using System.Collections.Immutable;
using System.Linq;

namespace StellaOps.Policy.Exceptions.Models;

/// <summary>
/// Policy defining conditions that trigger exception re-evaluation.
/// When any condition is met, the exception may be invalidated or flagged.
/// </summary>
public sealed record RecheckPolicy
{
    /// <summary>
    /// Unique identifier for this policy configuration.
    /// </summary>
    public required string PolicyId { get; init; }

    /// <summary>
    /// Human-readable name for this policy.
    /// </summary>
    public required string Name { get; init; }

    /// <summary>
    /// Conditions that trigger recheck.
    /// </summary>
    public required ImmutableArray<RecheckCondition> Conditions { get; init; }

    /// <summary>
    /// Default action when any condition is triggered.
    /// </summary>
    public required RecheckAction DefaultAction { get; init; }

    /// <summary>
    /// Whether this policy is active.
    /// </summary>
    public bool IsActive { get; init; } = true;

    /// <summary>
    /// When this policy was created.
    /// </summary>
    public required DateTimeOffset CreatedAt { get; init; }
}

/// <summary>
/// A single condition that triggers exception re-evaluation.
/// </summary>
public sealed record RecheckCondition
{
    /// <summary>
    /// Type of condition to check.
    /// </summary>
    public required RecheckConditionType Type { get; init; }

    /// <summary>
    /// Threshold value (interpretation depends on Type).
    /// </summary>
    public decimal? Threshold { get; init; }

    /// <summary>
    /// Environment scopes where this condition applies.
    /// </summary>
    public ImmutableArray<string> EnvironmentScope { get; init; } = [];

    /// <summary>
    /// Action to take when this specific condition is triggered.
    /// If null, uses policy's DefaultAction.
    /// </summary>
    public RecheckAction? Action { get; init; }

    /// <summary>
    /// Human-readable description of this condition.
    /// </summary>
    public string? Description { get; init; }
}

/// <summary>
/// Types of recheck conditions.
/// </summary>
public enum RecheckConditionType
{
    /// <summary>Reachability graph changes (new paths discovered).</summary>
    ReachGraphChange,

    /// <summary>EPSS score exceeds threshold.</summary>
    EPSSAbove,

    /// <summary>CVSS score exceeds threshold.</summary>
    CVSSAbove,

    /// <summary>Unknown budget exceeds threshold.</summary>
    UnknownsAbove,

    /// <summary>New CVE added to same package.</summary>
    NewCVEInPackage,

    /// <summary>KEV (Known Exploited Vulnerability) flag set.</summary>
    KEVFlagged,

    /// <summary>Exception nearing expiry (days before).</summary>
    ExpiryWithin,

    /// <summary>VEX status changes (e.g., from NotAffected to Affected).</summary>
    VEXStatusChange,

    /// <summary>Package version changes.</summary>
    PackageVersionChange
}

/// <summary>
/// Action to take when a recheck condition is triggered.
/// </summary>
public enum RecheckAction
{
    /// <summary>Log warning but allow exception to remain active.</summary>
    Warn,

    /// <summary>Require manual re-approval of exception.</summary>
    RequireReapproval,

    /// <summary>Automatically revoke the exception.</summary>
    Revoke,

    /// <summary>Block build/deployment pipeline.</summary>
    Block
}

/// <summary>
/// Result of evaluating recheck conditions against an exception.
/// </summary>
public sealed record RecheckEvaluationResult
{
    /// <summary>Whether any conditions were triggered.</summary>
    public required bool IsTriggered { get; init; }

    /// <summary>List of triggered conditions with details.</summary>
    public required ImmutableArray<TriggeredCondition> TriggeredConditions { get; init; }

    /// <summary>Recommended action based on triggered conditions.</summary>
    public required RecheckAction? RecommendedAction { get; init; }

    /// <summary>When this evaluation was performed.</summary>
    public required DateTimeOffset EvaluatedAt { get; init; }

    /// <summary>Human-readable summary.</summary>
    public string Summary => IsTriggered
        ? $"{TriggeredConditions.Length} condition(s) triggered: {string.Join(", ", TriggeredConditions.Select(t => t.Type))}"
        : "No conditions triggered";
}

/// <summary>
/// Details of a triggered recheck condition.
/// </summary>
public sealed record TriggeredCondition(
    RecheckConditionType Type,
    string Description,
    decimal? CurrentValue,
    decimal? ThresholdValue,
    RecheckAction Action);