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

namespace Novelly.Api.Beats;

public class BeatService(
    INovelDbContext db,
    NovelAccessService access,
    TagService tags,
    ILogger<BeatService> logger,
    IModelValidator<CreateBeatRequest> createValidator,
    IModelValidator<UpdateBeatRequest> updateValidator,
    IModelValidator<ReorderBeatsRequest> reorderValidator,
    IModelValidator<AssignCharacterToBeatsRequest> assignCharacterValidator,
    IModelValidator<MoveBeatsRequest> moveValidator)
{
    public async Task<IReadOnlyList<Beat>> ListAsync(Guid chapterId, CancellationToken ct = default)
    {
        Guard.Default(chapterId, nameof(chapterId));

        logger.LogInformation("Listing beats for chapter {ChapterId}", chapterId);

        await RequireChapterAccessAsync(chapterId, NovelPermission.Read, ct);

        return await Query()
            .Where(b => b.ChapterId == chapterId)
            .OrderBy(b => b.SortOrder)
            .ToListAsync(ct);
    }

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

        logger.LogInformation("Getting beat {BeatId}", id);

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

        await RequireBeatAccessAsync(beat, NovelPermission.Read, ct);
        return beat;
    }

    public async Task<IReadOnlyList<Beat>?> ListForCharacterAsync(
        Guid characterId, CancellationToken ct = default)
    {
        Guard.Default(characterId, nameof(characterId));

        logger.LogInformation("Listing beats for character {CharacterId}", characterId);

        var characterNovelId = await db.Characters.Where(c => c.Id == characterId).Select(c => (Guid?)c.NovelId).FirstOrDefaultAsync(ct);
        if (characterNovelId is null)
        {
            logger.LogWarning("Character {CharacterId} not found", characterId);
            return null;
        }

        await access.RequireAsync(characterNovelId.Value, NovelPermission.Read, ct);

        var beats = await db.Beats
            .Include(b => b.Chapter)
            .Include(b => b.ArcStages)
            .Where(b => b.Characters.Any(c => c.Id == characterId))
            .ToListAsync(ct);

        return
        [
            .. beats
                .OrderBy(b => b.Chapter?.Number ?? 0)
                .ThenBy(b => b.SortOrder)
        ];
    }

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

        logger.LogInformation("Creating beat {Title} for chapter {ChapterId}", request.Title, chapterId);

        var chapter = await db.Chapters.FirstOrDefaultAsync(c => c.Id == chapterId, ct);
        if (chapter is null)
        {
            logger.LogWarning("Rejected beat creation: chapter {ChapterId} not found", chapterId);
            return null;
        }

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

        var beat = new Beat
        {
            ChapterId = chapterId,
            Title = request.Title,
            SortOrder = request.SortOrder ?? await NextSortOrderAsync(chapterId, ct),
            WhatHappened = request.WhatHappened,
            WhatsNext = request.WhatsNext
        };

        if (request.CharacterIds is { } characterIds)
        {
            beat.Characters = await ResolveCharactersAsync(chapter.NovelId, characterIds, ct);
        }

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

        chapter.UpdatedAt = DateTimeOffset.UtcNow;

        db.Beats.Add(beat);
        await db.SaveChangesAsync(ct);

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

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

        logger.LogInformation("Updating beat {BeatId}", id);

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

        var chapter = await db.Chapters.FirstOrDefaultAsync(c => c.Id == beat.ChapterId, ct);
        if (chapter is null)
        {
            logger.LogError("Beat {BeatId} references chapter {ChapterId} which does not exist", id, beat.ChapterId);
            return null;
        }

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

        beat.Title = Patch.Apply(beat.Title, request.Title) ?? beat.Title;
        beat.SortOrder = request.SortOrder ?? beat.SortOrder;
        beat.WhatHappened = Patch.Apply(beat.WhatHappened, request.WhatHappened);
        beat.WhatsNext = Patch.Apply(beat.WhatsNext, request.WhatsNext);
        beat.UpdatedAt = DateTimeOffset.UtcNow;
        chapter.UpdatedAt = beat.UpdatedAt;

        if (request.CharacterIds is { } characterIds)
        {
            beat.Characters = await ResolveCharactersAsync(chapter.NovelId, characterIds, ct);
        }

        if (request.Tags is { } names)
        {
            beat.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 beat {BeatId}", id);

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

        await RequireBeatAccessAsync(beat, NovelPermission.DeleteContent, ct);

        var chapter = await db.Chapters.FirstOrDefaultAsync(c => c.Id == beat.ChapterId, ct);
        if (chapter is not null) chapter.UpdatedAt = DateTimeOffset.UtcNow;

        db.Beats.Remove(beat);
        await db.SaveChangesAsync(ct);
        return true;
    }

    public async Task<IReadOnlyList<Beat>?> ReorderAsync(
        Guid chapterId, ReorderBeatsRequest request, CancellationToken ct = default)
    {
        Guard.Default(chapterId, nameof(chapterId));
        Guard.Null(request, nameof(request));
        reorderValidator.Validate(request).ThrowIfInvalid(logger);

        logger.LogInformation("Reordering {Count} beats for chapter {ChapterId}", request.BeatIds.Count, chapterId);

        await RequireChapterAccessAsync(chapterId, NovelPermission.Write, ct);

        var beats = await db.Beats.Where(b => b.ChapterId == chapterId).ToListAsync(ct);

        var missing = request.BeatIds.Where(id => beats.All(b => b.Id != id)).ToList();
        if (missing.Count > 0)
        {
            logger.LogWarning("Reorder for chapter {ChapterId} referenced missing beat {BeatId}", chapterId, missing[0]);
            return null;
        }

        var order = 1;
        foreach (var id in request.BeatIds)
        {
            beats.Single(b => b.Id == id).SortOrder = order++;
        }

        foreach (var beat in beats.Where(b => !request.BeatIds.Contains(b.Id)).OrderBy(b => b.SortOrder))
        {
            beat.SortOrder = order++;
        }

        var chapter = await db.Chapters.FirstOrDefaultAsync(c => c.Id == chapterId, ct);
        if (chapter is not null) chapter.UpdatedAt = DateTimeOffset.UtcNow;

        await db.SaveChangesAsync(ct);
        return await ListAsync(chapterId, ct);
    }

    public async Task<IReadOnlyList<Beat>?> AssignCharacterAsync(
        Guid chapterId, AssignCharacterToBeatsRequest request, CancellationToken ct = default)
    {
        Guard.Default(chapterId, nameof(chapterId));
        Guard.Null(request, nameof(request));
        assignCharacterValidator.Validate(request).ThrowIfInvalid(logger);

        logger.LogInformation(
            "Assigning character {CharacterId} to {Count} beats in chapter {ChapterId}",
            request.CharacterId, request.BeatIds.Count, chapterId);

        var chapter = await db.Chapters.FirstOrDefaultAsync(c => c.Id == chapterId, ct);
        if (chapter is null)
        {
            logger.LogWarning("Rejected character assignment: chapter {ChapterId} not found", chapterId);
            return null;
        }

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

        var character = await db.Characters
            .FirstOrDefaultAsync(c => c.Id == request.CharacterId && c.NovelId == chapter.NovelId, ct);
        if (character is null)
        {
            logger.LogWarning(
                "Rejected character assignment: character {CharacterId} not found in novel {NovelId}",
                request.CharacterId, chapter.NovelId);
            return null;
        }

        var beats = await Query().Where(b => b.ChapterId == chapterId && request.BeatIds.Contains(b.Id)).ToListAsync(ct);
        var missing = request.BeatIds.Where(id => beats.All(b => b.Id != id)).ToList();
        if (missing.Count > 0)
        {
            logger.LogWarning(
                "Rejected character assignment: chapter {ChapterId} referenced missing beat {BeatId}", chapterId, missing[0]);
            return null;
        }

        foreach (var beat in beats.Where(b => b.Characters.All(c => c.Id != character.Id)))
        {
            beat.Characters.Add(character);
            beat.UpdatedAt = DateTimeOffset.UtcNow;
            chapter.UpdatedAt = beat.UpdatedAt;
        }

        await db.SaveChangesAsync(ct);
        return await ListAsync(chapterId, ct);
    }

    public async Task<IReadOnlyList<Beat>?> MoveAsync(
        Guid chapterId, MoveBeatsRequest request, CancellationToken ct = default)
    {
        Guard.Default(chapterId, nameof(chapterId));
        Guard.Null(request, nameof(request));
        moveValidator.Validate(request).ThrowIfInvalid(logger);

        logger.LogInformation(
            "Moving {Count} beats from chapter {ChapterId} to chapter {TargetChapterId}",
            request.BeatIds.Count, chapterId, request.TargetChapterId);

        var chapter = await db.Chapters.FirstOrDefaultAsync(c => c.Id == chapterId, ct);
        if (chapter is null)
        {
            logger.LogWarning("Rejected beat move: chapter {ChapterId} not found", chapterId);
            return null;
        }

        var targetChapter = await db.Chapters.FirstOrDefaultAsync(
            c => c.Id == request.TargetChapterId && c.NovelId == chapter.NovelId, ct);
        if (targetChapter is null)
        {
            logger.LogWarning(
                "Rejected beat move: target chapter {TargetChapterId} not found in novel {NovelId}",
                request.TargetChapterId, chapter.NovelId);
            return null;
        }

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

        var beats = await Query().Where(b => b.ChapterId == chapterId && request.BeatIds.Contains(b.Id)).ToListAsync(ct);
        var missing = request.BeatIds.Where(id => beats.All(b => b.Id != id)).ToList();
        if (missing.Count > 0)
        {
            logger.LogWarning("Rejected beat move: chapter {ChapterId} referenced missing beat {BeatId}", chapterId, missing[0]);
            return null;
        }

        if (chapterId == request.TargetChapterId)
        {
            return beats;
        }

        var nextSortOrder = await NextSortOrderAsync(request.TargetChapterId, ct);
        var now = DateTimeOffset.UtcNow;
        foreach (var beatId in request.BeatIds)
        {
            var beat = beats.Single(b => b.Id == beatId);
            beat.ChapterId = request.TargetChapterId;
            beat.SortOrder = nextSortOrder++;
            beat.UpdatedAt = now;
        }

        chapter.UpdatedAt = now;
        targetChapter.UpdatedAt = now;

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

    private async Task<List<Character>> ResolveCharactersAsync(Guid novelId, IReadOnlyList<Guid> characterIds, CancellationToken ct)
    {
        logger.LogDebug("Resolving {Count} characters for novel {NovelId}", characterIds.Count, novelId);

        var distinct = characterIds.Distinct().ToList();
        if (distinct.Count == 0)
        {
            return [];
        }

        var found = await db.Characters
            .Where(c => c.NovelId == novelId && distinct.Contains(c.Id))
            .ToListAsync(ct);

        if (found.Count != distinct.Count)
        {
            logger.LogWarning("Rejected beat reference: one or more characters do not belong to novel {NovelId}", novelId);
            throw new InvalidOperationException(
                "A beat's characters must belong to the same novel as its chapter.");
        }

        logger.LogDebug("Resolved {Count} characters for novel {NovelId}", found.Count, novelId);
        return found;
    }

    private async Task<int> NextSortOrderAsync(Guid chapterId, CancellationToken ct)
    {
        logger.LogDebug("Computing next sort order for chapter {ChapterId}", chapterId);

        var max = await db.Beats
            .Where(b => b.ChapterId == chapterId)
            .MaxAsync(b => (int?)b.SortOrder, ct);

        var next = (max ?? 0) + 1;
        logger.LogDebug("Next sort order for chapter {ChapterId} is {SortOrder}", chapterId, next);
        return next;
    }

    private async Task RequireChapterAccessAsync(Guid chapterId, NovelPermission permission, CancellationToken ct)
    {
        var novelId = await db.Chapters.Where(c => c.Id == chapterId).Select(c => c.NovelId).FirstOrDefaultAsync(ct);
        await access.RequireAsync(novelId, permission, ct);
    }

    private Task RequireBeatAccessAsync(Beat beat, NovelPermission permission, CancellationToken ct) =>
        RequireChapterAccessAsync(beat.ChapterId, permission, ct);

    private IQueryable<Beat> Query() =>
        db.Beats
            .Include(b => b.Characters)
            .Include(b => b.Tags);

    private async Task<Beat?> FindAsync(Guid id, CancellationToken ct)
    {
        logger.LogDebug("Finding beat {BeatId}", id);

        var beat = await Query().FirstOrDefaultAsync(b => b.Id == id, ct);
        if (beat is null)
        {
            logger.LogWarning("Beat {BeatId} not found", id);
            return beat;
        }

        logger.LogDebug("Found beat {BeatId}", id);
        return beat;
    }
}