using StackExchange.Redis;

public static class SirsEvaluator
{
    // The four SIRS codes defined by this project's simplified SIRS criteria.
    // Observations for any other code are ignored by the sepsis engine entirely —
    // they pass through to the outbox and Elasticsearch but do not affect SIRS state.
    public static readonly IReadOnlySet<string> SirsCodes =
        new HashSet<string> { "TEMP_C", "HEART_RATE", "RESP_RATE", "WBC_K_UL" };

    // Returns true if the observation value meets the SIRS criterion for its code.
    // These thresholds are clinical parameters, not configuration — changing them
    // requires clinical review, not a config file edit. They live here as named constants.
    public static bool MeetsCriterion(string observationCode, decimal value) =>
        observationCode switch
        {
            // Fever (> 38.3 °C) or hypothermia (< 36.0 °C)
            "TEMP_C"     => value > 38.3m || value < 36.0m,
            // Tachycardia
            "HEART_RATE" => value > 90m,
            // Tachypnea
            "RESP_RATE"  => value > 20m,
            // Leukocytosis or leukopenia
            "WBC_K_UL"   => value > 12.0m || value < 4.0m,
            _             => false
        };

    // Redis key for one SIRS criterion for one encounter.
    public static string CriterionKey(Guid encounterId, string code) =>
        $"sirs:{encounterId}:{code}";

    // All four Redis keys for one encounter — used in MGET to count active criteria.
    // The order is stable so the MGET result array always maps to the same codes.
    public static RedisKey[] AllCriterionKeys(Guid encounterId) =>
        SirsCodes
            .Select(code => (RedisKey)CriterionKey(encounterId, code))
            .ToArray();
}