// SPDX-License-Identifier: BUSL-1.1
// Sprint: SPRINT_20260102_001_BE
// Task: DS-041 - VEX evidence emission for backport detection

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

namespace StellaOps.Scanner.Evidence.Models;

/// <summary>
/// Evidence from binary delta signature analysis.
/// Provides cryptographic proof of backport status by comparing
/// normalized binary code against known patched/vulnerable signatures.
/// </summary>
public sealed record DeltaSignatureEvidence
{
    /// <summary>
    /// Schema version for this evidence type.
    /// </summary>
    [JsonPropertyName("schema")]
    public string Schema { get; init; } = "stellaops.evidence.deltasig.v1";

    /// <summary>
    /// Overall result: patched, vulnerable, inconclusive.
    /// </summary>
    [JsonPropertyName("result")]
    public required DeltaSigResult Result { get; init; }

    /// <summary>
    /// CVE identifier(s) that were evaluated.
    /// </summary>
    [JsonPropertyName("cveIds")]
    public required ImmutableArray<string> CveIds { get; init; }

    /// <summary>
    /// Package reference (PURL) being analyzed.
    /// </summary>
    [JsonPropertyName("packagePurl")]
    public required string PackagePurl { get; init; }

    /// <summary>
    /// Binary identifier (path or Build-ID).
    /// </summary>
    [JsonPropertyName("binaryId")]
    public required string BinaryId { get; init; }

    /// <summary>
    /// Target architecture (x86_64, aarch64, etc.).
    /// </summary>
    [JsonPropertyName("architecture")]
    public required string Architecture { get; init; }

    /// <summary>
    /// Symbol-level match results.
    /// </summary>
    [JsonPropertyName("symbolMatches")]
    public required ImmutableArray<SymbolMatchEvidence> SymbolMatches { get; init; }

    /// <summary>
    /// Confidence score [0, 1] of the overall determination.
    /// </summary>
    [JsonPropertyName("confidence")]
    public required decimal Confidence { get; init; }

    /// <summary>
    /// Normalization recipe used for comparison.
    /// </summary>
    [JsonPropertyName("normalizationRecipe")]
    public required NormalizationRecipeRef NormalizationRecipe { get; init; }

    /// <summary>
    /// When this evidence was generated.
    /// </summary>
    [JsonPropertyName("generatedAt")]
    public required DateTimeOffset GeneratedAt { get; init; }

    /// <summary>
    /// Human-readable summary of the determination.
    /// </summary>
    [JsonPropertyName("summary")]
    public required string Summary { get; init; }

    /// <summary>
    /// Optional DSSE envelope URI containing the signed attestation.
    /// </summary>
    [JsonPropertyName("attestationUri")]
    public string? AttestationUri { get; init; }

    /// <summary>
    /// Creates evidence for a patched binary.
    /// </summary>
    public static DeltaSignatureEvidence CreatePatched(
        ImmutableArray<string> cveIds,
        string packagePurl,
        string binaryId,
        string architecture,
        ImmutableArray<SymbolMatchEvidence> symbolMatches,
        decimal confidence,
        NormalizationRecipeRef recipe,
        TimeProvider? timeProvider = null)
    {
        var matchSummary = symbolMatches.IsDefaultOrEmpty
            ? "No symbols analyzed"
            : $"{symbolMatches.Count(m => m.State == SignatureState.Patched)} patched, " +
              $"{symbolMatches.Count(m => m.State == SignatureState.Vulnerable)} vulnerable";

        return new DeltaSignatureEvidence
        {
            Result = DeltaSigResult.Patched,
            CveIds = cveIds,
            PackagePurl = packagePurl,
            BinaryId = binaryId,
            Architecture = architecture,
            SymbolMatches = symbolMatches,
            Confidence = confidence,
            NormalizationRecipe = recipe,
            GeneratedAt = (timeProvider ?? TimeProvider.System).GetUtcNow(),
            Summary = $"Binary confirmed PATCHED with {confidence:P0} confidence. {matchSummary}."
        };
    }

    /// <summary>
    /// Creates evidence for a vulnerable binary.
    /// </summary>
    public static DeltaSignatureEvidence CreateVulnerable(
        ImmutableArray<string> cveIds,
        string packagePurl,
        string binaryId,
        string architecture,
        ImmutableArray<SymbolMatchEvidence> symbolMatches,
        decimal confidence,
        NormalizationRecipeRef recipe,
        TimeProvider? timeProvider = null)
    {
        var matchSummary = symbolMatches.IsDefaultOrEmpty
            ? "No symbols analyzed"
            : $"{symbolMatches.Count(m => m.State == SignatureState.Vulnerable)} vulnerable symbols matched";

        return new DeltaSignatureEvidence
        {
            Result = DeltaSigResult.Vulnerable,
            CveIds = cveIds,
            PackagePurl = packagePurl,
            BinaryId = binaryId,
            Architecture = architecture,
            SymbolMatches = symbolMatches,
            Confidence = confidence,
            NormalizationRecipe = recipe,
            GeneratedAt = (timeProvider ?? TimeProvider.System).GetUtcNow(),
            Summary = $"Binary confirmed VULNERABLE with {confidence:P0} confidence. {matchSummary}."
        };
    }

    /// <summary>
    /// Creates evidence for an inconclusive analysis.
    /// </summary>
    public static DeltaSignatureEvidence CreateInconclusive(
        ImmutableArray<string> cveIds,
        string packagePurl,
        string binaryId,
        string architecture,
        string reason,
        ImmutableArray<SymbolMatchEvidence> symbolMatches,
        NormalizationRecipeRef recipe,
        TimeProvider? timeProvider = null)
    {
        return new DeltaSignatureEvidence
        {
            Result = DeltaSigResult.Inconclusive,
            CveIds = cveIds,
            PackagePurl = packagePurl,
            BinaryId = binaryId,
            Architecture = architecture,
            SymbolMatches = symbolMatches,
            Confidence = 0m,
            NormalizationRecipe = recipe,
            GeneratedAt = (timeProvider ?? TimeProvider.System).GetUtcNow(),
            Summary = $"Analysis INCONCLUSIVE: {reason}"
        };
    }
}

/// <summary>
/// Result of delta signature analysis.
/// </summary>
[JsonConverter(typeof(JsonStringEnumConverter<DeltaSigResult>))]
public enum DeltaSigResult
{
    /// <summary>
    /// Binary contains patched code - security fix is applied.
    /// </summary>
    [JsonStringEnumMemberName("patched")]
    Patched,

    /// <summary>
    /// Binary contains vulnerable code - security fix is NOT applied.
    /// </summary>
    [JsonStringEnumMemberName("vulnerable")]
    Vulnerable,

    /// <summary>
    /// Unable to determine patch status (symbols not found, LTO obfuscation, etc.).
    /// </summary>
    [JsonStringEnumMemberName("inconclusive")]
    Inconclusive
}

/// <summary>
/// Evidence for a single symbol match.
/// </summary>
public sealed record SymbolMatchEvidence
{
    /// <summary>
    /// Symbol/function name.
    /// </summary>
    [JsonPropertyName("symbolName")]
    public required string SymbolName { get; init; }

    /// <summary>
    /// Normalized hash of the symbol (SHA-256).
    /// </summary>
    [JsonPropertyName("hashHex")]
    public required string HashHex { get; init; }

    /// <summary>
    /// Matched signature state (patched or vulnerable).
    /// </summary>
    [JsonPropertyName("state")]
    public required SignatureState State { get; init; }

    /// <summary>
    /// Match confidence [0, 1].
    /// </summary>
    [JsonPropertyName("confidence")]
    public required decimal Confidence { get; init; }

    /// <summary>
    /// Whether this was an exact full-hash match.
    /// </summary>
    [JsonPropertyName("exactMatch")]
    public required bool ExactMatch { get; init; }

    /// <summary>
    /// Number of chunks matched (for partial matching).
    /// </summary>
    [JsonPropertyName("chunksMatched")]
    public int? ChunksMatched { get; init; }

    /// <summary>
    /// Total chunks in signature.
    /// </summary>
    [JsonPropertyName("chunksTotal")]
    public int? ChunksTotal { get; init; }

    /// <summary>
    /// Reference to the matched signature (PURL of the signature source package).
    /// </summary>
    [JsonPropertyName("signatureSourcePurl")]
    public string? SignatureSourcePurl { get; init; }
}

/// <summary>
/// State of a signature: vulnerable or patched.
/// </summary>
[JsonConverter(typeof(JsonStringEnumConverter<SignatureState>))]
public enum SignatureState
{
    /// <summary>
    /// Signature represents vulnerable code (before fix).
    /// </summary>
    [JsonStringEnumMemberName("vulnerable")]
    Vulnerable,

    /// <summary>
    /// Signature represents patched code (after fix).
    /// </summary>
    [JsonStringEnumMemberName("patched")]
    Patched
}

/// <summary>
/// Reference to the normalization recipe used.
/// </summary>
public sealed record NormalizationRecipeRef
{
    /// <summary>
    /// Recipe identifier (e.g., "stellaops.normalize.x64.v1").
    /// </summary>
    [JsonPropertyName("recipeId")]
    public required string RecipeId { get; init; }

    /// <summary>
    /// Recipe version.
    /// </summary>
    [JsonPropertyName("version")]
    public required string Version { get; init; }

    /// <summary>
    /// Normalization steps applied.
    /// </summary>
    [JsonPropertyName("steps")]
    public ImmutableArray<string> Steps { get; init; } = [];
}