using Microsoft.EntityFrameworkCore;
using Novelly.Api.Common;
using Novelly.Api.Common.Validation;
using Novelly.Api.Data;
using Novelly.Api.Tags;
using Novelly.Api.Users;

namespace Novelly.Api.Chapters;

public class ChapterService(
    INovelDbContext db,
    NovelAccessService access,
    TagService tags,
    ILogger<ChapterService> logger,
    IModelValidator<CreateChapterRequest> createValidator,
    IModelValidator<UpdateChapterRequest> updateValidator)
{
    public async Task<IReadOnlyList<Chapter>> ListAsync(Guid novelId, CancellationToken ct = default)
    {
        Guard.Default(novelId, nameof(novelId));

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

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

        return await db.Chapters
            .Include(c => c.Beats)
            .Include(c => c.Tags)
            .Where(c => c.NovelId == novelId)
            .OrderBy(c => c.Number)
            .ToListAsync(ct);
    }

    public async Task<Chapter?> GetAsync(Guid id, CancellationToken ct = default)
    {
        Guard.Default(id, nameof(id));

        logger.LogInformation("Getting chapter {ChapterId}", id);

        var chapter = await FindAsync(id, ct);
        if (chapter is null)
        {
            return null;
        }

        await access.RequireAsync(chapter.NovelId, NovelPermission.Read, ct);
        return chapter;
    }

    public async Task<Chapter?> CreateAsync(Guid novelId, CreateChapterRequest request, CancellationToken ct = default)
    {
        Guard.Default(novelId, nameof(novelId));
        Guard.Null(request, nameof(request));
        createValidator.Validate(request).ThrowIfInvalid(logger);

        logger.LogInformation("Creating chapter {Title} for novel {NovelId}", request.Title, novelId);

        if (!await db.Novels.AnyAsync(p => p.Id == novelId, ct))
        {
            logger.LogWarning("Rejected chapter creation: novel {NovelId} not found", novelId);
            return null;
        }

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

        var chapter = new Chapter
        {
            NovelId = novelId,
            Title = request.Title,
            Number = request.Number ?? await NextChapterNumberAsync(novelId, ct),
            Summary = request.Summary,
            Setting = request.Setting,
            Notes = request.Notes,
            Status = request.Status,
            TargetWordCount = request.TargetWordCount,
            Prose = request.Prose,
            WordCount = ChapterMapping.CountWords(request.Prose)
        };

        if (request.Tags is { } names)
        {
            chapter.Tags = await tags.ResolveAsync(novelId, names, ct);
        }

        db.Chapters.Add(chapter);
        await db.SaveChangesAsync(ct);

        return (await FindAsync(chapter.Id, ct))!;
    }

    public async Task<Chapter?> UpdateAsync(Guid id, UpdateChapterRequest request, CancellationToken ct = default)
    {
        Guard.Default(id, nameof(id));
        Guard.Null(request, nameof(request));
        updateValidator.Validate(request).ThrowIfInvalid(logger);

        logger.LogInformation("Updating chapter {ChapterId}", id);

        var chapter = await FindAsync(id, ct);
        if (chapter is null)
        {
            return null;
        }

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

        chapter.Title = Patch.Apply(chapter.Title, request.Title) ?? chapter.Title;
        chapter.Number = request.Number ?? chapter.Number;
        chapter.Summary = Patch.Apply(chapter.Summary, request.Summary);
        chapter.Setting = Patch.Apply(chapter.Setting, request.Setting);
        chapter.Notes = Patch.Apply(chapter.Notes, request.Notes);
        chapter.Status = request.Status ?? chapter.Status;
        chapter.TargetWordCount = request.TargetWordCount ?? chapter.TargetWordCount;

        if (request.Prose is not null)
        {
            chapter.Prose = Patch.Apply(chapter.Prose, request.Prose);
            chapter.WordCount = ChapterMapping.CountWords(chapter.Prose);
        }

        chapter.UpdatedAt = DateTimeOffset.UtcNow;

        if (request.Tags is { } names)
        {
            chapter.Tags = await tags.ResolveAsync(chapter.NovelId, names, ct);
        }

        await db.SaveChangesAsync(ct);
        return (await FindAsync(id, ct))!;
    }

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

        logger.LogInformation("Deleting chapter {ChapterId}", id);

        var chapter = await FindAsync(id, ct);
        if (chapter is null)
        {
            return false;
        }

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

        db.Chapters.Remove(chapter);
        await db.SaveChangesAsync(ct);
        return true;
    }

    private async Task<int> NextChapterNumberAsync(Guid novelId, CancellationToken ct)
    {
        logger.LogDebug("Computing next chapter number for novel {NovelId}", novelId);

        var max = await db.Chapters
            .Where(c => c.NovelId == novelId)
            .MaxAsync(c => (int?)c.Number, ct);

        var next = (max ?? 0) + 1;
        logger.LogDebug("Next chapter number for novel {NovelId} is {Number}", novelId, next);
        return next;
    }

    private async Task<Chapter?> FindAsync(Guid id, CancellationToken ct)
    {
        logger.LogDebug("Finding chapter {ChapterId}", id);

        var chapter = await db.Chapters
            .Include(c => c.Beats).ThenInclude(b => b.Characters)
            .Include(c => c.Beats).ThenInclude(b => b.Tags)
            .Include(c => c.Tags)
            .FirstOrDefaultAsync(c => c.Id == id, ct);

        if (chapter is null)
        {
            logger.LogWarning("Chapter {ChapterId} not found", id);
            return chapter;
        }

        logger.LogDebug("Found chapter {ChapterId}", id);
        return chapter;
    }
}