// © 2017 and later: Unicode, Inc. and others.
// License & terms of use: http://www.unicode.org/copyright.html#License
package com.ibm.icu.impl.number;

public class Padder {
    public static final String FALLBACK_PADDING_STRING = "\u0020"; // i.e. a space

    public enum PadPosition {
        BEFORE_PREFIX, AFTER_PREFIX, BEFORE_SUFFIX, AFTER_SUFFIX;

        public static PadPosition fromOld(int old) {
            switch (old) {
            case com.ibm.icu.text.DecimalFormat.PAD_BEFORE_PREFIX:
                return PadPosition.BEFORE_PREFIX;
            case com.ibm.icu.text.DecimalFormat.PAD_AFTER_PREFIX:
                return PadPosition.AFTER_PREFIX;
            case com.ibm.icu.text.DecimalFormat.PAD_BEFORE_SUFFIX:
                return PadPosition.BEFORE_SUFFIX;
            case com.ibm.icu.text.DecimalFormat.PAD_AFTER_SUFFIX:
                return PadPosition.AFTER_SUFFIX;
            default:
                throw new IllegalArgumentException("Don't know how to map " + old);
            }
        }

        public int toOld() {
            switch (this) {
            case BEFORE_PREFIX:
                return com.ibm.icu.text.DecimalFormat.PAD_BEFORE_PREFIX;
            case AFTER_PREFIX:
                return com.ibm.icu.text.DecimalFormat.PAD_AFTER_PREFIX;
            case BEFORE_SUFFIX:
                return com.ibm.icu.text.DecimalFormat.PAD_BEFORE_SUFFIX;
            case AFTER_SUFFIX:
                return com.ibm.icu.text.DecimalFormat.PAD_AFTER_SUFFIX;
            default:
                return -1; // silence compiler errors
            }
        }
    }

    /* like package-private */ public static final Padder NONE = new Padder(null, -1, null);

    String paddingString;
    int targetWidth;
    PadPosition position;

    public Padder(String paddingString, int targetWidth, PadPosition position) {
        // TODO: Add a few default instances
        this.paddingString = (paddingString == null) ? FALLBACK_PADDING_STRING : paddingString;
        this.targetWidth = targetWidth;
        this.position = (position == null) ? PadPosition.BEFORE_PREFIX : position;
    }

    public static Padder none() {
        return NONE;
    }

    public static Padder codePoints(int cp, int targetWidth, PadPosition position) {
        // TODO: Validate the code point
        if (targetWidth >= 0) {
            String paddingString = String.valueOf(Character.toChars(cp));
            return new Padder(paddingString, targetWidth, position);
        } else {
            throw new IllegalArgumentException("Padding width must not be negative");
        }
    }

    public static Padder forProperties(DecimalFormatProperties properties) {
        return new Padder(properties.getPadString(),
                properties.getFormatWidth(),
                properties.getPadPosition());
    }

    public boolean isValid() {
        return targetWidth > 0;
    }

    public int padAndApply(
            Modifier mod1,
            Modifier mod2,
            NumberStringBuilder string,
            int leftIndex,
            int rightIndex) {
        int modLength = mod1.getCodePointCount() + mod2.getCodePointCount();
        int requiredPadding = targetWidth - modLength - string.codePointCount();
        assert leftIndex == 0 && rightIndex == string.length(); // fix the previous line to remove this
                                                                // assertion

        int length = 0;
        if (requiredPadding <= 0) {
            // Padding is not required.
            length += mod1.apply(string, leftIndex, rightIndex);
            length += mod2.apply(string, leftIndex, rightIndex + length);
            return length;
        }

        if (position == PadPosition.AFTER_PREFIX) {
            length += addPaddingHelper(paddingString, requiredPadding, string, leftIndex);
        } else if (position == PadPosition.BEFORE_SUFFIX) {
            length += addPaddingHelper(paddingString, requiredPadding, string, rightIndex + length);
        }
        length += mod1.apply(string, leftIndex, rightIndex + length);
        length += mod2.apply(string, leftIndex, rightIndex + length);
        if (position == PadPosition.BEFORE_PREFIX) {
            length += addPaddingHelper(paddingString, requiredPadding, string, leftIndex);
        } else if (position == PadPosition.AFTER_SUFFIX) {
            length += addPaddingHelper(paddingString, requiredPadding, string, rightIndex + length);
        }

        return length;
    }

    private static int addPaddingHelper(
            String paddingString,
            int requiredPadding,
            NumberStringBuilder string,
            int index) {
        for (int i = 0; i < requiredPadding; i++) {
            // TODO: If appending to the end, this will cause actual insertion operations. Improve.
            string.insert(index, paddingString, null);
        }
        return paddingString.length() * requiredPadding;
    }
}