﻿/* Copyright (c) 2012-2017 The ANTLR Project. All rights reserved.
 * Use of this file is governed by the BSD 3-clause license that
 * can be found in the LICENSE.txt file in the project root.
 */

#pragma once

#include "antlr4-common.h"

namespace antlr4 {

  /// <summary>
  /// A simple stream of symbols whose values are represented as integers. This
  /// interface provides <em>marked ranges</em> with support for a minimum level
  /// of buffering necessary to implement arbitrary lookahead during prediction.
  /// For more information on marked ranges, see <seealso cref="#mark"/>.
  /// <p/>
  /// <strong>Initializing Methods:</strong> Some methods in this interface have
  /// unspecified behavior if no call to an initializing method has occurred after
  /// the stream was constructed. The following is a list of initializing methods:
  ///
  /// <ul>
  ///   <li><seealso cref="#LA"/></li>
  ///   <li><seealso cref="#consume"/></li>
  ///   <li><seealso cref="#size"/></li>
  /// </ul>
  /// </summary>
  class ANTLR4CPP_PUBLIC IntStream {
  public:
#if __cplusplus >= 201703L
    static constexpr size_t EOF = std::numeric_limits<size_t>::max();
#else
    enum : size_t {
      EOF = static_cast<size_t>(-1), // std::numeric_limits<size_t>::max(); doesn't work in VS 2013
    };
#endif

    /// The value returned by <seealso cref="#LA LA()"/> when the end of the stream is
    /// reached.
    /// No explicit EOF definition. We got EOF on all platforms.
    //static const size_t _EOF = std::ios::eofbit;

    /// <summary>
    /// The value returned by <seealso cref="#getSourceName"/> when the actual name of the
    /// underlying source is not known.
    /// </summary>
    static const std::string UNKNOWN_SOURCE_NAME;

    virtual ~IntStream();

    /// <summary>
    /// Consumes the current symbol in the stream. This method has the following
    /// effects:
    ///
    /// <ul>
    ///   <li><strong>Forward movement:</strong> The value of <seealso cref="#index index()"/>
    ///		before calling this method is less than the value of {@code index()}
    ///		after calling this method.</li>
    ///   <li><strong>Ordered lookahead:</strong> The value of {@code LA(1)} before
    ///		calling this method becomes the value of {@code LA(-1)} after calling
    ///		this method.</li>
    /// </ul>
    ///
    /// Note that calling this method does not guarantee that {@code index()} is
    /// incremented by exactly 1, as that would preclude the ability to implement
    /// filtering streams (e.g. <seealso cref="CommonTokenStream"/> which distinguishes
    /// between "on-channel" and "off-channel" tokens).
    /// </summary>
    /// <exception cref="IllegalStateException"> if an attempt is made to consume the the
    /// end of the stream (i.e. if {@code LA(1)==}<seealso cref="#EOF EOF"/> before calling
    /// {@code consume}). </exception>
    virtual void consume() = 0;

    /// <summary>
    /// Gets the value of the symbol at offset {@code i} from the current
    /// position. When {@code i==1}, this method returns the value of the current
    /// symbol in the stream (which is the next symbol to be consumed). When
    /// {@code i==-1}, this method returns the value of the previously read
    /// symbol in the stream. It is not valid to call this method with
    /// {@code i==0}, but the specific behavior is unspecified because this
    /// method is frequently called from performance-critical code.
    /// <p/>
    /// This method is guaranteed to succeed if any of the following are true:
    ///
    /// <ul>
    ///   <li>{@code i>0}</li>
    ///   <li>{@code i==-1} and <seealso cref="#index index()"/> returns a value greater
    ///     than the value of {@code index()} after the stream was constructed
    ///     and {@code LA(1)} was called in that order. Specifying the current
    ///     {@code index()} relative to the index after the stream was created
    ///     allows for filtering implementations that do not return every symbol
    ///     from the underlying source. Specifying the call to {@code LA(1)}
    ///     allows for lazily initialized streams.</li>
    ///   <li>{@code LA(i)} refers to a symbol consumed within a marked region
    ///     that has not yet been released.</li>
    /// </ul>
    ///
    /// If {@code i} represents a position at or beyond the end of the stream,
    /// this method returns <seealso cref="#EOF"/>.
    /// <p/>
    /// The return value is unspecified if {@code i<0} and fewer than {@code -i}
    /// calls to <seealso cref="#consume consume()"/> have occurred from the beginning of
    /// the stream before calling this method.
    /// </summary>
    /// <exception cref="UnsupportedOperationException"> if the stream does not support
    /// retrieving the value of the specified symbol </exception>
    virtual size_t LA(ssize_t i) = 0;

    /// <summary>
    /// A mark provides a guarantee that <seealso cref="#seek seek()"/> operations will be
    /// valid over a "marked range" extending from the index where {@code mark()}
    /// was called to the current <seealso cref="#index index()"/>. This allows the use of
    /// streaming input sources by specifying the minimum buffering requirements
    /// to support arbitrary lookahead during prediction.
    /// <p/>
    /// The returned mark is an opaque handle (type {@code int}) which is passed
    /// to <seealso cref="#release release()"/> when the guarantees provided by the marked
    /// range are no longer necessary. When calls to
    /// {@code mark()}/{@code release()} are nested, the marks must be released
    /// in reverse order of which they were obtained. Since marked regions are
    /// used during performance-critical sections of prediction, the specific
    /// behavior of invalid usage is unspecified (i.e. a mark is not released, or
    /// a mark is released twice, or marks are not released in reverse order from
    /// which they were created).
    /// <p/>
    /// The behavior of this method is unspecified if no call to an
    /// <seealso cref="IntStream initializing method"/> has occurred after this stream was
    /// constructed.
    /// <p/>
    /// This method does not change the current position in the input stream.
    /// <p/>
    /// The following example shows the use of <seealso cref="#mark mark()"/>,
    /// <seealso cref="#release release(mark)"/>, <seealso cref="#index index()"/>, and
    /// <seealso cref="#seek seek(index)"/> as part of an operation to safely work within a
    /// marked region, then restore the stream position to its original value and
    /// release the mark.
    /// <pre>
    /// IntStream stream = ...;
    /// int index = -1;
    /// int mark = stream.mark();
    /// try {
    ///   index = stream.index();
    ///   // perform work here...
    /// } finally {
    ///   if (index != -1) {
    ///     stream.seek(index);
    ///   }
    ///   stream.release(mark);
    /// }
    /// </pre>
    /// </summary>
    /// <returns> An opaque marker which should be passed to
    /// <seealso cref="#release release()"/> when the marked range is no longer required. </returns>
    virtual ssize_t mark() = 0;

    /// <summary>
    /// This method releases a marked range created by a call to
    /// <seealso cref="#mark mark()"/>. Calls to {@code release()} must appear in the
    /// reverse order of the corresponding calls to {@code mark()}. If a mark is
    /// released twice, or if marks are not released in reverse order of the
    /// corresponding calls to {@code mark()}, the behavior is unspecified.
    /// <p/>
    /// For more information and an example, see <seealso cref="#mark"/>.
    /// </summary>
    /// <param name="marker"> A marker returned by a call to {@code mark()}. </param>
    /// <seealso cref= #mark </seealso>
    virtual void release(ssize_t marker) = 0;

    /// <summary>
    /// Return the index into the stream of the input symbol referred to by
    /// {@code LA(1)}.
    /// <p/>
    /// The behavior of this method is unspecified if no call to an
    /// <seealso cref="IntStream initializing method"/> has occurred after this stream was
    /// constructed.
    /// </summary>
    virtual size_t index() = 0;

    /// <summary>
    /// Set the input cursor to the position indicated by {@code index}. If the
    /// specified index lies past the end of the stream, the operation behaves as
    /// though {@code index} was the index of the EOF symbol. After this method
    /// returns without throwing an exception, the at least one of the following
    /// will be true.
    ///
    /// <ul>
    ///   <li><seealso cref="#index index()"/> will return the index of the first symbol
    ///     appearing at or after the specified {@code index}. Specifically,
    ///     implementations which filter their sources should automatically
    ///     adjust {@code index} forward the minimum amount required for the
    ///     operation to target a non-ignored symbol.</li>
    ///   <li>{@code LA(1)} returns <seealso cref="#EOF"/></li>
    /// </ul>
    ///
    /// This operation is guaranteed to not throw an exception if {@code index}
    /// lies within a marked region. For more information on marked regions, see
    /// <seealso cref="#mark"/>. The behavior of this method is unspecified if no call to
    /// an <seealso cref="IntStream initializing method"/> has occurred after this stream
    /// was constructed.
    /// </summary>
    /// <param name="index"> The absolute index to seek to.
    /// </param>
    /// <exception cref="IllegalArgumentException"> if {@code index} is less than 0 </exception>
    /// <exception cref="UnsupportedOperationException"> if the stream does not support
    /// seeking to the specified index </exception>
    virtual void seek(size_t index) = 0;

    /// <summary>
    /// Returns the total number of symbols in the stream, including a single EOF
    /// symbol.
    /// </summary>
    /// <exception cref="UnsupportedOperationException"> if the size of the stream is
    /// unknown. </exception>
    virtual size_t size() = 0;

    /// <summary>
    /// Gets the name of the underlying symbol source. This method returns a
    /// non-null, non-empty string. If such a name is not known, this method
    /// returns <seealso cref="#UNKNOWN_SOURCE_NAME"/>.
    /// </summary>
    virtual std::string getSourceName() const = 0;
  };

} // namespace antlr4