Simple and fast, single-file template system, designed for: create once, render often/concurrently

Template.java

/*
 * Copyright (C) 2015 René Jeschke <rene_jeschke@yahoo.de>
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package rjeschke.toolbox;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.HashMap;
import java.util.Map;
import java.util.Map.Entry;

/**
 * <p>
 * Placeholders: <code>${key[:default value]}</code>
 * </p>
 * <ul>
 * <li><code>key</code> is case sensitive and gets surrounding whitespace
 * removed.</li>
 * <li><code>default value</code> can be anything, does not get changed except
 * for delimiter escape sequences (see below).</li>
 * </ul>
 * <p>
 * Delimiter escape sequences:
 * </p>
 * <ul>
 * <li><code>$\{</code> gets replaced by <code>${</code> outside of placeholders
 * and inside default values.</li>
 * <li><code>\}</code> only gets replaced by <code>}</code> inside default
 * values.</li>
 * </ul>
 *
 * @author René Jeschke &lt;rene_jeschke@yahoo.de&gt;
 */
public class Template
{
    private final String[]                 parts;
    private final String[]                 defaults;
    private final int[]                    keyIndices;
    private final HashMap<String, Integer> keyMap;
    private final int                      length;

    private Template(final String[] parts,
            final String[] defaults,
            final int[] keyIndices,
            final HashMap<String, Integer> keyMap)
    {
        this.parts = parts;
        this.defaults = defaults;
        this.keyIndices = keyIndices;
        this.keyMap = keyMap;

        int len = 0;
        for (int i = 0; i < parts.length; i++)
        {
            len += parts[i].length();
        }
        this.length = len;
    }

    public Filler filler()
    {
        return new Filler(this);
    }

    public static class Filler
    {
        private final Template       template;
        private final CharSequence[] values;

        private Filler(final Template template)
        {
            this.template = template;
            this.values = new CharSequence[template.keyMap.size()];
            this.reset();
        }

        public Filler reset()
        {
            System.arraycopy(this.template.defaults, 0, this.values, 0, this.values.length);
            return this;
        }

        public Filler set(final String key, final CharSequence value)
        {
            final Integer idx = this.template.keyMap.get(key);
            if (idx != null)
            {
                this.values[idx.intValue()] = value;
            }
            return this;
        }

        public Filler set(final Map<String, ? extends CharSequence> map)
        {
            for (final Entry<String, ? extends CharSequence> e : map.entrySet())
            {
                this.set(e.getKey(), e.getValue());
            }
            return this;
        }

        public int calculateSize()
        {
            int size = this.template.length;
            for (int i = 0; i < this.template.keyIndices.length; i++)
            {
                final int idx = this.template.keyIndices[i];
                if (idx > -1)
                {
                    size += this.values[idx].length();
                }
            }
            return size;
        }

        public String process()
        {
            final StringBuilder sb = new StringBuilder();
            this.process(sb);
            return sb.toString();
        }

        public Filler process(final StringBuilder out)
        {
            out.ensureCapacity(this.calculateSize());

            for (int i = 0; i < this.template.parts.length; i++)
            {
                out.append(this.template.parts[i]);
                final int index = this.template.keyIndices[i];
                if (index > -1)
                {
                    out.append(this.values[index]);
                }
            }

            return this;
        }

        public Filler apply(final Collection<Map<String, ? extends CharSequence>> listOfMaps, final StringBuilder out)
        {
            return this.apply(listOfMaps, false, out);
        }

        public Filler apply(final Collection<Map<String, ? extends CharSequence>> listOfMaps, final boolean reset,
                final StringBuilder out)
        {
            for (final Map<String, ? extends CharSequence> map : listOfMaps)
            {
                if (reset)
                {
                    this.reset();
                }
                this.set(map);
                this.process(out);
            }
            return this;
        }

        @Override
        public String toString()
        {
            return this.process();
        }
    }

    public static Template create(final String input)
    {
        final ArrayList<String> parts = new ArrayList<String>();
        final HashMap<String, Integer> keys = new HashMap<String, Integer>();
        final IntArrayBuilder inserts = new IntArrayBuilder(32);
        final ArrayList<String> defaults = new ArrayList<String>();

        final StringBuilder sb = new StringBuilder();
        for (int i = 0; i < input.length(); i++)
        {
            final char current = input.charAt(i);
            final char next = i + 1 < input.length() ? input.charAt(i + 1) : '\0';
            final char next2 = i + 2 < input.length() ? input.charAt(i + 2) : '\0';

            if (current == '$' && next == '\\' && next2 == '{')
            {
                sb.append("${");
                i += 2;
            }
            else if (current == '$' && next == '{')
            {
                int n = i + 2;
                boolean inDefault = false;
                final StringBuilder key = new StringBuilder();
                final StringBuilder def = new StringBuilder();
                while (n < input.length())
                {
                    final char c0 = input.charAt(n);
                    final char c1 = n + 1 < input.length() ? input.charAt(n + 1) : '\0';
                    if (!inDefault)
                    {
                        if (c0 == '}')
                        {
                            break;
                        }
                        else if (c0 == ':')
                        {
                            inDefault = true;
                        }
                        else
                        {
                            key.append(c0);
                        }
                    }
                    else
                    {
                        if (c0 == '\\' && c1 == '}')
                        {
                            def.append('}');
                            n++;
                        }
                        else if (c0 == '}')
                        {
                            break;
                        }
                        else
                        {
                            def.append(c0);
                        }
                    }
                    n++;
                }
                i = n;
                parts.add(sb.toString());
                sb.setLength(0);

                final String sKey = key.toString().trim();
                final String sDef = def.toString();

                if (!keys.containsKey(sKey))
                {
                    keys.put(sKey, Integer.valueOf(keys.size()));
                    defaults.add("");
                }
                final int kIdx = keys.get(sKey).intValue();
                inserts.add(kIdx);

                if (sDef.length() > 0)
                {
                    defaults.set(kIdx, sDef);
                }
            }
            else
            {
                sb.append(current);
            }
        }

        parts.add(sb.toString());
        inserts.add(-1);

        return new Template(
                parts.toArray(new String[parts.size()]),
                defaults.toArray(new String[defaults.size()]),
                inserts.toArray(),
                keys);
    }

    private final static class IntArrayBuilder
    {
        private int[] array;
        private int   size;

        public IntArrayBuilder(final int initialSize)
        {
            this.array = new int[Math.max(0, initialSize)];
        }

        public void add(final int x)
        {
            if (this.size == this.array.length)
            {
                this.resize();
            }
            this.array[this.size++] = x;
        }

        public int[] toArray()
        {
            return Arrays.copyOf(this.array, this.size);
        }

        private static int guardedDouble(final int x)
        {
            final int y = Math.max(1, x) << 1;
            return y <= 0 ? Integer.MAX_VALUE : y;
        }

        private void resize()
        {
            final int newSize = guardedDouble(this.array.length);
            if (this.array.length != newSize)
            {
                this.array = Arrays.copyOf(this.array, newSize);
            }
        }
    }
}