using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.Options;
using Novelly.Api.Activity;
using Novelly.Api.Common;
using Novelly.Api.Data;
using Novelly.Api.Users;

namespace Novelly.Api.Trash;

public class TrashService(
    INovelDbContext db,
    NovelAccessService access,
    ActivityLog activity,
    IOptions<TrashOptions> options,
    ILogger<TrashService> logger)
{
    public async Task<IReadOnlyList<TrashedItemResponse>> ListAsync(Guid novelId, CancellationToken ct = default)
    {
        Guard.Default(novelId, nameof(novelId));

        logger.LogInformation("Listing trash for novel {NovelId}", novelId);

        await access.RequireAsync(novelId, NovelPermission.Read, ct);

        var retentionDays = options.Value.RetentionDays;

        var characters = await db.Characters
            .IgnoreQueryFilters()
            .Where(c => c.NovelId == novelId && c.DeletedAt != null)
            .Select(c => new TrashedItemResponse(
                c.Id, TrashEntityKind.Character, c.Name,
                c.ArcStages.Count > 0 ? $"{c.ArcStages.Count} arc stages" : null,
                c.DeletedAt!.Value, c.DeletedAt!.Value.AddDays(retentionDays)))
            .ToListAsync(ct);

        var chapters = await db.Chapters
            .IgnoreQueryFilters()
            .Where(c => c.NovelId == novelId && c.DeletedAt != null)
            .Select(c => new TrashedItemResponse(
                c.Id, TrashEntityKind.Chapter, c.Title,
                c.Beats.Count > 0 ? $"{c.Beats.Count} beats" : null,
                c.DeletedAt!.Value, c.DeletedAt!.Value.AddDays(retentionDays)))
            .ToListAsync(ct);

        var locations = await db.Locations
            .IgnoreQueryFilters()
            .Where(l => l.NovelId == novelId && l.DeletedAt != null)
            .Select(l => new TrashedItemResponse(
                l.Id, TrashEntityKind.Location, l.Name,
                l.Chapters.Count > 0 ? $"used by {l.Chapters.Count} chapters" : null,
                l.DeletedAt!.Value, l.DeletedAt!.Value.AddDays(retentionDays)))
            .ToListAsync(ct);

        return [.. characters.Concat(chapters).Concat(locations).OrderByDescending(i => i.DeletedAt)];
    }

    public async Task<bool> RestoreAsync(TrashEntityKind kind, Guid id, CancellationToken ct = default)
    {
        Guard.Default(id, nameof(id));

        logger.LogInformation("Restoring {Kind} {ItemId} from trash", kind, id);

        return kind switch
        {
            TrashEntityKind.Character => await RestoreCharacterAsync(id, ct),
            TrashEntityKind.Chapter => await RestoreChapterAsync(id, ct),
            TrashEntityKind.Location => await RestoreLocationAsync(id, ct),
            _ => throw new ArgumentOutOfRangeException(nameof(kind), kind, null)
        };
    }

    public async Task<bool> PurgeAsync(TrashEntityKind kind, Guid id, CancellationToken ct = default)
    {
        Guard.Default(id, nameof(id));

        logger.LogInformation("Purging {Kind} {ItemId} from trash", kind, id);

        var novelId = await NovelIdOfTrashedAsync(kind, id, ct);
        if (novelId is null)
        {
            return false;
        }

        await access.RequireAsync(novelId.Value, NovelPermission.DeleteContent, ct);

        var removed = await TrashPurge.RemoveAsync(db, kind, id, ct);
        if (!removed)
        {
            return false;
        }

        await db.SaveChangesAsync(ct);
        return true;
    }

    public async Task<int> EmptyAsync(Guid novelId, CancellationToken ct = default)
    {
        Guard.Default(novelId, nameof(novelId));

        logger.LogInformation("Emptying trash for novel {NovelId}", novelId);

        await access.RequireAsync(novelId, NovelPermission.DeleteContent, ct);

        var items = await ListAsync(novelId, ct);

        var purged = 0;
        foreach (var item in items)
        {
            if (await TrashPurge.RemoveAsync(db, item.Kind, item.Id, ct))
            {
                purged++;
            }
        }

        await db.SaveChangesAsync(ct);
        logger.LogInformation("Emptied {Count} items from trash for novel {NovelId}", purged, novelId);
        return purged;
    }

    private async Task<bool> RestoreCharacterAsync(Guid id, CancellationToken ct)
    {
        var character = await db.Characters.IgnoreQueryFilters().FirstOrDefaultAsync(c => c.Id == id && c.DeletedAt != null, ct);
        if (character is null)
        {
            logger.LogWarning("Trashed character {CharacterId} not found", id);
            return false;
        }

        await access.RequireAsync(character.NovelId, NovelPermission.DeleteContent, ct);

        character.DeletedAt = null;
        activity.Record(character.NovelId, ActivityEntityKind.Character, ActivityAction.Restored, character.Id);
        await db.SaveChangesAsync(ct);
        return true;
    }

    private async Task<bool> RestoreChapterAsync(Guid id, CancellationToken ct)
    {
        var chapter = await db.Chapters.IgnoreQueryFilters().FirstOrDefaultAsync(c => c.Id == id && c.DeletedAt != null, ct);
        if (chapter is null)
        {
            logger.LogWarning("Trashed chapter {ChapterId} not found", id);
            return false;
        }

        await access.RequireAsync(chapter.NovelId, NovelPermission.DeleteContent, ct);

        chapter.DeletedAt = null;
        activity.Record(chapter.NovelId, ActivityEntityKind.Chapter, ActivityAction.Restored, chapter.Id, chapter.WordCount);
        await db.SaveChangesAsync(ct);
        return true;
    }

    private async Task<bool> RestoreLocationAsync(Guid id, CancellationToken ct)
    {
        var location = await db.Locations.IgnoreQueryFilters().FirstOrDefaultAsync(l => l.Id == id && l.DeletedAt != null, ct);
        if (location is null)
        {
            logger.LogWarning("Trashed location {LocationId} not found", id);
            return false;
        }

        await access.RequireAsync(location.NovelId, NovelPermission.DeleteContent, ct);

        var clash = await db.Locations.FirstOrDefaultAsync(
            l => l.NovelId == location.NovelId && EF.Functions.Like(l.Name, location.Name), ct);
        if (clash is not null)
        {
            logger.LogWarning("Rejected restore of location {LocationId}: '{Name}' already exists as {ClashLocationId}", id, location.Name, clash.Id);
            throw new InvalidOperationException($"The novel already has a location called '{clash.Name}'.");
        }

        location.DeletedAt = null;
        activity.Record(location.NovelId, ActivityEntityKind.Location, ActivityAction.Restored, location.Id);
        await db.SaveChangesAsync(ct);
        return true;
    }

    private async Task<Guid?> NovelIdOfTrashedAsync(TrashEntityKind kind, Guid id, CancellationToken ct) => kind switch
    {
        TrashEntityKind.Character => (await db.Characters.IgnoreQueryFilters().Where(c => c.Id == id && c.DeletedAt != null).Select(c => (Guid?)c.NovelId).FirstOrDefaultAsync(ct)),
        TrashEntityKind.Chapter => (await db.Chapters.IgnoreQueryFilters().Where(c => c.Id == id && c.DeletedAt != null).Select(c => (Guid?)c.NovelId).FirstOrDefaultAsync(ct)),
        TrashEntityKind.Location => (await db.Locations.IgnoreQueryFilters().Where(l => l.Id == id && l.DeletedAt != null).Select(l => (Guid?)l.NovelId).FirstOrDefaultAsync(ct)),
        _ => throw new ArgumentOutOfRangeException(nameof(kind), kind, null)
    };
}