/*
 * [The "BSD license"]
 *  Copyright (c) 2013 Terence Parr
 *  Copyright (c) 2013 Sam Harwell
 *  All rights reserved.
 *
 *  Redistribution and use in source and binary forms, with or without
 *  modification, are permitted provided that the following conditions
 *  are met:
 *
 *  1. Redistributions of source code must retain the above copyright
 *     notice, this list of conditions and the following disclaimer.
 *  2. Redistributions in binary form must reproduce the above copyright
 *     notice, this list of conditions and the following disclaimer in the
 *     documentation and/or other materials provided with the distribution.
 *  3. The name of the author may not be used to endorse or promote products
 *     derived from this software without specific prior written permission.
 *
 *  THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 *  IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 *  OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 *  IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 *  INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 *  NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 *  DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 *  THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 *  (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 *  THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */
using System;
using System.IO;
using Antlr4.Runtime;
using Antlr4.Runtime.Misc;
using Sharpen;

namespace Antlr4.Runtime
{
    /// <summary>Do not buffer up the entire char stream.</summary>
    /// <remarks>
    /// Do not buffer up the entire char stream. It does keep a small buffer
    /// for efficiency and also buffers while a mark exists (set by the
    /// lookahead prediction in parser). "Unbuffered" here refers to fact
    /// that it doesn't buffer all data, not that's it's on demand loading of char.
    /// </remarks>
    public class UnbufferedCharStream : ICharStream
    {
        /// <summary>A moving window buffer of the data being scanned.</summary>
        /// <remarks>
        /// A moving window buffer of the data being scanned. While there's a marker,
        /// we keep adding to buffer. Otherwise,
        /// <see cref="Consume()">consume()</see>
        /// resets so
        /// we start filling at index 0 again.
        /// </remarks>
        protected internal char[] data;

        /// <summary>
        /// The number of characters currently in
        /// <see cref="data">data</see>
        /// .
        /// <p/>
        /// This is not the buffer capacity, that's
        /// <code>data.length</code>
        /// .
        /// </summary>
        protected internal int n;

        /// <summary>
        /// 0..n-1 index into
        /// <see cref="data">data</see>
        /// of next character.
        /// <p/>
        /// The
        /// <code>LA(1)</code>
        /// character is
        /// <code>data[p]</code>
        /// . If
        /// <code>p == n</code>
        /// , we are
        /// out of buffered characters.
        /// </summary>
        protected internal int p = 0;

        /// <summary>
        /// Count up with
        /// <see cref="Mark()">mark()</see>
        /// and down with
        /// <see cref="Release(int)">release()</see>
        /// . When we
        /// <code>release()</code>
        /// the last mark,
        /// <code>numMarkers</code>
        /// reaches 0 and we reset the buffer. Copy
        /// <code>data[p]..data[n-1]</code>
        /// to
        /// <code>data[0]..data[(n-1)-p]</code>
        /// .
        /// </summary>
        protected internal int numMarkers = 0;

        /// <summary>
        /// This is the
        /// <code>LA(-1)</code>
        /// character for the current position.
        /// </summary>
        protected internal int lastChar = -1;

        /// <summary>
        /// When
        /// <code>numMarkers &gt; 0</code>
        /// , this is the
        /// <code>LA(-1)</code>
        /// character for the
        /// first character in
        /// <see cref="data">data</see>
        /// . Otherwise, this is unspecified.
        /// </summary>
        protected internal int lastCharBufferStart;

        /// <summary>Absolute character index.</summary>
        /// <remarks>
        /// Absolute character index. It's the index of the character about to be
        /// read via
        /// <code>LA(1)</code>
        /// . Goes from 0 to the number of characters in the
        /// entire stream, although the stream size is unknown before the end is
        /// reached.
        /// </remarks>
        protected internal int currentCharIndex = 0;

        protected internal StreamReader input;

        /// <summary>The name or source of this char stream.</summary>
        /// <remarks>The name or source of this char stream.</remarks>
        public string name;

        /// <summary>Useful for subclasses that pull char from other than this.input.</summary>
        /// <remarks>Useful for subclasses that pull char from other than this.input.</remarks>
        public UnbufferedCharStream()
            : this(256)
        {
        }

        /// <summary>Useful for subclasses that pull char from other than this.input.</summary>
        /// <remarks>Useful for subclasses that pull char from other than this.input.</remarks>
        public UnbufferedCharStream(int bufferSize)
        {
            n = 0;
            data = new char[bufferSize];
        }

        public UnbufferedCharStream(Stream input)
            : this(input, 256)
        {
        }

        public UnbufferedCharStream(StreamReader input)
            : this(input, 256)
        {
        }

        public UnbufferedCharStream(Stream input, int bufferSize)
            : this(bufferSize)
        {
            this.input = new StreamReader(input);
            Fill(1);
        }

        public UnbufferedCharStream(StreamReader input, int bufferSize)
            : this(bufferSize)
        {
            // prime
            this.input = input;
            Fill(1);
        }

        // prime
        public virtual void Consume()
        {
            if (La(1) == IntStreamConstants.Eof)
            {
                throw new InvalidOperationException("cannot consume EOF");
            }
            // buf always has at least data[p==0] in this method due to ctor
            lastChar = data[p];
            // track last char for LA(-1)
            if (p == n - 1 && numMarkers == 0)
            {
                n = 0;
                p = -1;
                // p++ will leave this at 0
                lastCharBufferStart = lastChar;
            }
            p++;
            currentCharIndex++;
            Sync(1);
        }

        /// <summary>
        /// Make sure we have 'need' elements from current position
        /// <see cref="p">p</see>
        /// .
        /// Last valid
        /// <code>p</code>
        /// index is
        /// <code>data.length-1</code>
        /// .
        /// <code>p+need-1</code>
        /// is
        /// the char index 'need' elements ahead. If we need 1 element,
        /// <code>(p+1-1)==p</code>
        /// must be less than
        /// <code>data.length</code>
        /// .
        /// </summary>
        protected internal virtual void Sync(int want)
        {
            int need = (p + want - 1) - n + 1;
            // how many more elements we need?
            if (need > 0)
            {
                Fill(need);
            }
        }

        /// <summary>
        /// Add
        /// <code>n</code>
        /// characters to the buffer. Returns the number of characters
        /// actually added to the buffer. If the return value is less than
        /// <code>n</code>
        /// ,
        /// then EOF was reached before
        /// <code>n</code>
        /// characters could be added.
        /// </summary>
        protected internal virtual int Fill(int n)
        {
            for (int i = 0; i < n; i++)
            {
                if (this.n > 0 && data[this.n - 1] == (char)IntStreamConstants.Eof)
                {
                    return i;
                }
                try
                {
                    int c = NextChar();
                    Add(c);
                }
                catch (IOException ioe)
                {
                    throw new RuntimeException(ioe);
                }
            }
            return n;
        }

        /// <summary>
        /// Override to provide different source of characters than
        /// <see cref="input">input</see>
        /// .
        /// </summary>
        /// <exception cref="System.IO.IOException"></exception>
        protected internal virtual int NextChar()
        {
            return input.Read();
        }

        protected internal virtual void Add(int c)
        {
            if (n >= data.Length)
            {
                data = Arrays.CopyOf(data, data.Length * 2);
            }
            data[n++] = (char)c;
        }

        public virtual int La(int i)
        {
            if (i == -1)
            {
                return lastChar;
            }
            // special case
            Sync(i);
            int index = p + i - 1;
            if (index < 0)
            {
                throw new ArgumentOutOfRangeException();
            }
            if (index >= n)
            {
                return IntStreamConstants.Eof;
            }
            char c = data[index];
            if (c == (char)IntStreamConstants.Eof)
            {
                return IntStreamConstants.Eof;
            }
            return c;
        }

        /// <summary>Return a marker that we can release later.</summary>
        /// <remarks>
        /// Return a marker that we can release later.
        /// <p/>
        /// The specific marker value used for this class allows for some level of
        /// protection against misuse where
        /// <code>seek()</code>
        /// is called on a mark or
        /// <code>release()</code>
        /// is called in the wrong order.
        /// </remarks>
        public virtual int Mark()
        {
            if (numMarkers == 0)
            {
                lastCharBufferStart = lastChar;
            }
            int mark = -numMarkers - 1;
            numMarkers++;
            return mark;
        }

        /// <summary>Decrement number of markers, resetting buffer if we hit 0.</summary>
        /// <remarks>Decrement number of markers, resetting buffer if we hit 0.</remarks>
        /// <param name="marker"></param>
        public virtual void Release(int marker)
        {
            int expectedMark = -numMarkers;
            if (marker != expectedMark)
            {
                throw new InvalidOperationException("release() called with an invalid marker.");
            }
            numMarkers--;
            if (numMarkers == 0 && p > 0)
            {
                // release buffer when we can, but don't do unnecessary work
                // Copy data[p]..data[n-1] to data[0]..data[(n-1)-p], reset ptrs
                // p is last valid char; move nothing if p==n as we have no valid char
                System.Array.Copy(data, p, data, 0, n - p);
                // shift n-p char from p to 0
                n = n - p;
                p = 0;
                lastCharBufferStart = lastChar;
            }
        }

        public virtual int Index
        {
            get
            {
                return currentCharIndex;
            }
        }

        /// <summary>
        /// Seek to absolute character index, which might not be in the current
        /// sliding window.
        /// </summary>
        /// <remarks>
        /// Seek to absolute character index, which might not be in the current
        /// sliding window.  Move
        /// <code>p</code>
        /// to
        /// <code>index-bufferStartIndex</code>
        /// .
        /// </remarks>
        public virtual void Seek(int index)
        {
            if (index == currentCharIndex)
            {
                return;
            }
            if (index > currentCharIndex)
            {
                Sync(index - currentCharIndex);
                index = Math.Min(index, GetBufferStartIndex() + n - 1);
            }
            // index == to bufferStartIndex should set p to 0
            int i = index - GetBufferStartIndex();
            if (i < 0)
            {
                throw new ArgumentException("cannot seek to negative index " + index);
            }
            else
            {
                if (i >= n)
                {
                    throw new NotSupportedException("seek to index outside buffer: " + index + " not in "
                         + GetBufferStartIndex() + ".." + (GetBufferStartIndex() + n));
                }
            }
            p = i;
            currentCharIndex = index;
            if (p == 0)
            {
                lastChar = lastCharBufferStart;
            }
            else
            {
                lastChar = data[p - 1];
            }
        }

        public virtual int Size
        {
            get
            {
                throw new NotSupportedException("Unbuffered stream cannot know its size");
            }
        }

        public virtual string SourceName
        {
            get
            {
                return name;
            }
        }

        public virtual string GetText(Interval interval)
        {
            if (interval.a < 0 || interval.b < interval.a - 1)
            {
                throw new ArgumentException("invalid interval");
            }
            int bufferStartIndex = GetBufferStartIndex();
            if (n > 0 && data[n - 1] == char.MaxValue)
            {
                if (interval.a + interval.Length > bufferStartIndex + n)
                {
                    throw new ArgumentException("the interval extends past the end of the stream");
                }
            }
            if (interval.a < bufferStartIndex || interval.b >= bufferStartIndex + n)
            {
                throw new NotSupportedException("interval " + interval + " outside buffer: " + bufferStartIndex
                     + ".." + (bufferStartIndex + n - 1));
            }
            // convert from absolute to local index
            int i = interval.a - bufferStartIndex;
            return new string(data, i, interval.Length);
        }

        protected internal int GetBufferStartIndex()
        {
            return currentCharIndex - p;
        }
    }
}