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);
}

public sealed class ImportService(IImportRepository imports) : IImportService
{
    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 (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);
        }
        catch (Exception ex)
        {
            return new ImportResult
            {
                Succeeded = false,
                Message = $"The import could not be completed, so no data was saved. {ex.Message}"
            };
        }
    }

    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());

        if (duplicate)
        {
            validation.Warnings.Add("A project with the same title already exists. Import is blocked until you confirm that duplicate title.");
        }

        return new ImportPreview
        {
            Package = package,
            Validation = validation,
            HasDuplicateProjectTitle = duplicate
        };
    }

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

        if (string.IsNullOrWhiteSpace(package.Project.Title))
        {
            result.Errors.Add("Project title is required.");
        }

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

        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.");
            }

            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.");
                }

                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++)
                {
                    if (string.IsNullOrWhiteSpace(chapter.Scenes[sceneIndex].Title))
                    {
                        result.Errors.Add($"{bookLabel} / {chapterLabel} scene {sceneIndex + 1} is missing a title.");
                    }
                }
            }
        }

        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 1A.");
        }

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

    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;
    }
}