using System.Text.Json;

namespace ZB.MOM.WW.OtOpcUa.Core.Abstractions;

/// <summary>
///     Gitea #610 — the single authority on whether a driver can WRITE a 1-D array tag. The address-space
///     composer consults it at compose time (both compose seams run the same composer, so the live-edit and
///     artifact-decode sides cannot disagree) to decide whether an authored-<c>ReadWrite</c> array tag
///     materialises as a writable OPC UA node. Before #610 every array node was forced read-only regardless of
///     driver; that remains the answer for every (driver, element type) pair NOT listed here.
///     <para>
///         <b>The rule is "never advertise a write the driver will refuse".</b> A pair is listed only when the
///         driver's <c>IWritable.WriteAsync</c> encodes a whole-array value end to end; a driver that refuses an
///         array value (a scalar-only encoder, a <c>NotSupportedException</c> guard) is left out so its array
///         nodes stay read-only and a client write is refused at the node (<c>BadNotWritable</c>) rather than
///         optimistically applied and reverted. The table is pure data, keyed off the same TagConfig keys the
///         drivers' own tag-definition factories read, because the composer has no reference to driver
///         assemblies. Each listed driver's test project pins its row against the real encoder
///         (<c>*ArrayWriteSupportParityTests</c>), so a driver gaining or losing an array encoder fails a test
///         until this table follows.
///     </para>
///     <list type="bullet">
///         <item><b>Modbus</b> — <c>region: Coils</c> (FC15, any element, at most 1968 coils) and
///             <c>region: HoldingRegisters</c> with a fixed-width numeric <c>dataType</c> (FC16) whose
///             <c>arrayLength × registers-per-element</c> fits the driver's <c>maxRegistersPerWrite</c> (default
///             123 — the driver refuses rather than chunks a longer FC16). Bit-in-register, String and
///             Bool-in-register arrays have no array encoder; input regions are read-only.</item>
///         <item><b>S7</b> — <c>dataType</c> Byte / Int16 / UInt16 / Int32 / UInt32 / Float32 (one contiguous
///             block, <c>EncodeArrayBlock</c>). Bool arrays would clobber neighbouring bits; the wide / String /
///             DateTime element types have no array encoder.</item>
///         <item><b>OpcUaClient</b> — every element type: the value is forwarded to the upstream server as a
///             <c>Variant</c> unchanged, and the upstream server is the arbiter (of shape, too).</item>
///         <item><b>Galaxy</b> — the array variants <c>MxValueEncoder</c> encodes, keyed by the OPC UA
///             <c>DataType</c> the node is created with: Boolean / Int32 / Int64 / Float / Double / String /
///             DateTime — and only with a declared <c>arrayLength</c>: an undeclared length materialises an
///             unbounded node, and a short whole-array write to it would RESIZE the Galaxy attribute (the
///             mxaccessgw <c>gateway.md</c> contract), which is never what a client meant.</item>
///         <item>Everything else (AbCip, AbLegacy, TwinCAT, FOCAS, MQTT, MTConnect, Sql, Calculation) — scalar
///             write encoders only; array nodes stay read-only.</item>
///     </list>
///     <para>Modbus, S7 and Galaxy require a declared length — <c>isArray: true</c> AND an integer
///     <c>arrayLength &gt;= 1</c>. The Modbus and S7 tag factories treat anything else as a SCALAR tag (whose
///     scalar encoder cannot take an array value), though the composer still materialises an array node.</para>
///     <para>Multi-dimensional arrays (<c>ValueRank &gt; 1</c>) are out of scope altogether — every array node
///     is materialised 1-D (<c>ValueRank = OneDimension</c>), so nothing here considers more than one rank.</para>
/// </summary>
public static class DriverArrayWriteSupport
{
    /// <summary>The Modbus driver's FC16 write cap when <c>maxRegistersPerWrite</c> is absent or <c>0</c>
    /// (<c>ModbusDriver</c> resolves it the same way).</summary>
    public const int ModbusDefaultMaxRegistersPerWrite = 123;

    /// <summary>Modbus FC15's protocol ceiling on coils per request (0x07B0). The driver sends one FC15 for the
    /// whole array without chunking, so a longer coil array is refused by every conformant device.</summary>
    public const int ModbusMaxCoilsPerWrite = 1968;

    // Element type → registers per element (ModbusDriver.RegisterCount).
    private static readonly Dictionary<string, int> ModbusRegisterArrayTypes = new(StringComparer.OrdinalIgnoreCase)
    {
        ["Int16"] = 1, ["UInt16"] = 1, ["Bcd16"] = 1,
        ["Int32"] = 2, ["UInt32"] = 2, ["Bcd32"] = 2, ["Float32"] = 2,
        ["Int64"] = 4, ["UInt64"] = 4, ["Float64"] = 4,
    };

    private static readonly HashSet<string> S7ArrayTypes = new(StringComparer.OrdinalIgnoreCase)
    {
        "Byte", "Int16", "UInt16", "Int32", "UInt32", "Float32",
    };

    private static readonly HashSet<string> GalaxyArrayDataTypes = new(StringComparer.Ordinal)
    {
        "Boolean", "Int32", "Int64", "Float", "Double", "String", "DateTime",
    };

    /// <summary>
    ///     Whether a driver of <paramref name="driverType"/> can write a 1-D array tag of the given shape.
    /// </summary>
    /// <param name="driverType">The owning driver instance's <c>DriverType</c> (a <see cref="DriverTypeNames"/>
    ///     constant); <see langword="null"/> or unknown ⇒ <see langword="false"/>.</param>
    /// <param name="dataType">The tag's OPC UA <c>DataType</c> name (<c>Tag.DataType</c>).</param>
    /// <param name="tagConfig">The tag's <c>TagConfig</c> JSON (driver-native address + element type).</param>
    /// <param name="driverConfigs">The <c>DriverConfig</c> / <c>DeviceConfig</c> JSON blobs that can carry a
    ///     driver write cap (Modbus <c>maxRegistersPerWrite</c>). Every one is consulted and the SMALLEST cap
    ///     wins, so the answer stays conservative however the driver's config merge resolves them.</param>
    /// <returns><see langword="true"/> only when the driver encodes a whole-array write for this tag.</returns>
    public static bool Supports(string? driverType, string? dataType, string? tagConfig, params string?[] driverConfigs)
    {
        switch (driverType)
        {
            case DriverTypeNames.OpcUaClient:
                return true;
            case DriverTypeNames.Galaxy:
                return dataType is not null && GalaxyArrayDataTypes.Contains(dataType)
                    && TryParseObject(tagConfig, out var galaxyRoot) && ReadArrayLength(galaxyRoot) is not null;
            case DriverTypeNames.Modbus:
            {
                // Same reads as ModbusTagDefinitionFactory: a blob with no `region` or no numeric `address` is not
                // a Modbus tag at all (the factory refuses it). A present non-string region is read as absent ⇒
                // HoldingRegisters, and an absent dataType ⇒ Int16 (TagConfigJson.TryReadEnumStrict).
                if (!TryParseObject(tagConfig, out var root)
                    || !root.TryGetProperty("region", out _)
                    || !root.TryGetProperty("address", out var address) || address.ValueKind != JsonValueKind.Number
                    || ReadArrayLength(root) is not { } count)
                    return false;
                var region = ReadEnumName(root, "region") ?? "HoldingRegisters";
                var native = ReadEnumName(root, "dataType") ?? "Int16";
                if (string.Equals(region, "Coils", StringComparison.OrdinalIgnoreCase)) return count <= ModbusMaxCoilsPerWrite;
                return string.Equals(region, "HoldingRegisters", StringComparison.OrdinalIgnoreCase)
                    && ModbusRegisterArrayTypes.TryGetValue(native, out var registersPerElement)
                    && (long)count * registersPerElement <= ModbusMaxRegistersPerWrite(driverConfigs);
            }
            case DriverTypeNames.S7:
            {
                // S7TagDefinitionFactory requires a dataType key (absent ⇒ not an S7 tag at all); a present
                // non-string value falls back to Int16, exactly as the factory's strict enum read does.
                if (!TryParseObject(tagConfig, out var root) || !root.TryGetProperty("dataType", out _)
                    || ReadArrayLength(root) is null)
                    return false;
                var native = ReadEnumName(root, "dataType") ?? "Int16";
                return S7ArrayTypes.Contains(native);
            }
            default:
                return false;
        }
    }

    // The smallest Modbus write cap configured in any config; none configured (absent / non-positive) ⇒ the driver
    // default (123). The key is matched case-insensitively, like the driver's DTO binding.
    private static int ModbusMaxRegistersPerWrite(string?[]? driverConfigs)
    {
        int? cap = null;
        foreach (var config in driverConfigs ?? [])
        {
            if (!TryParseObject(config, out var root)) continue;
            foreach (var prop in root.EnumerateObject())
            {
                if (string.Equals(prop.Name, "maxRegistersPerWrite", StringComparison.OrdinalIgnoreCase)
                    && prop.Value.ValueKind == JsonValueKind.Number
                    && prop.Value.TryGetInt32(out var configured) && configured > 0)
                {
                    cap = Math.Min(cap ?? int.MaxValue, configured);
                }
            }
        }
        return cap ?? ModbusDefaultMaxRegistersPerWrite;
    }

    // The declared element count: isArray is the JSON literal true AND arrayLength is an Int32 >= 1 — the rule the
    // Modbus and S7 tag factories apply. Anything else is a scalar to those drivers ⇒ null.
    private static int? ReadArrayLength(JsonElement root) =>
        root.TryGetProperty("isArray", out var isArray) && isArray.ValueKind == JsonValueKind.True
        && root.TryGetProperty("arrayLength", out var length) && length.ValueKind == JsonValueKind.Number
        && length.TryGetInt32(out var count) && count >= 1
            ? count
            : null;

    // Parses the TagConfig root object; a blank / malformed / non-object blob is "no tag" ⇒ false. The clone
    // detaches the element from the disposed document.
    private static bool TryParseObject(string? tagConfig, out JsonElement root)
    {
        root = default;
        if (string.IsNullOrWhiteSpace(tagConfig)) return false;
        try
        {
            using var doc = JsonDocument.Parse(tagConfig);
            if (doc.RootElement.ValueKind != JsonValueKind.Object) return false;
            root = doc.RootElement.Clone();
            return true;
        }
        catch (JsonException)
        {
            return false;
        }
    }

    // An enum-valued field's NAME, or null when absent or not a JSON string — the drivers' strict reads treat a
    // non-string token (a numerically-serialised enum) as absent and apply the field's default.
    private static string? ReadEnumName(JsonElement root, string name) =>
        root.TryGetProperty(name, out var el) && el.ValueKind == JsonValueKind.String ? el.GetString() : null;
}