using System;
using System.Buffers.Binary;
using System.Numerics;
using AcDream.Core.Net.Messages;
using Xunit;

namespace AcDream.Core.Net.Tests.Messages;

public class MoveToStateTests
{
    [Fact]
    public void Build_IdleState_ProducesValidGameAction()
    {
        var body = MoveToState.Build(
            gameActionSequence: 1,
            forwardCommand: null,
            forwardSpeed: null,
            sidestepCommand: null,
            sidestepSpeed: null,
            turnCommand: null,
            turnSpeed: null,
            holdKey: null,
            cellId: 0xA9B40001u,
            position: new Vector3(96f, 96f, 50f),
            rotation: Quaternion.Identity,
            instanceSequence: 0,
            serverControlSequence: 0,
            teleportSequence: 0,
            forcePositionSequence: 0);

        // First 4 bytes: GameAction opcode 0xF7B1
        uint opcode = BinaryPrimitives.ReadUInt32LittleEndian(body.AsSpan(0));
        Assert.Equal(0xF7B1u, opcode);

        // Bytes 4-7: game action sequence
        uint seq = BinaryPrimitives.ReadUInt32LittleEndian(body.AsSpan(4));
        Assert.Equal(1u, seq);

        // Bytes 8-11: MoveToState action type 0xF61C
        uint actionType = BinaryPrimitives.ReadUInt32LittleEndian(body.AsSpan(8));
        Assert.Equal(0xF61Cu, actionType);
    }

    [Fact]
    public void Build_WalkForward_IncludesForwardCommandInFlags()
    {
        var body = MoveToState.Build(
            gameActionSequence: 2,
            forwardCommand: 0x45000005u,  // WalkForward
            forwardSpeed: 1.0f,
            sidestepCommand: null,
            sidestepSpeed: null,
            turnCommand: null,
            turnSpeed: null,
            holdKey: null,
            cellId: 0xA9B40001u,
            position: new Vector3(96f, 96f, 50f),
            rotation: Quaternion.Identity,
            instanceSequence: 0,
            serverControlSequence: 0,
            teleportSequence: 0,
            forcePositionSequence: 0);

        // After the 12-byte GameAction header comes RawMotionState.
        // First u32 is the packed flags word. ForwardCommand flag = 0x4.
        uint flags = BinaryPrimitives.ReadUInt32LittleEndian(body.AsSpan(12));
        Assert.True((flags & 0x4u) != 0, "ForwardCommand flag (0x4) should be set");
        // ForwardSpeed flag = 0x10
        Assert.True((flags & 0x10u) != 0, "ForwardSpeed flag (0x10) should be set");
    }

    [Fact]
    public void Build_IdleState_RawMotionFlagsAreZero()
    {
        var body = MoveToState.Build(
            gameActionSequence: 3,
            forwardCommand: null,
            forwardSpeed: null,
            sidestepCommand: null,
            sidestepSpeed: null,
            turnCommand: null,
            turnSpeed: null,
            holdKey: null,
            cellId: 0xA9B40001u,
            position: Vector3.Zero,
            rotation: Quaternion.Identity,
            instanceSequence: 0,
            serverControlSequence: 0,
            teleportSequence: 0,
            forcePositionSequence: 0);

        uint flags = BinaryPrimitives.ReadUInt32LittleEndian(body.AsSpan(12));
        Assert.Equal(0u, flags);
    }

    [Fact]
    public void Build_IdleState_WorldPositionFollowsMotionState()
    {
        // With no motion state, flags = 0 and no conditional fields are written.
        // So WorldPosition starts at offset 12 (envelope) + 4 (flags) = 16.
        var body = MoveToState.Build(
            gameActionSequence: 4,
            forwardCommand: null,
            forwardSpeed: null,
            sidestepCommand: null,
            sidestepSpeed: null,
            turnCommand: null,
            turnSpeed: null,
            holdKey: null,
            cellId: 0xDEADBEEFu,
            position: Vector3.Zero,
            rotation: Quaternion.Identity,
            instanceSequence: 0,
            serverControlSequence: 0,
            teleportSequence: 0,
            forcePositionSequence: 0);

        uint cellId = BinaryPrimitives.ReadUInt32LittleEndian(body.AsSpan(16));
        Assert.Equal(0xDEADBEEFu, cellId);
    }

    [Fact]
    public void Build_IsAlignedTo4Bytes()
    {
        var body = MoveToState.Build(
            gameActionSequence: 5,
            forwardCommand: null,
            forwardSpeed: null,
            sidestepCommand: null,
            sidestepSpeed: null,
            turnCommand: null,
            turnSpeed: null,
            holdKey: null,
            cellId: 0xA9B40001u,
            position: Vector3.Zero,
            rotation: Quaternion.Identity,
            instanceSequence: 0,
            serverControlSequence: 0,
            teleportSequence: 0,
            forcePositionSequence: 0);

        Assert.Equal(0, body.Length % 4);
    }

    [Fact]
    public void Build_WithHoldKey_IncludesHoldKeyFlag()
    {
        var body = MoveToState.Build(
            gameActionSequence: 6,
            forwardCommand: null,
            forwardSpeed: null,
            sidestepCommand: null,
            sidestepSpeed: null,
            turnCommand: null,
            turnSpeed: null,
            holdKey: 2u,  // Run
            cellId: 0xA9B40001u,
            position: Vector3.Zero,
            rotation: Quaternion.Identity,
            instanceSequence: 0,
            serverControlSequence: 0,
            teleportSequence: 0,
            forcePositionSequence: 0);

        uint flags = BinaryPrimitives.ReadUInt32LittleEndian(body.AsSpan(12));
        Assert.True((flags & 0x1u) != 0, "CurrentHoldKey flag (0x1) should be set");

        // The hold key value (u32 = 2) should immediately follow the flags
        uint holdKeyValue = BinaryPrimitives.ReadUInt32LittleEndian(body.AsSpan(16));
        Assert.Equal(2u, holdKeyValue);
    }
}