Nexus.Reader/src/NexusReader.UI.Shared/Components/MarkdownEditor.razor

@using Microsoft.JSInterop
@implements IAsyncDisposable
@inject IJSRuntime JS
@inject HttpClient Http
@inject NexusReader.Application.Abstractions.Services.INativeStorageService StorageService

<div class="markdown-editor-container" style="height: @Height; width: @Width;">
    @if (_showRestorationBanner)
    {
        <div class="restoration-banner">
            <span class="banner-text">You have unsaved changes from an interrupted session.</span>
            <div class="banner-actions">
                <button type="button" class="banner-btn restore-btn" @onclick="RestoreBackupAsync">Restore</button>
                <button type="button" class="banner-btn dismiss-btn" @onclick="DismissBackupAsync">Dismiss</button>
            </div>
        </div>
    }
    else
    {
        <div @key="_editorRenderKey" id="@EditorId" class="milkdown-editor-wrapper"></div>

        <div class="editor-footer">
            <div class="status-indicator">
                <span class="status-dot @StatusClass"></span>
                <span class="status-text">@StatusText</span>
            </div>
            @if (ShowFetchButton)
            {
                <div class="editor-actions">
                    <button type="button" @onclick="FetchContentAsync" class="nexus-btn">
                        Fetch Markdown Content
                    </button>
                </div>
            }
        </div>
    }
</div>

@code {
    private string EditorId { get; set; } = $"milkdown-editor-{Guid.NewGuid():N}";
    private Guid _editorRenderKey = Guid.NewGuid();
    private readonly CancellationTokenSource _cts = new();
    private IJSObjectReference? _module;
    private DotNetObjectReference<MarkdownEditor>? _dotNetHelper;
    private string? _lastInitializedEditorId;
    private bool _disposed;

    private enum SaveStatus
    {
        SavedToCloud,
        Saving,
        OfflineLocalBackup
    }

    private SaveStatus _status = SaveStatus.SavedToCloud;
    private string _currentMarkdown = string.Empty;
    private CancellationTokenSource? _debounceCts;
    private readonly object _timerLock = new();

    private bool _showRestorationBanner = false;
    private NexusReader.Application.DTOs.Media.LocalBackupEnvelope? _pendingBackup;
    private bool _hasRunStorageInit = false;
    private bool _reinitializeEditor = false;

    private string StatusClass => _status switch
    {
        SaveStatus.SavedToCloud => "saved",
        SaveStatus.Saving => "saving",
        SaveStatus.OfflineLocalBackup => "offline",
        _ => "saved"
    };

    private string StatusText => _status switch
    {
        SaveStatus.SavedToCloud => "Saved to Cloud",
        SaveStatus.Saving => "Saving...",
        SaveStatus.OfflineLocalBackup => "Offline - Local Backup Only",
        _ => "Saved to Cloud"
    };

    [Parameter]
    public bool ShowFetchButton { get; set; } = true;

    [Parameter]
    public string InitialMarkdown { get; set; } = string.Empty;

    [Parameter]
    public EventCallback<string> OnSave { get; set; }

    [Parameter]
    public string Height { get; set; } = "500px";

    [Parameter]
    public string Width { get; set; } = "100%";

    [Parameter]
    public Guid ChapterId { get; set; } = Guid.Empty;

    [Parameter]
    public DateTime? ServerTimestamp { get; set; }

    protected override async Task OnInitializedAsync()
    {
        await base.OnInitializedAsync();
        // Sweep keys and check restoration on init
        await RunStorageSweepAndRestorationCheckAsync();
    }

    private Guid _prevChapterId = Guid.Empty;

    protected override async Task OnParametersSetAsync()
    {
        await base.OnParametersSetAsync();
        if (ChapterId != Guid.Empty && ChapterId != _prevChapterId)
        {
            _prevChapterId = ChapterId;
            _hasRunStorageInit = false;
            
            if (_module != null)
            {
                try
                {
                    await _module.InvokeVoidAsync("destroyEditor", EditorId);
                }
                catch (Exception ex)
                {
                    Console.WriteLine($"[MarkdownEditor] Error destroying old editor on chapter switch: {ex.Message}");
                }
            }

            _reinitializeEditor = true;
            EditorId = $"milkdown-editor-{Guid.NewGuid():N}";
            _editorRenderKey = Guid.NewGuid();

            await RunStorageSweepAndRestorationCheckAsync();
        }
    }

    protected override async Task OnAfterRenderAsync(bool firstRender)
    {
        var shouldInit = (firstRender || _reinitializeEditor) && (EditorId != _lastInitializedEditorId);
        if (shouldInit)
        {
            _reinitializeEditor = false;
            _lastInitializedEditorId = EditorId; // Set immediately before any async yield to prevent concurrent triggers

            if (firstRender)
            {
                _dotNetHelper = DotNetObjectReference.Create(this);
                // Retry if deferred during prerendering OnInitializedAsync
                await RunStorageSweepAndRestorationCheckAsync();
            }

            try
            {
                if (_module == null)
                {
                    _module = await JS.InvokeAsync<IJSObjectReference>(
                        "import", 
                        $"./_content/NexusReader.UI.Shared/js/milkdownWrapper.js?v={Guid.NewGuid():N}"
                    );
                }
                await _module.InvokeVoidAsync("initEditor", EditorId, _dotNetHelper, InitialMarkdown);
            }
            catch (Exception ex)
            {
                Console.WriteLine($"[MarkdownEditor] Error initializing Milkdown editor: {ex.Message}");
            }
        }
    }

    private async Task RunStorageSweepAndRestorationCheckAsync()
    {
        if (_hasRunStorageInit) return;

        try
        {
            _hasRunStorageInit = true;

            // Import wrapper module if not already loaded to access helper
            if (_module == null)
            {
                _module = await JS.InvokeAsync<IJSObjectReference>(
                    "import", 
                    $"./_content/NexusReader.UI.Shared/js/milkdownWrapper.js?v={Guid.NewGuid():N}"
                );
            }

            // Sweep and filter backup keys defensively
            var keys = await _module.InvokeAsync<List<string>>("getBackupKeys");
            if (keys != null)
            {
                var now = DateTime.UtcNow;
                foreach (var key in keys)
                {
                    // Strict defensive check before doing any JSON deserialization
                    if (!key.StartsWith("nexus-bkp-")) continue;

                    try
                    {
                        var backupResult = await StorageService.GetStringAsync(key);
                        if (backupResult.IsSuccess && !string.IsNullOrEmpty(backupResult.Value))
                        {
                            var envelope = System.Text.Json.JsonSerializer.Deserialize<NexusReader.Application.DTOs.Media.LocalBackupEnvelope>(
                                backupResult.Value, 
                                NexusReader.Application.Common.AppJsonContext.Default.LocalBackupEnvelope
                            );
                            if (envelope != null)
                            {
                                // Remove expired backups
                                if ((now - envelope.Timestamp).TotalDays > 7)
                                {
                                    await StorageService.RemoveAsync(key);
                                    Console.WriteLine($"[MarkdownEditor] Boot-up Eviction: Deleted expired backup key {key}");
                                }
                            }
                        }
                    }
                    catch (Exception ex)
                    {
                        Console.WriteLine($"[MarkdownEditor] Error sweeping key {key}: {ex.Message}");
                    }
                }
            }

            // Restoration guard for this specific Chapter ID
            var currentBackupKey = $"nexus-bkp-{ChapterId}";
            var currentBackupResult = await StorageService.GetStringAsync(currentBackupKey);
            if (currentBackupResult.IsSuccess && !string.IsNullOrEmpty(currentBackupResult.Value))
            {
                var envelope = System.Text.Json.JsonSerializer.Deserialize<NexusReader.Application.DTOs.Media.LocalBackupEnvelope>(
                    currentBackupResult.Value, 
                    NexusReader.Application.Common.AppJsonContext.Default.LocalBackupEnvelope
                );
                if (envelope != null)
                {
                    var serverTime = ServerTimestamp ?? DateTime.MinValue;
                    if (envelope.Timestamp > serverTime && envelope.MarkdownContent != InitialMarkdown)
                    {
                        _pendingBackup = envelope;
                        _showRestorationBanner = true;
                        StateHasChanged();
                    }
                }
            }
        }
        catch (Exception ex)
        {
            _hasRunStorageInit = false; // Reset to allow retry on client render
            Console.WriteLine($"[MarkdownEditor] Storage initialization deferred/failed: {ex.Message}");
        }
    }

    private async Task RestoreBackupAsync()
    {
        if (_pendingBackup != null)
        {
            if (_module != null)
            {
                try
                {
                    // Prevent memory leak by cleaning up old instance in JS
                    await _module.InvokeVoidAsync("destroyEditor", EditorId);
                }
                catch (Exception ex)
                {
                    Console.WriteLine($"[MarkdownEditor] Error destroying old editor during restore: {ex.Message}");
                }
            }

            InitialMarkdown = _pendingBackup.MarkdownContent;
            _showRestorationBanner = false;
            _pendingBackup = null;

            // Regenerate render key and ID to trigger clean Blazor element-level re-initialization
            _reinitializeEditor = true;
            EditorId = $"milkdown-editor-{Guid.NewGuid():N}";
            _editorRenderKey = Guid.NewGuid();

            // Trigger an immediate background API autosave to synchronize the database with the restored content
            _ = TriggerAutosaveAsync(InitialMarkdown, _cts.Token);

            StateHasChanged();
        }
    }

    private async Task DismissBackupAsync()
    {
        _showRestorationBanner = false;
        _pendingBackup = null;
        try
        {
            await StorageService.RemoveAsync($"nexus-bkp-{ChapterId}");
        }
        catch (Exception ex)
        {
            Console.WriteLine($"[MarkdownEditor] Failed to dismiss backup from LocalStorage: {ex.Message}");
        }
        StateHasChanged();
    }

    public async Task FetchContentAsync()
    {
        if (_module is not null)
        {
            try
            {
                var markdown = await _module.InvokeAsync<string>("getMarkdownContent", EditorId);
                
                if (OnSave.HasDelegate)
                {
                    await OnSave.InvokeAsync(markdown);
                }
            }
            catch (Exception ex)
            {
                Console.WriteLine($"[MarkdownEditor] Error fetching markdown content: {ex.Message}");
            }
        }
    }

    [JSInvokable]
    public async Task OnEditorContentChanged(string currentMarkdown)
    {
        _currentMarkdown = currentMarkdown;

        // Structured JSON Envelope Pattern
        var envelope = new NexusReader.Application.DTOs.Media.LocalBackupEnvelope
        {
            ChapterId = ChapterId,
            Timestamp = DateTime.UtcNow,
            MarkdownContent = currentMarkdown
        };

        try
        {
            var envelopeJson = System.Text.Json.JsonSerializer.Serialize(
                envelope, 
                NexusReader.Application.Common.AppJsonContext.Default.LocalBackupEnvelope
            );
            await StorageService.SaveStringAsync($"nexus-bkp-{ChapterId}", envelopeJson);
        }
        catch (Exception ex)
        {
            Console.WriteLine($"[MarkdownEditor] Failed to save backup to LocalStorage: {ex.Message}");
        }

        // Status indicator to Offline - Local Backup Only
        _status = SaveStatus.OfflineLocalBackup;
        await InvokeAsync(StateHasChanged);

        // Cancel pending timers thread-safely
        CancellationTokenSource? ctsToCancel = null;
        CancellationToken token;
        lock (_timerLock)
        {
            if (_debounceCts != null)
            {
                ctsToCancel = _debounceCts;
                _debounceCts = null;
            }
            _debounceCts = new CancellationTokenSource();
            token = _debounceCts.Token; // Capture token synchronously under lock on UI thread
        }

        if (ctsToCancel != null)
        {
            try
            {
                await ctsToCancel.CancelAsync();
                ctsToCancel.Dispose();
            }
            catch (Exception ex)
            {
                Console.WriteLine($"[MarkdownEditor] Error cancelling debounce timer: {ex.Message}");
            }
        }

        // Start 5-second idle debounce timer
        _ = Task.Run(async () =>
        {
            try
            {
                await Task.Delay(5000, token);
                await TriggerAutosaveAsync(currentMarkdown, token);
            }
            catch (TaskCanceledException)
            {
                // Task cancelled on new keystroke
            }
            catch (Exception ex)
            {
                Console.WriteLine($"[MarkdownEditor] Debounce timer exception: {ex.Message}");
            }
        });
    }

    private async Task TriggerAutosaveAsync(string markdown, CancellationToken token)
    {
        if (token.IsCancellationRequested || _disposed) return;

        _status = SaveStatus.Saving;
        await InvokeAsync(StateHasChanged);

        try
        {
            var request = new NexusReader.Application.DTOs.Media.AutosaveChapterRequest(markdown);
            var response = await Http.PutAsJsonAsync(
                $"/api/chapters/{ChapterId}/autosave", 
                request, 
                NexusReader.Application.Common.AppJsonContext.Default.AutosaveChapterRequest, 
                token
            );

            if (_disposed) return;

            if (response.IsSuccessStatusCode)
            {
                // Purge LocalStorage backup key on HTTP success
                await StorageService.RemoveAsync($"nexus-bkp-{ChapterId}");
                _status = SaveStatus.SavedToCloud;
            }
            else
            {
                _status = SaveStatus.OfflineLocalBackup;
                var errorMsg = await response.Content.ReadAsStringAsync(token);
                Console.WriteLine($"[MarkdownEditor] Autosave HTTP error: {response.StatusCode} - {errorMsg}");
            }
        }
        catch (Exception ex)
        {
            if (_disposed) return;
            _status = SaveStatus.OfflineLocalBackup;
            Console.WriteLine($"[MarkdownEditor] Autosave HTTP exception: {ex.Message}");
        }

        if (_disposed) return;
        await InvokeAsync(StateHasChanged);
    }

    [JSInvokable]
    public async Task<string> UploadImageFromJs(string filename, string contentType, IJSStreamReference streamRef)
    {
        try
        {
            const long maxFileSize = 5 * 1024 * 1024; // 5MB limit
            using var stream = await streamRef.OpenReadStreamAsync(maxFileSize, _cts.Token);
            using var memoryStream = new MemoryStream();
            await stream.CopyToAsync(memoryStream, _cts.Token);
            var fileBytes = memoryStream.ToArray();

            using var content = new MultipartFormDataContent();
            using var fileContent = new ByteArrayContent(fileBytes);
            fileContent.Headers.ContentType = new System.Net.Http.Headers.MediaTypeHeaderValue(contentType);
            content.Add(fileContent, "file", filename);

            var response = await Http.PostAsync("/api/media/upload", content, _cts.Token);
            if (response.IsSuccessStatusCode)
            {
                var result = await response.Content.ReadFromJsonAsync<NexusReader.Application.DTOs.Media.UploadResultDto>(
                    NexusReader.Application.Common.AppJsonContext.Default.UploadResultDto, _cts.Token);
                return result?.Url ?? "https://placehold.co/600x400?text=Upload+Failed";
            }
            else
            {
                var errorMsg = await response.Content.ReadAsStringAsync(_cts.Token);
                Console.WriteLine($"[MarkdownEditor] Image upload failed: {response.StatusCode} - {errorMsg}");
                return "https://placehold.co/600x400?text=Upload+Failed";
            }
        }
        catch (Exception ex)
        {
            Console.WriteLine($"[MarkdownEditor] Exception during image upload: {ex.Message}");
            return "https://placehold.co/600x400?text=Upload+Failed";
        }
    }

    public async ValueTask DisposeAsync()
    {
        _disposed = true;
        try
        {
            _cts.Cancel();
            _cts.Dispose();
        }
        catch
        {
            // Fail silently
        }

        CancellationTokenSource? ctsToCancel = null;
        lock (_timerLock)
        {
            if (_debounceCts != null)
            {
                ctsToCancel = _debounceCts;
                _debounceCts = null;
            }
        }

        if (ctsToCancel != null)
        {
            try
            {
                ctsToCancel.Cancel();
                ctsToCancel.Dispose();
            }
            catch
            {
                // Fail silently
            }
        }

        try
        {
            // Always try to destroy via global window registration first to handle null _module
            await JS.InvokeVoidAsync("milkdownWrapper.destroyEditor", EditorId);
        }
        catch
        {
            // Fallback to module if global is not set
            if (_module is not null)
            {
                try
                {
                    await _module.InvokeVoidAsync("destroyEditor", EditorId);
                }
                catch
                {
                    // Fail silently
                }
            }
        }

        try
        {
            if (_module is not null)
            {
                await _module.DisposeAsync();
            }
        }
        catch (JSDisconnectedException)
        {
            // Fail silently during circuit disconnection
        }
        catch (ObjectDisposedException)
        {
            // Fail silently if JS runtime/module is already disposed
        }
        catch (Exception ex)
        {
            Console.WriteLine($"[MarkdownEditor] Unexpected error during JS cleanup: {ex.Message}");
        }
        finally
        {
            _dotNetHelper?.Dispose();
        }
    }
}