using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace Implab.Diagnostics {
    public abstract class TextListenerBase : ServiceLocator, IEventTextFormatter<object>, IEventTextFormatter<TraceEvent> {

        readonly Dictionary<object, Action> m_subscriptions = new Dictionary<object, Action>();

        protected TextListenerBase() {
            Register(this);
        }

        public void Subscribe(Type eventType) {
            if (eventType == null)
                throw new ArgumentNullException("eventType");
            GetType().GetMethod("Subscribe", new Type[0]).MakeGenericMethod(eventType).Invoke(this, null);
        }

        public void Subscribe<TEvent>() {
            Subscribe<TEvent>(LogChannel<TEvent>.Default);
        }

        public void Subscribe<TEvent>(LogChannel<TEvent> channel) {
            if (channel == null)
                throw new ArgumentNullException("channel");

            lock (m_subscriptions) {
                AssertNotDisposed();

                var formatter = GetService<IEventTextFormatter<TEvent>>();

                EventHandler<ValueEventArgs<TEvent>> handler = (sender, args) => {
                    WriteEntry((TraceContext)sender, formatter.Format((TraceContext)sender, args.Value));
                };

                if (m_subscriptions.ContainsKey(channel))
                    return;

                channel.Events += handler;

                Action unsubscribe = () => {
                    channel.Events -= handler;
                };

                m_subscriptions.Add(channel, unsubscribe);
            }
        }

        public void Unsubscribe<TEvent>(LogChannel<TEvent> channel) {
            if (channel == null)
                throw new ArgumentNullException("channel");

            lock (m_subscriptions) {
                Action subscription;
                if (m_subscriptions.TryGetValue(channel, out subscription)) {
                    subscription();
                    m_subscriptions.Remove(channel);
                }
            }
        }

        public void UnsubscribeAll() {
            lock (m_subscriptions) {
                foreach (var subscription in m_subscriptions.Values)
                    subscription();
                m_subscriptions.Clear();
            }
        }

        protected abstract void WriteEntry(TraceContext context, EventText text);
        
        public EventText Format(TraceContext context, object data) {
            return new EventText {
                indent = context.CurrentOperation.Level,
                content = data.ToString()
            };
        }

        public EventText Format(TraceContext context, TraceEvent data) {
            var level = context.CurrentOperation.Level;
            if (data.EventType == TraceEventType.OperationCompleted || data.EventType == TraceEventType.OperationStarted)
                level--;

            return new EventText {
                indent = level,
                content = data.ToString()
            };
        }

        protected override void Dispose(bool disposing) {
            if (disposing) {
                UnsubscribeAll();
            }
            base.Dispose(disposing);
        }
    }
}