using System.Collections.Immutable;
using System.Security.Cryptography;
using System.Text;
using System.Text.Json.Serialization;

namespace StellaOps.Policy.Engine.Events;

/// <summary>
/// Type of policy effective event.
/// </summary>
[JsonConverter(typeof(JsonStringEnumConverter<PolicyEffectiveEventType>))]
public enum PolicyEffectiveEventType
{
    /// <summary>Policy decision changed for a subject.</summary>
    [JsonPropertyName("policy.effective.updated")]
    EffectiveUpdated,

    /// <summary>Policy decision added for new subject.</summary>
    [JsonPropertyName("policy.effective.added")]
    EffectiveAdded,

    /// <summary>Policy decision removed (subject no longer affected).</summary>
    [JsonPropertyName("policy.effective.removed")]
    EffectiveRemoved,

    /// <summary>Batch re-evaluation completed.</summary>
    [JsonPropertyName("policy.effective.batch_completed")]
    BatchCompleted
}

/// <summary>
/// Base class for policy effective events.
/// </summary>
public abstract record PolicyEffectiveEvent(
    [property: JsonPropertyName("event_id")] string EventId,
    [property: JsonPropertyName("event_type")] PolicyEffectiveEventType EventType,
    [property: JsonPropertyName("tenant_id")] string TenantId,
    [property: JsonPropertyName("timestamp")] DateTimeOffset Timestamp,
    [property: JsonPropertyName("correlation_id")] string? CorrelationId);

/// <summary>
/// Event emitted when a policy decision is updated for a subject.
/// </summary>
public sealed record PolicyEffectiveUpdatedEvent(
    string EventId,
    string TenantId,
    DateTimeOffset Timestamp,
    string? CorrelationId,
    [property: JsonPropertyName("pack_id")] string PackId,
    [property: JsonPropertyName("pack_version")] int PackVersion,
    [property: JsonPropertyName("subject_purl")] string SubjectPurl,
    [property: JsonPropertyName("advisory_id")] string AdvisoryId,
    [property: JsonPropertyName("trigger_type")] string TriggerType,
    [property: JsonPropertyName("diff")] PolicyDecisionDiff Diff)
    : PolicyEffectiveEvent(EventId, PolicyEffectiveEventType.EffectiveUpdated, TenantId, Timestamp, CorrelationId);

/// <summary>
/// Diff metadata for policy decision changes.
/// </summary>
public sealed record PolicyDecisionDiff(
    [property: JsonPropertyName("old_status")] string? OldStatus,
    [property: JsonPropertyName("new_status")] string NewStatus,
    [property: JsonPropertyName("old_severity")] string? OldSeverity,
    [property: JsonPropertyName("new_severity")] string? NewSeverity,
    [property: JsonPropertyName("old_rule")] string? OldRule,
    [property: JsonPropertyName("new_rule")] string? NewRule,
    [property: JsonPropertyName("old_priority")] int? OldPriority,
    [property: JsonPropertyName("new_priority")] int? NewPriority,
    [property: JsonPropertyName("status_changed")] bool StatusChanged,
    [property: JsonPropertyName("severity_changed")] bool SeverityChanged,
    [property: JsonPropertyName("rule_changed")] bool RuleChanged,
    [property: JsonPropertyName("annotations_added")] ImmutableArray<string> AnnotationsAdded,
    [property: JsonPropertyName("annotations_removed")] ImmutableArray<string> AnnotationsRemoved)
{
    /// <summary>
    /// Creates a diff between two policy decisions.
    /// </summary>
    public static PolicyDecisionDiff Create(
        string? oldStatus, string newStatus,
        string? oldSeverity, string? newSeverity,
        string? oldRule, string? newRule,
        int? oldPriority, int? newPriority,
        ImmutableDictionary<string, string>? oldAnnotations,
        ImmutableDictionary<string, string>? newAnnotations)
    {
        var oldKeys = oldAnnotations?.Keys ?? Enumerable.Empty<string>();
        var newKeys = newAnnotations?.Keys ?? Enumerable.Empty<string>();

        var annotationsAdded = newKeys
            .Where(k => oldAnnotations?.ContainsKey(k) != true)
            .OrderBy(k => k)
            .ToImmutableArray();

        var annotationsRemoved = oldKeys
            .Where(k => newAnnotations?.ContainsKey(k) != true)
            .OrderBy(k => k)
            .ToImmutableArray();

        return new PolicyDecisionDiff(
            OldStatus: oldStatus,
            NewStatus: newStatus,
            OldSeverity: oldSeverity,
            NewSeverity: newSeverity,
            OldRule: oldRule,
            NewRule: newRule,
            OldPriority: oldPriority,
            NewPriority: newPriority,
            StatusChanged: !string.Equals(oldStatus, newStatus, StringComparison.Ordinal),
            SeverityChanged: !string.Equals(oldSeverity, newSeverity, StringComparison.Ordinal),
            RuleChanged: !string.Equals(oldRule, newRule, StringComparison.Ordinal),
            AnnotationsAdded: annotationsAdded,
            AnnotationsRemoved: annotationsRemoved);
    }
}

/// <summary>
/// Event emitted when batch re-evaluation completes.
/// </summary>
public sealed record PolicyBatchCompletedEvent(
    string EventId,
    string TenantId,
    DateTimeOffset Timestamp,
    string? CorrelationId,
    [property: JsonPropertyName("batch_id")] string BatchId,
    [property: JsonPropertyName("trigger_type")] string TriggerType,
    [property: JsonPropertyName("subjects_evaluated")] int SubjectsEvaluated,
    [property: JsonPropertyName("decisions_changed")] int DecisionsChanged,
    [property: JsonPropertyName("duration_ms")] long DurationMs,
    [property: JsonPropertyName("summary")] PolicyBatchSummary Summary)
    : PolicyEffectiveEvent(EventId, PolicyEffectiveEventType.BatchCompleted, TenantId, Timestamp, CorrelationId);

/// <summary>
/// Summary of changes in a batch re-evaluation.
/// </summary>
public sealed record PolicyBatchSummary(
    [property: JsonPropertyName("status_upgrades")] int StatusUpgrades,
    [property: JsonPropertyName("status_downgrades")] int StatusDowngrades,
    [property: JsonPropertyName("new_blocks")] int NewBlocks,
    [property: JsonPropertyName("blocks_removed")] int BlocksRemoved,
    [property: JsonPropertyName("affected_advisories")] ImmutableArray<string> AffectedAdvisories,
    [property: JsonPropertyName("affected_purls")] ImmutableArray<string> AffectedPurls);

/// <summary>
/// Request to schedule a re-evaluation job.
/// </summary>
public sealed record ReEvaluationJobRequest(
    string JobId,
    string TenantId,
    string PackId,
    int PackVersion,
    string TriggerType,
    string? CorrelationId,
    DateTimeOffset CreatedAt,
    PolicyChangePriority Priority,
    ImmutableArray<string> AdvisoryIds,
    ImmutableArray<string> SubjectPurls,
    ImmutableArray<string> SbomIds,
    ImmutableDictionary<string, string> Metadata)
{
    /// <summary>
    /// Creates a deterministic job ID.
    /// </summary>
    public static string CreateJobId(
        string tenantId,
        string packId,
        int packVersion,
        string triggerType,
        DateTimeOffset createdAt)
    {
        var seed = $"{tenantId}|{packId}|{packVersion}|{triggerType}|{createdAt:O}";
        var bytes = SHA256.HashData(Encoding.UTF8.GetBytes(seed));
        return $"rej-{Convert.ToHexStringLower(bytes)[..16]}";
    }
}

/// <summary>
/// Policy change priority from IncrementalOrchestrator namespace.
/// </summary>
public enum PolicyChangePriority
{
    Normal = 0,
    High = 1,
    Emergency = 2
}