// -----------------------------------------------------------------------------
// AttestationChain.cs
// Sprint: SPRINT_3801_0001_0003_chain_verification (CHAIN-002)
// Description: Models for attestation chain verification.
// -----------------------------------------------------------------------------

using System;
using System.Collections.Generic;
using System.Collections.Immutable;
using System.Text.Json.Serialization;

namespace StellaOps.Scanner.WebService.Contracts;

/// <summary>
/// Represents a chain of attestations for a finding.
/// </summary>
public sealed record AttestationChain
{
    /// <summary>
    /// Content-addressed chain identifier.
    /// </summary>
    [JsonPropertyName("chain_id")]
    public required string ChainId { get; init; }

    /// <summary>
    /// The scan ID this chain belongs to.
    /// </summary>
    [JsonPropertyName("scan_id")]
    public required string ScanId { get; init; }

    /// <summary>
    /// The finding ID (e.g., CVE identifier) this chain is for.
    /// </summary>
    [JsonPropertyName("finding_id")]
    public required string FindingId { get; init; }

    /// <summary>
    /// The root digest (typically the scan/image digest).
    /// </summary>
    [JsonPropertyName("root_digest")]
    public required string RootDigest { get; init; }

    /// <summary>
    /// The attestations in this chain, ordered from root to leaf.
    /// </summary>
    [JsonPropertyName("attestations")]
    public required ImmutableList<ChainAttestation> Attestations { get; init; }

    /// <summary>
    /// Whether the entire chain is verified.
    /// </summary>
    [JsonPropertyName("verified")]
    public required bool Verified { get; init; }

    /// <summary>
    /// When the chain was verified.
    /// </summary>
    [JsonPropertyName("verified_at")]
    public required DateTimeOffset VerifiedAt { get; init; }

    /// <summary>
    /// The chain status.
    /// </summary>
    [JsonPropertyName("chain_status")]
    public required ChainStatus Status { get; init; }

    /// <summary>
    /// When the earliest attestation in the chain expires.
    /// </summary>
    [JsonPropertyName("expires_at")]
    public DateTimeOffset? ExpiresAt { get; init; }
}

/// <summary>
/// Represents a single attestation in the chain.
/// </summary>
public sealed record ChainAttestation
{
    /// <summary>
    /// The type of attestation (e.g., "richgraph", "policy_decision", "human_approval").
    /// </summary>
    [JsonPropertyName("type")]
    public required AttestationType Type { get; init; }

    /// <summary>
    /// The attestation ID.
    /// </summary>
    [JsonPropertyName("attestation_id")]
    public required string AttestationId { get; init; }

    /// <summary>
    /// When the attestation was created.
    /// </summary>
    [JsonPropertyName("created_at")]
    public required DateTimeOffset CreatedAt { get; init; }

    /// <summary>
    /// When the attestation expires.
    /// </summary>
    [JsonPropertyName("expires_at")]
    public required DateTimeOffset ExpiresAt { get; init; }

    /// <summary>
    /// Whether the attestation signature verified.
    /// </summary>
    [JsonPropertyName("verified")]
    public required bool Verified { get; init; }

    /// <summary>
    /// The verification status of this attestation.
    /// </summary>
    [JsonPropertyName("verification_status")]
    public required AttestationVerificationStatus VerificationStatus { get; init; }

    /// <summary>
    /// The subject digest this attestation covers.
    /// </summary>
    [JsonPropertyName("subject_digest")]
    public required string SubjectDigest { get; init; }

    /// <summary>
    /// The predicate type URI.
    /// </summary>
    [JsonPropertyName("predicate_type")]
    public required string PredicateType { get; init; }

    /// <summary>
    /// Optional error message if verification failed.
    /// </summary>
    [JsonPropertyName("error")]
    public string? Error { get; init; }
}

/// <summary>
/// The type of attestation.
/// </summary>
[JsonConverter(typeof(JsonStringEnumConverter))]
public enum AttestationType
{
    /// <summary>
    /// RichGraph computation attestation.
    /// </summary>
    RichGraph,

    /// <summary>
    /// Policy decision attestation.
    /// </summary>
    PolicyDecision,

    /// <summary>
    /// Human approval attestation.
    /// </summary>
    HumanApproval,

    /// <summary>
    /// SBOM generation attestation.
    /// </summary>
    Sbom,

    /// <summary>
    /// Vulnerability scan attestation.
    /// </summary>
    VulnerabilityScan
}

/// <summary>
/// The verification status of an attestation.
/// </summary>
[JsonConverter(typeof(JsonStringEnumConverter))]
public enum AttestationVerificationStatus
{
    /// <summary>
    /// Verification succeeded.
    /// </summary>
    Valid,

    /// <summary>
    /// Attestation has expired.
    /// </summary>
    Expired,

    /// <summary>
    /// Signature verification failed.
    /// </summary>
    InvalidSignature,

    /// <summary>
    /// Attestation not found.
    /// </summary>
    NotFound,

    /// <summary>
    /// Chain link broken (digest mismatch).
    /// </summary>
    ChainBroken,

    /// <summary>
    /// Attestation has been revoked.
    /// </summary>
    Revoked,

    /// <summary>
    /// Verification pending.
    /// </summary>
    Pending
}

/// <summary>
/// The overall status of the attestation chain.
/// </summary>
[JsonConverter(typeof(JsonStringEnumConverter))]
public enum ChainStatus
{
    /// <summary>
    /// All attestations present and valid.
    /// </summary>
    Complete,

    /// <summary>
    /// Some attestations missing but core valid.
    /// </summary>
    Partial,

    /// <summary>
    /// One or more attestations past TTL.
    /// </summary>
    Expired,

    /// <summary>
    /// Signature verification failed.
    /// </summary>
    Invalid,

    /// <summary>
    /// Chain link missing or digest mismatch.
    /// </summary>
    Broken,

    /// <summary>
    /// Chain is empty (no attestations).
    /// </summary>
    Empty
}

/// <summary>
/// Input for chain verification.
/// </summary>
public sealed record ChainVerificationInput
{
    /// <summary>
    /// The scan ID to verify chain for.
    /// </summary>
    public required Domain.ScanId ScanId { get; init; }

    /// <summary>
    /// The finding ID to verify chain for.
    /// </summary>
    public required string FindingId { get; init; }

    /// <summary>
    /// The expected root digest.
    /// </summary>
    public required string RootDigest { get; init; }

    /// <summary>
    /// Optional: specific attestation types to verify.
    /// If null, verifies all available attestations.
    /// </summary>
    public IReadOnlyList<AttestationType>? RequiredTypes { get; init; }

    /// <summary>
    /// Whether to require human approval in the chain.
    /// </summary>
    public bool RequireHumanApproval { get; init; }

    /// <summary>
    /// Grace period for expired attestations (default: 0).
    /// </summary>
    public TimeSpan ExpirationGracePeriod { get; init; } = TimeSpan.Zero;
}

/// <summary>
/// Result of chain verification.
/// </summary>
public sealed record ChainVerificationResult
{
    /// <summary>
    /// Whether verification succeeded.
    /// </summary>
    public required bool Success { get; init; }

    /// <summary>
    /// The verified chain.
    /// </summary>
    public AttestationChain? Chain { get; init; }

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

    /// <summary>
    /// Detailed verification results per attestation.
    /// </summary>
    public IReadOnlyList<AttestationVerificationDetail>? Details { get; init; }

    /// <summary>
    /// Creates a successful result.
    /// </summary>
    public static ChainVerificationResult Succeeded(
        AttestationChain chain,
        IReadOnlyList<AttestationVerificationDetail>? details = null)
        => new()
        {
            Success = true,
            Chain = chain,
            Details = details
        };

    /// <summary>
    /// Creates a failed result.
    /// </summary>
    public static ChainVerificationResult Failed(string error, AttestationChain? chain = null)
        => new()
        {
            Success = false,
            Chain = chain,
            Error = error
        };
}

/// <summary>
/// Detailed verification result for a single attestation.
/// </summary>
public sealed record AttestationVerificationDetail
{
    /// <summary>
    /// The attestation type.
    /// </summary>
    public required AttestationType Type { get; init; }

    /// <summary>
    /// The attestation ID.
    /// </summary>
    public required string AttestationId { get; init; }

    /// <summary>
    /// The verification status.
    /// </summary>
    public required AttestationVerificationStatus Status { get; init; }

    /// <summary>
    /// Whether the attestation was verified successfully.
    /// </summary>
    public required bool Verified { get; init; }

    /// <summary>
    /// Time taken for verification.
    /// </summary>
    public TimeSpan? VerificationTime { get; init; }

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