using System.Globalization;
using S7.Net.Protocol;

namespace ZB.MOM.WW.OtOpcUa.Driver.S7;

/// <summary>
///     ISO-TSAP helpers for the optional <c>LocalTsap</c> / <c>RemoteTsap</c> / <c>ConnectionType</c>
///     config: parsing the hex text form and resolving the effective <see cref="TsapPair"/> handed to
///     S7.Net. Pure — no I/O — so the resolution rules are unit-testable without a PLC.
/// </summary>
internal static class S7Tsap
{
    /// <summary>
    ///     Parses a TSAP written as two hex bytes — <c>"01.00"</c>, <c>"03:01"</c> (1–2 digits per byte) — or
    ///     as one 16-bit hex value, <c>"0100"</c> / <c>"0x0301"</c>. High byte first.
    /// </summary>
    /// <param name="text">The configured text.</param>
    /// <param name="tsap">The 16-bit TSAP (<c>first &lt;&lt; 8 | second</c>).</param>
    /// <returns>True when <paramref name="text"/> is a valid TSAP.</returns>
    internal static bool TryParse(string? text, out ushort tsap)
    {
        tsap = 0;
        if (string.IsNullOrWhiteSpace(text)) return false;
        var t = text.Trim();
        var sep = t.IndexOfAny(['.', ':', '-']);
        if (sep >= 0)
        {
            if (!TryHexByte(t[..sep], out var hi) || !TryHexByte(t[(sep + 1)..], out var lo)) return false;
            tsap = (ushort)((hi << 8) | lo);
            return true;
        }
        if (t.StartsWith("0x", StringComparison.OrdinalIgnoreCase)) t = t[2..];
        if (t.Length is < 1 or > 4) return false;
        return ushort.TryParse(t, NumberStyles.AllowHexSpecifier, CultureInfo.InvariantCulture, out tsap);
    }

    private static bool TryHexByte(string s, out byte b)
    {
        b = 0;
        s = s.Trim();
        return s.Length is >= 1 and <= 2
            && byte.TryParse(s, NumberStyles.AllowHexSpecifier, CultureInfo.InvariantCulture, out b);
    }

    /// <summary>Formats a 16-bit TSAP as canonical <c>"XX.YY"</c> (upper-case hex).</summary>
    /// <param name="tsap">The 16-bit TSAP.</param>
    /// <returns>The canonical text.</returns>
    internal static string Format(ushort tsap) => $"{tsap >> 8:X2}.{tsap & 0xFF:X2}";

    /// <summary>
    ///     Resolves the TSAP pair to connect with, or <c>null</c> when the options carry no override (the
    ///     caller then keeps the plain <c>Plc(cpu, host, port, rack, slot)</c> construction, unchanged).
    ///     Starts from S7.Net's own per-CPU default for <paramref name="options"/>'s rack/slot, then applies,
    ///     in order: <c>LocalTsap</c> replaces the local TSAP; <c>RemoteTsap</c> replaces the remote TSAP;
    ///     <c>ConnectionType</c> replaces only the remote TSAP's first byte.
    /// </summary>
    /// <param name="options">The driver options.</param>
    /// <returns>The effective pair, or null for "no override".</returns>
    internal static TsapPair? Resolve(S7DriverOptions options)
    {
        ArgumentNullException.ThrowIfNull(options);
        var hasLocal = !string.IsNullOrWhiteSpace(options.LocalTsap);
        var hasRemote = !string.IsNullOrWhiteSpace(options.RemoteTsap);
        if (!hasLocal && !hasRemote && options.ConnectionType is null) return null;

        var def = TsapPair.GetDefaultTsapPair(S7CpuTypeMap.ToS7Net(options.CpuType), options.Rack, options.Slot);
        var local = def.Local;
        var remote = def.Remote;

        if (hasLocal)
        {
            if (!TryParse(options.LocalTsap, out var l))
                throw new FormatException($"S7 LocalTsap '{options.LocalTsap}' is not a valid TSAP (expected e.g. \"01.00\").");
            local = new Tsap((byte)(l >> 8), (byte)(l & 0xFF));
        }
        if (hasRemote)
        {
            if (!TryParse(options.RemoteTsap, out var r))
                throw new FormatException($"S7 RemoteTsap '{options.RemoteTsap}' is not a valid TSAP (expected e.g. \"03.01\").");
            remote = new Tsap((byte)(r >> 8), (byte)(r & 0xFF));
        }
        else if (options.ConnectionType is { } ct)
        {
            remote = new Tsap((byte)ct, remote.SecondByte);
        }
        return new TsapPair(local, remote);
    }
}