using System.Diagnostics;
using System.Text.Json;
using System.Text.Json.Serialization;
using Microsoft.Extensions.Logging;

namespace StellaOps.Policy.Engine.Telemetry;

/// <summary>
/// Provides structured timeline events for policy evaluation and decision flows.
/// Events are emitted as structured logs with correlation to traces.
/// </summary>
public sealed class PolicyTimelineEvents
{
    private readonly ILogger<PolicyTimelineEvents> _logger;
    private readonly TimeProvider _timeProvider;

    public PolicyTimelineEvents(ILogger<PolicyTimelineEvents> logger, TimeProvider timeProvider)
    {
        _logger = logger ?? throw new ArgumentNullException(nameof(logger));
        _timeProvider = timeProvider ?? throw new ArgumentNullException(nameof(timeProvider));
    }

    #region Evaluation Flow Events

    /// <summary>
    /// Emits an event when a policy evaluation run starts.
    /// </summary>
    public void EmitRunStarted(string runId, string tenant, string policyId, string policyVersion, string mode)
    {
        var evt = new TimelineEvent
        {
            EventType = TimelineEventType.RunStarted,
            Timestamp = _timeProvider.GetUtcNow(),
            RunId = runId,
            Tenant = tenant,
            PolicyId = policyId,
            PolicyVersion = policyVersion,
            TraceId = Activity.Current?.TraceId.ToString(),
            SpanId = Activity.Current?.SpanId.ToString(),
            Data = new Dictionary<string, object?>
            {
                ["mode"] = mode,
            },
        };

        LogTimelineEvent(evt);
    }

    /// <summary>
    /// Emits an event when a policy evaluation run completes.
    /// </summary>
    public void EmitRunCompleted(
        string runId,
        string tenant,
        string policyId,
        string outcome,
        double durationSeconds,
        int findingsCount,
        string? determinismHash = null)
    {
        var evt = new TimelineEvent
        {
            EventType = TimelineEventType.RunCompleted,
            Timestamp = _timeProvider.GetUtcNow(),
            RunId = runId,
            Tenant = tenant,
            PolicyId = policyId,
            TraceId = Activity.Current?.TraceId.ToString(),
            SpanId = Activity.Current?.SpanId.ToString(),
            Data = new Dictionary<string, object?>
            {
                ["outcome"] = outcome,
                ["duration_seconds"] = durationSeconds,
                ["findings_count"] = findingsCount,
                ["determinism_hash"] = determinismHash,
            },
        };

        LogTimelineEvent(evt);
    }

    /// <summary>
    /// Emits an event when a batch selection phase starts.
    /// </summary>
    public void EmitSelectionStarted(string runId, string tenant, string policyId, int batchNumber)
    {
        var evt = new TimelineEvent
        {
            EventType = TimelineEventType.SelectionStarted,
            Timestamp = _timeProvider.GetUtcNow(),
            RunId = runId,
            Tenant = tenant,
            PolicyId = policyId,
            TraceId = Activity.Current?.TraceId.ToString(),
            SpanId = Activity.Current?.SpanId.ToString(),
            Data = new Dictionary<string, object?>
            {
                ["batch_number"] = batchNumber,
            },
        };

        LogTimelineEvent(evt);
    }

    /// <summary>
    /// Emits an event when a batch selection phase completes.
    /// </summary>
    public void EmitSelectionCompleted(
        string runId,
        string tenant,
        string policyId,
        int batchNumber,
        int tupleCount,
        double durationSeconds)
    {
        var evt = new TimelineEvent
        {
            EventType = TimelineEventType.SelectionCompleted,
            Timestamp = _timeProvider.GetUtcNow(),
            RunId = runId,
            Tenant = tenant,
            PolicyId = policyId,
            TraceId = Activity.Current?.TraceId.ToString(),
            SpanId = Activity.Current?.SpanId.ToString(),
            Data = new Dictionary<string, object?>
            {
                ["batch_number"] = batchNumber,
                ["tuple_count"] = tupleCount,
                ["duration_seconds"] = durationSeconds,
            },
        };

        LogTimelineEvent(evt);
    }

    /// <summary>
    /// Emits an event when batch evaluation starts.
    /// </summary>
    public void EmitEvaluationStarted(string runId, string tenant, string policyId, int batchNumber, int tupleCount)
    {
        var evt = new TimelineEvent
        {
            EventType = TimelineEventType.EvaluationStarted,
            Timestamp = _timeProvider.GetUtcNow(),
            RunId = runId,
            Tenant = tenant,
            PolicyId = policyId,
            TraceId = Activity.Current?.TraceId.ToString(),
            SpanId = Activity.Current?.SpanId.ToString(),
            Data = new Dictionary<string, object?>
            {
                ["batch_number"] = batchNumber,
                ["tuple_count"] = tupleCount,
            },
        };

        LogTimelineEvent(evt);
    }

    /// <summary>
    /// Emits an event when batch evaluation completes.
    /// </summary>
    public void EmitEvaluationCompleted(
        string runId,
        string tenant,
        string policyId,
        int batchNumber,
        int rulesEvaluated,
        int rulesFired,
        double durationSeconds)
    {
        var evt = new TimelineEvent
        {
            EventType = TimelineEventType.EvaluationCompleted,
            Timestamp = _timeProvider.GetUtcNow(),
            RunId = runId,
            Tenant = tenant,
            PolicyId = policyId,
            TraceId = Activity.Current?.TraceId.ToString(),
            SpanId = Activity.Current?.SpanId.ToString(),
            Data = new Dictionary<string, object?>
            {
                ["batch_number"] = batchNumber,
                ["rules_evaluated"] = rulesEvaluated,
                ["rules_fired"] = rulesFired,
                ["duration_seconds"] = durationSeconds,
            },
        };

        LogTimelineEvent(evt);
    }

    #endregion

    #region Decision Flow Events

    /// <summary>
    /// Emits an event when a rule matches during evaluation.
    /// </summary>
    public void EmitRuleMatched(
        string runId,
        string tenant,
        string policyId,
        string ruleId,
        string findingKey,
        string? severity = null)
    {
        var evt = new TimelineEvent
        {
            EventType = TimelineEventType.RuleMatched,
            Timestamp = _timeProvider.GetUtcNow(),
            RunId = runId,
            Tenant = tenant,
            PolicyId = policyId,
            TraceId = Activity.Current?.TraceId.ToString(),
            SpanId = Activity.Current?.SpanId.ToString(),
            Data = new Dictionary<string, object?>
            {
                ["rule_id"] = ruleId,
                ["finding_key"] = findingKey,
                ["severity"] = severity,
            },
        };

        LogTimelineEvent(evt);
    }

    /// <summary>
    /// Emits an event when a VEX override is applied.
    /// </summary>
    public void EmitVexOverrideApplied(
        string runId,
        string tenant,
        string policyId,
        string findingKey,
        string vendor,
        string status,
        string? justification = null)
    {
        var evt = new TimelineEvent
        {
            EventType = TimelineEventType.VexOverrideApplied,
            Timestamp = _timeProvider.GetUtcNow(),
            RunId = runId,
            Tenant = tenant,
            PolicyId = policyId,
            TraceId = Activity.Current?.TraceId.ToString(),
            SpanId = Activity.Current?.SpanId.ToString(),
            Data = new Dictionary<string, object?>
            {
                ["finding_key"] = findingKey,
                ["vendor"] = vendor,
                ["status"] = status,
                ["justification"] = justification,
            },
        };

        LogTimelineEvent(evt);
    }

    /// <summary>
    /// Emits an event when a final verdict is determined for a finding.
    /// </summary>
    public void EmitVerdictDetermined(
        string runId,
        string tenant,
        string policyId,
        string findingKey,
        string verdict,
        string severity,
        string? reachabilityState = null,
        IReadOnlyList<string>? contributingRules = null)
    {
        var evt = new TimelineEvent
        {
            EventType = TimelineEventType.VerdictDetermined,
            Timestamp = _timeProvider.GetUtcNow(),
            RunId = runId,
            Tenant = tenant,
            PolicyId = policyId,
            TraceId = Activity.Current?.TraceId.ToString(),
            SpanId = Activity.Current?.SpanId.ToString(),
            Data = new Dictionary<string, object?>
            {
                ["finding_key"] = findingKey,
                ["verdict"] = verdict,
                ["severity"] = severity,
                ["reachability_state"] = reachabilityState,
                ["contributing_rules"] = contributingRules,
            },
        };

        LogTimelineEvent(evt);
    }

    /// <summary>
    /// Emits an event when materialization of findings starts.
    /// </summary>
    public void EmitMaterializationStarted(string runId, string tenant, string policyId, int findingsCount)
    {
        var evt = new TimelineEvent
        {
            EventType = TimelineEventType.MaterializationStarted,
            Timestamp = _timeProvider.GetUtcNow(),
            RunId = runId,
            Tenant = tenant,
            PolicyId = policyId,
            TraceId = Activity.Current?.TraceId.ToString(),
            SpanId = Activity.Current?.SpanId.ToString(),
            Data = new Dictionary<string, object?>
            {
                ["findings_count"] = findingsCount,
            },
        };

        LogTimelineEvent(evt);
    }

    /// <summary>
    /// Emits an event when materialization of findings completes.
    /// </summary>
    public void EmitMaterializationCompleted(
        string runId,
        string tenant,
        string policyId,
        int findingsWritten,
        int findingsUpdated,
        double durationSeconds)
    {
        var evt = new TimelineEvent
        {
            EventType = TimelineEventType.MaterializationCompleted,
            Timestamp = _timeProvider.GetUtcNow(),
            RunId = runId,
            Tenant = tenant,
            PolicyId = policyId,
            TraceId = Activity.Current?.TraceId.ToString(),
            SpanId = Activity.Current?.SpanId.ToString(),
            Data = new Dictionary<string, object?>
            {
                ["findings_written"] = findingsWritten,
                ["findings_updated"] = findingsUpdated,
                ["duration_seconds"] = durationSeconds,
            },
        };

        LogTimelineEvent(evt);
    }

    #endregion

    #region Error Events

    /// <summary>
    /// Emits an event when an error occurs during evaluation.
    /// </summary>
    public void EmitError(
        string runId,
        string tenant,
        string policyId,
        string errorCode,
        string errorMessage,
        string? phase = null)
    {
        var evt = new TimelineEvent
        {
            EventType = TimelineEventType.Error,
            Timestamp = _timeProvider.GetUtcNow(),
            RunId = runId,
            Tenant = tenant,
            PolicyId = policyId,
            TraceId = Activity.Current?.TraceId.ToString(),
            SpanId = Activity.Current?.SpanId.ToString(),
            Data = new Dictionary<string, object?>
            {
                ["error_code"] = errorCode,
                ["error_message"] = errorMessage,
                ["phase"] = phase,
            },
        };

        LogTimelineEvent(evt, LogLevel.Error);
    }

    /// <summary>
    /// Emits an event when a determinism violation is detected.
    /// </summary>
    public void EmitDeterminismViolation(
        string runId,
        string tenant,
        string policyId,
        string violationType,
        string details)
    {
        var evt = new TimelineEvent
        {
            EventType = TimelineEventType.DeterminismViolation,
            Timestamp = _timeProvider.GetUtcNow(),
            RunId = runId,
            Tenant = tenant,
            PolicyId = policyId,
            TraceId = Activity.Current?.TraceId.ToString(),
            SpanId = Activity.Current?.SpanId.ToString(),
            Data = new Dictionary<string, object?>
            {
                ["violation_type"] = violationType,
                ["details"] = details,
            },
        };

        LogTimelineEvent(evt, LogLevel.Warning);
    }

    #endregion

    private void LogTimelineEvent(TimelineEvent evt, LogLevel level = LogLevel.Information)
    {
        _logger.Log(
            level,
            "PolicyTimeline: {EventType} | run={RunId} tenant={Tenant} policy={PolicyId} trace={TraceId} span={SpanId} data={Data}",
            evt.EventType,
            evt.RunId,
            evt.Tenant,
            evt.PolicyId,
            evt.TraceId,
            evt.SpanId,
            JsonSerializer.Serialize(evt.Data, TimelineEventJsonContext.Default.DictionaryStringObject));
    }
}

/// <summary>
/// Types of timeline events emitted during policy evaluation.
/// </summary>
public enum TimelineEventType
{
    RunStarted,
    RunCompleted,
    SelectionStarted,
    SelectionCompleted,
    EvaluationStarted,
    EvaluationCompleted,
    RuleMatched,
    VexOverrideApplied,
    VerdictDetermined,
    MaterializationStarted,
    MaterializationCompleted,
    Error,
    DeterminismViolation,
}

/// <summary>
/// Represents a timeline event for policy evaluation flows.
/// </summary>
public sealed record TimelineEvent
{
    public required TimelineEventType EventType { get; init; }
    public required DateTimeOffset Timestamp { get; init; }
    public required string RunId { get; init; }
    public required string Tenant { get; init; }
    public required string PolicyId { get; init; }
    public string? PolicyVersion { get; init; }
    public string? TraceId { get; init; }
    public string? SpanId { get; init; }
    public Dictionary<string, object?>? Data { get; init; }
}

[JsonSerializable(typeof(Dictionary<string, object?>))]
[JsonSourceGenerationOptions(WriteIndented = false)]
internal partial class TimelineEventJsonContext : JsonSerializerContext
{
}