// <copyright file="IFacetDriftVexDraftStore.cs" company="StellaOps">
// Copyright (c) StellaOps. Licensed under BUSL-1.1.
// </copyright>
// Sprint: SPRINT_20260105_002_003_FACET (QTA-018)

using System.Collections.Concurrent;
using System.Collections.Immutable;

namespace StellaOps.Facet;

/// <summary>
/// Query parameters for listing VEX drafts.
/// </summary>
public sealed record FacetDriftVexDraftQuery
{
    /// <summary>
    /// Filter by image digest.
    /// </summary>
    public string? ImageDigest { get; init; }

    /// <summary>
    /// Filter by facet ID.
    /// </summary>
    public string? FacetId { get; init; }

    /// <summary>
    /// Filter by review status.
    /// </summary>
    public FacetDriftVexReviewStatus? ReviewStatus { get; init; }

    /// <summary>
    /// Include only drafts created since this time.
    /// </summary>
    public DateTimeOffset? Since { get; init; }

    /// <summary>
    /// Include only drafts created until this time.
    /// </summary>
    public DateTimeOffset? Until { get; init; }

    /// <summary>
    /// Maximum number of results to return.
    /// </summary>
    public int Limit { get; init; } = 100;

    /// <summary>
    /// Offset for pagination.
    /// </summary>
    public int Offset { get; init; } = 0;
}

/// <summary>
/// Review status for facet drift VEX drafts.
/// </summary>
public enum FacetDriftVexReviewStatus
{
    /// <summary>
    /// Draft is pending review.
    /// </summary>
    Pending,

    /// <summary>
    /// Draft has been approved.
    /// </summary>
    Approved,

    /// <summary>
    /// Draft has been rejected.
    /// </summary>
    Rejected,

    /// <summary>
    /// Draft has expired without review.
    /// </summary>
    Expired
}

/// <summary>
/// Storage abstraction for facet drift VEX drafts.
/// </summary>
public interface IFacetDriftVexDraftStore
{
    /// <summary>
    /// Saves a new draft. Throws if a draft with the same ID already exists.
    /// </summary>
    Task SaveAsync(FacetDriftVexDraft draft, CancellationToken ct = default);

    /// <summary>
    /// Saves multiple drafts atomically.
    /// </summary>
    Task SaveBatchAsync(IEnumerable<FacetDriftVexDraft> drafts, CancellationToken ct = default);

    /// <summary>
    /// Finds a draft by its unique ID.
    /// </summary>
    Task<FacetDriftVexDraft?> FindByIdAsync(string draftId, CancellationToken ct = default);

    /// <summary>
    /// Finds drafts matching the query parameters.
    /// </summary>
    Task<ImmutableArray<FacetDriftVexDraft>> QueryAsync(FacetDriftVexDraftQuery query, CancellationToken ct = default);

    /// <summary>
    /// Updates a draft's review status.
    /// </summary>
    Task UpdateReviewStatusAsync(
        string draftId,
        FacetDriftVexReviewStatus status,
        string? reviewedBy = null,
        string? reviewNotes = null,
        CancellationToken ct = default);

    /// <summary>
    /// Gets pending drafts that have passed their review deadline.
    /// </summary>
    Task<ImmutableArray<FacetDriftVexDraft>> GetOverdueAsync(DateTimeOffset asOf, CancellationToken ct = default);

    /// <summary>
    /// Deletes expired drafts older than the retention period.
    /// </summary>
    Task<int> PurgeExpiredAsync(DateTimeOffset asOf, CancellationToken ct = default);

    /// <summary>
    /// Checks if a draft exists for the given image/facet combination.
    /// </summary>
    Task<bool> ExistsAsync(string imageDigest, string facetId, CancellationToken ct = default);
}

/// <summary>
/// Extended draft record with review tracking.
/// </summary>
public sealed record FacetDriftVexDraftWithReview
{
    /// <summary>
    /// The original draft.
    /// </summary>
    public required FacetDriftVexDraft Draft { get; init; }

    /// <summary>
    /// Current review status.
    /// </summary>
    public FacetDriftVexReviewStatus ReviewStatus { get; init; } = FacetDriftVexReviewStatus.Pending;

    /// <summary>
    /// Who reviewed the draft.
    /// </summary>
    public string? ReviewedBy { get; init; }

    /// <summary>
    /// When the draft was reviewed.
    /// </summary>
    public DateTimeOffset? ReviewedAt { get; init; }

    /// <summary>
    /// Notes from the reviewer.
    /// </summary>
    public string? ReviewNotes { get; init; }
}

/// <summary>
/// In-memory implementation of <see cref="IFacetDriftVexDraftStore"/> for testing.
/// </summary>
public sealed class InMemoryFacetDriftVexDraftStore : IFacetDriftVexDraftStore
{
    private readonly ConcurrentDictionary<string, FacetDriftVexDraftWithReview> _drafts = new(StringComparer.Ordinal);
    private readonly TimeProvider _timeProvider;

    /// <summary>
    /// Initializes a new instance of the <see cref="InMemoryFacetDriftVexDraftStore"/> class.
    /// </summary>
    public InMemoryFacetDriftVexDraftStore(TimeProvider? timeProvider = null)
    {
        _timeProvider = timeProvider ?? TimeProvider.System;
    }

    /// <inheritdoc />
    public Task SaveAsync(FacetDriftVexDraft draft, CancellationToken ct = default)
    {
        ArgumentNullException.ThrowIfNull(draft);

        var wrapper = new FacetDriftVexDraftWithReview { Draft = draft };
        if (!_drafts.TryAdd(draft.DraftId, wrapper))
        {
            throw new InvalidOperationException($"Draft with ID '{draft.DraftId}' already exists.");
        }

        return Task.CompletedTask;
    }

    /// <inheritdoc />
    public Task SaveBatchAsync(IEnumerable<FacetDriftVexDraft> drafts, CancellationToken ct = default)
    {
        ArgumentNullException.ThrowIfNull(drafts);

        foreach (var draft in drafts)
        {
            var wrapper = new FacetDriftVexDraftWithReview { Draft = draft };
            if (!_drafts.TryAdd(draft.DraftId, wrapper))
            {
                throw new InvalidOperationException($"Draft with ID '{draft.DraftId}' already exists.");
            }
        }

        return Task.CompletedTask;
    }

    /// <inheritdoc />
    public Task<FacetDriftVexDraft?> FindByIdAsync(string draftId, CancellationToken ct = default)
    {
        ArgumentException.ThrowIfNullOrWhiteSpace(draftId);

        _drafts.TryGetValue(draftId, out var wrapper);
        return Task.FromResult<FacetDriftVexDraft?>(wrapper?.Draft);
    }

    /// <inheritdoc />
    public Task<ImmutableArray<FacetDriftVexDraft>> QueryAsync(FacetDriftVexDraftQuery query, CancellationToken ct = default)
    {
        ArgumentNullException.ThrowIfNull(query);

        var results = _drafts.Values.AsEnumerable();

        if (!string.IsNullOrEmpty(query.ImageDigest))
        {
            results = results.Where(w => w.Draft.ImageDigest == query.ImageDigest);
        }

        if (!string.IsNullOrEmpty(query.FacetId))
        {
            results = results.Where(w => w.Draft.FacetId == query.FacetId);
        }

        if (query.ReviewStatus.HasValue)
        {
            results = results.Where(w => w.ReviewStatus == query.ReviewStatus.Value);
        }

        if (query.Since.HasValue)
        {
            results = results.Where(w => w.Draft.GeneratedAt >= query.Since.Value);
        }

        if (query.Until.HasValue)
        {
            results = results.Where(w => w.Draft.GeneratedAt <= query.Until.Value);
        }

        var paged = results
            .OrderByDescending(w => w.Draft.GeneratedAt)
            .Skip(query.Offset)
            .Take(query.Limit)
            .Select(w => w.Draft)
            .ToImmutableArray();

        return Task.FromResult(paged);
    }

    /// <inheritdoc />
    public Task UpdateReviewStatusAsync(
        string draftId,
        FacetDriftVexReviewStatus status,
        string? reviewedBy = null,
        string? reviewNotes = null,
        CancellationToken ct = default)
    {
        ArgumentException.ThrowIfNullOrWhiteSpace(draftId);

        if (!_drafts.TryGetValue(draftId, out var wrapper))
        {
            throw new KeyNotFoundException($"Draft with ID '{draftId}' not found.");
        }

        var updated = wrapper with
        {
            ReviewStatus = status,
            ReviewedBy = reviewedBy,
            ReviewedAt = _timeProvider.GetUtcNow(),
            ReviewNotes = reviewNotes
        };

        _drafts[draftId] = updated;
        return Task.CompletedTask;
    }

    /// <inheritdoc />
    public Task<ImmutableArray<FacetDriftVexDraft>> GetOverdueAsync(DateTimeOffset asOf, CancellationToken ct = default)
    {
        var overdue = _drafts.Values
            .Where(w => w.ReviewStatus == FacetDriftVexReviewStatus.Pending)
            .Where(w => w.Draft.ReviewDeadline < asOf)
            .Select(w => w.Draft)
            .ToImmutableArray();

        return Task.FromResult(overdue);
    }

    /// <inheritdoc />
    public Task<int> PurgeExpiredAsync(DateTimeOffset asOf, CancellationToken ct = default)
    {
        var expiredIds = _drafts
            .Where(kvp => kvp.Value.Draft.ExpiresAt < asOf)
            .Select(kvp => kvp.Key)
            .ToList();

        foreach (var id in expiredIds)
        {
            _drafts.TryRemove(id, out _);
        }

        return Task.FromResult(expiredIds.Count);
    }

    /// <inheritdoc />
    public Task<bool> ExistsAsync(string imageDigest, string facetId, CancellationToken ct = default)
    {
        var exists = _drafts.Values.Any(w =>
            w.Draft.ImageDigest == imageDigest &&
            w.Draft.FacetId == facetId &&
            w.ReviewStatus == FacetDriftVexReviewStatus.Pending);

        return Task.FromResult(exists);
    }

    /// <summary>
    /// Gets all drafts for testing purposes.
    /// </summary>
    public IReadOnlyCollection<FacetDriftVexDraftWithReview> GetAllForTesting()
        => _drafts.Values.ToList();
}