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

namespace StellaOps.Policy.Engine.WhatIfSimulation;

/// <summary>
/// Request for what-if simulation supporting hypothetical SBOM diffs and draft policies.
/// </summary>
public sealed record WhatIfSimulationRequest
{
    /// <summary>
    /// Tenant identifier.
    /// </summary>
    [JsonPropertyName("tenant_id")]
    public required string TenantId { get; init; }

    /// <summary>
    /// Base snapshot ID to apply diffs to.
    /// </summary>
    [JsonPropertyName("base_snapshot_id")]
    public required string BaseSnapshotId { get; init; }

    /// <summary>
    /// Active policy pack ID to use as baseline.
    /// If DraftPolicy is provided, this will be compared against.
    /// </summary>
    [JsonPropertyName("baseline_pack_id")]
    public string? BaselinePackId { get; init; }

    /// <summary>
    /// Baseline policy version. If null, uses active version.
    /// </summary>
    [JsonPropertyName("baseline_pack_version")]
    public int? BaselinePackVersion { get; init; }

    /// <summary>
    /// Draft policy to simulate (not yet activated).
    /// If null, uses baseline policy.
    /// </summary>
    [JsonPropertyName("draft_policy")]
    public WhatIfDraftPolicy? DraftPolicy { get; init; }

    /// <summary>
    /// SBOM diffs to apply hypothetically.
    /// </summary>
    [JsonPropertyName("sbom_diffs")]
    public ImmutableArray<WhatIfSbomDiff> SbomDiffs { get; init; } = ImmutableArray<WhatIfSbomDiff>.Empty;

    /// <summary>
    /// Specific component PURLs to evaluate. If empty, evaluates affected by diffs.
    /// </summary>
    [JsonPropertyName("target_purls")]
    public ImmutableArray<string> TargetPurls { get; init; } = ImmutableArray<string>.Empty;

    /// <summary>
    /// Maximum number of components to evaluate.
    /// </summary>
    [JsonPropertyName("limit")]
    public int Limit { get; init; } = 1000;

    /// <summary>
    /// Whether to include detailed explanations for each decision.
    /// </summary>
    [JsonPropertyName("include_explanations")]
    public bool IncludeExplanations { get; init; } = false;

    /// <summary>
    /// Correlation ID for tracing.
    /// </summary>
    [JsonPropertyName("correlation_id")]
    public string? CorrelationId { get; init; }
}

/// <summary>
/// Draft policy definition for simulation.
/// </summary>
public sealed record WhatIfDraftPolicy
{
    /// <summary>
    /// Draft policy pack ID.
    /// </summary>
    [JsonPropertyName("pack_id")]
    public required string PackId { get; init; }

    /// <summary>
    /// Draft policy version.
    /// </summary>
    [JsonPropertyName("version")]
    public int Version { get; init; }

    /// <summary>
    /// Raw YAML policy definition to compile and evaluate.
    /// If provided, this is compiled on-the-fly.
    /// </summary>
    [JsonPropertyName("policy_yaml")]
    public string? PolicyYaml { get; init; }

    /// <summary>
    /// Pre-compiled bundle digest if available.
    /// </summary>
    [JsonPropertyName("bundle_digest")]
    public string? BundleDigest { get; init; }
}

/// <summary>
/// Hypothetical SBOM modification for what-if simulation.
/// </summary>
public sealed record WhatIfSbomDiff
{
    /// <summary>
    /// Type of modification: add, remove, upgrade, downgrade.
    /// </summary>
    [JsonPropertyName("operation")]
    public required string Operation { get; init; }

    /// <summary>
    /// Component PURL being modified.
    /// </summary>
    [JsonPropertyName("purl")]
    public required string Purl { get; init; }

    /// <summary>
    /// New version for upgrade/downgrade operations.
    /// </summary>
    [JsonPropertyName("new_version")]
    public string? NewVersion { get; init; }

    /// <summary>
    /// Original version (for reference in upgrades/downgrades).
    /// </summary>
    [JsonPropertyName("original_version")]
    public string? OriginalVersion { get; init; }

    /// <summary>
    /// Hypothetical advisory IDs affecting this component.
    /// </summary>
    [JsonPropertyName("advisory_ids")]
    public ImmutableArray<string> AdvisoryIds { get; init; } = ImmutableArray<string>.Empty;

    /// <summary>
    /// Hypothetical VEX status for this component.
    /// </summary>
    [JsonPropertyName("vex_status")]
    public string? VexStatus { get; init; }

    /// <summary>
    /// Hypothetical reachability state.
    /// </summary>
    [JsonPropertyName("reachability")]
    public string? Reachability { get; init; }
}

/// <summary>
/// Response from what-if simulation.
/// </summary>
public sealed record WhatIfSimulationResponse
{
    /// <summary>
    /// Simulation identifier.
    /// </summary>
    [JsonPropertyName("simulation_id")]
    public required string SimulationId { get; init; }

    /// <summary>
    /// Tenant identifier.
    /// </summary>
    [JsonPropertyName("tenant_id")]
    public required string TenantId { get; init; }

    /// <summary>
    /// Base snapshot ID used.
    /// </summary>
    [JsonPropertyName("base_snapshot_id")]
    public required string BaseSnapshotId { get; init; }

    /// <summary>
    /// Baseline policy used for comparison.
    /// </summary>
    [JsonPropertyName("baseline_policy")]
    public required WhatIfPolicyRef BaselinePolicy { get; init; }

    /// <summary>
    /// Simulated policy (draft or modified).
    /// </summary>
    [JsonPropertyName("simulated_policy")]
    public WhatIfPolicyRef? SimulatedPolicy { get; init; }

    /// <summary>
    /// Decision changes between baseline and simulation.
    /// </summary>
    [JsonPropertyName("decision_changes")]
    public required ImmutableArray<WhatIfDecisionChange> DecisionChanges { get; init; }

    /// <summary>
    /// Summary of changes.
    /// </summary>
    [JsonPropertyName("summary")]
    public required WhatIfSummary Summary { get; init; }

    /// <summary>
    /// When the simulation was executed.
    /// </summary>
    [JsonPropertyName("executed_at")]
    public required DateTimeOffset ExecutedAt { get; init; }

    /// <summary>
    /// Execution duration in milliseconds.
    /// </summary>
    [JsonPropertyName("duration_ms")]
    public long DurationMs { get; init; }

    /// <summary>
    /// Correlation ID.
    /// </summary>
    [JsonPropertyName("correlation_id")]
    public string? CorrelationId { get; init; }
}

/// <summary>
/// Policy reference in simulation.
/// </summary>
public sealed record WhatIfPolicyRef(
    [property: JsonPropertyName("pack_id")] string PackId,
    [property: JsonPropertyName("version")] int Version,
    [property: JsonPropertyName("bundle_digest")] string? BundleDigest,
    [property: JsonPropertyName("is_draft")] bool IsDraft);

/// <summary>
/// A decision change detected in what-if simulation.
/// </summary>
public sealed record WhatIfDecisionChange
{
    /// <summary>
    /// Component PURL.
    /// </summary>
    [JsonPropertyName("purl")]
    public required string Purl { get; init; }

    /// <summary>
    /// Advisory ID if applicable.
    /// </summary>
    [JsonPropertyName("advisory_id")]
    public string? AdvisoryId { get; init; }

    /// <summary>
    /// Type of change: new, removed, status_changed, severity_changed.
    /// </summary>
    [JsonPropertyName("change_type")]
    public required string ChangeType { get; init; }

    /// <summary>
    /// Baseline decision.
    /// </summary>
    [JsonPropertyName("baseline")]
    public WhatIfDecision? Baseline { get; init; }

    /// <summary>
    /// Simulated decision.
    /// </summary>
    [JsonPropertyName("simulated")]
    public WhatIfDecision? Simulated { get; init; }

    /// <summary>
    /// SBOM diff that caused this change, if any.
    /// </summary>
    [JsonPropertyName("caused_by_diff")]
    public WhatIfSbomDiff? CausedByDiff { get; init; }

    /// <summary>
    /// Explanation for the change.
    /// </summary>
    [JsonPropertyName("explanation")]
    public WhatIfExplanation? Explanation { get; init; }
}

/// <summary>
/// A decision in what-if simulation.
/// </summary>
public sealed record WhatIfDecision(
    [property: JsonPropertyName("status")] string Status,
    [property: JsonPropertyName("severity")] string? Severity,
    [property: JsonPropertyName("rule_name")] string? RuleName,
    [property: JsonPropertyName("priority")] int? Priority,
    [property: JsonPropertyName("exception_applied")] bool ExceptionApplied);

/// <summary>
/// Explanation for a what-if decision.
/// </summary>
public sealed record WhatIfExplanation
{
    /// <summary>
    /// Rules that matched.
    /// </summary>
    [JsonPropertyName("matched_rules")]
    public ImmutableArray<string> MatchedRules { get; init; } = ImmutableArray<string>.Empty;

    /// <summary>
    /// Key factors in the decision.
    /// </summary>
    [JsonPropertyName("factors")]
    public ImmutableArray<string> Factors { get; init; } = ImmutableArray<string>.Empty;

    /// <summary>
    /// VEX evidence considered.
    /// </summary>
    [JsonPropertyName("vex_evidence")]
    public string? VexEvidence { get; init; }

    /// <summary>
    /// Reachability state.
    /// </summary>
    [JsonPropertyName("reachability")]
    public string? Reachability { get; init; }
}

/// <summary>
/// Summary of what-if simulation results.
/// </summary>
public sealed record WhatIfSummary
{
    /// <summary>
    /// Total components evaluated.
    /// </summary>
    [JsonPropertyName("total_evaluated")]
    public int TotalEvaluated { get; init; }

    /// <summary>
    /// Components with changed decisions.
    /// </summary>
    [JsonPropertyName("total_changed")]
    public int TotalChanged { get; init; }

    /// <summary>
    /// Components newly affected.
    /// </summary>
    [JsonPropertyName("newly_affected")]
    public int NewlyAffected { get; init; }

    /// <summary>
    /// Components no longer affected.
    /// </summary>
    [JsonPropertyName("no_longer_affected")]
    public int NoLongerAffected { get; init; }

    /// <summary>
    /// Status changes by type.
    /// </summary>
    [JsonPropertyName("status_changes")]
    public required ImmutableDictionary<string, int> StatusChanges { get; init; }

    /// <summary>
    /// Severity changes by type (e.g., "low_to_high").
    /// </summary>
    [JsonPropertyName("severity_changes")]
    public required ImmutableDictionary<string, int> SeverityChanges { get; init; }

    /// <summary>
    /// Impact assessment.
    /// </summary>
    [JsonPropertyName("impact")]
    public required WhatIfImpact Impact { get; init; }
}

/// <summary>
/// Impact assessment from what-if simulation.
/// </summary>
public sealed record WhatIfImpact(
    [property: JsonPropertyName("risk_delta")] string RiskDelta, // increased, decreased, unchanged
    [property: JsonPropertyName("blocked_count_delta")] int BlockedCountDelta,
    [property: JsonPropertyName("warning_count_delta")] int WarningCountDelta,
    [property: JsonPropertyName("recommendation")] string? Recommendation);