using System.Text.RegularExpressions;
using PlotLine.Data;
using PlotLine.Models;

namespace PlotLine.Services;

public interface IWordCompanionService
{
    Task<WordCompanionProjectsResponse> ListProjectsAsync();
    Task<WordCompanionBooksResponse?> ListBooksAsync(int projectId);
    Task<WordCompanionCreateBookResponse?> CreateBookAsync(int projectId, WordCompanionCreateBookRequest request);
    Task<WordCompanionBookStructureResponse?> GetBookStructureAsync(int bookId);
    Task<WordCompanionChaptersResponse?> ListChaptersAsync(int bookId);
    Task<WordCompanionResolveSceneResponse?> ResolveSceneAsync(int bookId, WordCompanionResolveSceneRequest request);
    Task<WordCompanionSceneCompanionResponse?> GetSceneCompanionAsync(int sceneId);
    Task<WordCompanionCreateChapterResponse?> CreateChapterAsync(int bookId, WordCompanionCreateChapterRequest request);
    Task<WordCompanionCreateSceneResponse?> CreateSceneAsync(int bookId, int chapterId, WordCompanionCreateSceneRequest request);
    Task<WordCompanionSyncSceneResponse?> SyncSceneAsync(int bookId, WordCompanionSyncSceneRequest request);
    Task<WordCompanionSyncManuscriptResponse?> SyncManuscriptAsync(int bookId, WordCompanionSyncManuscriptRequest request);
    Task<WordCompanionUpdateSceneLinksResponse?> UpdateSceneLinksAsync(int sceneId, WordCompanionUpdateSceneLinksRequest request);
    Task<WordCompanionUpdateWordCountResponse?> UpdateWordCountAsync(int sceneId, WordCompanionUpdateWordCountRequest request);
    Task<WordCompanionManuscriptBookResponse?> GetManuscriptForBookAsync(int bookId);
    Task<WordCompanionManuscriptLinkResponse?> LinkManuscriptAsync(WordCompanionManuscriptLinkRequest request);
    Task<WordCompanionManuscriptAnalyseResponse?> AnalyseManuscriptAsync(WordCompanionManuscriptAnalyseRequest request);
    Task<WordCompanionManuscriptImportResponse?> ImportManuscriptAsync(WordCompanionManuscriptImportRequest request);
    Task<WordCompanionDiscoverCharactersResponse?> DiscoverCharacterCandidatesAsync(WordCompanionDiscoverCharactersRequest request);
    Task<WordCompanionCreateDiscoveredCharactersResponse?> CreateDiscoveredCharactersAsync(WordCompanionCreateDiscoveredCharactersRequest request);
}

public sealed class WordCompanionService(
    IWordCompanionRepository repository,
    IManuscriptDocumentRepository manuscriptDocuments,
    ICurrentUserService currentUser) : IWordCompanionService
{
    private const int CharacterDiscoveryMinimumMentions = 5;
    private const int CharacterDiscoverySuggestionLimit = 50;
    private static readonly Regex CharacterCandidateRegex = new(
        @"\b(?:(?:Mr|Mrs|Ms|Miss|Dr|Rev|Fr|Sir|Lady|Lord|DS|DI|DC|PC)\.?\s+)?[A-Z][a-z]+(?:[-'][A-Z]?[a-z]+)?(?:\s+[A-Z][a-z]+(?:[-'][A-Z]?[a-z]+)?){0,2}\b",
        RegexOptions.Compiled);
    private static readonly HashSet<string> CharacterDiscoveryStopWords = new(StringComparer.OrdinalIgnoreCase)
    {
        "A", "An", "And", "As", "At", "But", "By", "For", "From", "He", "Her", "His", "I", "If", "In", "Into",
        "It", "Its", "Of", "On", "Or", "Our", "She", "So", "That", "The", "Their", "Then", "There", "They",
        "This", "To", "We", "When", "Where", "Who", "With", "You", "Your",
        "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday", "Sunday",
        "January", "February", "March", "April", "May", "June", "July", "August", "September", "October", "November", "December",
        "Christmas", "Easter", "Morning", "Afternoon", "Evening", "Night", "Today", "Tomorrow", "Yesterday",
        "Chapter", "Scene", "Part", "Prologue", "Epilogue", "Book", "Volume", "Act",
        "Mum", "Dad", "Mother", "Father", "Grandma", "Grandad", "Nan", "Nana", "Granny",
        "Yes", "No", "Okay", "Ok", "Hello", "Goodbye"
    };
    public async Task<WordCompanionProjectsResponse> ListProjectsAsync()
    {
        var userId = RequireUserId();
        return new WordCompanionProjectsResponse { Projects = await repository.ListProjectsAsync(userId) };
    }

    public async Task<WordCompanionBooksResponse?> ListBooksAsync(int projectId)
    {
        if (projectId <= 0)
        {
            return null;
        }

        var books = await repository.ListBooksAsync(projectId, RequireUserId());
        return new WordCompanionBooksResponse { Books = books };
    }

    public Task<WordCompanionCreateBookResponse?> CreateBookAsync(int projectId, WordCompanionCreateBookRequest request)
    {
        if (projectId <= 0 || string.IsNullOrWhiteSpace(request.Title))
        {
            return Task.FromResult<WordCompanionCreateBookResponse?>(null);
        }

        request.Title = request.Title.Trim();
        return repository.CreateBookAsync(projectId, RequireUserId(), request);
    }

    public Task<WordCompanionBookStructureResponse?> GetBookStructureAsync(int bookId)
    {
        return bookId <= 0 ? Task.FromResult<WordCompanionBookStructureResponse?>(null) : repository.GetBookStructureAsync(bookId, RequireUserId());
    }

    public async Task<WordCompanionChaptersResponse?> ListChaptersAsync(int bookId)
    {
        if (bookId <= 0)
        {
            return null;
        }

        var chapters = await repository.ListChaptersAsync(bookId, RequireUserId());
        return new WordCompanionChaptersResponse { Chapters = chapters };
    }

    public Task<WordCompanionResolveSceneResponse?> ResolveSceneAsync(int bookId, WordCompanionResolveSceneRequest request)
    {
        if (bookId <= 0 || string.IsNullOrWhiteSpace(request.ChapterTitle) || string.IsNullOrWhiteSpace(request.SceneTitle))
        {
            return Task.FromResult<WordCompanionResolveSceneResponse?>(null);
        }

        return ResolveSceneCoreAsync(bookId, request);
    }

    public Task<WordCompanionSceneCompanionResponse?> GetSceneCompanionAsync(int sceneId)
    {
        return sceneId <= 0 ? Task.FromResult<WordCompanionSceneCompanionResponse?>(null) : repository.GetSceneCompanionAsync(sceneId, RequireUserId());
    }

    public Task<WordCompanionCreateChapterResponse?> CreateChapterAsync(int bookId, WordCompanionCreateChapterRequest request)
    {
        if (bookId <= 0 || string.IsNullOrWhiteSpace(request.Title) || request.SortOrder is <= 0)
        {
            return Task.FromResult<WordCompanionCreateChapterResponse?>(null);
        }

        request.Title = request.Title.Trim();
        return repository.CreateChapterAsync(bookId, RequireUserId(), request);
    }

    public Task<WordCompanionCreateSceneResponse?> CreateSceneAsync(int bookId, int chapterId, WordCompanionCreateSceneRequest request)
    {
        if (bookId <= 0 || chapterId <= 0 || string.IsNullOrWhiteSpace(request.SceneTitle))
        {
            return Task.FromResult<WordCompanionCreateSceneResponse?>(null);
        }

        request.SceneTitle = request.SceneTitle.Trim();
        return repository.CreateSceneAsync(bookId, chapterId, RequireUserId(), request);
    }

    public Task<WordCompanionSyncSceneResponse?> SyncSceneAsync(int bookId, WordCompanionSyncSceneRequest request)
    {
        if (bookId <= 0
            || string.IsNullOrWhiteSpace(request.ChapterTitle)
            || string.IsNullOrWhiteSpace(request.SceneTitle)
            || request.ActualWords < 0
            || request.ChapterSortOrder is <= 0
            || request.SceneSortOrder is <= 0)
        {
            return Task.FromResult<WordCompanionSyncSceneResponse?>(null);
        }

        request.ChapterTitle = request.ChapterTitle.Trim();
        request.SceneTitle = request.SceneTitle.Trim();
        return repository.SyncSceneAsync(bookId, RequireUserId(), request);
    }

    public Task<WordCompanionSyncManuscriptResponse?> SyncManuscriptAsync(int bookId, WordCompanionSyncManuscriptRequest request)
    {
        if (bookId <= 0 || request.Chapters.Any(chapter =>
                string.IsNullOrWhiteSpace(chapter.Title)
                || chapter.WordCount < 0
                || chapter.SortOrder is <= 0
                || chapter.Scenes.Any(scene => string.IsNullOrWhiteSpace(scene.Title) || scene.WordCount < 0 || scene.SortOrder is <= 0)))
        {
            return Task.FromResult<WordCompanionSyncManuscriptResponse?>(null);
        }

        foreach (var chapter in request.Chapters)
        {
            chapter.Title = chapter.Title?.Trim();
            foreach (var scene in chapter.Scenes)
            {
                scene.Title = scene.Title?.Trim();
            }
        }

        return repository.SyncManuscriptAsync(bookId, RequireUserId(), request);
    }

    public Task<WordCompanionUpdateSceneLinksResponse?> UpdateSceneLinksAsync(int sceneId, WordCompanionUpdateSceneLinksRequest request)
    {
        if (sceneId <= 0
            || request.PrimaryLocationId is <= 0
            || HasInvalidIds(request.CharacterIds)
            || HasInvalidIds(request.AssetIds)
            || HasInvalidIds(request.LocationIds))
        {
            return Task.FromResult<WordCompanionUpdateSceneLinksResponse?>(null);
        }

        return repository.UpdateSceneLinksAsync(sceneId, RequireUserId(), request);
    }

    public Task<WordCompanionUpdateWordCountResponse?> UpdateWordCountAsync(int sceneId, WordCompanionUpdateWordCountRequest request)
    {
        var actualWords = request.ActualWordCount ?? request.ActualWords;
        return sceneId <= 0 || actualWords is null or < 0
            ? Task.FromResult<WordCompanionUpdateWordCountResponse?>(null)
            : repository.UpdateWordCountAsync(sceneId, RequireUserId(), actualWords.Value, request.LastWorkedOn);
    }

    public async Task<WordCompanionManuscriptBookResponse?> GetManuscriptForBookAsync(int bookId)
    {
        if (bookId <= 0)
        {
            return null;
        }

        var document = await manuscriptDocuments.GetByBookAsync(bookId, RequireUserId());
        return new WordCompanionManuscriptBookResponse
        {
            BookId = bookId,
            ManuscriptDocument = document is null ? null : ToDto(document)
        };
    }

    public async Task<WordCompanionManuscriptLinkResponse?> LinkManuscriptAsync(WordCompanionManuscriptLinkRequest request)
    {
        if (request.BookId <= 0)
        {
            return null;
        }

        var documentGuid = request.DocumentGuid.GetValueOrDefault();
        if (documentGuid == Guid.Empty)
        {
            documentGuid = Guid.NewGuid();
        }

        ManuscriptDocumentModel? document;
        try
        {
            document = await manuscriptDocuments.SaveAsync(request.BookId, documentGuid, RequireUserId());
        }
        catch (InvalidOperationException)
        {
            return null;
        }

        return document is null
            ? null
            : new WordCompanionManuscriptLinkResponse
            {
                BookId = document.BookID,
                ManuscriptDocument = ToDto(document),
                Message = "Manuscript linked."
            };
    }

    public Task<WordCompanionManuscriptAnalyseResponse?> AnalyseManuscriptAsync(WordCompanionManuscriptAnalyseRequest request)
    {
        if (request.ProjectId <= 0
            || request.BookId <= 0
            || request.ChapterCount < 0
            || request.SceneCount < 0
            || request.WordCount < 0)
        {
            return Task.FromResult<WordCompanionManuscriptAnalyseResponse?>(null);
        }

        return repository.AnalyseManuscriptAsync(RequireUserId(), request);
    }

    public Task<WordCompanionManuscriptImportResponse?> ImportManuscriptAsync(WordCompanionManuscriptImportRequest request)
    {
        if (request.ProjectId <= 0
            || request.BookId <= 0
            || request.BindingVersion <= 0
            || request.Chapters.Count == 0
            || request.Chapters.Any(chapter =>
                string.IsNullOrWhiteSpace(chapter.Title)
                || chapter.SortOrder is <= 0
                || chapter.WordCount < 0
                || chapter.Scenes.Count == 0
                || chapter.Scenes.Any(scene => string.IsNullOrWhiteSpace(scene.Title) || scene.SortOrder is <= 0 || scene.WordCount < 0)))
        {
            return Task.FromResult<WordCompanionManuscriptImportResponse?>(null);
        }

        request.DocumentGuid = request.DocumentGuid.GetValueOrDefault() == Guid.Empty ? Guid.NewGuid() : request.DocumentGuid;

        foreach (var chapter in request.Chapters)
        {
            chapter.Title = chapter.Title?.Trim();
            foreach (var scene in chapter.Scenes)
            {
                scene.Title = scene.Title?.Trim();
            }
        }

        return repository.ImportManuscriptAsync(RequireUserId(), request);
    }

    public async Task<WordCompanionDiscoverCharactersResponse?> DiscoverCharacterCandidatesAsync(WordCompanionDiscoverCharactersRequest request)
    {
        if (request.ProjectId <= 0)
        {
            return null;
        }

        var userId = RequireUserId();
        if (!await repository.HasProjectAccessAsync(request.ProjectId, userId))
        {
            return null;
        }

        var candidates = DiscoverCharacterCandidates(request.DocumentText ?? string.Empty);
        return new WordCompanionDiscoverCharactersResponse
        {
            ProjectId = request.ProjectId,
            Candidates = candidates
        };
    }

    public Task<WordCompanionCreateDiscoveredCharactersResponse?> CreateDiscoveredCharactersAsync(WordCompanionCreateDiscoveredCharactersRequest request)
    {
        if (request.ProjectId <= 0 || request.CandidateNames.Count == 0)
        {
            return Task.FromResult<WordCompanionCreateDiscoveredCharactersResponse?>(null);
        }

        request.CandidateNames = request.CandidateNames
            .Select(NormalizeCandidateName)
            .Where(name => !string.IsNullOrWhiteSpace(name) && name.Length <= 200)
            .Distinct(StringComparer.OrdinalIgnoreCase)
            .Take(CharacterDiscoverySuggestionLimit)
            .ToList();

        return request.CandidateNames.Count == 0
            ? Task.FromResult<WordCompanionCreateDiscoveredCharactersResponse?>(null)
            : repository.CreateDiscoveredCharactersAsync(RequireUserId(), request);
    }

    private async Task<WordCompanionResolveSceneResponse?> ResolveSceneCoreAsync(int bookId, WordCompanionResolveSceneRequest request)
    {
        return await repository.ResolveSceneAsync(bookId, RequireUserId(), request.ChapterTitle!.Trim(), request.SceneTitle!.Trim());
    }

    private int RequireUserId()
    {
        return currentUser.UserId ?? throw new InvalidOperationException("An authenticated user is required.");
    }

    private static bool HasInvalidIds(IEnumerable<int> ids) => ids.Any(id => id <= 0);

    private static IReadOnlyList<WordCompanionCharacterCandidateDto> DiscoverCharacterCandidates(string manuscriptText)
    {
        if (string.IsNullOrWhiteSpace(manuscriptText))
        {
            return [];
        }

        var mentions = new Dictionary<string, int>(StringComparer.Ordinal);
        foreach (Match match in CharacterCandidateRegex.Matches(manuscriptText))
        {
            var candidate = NormalizeCandidateName(match.Value);
            if (!IsLikelyCharacterCandidate(candidate))
            {
                continue;
            }

            mentions[candidate] = mentions.TryGetValue(candidate, out var count) ? count + 1 : 1;
        }

        return mentions
            .Where(item => item.Value >= CharacterDiscoveryMinimumMentions)
            .OrderByDescending(item => item.Value)
            .ThenBy(item => item.Key, StringComparer.OrdinalIgnoreCase)
            .Take(CharacterDiscoverySuggestionLimit)
            .Select(item => new WordCompanionCharacterCandidateDto { Text = item.Key, MentionCount = item.Value })
            .ToList();
    }

    private static bool IsLikelyCharacterCandidate(string candidate)
    {
        if (string.IsNullOrWhiteSpace(candidate) || candidate.Length > 200)
        {
            return false;
        }

        var words = candidate.Split(' ', StringSplitOptions.RemoveEmptyEntries);
        if (words.Length == 0 || words.Any(word => CharacterDiscoveryStopWords.Contains(TrimHonorificPunctuation(word))))
        {
            return false;
        }

        var first = TrimHonorificPunctuation(words[0]);
        return words.Length > 1 || first.Length > 2;
    }

    private static string NormalizeCandidateName(string candidate)
    {
        return Regex.Replace(candidate ?? string.Empty, @"\s+", " ").Trim().Trim(',', '.', ';', ':', '!', '?', '"', '\'');
    }

    private static string TrimHonorificPunctuation(string word)
    {
        return (word ?? string.Empty).Trim().TrimEnd('.');
    }

    private static WordCompanionManuscriptDocumentDto ToDto(ManuscriptDocumentModel document) => new()
    {
        ManuscriptDocumentId = document.ManuscriptDocumentID,
        BookId = document.BookID,
        ProjectId = document.ProjectID,
        DocumentGuid = document.DocumentGuid,
        BindingVersion = document.BindingVersion,
        CreatedUtc = document.CreatedUtc,
        LastSyncUtc = document.LastSyncUtc,
        LastOpenedUtc = document.LastOpenedUtc,
        IsActive = document.IsActive
    };
}