using System;
using TriangleNet.Topology;

namespace TriangleNet.Tools
{
	public class AdjacencyMatrix
	{
		private int nnz;

		private int[] pcol;

		private int[] irow;

		public readonly int N;

		public int[] ColumnPointers => pcol;

		public int[] RowIndices => irow;

		public AdjacencyMatrix(Mesh mesh)
		{
			N = mesh.vertices.Count;
			pcol = AdjacencyCount(mesh);
			nnz = pcol[N];
			irow = AdjacencySet(mesh, pcol);
			SortIndices();
		}

		public AdjacencyMatrix(int[] pcol, int[] irow)
		{
			N = pcol.Length - 1;
			nnz = pcol[N];
			this.pcol = pcol;
			this.irow = irow;
			if (pcol[0] != 0)
			{
				throw new ArgumentException("Expected 0-based indexing.", "pcol");
			}
			if (irow.Length < nnz)
			{
				throw new ArgumentException();
			}
		}

		public int Bandwidth()
		{
			int num = 0;
			int num2 = 0;
			for (int i = 0; i < N; i++)
			{
				for (int j = pcol[i]; j < pcol[i + 1]; j++)
				{
					int num3 = irow[j];
					num = Math.Max(num, i - num3);
					num2 = Math.Max(num2, num3 - i);
				}
			}
			return num + 1 + num2;
		}

		private int[] AdjacencyCount(Mesh mesh)
		{
			int n = N;
			int[] array = new int[n + 1];
			for (int i = 0; i < n; i++)
			{
				array[i] = 1;
			}
			foreach (Triangle triangle in mesh.triangles)
			{
				int id = triangle.id;
				int id2 = triangle.vertices[0].id;
				int id3 = triangle.vertices[1].id;
				int id4 = triangle.vertices[2].id;
				int id5 = triangle.neighbors[2].tri.id;
				if (id5 < 0 || id < id5)
				{
					array[id2]++;
					array[id3]++;
				}
				id5 = triangle.neighbors[0].tri.id;
				if (id5 < 0 || id < id5)
				{
					array[id3]++;
					array[id4]++;
				}
				id5 = triangle.neighbors[1].tri.id;
				if (id5 < 0 || id < id5)
				{
					array[id4]++;
					array[id2]++;
				}
			}
			for (int num = n; num > 0; num--)
			{
				array[num] = array[num - 1];
			}
			array[0] = 0;
			for (int j = 1; j <= n; j++)
			{
				array[j] = array[j - 1] + array[j];
			}
			return array;
		}

		private int[] AdjacencySet(Mesh mesh, int[] pcol)
		{
			int n = N;
			int[] array = new int[n];
			Array.Copy(pcol, array, n);
			int[] array2 = new int[pcol[n]];
			for (int i = 0; i < n; i++)
			{
				array2[array[i]] = i;
				array[i]++;
			}
			foreach (Triangle triangle in mesh.triangles)
			{
				int id = triangle.id;
				int id2 = triangle.vertices[0].id;
				int id3 = triangle.vertices[1].id;
				int id4 = triangle.vertices[2].id;
				int id5 = triangle.neighbors[2].tri.id;
				if (id5 < 0 || id < id5)
				{
					array2[array[id2]++] = id3;
					array2[array[id3]++] = id2;
				}
				id5 = triangle.neighbors[0].tri.id;
				if (id5 < 0 || id < id5)
				{
					array2[array[id3]++] = id4;
					array2[array[id4]++] = id3;
				}
				id5 = triangle.neighbors[1].tri.id;
				if (id5 < 0 || id < id5)
				{
					array2[array[id2]++] = id4;
					array2[array[id4]++] = id2;
				}
			}
			return array2;
		}

		public void SortIndices()
		{
			int n = N;
			int[] array = irow;
			for (int i = 0; i < n; i++)
			{
				int num = pcol[i];
				int num2 = pcol[i + 1];
				Array.Sort(array, num, num2 - num);
			}
		}
	}
}