.GetFormat() != Image.Format.Rgba8) src.Convert(Image.Format.Rgba8);
                if (Age.Engine.Model.BlendMath.HasColorKey(colorKey)) BakeColorKey(src, colorKey);
            }
            _imgCache[cacheKey] = src;
        }
        if (src == null) return;

        int sw = w > 0 ? w : src.GetWidth();
        int sh = h > 0 ? h : src.GetHeight();
        sw = System.Math.Min(sw, src.GetWidth() - srcX);
        sh = System.Math.Min(sh, src.GetHeight() - srcY);
        if (sw <= 0 || sh <= 0) return;

        bool plainOpaque = alpha >= 0.999f && tint == 0xFFFFFF && !Age.Engine.Model.BlendMath.HasColorKey(colorKey);
        if (plainOpaque)   // fast path: unchanged behaviour for opaque, un-keyed, un-tinted layers
        {
            _screen.BlitRect(src, new Rect2I(srcX, srcY, sw, sh), new Vector2I(dstX, dstY));
            return;
        }

        int tr = (int)((tint >> 16) & 0xff), tg = (int)((tint >> 8) & 0xff), tb = (int)(tint & 0xff);
        byte[] dst = _screen.GetData(); byte[] ss = src.GetData();
        int dw = _screen.GetWidth(), dh = _screen.GetHeight(), sfw = src.GetWidth();
        int ia = (int)(System.Math.Clamp(alpha, 0f, 1f) * 255);
        for (int y = 0; y < sh; y++)
            for (int x = 0; x < sw; x++)
            {
                int dxp = dstX + x, dyp = dstY + y;
                if (dxp < 0 || dyp < 0 || dxp >= dw || dyp >= dh) continue;
                int di = (dyp * dw + dxp) * 4;
                int si = ((srcY + y) * sfw + (srcX + x)) * 4;
                int sa = ss[si + 3] * ia / 255;                 // texel alpha (colorkey already 0) × object alpha
                if (sa == 0) continue;
                int sr = ss[si] * tr / 255, sg = ss[si + 1] * tg / 255, sb = ss[si + 2] * tb / 255;   // tint modulate
                dst[di]     = (byte)((sr * sa + dst[di]     * (255 - sa)) / 255);
                dst[di + 1] = (byte)((sg * sa + dst[di + 1] * (255 - sa)) / 255);
                dst[di + 2] = (byte)((sb * sa + dst[di + 2] * (255 - sa)) / 255);
                dst[di + 3] = (byte)System.Math.Min(255, dst[di + 3] + sa);
            }
        _screen.SetData(dw, dh, false, _screen.GetFormat(), dst);
    }

    // Alpha-blend a solid tint (0xRRGGBB) rectangle over the screen — the surfaceless fade/flash fill.
    private void FillQuad(int dstX, int dstY, int w, int h, long tint, float alpha)
    {
        int ia = (int)(System.Math.Clamp(alpha, 0f, 1f) * 255);
        if (ia == 0) return;
        int tr = (int)((tint >> 16) & 0xff), tg = (int)((tint >> 8) & 0xff), tb = (int)(tint & 0xff);
        byte[] dst = _screen.GetData();
        int dw = _screen.GetWidth(), dh = _screen.GetHeight();
        for (int y = 0; y < h; y++)
            for (int x = 0; x < w; x++)
            {
                int dxp = dstX + x, dyp = dstY + y;
                if (dxp < 0 || dyp < 0 || dxp >= dw || dyp >= dh) continue;
                int di = (dyp * dw + dxp) * 4;
                dst[di]     = (byte)((tr * ia + dst[di]     * (255 - ia)) / 255);
                dst[di + 1] = (byte)((tg * ia + dst[di + 1] * (255 - ia)) / 255);
                dst[di + 2] = (byte)((tb * ia + dst[di + 2] * (255 - ia)) / 255);
                dst[di + 3] = (byte)System.Math.Min(255, dst[di + 3] + ia);
            }
        _screen.SetData(dw, dh, false, _screen.GetFormat(), dst);
    }

    // Make colorkey-matching texels transparent (native colorkey is baked at surface load).
    private static void BakeColorKey(Image img, long colorKey)
    {
        byte[] px = img.GetData();
        int w = img.GetWidth(), h = img.GetHeight();
        for (int i = 0; i < px.Length; i += 4)
            if (Age.Engine.Model.BlendMath.ColorKeyMatches(px[i], px[i + 1], px[i + 2], colorKey))
                px[i + 3] = 0;
        img.SetData(w, h, false, img.GetFormat(), px);
    }

    // Load an OGG off disk and play it. BGM loops; voice plays once, cutting off any prior line.
    public void PlayBgm(string oggPath)
    {
        var stream = AudioStreamOggVorbis.LoadFromBuffer(System.IO.File.ReadAllBytes(oggPath));
        if (stream == null) { GD.Print($"OGG load failed {oggPath}"); return; }
        stream.Loop = true;
        _bgm.Stream = stream;
        _bgm.Play();
    }

    public void PlayVoice(string oggPath)
    {
        var stream = AudioStreamOggVorbis.LoadFromBuffer(System.IO.File.ReadAllBytes(oggPath));
        if (stream == null) { GD.Print($"OGG load failed {oggPath}"); return; }
        stream.Loop = false;
        _voice.Stream = stream;
        _voice.Play();
    }

    public void AppendLine(string text) => _text.Text += text + "\n";
    public void PageBreak() { _pageCount++; _status.Text = "▼ click / Enter"; }
    public void ClearPage() { _text.Text = ""; _status.Text = ""; }
    public void ShowEnd() => _status.Text = "— end —";

    // The selftest verifies the GODOT PLUMBING (background thread + semaphore suspend on wait-for-input
    // + CallDeferred marshalling) drives the VM faithfully — i.e. produces the SAME output as a plain
    // in-process run of the identical scene. Full op handling is on (the synthetic scene includes a real
    // nested call-script); the expected value is computed live from a headless run, not a frozen golden.
    // Reports (from the main thread) the call-scripts the VM executed as nested subroutines this run.
    private void ReportSubroutines()
    {
        var ids = new List<long>();
        while (_trace.CallScripts.TryDequeue(out var id)) ids.Add(id);
        if (ids.Count == 0) { GD.Print("[subroutines] none dispatched on this path"); return; }
        var distinct = new List<string>();
        foreach (var id in ids) { var h = "0x" + id.ToString("x"); if (!distinct.Contains(h)) distinct.Add(h); }
        GD.Print($"[subroutines] {ids.Count} call-scripts executed as nested frames ({distinct.Count} distinct: {string.Join(", ", distinct)})");
    }

    private void RunSelfTest()
    {
        var table = OpcodeTableJson.Load(Paths.OpcodesJson);
        var (script, provider) = BuildSelfTestScene(table);
        var headless = new VirtualMachine(script, table, new CaptureHost(), null, provider);
        headless.Run();
        var expected = headless.Emitted.ConvertAll(e => e.Offset);

        var actual = _host.Captured.ConvertAll(c => c.Offset);
        bool ok = actual.Count == expected.Count;
        for (int i = 0; ok && i < actual.Count; i++) ok = actual[i] == expected[i];
        if (ok) GD.Print($"SELFTEST OK: threaded host matches headless ({actual.Count} lines, full handling)");
        else GD.Print($"SELFTEST FAIL: threaded={actual.Count} vs headless={expected.Count}");
        GetTree().Quit(ok ? 0 : 1);
    }

    // A deterministic synthesized scene: show-text, wait-for-input (exercises the suspend plumbing), a
    // nested call-script into a synthetic subroutine (exercises call-script handling), shared globals.
    private static (Script, IScriptProvider) BuildSelfTestScene(OpcodeTable table)
    {
        (int, Operand[]) ShowText(int s) => (0x6e, new[] { new Operand(2, s), new Operand(0, 0) });
        (int, Operand[]) Wait() => (0x72, new[] { new Operand(0, 0) });
        (int, Operand[]) CallScript(long id) => (0x3, new[] { new Operand(0, id) });
        (int, Operand[]) MovGG(int d, int s) => (0x55, new[] { new Operand(3, d), new Operand(3, s) });
        (int, Operand[]) MovGI(int d, long v) => (0x55, new[] { new Operand(3, d), new Operand(0, v) });
        (int, Operand[]) Exit() => (0x2, System.Array.Empty<Operand>());

        var callee = ScriptAssembler.Assemble(table, "SUBSCENE",
            new List<(int, Operand[])> { ShowText(0), MovGI(0x31, 42), Exit() }, new[] { "Sub" });
        var caller = ScriptAssembler.Assemble(table, "SELFTEST",
            new List<(int, Operand[])> { ShowText(0), Wait(), ShowText(1), CallScript(5), MovGG(0x30, 0x31), Exit() },
            new[] { "Hello", "World" });
        return (caller, new SelfTestProvider(callee));
    }

    private sealed class SelfTestProvider : IScriptProvider
    {
        private readonly Script _callee;
        public SelfTestProvider(Script callee) => _callee = callee;
        public Script? GetById(long id) => id == 5 ? _callee : null;
    }
}