// ----------------------------------------------------------------------------
//
//  Copyright (c) Microsoft Corporation.  All rights reserved.
//
// ----------------------------------------------------------------------------

namespace Microsoft.Singularity.Security.AccessControl
{
    using System;

	internal class StringReader : DataReader
	{
        private String s;
        private int pos;
        private int length;
    
        public StringReader(String s) 
        {
            if (s == null) {
                throw new ArgumentNullException("s");
            }

            this.s = s;
            this.length = s == null? 0: s.Length;
        }
    
        protected override void Dispose(bool disposing) 
        {
            base.Dispose(disposing);
            
            s = null;
            pos = 0;
            length = 0;
        }

        // Returns the next available character without actually reading it from
        // the underlying string. The current position of the StringReader is not
        // changed by this operation. The returned value is -1 if no further
        // characters are available.
        public override int Peek() 
        {
            if (s == null) {
                throw new Exception("Reader closed");
            }
            if (pos == length) return -1;
            return s[pos];
        }
    
        // Reads the next character from the underlying string. The returned value
        // is -1 if no further characters are available.
        public override int Read() 
        {
            if (s == null) {
                throw new Exception("Reader closed");
            }
            if (pos == length) return -1;
            return s[pos++];
        }
    
        // Reads a block of characters. This method will read up to count
        // characters from this StringReader into the buffer character
        // array starting at position index. Returns the actual number of
        // characters read, or zero if the end of the string is reached.
        public override int Read(char[] buffer, int index, int count) 
        {
            if (buffer == null)
                throw new ArgumentNullException("Argument null buffer");
            if (index < 0)
                throw new ArgumentOutOfRangeException("Argument out of range");
            if (count < 0)
                throw new ArgumentOutOfRangeException("Argument out of range");
            if (buffer.Length - index < count)
                throw new ArgumentException("Invalid offset");
            if (s == null)
                throw new Exception("Reader closed");

            int n = length - pos;
            if (n > 0) {
                if (n > count) n = count;
                s.CopyTo(pos, buffer, index, n);
                pos += n;
            }
            return n;
        }
    
        //| <include file='doc\StringReader.uex' path='docs/doc[@for="StringReader.ReadToEnd"]/*' />
        public String ReadToEnd()
        {
            if (s == null) {
                throw new Exception("Reader closed");
            }
            String result;
            if (pos == 0)
                result = s;
            else
                result = s.Substring(pos, length - pos);
            pos = length;
            return result;
        }

        // Reads a line. A line is defined as a sequence of characters followed by
        // a carriage return ('\r'), a line feed ('\n'), or a carriage return
        // immediately followed by a line feed. The resulting string does not
        // contain the terminating carriage return and/or line feed. The returned
        // value is null if the end of the underlying string has been reached.
        //
        public String ReadLine() 
        {
            if (s == null) {
                throw new Exception("Reader closed");
            }
            int i = pos;
            while (i < length) {
                char ch = s[i];
                if (ch == '\r' || ch == '\n') {
                    String result = s.Substring(pos, i - pos);
                    pos = i + 1;
                    if (ch == '\r' && pos < length && s[pos] == '\n') pos++;
                    return result;
                }
                i++;
            }
            if (i > pos) {
                String result = s.Substring(pos, i - pos);
                pos = i;
                return result;
            }
            return null;
        }
    }
}