using System;
using System.Collections.Generic;
using System.Data;
using System.Linq;

namespace Terminal.Gui.Views {

	/// <summary>
	/// View for tabular data based on a <see cref="DataTable"/>
	/// </summary>
	public class TableView : View {

		private int columnOffset;
		private int rowOffset;

		public DataTable Table { get; private set; }

		/// <summary>
		/// Zero indexed offset for the upper left <see cref="DataColumn"/> to display in <see cref="Table"/>.
		/// </summary>
		/// <remarks>This property allows very wide tables to be rendered with horizontal scrolling</remarks>
		public int ColumnOffset {
			get {
				return columnOffset; 
			}

			//try to prevent this being set to an out of bounds column
			set {
				//the value before we changed it
				var origValue = columnOffset;

				columnOffset = Math.Min (Table.Columns.Count - 1, Math.Max (0, value));
				
				//if value actually changed we must update UI
				if(columnOffset != origValue)
					SetNeedsDisplay();
			}
		}


		/// <summary>
		/// Zero indexed offset for the <see cref="DataRow"/> to display in <see cref="Table"/> on line 2 of the control (first line being headers)
		/// </summary>
		/// <remarks>This property allows very wide tables to be rendered with horizontal scrolling</remarks>
		public int RowOffset { 
			get {
				return rowOffset; 
			}
			set {
				//the value before we changed it
				var origValue = rowOffset;

				rowOffset = Math.Min (Table.Rows.Count - 1, Math.Max (0, value));

				//if value actually changed we must update UI
				if(rowOffset != origValue)
					SetNeedsDisplay();
			}
		}

		/// <summary>
		/// The maximum number of characters to render in any given column.  This prevents one long column from pushing out all the others
		/// </summary>
		public int MaximumCellWidth {get;set;} = 100;

		/// <summary>
		/// The text representation that should be rendered for cells with the value <see cref="DBNull.Value"/>
		/// </summary>
		public string NullSymbol {get;set;} = "-";

		/// <summary>
		/// The symbol to add after each cell value and header value to visually seperate values
		/// </summary>
		public char SeparatorSymbol {get;set; } = ' ';

		/// <summary>
		/// Initialzies a <see cref="TableView"/> class using <see cref="LayoutStyle.Computed"/> layout. 
		/// </summary>
		/// <param name="table">The table to display in the control</param>
		public TableView (DataTable table) : base ()
		{
			this.Table = table ?? throw new ArgumentNullException (nameof (table));
		}
		///<inheritdoc/>
		public override void Redraw (Rect bounds)
		{
			Attribute currentAttribute;
			var current = ColorScheme.Focus;
			Driver.SetAttribute (current);
			Move (0, 0);

			var frame = Frame;

			int activeColor = ColorScheme.HotNormal;
			int trackingColor = ColorScheme.HotFocus;

			// What columns to render at what X offset in viewport
			Dictionary<DataColumn, int> columnsToRender = CalculateViewport(bounds);

			Driver.SetAttribute (ColorScheme.HotNormal);

			//invalidate current row (prevents scrolling around leaving old characters in the frame
			Driver.AddStr(new string (' ',bounds.Width));

			// Render the headers
			foreach(var kvp in columnsToRender) {
				
				Move (kvp.Value,0);
				Driver.AddStr(kvp.Key.ColumnName+ SeparatorSymbol);
			}

			//render the cells
			for (int line = 1; line < frame.Height; line++) {
				
				//invalidate current row (prevents scrolling around leaving old characters in the frame
				Move (0,line);
				Driver.AddStr(new string (' ',bounds.Width));

				//work out what Row to render
				var rowToRender = RowOffset + (line-1);

				//if we have run off the end of the table
				if(rowToRender >= Table.Rows.Count)
					continue;

				foreach(var kvp in columnsToRender) {
					Move (kvp.Value,line);
					Driver.AddStr(GetRenderedVal(Table.Rows[rowToRender][kvp.Key]) + SeparatorSymbol);
				}
			}

			void SetAttribute (Attribute attribute)
			{
				if (currentAttribute != attribute) {
					currentAttribute = attribute;
					Driver.SetAttribute (attribute);
				}
			}

		}
		
		/// <inheritdoc/>
		public override bool ProcessKey (KeyEvent keyEvent)
		{
			switch (keyEvent.Key) {
			case Key.CursorLeft:
				ColumnOffset--;
				break;
			case Key.CursorRight:
				ColumnOffset++;
				break;
			case Key.CursorDown:
				RowOffset++;
				break;
			case Key.CursorUp:
				RowOffset--;
				break;
			case Key.PageUp:
				 RowOffset -= Frame.Height;
				break;
			case Key.V | Key.CtrlMask:
			case Key.PageDown:
				 RowOffset += Frame.Height;
				break;
			case Key.Home | Key.CtrlMask:
				RowOffset = 0;
				ColumnOffset = 0;
				break;
			case Key.Home:
				ColumnOffset = 0;
				break;
			case Key.End | Key.CtrlMask:
				//jump to end of table
				RowOffset = Table.Rows.Count-1;
				ColumnOffset = Table.Columns.Count-1;
				break;
			case Key.End:
				//jump to end of row
				ColumnOffset = Table.Columns.Count-1;				
				break;
			}
			PositionCursor ();
			return true;
		}
		/// <summary>
		/// Calculates which columns should be rendered given the <paramref name="bounds"/> in which to display and the <see cref="ColumnOffset"/>
		/// </summary>
		/// <param name="bounds"></param>
		/// <param name="padding"></param>
		/// <returns></returns>
		private Dictionary<DataColumn,int> CalculateViewport(Rect bounds, int padding = 1)
		{
			Dictionary<DataColumn,int> toReturn = new Dictionary<DataColumn, int>();

			int usedSpace = 0;
			int availableHorizontalSpace = bounds.Width;
			int rowsToRender = bounds.Height-1; //1 reserved for the headers row
			
			foreach(var col in Table.Columns.Cast<DataColumn>().Skip(ColumnOffset)) {
				
				toReturn.Add(col,usedSpace);
				usedSpace += CalculateMaxRowSize(col,rowsToRender) + padding;

				if(usedSpace > availableHorizontalSpace)
					return toReturn;
				
			}
			
			return toReturn;
		}

		/// <summary>
		/// Returns the maximum of the <paramref name="col"/> name and the maximum length of data that will be rendered starting at <see cref="RowOffset"/> and rendering <paramref name="rowsToRender"/>
		/// </summary>
		/// <param name="col"></param>
		/// <param name="rowsToRender"></param>
		/// <returns></returns>
		private int CalculateMaxRowSize (DataColumn col, int rowsToRender)
		{
			int spaceRequired = col.ColumnName.Length;

			for(int i = RowOffset; i<RowOffset + rowsToRender && i<Table.Rows.Count;i++) {

				//expand required space if cell is bigger than the last biggest cell or header
				spaceRequired = Math.Max(spaceRequired,GetRenderedVal(Table.Rows[i][col]).Length);
			}

			return spaceRequired;
		}

		/// <summary>
		/// Returns the value that should be rendered to best represent a strongly typed <paramref name="value"/> read from <see cref="Table"/>
		/// </summary>
		/// <param name="value"></param>
		/// <returns></returns>
		private string GetRenderedVal (object value)
		{
			if(value == null || value == DBNull.Value) 
			{
				return NullSymbol;
			}
			
			var representation = value.ToString();

			//if it is too long to fit
			if(representation.Length > MaximumCellWidth)
				return representation.Substring(0,MaximumCellWidth);

			return representation;
		}
	}
}