feature: Trend Detection & Alert Suppression Windows
This commit is contained in:
voltsrage
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using StackExchange.Redis;
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public static class TrendCalculator
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{
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// NEWS2-relevant codes that support trend detection.
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public static readonly IReadOnlyList<string> TrendCodes = new[]
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{
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"HEART_RATE", "RESP_RATE", "SYSTOLIC_BP", "TEMP_C", "SPO2"
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};
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public static bool IsTrendCode(string observationCode) =>
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TrendCodes.Contains(observationCode);
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public static string HistoryKey(Guid encounterId, string code) =>
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$"trend:{encounterId}:{code}";
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public static RedisKey[] AllHistoryKeys(Guid encounterId) =>
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TrendCodes.Select(c => (RedisKey)HistoryKey(encounterId, c)).ToArray();
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/// <summary>
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/// Computes rate of change (units per minute) between the oldest and newest
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/// entries within the window. Returns null if fewer than 2 entries or window exceeded.
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/// </summary>
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public static decimal? ComputeRatePerMinute(
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IReadOnlyList<TrendHistoryEntry> entries,
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int windowMinutes)
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{
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if (entries.Count < 2) return null;
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var newest = entries[^1];
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var oldest = entries[0];
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var deltaMinutes = (newest.RecordedAt - oldest.RecordedAt).TotalMinutes;
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if (deltaMinutes <= 0 || deltaMinutes > windowMinutes) return null;
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return (newest.Value - oldest.Value) / (decimal)deltaMinutes;
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}
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/// <summary>
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/// Returns true if the rate exceeds the configured threshold.
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/// For SPO2 and SYSTOLIC_BP, checks negative rate (decline) as clinically significant.
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/// </summary>
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public static bool ExceedsThreshold(
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string observationCode,
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decimal ratePerMinute,
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decimal thresholdPerMinute) =>
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observationCode switch
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{
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"SPO2" or "SYSTOLIC_BP" => ratePerMinute <= -thresholdPerMinute,
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_ => ratePerMinute >= thresholdPerMinute
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};
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public static string DescribeTrend(
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string observationCode, decimal ratePerMinute, decimal currentValue) =>
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observationCode switch
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{
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"SPO2" or "SYSTOLIC_BP" =>
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$"Rapid decline: {observationCode} falling at {Math.Abs(ratePerMinute):F2}/min (current {currentValue})",
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_ =>
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$"Rapid rise: {observationCode} rising at {ratePerMinute:F2}/min (current {currentValue})"
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};
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}
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@@ -0,0 +1,152 @@
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using System.Text.Json;
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using Microsoft.EntityFrameworkCore;
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using Microsoft.Extensions.Options;
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using Prometheus;
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using StackExchange.Redis;
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public class TrendDetector
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{
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private readonly IConnectionMultiplexer _redis;
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private readonly IServiceProvider _services;
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private readonly TrendDetectionOptions _options;
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private readonly ClinicalMetrics _metrics;
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private readonly ILogger<TrendDetector> _logger;
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public TrendDetector(
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ILogger<TrendDetector> logger,
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ClinicalMetrics metrics,
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IServiceProvider services,
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IConnectionMultiplexer redis,
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IOptions<TrendDetectionOptions> options)
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{
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_logger = logger;
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_metrics = metrics;
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_services = services;
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_redis = redis;
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_options = options.Value;
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}
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public async Task<TrendResult> ProcessObservationAsync(
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Guid encounterId,
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Guid patientId,
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string observationCode,
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decimal value,
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DateTimeOffset recordedAt,
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CancellationToken ct = default)
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{
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if (!TrendCalculator.IsTrendCode(observationCode))
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return new TrendResult(TrendOutcome.NotTrendCode);
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using var timer = _metrics.TrendAnalysisDuration.NewTimer();
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var cache = _redis.GetDatabase();
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var key = TrendCalculator.HistoryKey(encounterId, observationCode);
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// Append new entry to history list
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var entry = new TrendHistoryEntry(value, recordedAt);
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var historyJson = await cache.StringGetAsync(key);
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var history = historyJson.HasValue
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? JsonSerializer.Deserialize<List<TrendHistoryEntry>>(historyJson!) ?? new()
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: new List<TrendHistoryEntry>();
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history.Add(entry);
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// Trim to max entries and evict entries outside window
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var cutoff = recordedAt.AddMinutes(-_options.WindowMinutes);
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history = history
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.Where(e => e.RecordedAt >= cutoff)
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.TakeLast(_options.MaxHistoryEntries)
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.ToList();
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await cache.StringSetAsync(
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key,
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JsonSerializer.Serialize(history),
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TimeSpan.FromSeconds(_options.HistoryTtlSeconds));
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if (history.Count < 2)
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return new TrendResult(TrendOutcome.InsufficientHistory, observationCode);
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var rate = TrendCalculator.ComputeRatePerMinute(history, _options.WindowMinutes);
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if (rate is null)
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return new TrendResult(TrendOutcome.InsufficientHistory, observationCode);
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if (!_options.RateThresholdsPerMinute.TryGetValue(observationCode, out var threshold))
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return new TrendResult(TrendOutcome.Stable, observationCode, rate);
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if (!TrendCalculator.ExceedsThreshold(observationCode, rate.Value, threshold))
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return new TrendResult(TrendOutcome.Stable, observationCode, rate);
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var details = TrendCalculator.DescribeTrend(observationCode, rate.Value, value);
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var created = await TryCreateAlertAsync(
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encounterId, patientId, observationCode, details, rate.Value, ct);
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return new TrendResult(
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created ? TrendOutcome.RapidDeterioration : TrendOutcome.AlertAlreadyOpen,
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observationCode, rate, created);
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}
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private async Task<bool> TryCreateAlertAsync(
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Guid encounterId, Guid patientId,
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string observationCode, string details, decimal ratePerMinute,
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CancellationToken ct)
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{
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using var scope = _services.CreateScope();
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var db = scope.ServiceProvider.GetRequiredService<AppDbContext>();
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await using var tx = await db.Database.BeginTransactionAsync(ct);
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var alertId = Guid.NewGuid();
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var triggeredAt = DateTimeOffset.UtcNow;
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var fullDetails = $"{details} — velocity {ratePerMinute:F2}/min over {_options.WindowMinutes}min window.";
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var affected = await db.Database.ExecuteSqlInterpolatedAsync($"""
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INSERT INTO clinical_alerts
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(id, encounter_id, patient_id, alert_type, severity, details, status, triggered_at)
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SELECT {alertId}, {encounterId}, {patientId},
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'RAPID_DETERIORATION', 'WARNING', {fullDetails}, 'OPEN', {triggeredAt}
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WHERE NOT EXISTS (
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SELECT 1 FROM clinical_alerts
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WHERE encounter_id = {encounterId}
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AND alert_type = 'RAPID_DETERIORATION'
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AND details LIKE {$"%{observationCode}%"}
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AND status IN ('OPEN', 'ESCALATED')
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)
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""", ct);
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if (affected == 0)
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{
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await tx.RollbackAsync(ct);
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return false;
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}
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db.OutboxEvents.Add(new OutboxEvent
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{
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Id = Guid.NewGuid(),
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Topic = "alert.generated",
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Payload = JsonSerializer.Serialize(new
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{
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alertId,
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encounterId,
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patientId,
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alertType = "RAPID_DETERIORATION",
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severity = "Warning",
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details = fullDetails,
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triggeredAt,
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observationCode,
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ratePerMinute,
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partitionKey = encounterId.ToString()
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}),
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PartitionKey = encounterId.ToString(),
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CreatedAt = DateTimeOffset.UtcNow
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});
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await db.SaveChangesAsync(ct);
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await tx.CommitAsync(ct);
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_metrics.TrendAlertsTotal.WithLabels(observationCode).Inc();
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_metrics.ClinicalAlertsTotal
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.WithLabels("RAPID_DETERIORATION", "Warning").Inc();
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return true;
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}
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}
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