using System;
using System.Globalization;
using System.Xml.Serialization;

namespace PDFPatcher.Common
{
	public class UnitConverter
	{
		const string Null = "null";
		internal const string ToStringFormat = "0.###";

		/// <summary>
		/// 获取单位转换因数。
		/// </summary>
		[XmlIgnore]
		public float UnitFactor { get; private set; }

		private int _Precision;
		private float _PreservedValue;
		///<summary>获取或指定转换精度的值。</summary>
		[XmlIgnore]
		public int Precision {
			get => _Precision;
			set {
				if (value < 0 || value > 6) {
					throw new ArgumentException("转换精度不能小于 0 或大于 6。");
				}
				_Precision = value;
				_PreservedValue = (float)Math.Pow(0.1, _Precision);
			}
		}

		private string _Unit;
		///<summary>获取或指定转换使用的单位。</summary>
		[XmlAttribute("单位")]
		public string Unit {
			get => _Unit;
			set {
				var f = ValueHelper.MapValue(value, Constants.Units.Names, Constants.Units.Factors, 0);
				if (f == 0) {
					throw new ArgumentException("尺寸单位无效。");
				}
				UnitFactor = f;
				_Unit = value;
			}
		}

		public UnitConverter() {
			Unit = Constants.Units.CM;
			Precision = 3;
		}

		internal float FromPoint(float point) {
			return (point < _PreservedValue && point >= 0) // preserve small fragment
					? point
					: (float)Math.Round(point / UnitFactor, _Precision);
		}

		internal float ToPoint(float value) {
			return (value < _PreservedValue && value >= 0 || value >= 10000) // preserve small fragment or extra large values
					? value
					: (float)Math.Round(value * UnitFactor, _Precision);
		}

		internal static string FromPoint(string point, float unitFactor) {
			if (String.IsNullOrEmpty(point) || point == Null) {
				return Null;
			}
			if (unitFactor == 1) {
				return point;
			}
			if (point.TryParse(out float v)) {
				return (v < 0.01 && v >= 0) // preserve small fragment
					? point
					: (v / unitFactor).ToString(ToStringFormat, NumberFormatInfo.InvariantInfo);
			}
			return point;
		}

		internal static string FromPoint(float point, float unitFactor) {
			return ((point < 0.01 && point >= 0) || unitFactor == 1 // preserve small fragment
				? point.ToString(NumberFormatInfo.InvariantInfo)
				: (point / unitFactor).ToString(ToStringFormat, NumberFormatInfo.InvariantInfo));
		}

		internal static string ToPoint(string value, float unitFactor) {
			if (String.IsNullOrEmpty(value) || value == Null) {
				return Null;
			}
			if (value.TryParse(out float v)) {
				return (v < 0.01 && v >= 0) // preserve small fragment
					? value
					: (v * unitFactor).ToString(ToStringFormat, NumberFormatInfo.InvariantInfo);
			}
			return value;
		}

		internal static float ToPoint(float value, float unitFactor) {
			return (value < 0.01 && value >= 0 || value >= 10000) // preserve small fragment or extra large values
					? value
					: (value * unitFactor);
		}

		internal static float[] ConvertUnit(float[] source, float factor) {
			return Array.ConvertAll(source, i => ToPoint(i, factor));
		}


	}
}