// Licensed to StellaOps under the AGPL-3.0-or-later license.

using System.Collections.Immutable;
using System.Globalization;

namespace StellaOps.VexLens.Delta;

/// <summary>
/// A report summarizing changes between two vulnerability graph snapshots.
/// </summary>
/// <remarks>
/// DeltaReport groups changes by section for efficient triage:
/// - Users can focus on New findings first
/// - Resolved items can be quickly acknowledged
/// - Confidence changes help reprioritize existing findings
/// - Policy impacts highlight workflow-affecting changes
/// </remarks>
public sealed record DeltaReport
{
    /// <summary>
    /// Gets the unique identifier for this report.
    /// </summary>
    public required string ReportId { get; init; }

    /// <summary>
    /// Gets the digest of the previous snapshot.
    /// </summary>
    public required string FromSnapshotDigest { get; init; }

    /// <summary>
    /// Gets the digest of the current snapshot.
    /// </summary>
    public required string ToSnapshotDigest { get; init; }

    /// <summary>
    /// Gets the timestamp when the report was generated.
    /// </summary>
    public required DateTimeOffset GeneratedAt { get; init; }

    /// <summary>
    /// Gets all delta entries in this report.
    /// </summary>
    public required ImmutableArray<DeltaEntry> Entries { get; init; }

    /// <summary>
    /// Gets the summary counts by section.
    /// </summary>
    public required DeltaSummary Summary { get; init; }

    /// <summary>
    /// Gets entries grouped by section for UI consumption.
    /// </summary>
    public ImmutableDictionary<DeltaSection, ImmutableArray<DeltaEntry>> BySection =>
        Entries
            .GroupBy(e => e.Section)
            .ToImmutableDictionary(
                g => g.Key,
                g => g.ToImmutableArray());

    /// <summary>
    /// Gets entries for a specific section.
    /// </summary>
    public ImmutableArray<DeltaEntry> GetSection(DeltaSection section) =>
        BySection.TryGetValue(section, out var entries)
            ? entries
            : [];

    /// <summary>
    /// Gets whether this report has any actionable changes.
    /// </summary>
    public bool HasActionableChanges =>
        Summary.NewCount > 0 ||
        Summary.PolicyImpactCount > 0 ||
        Summary.ConfidenceUpCount > 0;

    /// <summary>
    /// Gets a one-line summary suitable for notifications.
    /// </summary>
    public string ToNotificationSummary()
    {
        var parts = new List<string>();

        if (Summary.NewCount > 0)
        {
            parts.Add(string.Create(CultureInfo.InvariantCulture,
                $"{Summary.NewCount} new"));
        }

        if (Summary.ResolvedCount > 0)
        {
            parts.Add(string.Create(CultureInfo.InvariantCulture,
                $"{Summary.ResolvedCount} resolved"));
        }

        if (Summary.PolicyImpactCount > 0)
        {
            parts.Add(string.Create(CultureInfo.InvariantCulture,
                $"{Summary.PolicyImpactCount} policy impact"));
        }

        if (Summary.ConfidenceUpCount > 0)
        {
            parts.Add(string.Create(CultureInfo.InvariantCulture,
                $"{Summary.ConfidenceUpCount} confidence up"));
        }

        if (Summary.ConfidenceDownCount > 0)
        {
            parts.Add(string.Create(CultureInfo.InvariantCulture,
                $"{Summary.ConfidenceDownCount} confidence down"));
        }

        return parts.Count == 0
            ? "No significant changes"
            : string.Join(", ", parts);
    }
}

/// <summary>
/// Summary counts for a delta report.
/// </summary>
public sealed record DeltaSummary
{
    /// <summary>
    /// Gets the total number of entries.
    /// </summary>
    public required int TotalCount { get; init; }

    /// <summary>
    /// Gets the count of new findings.
    /// </summary>
    public required int NewCount { get; init; }

    /// <summary>
    /// Gets the count of resolved findings.
    /// </summary>
    public required int ResolvedCount { get; init; }

    /// <summary>
    /// Gets the count of confidence increases.
    /// </summary>
    public required int ConfidenceUpCount { get; init; }

    /// <summary>
    /// Gets the count of confidence decreases.
    /// </summary>
    public required int ConfidenceDownCount { get; init; }

    /// <summary>
    /// Gets the count of policy impact changes.
    /// </summary>
    public required int PolicyImpactCount { get; init; }

    /// <summary>
    /// Gets the count of damped (suppressed) changes.
    /// </summary>
    public int DampedCount { get; init; }

    /// <summary>
    /// Gets the count of evidence-only changes.
    /// </summary>
    public int EvidenceChangedCount { get; init; }

    /// <summary>
    /// Creates a summary from a list of entries.
    /// </summary>
    public static DeltaSummary FromEntries(IEnumerable<DeltaEntry> entries)
    {
        var list = entries.ToList();

        return new DeltaSummary
        {
            TotalCount = list.Count,
            NewCount = list.Count(e => e.Section == DeltaSection.New),
            ResolvedCount = list.Count(e => e.Section == DeltaSection.Resolved),
            ConfidenceUpCount = list.Count(e => e.Section == DeltaSection.ConfidenceUp),
            ConfidenceDownCount = list.Count(e => e.Section == DeltaSection.ConfidenceDown),
            PolicyImpactCount = list.Count(e => e.Section == DeltaSection.PolicyImpact),
            DampedCount = list.Count(e => e.Section == DeltaSection.Damped),
            EvidenceChangedCount = list.Count(e => e.Section == DeltaSection.EvidenceChanged)
        };
    }
}