@page "/students/import"
@page "/import"
@attribute [Authorize(Roles = AuthRoles.Administrator)]
@implements IAsyncDisposable
@using Core.Parsers
@using Core.Services
@using Microsoft.EntityFrameworkCore
@using WebApp.Authentication
@inject AppDbContext Context
@inject IStudentNotesImportService NotesImportService
@inject IStudentNotesImportSaveService NotesSaveService
@inject INotesService NotesService
@inject NavigationManager NavigationManager
@inject ISnackbar Snackbar
@inject ILogger<StudentImport> Logger
@rendermode InteractiveServer

<PageHeader
    Title="Import Students"
    Description="Add new students from CSV. Existing first+last names are skipped; leftover columns merge into student notes."
    ShowBackButton="true"
    BackButtonUrl="/students" />

<MudGrid>
    <MudItem xs="12" md="5">
        <MudPaper Elevation="2" Class="pa-3 pa-md-6">
            <MudText Typo="Typo.h5" Class="mb-4">Upload CSV</MudText>
            <MudStack Spacing="3">
                <MudText Typo="Typo.body2">
                    Required columns: <code>Student Name</code>, <code>Grade</code>, <code>TSA year</code>.
                    Optional IDs are saved on new students. Every other column is merged into that student's notes.
                </MudText>
                <InputFile OnChange="HandleFileChanged" accept=".csv,text/csv" />
                @if (!string.IsNullOrEmpty(_fileName))
                {
                    <MudText Typo="Typo.caption">@_fileName</MudText>
                }
                <MudStack Row="true" Spacing="2">
                    <MudButton Variant="Variant.Filled" Color="Color.Primary"
                               StartIcon="@Icons.Material.Filled.Article"
                               OnClick="HandleParse"
                               Disabled="@(_isParsing || _fileBytes is null)">
                        Parse
                    </MudButton>
                    <MudButton Variant="Variant.Text" OnClick="HandleClear" Disabled="@_isParsing">
                        Clear
                    </MudButton>
                </MudStack>
            </MudStack>
        </MudPaper>
    </MudItem>

    <MudItem xs="12" md="7">
        <MudPaper Elevation="2" Class="pa-3 pa-md-6">
            <MudText Typo="Typo.h5" Class="mb-4">Parsed Results</MudText>
            @if (_isParsing)
            {
                <MudProgressLinear Indeterminate="true" Class="mb-4" />
                <MudText>Parsing...</MudText>
            }
            else if (!string.IsNullOrEmpty(_parseError))
            {
                <MudAlert Severity="Severity.Error">@_parseError</MudAlert>
            }
            else if (_students is null)
            {
                <MudText Class="mud-text-secondary">Upload and parse a CSV to see results here</MudText>
            }
            else
            {
                <MudStack Spacing="3">
                    <MudAlert Severity="Severity.Success" Dense="true">
                        @_students.Length student(s) parsed.
                        @_newStudentCount new, @_existingStudentCount already in the database.
                    </MudAlert>
                    @if (_leftoverFieldNames.Count > 0)
                    {
                        <MudText Typo="Typo.body2">Leftover note fields: @string.Join(", ", _leftoverFieldNames)</MudText>
                    }
                    else
                    {
                        <MudText Typo="Typo.body2" Class="mud-text-secondary">No leftover note fields in this file.</MudText>
                    }

                    <MudButton Variant="Variant.Filled" Color="Color.Success"
                               StartIcon="@Icons.Material.Filled.Save"
                               OnClick="HandleSave"
                               Disabled="@(_isSaving || _students.Length == 0)">
                        Save to Database
                    </MudButton>
                </MudStack>
            }
        </MudPaper>
    </MudItem>
</MudGrid>

@code {
    private byte[]? _fileBytes;
    private string? _fileName;
    private Student[]? _students;
    private List<string> _leftoverFieldNames = [];
    private int _newStudentCount;
    private int _existingStudentCount;
    private string? _parseError;
    private bool _isParsing;
    private bool _isSaving;
    private CancellationTokenSource? _cancellationTokenSource;
    private bool _isDisposed;

    protected override void OnInitialized()
    {
        _cancellationTokenSource = new CancellationTokenSource();
    }

    private async Task HandleFileChanged(InputFileChangeEventArgs args)
    {
        if (_isDisposed)
            return;

        try
        {
            await using var stream = args.File.OpenReadStream(maxAllowedSize: 1024 * 1024);
            await using var memory = new MemoryStream();
            await stream.CopyToAsync(memory, _cancellationTokenSource?.Token ?? CancellationToken.None);
            _fileBytes = memory.ToArray();
            _fileName = args.File.Name;
            ResetParse();
        }
        catch (TaskCanceledException)
        {
        }
        catch (JSDisconnectedException)
        {
        }
        catch (Exception ex)
        {
            Logger.LogError(ex, "Error reading student CSV");
            if (!_isDisposed)
                Snackbar.Add($"Could not read file: {ex.Message}", Severity.Error);
        }
    }

    private async Task HandleParse()
    {
        if (_fileBytes is null)
        {
            Snackbar.Add("Please choose a CSV file first", Severity.Warning);
            return;
        }

        _isParsing = true;
        _parseError = null;
        try
        {
            var token = _cancellationTokenSource?.Token ?? CancellationToken.None;
            using var reader = new StreamReader(new MemoryStream(_fileBytes));
            _students = new StudentParser(reader).Parse();
            _leftoverFieldNames = PeekLeftoverFieldNames(_fileBytes);

            var existingNames = await Context.Students
                .AsNoTracking()
                .Select(s => new { s.FirstName, s.LastName })
                .ToListAsync(token);
            var existingSet = existingNames
                .Select(s => (s.FirstName, s.LastName))
                .ToHashSet();

            _existingStudentCount = _students.Count(s => existingSet.Contains((s.FirstName, s.LastName)));
            _newStudentCount = _students.Length - _existingStudentCount;
        }
        catch (TaskCanceledException)
        {
        }
        catch (JSDisconnectedException)
        {
        }
        catch (Exception ex)
        {
            Logger.LogError(ex, "Error parsing student CSV");
            _students = null;
            _leftoverFieldNames = [];
            _parseError = $"Error parsing CSV: {ex.Message}";
            if (!_isDisposed)
                Snackbar.Add(_parseError, Severity.Error);
        }
        finally
        {
            _isParsing = false;
        }
    }

    private async Task HandleSave()
    {
        if (_students is null || _fileBytes is null)
        {
            Snackbar.Add("Parse a CSV first", Severity.Warning);
            return;
        }

        _isSaving = true;
        try
        {
            var token = _cancellationTokenSource?.Token ?? CancellationToken.None;
            var added = 0;
            foreach (var student in _students)
            {
                token.ThrowIfCancellationRequested();
                var exists = await Context.Students
                    .FirstOrDefaultAsync(e => e.FirstName == student.FirstName && e.LastName == student.LastName, token);
                if (exists != null)
                    continue;
                await Context.Students.AddAsync(student, token);
                added++;
            }

            await Context.SaveChangesAsync(token);

            var notesCreated = 0;
            var notesUpdated = 0;
            if (_leftoverFieldNames.Count > 0)
            {
                var students = await Context.Students
                    .AsNoTracking()
                    .OrderBy(s => s.LastName)
                    .ThenBy(s => s.FirstName)
                    .ToListAsync(token);
                var notes = await NotesService.GetStudentNotesAsync(students.Select(s => s.Id));
                var existing = notes.ToDictionary(k => k.Key, v => v.Value.Content);

                await using var csvStream = new MemoryStream(_fileBytes, writable: false);
                var parseResult = NotesImportService.Parse(csvStream, students, existing);
                if (parseResult.IsSuccess && parseResult.StudentsWithChanges > 0)
                {
                    var saveResult = await NotesSaveService.SaveAsync(parseResult, token);
                    notesCreated = saveResult.NotesCreated;
                    notesUpdated = saveResult.NotesUpdated;
                }
            }

            if (_isDisposed)
                return;

            Snackbar.Add(
                $"Added {added} student(s). Notes created {notesCreated}, updated {notesUpdated}.",
                Severity.Success);
            NavigationManager.NavigateTo("/students");
        }
        catch (TaskCanceledException)
        {
        }
        catch (JSDisconnectedException)
        {
        }
        catch (Exception ex)
        {
            Logger.LogError(ex, "Error saving imported students");
            if (!_isDisposed)
                Snackbar.Add($"Error saving students: {ex.Message}", Severity.Error);
        }
        finally
        {
            _isSaving = false;
        }
    }

    private void HandleClear()
    {
        _fileBytes = null;
        _fileName = null;
        ResetParse();
    }

    private void ResetParse()
    {
        _students = null;
        _leftoverFieldNames = [];
        _newStudentCount = 0;
        _existingStudentCount = 0;
        _parseError = null;
    }

    private static List<string> PeekLeftoverFieldNames(byte[] csvBytes)
    {
        using var reader = new StreamReader(new MemoryStream(csvBytes));
        using var parser = new StudentNotesFieldParser(reader);
        return parser.PeekLeftoverFieldNames();
    }

    public async ValueTask DisposeAsync()
    {
        if (!_isDisposed)
        {
            _isDisposed = true;
            _cancellationTokenSource?.Cancel();
            _cancellationTokenSource?.Dispose();
            _cancellationTokenSource = null;
        }

        await ValueTask.CompletedTask;
    }
}