using System.Collections.Immutable;
using System.Diagnostics;
using System.Text.Json.Nodes;
using Microsoft.Extensions.Logging;
using StellaOps.Notify.Engine;
using StellaOps.Notify.Models;
using StellaOps.Notifier.Worker.Storage;
using StellaOps.Notifier.Worker.Correlation;

namespace StellaOps.Notifier.Worker.Simulation;

/// <summary>
/// Default implementation of the notification simulation engine.
/// Dry-runs rules against events to preview what actions would be triggered.
/// </summary>
public sealed class DefaultNotifySimulationEngine : INotifySimulationEngine
{
    private readonly INotifyRuleRepository _ruleRepository;
    private readonly INotifyChannelRepository _channelRepository;
    private readonly INotifyAuditRepository _auditRepository;
    private readonly INotifyRuleEvaluator _ruleEvaluator;
    private readonly INotifyThrottler? _throttler;
    private readonly IQuietHoursEvaluator? _quietHoursEvaluator;
    private readonly TimeProvider _timeProvider;
    private readonly ILogger<DefaultNotifySimulationEngine> _logger;

    private static readonly TimeSpan DefaultThrottleWindow = TimeSpan.FromMinutes(5);

    public DefaultNotifySimulationEngine(
        INotifyRuleRepository ruleRepository,
        INotifyChannelRepository channelRepository,
        INotifyAuditRepository auditRepository,
        INotifyRuleEvaluator ruleEvaluator,
        INotifyThrottler? throttler,
        IQuietHoursEvaluator? quietHoursEvaluator,
        TimeProvider timeProvider,
        ILogger<DefaultNotifySimulationEngine> logger)
    {
        _ruleRepository = ruleRepository ?? throw new ArgumentNullException(nameof(ruleRepository));
        _channelRepository = channelRepository ?? throw new ArgumentNullException(nameof(channelRepository));
        _auditRepository = auditRepository ?? throw new ArgumentNullException(nameof(auditRepository));
        _ruleEvaluator = ruleEvaluator ?? throw new ArgumentNullException(nameof(ruleEvaluator));
        _throttler = throttler;
        _quietHoursEvaluator = quietHoursEvaluator;
        _timeProvider = timeProvider ?? TimeProvider.System;
        _logger = logger ?? throw new ArgumentNullException(nameof(logger));
    }

    public async Task<NotifySimulationResult> SimulateAsync(
        NotifySimulationRequest request,
        CancellationToken cancellationToken = default)
    {
        ArgumentNullException.ThrowIfNull(request);

        var stopwatch = Stopwatch.StartNew();
        var simulationId = Guid.NewGuid().ToString("N");
        var evaluationTime = request.EvaluationTimestamp ?? _timeProvider.GetUtcNow();

        _logger.LogInformation(
            "Starting simulation {SimulationId} for tenant {TenantId}: period {PeriodStart} to {PeriodEnd}",
            simulationId, request.TenantId, request.PeriodStart, request.PeriodEnd);

        // Load rules
        var allRules = await _ruleRepository.ListAsync(request.TenantId, cancellationToken).ConfigureAwait(false);
        var rules = FilterRules(allRules, request.RuleIds);

        _logger.LogDebug(
            "Simulation {SimulationId}: loaded {RuleCount} rules ({FilteredCount} after filtering)",
            simulationId, allRules.Count, rules.Count);

        // Load historical events from audit log
        var auditEntries = await _auditRepository.QueryAsync(
            request.TenantId,
            request.PeriodStart,
            request.MaxEvents,
            cancellationToken).ConfigureAwait(false);

        // Convert audit entries to events for simulation
        var events = ConvertAuditEntriesToEvents(auditEntries, request.PeriodStart, request.PeriodEnd, request.EventKinds);

        _logger.LogDebug(
            "Simulation {SimulationId}: loaded {EventCount} events from audit log",
            simulationId, events.Count);

        // Load channels for action evaluation
        var channels = await LoadChannelsAsync(request.TenantId, rules, cancellationToken).ConfigureAwait(false);

        // Run simulation
        var eventResults = new List<SimulatedEventResult>();
        var ruleSummaries = new Dictionary<string, RuleSummaryBuilder>(StringComparer.Ordinal);

        foreach (var rule in rules)
        {
            ruleSummaries[rule.RuleId] = new RuleSummaryBuilder(rule);
        }

        foreach (var @event in events)
        {
            cancellationToken.ThrowIfCancellationRequested();

            var eventResult = await SimulateEventAsync(
                @event, rules, channels, request, evaluationTime, ruleSummaries, cancellationToken).ConfigureAwait(false);
            eventResults.Add(eventResult);
        }

        stopwatch.Stop();

        var result = new NotifySimulationResult
        {
            SimulationId = simulationId,
            TenantId = request.TenantId,
            SimulatedAt = _timeProvider.GetUtcNow(),
            EventsEvaluated = events.Count,
            RulesEvaluated = rules.Count,
            TotalMatches = eventResults.Sum(e => e.MatchedRules),
            TotalActions = eventResults.Sum(e => e.TriggeredActions),
            EventResults = eventResults.ToImmutableArray(),
            RuleSummaries = ruleSummaries.Values
                .Select(b => b.Build())
                .OrderByDescending(s => s.MatchCount)
                .ToImmutableArray(),
            Duration = stopwatch.Elapsed
        };

        _logger.LogInformation(
            "Completed simulation {SimulationId}: {EventsEvaluated} events, {TotalMatches} matches, {TotalActions} actions in {Duration}ms",
            simulationId, result.EventsEvaluated, result.TotalMatches, result.TotalActions, result.Duration.TotalMilliseconds);

        return result;
    }

    public async Task<SimulatedEventResult> SimulateSingleEventAsync(
        string tenantId,
        JsonObject eventPayload,
        IEnumerable<string>? ruleIds = null,
        DateTimeOffset? evaluationTimestamp = null,
        CancellationToken cancellationToken = default)
    {
        ArgumentException.ThrowIfNullOrWhiteSpace(tenantId);
        ArgumentNullException.ThrowIfNull(eventPayload);

        var evaluationTime = evaluationTimestamp ?? _timeProvider.GetUtcNow();

        // Parse event from payload
        var @event = ParseEventFromPayload(tenantId, eventPayload);

        // Load rules
        var allRules = await _ruleRepository.ListAsync(tenantId, cancellationToken).ConfigureAwait(false);
        var rules = FilterRules(allRules, ruleIds?.ToImmutableArray() ?? []);

        // Load channels
        var channels = await LoadChannelsAsync(tenantId, rules, cancellationToken).ConfigureAwait(false);

        // Create dummy request for simulation
        var request = new NotifySimulationRequest
        {
            TenantId = tenantId,
            PeriodStart = evaluationTime.AddHours(-1),
            PeriodEnd = evaluationTime,
            EvaluationTimestamp = evaluationTime,
            EvaluateThrottling = true,
            EvaluateQuietHours = true,
            IncludeNonMatches = true
        };

        var ruleSummaries = new Dictionary<string, RuleSummaryBuilder>(StringComparer.Ordinal);
        return await SimulateEventAsync(@event, rules, channels, request, evaluationTime, ruleSummaries, cancellationToken)
            .ConfigureAwait(false);
    }

    private async Task<SimulatedEventResult> SimulateEventAsync(
        NotifyEvent @event,
        IReadOnlyList<NotifyRule> rules,
        IReadOnlyDictionary<string, NotifyChannel> channels,
        NotifySimulationRequest request,
        DateTimeOffset evaluationTime,
        Dictionary<string, RuleSummaryBuilder> ruleSummaries,
        CancellationToken cancellationToken)
    {
        var matches = new List<SimulatedRuleMatch>();
        var nonMatches = new List<SimulatedRuleNonMatch>();

        foreach (var rule in rules)
        {
            var outcome = _ruleEvaluator.Evaluate(rule, @event, evaluationTime);

            if (outcome.IsMatch)
            {
                var actionResults = await EvaluateActionsAsync(
                    @event, rule, outcome.Actions, channels, request, evaluationTime, cancellationToken).ConfigureAwait(false);

                var explanations = BuildMatchExplanations(rule, @event);

                matches.Add(new SimulatedRuleMatch
                {
                    RuleId = rule.RuleId,
                    RuleName = rule.Name ?? rule.RuleId,
                    Priority = 0, // NotifyRule doesn't have priority, default to 0
                    MatchedAt = outcome.MatchedAt ?? evaluationTime,
                    Actions = actionResults,
                    MatchExplanations = explanations
                });

                if (ruleSummaries.TryGetValue(rule.RuleId, out var summary))
                {
                    summary.RecordMatch(actionResults.Length);
                }
            }
            else if (request.IncludeNonMatches)
            {
                var explanation = BuildNonMatchExplanation(outcome.Reason ?? "unknown", rule, @event);

                nonMatches.Add(new SimulatedRuleNonMatch
                {
                    RuleId = rule.RuleId,
                    RuleName = rule.Name ?? rule.RuleId,
                    Reason = outcome.Reason ?? "unknown",
                    Explanation = explanation
                });

                if (ruleSummaries.TryGetValue(rule.RuleId, out var summary))
                {
                    summary.RecordNonMatch(outcome.Reason ?? "unknown");
                }
            }
        }

        return new SimulatedEventResult
        {
            EventId = @event.EventId,
            Kind = @event.Kind,
            EventTimestamp = @event.Ts,
            MatchedRules = matches.Count,
            TriggeredActions = matches.Sum(m => m.Actions.Count(a => a.WouldDeliver)),
            Matches = matches.OrderBy(m => m.Priority).ToImmutableArray(),
            NonMatches = nonMatches.ToImmutableArray()
        };
    }

    private async Task<ImmutableArray<SimulatedActionResult>> EvaluateActionsAsync(
        NotifyEvent @event,
        NotifyRule rule,
        ImmutableArray<NotifyRuleAction> actions,
        IReadOnlyDictionary<string, NotifyChannel> channels,
        NotifySimulationRequest request,
        DateTimeOffset evaluationTime,
        CancellationToken cancellationToken)
    {
        var results = new List<SimulatedActionResult>();

        foreach (var action in actions)
        {
            if (!action.Enabled)
            {
                continue;
            }

            var channelId = action.Channel?.Trim() ?? string.Empty;
            channels.TryGetValue(channelId, out var channel);

            var wouldDeliver = true;
            var deliveryExplanation = "Would be delivered successfully";
            string? throttleReason = null;
            string? quietHoursReason = null;
            string? channelBlockReason = null;

            // Check channel availability
            if (channel is null)
            {
                wouldDeliver = false;
                channelBlockReason = $"Channel '{channelId}' not found";
                deliveryExplanation = channelBlockReason;
            }
            else if (!channel.Enabled)
            {
                wouldDeliver = false;
                channelBlockReason = $"Channel '{channelId}' is disabled";
                deliveryExplanation = channelBlockReason;
            }

            // Check throttling
            if (wouldDeliver && request.EvaluateThrottling && _throttler is not null)
            {
                var throttleKey = $"{rule.RuleId}:{action.ActionId}:{@event.Kind}";
                var throttleWindow = action.Throttle is { Ticks: > 0 } ? action.Throttle.Value : DefaultThrottleWindow;
                var throttleResult = await _throttler.CheckAsync(
                    @event.Tenant,
                    throttleKey,
                    throttleWindow,
                    null,
                    cancellationToken).ConfigureAwait(false);

                if (throttleResult.IsThrottled)
                {
                    wouldDeliver = false;
                    throttleReason = $"Would be throttled (key: {throttleKey})";
                    deliveryExplanation = throttleReason;
                }
            }

            // Check quiet hours
            if (wouldDeliver && request.EvaluateQuietHours && _quietHoursEvaluator is not null)
            {
                var quietHoursResult = await _quietHoursEvaluator.EvaluateAsync(
                    @event.Tenant, @event.Kind, cancellationToken).ConfigureAwait(false);

                if (quietHoursResult.IsSuppressed)
                {
                    wouldDeliver = false;
                    quietHoursReason = quietHoursResult.Reason ?? "In quiet hours period";
                    deliveryExplanation = quietHoursReason;
                }
            }

            if (wouldDeliver)
            {
                deliveryExplanation = $"Would deliver to {channel?.Type.ToString() ?? "unknown"} channel '{channelId}'";
                if (!string.IsNullOrWhiteSpace(action.Template))
                {
                    deliveryExplanation += $" using template '{action.Template}'";
                }
            }

            results.Add(new SimulatedActionResult
            {
                ActionId = action.ActionId,
                ChannelId = channelId,
                ChannelType = channel?.Type ?? NotifyChannelType.Custom,
                TemplateId = action.Template,
                WouldDeliver = wouldDeliver,
                DeliveryExplanation = deliveryExplanation,
                ThrottleReason = throttleReason,
                QuietHoursReason = quietHoursReason,
                ChannelBlockReason = channelBlockReason
            });
        }

        return results.ToImmutableArray();
    }

    private static ImmutableArray<string> BuildMatchExplanations(NotifyRule rule, NotifyEvent @event)
    {
        var explanations = new List<string>();
        var match = rule.Match;

        if (!match.EventKinds.IsDefaultOrEmpty)
        {
            explanations.Add($"Event kind '{@event.Kind}' matched filter [{string.Join(", ", match.EventKinds)}]");
        }
        else
        {
            explanations.Add("Event kind matched (no filter specified)");
        }

        if (!match.Namespaces.IsDefaultOrEmpty && !string.IsNullOrWhiteSpace(@event.Scope?.Namespace))
        {
            explanations.Add($"Namespace '{@event.Scope.Namespace}' matched filter");
        }

        if (!match.Repositories.IsDefaultOrEmpty && !string.IsNullOrWhiteSpace(@event.Scope?.Repo))
        {
            explanations.Add($"Repository '{@event.Scope.Repo}' matched filter");
        }

        if (!string.IsNullOrWhiteSpace(match.MinSeverity))
        {
            explanations.Add($"Severity met minimum threshold of '{match.MinSeverity}'");
        }

        if (!match.Labels.IsDefaultOrEmpty)
        {
            explanations.Add($"Labels matched required set: [{string.Join(", ", match.Labels)}]");
        }

        return explanations.ToImmutableArray();
    }

    private static string BuildNonMatchExplanation(string reason, NotifyRule rule, NotifyEvent @event)
    {
        return reason switch
        {
            "rule_disabled" => $"Rule '{rule.Name ?? rule.RuleId}' is disabled",
            "event_kind_mismatch" => $"Event kind '{@event.Kind}' not in rule filter [{string.Join(", ", rule.Match.EventKinds)}]",
            "namespace_mismatch" => $"Namespace '{@event.Scope?.Namespace ?? "(none)"}' not in rule filter [{string.Join(", ", rule.Match.Namespaces)}]",
            "repository_mismatch" => $"Repository '{@event.Scope?.Repo ?? "(none)"}' not in rule filter [{string.Join(", ", rule.Match.Repositories)}]",
            "digest_mismatch" => $"Digest '{@event.Scope?.Digest ?? "(none)"}' not in rule filter",
            "component_mismatch" => "Event component PURLs did not match rule filter",
            "kev_required" => "Rule requires KEV label but event does not have it",
            "label_mismatch" => $"Event labels did not match required set [{string.Join(", ", rule.Match.Labels)}]",
            "severity_below_threshold" => $"Event severity below minimum '{rule.Match.MinSeverity}'",
            "verdict_mismatch" => $"Event verdict not in rule filter [{string.Join(", ", rule.Match.Verdicts)}]",
            "no_enabled_actions" => "Rule has no enabled actions",
            _ => $"Rule did not match: {reason}"
        };
    }

    private static IReadOnlyList<NotifyRule> FilterRules(
        IReadOnlyList<NotifyRule> rules,
        ImmutableArray<string> ruleIds)
    {
        if (ruleIds.IsDefaultOrEmpty)
        {
            return rules.Where(r => r.Enabled).ToList();
        }

        var ruleIdSet = ruleIds.ToHashSet(StringComparer.OrdinalIgnoreCase);
        return rules.Where(r => ruleIdSet.Contains(r.RuleId)).ToList();
    }

    private async Task<IReadOnlyDictionary<string, NotifyChannel>> LoadChannelsAsync(
        string tenantId,
        IReadOnlyList<NotifyRule> rules,
        CancellationToken cancellationToken)
    {
        var channelIds = rules
            .SelectMany(r => r.Actions)
            .Where(a => !string.IsNullOrWhiteSpace(a.Channel))
            .Select(a => a.Channel!.Trim())
            .Distinct(StringComparer.OrdinalIgnoreCase)
            .ToList();

        var channels = new Dictionary<string, NotifyChannel>(StringComparer.OrdinalIgnoreCase);

        foreach (var channelId in channelIds)
        {
            var channel = await _channelRepository.GetAsync(tenantId, channelId, cancellationToken).ConfigureAwait(false);
            if (channel is not null)
            {
                channels[channelId] = channel;
            }
        }

        return channels;
    }

    private static IReadOnlyList<NotifyEvent> ConvertAuditEntriesToEvents(
        IReadOnlyList<NotifyAuditEntry> auditEntries,
        DateTimeOffset periodStart,
        DateTimeOffset periodEnd,
        ImmutableArray<string> eventKinds)
    {
        var kindSet = eventKinds.IsDefaultOrEmpty
            ? null
            : eventKinds.ToHashSet(StringComparer.OrdinalIgnoreCase);

        var events = new List<NotifyEvent>();

        foreach (var entry in auditEntries)
        {
            if (entry.Timestamp < periodStart || entry.Timestamp >= periodEnd)
            {
                continue;
            }

            var eventKind = ExtractEventKindFromAuditEntry(entry);
            if (string.IsNullOrWhiteSpace(eventKind))
            {
                continue;
            }

            if (kindSet is not null && !kindSet.Contains(eventKind))
            {
                continue;
            }

            var eventId = ExtractEventIdFromAuditEntry(entry);
            var payload = ToPayload(entry.Data);

            var @event = NotifyEvent.Create(
                eventId: eventId,
                kind: eventKind,
                tenant: entry.TenantId,
                ts: entry.Timestamp,
                payload: payload);

            events.Add(@event);
        }

        return events;
    }

    private static string? ExtractEventKindFromAuditEntry(NotifyAuditEntry entry)
    {
        // The event kind might be encoded in the action field or payload
        // Action format is typically "event.kind.action" or we look in payload
        var action = entry.Action;

        // Try to extract from action (e.g., "pack.approval.ingested" -> "pack.approval")
        if (!string.IsNullOrWhiteSpace(action))
        {
            var parts = action.Split('.', StringSplitOptions.RemoveEmptyEntries);
            if (parts.Length >= 2)
            {
                return string.Join(".", parts.Take(parts.Length - 1));
            }
        }

        // Try to extract from payload
        if (entry.Data.TryGetValue("Kind", out var kind) ||
            entry.Data.TryGetValue("kind", out kind))
        {
            return kind;
        }

        return null;
    }

    private static Guid ExtractEventIdFromAuditEntry(NotifyAuditEntry entry)
    {
        if (entry.Data.TryGetValue("eventId", out var eventId) &&
            Guid.TryParse(eventId, out var parsed))
        {
            return parsed;
        }

        return Guid.NewGuid();
    }

    private static JsonNode ToPayload(IReadOnlyDictionary<string, string> data)
    {
        var obj = new JsonObject();
        foreach (var (key, value) in data)
        {
            obj[key] = value;
        }
        return obj;
    }

    private static NotifyEvent ParseEventFromPayload(string tenantId, JsonObject payload)
    {
        var eventId = payload.TryGetPropertyValue("eventId", out var idNode) && idNode is JsonValue idValue
            ? (Guid.TryParse(idValue.ToString(), out var id) ? id : Guid.NewGuid())
            : Guid.NewGuid();

        var kind = payload.TryGetPropertyValue("kind", out var kindNode) && kindNode is JsonValue kindValue
            ? kindValue.ToString()
            : "simulation.test";

        var ts = payload.TryGetPropertyValue("ts", out var tsNode) && tsNode is JsonValue tsValue
            && DateTimeOffset.TryParse(tsValue.ToString(), out var timestamp)
            ? timestamp
            : DateTimeOffset.UtcNow;

        var eventPayload = payload.TryGetPropertyValue("payload", out var payloadNode)
            ? payloadNode
            : payload;

        NotifyEventScope? scope = null;
        if (payload.TryGetPropertyValue("scope", out var scopeNode) && scopeNode is JsonObject scopeObj)
        {
            scope = NotifyEventScope.Create(
                @namespace: GetStringProperty(scopeObj, "namespace"),
                repo: GetStringProperty(scopeObj, "repo"),
                digest: GetStringProperty(scopeObj, "digest"),
                component: GetStringProperty(scopeObj, "component"),
                image: GetStringProperty(scopeObj, "image"));
        }

        var attributes = ImmutableDictionary<string, string>.Empty;
        if (payload.TryGetPropertyValue("attributes", out var attrNode) && attrNode is JsonObject attrObj)
        {
            var builder = ImmutableDictionary.CreateBuilder<string, string>(StringComparer.Ordinal);
            foreach (var prop in attrObj)
            {
                if (prop.Value is JsonValue value)
                {
                    builder[prop.Key] = value.ToString();
                }
            }
            attributes = builder.ToImmutable();
        }

        return NotifyEvent.Create(
            eventId: eventId,
            kind: kind,
            tenant: tenantId,
            ts: ts,
            payload: eventPayload,
            scope: scope,
            attributes: attributes);
    }

    private static string? GetStringProperty(JsonObject obj, string name)
    {
        return obj.TryGetPropertyValue(name, out var node) && node is JsonValue value
            ? value.ToString()
            : null;
    }

    private sealed class RuleSummaryBuilder
    {
        private readonly NotifyRule _rule;
        private int _matchCount;
        private int _actionCount;
        private readonly Dictionary<string, int> _nonMatchReasons = new(StringComparer.Ordinal);

        public RuleSummaryBuilder(NotifyRule rule)
        {
            _rule = rule;
        }

        public void RecordMatch(int actions)
        {
            _matchCount++;
            _actionCount += actions;
        }

        public void RecordNonMatch(string reason)
        {
            _nonMatchReasons.TryGetValue(reason, out var count);
            _nonMatchReasons[reason] = count + 1;
        }

        public SimulatedRuleSummary Build()
        {
            return new SimulatedRuleSummary
            {
                RuleId = _rule.RuleId,
                RuleName = _rule.Name ?? _rule.RuleId,
                MatchCount = _matchCount,
                ActionCount = _actionCount,
                NonMatchReasons = _nonMatchReasons.ToImmutableDictionary()
            };
        }
    }
}