using System.Collections.Concurrent;
using Microsoft.Extensions.Logging;
using Polly;
using Polly.CircuitBreaker;
using Polly.Retry;
using Polly.Timeout;
using ZB.MOM.WW.OtOpcUa.Core.Abstractions;

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

/// <summary>
///     Builds and caches Polly resilience pipelines keyed on
///     <c>(DriverInstanceId, HostName, DriverCapability)</c>. One dead PLC behind a multi-device
///     driver cannot open the circuit breaker for healthy sibling hosts.
/// </summary>
/// <remarks>
///     Per-device isolation. Composition from outside-in:
///     <b>Timeout → Retry (when capability permits) → Circuit Breaker (when tier permits)</b>.
///
///     <para>Pipeline resolution is lock-free on the hot path: the inner
///     <see cref="ConcurrentDictionary{TKey,TValue}"/> caches a <see cref="ResiliencePipeline"/> per key;
///     first-call cost is one <see cref="ResiliencePipelineBuilder"/>.Build. Thereafter reads are O(1).</para>
///
///     <para><b>Never-throws invariant (01/S-6):</b> <see cref="Build"/> clamps every policy value to
///     <see cref="ResiliencePolicyRanges"/> before constructing strategy options, so a hostile
///     <see cref="DriverResilienceOptions"/> (constructed directly, bypassing the parser) can never make
///     the memoizing <c>GetOrAdd</c> factory throw Polly's <c>ValidationException</c> — which would
///     otherwise brick every capability call for that key.</para>
/// </remarks>
public sealed class DriverResiliencePipelineBuilder
{
    private readonly ConcurrentDictionary<PipelineKey, ResiliencePipeline> _pipelines = new();
    private readonly TimeProvider _timeProvider;
    private readonly DriverResilienceStatusTracker? _statusTracker;
    private readonly ILogger? _logger;

    /// <summary>Construct with the ambient clock (use <see cref="TimeProvider.System"/> in prod).</summary>
    /// <param name="timeProvider">Clock source for pipeline timeouts + breaker sampling. Defaults to system.</param>
    /// <param name="statusTracker">When non-null, every built pipeline wires Polly telemetry into
    ///     the tracker — retries increment <c>ConsecutiveFailures</c>, breaker-open stamps
    ///     <c>LastBreakerOpenUtc</c>, breaker-close resets failures. Feeds Admin <c>/hosts</c> +
    ///     the in-flight-call-depth column. Absent tracker means no telemetry (unit tests +
    ///     deployments that don't care about resilience observability).</param>
    /// <param name="logger">When non-null, retry / circuit-breaker-open / breaker-close events are
    ///     logged (instance + host + capability + attempt/exception). This is the operator-facing
    ///     observability surface for the resilience pipeline until the Admin <c>/hosts</c> reader
    ///     (Phase 6.1 Stream E.2/E.3) ships — without it the pipeline runs silently. Absent logger =
    ///     no resilience logging (unit tests).</param>
    public DriverResiliencePipelineBuilder(
        TimeProvider? timeProvider = null,
        DriverResilienceStatusTracker? statusTracker = null,
        ILogger? logger = null)
    {
        _timeProvider = timeProvider ?? TimeProvider.System;
        _statusTracker = statusTracker;
        _logger = logger;
    }

    /// <summary>
    ///     Get or build the pipeline for a given <c>(driver instance, host, capability)</c> triple.
    ///     Calls with the same key + same options reuse the same pipeline instance; the first caller
    ///     wins if a race occurs (both pipelines would be behaviourally identical).
    /// </summary>
    /// <param name="driverInstanceId">DriverInstance primary key — opaque to this layer.</param>
    /// <param name="hostName">
    ///     Host the call targets. For single-host drivers (Galaxy, some OPC UA Client configs) pass the
    ///     driver's canonical host string. For multi-host drivers (Modbus with N PLCs), pass the
    ///     specific PLC so one dead PLC doesn't poison healthy siblings.
    /// </param>
    /// <param name="capability">Which capability surface is being called.</param>
    /// <param name="options">Per-driver-instance options (tier + per-capability overrides).</param>
    /// <param name="optionsGeneration">
    ///     Monotonic options epoch stamped by <see cref="DriverCapabilityInvokerFactory"/> per invoker
    ///     (01/S-7). Part of the cache key so a lingering old child's post-invalidate re-cache lands under
    ///     its OWN (old) generation — a key the new invoker's generation never reads. Defaults to 0 so
    ///     every existing caller/test compiles unchanged.
    /// </param>
    /// <returns>The cached or newly built resilience pipeline for the key.</returns>
    public ResiliencePipeline GetOrCreate(
        string driverInstanceId,
        string hostName,
        DriverCapability capability,
        DriverResilienceOptions options,
        long optionsGeneration = 0)
    {
        ArgumentNullException.ThrowIfNull(options);
        ArgumentException.ThrowIfNullOrWhiteSpace(hostName);

        var key = new PipelineKey(driverInstanceId, hostName, capability, optionsGeneration);
        return _pipelines.GetOrAdd(key, static (k, state) => Build(
                k.DriverInstanceId, k.HostName, state.capability, state.options, state.timeProvider, state.tracker, state.logger),
            (capability, options, timeProvider: _timeProvider, tracker: _statusTracker, logger: _logger));
    }

    /// <summary>
    ///     Drop cached pipelines for one driver instance (e.g. on ResilienceConfig change), across ALL
    ///     option generations. With generation-keyed entries (01/S-7) correctness no longer depends on this
    ///     sweep — a stale-epoch re-cache is already unreachable by the new generation — but it bounds the
    ///     cache by clearing lingering old-generation entries on the next respawn. Test + Admin-reload use.
    /// </summary>
    /// <param name="driverInstanceId">The driver instance ID whose pipelines should be invalidated.</param>
    /// <returns>The number of pipelines removed.</returns>
    public int Invalidate(string driverInstanceId)
    {
        var removed = 0;
        foreach (var key in _pipelines.Keys)
        {
            if (key.DriverInstanceId == driverInstanceId && _pipelines.TryRemove(key, out _))
                removed++;
        }
        return removed;
    }

    /// <summary>Snapshot of the current number of cached pipelines. For diagnostics only.</summary>
    public int CachedPipelineCount => _pipelines.Count;

    private static ResiliencePipeline Build(
        string driverInstanceId,
        string hostName,
        DriverCapability capability,
        DriverResilienceOptions options,
        TimeProvider timeProvider,
        DriverResilienceStatusTracker? tracker,
        ILogger? logger)
    {
        var policy = options.Resolve(capability);
        var builder = new ResiliencePipelineBuilder { TimeProvider = timeProvider };

        // Belt-and-braces: clamp the resolved policy to ResiliencePolicyRanges so building a pipeline can
        // NEVER throw Polly's ValidationException (01/S-6). The parser already clamps every JSON→options
        // funnel, but DriverResilienceOptions is a public record constructible by paths that never traverse
        // the parser (tests today; any future caller), so this makes "a pipeline build never throws" a
        // builder invariant. Three integer ops once per pipeline build (not per call).
        var timeoutSeconds = Math.Clamp(
            policy.TimeoutSeconds, ResiliencePolicyRanges.MinTimeoutSeconds, ResiliencePolicyRanges.MaxTimeoutSeconds);
        builder.AddTimeout(new TimeoutStrategyOptions
        {
            Timeout = TimeSpan.FromSeconds(timeoutSeconds),
        });

        if (policy.RetryCount > 0)
        {
            var retryOptions = new RetryStrategyOptions
            {
                MaxRetryAttempts = Math.Min(policy.RetryCount, ResiliencePolicyRanges.MaxRetryCount),
                BackoffType = DelayBackoffType.Exponential,
                UseJitter = true,
                Delay = TimeSpan.FromMilliseconds(100),
                MaxDelay = TimeSpan.FromSeconds(5),
                ShouldHandle = new PredicateBuilder().Handle<Exception>(ex => ex is not OperationCanceledException),
            };
            if (tracker is not null || logger is not null)
            {
                retryOptions.OnRetry = args =>
                {
                    tracker?.RecordFailure(driverInstanceId, hostName, timeProvider.GetUtcNow().UtcDateTime);
                    logger?.LogWarning(
                        "Driver resilience retry: instance={DriverInstanceId} host={HostName} capability={Capability} attempt={Attempt}: {Reason}",
                        driverInstanceId, hostName, capability, args.AttemptNumber, args.Outcome.Exception?.Message ?? "unknown");
                    return default;
                };
            }
            builder.AddRetry(retryOptions);
        }

        if (policy.BreakerFailureThreshold > 0)
        {
            var breakerOptions = new CircuitBreakerStrategyOptions
            {
                FailureRatio = 1.0,
                MinimumThroughput = Math.Max(ResiliencePolicyRanges.MinEnabledBreakerFailureThreshold, policy.BreakerFailureThreshold),
                SamplingDuration = TimeSpan.FromSeconds(30),
                BreakDuration = TimeSpan.FromSeconds(15),
                ShouldHandle = new PredicateBuilder().Handle<Exception>(ex => ex is not OperationCanceledException),
            };
            if (tracker is not null || logger is not null)
            {
                breakerOptions.OnOpened = args =>
                {
                    tracker?.RecordBreakerOpen(driverInstanceId, hostName, timeProvider.GetUtcNow().UtcDateTime);
                    logger?.LogWarning(
                        "Driver resilience circuit-breaker OPENED: instance={DriverInstanceId} host={HostName} capability={Capability} breakDuration={BreakDuration}: {Reason}",
                        driverInstanceId, hostName, capability, args.BreakDuration, args.Outcome.Exception?.Message ?? "unknown");
                    return default;
                };
                breakerOptions.OnClosed = args =>
                {
                    // Closing the breaker means the target recovered — reset the consecutive-
                    // failure counter so Admin UI stops flashing red for this host.
                    tracker?.RecordSuccess(driverInstanceId, hostName, timeProvider.GetUtcNow().UtcDateTime);
                    logger?.LogInformation(
                        "Driver resilience circuit-breaker closed (recovered): instance={DriverInstanceId} host={HostName} capability={Capability}",
                        driverInstanceId, hostName, capability);
                    return default;
                };
            }
            builder.AddCircuitBreaker(breakerOptions);
        }

        return builder.Build();
    }

    private readonly record struct PipelineKey(string DriverInstanceId, string HostName, DriverCapability Capability, long Generation);
}