using System.Collections.Concurrent;

using AIStudio.Chat;
using AIStudio.Provider;
using AIStudio.Settings;
using AIStudio.Tools.AssistantSessions;

namespace AIStudio.Assistants.BeyondFactsLab;

/// <summary>
/// Runs the chats of the steps of the BeyondFacts Lab.
/// </summary>
/// <remarks>
/// A singleton, so that an answer goes on while the person looks at another page: the page asks for the chat again
/// when it comes back and listens to ConversationChanged. Each request registers in AssistantSessionService, which
/// shows the work in the navigation. The service does nothing until the page of the lab asks for a chat.
/// </remarks>
/// <param name="store">The store of the lab.</param>
/// <param name="settingsManager">The settings.</param>
/// <param name="sessionService">The registry of running assistant sessions.</param>
/// <param name="messageBus">The message bus, for errors.</param>
/// <param name="logger">The logger.</param>
public sealed class BflConversationService(BeyondFactsLabStore store, SettingsManager settingsManager, AssistantSessionService sessionService, MessageBus messageBus, ILogger<BflConversationService> logger)
{
    /// <summary>
    /// The request which lets the model open the conversation of a step. The person does not see it.
    /// </summary>
    /// <remarks>
    /// German, like the prompts: what the first message does is up to the prompt of the step.
    /// </remarks>
    public const string OPENING_REQUEST = "Beginne das Gespräch dieses Schritts mit deiner ersten Nachricht, wie es der Abschnitt „Dieser Schritt“ beschreibt.";

    /// <summary>
    /// How often a streamed answer renders at most.
    /// </summary>
    private static readonly TimeSpan STREAMING_RENDER_MIN_TIME = TimeSpan.FromMilliseconds(100);

    private static string TB(string fallbackEN) => Tools.PluginSystem.I18N.I.T(fallbackEN, typeof(BflConversationService).Namespace, nameof(BflConversationService));

    private static string TA(string fallbackEN) => Tools.PluginSystem.I18N.I.TA(fallbackEN, typeof(BflConversationService).Namespace, nameof(BflConversationService));

    /// <summary>
    /// The chats loaded so far, by their steps.
    /// </summary>
    private readonly ConcurrentDictionary<BflThreadLocation, BflConversation> conversations = new();

    /// <summary>
    /// Serializes loading a chat, so that two pages never load the same chat twice.
    /// </summary>
    private readonly SemaphoreSlim loadLock = new(1, 1);

    /// <summary>
    /// Guards whether a chat answers right now, so that two requests never run in the same chat.
    /// </summary>
    private readonly Lock runningLock = new();

    /// <summary>
    /// Happens whenever a chat changed: a message, a chunk of an answer, or the end of a request.
    /// </summary>
    /// <remarks>
    /// Called on the thread of the request. A page renders through InvokeAsync.
    /// </remarks>
    public event Func<BflThreadLocation, Task>? ConversationChanged;

    /// <summary>
    /// Gets the chat of a step, loading it on the first call.
    /// </summary>
    /// <param name="location">The step of the preparation.</param>
    /// <param name="token">The cancellation token.</param>
    /// <returns>The chat; it is not available when this version cannot open the stored one.</returns>
    public async Task<BflConversation> GetAsync(BflThreadLocation location, CancellationToken token = default)
    {
        if (this.conversations.TryGetValue(location, out var conversation))
            return conversation;

        await this.loadLock.WaitAsync(token);
        try
        {
            if (this.conversations.TryGetValue(location, out conversation))
                return conversation;

            ChatThread? thread;
            try
            {
                thread = await store.LoadThreadAsync(location, token) ?? BflThreadFactory.Create(location);
            }
            catch (InvalidDataException exception)
            {
                // The file stays as it is, see BeyondFactsLabStore.SaveThreadAsync:
                logger.LogWarning(exception, "Could not open the chat of the step '{Step}' of the preparation '{ProjectId}' of the BeyondFacts Lab.", location.Step, location.ProjectId);
                thread = null;
            }

            conversation = new BflConversation { Location = location, Thread = thread };
            this.conversations[location] = conversation;
            return conversation;
        }
        finally
        {
            this.loadLock.Release();
        }
    }

    /// <summary>
    /// Lets the model open the conversation of a step, as the prompt of the step describes.
    /// </summary>
    /// <param name="location">The step of the preparation.</param>
    /// <param name="provider">The provider which answers.</param>
    public Task StartAsync(BflThreadLocation location, AIStudio.Settings.Provider provider) => this.SendAsync(location, provider, OPENING_REQUEST, isHidden: true);

    /// <summary>
    /// Sends a message of the person and lets the model answer it.
    /// </summary>
    /// <remarks>
    /// The message is stored before the model answers, so that a crash loses at most the answer. What goes wrong is
    /// reported through the message bus; the method itself does not fail.
    /// </remarks>
    /// <param name="location">The step of the preparation.</param>
    /// <param name="provider">The provider which answers.</param>
    /// <param name="text">The message.</param>
    /// <param name="isHidden">Whether the person does not see the message, e.g., the request which opens a conversation.</param>
    public async Task SendAsync(BflThreadLocation location, AIStudio.Settings.Provider provider, string text, bool isHidden = false)
    {
        if (string.IsNullOrWhiteSpace(text))
            return;

        var conversation = await this.GetAsync(location);
        if (conversation.Thread is not { } thread || !await this.CheckProviderAsync(thread, provider))
            return;

        string systemPrompt;
        try
        {
            systemPrompt = await this.ComposeSystemPromptAsync(location);
        }
        catch (Exception exception) when (exception is IOException or UnauthorizedAccessException or FormatException)
        {
            logger.LogError(exception, "The BeyondFacts Lab could not put together the system prompt of the step '{Step}'.", location.Step);
            await messageBus.SendError(new(Icons.Material.Filled.ErrorOutline, TB("The BeyondFacts Lab could not put together its instructions for the model. Please report this as a bug.")));
            return;
        }

        lock (this.runningLock)
        {
            if (conversation.IsRunning)
                return;

            conversation.IsRunning = true;
        }

        ContentBlock? answerBlock = null;
        var sessionKey = SessionKey(location);
        var sessionId = Guid.Empty;
        var status = AssistantSessionStatus.FAILED;
        try
        {
            BflThreadFactory.PrepareForRequest(thread, provider, systemPrompt);
            var request = new ContentText { Text = text };
            thread.Blocks.Add(new ContentBlock
            {
                Time = DateTimeOffset.Now,
                ContentType = ContentType.TEXT,
                Role = ChatRole.USER,
                Content = request,
                HideFromUser = isHidden
            });

            await store.SaveThreadAsync(location, thread);

            var answer = new ContentText { InitialRemoteWait = true };
            answerBlock = new ContentBlock
            {
                Time = DateTimeOffset.Now,
                ContentType = ContentType.TEXT,
                Role = ChatRole.AI,
                Content = answer
            };

            var lastRendering = DateTimeOffset.MinValue;
            answer.StreamingEvent = async () =>
            {
                var now = DateTimeOffset.Now;
                if (now - lastRendering < STREAMING_RENDER_MIN_TIME)
                    return;

                lastRendering = now;
                await this.NotifyAsync(location);
            };

            answer.StreamingDone = () => this.NotifyAsync(location);
            thread.Blocks.Add(answerBlock);

            var cancellation = new CancellationTokenSource();
            sessionId = (await sessionService.TryBeginAsync(sessionKey, Tools.Components.BEYOND_FACTS_LAB_ASSISTANT.Name, cancellation, thread, new(StringComparer.Ordinal))).SessionId;
            await this.NotifyAsync(location);

            await answer.CreateFromProviderAsync(provider.CreateProvider(), provider.Model, request, thread, cancellation.Token);
            status = cancellation.IsCancellationRequested ? AssistantSessionStatus.CANCELED : AssistantSessionStatus.COMPLETED;
        }
        catch (OperationCanceledException)
        {
            status = AssistantSessionStatus.CANCELED;
        }
        catch (ProviderRequestException exception)
        {
            logger.LogError(exception, "The provider request of the BeyondFacts Lab failed. Status={StatusCode}, Reason='{ReasonPhrase}'.", exception.StatusCode, exception.ReasonPhrase);
            await messageBus.SendError(new(Icons.Material.Filled.CloudOff, exception.UserMessage));
        }
        catch (Exception exception) when (exception is IOException or UnauthorizedAccessException or InvalidDataException)
        {
            logger.LogError(exception, "The BeyondFacts Lab could not store the chat of the step '{Step}'.", location.Step);
            await messageBus.SendError(new(Icons.Material.Filled.SaveAs, TA("AI Studio could not save this conversation. Please try again.")));
        }
        finally
        {
            await this.FinishAsync(conversation, thread, answerBlock, sessionKey, sessionId, status);
        }
    }

    /// <summary>
    /// Stops the answer the model writes in a step.
    /// </summary>
    /// <param name="location">The step of the preparation.</param>
    public Task CancelAsync(BflThreadLocation location) => sessionService.CancelAsync(SessionKey(location));

    /// <summary>
    /// Deletes the conversation of a step, so that it starts over.
    /// </summary>
    /// <param name="location">The step of the preparation.</param>
    /// <returns>False while the model answers in the step.</returns>
    public async Task<bool> ResetAsync(BflThreadLocation location)
    {
        var conversation = await this.GetAsync(location);
        lock (this.runningLock)
        {
            if (conversation.IsRunning)
                return false;
        }

        await store.DeleteThreadAsync(location);
        conversation.Thread = BflThreadFactory.Create(location);

        // The new conversation keeps the ID of the chat, so what the old one received would otherwise wait for the next start:
        await ChatProvenance.ForgetChatsAsync([location.ChatId]);
        await this.NotifyAsync(location);
        return true;
    }

    /// <summary>
    /// Stops every answer of a preparation and forgets its chats, e.g., because the person deleted it.
    /// </summary>
    /// <param name="projectId">The ID of the preparation.</param>
    /// <returns>The IDs of the chats the preparation could have had.</returns>
    public async Task<IReadOnlyList<Guid>> ForgetProjectAsync(Guid projectId)
    {
        var locations = BflStep.All.Select(step => new BflThreadLocation(projectId, step)).ToList();
        foreach (var location in locations)
        {
            await sessionService.CancelAsync(SessionKey(location));
            this.conversations.TryRemove(location, out _);
        }

        return [.. locations.Select(location => location.ChatId)];
    }

    /// <summary>
    /// Puts together the system prompt of a step, anew for every request, so that changed details and a changed form
    /// of address count right away. The chat also uses it to count what the next request carries.
    /// </summary>
    /// <param name="location">The step of the preparation.</param>
    /// <returns>The system prompt.</returns>
    /// <exception cref="FileNotFoundException">The app comes without one of the prompts.</exception>
    /// <exception cref="FormatException">A prompt has a placeholder without a value.</exception>
    public async Task<string> ComposeSystemPromptAsync(BflThreadLocation location)
    {
        var forms = await store.LoadFormsAsync(location.ProjectId);
        var parts = await BflPromptLibrary.LoadPartsAsync(location.Step, Tools.PluginSystem.I18N.I.AddressForm);
        var language = (await settingsManager.GetActiveLanguagePlugin()).LangName;
        return BflPromptComposer.Compose(parts, location.Step, forms, language);
    }

    /// <summary>
    /// Checks whether a provider may answer in a chat, and tells the person why not.
    /// </summary>
    /// <param name="thread">The chat.</param>
    /// <param name="provider">The provider.</param>
    /// <returns>True when the provider may answer.</returns>
    private async Task<bool> CheckProviderAsync(ChatThread thread, AIStudio.Settings.Provider provider)
    {
        string? reason = null;
        if (provider.UsedLLMProvider is LLMProviders.NONE)
            reason = TA("Please select a provider.");
        else if (!settingsManager.IsProviderConfident(provider, Tools.Components.BEYOND_FACTS_LAB_ASSISTANT) || !thread.IsLLMProviderAllowed(provider))
            reason = TA("The selected provider may not see your preparation. Please select another provider.");
        else if (!BflModelRequirements.HasEnoughContext(provider.GetModelProfile().Context))
            reason = TA("The model of the selected provider reads too little at once for the lab. Please select another provider.");

        if (reason is null)
            return true;

        await messageBus.SendError(new(Icons.Material.Filled.CloudOff, reason));
        return false;
    }

    /// <summary>
    /// Ends a request: removes an empty answer, stores the chat, and closes the session.
    /// </summary>
    /// <param name="conversation">The chat.</param>
    /// <param name="thread">The thread of the chat.</param>
    /// <param name="answerBlock">The block of the answer, or null when the request did not get that far.</param>
    /// <param name="sessionKey">The key of the session.</param>
    /// <param name="sessionId">The ID of the session, or Guid.Empty when none began.</param>
    /// <param name="status">How the request ended.</param>
    private async Task FinishAsync(BflConversation conversation, ChatThread thread, ContentBlock? answerBlock, AssistantSessionKey sessionKey, Guid sessionId, AssistantSessionStatus status)
    {
        if (answerBlock is { Content: ContentText answer } && string.IsNullOrWhiteSpace(answer.Text))
            thread.Blocks.Remove(answerBlock);

        if (answerBlock is not null)
        {
            try
            {
                await store.SaveThreadAsync(conversation.Location, thread);
            }
            catch (FileNotFoundException)
            {
                // The person deleted the preparation while the model answered; nothing is left to store.
            }
            catch (Exception exception) when (exception is IOException or UnauthorizedAccessException or InvalidDataException)
            {
                logger.LogError(exception, "The BeyondFacts Lab could not store the chat of the step '{Step}'.", conversation.Location.Step);
                await messageBus.SendError(new(Icons.Material.Filled.SaveAs, TA("AI Studio could not save this conversation. Please try again.")));
            }
        }

        lock (this.runningLock)
            conversation.IsRunning = false;

        if (sessionId != Guid.Empty)
        {
            await sessionService.CompleteAsync(sessionKey, sessionId, status, string.Empty, thread, new(StringComparer.Ordinal));

            // The lab keeps the chat itself; the registry only shows that the lab is at work:
            await sessionService.ClearAsync(sessionKey);
        }

        await this.NotifyAsync(conversation.Location);
    }

    /// <summary>
    /// Tells every page which listens that a chat changed.
    /// </summary>
    /// <param name="location">The step of the chat.</param>
    private async Task NotifyAsync(BflThreadLocation location)
    {
        if (this.ConversationChanged is not { } handlers)
            return;

        foreach (var handler in handlers.GetInvocationList().Cast<Func<BflThreadLocation, Task>>())
        {
            try
            {
                await handler(location);
            }
            catch (Exception exception)
            {
                // A page which went away meanwhile must not stop the answer:
                logger.LogDebug(exception, "A page of the BeyondFacts Lab could not show a change of a chat.");
            }
        }
    }

    /// <summary>
    /// Gets the key under which a request of a step registers in AssistantSessionService.
    /// </summary>
    /// <param name="location">The step of the preparation.</param>
    private static AssistantSessionKey SessionKey(BflThreadLocation location) => new(Tools.Components.BEYOND_FACTS_LAB_ASSISTANT, $"{location.ProjectId:D}/{location.Step.FolderName}");
}