using System;
using System.Text.RegularExpressions;

namespace NaGet.Packages
{
	// TODO Debian-aptのコードを利用しているのでGPLになるのに注意
	
	
	public class VersionComparetor : System.Collections.Generic.IComparer<string>
	{
		public VersionComparetor()
		{
		}
		
		private static int order(char x)
		{
			return (char.IsDigit(x) ? 0
				: (x==0) ? 0
				: char.IsLetter(x) ? (x)
				: (x) + 256);
		}
		
		public int Compare(string a, string b)
		{
			// 前処理
			a = a.ToLower();
			b = b.ToLower();
			if (Regex.IsMatch(a, @"\.0*$")) 
				Regex.Replace(a, @"\.0*$", string.Empty);
			if (Regex.IsMatch(b, @"\.0*$")) 
				Regex.Replace(b, @"\.0*$", string.Empty);
			
			if (a == b) {
				return 0;
			}
			
			
			int apos = 0, bpos = 0;
			int alen = a.Length, blen = b.Length;
			
			while ((apos < alen) && (bpos < blen)) {
				int first_diff = 0;
				
				while ((apos < alen) && (bpos < blen) &&
				       (!char.IsDigit(a[apos]) || !char.IsDigit(b[bpos])) ) {
					int vc = order(a[apos]);
					int rc = order(b[bpos]);
					if (vc != rc)
						return vc - rc;
					apos ++; bpos ++;
				}
				
				if (a[apos] == '0') apos ++;
				if (b[bpos] == '0') bpos ++;
				
				while ((apos < alen) && (bpos < blen) &&
				       char.IsDigit(a[apos]) && char.IsDigit(b[bpos])) {
					if (first_diff == 0)
						first_diff = a[apos] - b[bpos];
					apos ++; bpos ++;
				}
				
				if (apos < alen && char.IsDigit(a[apos])) {
					return 1;
				} else if (bpos < blen && char.IsDigit(b[bpos])) {
					return -1;
				} else if (first_diff != 0) {
					return first_diff;
				}
			}
			
			if (apos == alen && bpos == blen) {
				return 0;
			} else if (apos == alen) {
				return -1;
			} else if (bpos == blen) {
				return 1;
			} else {
				return 1; // Shouldnt happen
			}
		}
		
		
	}
}