using System.Text;
using Shouldly;
using Xunit;
using ZB.MOM.WW.OtOpcUa.Driver.TwinCAT;

namespace ZB.MOM.WW.OtOpcUa.Driver.TwinCAT.Tests;

/// <summary>
///     Pins <see cref="TwinCATStringCodec"/> — how an IEC <c>STRING(n)</c> / <c>WSTRING(n)</c> buffer,
///     read at the PLC's own declared width, becomes a value. Ported from the ignitionoee TwinCAT
///     driver (0.19.3 first-NUL STRING, 0.19.4 TwinCAT-007 first-NUL WSTRING and TwinCAT-010
///     Windows-1252), whose byte fixtures these reuse.
/// </summary>
[Trait("Category", "Unit")]
public sealed class TwinCATStringCodecTests
{
    /// <summary>
    ///     An IEC STRING ends at its FIRST NUL; the buffer beyond keeps whatever a longer earlier value
    ///     left there. Live on the Elma cleaner Z33856 (2026-09-24) a decoder that only trimmed trailing
    ///     NULs published work order <c>67504440</c> as <c>"67504440\0" + "1"</c> and part
    ///     <c>110032285</c> as <c>"110032285\0" + "1\0" + "30"</c> — a wrong value at Good quality.
    /// </summary>
    [Fact]
    public void String_stops_at_the_first_nul_and_ignores_stale_bytes_after_it()
    {
        byte[] workOrder = [(byte)'6', (byte)'7', (byte)'5', (byte)'0', (byte)'4', (byte)'4', (byte)'4', (byte)'0',
            0x00, (byte)'1', 0x00, (byte)'3', (byte)'0', 0x00];
        TwinCATStringCodec.DecodeString(workOrder, utf8: false).ShouldBe("67504440");

        byte[] emptied = [0x00, (byte)'O', (byte)'L', (byte)'D'];
        TwinCATStringCodec.DecodeString(emptied, utf8: false).ShouldBe("");
    }

    /// <summary>A buffer with no NUL at all (a full-length value) decodes whole.</summary>
    [Fact]
    public void String_without_a_nul_decodes_the_whole_buffer()
        => TwinCATStringCodec.DecodeString("ABC"u8.ToArray(), utf8: false).ShouldBe("ABC");

    /// <summary>
    ///     An IEC STRING on TwinCAT is single-byte Windows-1252, not ASCII and not the host's culture
    ///     code page: <c>°</c> (0xB0, an Elma alarm text), <c>ä</c> (0xE4) and <c>€</c> (0x80, the one
    ///     byte where 1252 and ISO-8859-1 differ) must decode to themselves on any host.
    /// </summary>
    [Fact]
    public void String_decodes_windows_1252_high_bytes()
    {
        byte[] text = [(byte)'8', (byte)'0', 0xB0, (byte)'C', (byte)' ', 0xE4, 0x80, 0x00, 0xFF];
        TwinCATStringCodec.DecodeString(text, utf8: false).ShouldBe("80°C ä€");
    }

    /// <summary>
    ///     A TwinCAT 3.1 build 4026+ project with "UTF8 Encoding for STRING" on reports UTF-8 string
    ///     data; the codec honours it (still ending at the first NUL).
    /// </summary>
    [Fact]
    public void String_decodes_utf8_when_the_target_reports_utf8_strings()
    {
        var bytes = Encoding.UTF8.GetBytes("80°C ä€").Concat(new byte[] { 0x00, (byte)'X' }).ToArray();
        TwinCATStringCodec.DecodeString(bytes, utf8: true).ShouldBe("80°C ä€");
    }

    /// <summary>
    ///     A WSTRING ends at its first ALIGNED <c>U+0000</c> code unit (TwinCAT-007): <c>"NEW\0LD"</c>
    ///     must publish <c>"NEW"</c>. A zero HIGH byte of a non-NUL unit (every ASCII character in
    ///     UTF-16LE) is not a terminator.
    /// </summary>
    [Fact]
    public void WString_stops_at_the_first_aligned_nul_code_unit()
    {
        var bytes = Encoding.Unicode.GetBytes("NEW\0LD\0");
        TwinCATStringCodec.DecodeWString(bytes).ShouldBe("NEW");
        TwinCATStringCodec.DecodeWString(Encoding.Unicode.GetBytes("Grüße")).ShouldBe("Grüße");
    }

    /// <summary>A trailing odd byte is not half a character — it is ignored.</summary>
    [Fact]
    public void WString_ignores_a_trailing_odd_byte()
    {
        var bytes = Encoding.Unicode.GetBytes("AB").Concat(new byte[] { 0x43 }).ToArray();
        TwinCATStringCodec.DecodeWString(bytes).ShouldBe("AB");
    }
}