package java.lang;

import java.util.Arrays;

abstract class AbstractStringBuilder implements Appendable, CharSequence {

    char[] value;
    int count;

    AbstractStringBuilder(int capacity) {
        value = new char[capacity];
    }

    public void setLength(int newLength) {
        if (newLength < 0) {
            throw new StringIndexOutOfBoundsException(newLength);
        }
        ensureCapacityInternal(newLength);

        if (count < newLength) {
            for (; count < newLength; count++) {
                value[count] = '\0';
            }
        } else {
            count = newLength;
        }
    }

    public AbstractStringBuilder append(String str) {
        if (str == null) {
            str = "null";
        }
        int len = str.length();
        ensureCapacityInternal(count + len);
        str.getChars(0, len, value, count);
        count += len;
        return this;
    }

    void expandCapacity(int minimumCapacity) {
        int newCapacity = value.length * 2 + 2;
        if (newCapacity - minimumCapacity < 0) {
            newCapacity = minimumCapacity;
        }
        if (newCapacity < 0) {
            if (minimumCapacity < 0) // overflow
            {
                throw new OutOfMemoryError();
            }
            newCapacity = Integer.MAX_VALUE;
        }
        value = Arrays.copyOf(value, newCapacity);
    }

    private void ensureCapacityInternal(int minimumCapacity) {
        if (minimumCapacity - value.length > 0) {
            expandCapacity(minimumCapacity);
        }
    }
}