Joseph Doherty
69 lines
3.0 KiB
C#
69 lines
3.0 KiB
C#
using Serilog;
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using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
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using ZB.MOM.WW.OtOpcUa.Core.Scripting;
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namespace ZB.MOM.WW.OtOpcUa.Core.ScriptedAlarms;
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/// <summary>
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/// <see cref="ScriptContext"/> subclass for alarm predicate evaluation. Reads from
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/// the engine's shared tag cache (driver + virtual tags), writes are rejected —
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/// predicates must be side-effect free so their output doesn't depend on evaluation
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/// order or drive cascade behavior.
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/// </summary>
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/// <remarks>
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/// Per Phase 7 plan Shape A decision, alarm scripts are one-script-per-alarm
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/// returning <c>bool</c>. They read any tag they want but should not write
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/// anything (the owning alarm's state is tracked by the engine, not the script).
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/// </remarks>
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public sealed class AlarmPredicateContext : ScriptContext
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{
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private readonly IReadOnlyDictionary<string, DataValueSnapshot> _readCache;
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private readonly Func<DateTime> _clock;
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/// <summary>Initializes a new instance of the <see cref="AlarmPredicateContext"/> class.</summary>
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/// <param name="readCache">The cached read values from tags.</param>
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/// <param name="logger">The logger for diagnostics.</param>
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/// <param name="clock">Optional custom clock for testing.</param>
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public AlarmPredicateContext(
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IReadOnlyDictionary<string, DataValueSnapshot> readCache,
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ILogger logger,
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Func<DateTime>? clock = null)
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{
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_readCache = readCache ?? throw new ArgumentNullException(nameof(readCache));
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Logger = logger ?? throw new ArgumentNullException(nameof(logger));
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_clock = clock ?? (() => DateTime.UtcNow);
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}
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/// <summary>Gets a tag value from the read cache.</summary>
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/// <param name="path">The tag path to retrieve.</param>
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/// <inheritdoc />
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public override DataValueSnapshot GetTag(string path)
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{
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if (string.IsNullOrWhiteSpace(path))
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return new DataValueSnapshot(null, 0x80340000u, null, _clock());
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return _readCache.TryGetValue(path, out var v)
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? v
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: new DataValueSnapshot(null, 0x80340000u, null, _clock());
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}
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/// <summary>Rejects virtual tag writes for pure predicate semantics.</summary>
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/// <param name="path">The virtual tag path.</param>
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/// <param name="value">The value to write.</param>
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/// <inheritdoc />
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public override void SetVirtualTag(string path, object? value)
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{
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// Predicates must be pure — writing from an alarm script couples alarm state to
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// virtual-tag state in a way that's near-impossible to reason about. Rejected
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// at runtime with a clear message; operators see it in the scripts-*.log.
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throw new InvalidOperationException(
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"Alarm predicate scripts cannot write to virtual tags. Move the write logic " +
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"into a virtual tag whose value the alarm predicate then reads.");
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}
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/// <inheritdoc />
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public override DateTime Now => _clock();
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/// <inheritdoc />
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public override ILogger Logger { get; }
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}
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