// <copyright file="FacetDrift.cs" company="StellaOps">
// Copyright (c) StellaOps. Licensed under BUSL-1.1.
// </copyright>

using System.Collections.Immutable;

namespace StellaOps.Facet;

/// <summary>
/// Drift detection result for a single facet.
/// </summary>
public sealed record FacetDrift
{
    /// <summary>
    /// Gets the facet this drift applies to.
    /// </summary>
    public required string FacetId { get; init; }

    /// <summary>
    /// Gets the files added since baseline.
    /// </summary>
    public required ImmutableArray<FacetFileEntry> Added { get; init; }

    /// <summary>
    /// Gets the files removed since baseline.
    /// </summary>
    public required ImmutableArray<FacetFileEntry> Removed { get; init; }

    /// <summary>
    /// Gets the files modified since baseline.
    /// </summary>
    public required ImmutableArray<FacetFileModification> Modified { get; init; }

    /// <summary>
    /// Gets the drift score (0-100, higher = more drift).
    /// </summary>
    /// <remarks>
    /// The drift score weighs additions, removals, and modifications
    /// to produce a single measure of change magnitude.
    /// </remarks>
    public required decimal DriftScore { get; init; }

    /// <summary>
    /// Gets the quota evaluation result.
    /// </summary>
    public required QuotaVerdict QuotaVerdict { get; init; }

    /// <summary>
    /// Gets the number of files in baseline facet seal.
    /// </summary>
    public required int BaselineFileCount { get; init; }

    /// <summary>
    /// Gets the total number of changes (added + removed + modified).
    /// </summary>
    public int TotalChanges => Added.Length + Removed.Length + Modified.Length;

    /// <summary>
    /// Gets the churn percentage = (changes / baseline count) * 100.
    /// </summary>
    public decimal ChurnPercent => BaselineFileCount > 0
        ? TotalChanges / (decimal)BaselineFileCount * 100
        : Added.Length > 0 ? 100m : 0m;

    /// <summary>
    /// Gets whether this facet has any drift.
    /// </summary>
    public bool HasDrift => TotalChanges > 0;

    /// <summary>
    /// Gets a no-drift instance for a facet.
    /// </summary>
    public static FacetDrift NoDrift(string facetId, int baselineFileCount) => new()
    {
        FacetId = facetId,
        Added = [],
        Removed = [],
        Modified = [],
        DriftScore = 0m,
        QuotaVerdict = QuotaVerdict.Ok,
        BaselineFileCount = baselineFileCount
    };
}

/// <summary>
/// Aggregated drift report for all facets in an image.
/// </summary>
public sealed record FacetDriftReport
{
    /// <summary>
    /// Gets the image digest analyzed.
    /// </summary>
    public required string ImageDigest { get; init; }

    /// <summary>
    /// Gets the baseline seal used for comparison.
    /// </summary>
    public required string BaselineSealId { get; init; }

    /// <summary>
    /// Gets when the analysis was performed.
    /// </summary>
    public required DateTimeOffset AnalyzedAt { get; init; }

    /// <summary>
    /// Gets the per-facet drift results.
    /// </summary>
    public required ImmutableArray<FacetDrift> FacetDrifts { get; init; }

    /// <summary>
    /// Gets the overall verdict (worst of all facets).
    /// </summary>
    public required QuotaVerdict OverallVerdict { get; init; }

    /// <summary>
    /// Gets the total files changed across all facets.
    /// </summary>
    public int TotalChangedFiles => FacetDrifts.Sum(d => d.TotalChanges);

    /// <summary>
    /// Gets the facets with any drift.
    /// </summary>
    public IEnumerable<FacetDrift> DriftedFacets => FacetDrifts.Where(d => d.HasDrift);

    /// <summary>
    /// Gets the facets with quota violations.
    /// </summary>
    public IEnumerable<FacetDrift> QuotaViolations =>
        FacetDrifts.Where(d => d.QuotaVerdict is QuotaVerdict.Warning
                                              or QuotaVerdict.Blocked
                                              or QuotaVerdict.RequiresVex);
}