using System.Collections.Concurrent;
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 <c>docs/v2/plan.md</c> decision #144 (per-device isolation). Composition from outside-in:
///     <b>Timeout → Retry (when capability permits) → Circuit Breaker (when tier permits) → Bulkhead</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>
/// </remarks>
public sealed class DriverResiliencePipelineBuilder
{
    private readonly ConcurrentDictionary<PipelineKey, ResiliencePipeline> _pipelines = new();
    private readonly TimeProvider _timeProvider;
    private readonly DriverResilienceStatusTracker? _statusTracker;

    /// <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 Polly bulkhead-depth column. Absent tracker means no telemetry (unit tests +
    ///     deployments that don't care about resilience observability).</param>
    public DriverResiliencePipelineBuilder(
        TimeProvider? timeProvider = null,
        DriverResilienceStatusTracker? statusTracker = null)
    {
        _timeProvider = timeProvider ?? TimeProvider.System;
        _statusTracker = statusTracker;
    }

    /// <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>
    public ResiliencePipeline GetOrCreate(
        string driverInstanceId,
        string hostName,
        DriverCapability capability,
        DriverResilienceOptions options)
    {
        ArgumentNullException.ThrowIfNull(options);
        ArgumentException.ThrowIfNullOrWhiteSpace(hostName);

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

    /// <summary>Drop cached pipelines for one driver instance (e.g. on ResilienceConfig change). Test + Admin-reload use.</summary>
    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)
    {
        var policy = options.Resolve(capability);
        var builder = new ResiliencePipelineBuilder { TimeProvider = timeProvider };

        builder.AddTimeout(new TimeoutStrategyOptions
        {
            Timeout = TimeSpan.FromSeconds(policy.TimeoutSeconds),
        });

        if (policy.RetryCount > 0)
        {
            var retryOptions = new RetryStrategyOptions
            {
                MaxRetryAttempts = policy.RetryCount,
                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)
            {
                retryOptions.OnRetry = args =>
                {
                    tracker.RecordFailure(driverInstanceId, hostName, timeProvider.GetUtcNow().UtcDateTime);
                    return default;
                };
            }
            builder.AddRetry(retryOptions);
        }

        if (policy.BreakerFailureThreshold > 0)
        {
            var breakerOptions = new CircuitBreakerStrategyOptions
            {
                FailureRatio = 1.0,
                MinimumThroughput = 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)
            {
                breakerOptions.OnOpened = args =>
                {
                    tracker.RecordBreakerOpen(driverInstanceId, hostName, timeProvider.GetUtcNow().UtcDateTime);
                    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);
                    return default;
                };
            }
            builder.AddCircuitBreaker(breakerOptions);
        }

        return builder.Build();
    }

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