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// This file is available under and governed by the GNU General Public
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// file:
//
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// modification, are permitted provided that the following conditions are
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package jdk.nashorn.internal.runtime.doubleconv;

/**
 * A buffer for generating string representations of doubles.
 */
public class DtoaBuffer {

    // The character buffer
    final char[] chars;

    // The number of characters in the buffer
    int length = 0;

    // The position of the decimal point
    int decimalPoint = 0;

    // Is this a negative number?
    boolean isNegative = false;

    /**
     * Maximal length of numbers converted by FastDtoa
     */
    public static final int kFastDtoaMaximalLength = FastDtoa.kFastDtoaMaximalLength;

    /**
     * Create a buffer with the given capacity.
     * @param capacity the capacity of the buffer.
     */
    public DtoaBuffer(final int capacity) {
        chars = new char[capacity];
    }

    /**
     * Append a character to the buffer, increasing its length.
     * @param c character
     */
    void append(final char c) {
        chars[length++] = c;
    }

    /**
     * Clear the buffer contents and set its length to {@code 0}.
     */
    public void reset() {
        length = 0;
        decimalPoint = 0;
    }

    /**
     * Get the raw digits of this buffer as string.
     * @return the raw buffer contents
     */
    public String getRawDigits() {
        return new String(chars, 0, length);
    }

    /**
     * Get the position of the decimal point.
     * @return the decimal point position
     */
    public int getDecimalPoint() {
        return decimalPoint;
    }

    /**
     * Returns the number of characters in the buffer.
     * @return buffer length
     */
    public int getLength() {
        return length;
    }

    /**
     * Returns the formatted buffer content as string, using the specified conversion mode
     * and padding.
     *
     * @param mode conversion mode
     * @param digitsAfterPoint number of digits after point
     * @return formatted string
     */
    public String format(final DtoaMode mode, final int digitsAfterPoint) {
        final StringBuilder buffer = new StringBuilder();
        if (isNegative) {
            buffer.append('-');
        }

        // check for minus sign
        switch (mode) {
            case SHORTEST:
                if (decimalPoint < -5 || decimalPoint > 21) {
                    toExponentialFormat(buffer);
                } else {
                    toFixedFormat(buffer, digitsAfterPoint);
                }
                break;
            case FIXED:
                toFixedFormat(buffer, digitsAfterPoint);
                break;
            case PRECISION:
                if (decimalPoint < -5 || decimalPoint > length) {
                    toExponentialFormat(buffer);
                } else {
                    toFixedFormat(buffer, digitsAfterPoint);
                }
                break;
        }

        return buffer.toString();
    }

    private void toFixedFormat(final StringBuilder buffer, final int digitsAfterPoint) {
        if (decimalPoint <= 0) {
            // < 1,
            buffer.append('0');
            if (length > 0) {
                buffer.append('.');
                final int padding = -decimalPoint;
                for (int i = 0; i < padding; i++) {
                    buffer.append('0');
                }
                buffer.append(chars, 0, length);
            }
        } else if (decimalPoint >= length) {
            // large integer, add trailing zeroes
            buffer.append(chars, 0, length);
            for (int i = length; i < decimalPoint; i++) {
                buffer.append('0');
            }
        } else if (decimalPoint < length) {
            // >= 1, split decimals and insert decimalPoint
            buffer.append(chars, 0, decimalPoint);
            buffer.append('.');
            buffer.append(chars, decimalPoint, length - decimalPoint);
        }

        // Create trailing zeros if requested
        if (digitsAfterPoint > 0) {
            if (decimalPoint >= length) {
                buffer.append('.');
            }
            for (int i = Math.max(0, length - decimalPoint); i < digitsAfterPoint; i++) {
                buffer.append('0');
            }
        }
    }

    private void toExponentialFormat(final StringBuilder buffer) {
        buffer.append(chars[0]);
        if (length > 1) {
            // insert decimal decimalPoint if more than one digit was produced
            buffer.append('.');
            buffer.append(chars, 1, length - 1);
        }
        buffer.append('e');
        final int exponent = decimalPoint - 1;
        if (exponent > 0) {
            buffer.append('+');
        }
        buffer.append(exponent);
    }

    @Override
    public String toString() {
        return "[chars:" + new String(chars, 0, length) + ", decimalPoint:" + decimalPoint + "]";
    }
}