using System.Collections.Generic;
using Age.Engine.Hosting;
using Age.Engine.Model;
using Age.Engine.Sys4;
using Age.Engine.Vm;
using Xunit;

public class CallScriptTests
{
    // Opcodes (from build/opcodes.json): exit=0x2, call-script=0x3(argc1), mov=0x55(argc2).
    // Operand types: imm=0, global-int=3, local-int=9.
    private const uint OP_EXIT = 0x2, OP_CALLSCRIPT = 0x3, OP_MOV = 0x55, OP_SETTEXTURE = 0x1f9;

    private class NullHost : IHost
    {
        public virtual void EnterScriptContext(string scriptName) { }
        public virtual void ExitScriptContext() { }
        public void ShowText(int o, string t) { }
        public void WaitForInput() { }
        public void Sleep(long duration) { }
        public void FrameYield() { }
        public void CreateTexture(int s, int w, int h) { }
        public virtual void SetTexture(long r, int s) { }
        public void DrawTexture(int s, int sx, int sy, int w, int h, int dx, int dy) { }
        public (int Width, int Height) GetTextureSize(int s) => (0, 0);
        public void PlayBgm(long id) { }
        public void PlayVoice(long id) { }
    }

    private sealed class MapProvider : IScriptProvider
    {
        private readonly Dictionary<long, Script> _m;
        public MapProvider(Dictionary<long, Script> m) => _m = m;
        public Script? GetById(long id) => _m.TryGetValue(id, out var s) ? s : null;
    }

    private sealed class ContextHost : NullHost
    {
        private readonly Stack<string> _contexts = new();
        public List<string> Events { get; } = new();
        public List<(long ResourceId, int Slot)> Textures { get; } = new();

        public override void EnterScriptContext(string scriptName)
        {
            _contexts.Push(scriptName);
            Events.Add($"enter:{scriptName}");
        }

        public override void ExitScriptContext()
        {
            Events.Add($"exit:{_contexts.Pop()}");
        }

        public override void SetTexture(long resourceId, int slot) => Textures.Add((resourceId, slot));
    }

    // Build a Script from raw dwords via the real loader (guarantees identical decode).
    private static Script Asm(OpcodeTable t, string name, params uint[] body)
    {
        var bytes = new byte[0x3C + body.Length * 4];
        System.Text.Encoding.ASCII.GetBytes("SYS4422 ").CopyTo(bytes, 0);
        // fields[8] (F8 = code end) at header offset 8 + 8*4 = 0x28; set to body length (all code).
        System.BitConverter.GetBytes(body.Length).CopyTo(bytes, 8 + 8 * 4);
        for (int i = 0; i < body.Length; i++) System.BitConverter.GetBytes(body[i]).CopyTo(bytes, 0x3C + i * 4);
        return Sys4Loader.Parse(bytes, t, name);
    }

    private static OpcodeTable Table() => OpcodeTableJson.Load(Paths.OpcodesJson);

    [Fact]
    public void CalleeRunsAndControlResumesAfterTheCall()
    {
        var t = Table();
        // Callee (id 5): mov g[0x10] = 7, then exit.
        var callee = Asm(t, "CALLEE", OP_MOV, 3, 0x10, 0, 7, OP_EXIT);
        // Caller: call-script 5 ; mov g[0x11] = g[0x10] ; exit.
        var caller = Asm(t, "CALLER",
            OP_CALLSCRIPT, 0, 5,
            OP_MOV, 3, 0x11, 3, 0x10,
            OP_EXIT);
        var host = new NullHost();
        var sink = new RecordingTraceSink();
        var vm = new VirtualMachine(caller, t, host, null, new MapProvider(new() { [5] = callee }), sink);
        vm.Run();
        Assert.Equal(7, vm.Globals[0x10]);           // callee wrote a shared global
        Assert.Equal(7, vm.Globals[0x11]);           // caller read it AFTER the call returned
        Assert.Equal("exit", vm.HaltReason);         // top-level exit
        Assert.Contains(5L, sink.CallScriptIds);     // dispatch observed via the trace sink
    }

    [Fact]
    public void MissingProviderFallsBackToStub()
    {
        var t = Table();
        var caller = Asm(t, "CALLER", OP_CALLSCRIPT, 0, 5, OP_EXIT);
        var host = new NullHost();
        var sink = new RecordingTraceSink();
        var vm = new VirtualMachine(caller, t, host, null, null, sink);   // no provider
        vm.Run();
        Assert.Equal("exit", vm.HaltReason);        // did not halt on the call; stub + continue
        Assert.Contains(5L, sink.CallScriptIds);
    }

    [Fact]
    public void UnresolvedIdHalts()
    {
        var t = Table();
        var caller = Asm(t, "CALLER", OP_CALLSCRIPT, 0, 99, OP_EXIT);
        var vm = new VirtualMachine(caller, t, new NullHost(), null, new MapProvider(new()));
        vm.Run();
        Assert.StartsWith("callscript-unresolved", vm.HaltReason);
    }

    [Fact]
    public void LocalsDoNotLeakBetweenCallerAndCallee()
    {
        var t = Table();
        // Callee writes LOCAL-int 0 = 42 (mov to local-int, type 9), then exit.
        var callee = Asm(t, "CALLEE", OP_MOV, 9, 0, 0, 42, OP_EXIT);
        // Caller sets local-int 0 = 1, calls, then copies its own local-int 0 to global 0x20.
        var caller = Asm(t, "CALLER",
            OP_MOV, 9, 0, 0, 1,                  // l[0] = 1
            OP_CALLSCRIPT, 0, 5,                 // call-script 5 (callee sets ITS local 0 = 42)
            OP_MOV, 3, 0x20, 9, 0,               // g[0x20] = l[0]
            OP_EXIT);
        var vm = new VirtualMachine(caller, t, new NullHost(), null, new MapProvider(new() { [5] = callee }));
        vm.Run();
        Assert.Equal(1, vm.Globals[0x20]);   // caller's local 0 unchanged by callee's local 0
    }

    [Fact]
    public void PackedTextureIdsRemainUnchangedAcrossNestedFrames()
    {
        var t = Table();
        var callee = Asm(t, "CALLEE",
            OP_SETTEXTURE, 0, 7, 0, 2, 0, uint.MaxValue,
            OP_EXIT);
        var caller = Asm(t, "CALLER",
            OP_SETTEXTURE, 0, 7, 0, 1, 0, uint.MaxValue,
            OP_CALLSCRIPT, 0, 5,
            OP_SETTEXTURE, 0, 7, 0, 3, 0, uint.MaxValue,
            OP_EXIT);
        var host = new ContextHost();
        var vm = new VirtualMachine(caller, t, host, null, new MapProvider(new() { [5] = callee }));

        vm.Run();

        Assert.Equal(new[] { (7L, 1), (7L, 2), (7L, 3) }, host.Textures);
        Assert.Equal(new[] { "enter:CALLER", "enter:CALLEE", "exit:CALLEE", "exit:CALLER" }, host.Events);
    }
}