// -----------------------------------------------------------------------------
// VexGateOptions.cs
// Sprint: SPRINT_20260106_003_002_SCANNER_vex_gate_service
// Task: T028 - Add gate policy to tenant configuration
// Description: Configuration options for VEX gate, bindable from YAML/JSON config.
// -----------------------------------------------------------------------------

using System.Collections.Immutable;
using System.ComponentModel.DataAnnotations;

namespace StellaOps.Scanner.Gate;

/// <summary>
/// Configuration options for VEX gate service.
/// Binds to "VexGate" section in configuration files.
/// </summary>
public sealed class VexGateOptions : IValidatableObject
{
    /// <summary>
    /// Configuration section name.
    /// </summary>
    public const string SectionName = "VexGate";

    /// <summary>
    /// Enable VEX-first gating. Default: false.
    /// When disabled, all findings pass through to triage unchanged.
    /// </summary>
    public bool Enabled { get; set; } = false;

    /// <summary>
    /// Default decision when no rules match. Default: Warn.
    /// </summary>
    public string DefaultDecision { get; set; } = "Warn";

    /// <summary>
    /// Policy version for audit/replay purposes.
    /// Should be incremented when rules change.
    /// </summary>
    public string PolicyVersion { get; set; } = "1.0.0";

    /// <summary>
    /// Evaluation rules (ordered by priority, highest first).
    /// </summary>
    public List<VexGateRuleOptions> Rules { get; set; } = [];

    /// <summary>
    /// Caching settings for VEX observation lookups.
    /// </summary>
    public VexGateCacheOptions Cache { get; set; } = new();

    /// <summary>
    /// Audit logging settings.
    /// </summary>
    public VexGateAuditOptions Audit { get; set; } = new();

    /// <summary>
    /// Metrics settings.
    /// </summary>
    public VexGateMetricsOptions Metrics { get; set; } = new();

    /// <summary>
    /// Bypass settings for emergency scans.
    /// </summary>
    public VexGateBypassOptions Bypass { get; set; } = new();

    /// <summary>
    /// Converts this options instance to a VexGatePolicy.
    /// </summary>
    public VexGatePolicy ToPolicy()
    {
        var defaultDecision = ParseDecision(DefaultDecision);
        var rules = Rules
            .Select(r => r.ToRule())
            .OrderByDescending(r => r.Priority)
            .ToImmutableArray();

        return new VexGatePolicy
        {
            DefaultDecision = defaultDecision,
            Rules = rules,
        };
    }

    /// <summary>
    /// Creates options from a VexGatePolicy.
    /// </summary>
    public static VexGateOptions FromPolicy(VexGatePolicy policy)
    {
        return new VexGateOptions
        {
            Enabled = true,
            DefaultDecision = policy.DefaultDecision.ToString(),
            Rules = policy.Rules.Select(r => VexGateRuleOptions.FromRule(r)).ToList(),
        };
    }

    private static VexGateDecision ParseDecision(string value)
    {
        return value.ToUpperInvariant() switch
        {
            "PASS" => VexGateDecision.Pass,
            "WARN" => VexGateDecision.Warn,
            "BLOCK" => VexGateDecision.Block,
            _ => VexGateDecision.Warn,
        };
    }

    /// <inheritdoc/>
    public IEnumerable<ValidationResult> Validate(ValidationContext validationContext)
    {
        if (Enabled && Rules.Count == 0)
        {
            yield return new ValidationResult(
                "At least one rule is required when VexGate is enabled",
                [nameof(Rules)]);
        }

        var ruleIds = new HashSet<string>(StringComparer.OrdinalIgnoreCase);
        foreach (var rule in Rules)
        {
            if (string.IsNullOrWhiteSpace(rule.RuleId))
            {
                yield return new ValidationResult(
                    "Rule ID is required for all rules",
                    [nameof(Rules)]);
            }
            else if (!ruleIds.Add(rule.RuleId))
            {
                yield return new ValidationResult(
                    $"Duplicate rule ID: {rule.RuleId}",
                    [nameof(Rules)]);
            }
        }

        if (Cache.TtlSeconds <= 0)
        {
            yield return new ValidationResult(
                "Cache TTL must be positive",
                [nameof(Cache)]);
        }

        if (Cache.MaxEntries <= 0)
        {
            yield return new ValidationResult(
                "Cache max entries must be positive",
                [nameof(Cache)]);
        }
    }
}

/// <summary>
/// Configuration options for a single VEX gate rule.
/// </summary>
public sealed class VexGateRuleOptions
{
    /// <summary>
    /// Unique identifier for this rule.
    /// </summary>
    [Required]
    public string RuleId { get; set; } = string.Empty;

    /// <summary>
    /// Priority order (higher values evaluated first).
    /// </summary>
    public int Priority { get; set; } = 0;

    /// <summary>
    /// Decision to apply when this rule matches.
    /// </summary>
    [Required]
    public string Decision { get; set; } = "Warn";

    /// <summary>
    /// Condition that must match for this rule to apply.
    /// </summary>
    public VexGateConditionOptions Condition { get; set; } = new();

    /// <summary>
    /// Converts to a VexGatePolicyRule.
    /// </summary>
    public VexGatePolicyRule ToRule()
    {
        return new VexGatePolicyRule
        {
            RuleId = RuleId,
            Priority = Priority,
            Decision = ParseDecision(Decision),
            Condition = Condition.ToCondition(),
        };
    }

    /// <summary>
    /// Creates options from a VexGatePolicyRule.
    /// </summary>
    public static VexGateRuleOptions FromRule(VexGatePolicyRule rule)
    {
        return new VexGateRuleOptions
        {
            RuleId = rule.RuleId,
            Priority = rule.Priority,
            Decision = rule.Decision.ToString(),
            Condition = VexGateConditionOptions.FromCondition(rule.Condition),
        };
    }

    private static VexGateDecision ParseDecision(string value)
    {
        return value.ToUpperInvariant() switch
        {
            "PASS" => VexGateDecision.Pass,
            "WARN" => VexGateDecision.Warn,
            "BLOCK" => VexGateDecision.Block,
            _ => VexGateDecision.Warn,
        };
    }
}

/// <summary>
/// Configuration options for a rule condition.
/// </summary>
public sealed class VexGateConditionOptions
{
    /// <summary>
    /// Required VEX vendor status.
    /// Options: not_affected, fixed, affected, under_investigation.
    /// </summary>
    public string? VendorStatus { get; set; }

    /// <summary>
    /// Whether the vulnerability must be exploitable.
    /// </summary>
    public bool? IsExploitable { get; set; }

    /// <summary>
    /// Whether the vulnerable code must be reachable.
    /// </summary>
    public bool? IsReachable { get; set; }

    /// <summary>
    /// Whether compensating controls must be present.
    /// </summary>
    public bool? HasCompensatingControl { get; set; }

    /// <summary>
    /// Whether the CVE is in KEV (Known Exploited Vulnerabilities).
    /// </summary>
    public bool? IsKnownExploited { get; set; }

    /// <summary>
    /// Required severity levels (any match).
    /// </summary>
    public List<string>? SeverityLevels { get; set; }

    /// <summary>
    /// Minimum confidence score required.
    /// </summary>
    public double? ConfidenceThreshold { get; set; }

    /// <summary>
    /// Converts to a VexGatePolicyCondition.
    /// </summary>
    public VexGatePolicyCondition ToCondition()
    {
        return new VexGatePolicyCondition
        {
            VendorStatus = ParseVexStatus(VendorStatus),
            IsExploitable = IsExploitable,
            IsReachable = IsReachable,
            HasCompensatingControl = HasCompensatingControl,
            SeverityLevels = SeverityLevels?.ToArray(),
            MinConfidence = ConfidenceThreshold,
        };
    }

    /// <summary>
    /// Creates options from a VexGatePolicyCondition.
    /// </summary>
    public static VexGateConditionOptions FromCondition(VexGatePolicyCondition condition)
    {
        return new VexGateConditionOptions
        {
            VendorStatus = condition.VendorStatus?.ToString().ToLowerInvariant(),
            IsExploitable = condition.IsExploitable,
            IsReachable = condition.IsReachable,
            HasCompensatingControl = condition.HasCompensatingControl,
            SeverityLevels = condition.SeverityLevels?.ToList(),
            ConfidenceThreshold = condition.MinConfidence,
        };
    }

    private static VexStatus? ParseVexStatus(string? value)
    {
        if (string.IsNullOrWhiteSpace(value))
            return null;

        return value.ToLowerInvariant() switch
        {
            "not_affected" or "notaffected" => VexStatus.NotAffected,
            "fixed" => VexStatus.Fixed,
            "affected" => VexStatus.Affected,
            "under_investigation" or "underinvestigation" => VexStatus.UnderInvestigation,
            _ => null,
        };
    }
}

/// <summary>
/// Cache configuration options.
/// </summary>
public sealed class VexGateCacheOptions
{
    /// <summary>
    /// TTL for cached VEX observations (seconds). Default: 300.
    /// </summary>
    public int TtlSeconds { get; set; } = 300;

    /// <summary>
    /// Maximum cache entries. Default: 10000.
    /// </summary>
    public int MaxEntries { get; set; } = 10000;
}

/// <summary>
/// Audit logging configuration options.
/// </summary>
public sealed class VexGateAuditOptions
{
    /// <summary>
    /// Enable structured audit logging for compliance. Default: true.
    /// </summary>
    public bool Enabled { get; set; } = true;

    /// <summary>
    /// Include full evidence in audit logs. Default: true.
    /// </summary>
    public bool IncludeEvidence { get; set; } = true;

    /// <summary>
    /// Log level for gate decisions. Default: Information.
    /// </summary>
    public string LogLevel { get; set; } = "Information";
}

/// <summary>
/// Metrics configuration options.
/// </summary>
public sealed class VexGateMetricsOptions
{
    /// <summary>
    /// Enable OpenTelemetry metrics. Default: true.
    /// </summary>
    public bool Enabled { get; set; } = true;

    /// <summary>
    /// Histogram buckets for evaluation latency (milliseconds).
    /// </summary>
    public List<double> LatencyBuckets { get; set; } = [1, 5, 10, 25, 50, 100, 250];
}

/// <summary>
/// Bypass configuration options.
/// </summary>
public sealed class VexGateBypassOptions
{
    /// <summary>
    /// Allow gate bypass via CLI flag (--bypass-gate). Default: true.
    /// </summary>
    public bool AllowCliBypass { get; set; } = true;

    /// <summary>
    /// Require specific reason when bypassing. Default: false.
    /// </summary>
    public bool RequireReason { get; set; } = false;

    /// <summary>
    /// Emit warning when bypass is used. Default: true.
    /// </summary>
    public bool WarnOnBypass { get; set; } = true;
}