using System.Text;
using System.Text.Json;
using PlotLine.Data;
using PlotLine.Models;
using PlotLine.ViewModels;

namespace PlotLine.Services;

public interface IImportService
{
    Task<ImportIndexViewModel> PreviewAsync(ImportIndexViewModel model);
    Task<ImportResult> ImportAsync(ImportIndexViewModel model);
    Task<string> BuildValidationReportAsync(ImportIndexViewModel model);
}

public sealed class ImportService(IImportRepository imports, ILogger<ImportService> logger) : IImportService
{
    private const int TitleMaxLength = 200;
    private const int RelativeTimeMaxLength = 200;
    private const int LargeTextWarningLength = 100_000;
    private const int SuspiciousBookCount = 20;
    private const int SuspiciousChapterCount = 250;
    private const int SuspiciousSceneCount = 2_000;

    private static readonly JsonSerializerOptions JsonOptions = new()
    {
        PropertyNameCaseInsensitive = true,
        ReadCommentHandling = JsonCommentHandling.Skip,
        AllowTrailingCommas = true
    };

    public async Task<ImportIndexViewModel> PreviewAsync(ImportIndexViewModel model)
    {
        model.JsonText = await ReadJsonTextAsync(model);
        model.Preview = await BuildPreviewAsync(model.JsonText);
        return model;
    }

    public async Task<ImportResult> ImportAsync(ImportIndexViewModel model)
    {
        model.JsonText = await ReadJsonTextAsync(model);
        var preview = await BuildPreviewAsync(model.JsonText);
        model.Preview = preview;

        if (!preview.Validation.IsValid || preview.Package is null)
        {
            return new ImportResult
            {
                Succeeded = false,
                Message = "The JSON needs to pass validation before it can be imported."
            };
        }

        if (!model.ConfirmImport)
        {
            return new ImportResult
            {
                Succeeded = false,
                Message = "Confirm the import summary before creating records."
            };
        }

        if (preview.Validation.Warnings.Any() && !model.AcknowledgeWarnings)
        {
            return new ImportResult
            {
                Succeeded = false,
                Message = "Review and acknowledge the validation warnings before importing."
            };
        }

        if (preview.HasDuplicateProjectTitle && !model.AllowDuplicateProjectTitle)
        {
            return new ImportResult
            {
                Succeeded = false,
                Message = "A project with this title already exists. Confirm that you want to import another project with the same title."
            };
        }

        try
        {
            return await imports.ImportAsync(preview.Package, preview.HasDuplicateProjectTitle ? preview.DuplicateImportProjectTitle : null);
        }
        catch (Exception ex)
        {
            logger.LogError(ex, "JSON import failed for project title {ProjectTitle}", preview.Package.Project.Title);
            return new ImportResult
            {
                Succeeded = false,
                Message = "The import could not be completed, so no data was saved.",
                TechnicalDetail = ex.Message
            };
        }
    }

    public async Task<string> BuildValidationReportAsync(ImportIndexViewModel model)
    {
        model.JsonText = await ReadJsonTextAsync(model);
        var preview = await BuildPreviewAsync(model.JsonText);
        var builder = new StringBuilder();
        builder.AppendLine("PlotLine JSON Import Validation Report");
        builder.AppendLine($"Generated: {DateTime.UtcNow:yyyy-MM-dd HH:mm} UTC");
        builder.AppendLine();
        builder.AppendLine($"Project: {preview.Package?.Project.Title ?? "(unreadable)"}");
        builder.AppendLine($"Books: {preview.BookCount}");
        builder.AppendLine($"Chapters: {preview.ChapterCount}");
        builder.AppendLine($"Scenes: {preview.SceneCount}");
        builder.AppendLine();
        AppendReportSection(builder, "Errors", preview.Validation.Errors);
        AppendReportSection(builder, "Warnings", preview.Validation.Warnings);
        return builder.ToString();
    }

    private async Task<ImportPreview> BuildPreviewAsync(string jsonText)
    {
        if (string.IsNullOrWhiteSpace(jsonText))
        {
            var emptyValidation = new ImportValidationResult();
            emptyValidation.Errors.Add("Paste JSON or upload a JSON file before previewing.");
            return new ImportPreview { Validation = emptyValidation };
        }

        PlotLineImportPackage? package;
        try
        {
            package = JsonSerializer.Deserialize<PlotLineImportPackage>(jsonText, JsonOptions);
        }
        catch (JsonException ex)
        {
            var invalidJson = new ImportValidationResult();
            invalidJson.Errors.Add($"The JSON could not be read: {ex.Message}");
            return new ImportPreview { Validation = invalidJson };
        }

        if (package is null)
        {
            var invalidPackage = new ImportValidationResult();
            invalidPackage.Errors.Add("The JSON import package is empty.");
            return new ImportPreview { Validation = invalidPackage };
        }

        var validation = Validate(package);
        AddMetadataWarnings(package, validation);
        var duplicate = !string.IsNullOrWhiteSpace(package.Project.Title)
            && await imports.ProjectTitleExistsAsync(package.Project.Title.Trim());

        var duplicateTitle = duplicate
            ? $"{package.Project.Title.Trim()} (Imported {DateTime.Now:yyyy-MM-dd HH:mm})"
            : null;

        if (duplicate)
        {
            validation.Warnings.Add($"A project with the same title already exists. If imported anyway, the new project will be named \"{duplicateTitle}\".");
        }

        return new ImportPreview
        {
            Package = package,
            Validation = validation,
            HasDuplicateProjectTitle = duplicate,
            DuplicateImportProjectTitle = duplicateTitle,
            BookPreviews = BuildBookPreviews(package)
        };
    }

    private static ImportValidationResult Validate(PlotLineImportPackage package)
    {
        var result = new ImportValidationResult();

        if (string.IsNullOrWhiteSpace(package.Project.Title))
        {
            result.Errors.Add("Project title is required.");
        }
        else if (package.Project.Title.Trim().Length > TitleMaxLength)
        {
            result.Errors.Add($"Project title is longer than {TitleMaxLength} characters.");
        }

        ValidateLargeText(result, "Project description", package.Project.Description);
        ValidateLargeText(result, "Project notes", package.Project.Notes);

        if (string.IsNullOrWhiteSpace(package.PackageVersion))
        {
            result.Warnings.Add("packageVersion is missing. Version 1.0 is expected for Phase 1B.");
        }
        else if (package.PackageVersion.Trim() != "1.0")
        {
            result.Warnings.Add($"packageVersion \"{package.PackageVersion}\" is not the current supported version. The importer will continue if the structure is valid.");
        }

        if (package.Books.Count == 0)
        {
            result.Warnings.Add("No books were supplied. The import will create an empty project.");
        }

        var totalChapters = package.Books.Sum(book => book.Chapters.Count);
        var totalScenes = package.Books.Sum(book => book.Chapters.Sum(chapter => chapter.Scenes.Count));
        if (package.Books.Count > SuspiciousBookCount || totalChapters > SuspiciousChapterCount || totalScenes > SuspiciousSceneCount)
        {
            result.Warnings.Add($"This is a large import ({package.Books.Count} books, {totalChapters} chapters, {totalScenes} scenes). Review the preview carefully before importing.");
        }

        foreach (var group in package.Books.GroupBy(x => x.SeriesOrder).Where(x => x.Count() > 1))
        {
            result.Errors.Add($"Book order {group.Key} is used more than once.");
        }

        for (var bookIndex = 0; bookIndex < package.Books.Count; bookIndex++)
        {
            var book = package.Books[bookIndex];
            var bookLabel = string.IsNullOrWhiteSpace(book.Title) ? $"Book {bookIndex + 1}" : book.Title;
            if (string.IsNullOrWhiteSpace(book.Title))
            {
                result.Errors.Add($"Book {bookIndex + 1} is missing a title.");
            }
            else if (FormatBookTitle(book).Length > TitleMaxLength)
            {
                result.Errors.Add($"{bookLabel} title is longer than {TitleMaxLength} characters after combining title and subtitle.");
            }

            if (book.SeriesOrder <= 0)
            {
                result.Errors.Add($"{bookLabel} is missing a valid seriesOrder.");
            }

            if (book.Chapters.Count == 0)
            {
                result.Warnings.Add($"{bookLabel} has no chapters.");
            }

            ValidateLargeText(result, $"{bookLabel} description", book.Description);
            ValidateLargeText(result, $"{bookLabel} notes", book.Notes);

            foreach (var group in book.Chapters.GroupBy(x => x.Order).Where(x => x.Count() > 1))
            {
                result.Errors.Add($"{bookLabel} has duplicate chapter order {group.Key}.");
            }

            for (var chapterIndex = 0; chapterIndex < book.Chapters.Count; chapterIndex++)
            {
                var chapter = book.Chapters[chapterIndex];
                var chapterLabel = string.IsNullOrWhiteSpace(chapter.Title) ? $"chapter {chapterIndex + 1}" : chapter.Title;
                if (string.IsNullOrWhiteSpace(chapter.Title))
                {
                    result.Errors.Add($"{bookLabel} chapter {chapterIndex + 1} is missing a title.");
                }
                else if (chapter.Title.Trim().Length > TitleMaxLength)
                {
                    result.Errors.Add($"{bookLabel} / {chapterLabel} title is longer than {TitleMaxLength} characters.");
                }

                if (chapter.Order <= 0)
                {
                    result.Errors.Add($"{bookLabel} / {chapterLabel} is missing a valid chapter order.");
                }

                if (chapter.Scenes.Count == 0)
                {
                    result.Warnings.Add($"{bookLabel} / {chapterLabel} has no scenes.");
                }

                ValidateLargeText(result, $"{bookLabel} / {chapterLabel} summary", chapter.Summary);
                ValidateLargeText(result, $"{bookLabel} / {chapterLabel} notes", chapter.Notes);

                foreach (var group in chapter.Scenes.GroupBy(x => x.Order).Where(x => x.Count() > 1))
                {
                    result.Errors.Add($"{bookLabel} / {chapterLabel} has duplicate scene order {group.Key}.");
                }

                for (var sceneIndex = 0; sceneIndex < chapter.Scenes.Count; sceneIndex++)
                {
                    var scene = chapter.Scenes[sceneIndex];
                    var sceneLabel = string.IsNullOrWhiteSpace(scene.Title) ? $"scene {sceneIndex + 1}" : scene.Title;
                    if (string.IsNullOrWhiteSpace(scene.Title))
                    {
                        result.Errors.Add($"{bookLabel} / {chapterLabel} scene {sceneIndex + 1} is missing a title.");
                    }
                    else if (scene.Title.Trim().Length > TitleMaxLength)
                    {
                        result.Errors.Add($"{bookLabel} / {chapterLabel} / {sceneLabel} title is longer than {TitleMaxLength} characters.");
                    }

                    if (scene.Order <= 0)
                    {
                        result.Errors.Add($"{bookLabel} / {chapterLabel} / {sceneLabel} is missing a valid scene order.");
                    }

                    if (!string.IsNullOrWhiteSpace(scene.DateTimeText) && scene.DateTimeText.Trim().Length > RelativeTimeMaxLength)
                    {
                        result.Warnings.Add($"{bookLabel} / {chapterLabel} / {sceneLabel} dateTimeText is longer than {RelativeTimeMaxLength} characters and will be truncated.");
                    }

                    ValidateLargeText(result, $"{bookLabel} / {chapterLabel} / {sceneLabel} summary", scene.Summary);
                    ValidateLargeText(result, $"{bookLabel} / {chapterLabel} / {sceneLabel} notes", scene.Notes);
                    ValidateLargeText(result, $"{bookLabel} / {chapterLabel} / {sceneLabel} purposeText", scene.PurposeText);
                    ValidateLargeText(result, $"{bookLabel} / {chapterLabel} / {sceneLabel} outcomeText", scene.OutcomeText);
                }
            }
        }

        return result;
    }

    private static void AddMetadataWarnings(PlotLineImportPackage package, ImportValidationResult validation)
    {
        var hasPov = package.Books.Any(book => book.Chapters.Any(chapter => chapter.Scenes.Any(scene => !string.IsNullOrWhiteSpace(scene.PovCharacterName))));
        var hasLocation = package.Books.Any(book => book.Chapters.Any(chapter => chapter.Scenes.Any(scene => !string.IsNullOrWhiteSpace(scene.LocationName))));

        if (hasPov)
        {
            validation.Warnings.Add("POV character names will be kept as imported text notes in scene summaries. Character records are not created in Phase 1B.");
        }

        if (hasLocation)
        {
            validation.Warnings.Add("Location names will be kept as imported text notes in scene summaries. Location records are not created in Phase 1B.");
        }
    }

    private static IReadOnlyList<ImportBookPreview> BuildBookPreviews(PlotLineImportPackage package)
        => package.Books
            .OrderBy(x => x.SeriesOrder)
            .Select(book => new ImportBookPreview
            {
                Book = book,
                ChapterPreviews = book.Chapters
                    .OrderBy(x => x.Order)
                    .Select(chapter => new ImportChapterPreview { Chapter = chapter })
                    .ToList()
            })
            .ToList();

    private static void ValidateLargeText(ImportValidationResult result, string fieldName, string? value)
    {
        if (!string.IsNullOrWhiteSpace(value) && value.Length > LargeTextWarningLength)
        {
            result.Warnings.Add($"{fieldName} is unusually large. It can be imported, but review the source JSON for accidental pasted manuscript text.");
        }
    }

    private static string FormatBookTitle(ImportBookDto book)
        => string.IsNullOrWhiteSpace(book.Subtitle) ? book.Title.Trim() : $"{book.Title.Trim()}: {book.Subtitle.Trim()}";

    private static void AppendReportSection(StringBuilder builder, string title, IReadOnlyList<string> messages)
    {
        builder.AppendLine(title);
        if (messages.Count == 0)
        {
            builder.AppendLine("- None");
        }
        else
        {
            foreach (var message in messages)
            {
                builder.AppendLine($"- {message}");
            }
        }

        builder.AppendLine();
    }

    private static async Task<string> ReadJsonTextAsync(ImportIndexViewModel model)
    {
        if (model.JsonFile is { Length: > 0 })
        {
            using var reader = new StreamReader(model.JsonFile.OpenReadStream(), Encoding.UTF8, detectEncodingFromByteOrderMarks: true);
            return await reader.ReadToEndAsync();
        }

        return model.JsonText ?? string.Empty;
    }
}