using WhiteMagic.Assembly;

namespace WhiteMagicTest;

/// <summary>
/// Tests for <see cref="StubAssembler"/> emit primitives (<see cref="StubAssembler.EmitU8"/>,
/// <see cref="StubAssembler.EmitU32"/>, <see cref="StubAssembler.EmitU64"/>) and the
/// <see cref="IAssembler"/> interface contract.
/// </summary>
public class StubAssemblerTests
{
    private static StubAssembler Create() => new();

    // ── Emit primitives ────────────────────────────────────────────────────

    [Fact]
    public void EmitU8_appends_a_single_byte()
    {
        var sut = Create();
        var buffer = new List<byte>();
        sut.EmitU8(buffer, 0xAB);
        Assert.Equal([0xAB], buffer);
    }

    [Fact]
    public void EmitU32_appends_little_endian()
    {
        var sut = Create();
        var buffer = new List<byte>();
        sut.EmitU32(buffer, 0x11223344);
        Assert.Equal([0x44, 0x33, 0x22, 0x11], buffer);
    }

    [Fact]
    public void EmitU32_appends_zero()
    {
        var sut = Create();
        var buffer = new List<byte>();
        sut.EmitU32(buffer, 0);
        Assert.Equal([0x00, 0x00, 0x00, 0x00], buffer);
    }

    [Fact]
    public void EmitU64_appends_little_endian()
    {
        var sut = Create();
        var buffer = new List<byte>();
        sut.EmitU64(buffer, 0x1122334455667788);
        byte[] expected = [0x88, 0x77, 0x66, 0x55, 0x44, 0x33, 0x22, 0x11];
        Assert.Equal(expected, buffer);
    }

    [Fact]
    public void EmitU64_appends_high_bits()
    {
        var sut = Create();
        var buffer = new List<byte>();
        sut.EmitU64(buffer, 0xDEADBEEF_CAFEBABE);
        byte[] expected = [0xBE, 0xBA, 0xFE, 0xCA, 0xEF, 0xBE, 0xAD, 0xDE];
        Assert.Equal(expected, buffer);
    }

    // ── IAssembler interface ───────────────────────────────────────────────

    [Fact]
    public void StubAssembler_is_an_IAssembler()
    {
        var sut = Create();
        Assert.IsAssignableFrom<IAssembler>(sut);
    }

    [Fact]
    public void Assemble_from_StubAssembler_throws_NotSupported()
    {
        var sut = Create();
        Assert.Throws<NotSupportedException>(() => sut.Assemble("nop", 0));
    }
}