using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;

namespace Coroutine {
    /// <summary>
    /// An object of this class can be used to start, tick and otherwise manage active <see cref="ActiveCoroutine"/>s as well as their <see cref="Event"/>s.
    /// Note that a static implementation of this can be found in <see cref="CoroutineHandler"/>.
    /// </summary>
    public class CoroutineHandlerInstance {

        private readonly List<ActiveCoroutine> tickingCoroutines = new List<ActiveCoroutine>();
        private readonly Dictionary<Event, List<ActiveCoroutine>> eventCoroutines = new Dictionary<Event, List<ActiveCoroutine>>();
        private readonly HashSet<(Event, ActiveCoroutine)> eventCoroutinesToRemove = new HashSet<(Event, ActiveCoroutine)>();
        private readonly HashSet<ActiveCoroutine> outstandingEventCoroutines = new HashSet<ActiveCoroutine>();
        private readonly HashSet<ActiveCoroutine> outstandingTickingCoroutines = new HashSet<ActiveCoroutine>();
        private readonly Stopwatch stopwatch = new Stopwatch();
        private readonly object lockObject = new object();

        /// <summary>
        /// The amount of <see cref="ActiveCoroutine"/> instances that are currently waiting for a tick (waiting for time to pass)
        /// </summary>
        public int TickingCount {
            get {
                lock (this.lockObject)
                    return this.tickingCoroutines.Count;
            }
        }
        /// <summary>
        /// The amount of <see cref="ActiveCoroutine"/> instances that are currently waiting for an <see cref="Event"/>
        /// </summary>
        public int EventCount {
            get {
                lock (this.lockObject)
                    return this.eventCoroutines.Sum(c => c.Value.Count);
            }
        }

        /// <summary>
        /// Starts the given coroutine, returning a <see cref="ActiveCoroutine"/> object for management.
        /// Note that this calls <see cref="IEnumerable{T}.GetEnumerator"/> to get the enumerator.
        /// </summary>
        /// <param name="coroutine">The coroutine to start</param>
        /// <param name="name">The <see cref="ActiveCoroutine.Name"/> that this coroutine should have. Defaults to an empty string.</param>
        /// <param name="priority">The <see cref="ActiveCoroutine.Priority"/> that this coroutine should have. The higher the priority, the earlier it is advanced. Defaults to 0.</param>
        /// <returns>An active coroutine object representing this coroutine</returns>
        public ActiveCoroutine Start(IEnumerable<Wait> coroutine, string name = "", int priority = 0) {
            return this.Start(coroutine.GetEnumerator(), name, priority);
        }

        /// <summary>
        /// Starts the given coroutine, returning a <see cref="ActiveCoroutine"/> object for management.
        /// </summary>
        /// <param name="coroutine">The coroutine to start</param>
        /// <param name="name">The <see cref="ActiveCoroutine.Name"/> that this coroutine should have. Defaults to an empty string.</param>
        /// <param name="priority">The <see cref="ActiveCoroutine.Priority"/> that this coroutine should have. The higher the priority, the earlier it is advanced compared to other coroutines that advance around the same time. Defaults to 0.</param>
        /// <returns>An active coroutine object representing this coroutine</returns>
        public ActiveCoroutine Start(IEnumerator<Wait> coroutine, string name = "", int priority = 0) {
            var inst = new ActiveCoroutine(coroutine, name, priority, this.stopwatch);
            if (inst.MoveNext()) {
                lock (this.lockObject)
                    this.GetOutstandingCoroutines(inst.IsWaitingForEvent).Add(inst);
            }
            return inst;
        }

        /// <summary>
        /// Causes the given action to be invoked after the given <see cref="Wait"/>.
        /// This is equivalent to a coroutine that waits for the given wait and then executes the given <see cref="Action"/>.
        /// </summary>
        /// <param name="wait">The wait to wait for</param>
        /// <param name="action">The action to execute after waiting</param>
        /// <param name="name">The <see cref="ActiveCoroutine.Name"/> that the underlying coroutine should have. Defaults to an empty string.</param>
        /// <param name="priority">The <see cref="ActiveCoroutine.Priority"/> that the underlying coroutine should have. The higher the priority, the earlier it is advanced compared to other coroutines that advance around the same time. Defaults to 0.</param>
        /// <returns>An active coroutine object representing this coroutine</returns>
        public ActiveCoroutine InvokeLater(Wait wait, Action action, string name = "", int priority = 0) {
            return this.Start(CoroutineHandlerInstance.InvokeLaterImpl(wait, action), name, priority);
        }

        /// <summary>
        /// Causes the given action to be invoked after the given <see cref="Event"/>.
        /// This is equivalent to a coroutine that waits for the given wait and then executes the given <see cref="Action"/>.
        /// </summary>
        /// <param name="evt">The event to wait for</param>
        /// <param name="action">The action to execute after waiting</param>
        /// <param name="name">The <see cref="ActiveCoroutine.Name"/> that the underlying coroutine should have. Defaults to an empty string.</param>
        /// <param name="priority">The <see cref="ActiveCoroutine.Priority"/> that the underlying coroutine should have. The higher the priority, the earlier it is advanced compared to other coroutines that advance around the same time. Defaults to 0.</param>
        /// <returns>An active coroutine object representing this coroutine</returns>
        public ActiveCoroutine InvokeLater(Event evt, Action action, string name = "", int priority = 0) {
            return this.InvokeLater(new Wait(evt), action, name, priority);
        }

        /// <summary>
        /// Ticks this coroutine handler, causing all time-based <see cref="Wait"/>s to be ticked.
        /// </summary>
        /// <param name="deltaSeconds">The amount of seconds that have passed since the last time this method was invoked</param>
        public void Tick(double deltaSeconds) {
            lock (this.lockObject) {
                this.MoveOutstandingCoroutines(false);
                this.tickingCoroutines.RemoveAll(c => {
                    if (c.Tick(deltaSeconds)) {
                        return true;
                    } else if (c.IsWaitingForEvent) {
                        this.outstandingEventCoroutines.Add(c);
                        return true;
                    }
                    return false;
                });
            }
        }

        /// <summary>
        /// Ticks this coroutine handler, causing all time-based <see cref="Wait"/>s to be ticked.
        /// This is a convenience method that calls <see cref="Tick(double)"/>, but accepts a <see cref="TimeSpan"/> instead of an amount of seconds.
        /// </summary>
        /// <param name="delta">The time that has passed since the last time this method was invoked</param>
        public void Tick(TimeSpan delta) {
            this.Tick(delta.TotalSeconds);
        }

        /// <summary>
        /// Raises the given event, causing all event-based <see cref="Wait"/>s to be updated.
        /// </summary>
        /// <param name="evt">The event to raise</param>
        public void RaiseEvent(Event evt) {
            lock (this.lockObject) {
                this.MoveOutstandingCoroutines(true);
                var coroutines = this.GetEventCoroutines(evt, false);
                if (coroutines != null) {
                    for (var i = 0; i < coroutines.Count; i++) {
                        var c = coroutines[i];
                        var tup = (c.Event, c);
                        if (this.eventCoroutinesToRemove.Contains(tup))
                            continue;
                        if (c.OnEvent(evt)) {
                            this.eventCoroutinesToRemove.Add(tup);
                        } else if (!c.IsWaitingForEvent) {
                            this.eventCoroutinesToRemove.Add(tup);
                            this.outstandingTickingCoroutines.Add(c);
                        }
                    }
                }
            }
        }

        /// <summary>
        /// Returns a list of all currently active <see cref="ActiveCoroutine"/> objects under this handler.
        /// </summary>
        /// <returns>All active coroutines</returns>
        public IEnumerable<ActiveCoroutine> GetActiveCoroutines() {
            lock (this.lockObject)
                return this.tickingCoroutines.Concat(this.eventCoroutines.Values.SelectMany(c => c));
        }

        private void MoveOutstandingCoroutines(bool evt) {
            // RemoveWhere is twice as fast as iterating and then clearing
            if (this.eventCoroutinesToRemove.Count > 0) {
                this.eventCoroutinesToRemove.RemoveWhere(c => {
                    this.GetEventCoroutines(c.Item1, false).Remove(c.Item2);
                    return true;
                });
            }
            var coroutines = this.GetOutstandingCoroutines(evt);
            if (coroutines.Count > 0) {
                coroutines.RemoveWhere(c => {
                    var list = evt ? this.GetEventCoroutines(c.Event, true) : this.tickingCoroutines;
                    var position = list.BinarySearch(c);
                    list.Insert(position < 0 ? ~position : position, c);
                    return true;
                });
            }
        }

        private HashSet<ActiveCoroutine> GetOutstandingCoroutines(bool evt) {
            return evt ? this.outstandingEventCoroutines : this.outstandingTickingCoroutines;
        }

        private List<ActiveCoroutine> GetEventCoroutines(Event evt, bool create) {
            if (!this.eventCoroutines.TryGetValue(evt, out var ret) && create) {
                ret = new List<ActiveCoroutine>();
                this.eventCoroutines.Add(evt, ret);
            }
            return ret;
        }

        private static IEnumerator<Wait> InvokeLaterImpl(Wait wait, Action action) {
            yield return wait;
            action();
        }

    }
}