using Shouldly;
using Xunit;
using S7.Net.Types;

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

/// <summary>
///     Unit tests for the S7 wide-type (8-byte numeric) byte-buffer codec: the pure
///     <see cref="S7Driver.DecodeScalarBlock"/> / <see cref="S7Driver.EncodeScalarBlock"/>
///     helpers and <see cref="S7Driver.ScalarByteWidth"/>. These decode/encode an
///     Int64/UInt64/LReal (Float64) scalar from a contiguous big-endian byte block — the
///     network I/O half (<c>Plc.ReadBytesAsync</c>/<c>WriteBytesAsync</c>) has no in-process
///     fake so only the codec is unit-proven (mirrors <see cref="S7ArrayReadTests"/>).
///     String (S7 classic STRING) decode/encode is proven here via
///     <see cref="S7.Net.Types.S7String"/>; DateTime decode is still a deferred stub (T4) and
///     this file pins the NotSupportedException contract it lands against.
/// </summary>
[Trait("Category", "Unit")]
public sealed class S7ScalarBlockTests
{
    // ── Helpers ──────────────────────────────────────────────────────────────────────────

    // Wide scalars are byte-anchored: DB{n}.DBB{offset}, parser yields S7Size.Byte.
    private static S7TagDefinition Tag(S7DataType dt, int stringLength = 254) =>
        new("WideTag", "DB1.DBB0", dt, StringLength: stringLength);

    private static S7ParsedAddress Addr() =>
        new(S7Area.DataBlock, DbNumber: 1, S7Size.Byte, ByteOffset: 0, BitOffset: 0);

    // S7 is big-endian: most-significant byte first.
    private static byte[] BeUInt64(ulong v)
    {
        var b = new byte[8];
        for (var i = 0; i < 8; i++)
            b[i] = (byte)(v >> (56 - i * 8));
        return b;
    }

    // ── ScalarByteWidth ───────────────────────────────────────────────────────────────────

    /// <summary>Verifies the 8-byte numeric widths and the String/DateTime widths.</summary>
    [Theory]
    [InlineData(S7DataType.Int64, 8)]
    [InlineData(S7DataType.UInt64, 8)]
    [InlineData(S7DataType.Float64, 8)]
    [InlineData(S7DataType.DateTime, 8)]
    public void ScalarByteWidth_fixed_width_types(S7DataType dt, int expected)
        => S7Driver.ScalarByteWidth(Tag(dt)).ShouldBe(expected);

    /// <summary>Verifies String width is StringLength + 2 (S7 STRING header: max-len + actual-len).</summary>
    [Fact]
    public void ScalarByteWidth_String_is_length_plus_two()
        => S7Driver.ScalarByteWidth(Tag(S7DataType.String, stringLength: 10)).ShouldBe(12);

    // ── DecodeScalarBlock — Int64 ─────────────────────────────────────────────────────────

    /// <summary>Verifies an Int64 block decodes from big-endian bytes.</summary>
    [Fact]
    public void DecodeScalarBlock_Int64_reads_big_endian()
    {
        var block = BeUInt64(0x0123456789ABCDEFUL);
        // First byte is the most-significant byte (0x01) — proves big-endian, not little-endian.
        block[0].ShouldBe((byte)0x01);

        var result = S7Driver.DecodeScalarBlock(Tag(S7DataType.Int64), Addr(), block);
        result.ShouldBeOfType<long>().ShouldBe(0x0123456789ABCDEFL);
    }

    /// <summary>Verifies a negative Int64 decodes correctly (two's complement, high bit set).</summary>
    [Fact]
    public void DecodeScalarBlock_Int64_negative()
    {
        var block = BeUInt64(unchecked((ulong)-2L)); // 0xFFFF_FFFF_FFFF_FFFE
        var result = S7Driver.DecodeScalarBlock(Tag(S7DataType.Int64), Addr(), block);
        result.ShouldBeOfType<long>().ShouldBe(-2L);
    }

    // ── DecodeScalarBlock — UInt64 ────────────────────────────────────────────────────────

    /// <summary>Verifies a UInt64 block decodes a value larger than long.MaxValue.</summary>
    [Fact]
    public void DecodeScalarBlock_UInt64_reads_value_above_long_max()
    {
        var block = BeUInt64(ulong.MaxValue); // 0xFFFF_FFFF_FFFF_FFFF
        var result = S7Driver.DecodeScalarBlock(Tag(S7DataType.UInt64), Addr(), block);
        result.ShouldBeOfType<ulong>().ShouldBe(ulong.MaxValue);
    }

    // ── DecodeScalarBlock — Float64 (LReal) ───────────────────────────────────────────────

    /// <summary>Verifies a Float64 (LReal) block decodes from IEEE-754 big-endian.</summary>
    [Fact]
    public void DecodeScalarBlock_Float64_reads_ieee754_big_endian()
    {
        var bits = unchecked((ulong)BitConverter.DoubleToInt64Bits(Math.PI));
        var block = BeUInt64(bits);
        var result = S7Driver.DecodeScalarBlock(Tag(S7DataType.Float64), Addr(), block);
        result.ShouldBeOfType<double>().ShouldBe(Math.PI, tolerance: 1e-12);
    }

    // ── EncodeScalarBlock — big-endian byte production ────────────────────────────────────

    /// <summary>Verifies Int64 encodes to big-endian bytes (MSB first).</summary>
    [Fact]
    public void EncodeScalarBlock_Int64_writes_big_endian()
    {
        var bytes = S7Driver.EncodeScalarBlock(Tag(S7DataType.Int64), 0x0123456789ABCDEFL);
        bytes.Length.ShouldBe(8);
        bytes.ShouldBe(BeUInt64(0x0123456789ABCDEFUL));
        bytes[0].ShouldBe((byte)0x01); // MSB first — little-endian regression guard.
    }

    /// <summary>Verifies UInt64 encodes to big-endian bytes.</summary>
    [Fact]
    public void EncodeScalarBlock_UInt64_writes_big_endian()
    {
        var bytes = S7Driver.EncodeScalarBlock(Tag(S7DataType.UInt64), ulong.MaxValue);
        bytes.ShouldBe(BeUInt64(ulong.MaxValue));
    }

    /// <summary>Verifies Float64 encodes to IEEE-754 big-endian bytes.</summary>
    [Fact]
    public void EncodeScalarBlock_Float64_writes_ieee754_big_endian()
    {
        var bytes = S7Driver.EncodeScalarBlock(Tag(S7DataType.Float64), Math.PI);
        bytes.ShouldBe(BeUInt64(unchecked((ulong)BitConverter.DoubleToInt64Bits(Math.PI))));
    }

    // ── Round-trip identity (encode → decode) ─────────────────────────────────────────────

    /// <summary>Verifies Int64 round-trips through encode→decode for positive, negative and edge values.</summary>
    [Theory]
    [InlineData(0L)]
    [InlineData(1L)]
    [InlineData(-1L)]
    [InlineData(long.MaxValue)]
    [InlineData(long.MinValue)]
    [InlineData(0x0123456789ABCDEFL)]
    public void Int64_round_trips(long value)
    {
        var tag = Tag(S7DataType.Int64);
        var decoded = S7Driver.DecodeScalarBlock(tag, Addr(), S7Driver.EncodeScalarBlock(tag, value));
        decoded.ShouldBeOfType<long>().ShouldBe(value);
    }

    /// <summary>Verifies UInt64 round-trips, including a large value above long.MaxValue.</summary>
    [Theory]
    [InlineData(0UL)]
    [InlineData(70_000UL)]
    [InlineData(ulong.MaxValue)]
    [InlineData(0x8000_0000_0000_0001UL)]
    public void UInt64_round_trips(ulong value)
    {
        var tag = Tag(S7DataType.UInt64);
        var decoded = S7Driver.DecodeScalarBlock(tag, Addr(), S7Driver.EncodeScalarBlock(tag, value));
        decoded.ShouldBeOfType<ulong>().ShouldBe(value);
    }

    /// <summary>Verifies Float64 (LReal) round-trips for representative doubles, including
    /// the IEEE-754 specials (NaN / ±Infinity) — these pass through BinaryPrimitives unchanged.</summary>
    [Theory]
    [InlineData(0.0)]
    [InlineData(3.141592653589793)]
    [InlineData(-2.5e-300)]
    [InlineData(1.7976931348623157e308)]
    [InlineData(double.NaN)]
    [InlineData(double.PositiveInfinity)]
    [InlineData(double.NegativeInfinity)]
    public void Float64_round_trips(double value)
    {
        var tag = Tag(S7DataType.Float64);
        var decoded = S7Driver.DecodeScalarBlock(tag, Addr(), S7Driver.EncodeScalarBlock(tag, value));
        // double.NaN != double.NaN, so compare via Shouldly's IsNaN for that case.
        if (double.IsNaN(value))
            decoded.ShouldBeOfType<double>().ShouldBe(double.NaN);
        else
            decoded.ShouldBeOfType<double>().ShouldBe(value);
    }

    // ── DecodeScalarBlock — String (S7 classic STRING) ────────────────────────────────────

    /// <summary>Verifies an S7 STRING block decodes to its C# string, ignoring the
    /// two-byte <c>[maxLen][curLen]</c> header and any reserved padding past curLen.</summary>
    [Fact]
    public void DecodeScalarBlock_String_reads_header_and_chars()
    {
        // S7 classic STRING layout: [maxLen=10][curLen=5]['H']['E']['L']['L']['O'][pad…].
        var block = S7String.ToByteArray("HELLO", 10);
        block.Length.ShouldBe(12);          // StringLength(10) + 2-byte header.
        block[0].ShouldBe((byte)10);        // maxLen.
        block[1].ShouldBe((byte)5);         // curLen.

        var result = S7Driver.DecodeScalarBlock(Tag(S7DataType.String, stringLength: 10), Addr(), block);
        result.ShouldBeOfType<string>().ShouldBe("HELLO");
    }

    /// <summary>Verifies a hand-built STRING block (not produced by S7.Net) still decodes,
    /// pinning the on-the-wire layout we depend on.</summary>
    [Fact]
    public void DecodeScalarBlock_String_decodes_hand_built_block()
    {
        var block = new byte[12];
        block[0] = 10;                       // maxLen.
        block[1] = 5;                        // curLen.
        block[2] = (byte)'H'; block[3] = (byte)'E'; block[4] = (byte)'L';
        block[5] = (byte)'L'; block[6] = (byte)'O'; // bytes 7..11 stay zero (reserved padding).

        var result = S7Driver.DecodeScalarBlock(Tag(S7DataType.String, stringLength: 10), Addr(), block);
        result.ShouldBeOfType<string>().ShouldBe("HELLO");
    }

    /// <summary>Verifies an empty S7 STRING decodes to the empty string.</summary>
    [Fact]
    public void DecodeScalarBlock_String_empty()
    {
        var block = S7String.ToByteArray("", 10);
        var result = S7Driver.DecodeScalarBlock(Tag(S7DataType.String, stringLength: 10), Addr(), block);
        result.ShouldBeOfType<string>().ShouldBe("");
    }

    // ── EncodeScalarBlock — String (S7 classic STRING) ────────────────────────────────────

    /// <summary>Verifies a C# string encodes to a STRING block sized to the reserved field
    /// (StringLength + 2), with header <c>[maxLen=StringLength][curLen=value.Length]</c> and
    /// the chars laid out after it.</summary>
    [Fact]
    public void EncodeScalarBlock_String_writes_header_chars_and_pads_to_reserved()
    {
        var tag = Tag(S7DataType.String, stringLength: 10);
        var block = S7Driver.EncodeScalarBlock(tag, "HELLO");

        block.Length.ShouldBe(12);          // StringLength(10) + 2 — full reserved field, not curLen-sized.
        block[0].ShouldBe((byte)10);        // maxLen == declared StringLength.
        block[1].ShouldBe((byte)5);         // curLen == value.Length.
        block[2].ShouldBe((byte)'H');
        block[6].ShouldBe((byte)'O');
        block[7].ShouldBe((byte)0);         // reserved padding is zeroed.
        block[11].ShouldBe((byte)0);
    }

    /// <summary>Verifies a null value encodes as an empty STRING (curLen 0), not a throw.</summary>
    [Fact]
    public void EncodeScalarBlock_String_null_value_is_empty_string()
    {
        var tag = Tag(S7DataType.String, stringLength: 10);
        var block = S7Driver.EncodeScalarBlock(tag, value: null);

        block.Length.ShouldBe(12);
        block[0].ShouldBe((byte)10);        // maxLen.
        block[1].ShouldBe((byte)0);         // curLen 0.
    }

    /// <summary>Verifies a non-string value coerces via <c>Convert.ToString</c> before encoding.</summary>
    [Fact]
    public void EncodeScalarBlock_String_coerces_non_string_value()
    {
        var tag = Tag(S7DataType.String, stringLength: 10);
        var block = S7Driver.EncodeScalarBlock(tag, 1234);

        var decoded = S7Driver.DecodeScalarBlock(tag, Addr(), block);
        decoded.ShouldBeOfType<string>().ShouldBe("1234");
    }

    /// <summary>Verifies a string longer than the reserved length throws (S7.Net rejects it;
    /// we do NOT silently truncate). Pins the overflow behaviour.</summary>
    [Fact]
    public void EncodeScalarBlock_String_overflow_throws()
    {
        var tag = Tag(S7DataType.String, stringLength: 5);
        // 6 chars into a 5-char reserved field — S7.Net throws ArgumentException.
        Should.Throw<ArgumentException>(() => S7Driver.EncodeScalarBlock(tag, "ABCDEF"));
    }

    // ── String round-trip identity (encode → decode) ──────────────────────────────────────

    /// <summary>Verifies String round-trips through encode→decode, incl. empty and max-length.</summary>
    [Theory]
    [InlineData("")]
    [InlineData("A")]
    [InlineData("Hello, S7!")]          // 10 chars == StringLength (at max).
    [InlineData("Tag_Value 42")]
    public void String_round_trips(string value)
    {
        // StringLength sized to fit the longest sample (12) so none overflow.
        var tag = Tag(S7DataType.String, stringLength: 12);
        var decoded = S7Driver.DecodeScalarBlock(tag, Addr(), S7Driver.EncodeScalarBlock(tag, value));
        decoded.ShouldBeOfType<string>().ShouldBe(value);
    }

    /// <summary>Verifies a string exactly at the reserved length round-trips (boundary, no overflow).</summary>
    [Fact]
    public void String_at_max_length_round_trips()
    {
        var tag = Tag(S7DataType.String, stringLength: 5);
        var decoded = S7Driver.DecodeScalarBlock(tag, Addr(), S7Driver.EncodeScalarBlock(tag, "ABCDE"));
        decoded.ShouldBeOfType<string>().ShouldBe("ABCDE");
    }

    // ── Deferred-stub contract: DateTime throws NotSupportedException ──────────────────────

    /// <summary>Verifies DateTime decode is a deferred stub (NotSupportedException — T4).</summary>
    [Fact]
    public void DecodeScalarBlock_DateTime_throws_NotSupported()
    {
        var tag = Tag(S7DataType.DateTime);
        var block = new byte[S7Driver.ScalarByteWidth(tag)];
        Should.Throw<NotSupportedException>(() => S7Driver.DecodeScalarBlock(tag, Addr(), block));
    }

    /// <summary>Verifies DateTime encode is a deferred stub (NotSupportedException — T4).</summary>
    [Fact]
    public void EncodeScalarBlock_DateTime_throws_NotSupported()
        => Should.Throw<NotSupportedException>(() => S7Driver.EncodeScalarBlock(Tag(S7DataType.DateTime), "x"));
}