// -----------------------------------------------------------------------------
// IReplayVerificationService.cs
// Sprint: SPRINT_20251228_007_BE_sbom_lineage_graph_ii (LIN-BE-033)
// Task: Replay verification endpoint
// Description: Interface for verifying replay hashes and detecting drift.
// -----------------------------------------------------------------------------

using System.Collections.Immutable;

namespace StellaOps.SbomService.Services;

/// <summary>
/// Service for verifying replay hashes and detecting drift in security evaluations.
/// </summary>
public interface IReplayVerificationService
{
    /// <summary>
    /// Verifies a replay hash by re-computing it with provided or current inputs.
    /// </summary>
    /// <param name="request">Verification request.</param>
    /// <param name="ct">Cancellation token.</param>
    /// <returns>Verification result with match status and drift details.</returns>
    Task<ReplayVerificationResult> VerifyAsync(
        ReplayVerificationRequest request,
        CancellationToken ct = default);

    /// <summary>
    /// Compares two replay hashes and identifies drift between them.
    /// </summary>
    /// <param name="hashA">First replay hash.</param>
    /// <param name="hashB">Second replay hash.</param>
    /// <param name="tenantId">Tenant identifier.</param>
    /// <param name="ct">Cancellation token.</param>
    /// <returns>Drift analysis between the two evaluations.</returns>
    Task<ReplayDriftAnalysis> CompareDriftAsync(
        string hashA,
        string hashB,
        string tenantId,
        CancellationToken ct = default);
}

/// <summary>
/// Request for replay verification.
/// </summary>
public sealed record ReplayVerificationRequest
{
    /// <summary>
    /// The replay hash to verify.
    /// </summary>
    public required string ReplayHash { get; init; }

    /// <summary>
    /// Tenant identifier.
    /// </summary>
    public required string TenantId { get; init; }

    /// <summary>
    /// Optional: SBOM digest to use for verification.
    /// If not provided, will try to lookup from stored hash metadata.
    /// </summary>
    public string? SbomDigest { get; init; }

    /// <summary>
    /// Optional: Feeds snapshot digest to use.
    /// If not provided, uses current feeds.
    /// </summary>
    public string? FeedsSnapshotDigest { get; init; }

    /// <summary>
    /// Optional: Policy version to use.
    /// If not provided, uses current policy.
    /// </summary>
    public string? PolicyVersion { get; init; }

    /// <summary>
    /// Optional: VEX verdicts digest to use.
    /// If not provided, uses current VEX state.
    /// </summary>
    public string? VexVerdictsDigest { get; init; }

    /// <summary>
    /// Optional: Timestamp to use for verification.
    /// If not provided, uses current time.
    /// </summary>
    public DateTimeOffset? Timestamp { get; init; }

    /// <summary>
    /// Whether to freeze time to the original evaluation timestamp.
    /// </summary>
    public bool FreezeTime { get; init; } = true;

    /// <summary>
    /// Whether to re-evaluate policy with frozen feeds.
    /// </summary>
    public bool ReEvaluatePolicy { get; init; } = false;
}

/// <summary>
/// Result of replay verification.
/// </summary>
public sealed record ReplayVerificationResult
{
    /// <summary>
    /// Whether the replay hash matches.
    /// </summary>
    public required bool IsMatch { get; init; }

    /// <summary>
    /// The expected replay hash.
    /// </summary>
    public required string ExpectedHash { get; init; }

    /// <summary>
    /// The computed replay hash.
    /// </summary>
    public required string ComputedHash { get; init; }

    /// <summary>
    /// Overall verification status.
    /// </summary>
    public required ReplayVerificationStatus Status { get; init; }

    /// <summary>
    /// The inputs used for the expected hash (from storage).
    /// </summary>
    public ReplayHashInputs? ExpectedInputs { get; init; }

    /// <summary>
    /// The inputs used to compute the verification hash.
    /// </summary>
    public ReplayHashInputs? ComputedInputs { get; init; }

    /// <summary>
    /// Field-level differences between expected and computed.
    /// </summary>
    public ImmutableArray<ReplayFieldDrift> Drifts { get; init; } = ImmutableArray<ReplayFieldDrift>.Empty;

    /// <summary>
    /// When the verification was performed.
    /// </summary>
    public DateTimeOffset VerifiedAt { get; init; } = DateTimeOffset.UtcNow;

    /// <summary>
    /// Optional message with additional context.
    /// </summary>
    public string? Message { get; init; }

    /// <summary>
    /// Error message if verification failed.
    /// </summary>
    public string? Error { get; init; }
}

/// <summary>
/// Verification status enumeration.
/// </summary>
public enum ReplayVerificationStatus
{
    /// <summary>
    /// Hash matches exactly - evaluation is reproducible.
    /// </summary>
    Match,

    /// <summary>
    /// Hash doesn't match - drift detected.
    /// </summary>
    Drift,

    /// <summary>
    /// Unable to lookup original inputs.
    /// </summary>
    InputsNotFound,

    /// <summary>
    /// Verification failed due to error.
    /// </summary>
    Error
}

/// <summary>
/// Field-level drift in replay verification.
/// </summary>
public sealed record ReplayFieldDrift
{
    /// <summary>
    /// Name of the field that drifted.
    /// </summary>
    public required string FieldName { get; init; }

    /// <summary>
    /// Expected value (from original evaluation).
    /// </summary>
    public required string ExpectedValue { get; init; }

    /// <summary>
    /// Actual/computed value.
    /// </summary>
    public required string ActualValue { get; init; }

    /// <summary>
    /// Severity of the drift: "info", "warning", "critical".
    /// </summary>
    public required string Severity { get; init; }

    /// <summary>
    /// Human-readable description of the drift impact.
    /// </summary>
    public string? Description { get; init; }
}

/// <summary>
/// Analysis of drift between two replay evaluations.
/// </summary>
public sealed record ReplayDriftAnalysis
{
    /// <summary>
    /// First replay hash.
    /// </summary>
    public required string HashA { get; init; }

    /// <summary>
    /// Second replay hash.
    /// </summary>
    public required string HashB { get; init; }

    /// <summary>
    /// Whether the hashes are identical.
    /// </summary>
    public required bool IsIdentical { get; init; }

    /// <summary>
    /// Inputs for first hash.
    /// </summary>
    public ReplayHashInputs? InputsA { get; init; }

    /// <summary>
    /// Inputs for second hash.
    /// </summary>
    public ReplayHashInputs? InputsB { get; init; }

    /// <summary>
    /// Field-level drifts between A and B.
    /// </summary>
    public ImmutableArray<ReplayFieldDrift> Drifts { get; init; } = ImmutableArray<ReplayFieldDrift>.Empty;

    /// <summary>
    /// Summary of drift severity.
    /// </summary>
    public required string DriftSummary { get; init; }

    /// <summary>
    /// When the analysis was performed.
    /// </summary>
    public DateTimeOffset AnalyzedAt { get; init; } = DateTimeOffset.UtcNow;
}