app/src/syncbase/java/io/v/todos/persistence/syncbase/DigitRangeMapping.java

// Copyright 2015 The Vanadium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package io.v.todos.persistence.syncbase;

import com.google.common.collect.ContiguousSet;
import com.google.common.collect.ImmutableList;

/**
 * A {@link DigitMapping} optimized for mappings where ranges of consecutive characters map to
 * consecutive values. The overall mapping need not be monotonic to take advantage of this
 * optimization.
 */
public class DigitRangeMapping implements DigitMapping {
    private final ImmutableList<ContiguousSet<Character>> mRanges;
    private final int mRadix;

    public DigitRangeMapping(Iterable<ContiguousSet<Character>> ranges) {
        mRanges = ImmutableList.copyOf(ranges);
        int size = 0;
        for (ContiguousSet<Character> range : mRanges) {
            size += range.size();
        }
        mRadix = size;
    }

    @Override
    public char encode(int digit) {
        for (ContiguousSet<Character> range : mRanges) {
            if (digit < range.size()) {
                return range.asList().get(digit);
            } else {
                digit -= range.size();
            }
        }
        throw new IllegalArgumentException("No encoding for digit " + digit + " (radix " + radix() +
                ")");
    }

    @Override
    public int decode(char encoded) {
        int digit = 0;
        for (ContiguousSet<Character> range : mRanges) {
            if (range.contains(encoded)) {
                return digit + encoded - range.first();
            }
            digit += range.size();
        }
        throw new IllegalArgumentException();
    }

    @Override
    public int radix() {
        return mRadix;
    }
}