//------------------------------------------------------------------------------
// <copyright file="HWStack.cs" company="Microsoft">
//     Copyright (c) Microsoft Corporation.  All rights reserved.
// </copyright>
// <owner current="true" primary="true">[....]</owner>
//------------------------------------------------------------------------------

using System;


namespace System.Xml {

// This stack is designed to minimize object creation for the
// objects being stored in the stack by allowing them to be
// re-used over time.  It basically pushes the objects creating
// a high water mark then as Pop() is called they are not removed
// so that next time Push() is called it simply returns the last
// object that was already on the stack.

    internal class HWStack : ICloneable {
        internal HWStack(int GrowthRate) : this (GrowthRate, int.MaxValue) {}

        internal HWStack(int GrowthRate, int limit) {
            this.growthRate = GrowthRate;
            this.used = 0;
            this.stack = new Object[GrowthRate];
            this.size = GrowthRate;
            this.limit = limit;
        }

        internal Object Push() {
            if (this.used == this.size) {
                if (this.limit <= this.used) {
                    throw new XmlException(Res.Xml_StackOverflow, string.Empty);
                }
                Object[] newstack = new Object[this.size + this.growthRate];
                if (this.used > 0) {
                    System.Array.Copy(this.stack, 0, newstack, 0, this.used);
                }
                this.stack = newstack;
                this.size += this.growthRate;
            }
            return this.stack[this.used++];
        }

        internal Object Pop() {
            if (0 < this.used) {
                this.used--;
                Object result = this.stack[this.used];
                return result;
            }
            return null;
        }

        [System.Runtime.TargetedPatchingOptOutAttribute("Performance critical to inline across NGen image boundaries")]
        internal object Peek() {
            return this.used > 0 ? this.stack[this.used - 1] : null;
        }

        [System.Runtime.TargetedPatchingOptOutAttribute("Performance critical to inline across NGen image boundaries")]
        internal void AddToTop(object o) {
            if (this.used > 0) {
                this.stack[this.used - 1] = o;
            }
        }

        internal Object this[int index] {
            get {
                if (index >= 0 && index < this.used) {
                    Object result = this.stack[index];
                    return result;
                }
                else {
					throw new IndexOutOfRangeException();
				}
            }
            set {
                if (index >= 0 && index < this.used) {
					this.stack[index] = value;
				}
                else {
					throw new IndexOutOfRangeException();
				}
            }
        }

        internal int Length {
            get { return this.used;}
        }

        //
        // ICloneable
        //

        private HWStack(object[] stack, int growthRate, int used, int size) {
            this.stack      = stack;
            this.growthRate = growthRate;
            this.used       = used;
            this.size       = size;
        }

        public object Clone() {
            return new HWStack((object[]) this.stack.Clone(), this.growthRate, this.used, this.size);
        }

        private Object[] stack;
        private int growthRate;
        private int used;
        private int size;
        private int limit;
    };

}
