using System.Collections.Concurrent;
using ScadaLink.Commons.Messages.Health;
using ScadaLink.Commons.Types.Enums;

namespace ScadaLink.HealthMonitoring;

/// <summary>
/// Collects health metrics from all site subsystems.
/// Thread-safe: counters use Interlocked operations, connection/tag data uses ConcurrentDictionary.
/// </summary>
public class SiteHealthCollector : ISiteHealthCollector
{
    private int _scriptErrorCount;
    private int _alarmErrorCount;
    private int _deadLetterCount;
    private readonly ConcurrentDictionary<string, ConnectionHealth> _connectionStatuses = new();
    private readonly ConcurrentDictionary<string, TagResolutionStatus> _tagResolutionCounts = new();
    private IReadOnlyDictionary<string, int> _sfBufferDepths = new Dictionary<string, int>();
    private int _deployedInstanceCount, _enabledInstanceCount, _disabledInstanceCount;
    private volatile bool _isActiveNode;

    /// <summary>
    /// Increment the script error counter. Covers unhandled exceptions,
    /// timeouts, and recursion limit violations.
    /// </summary>
    public void IncrementScriptError()
    {
        Interlocked.Increment(ref _scriptErrorCount);
    }

    /// <summary>
    /// Increment the alarm evaluation error counter.
    /// </summary>
    public void IncrementAlarmError()
    {
        Interlocked.Increment(ref _alarmErrorCount);
    }

    /// <summary>
    /// Increment the dead letter counter for this reporting interval.
    /// </summary>
    public void IncrementDeadLetter()
    {
        Interlocked.Increment(ref _deadLetterCount);
    }

    /// <summary>
    /// Update the health status for a named data connection.
    /// Called by DCL when connection state changes.
    /// </summary>
    public void UpdateConnectionHealth(string connectionName, ConnectionHealth health)
    {
        _connectionStatuses[connectionName] = health;
    }

    /// <summary>
    /// Remove a connection from tracking (e.g., on connection disposal).
    /// </summary>
    public void RemoveConnection(string connectionName)
    {
        _connectionStatuses.TryRemove(connectionName, out _);
        _tagResolutionCounts.TryRemove(connectionName, out _);
    }

    /// <summary>
    /// Update tag resolution counts for a named data connection.
    /// Called by DCL after tag resolution attempts.
    /// </summary>
    public void UpdateTagResolution(string connectionName, int totalSubscribed, int successfullyResolved)
    {
        _tagResolutionCounts[connectionName] = new TagResolutionStatus(totalSubscribed, successfullyResolved);
    }

    /// <summary>
    /// Set the current store-and-forward buffer depths snapshot.
    /// Called before report collection with data from the S&amp;F service.
    /// </summary>
    public void SetStoreAndForwardDepths(IReadOnlyDictionary<string, int> depths)
    {
        _sfBufferDepths = depths;
    }

    /// <summary>
    /// Set the current instance counts.
    /// Called by the Deployment Manager after instance state changes.
    /// </summary>
    public void SetInstanceCounts(int deployed, int enabled, int disabled)
    {
        Interlocked.Exchange(ref _deployedInstanceCount, deployed);
        Interlocked.Exchange(ref _enabledInstanceCount, enabled);
        Interlocked.Exchange(ref _disabledInstanceCount, disabled);
    }

    public void SetActiveNode(bool isActive) => _isActiveNode = isActive;

    public bool IsActiveNode => _isActiveNode;

    /// <summary>
    /// Collect the current health report for the site and reset interval counters.
    /// Connection statuses and tag resolution counts are NOT reset (they reflect current state).
    /// Script errors, alarm errors, and dead letters ARE reset (they are per-interval counts).
    /// </summary>
    public SiteHealthReport CollectReport(string siteId)
    {
        // Atomically read and reset the counters
        var scriptErrors = Interlocked.Exchange(ref _scriptErrorCount, 0);
        var alarmErrors = Interlocked.Exchange(ref _alarmErrorCount, 0);
        var deadLetters = Interlocked.Exchange(ref _deadLetterCount, 0);

        // Snapshot current connection and tag resolution state
        var connectionStatuses = new Dictionary<string, ConnectionHealth>(_connectionStatuses);
        var tagResolution = new Dictionary<string, TagResolutionStatus>(_tagResolutionCounts);

        // Snapshot current S&F buffer depths
        var sfBufferDepths = new Dictionary<string, int>(_sfBufferDepths);

        // Determine node role from active/standby state
        var nodeRole = _isActiveNode ? "Active" : "Standby";

        return new SiteHealthReport(
            SiteId: siteId,
            SequenceNumber: 0, // Caller (HealthReportSender) assigns the sequence number
            ReportTimestamp: DateTimeOffset.UtcNow,
            DataConnectionStatuses: connectionStatuses,
            TagResolutionCounts: tagResolution,
            ScriptErrorCount: scriptErrors,
            AlarmEvaluationErrorCount: alarmErrors,
            StoreAndForwardBufferDepths: sfBufferDepths,
            DeadLetterCount: deadLetters,
            DeployedInstanceCount: _deployedInstanceCount,
            EnabledInstanceCount: _enabledInstanceCount,
            DisabledInstanceCount: _disabledInstanceCount,
            NodeRole: nodeRole);
    }
}