using System.Collections.ObjectModel;
using System.Diagnostics;

namespace MeetingAssistant.Workflow;

public sealed class WorkflowRulesEditorChatViewModel
{
    private const string ThinkingPlaceholder = "Thinking...";
    private readonly IWorkflowRulesEditorChatPipeline pipeline;

    public WorkflowRulesEditorChatViewModel(IWorkflowRulesEditorChatPipeline pipeline)
    {
        this.pipeline = pipeline;
    }

    public ObservableCollection<WorkflowRulesEditorConversationItem> Messages { get; } = [];

    public ObservableCollection<string> ActivityMessages { get; } = [];

    public string Draft { get; set; } = "";

    public bool IsThinking { get; private set; }

    public string ActivityMessage { get; private set; } = ThinkingPlaceholder;

    public event EventHandler? Changed;

    public async Task SendAsync(CancellationToken cancellationToken = default)
    {
        var prompt = Draft.Trim();
        if (string.IsNullOrWhiteSpace(prompt) || IsThinking)
        {
            return;
        }

        Draft = "";
        var startedAt = Stopwatch.GetTimestamp();
        var activityLines = new List<string>();
        var hasVisibleThinking = false;
        var activityContext = SynchronizationContext.Current;
        var priorConversation = Messages
            .Select(item => item.Message)
            .OfType<WorkflowRulesEditorChatMessage>()
            .ToList();
        Messages.Add(WorkflowRulesEditorConversationItem.ChatMessage(
            new WorkflowRulesEditorChatMessage(WorkflowRulesEditorChatRole.User, prompt)));
        ActivityMessages.Clear();
        IsThinking = true;
        ActivityMessage = ThinkingPlaceholder;
        OnChanged();

        try
        {
            var result = await pipeline.SendAsync(
                priorConversation,
                prompt,
                cancellationToken,
                update => hasVisibleThinking |= ApplyActivityUpdate(activityContext, update, activityLines));
            AddCompletedActivity(startedAt, activityLines, hasVisibleThinking);
            Messages.Add(WorkflowRulesEditorConversationItem.ChatMessage(
                new WorkflowRulesEditorChatMessage(
                    WorkflowRulesEditorChatRole.Agent,
                    string.IsNullOrWhiteSpace(result.Response)
                        ? "(No response text returned.)"
                        : result.Response.Trim())));
        }
        catch (Exception exception) when (exception is not OperationCanceledException || !cancellationToken.IsCancellationRequested)
        {
            AddCompletedActivity(startedAt, activityLines, hasVisibleThinking);
            Messages.Add(WorkflowRulesEditorConversationItem.ChatMessage(
                new WorkflowRulesEditorChatMessage(
                    WorkflowRulesEditorChatRole.Agent,
                    $"Meeting Summary Agent failed: {exception.Message}")));
        }
        finally
        {
            IsThinking = false;
            ActivityMessages.Clear();
            ActivityMessage = ThinkingPlaceholder;
            OnChanged();
        }
    }

    private bool ApplyActivityUpdate(
        SynchronizationContext? context,
        WorkflowRulesEditorActivityUpdate update,
        List<string> activityLines)
    {
        if (context is null || SynchronizationContext.Current == context)
        {
            return ApplyActivityUpdate(update, activityLines);
        }

        var hasVisibleThinking = false;
        Exception? exception = null;
        context.Send(
            _ =>
            {
                try
                {
                    hasVisibleThinking = ApplyActivityUpdate(update, activityLines);
                }
                catch (Exception caught)
                {
                    exception = caught;
                }
            },
            null);

        if (exception is not null)
        {
            throw exception;
        }

        return hasVisibleThinking;
    }

    private bool ApplyActivityUpdate(
        WorkflowRulesEditorActivityUpdate update,
        List<string> activityLines)
    {
        if (!IsThinking || string.IsNullOrWhiteSpace(update.Text))
        {
            return false;
        }

        var hasVisibleThinking = false;
        if (update.Kind == WorkflowRulesEditorActivityKind.ToolCall)
        {
            var line = $"Called tool: {update.Text.Trim()}";
            ActivityMessages.Add(line);
            activityLines.Add(line);
        }
        else if (update.Kind == WorkflowRulesEditorActivityKind.Thinking)
        {
            var line = update.Text.Trim();
            ActivityMessages.Add(line);
            activityLines.Add(line);
            hasVisibleThinking = true;
        }
        else
        {
            var line = update.Text.Trim();
            ActivityMessage = line;
            activityLines.Add(line);
        }

        OnChanged();
        return hasVisibleThinking;
    }

    private void AddCompletedActivity(
        long startedAt,
        IReadOnlyList<string> activityLines,
        bool hasVisibleThinking)
    {
        var completedActivityLines = hasVisibleThinking
            ? activityLines.ToArray()
            : new[] { ThinkingPlaceholder }.Concat(activityLines).ToArray();
        Messages.Add(WorkflowRulesEditorConversationItem.Activity(
            $"Worked for {FormatDuration(Stopwatch.GetElapsedTime(startedAt))}",
            completedActivityLines));
    }

    private static string FormatDuration(TimeSpan duration)
    {
        if (duration.TotalMinutes >= 1)
        {
            return $"{(int)duration.TotalMinutes}m {duration.Seconds}s";
        }

        return $"{Math.Max(0, (int)Math.Round(duration.TotalSeconds))}s";
    }

    private void OnChanged()
    {
        Changed?.Invoke(this, EventArgs.Empty);
    }
}