//-----------------------------------------------------------------------
// <copyright file="Map.cs" company="Mapbox">
//     Copyright (c) 2016 Mapbox. All rights reserved.
// </copyright>
//-----------------------------------------------------------------------

namespace Mapbox.Map
{
	using System;
	using System.Collections.Generic;
	using Mapbox.Platform;
	using Mapbox.Utils;

	/// <summary>
	///     The Mapbox Map abstraction will take care of fetching and decoding
	///     data for a geographic bounding box at a certain zoom level.
	/// </summary>
	/// <typeparam name="T">
	///     The tile type, currently <see cref="T:Mapbox.Map.Vector"/> or
	///     <see cref="T:Mapbox.Map.Raster"/>.
	/// </typeparam>
	/// <example>
	/// Request a map of the whole world:
	/// <code>
	/// var map = new Map&lt;RasterTile&gt;(MapboxAccess.Instance);
	/// map.Zoom = 2
	/// map.Vector2dBounds = Vector2dBounds.World();
	/// map.TilesetId = "mapbox://styles/mapbox/streets-v10
	///
	/// // Register for tile updates.
	/// map.Subscribe(this);
	///
	/// // Trigger the request.
	/// map.Update();
	/// </code>
	/// </example>
	public sealed class Map<T> : Mapbox.Utils.IObservable<T> where T : Tile, new()
	{
		/// <summary>
		///     Arbitrary limit of tiles this class will handle simultaneously.
		/// </summary>
		public const int TileMax = 256;

		private readonly IFileSource fs;
		private Vector2dBounds latLngBounds;
		private int zoom;
		private string tilesetId;

		private HashSet<T> tiles = new HashSet<T>();
		private List<Mapbox.Utils.IObserver<T>> observers = new List<Mapbox.Utils.IObserver<T>>();

		/// <summary>
		///     Initializes a new instance of the <see cref="T:Mapbox.Map.Map`1"/> class.
		/// </summary>
		/// <param name="fs"> The data source abstraction. </param>
		public Map(IFileSource fs)
		{
			this.fs = fs;
			this.latLngBounds = new Vector2dBounds();
			this.zoom = 0;
		}

		/// <summary>
		///     Gets or sets the tileset ID. If not set, it will use the default
		///     tileset ID for the tile type. I.e. "mapbox.satellite" for raster tiles
		///     and "mapbox.mapbox-streets-v7" for vector tiles.
		/// </summary>
		/// <value>
		///     The tileset ID, usually in the format "user.mapid". Exceptionally,
		///     <see cref="T:Mapbox.Map.RasterTile"/> will take the full style URL
		///     from where the tile is composited from, like "mapbox://styles/mapbox/streets-v9".
		/// </value>
		public string TilesetId
		{
			get
			{
				return this.tilesetId;
			}

			set
			{
				if (this.tilesetId == value)
				{
					return;
				}

				this.tilesetId = value;

				foreach (Tile tile in this.tiles)
				{
					tile.Cancel();
				}

				this.tiles.Clear();
			}
		}

		/// <summary>
		///     Gets the tiles, vector or raster. Tiles might be
		///     in a incomplete state.
		/// </summary>
		/// <value> The tiles. </value>
		public HashSet<T> Tiles
		{
			get
			{
				return this.tiles;
			}
		}

		/// <summary>Gets or sets a geographic bounding box.</summary>
		/// <value>New geographic bounding box.</value>
		public Vector2dBounds Vector2dBounds
		{
			get
			{
				return this.latLngBounds;
			}

			set
			{
				this.latLngBounds = value;
			}
		}

		/// <summary>Gets or sets the central coordinate of the map.</summary>
		/// <value>The central coordinate.</value>
		public Vector2d Center
		{
			get
			{
				return this.latLngBounds.Center;
			}

			set
			{
				this.latLngBounds.Center = value;
			}
		}

		/// <summary>Gets or sets the map zoom level.</summary>
		/// <value>The new zoom level.</value>
		public int Zoom
		{
			get
			{
				return this.zoom;
			}

			set
			{
				this.zoom = Math.Max(0, Math.Min(20, value));
			}
		}

		/// <summary>
		///     Sets the coordinates bounds and zoom at once.
		/// </summary>
		/// <param name="bounds"> Coordinates bounds. </param>
		/// <param name="zoom"> Zoom level. </param>
		public void SetVector2dBoundsZoom(Vector2dBounds bounds, int zoom)
		{
			this.latLngBounds = bounds;
			this.zoom = zoom;
		}

		/// <summary> Add an <see cref="T:IObserver" /> to the observer list. </summary>
		/// <param name="observer"> The object subscribing to events. </param>
		public void Subscribe(Mapbox.Utils.IObserver<T> observer)
		{
			this.observers.Add(observer);
		}

		/// <summary> Remove an <see cref="T:IObserver" /> to the observer list. </summary>
		/// <param name="observer"> The object unsubscribing to events. </param>
		public void Unsubscribe(Mapbox.Utils.IObserver<T> observer)
		{
			this.observers.Remove(observer);
		}

		private void NotifyNext(T next)
		{
			var copy = new List<Mapbox.Utils.IObserver<T>>(this.observers);

			foreach (Mapbox.Utils.IObserver<T> observer in copy)
			{
				observer.OnNext(next);
			}
		}

		/// <summary>
		/// Request tiles after changing map properties.
		/// </summary>
		public void Update()
		{
			var cover = TileCover.Get(this.latLngBounds, this.zoom);

			if (cover.Count > TileMax)
			{
				return;
			}

			// Do not request tiles that we are already requesting
			// but at the same time exclude the ones we don't need
			// anymore, cancelling the network request.
			this.tiles.RemoveWhere((T tile) =>
				{
					if (cover.Remove(tile.Id))
					{
						return false;
					}
					else
					{
						tile.Cancel();
						this.NotifyNext(tile);

						return true;
					}
				});

			foreach (CanonicalTileId id in cover)
			{
				var tile = new T();

				Tile.Parameters param;
				param.Id = id;
				param.TilesetId = this.tilesetId;
				param.Fs = this.fs;

				tile.Initialize(param, () => { this.NotifyNext(tile); });

				this.tiles.Add(tile);
			}
		}
	}
}