using System;
using System.Collections.Generic;

namespace Terminal.Gui {
	/// <summary>
	/// Represents the status of an ANSI escape sequence request made to the terminal using <see cref="EscSeqRequests"/>.
	/// </summary>
	/// <remarks>
	/// </remarks>
	public class EscSeqReqStatus {
		/// <summary>
		/// Gets the Escape Sequence Termintor (e.g. ESC[8t ... t is the terminator).
		/// </summary>
		public string Terminator { get; }
		/// <summary>
		/// Gets the number of requests.
		/// </summary>
		public int NumRequests { get; }
		/// <summary>
		/// Gets the number of unfinished requests.
		/// </summary>
		public int NumOutstanding { get; set; }

		/// <summary>
		/// Creates a new state of escape sequence request.
		/// </summary>
		/// <param name="terminator">The terminator.</param>
		/// <param name="numReq">The number of requests.</param>
		public EscSeqReqStatus (string terminator, int numReq)
		{
			Terminator = terminator;
			NumRequests = NumOutstanding = numReq;
		}
	}

	// TODO: This class is a singleton. It should use the singleton pattern.
	/// <summary>
	/// Manages ANSI Escape Sequence requests and responses. The list of <see cref="EscSeqReqStatus"/> contains the status of the request.
	/// Each request is identified by the terminator (e.g. ESC[8t ... t is the terminator).
	/// </summary>
	public class EscSeqRequests {
		/// <summary>
		/// Gets the <see cref="EscSeqReqStatus"/> list.
		/// </summary>
		public List<EscSeqReqStatus> Statuses { get; } = new List<EscSeqReqStatus> ();

		/// <summary>
		/// Adds a new request for the ANSI Escape Sequence defined by <paramref name="terminator"/>. Adds a <see cref="EscSeqReqStatus"/>
		/// instance to <see cref="Statuses"/> list.
		/// </summary>
		/// <param name="terminator">The terminator.</param>
		/// <param name="numReq">The number of requests.</param>
		public void Add (string terminator, int numReq = 1)
		{
			lock (Statuses) {
				var found = Statuses.Find (x => x.Terminator == terminator);
				if (found == null) {
					Statuses.Add (new EscSeqReqStatus (terminator, numReq));
				} else if (found != null && found.NumOutstanding < found.NumRequests) {
					found.NumOutstanding = Math.Min (found.NumOutstanding + numReq, found.NumRequests);
				}
			}
		}

		/// <summary>
		/// Removes a request defined by <paramref name="terminator"/>. If a matching <see cref="EscSeqReqStatus"/> is found
		/// and the number of outstanding
		/// requests is greater than 0, the number of outstanding requests is decremented. If the number of outstanding requests
		/// is 0, the <see cref="EscSeqReqStatus"/> is removed from <see cref="Statuses"/>.
		/// </summary>
		/// <param name="terminator">The terminating string.</param>
		public void Remove (string terminator)
		{
			lock (Statuses) {
				var found = Statuses.Find (x => x.Terminator == terminator);
				if (found == null) {
					return;
				}
				if (found != null && found.NumOutstanding == 0) {
					Statuses.Remove (found);
				} else if (found != null && found.NumOutstanding > 0) {
					found.NumOutstanding--;
					if (found.NumOutstanding == 0) {
						Statuses.Remove (found);
					}
				}
			}
		}

		/// <summary>
		/// Indicates if a <see cref="EscSeqReqStatus"/> with the <paramref name="terminator"/> exists
		/// in the <see cref="Statuses"/> list.
		/// </summary>
		/// <param name="terminator"></param>
		/// <returns><see langword="true"/> if exist, <see langword="false"/> otherwise.</returns>
		public bool HasResponse (string terminator)
		{
			lock (Statuses) {
				var found = Statuses.Find (x => x.Terminator == terminator);
				if (found == null) {
					return false;
				}
				if (found != null && found.NumOutstanding > 0) {
					return true;
				} else {
					// BUGBUG: Why does an API that returns a bool remove the entry from the list?
					// NetDriver and Unit tests never exercise this line of code. Maybe Curses does?
					Statuses.Remove (found);
				}
				return false;
			}
		}
	}
}