/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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
 *
 *      https://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 org.apache.commons.lang3.text;

import java.util.ArrayList;
import java.util.Enumeration;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Objects;
import java.util.Properties;

import org.apache.commons.lang3.StringUtils;

/**
 * Substitutes variables within a string by values.
 * <p>
 * This class takes a piece of text and substitutes all the variables within it.
 * The default definition of a variable is {@code ${variableName}}.
 * The prefix and suffix can be changed via constructors and set methods.
 * </p>
 * <p>
 * Variable values are typically resolved from a map, but could also be resolved
 * from system properties, or by supplying a custom variable resolver.
 * </p>
 * <p>
 * The simplest example is to use this class to replace Java System properties. For example:
 * </p>
 * <pre>
 * StrSubstitutor.replaceSystemProperties(
 *      "You are running with java.version = ${java.version} and os.name = ${os.name}.");
 * </pre>
 * <p>
 * Typical usage of this class follows the following pattern: First an instance is created
 * and initialized with the map that contains the values for the available variables.
 * If a prefix and/or suffix for variables should be used other than the default ones,
 * the appropriate settings can be performed. After that the {@code replace()}
 * method can be called passing in the source text for interpolation. In the returned
 * text all variable references (as long as their values are known) will be resolved.
 * The following example demonstrates this:
 * </p>
 * <pre>
 * Map valuesMap = HashMap();
 * valuesMap.put(&quot;animal&quot;, &quot;quick brown fox&quot;);
 * valuesMap.put(&quot;target&quot;, &quot;lazy dog&quot;);
 * String templateString = &quot;The ${animal} jumps over the ${target}.&quot;;
 * StrSubstitutor sub = new StrSubstitutor(valuesMap);
 * String resolvedString = sub.replace(templateString);
 * </pre>
 * yielding:
 * <pre>
 *      The quick brown fox jumps over the lazy dog.
 * </pre>
 * <p>
 * Also, this class allows to set a default value for unresolved variables.
 * The default value for a variable can be appended to the variable name after the variable
 * default value delimiter. The default value of the variable default value delimiter is ':-',
 * as in bash and other *nix shells, as those are arguably where the default ${} delimiter set originated.
 * The variable default value delimiter can be manually set by calling {@link #setValueDelimiterMatcher(StrMatcher)},
 * {@link #setValueDelimiter(char)} or {@link #setValueDelimiter(String)}.
 * The following shows an example with variable default value settings:
 * </p>
 * <pre>
 * Map valuesMap = HashMap();
 * valuesMap.put(&quot;animal&quot;, &quot;quick brown fox&quot;);
 * valuesMap.put(&quot;target&quot;, &quot;lazy dog&quot;);
 * String templateString = &quot;The ${animal} jumps over the ${target}. ${undefined.number:-1234567890}.&quot;;
 * StrSubstitutor sub = new StrSubstitutor(valuesMap);
 * String resolvedString = sub.replace(templateString);
 * </pre>
 * <p>
 * yielding:
 * </p>
 * <pre>
 *      The quick brown fox jumps over the lazy dog. 1234567890.
 * </pre>
 * <p>
 * In addition to this usage pattern there are some static convenience methods that
 * cover the most common use cases. These methods can be used without the need of
 * manually creating an instance. However if multiple replace operations are to be
 * performed, creating and reusing an instance of this class will be more efficient.
 * </p>
 * <p>
 * Variable replacement works in a recursive way. Thus, if a variable value contains
 * a variable then that variable will also be replaced. Cyclic replacements are
 * detected and will cause an exception to be thrown.
 * </p>
 * <p>
 * Sometimes the interpolation's result must contain a variable prefix. As an example
 * take the following source text:
 * </p>
 * <pre>
 *   The variable ${${name}} must be used.
 * </pre>
 * <p>
 * Here only the variable's name referred to in the text should be replaced resulting
 * in the text (assuming that the value of the {@code name} variable is {@code x}):
 * </p>
 * <pre>
 *   The variable ${x} must be used.
 * </pre>
 * <p>
 * To achieve this effect there are two possibilities: Either set a different prefix
 * and suffix for variables which do not conflict with the result text you want to
 * produce. The other possibility is to use the escape character, by default '$'.
 * If this character is placed before a variable reference, this reference is ignored
 * and won't be replaced. For example:
 * </p>
 * <pre>
 *   The variable $${${name}} must be used.
 * </pre>
 * <p>
 * An escape character at the end of a substituted value does not escape a following variable reference in the containing text.
 * For example, if {@code price} is {@code 5$} and {@code item} is {@code X}, then {@code ${price}${item}} becomes {@code 5$X}.
 * This also applies to default values and recursive substitutions. Escape characters before variable references within a value
 * are processed when that value is recursively substituted.
 * </p>
 * <p>
 * In some complex scenarios you might even want to perform substitution in the
 * names of variables, for instance:
 * </p>
 * <pre>
 * ${jre-${java.specification.version}}
 * </pre>
 * <p>
 * {@link StrSubstitutor} supports this recursive substitution in variable
 * names, but it has to be enabled explicitly by setting the
 * {@link #setEnableSubstitutionInVariables(boolean) enableSubstitutionInVariables}
 * property to <strong>true</strong>.
 * </p>
 * <p>
 * This class is <strong>not</strong> thread safe.
 * </p>
 *
 * @since 2.2
 * @deprecated As of <a href="https://commons.apache.org/proper/commons-lang/changes-report.html#a3.6">3.6</a>, use Apache Commons Text
 * <a href="https://commons.apache.org/proper/commons-text/javadocs/api-release/org/apache/commons/text/StringSubstitutor.html">
 * StringSubstitutor</a>.
 */
@Deprecated
public class StrSubstitutor {

    /**
     * Constant for the default escape character.
     */
    public static final char DEFAULT_ESCAPE = '$';

    /**
     * Constant for the default variable prefix.
     */
    public static final StrMatcher DEFAULT_PREFIX = StrMatcher.stringMatcher("${");

    /**
     * Constant for the default variable suffix.
     */
    public static final StrMatcher DEFAULT_SUFFIX = StrMatcher.stringMatcher("}");

    /**
     * Constant for the default value delimiter of a variable.
     *
     * @since 3.2
     */
    public static final StrMatcher DEFAULT_VALUE_DELIMITER = StrMatcher.stringMatcher(":-");

    /**
     * The maximum nesting depth of variable interpolation. The cyclic-substitution check only rejects a variable
     * already on the current substitution stack; without a depth bound, deeply nested (acyclic) references and
     * nested variable names (when {@link #isEnableSubstitutionInVariables()} is on) recurse once per level and
     * can end in {@link StackOverflowError}.
     */
    private static final int MAX_SUBSTITUTION_DEPTH = 256;

    /**
     * The maximum total number of characters that variable replacement may emit during one top-level substitution.
     * Bounds exponential acyclic fan-out (each of N references expanding to N more), which the cyclic-substitution
     * check cannot see.
     */
    private static final int MAX_SUBSTITUTION_LENGTH = 16 * 1024 * 1024;

    /**
     * Replaces all the occurrences of variables in the given source object with
     * their matching values from the map.
     *
     * @param <V> The type of the values in the map.
     * @param source  The source text containing the variables to substitute, null returns null.
     * @param valueMap  The map with the values, may be null.
     * @return The result of the replace operation.
     */
    public static <V> String replace(final Object source, final Map<String, V> valueMap) {
        return new StrSubstitutor(valueMap).replace(source);
    }

    /**
     * Replaces all the occurrences of variables in the given source object with
     * their matching values from the map. This method allows to specify a
     * custom variable prefix and suffix.
     *
     * @param <V> The type of the values in the map.
     * @param source  The source text containing the variables to substitute, null returns null.
     * @param valueMap  The map with the values, may be null.
     * @param prefix  The prefix of variables, not null.
     * @param suffix  The suffix of variables, not null.
     * @return The result of the replace operation.
     * @throws IllegalArgumentException Thrown if the prefix or suffix is null.
     */
    public static <V> String replace(final Object source, final Map<String, V> valueMap, final String prefix, final String suffix) {
        return new StrSubstitutor(valueMap, prefix, suffix).replace(source);
    }

    /**
     * Replaces all the occurrences of variables in the given source object with their matching
     * values from the properties.
     *
     * @param source The source text containing the variables to substitute, null returns null.
     * @param valueProperties The properties with values, may be null.
     * @return The result of the replace operation.
     */
    public static String replace(final Object source, final Properties valueProperties) {
        if (valueProperties == null) {
            return source.toString();
        }
        final Map<String, String> valueMap = new HashMap<>();
        final Enumeration<?> propNames = valueProperties.propertyNames();
        while (propNames.hasMoreElements()) {
            final String propName = String.valueOf(propNames.nextElement());
            final String propValue = valueProperties.getProperty(propName);
            valueMap.put(propName, propValue);
        }
        return replace(source, valueMap);
    }

    /**
     * Replaces all the occurrences of variables in the given source object with
     * their matching values from the system properties.
     *
     * @param source  The source text containing the variables to substitute, null returns null.
     * @return The result of the replace operation.
     */
    public static String replaceSystemProperties(final Object source) {
        return new StrSubstitutor(StrLookup.systemPropertiesLookup()).replace(source);
    }

    /**
     * Stores the escape character.
     */
    private char escapeChar;

    /**
     * Stores the variable prefix.
     */
    private StrMatcher prefixMatcher;

    /**
     * Stores the variable suffix.
     */
    private StrMatcher suffixMatcher;

    /**
     * Stores the default variable value delimiter
     */
    private StrMatcher valueDelimiterMatcher;

    /**
     * Variable resolution is delegated to an implementor of VariableResolver.
     */
    private StrLookup<?> variableResolver;

    /**
     * The flag whether substitution in variable names is enabled.
     */
    private boolean enableSubstitutionInVariables;

    /**
     * Whether escapes should be preserved.  Default is false;
     */
    private boolean preserveEscapes;

    /**
     * Current recursion depth of {@link #substitute(StrBuilder, int, int, List)}. Like the rest of this class,
     * not thread safe.
     */
    private int substitutionDepth;

    /**
     * Total number of characters emitted by variable replacement in the current top-level substitution.
     */
    private long substitutionLength;

    /**
     * Creates a new instance with defaults for variable prefix and suffix
     * and the escaping character.
     */
    public StrSubstitutor() {
        this(null, DEFAULT_PREFIX, DEFAULT_SUFFIX, DEFAULT_ESCAPE);
    }

    /**
     * Creates a new instance and initializes it. Uses defaults for variable
     * prefix and suffix and the escaping character.
     *
     * @param <V> The type of the values in the map.
     * @param valueMap  The map with the variables' values, may be null.
     */
    public <V> StrSubstitutor(final Map<String, V> valueMap) {
        this(StrLookup.mapLookup(valueMap), DEFAULT_PREFIX, DEFAULT_SUFFIX, DEFAULT_ESCAPE);
    }

    /**
     * Creates a new instance and initializes it. Uses a default escaping character.
     *
     * @param <V> The type of the values in the map.
     * @param valueMap  The map with the variables' values, may be null.
     * @param prefix  The prefix for variables, not null.
     * @param suffix  The suffix for variables, not null.
     * @throws IllegalArgumentException Thrown if the prefix or suffix is null.
     */
    public <V> StrSubstitutor(final Map<String, V> valueMap, final String prefix, final String suffix) {
        this(StrLookup.mapLookup(valueMap), prefix, suffix, DEFAULT_ESCAPE);
    }

    /**
     * Creates a new instance and initializes it.
     *
     * @param <V> The type of the values in the map.
     * @param valueMap  The map with the variables' values, may be null.
     * @param prefix  The prefix for variables, not null.
     * @param suffix  The suffix for variables, not null.
     * @param escape  The escape character.
     * @throws IllegalArgumentException Thrown if the prefix or suffix is null.
     */
    public <V> StrSubstitutor(final Map<String, V> valueMap, final String prefix, final String suffix, final char escape) {
        this(StrLookup.mapLookup(valueMap), prefix, suffix, escape);
    }

    /**
     * Creates a new instance and initializes it.
     *
     * @param <V> The type of the values in the map.
     * @param valueMap  The map with the variables' values, may be null.
     * @param prefix  The prefix for variables, not null.
     * @param suffix  The suffix for variables, not null.
     * @param escape  The escape character.
     * @param valueDelimiter  The variable default value delimiter, may be null.
     * @throws IllegalArgumentException Thrown if the prefix or suffix is null.
     * @since 3.2
     */
    public <V> StrSubstitutor(final Map<String, V> valueMap, final String prefix, final String suffix, final char escape, final String valueDelimiter) {
        this(StrLookup.mapLookup(valueMap), prefix, suffix, escape, valueDelimiter);
    }

    /**
     * Creates a new instance and initializes it.
     *
     * @param variableResolver  The variable resolver, may be null
     */
    public StrSubstitutor(final StrLookup<?> variableResolver) {
        this(variableResolver, DEFAULT_PREFIX, DEFAULT_SUFFIX, DEFAULT_ESCAPE);
    }

    /**
     * Creates a new instance and initializes it.
     *
     * @param variableResolver  The variable resolver, may be null.
     * @param prefix  The prefix for variables, not null.
     * @param suffix  The suffix for variables, not null.
     * @param escape  The escape character.
     * @throws IllegalArgumentException Thrown if the prefix or suffix is null.
     */
    public StrSubstitutor(final StrLookup<?> variableResolver, final String prefix, final String suffix, final char escape) {
        setVariableResolver(variableResolver);
        setVariablePrefix(prefix);
        setVariableSuffix(suffix);
        setEscapeChar(escape);
        setValueDelimiterMatcher(DEFAULT_VALUE_DELIMITER);
    }

    /**
     * Creates a new instance and initializes it.
     *
     * @param variableResolver  The variable resolver, may be null.
     * @param prefix  The prefix for variables, not null.
     * @param suffix  The suffix for variables, not null.
     * @param escape  The escape character.
     * @param valueDelimiter  The variable default value delimiter string, may be null.
     * @throws IllegalArgumentException Thrown if the prefix or suffix is null.
     * @since 3.2
     */
    public StrSubstitutor(final StrLookup<?> variableResolver, final String prefix, final String suffix, final char escape, final String valueDelimiter) {
        setVariableResolver(variableResolver);
        setVariablePrefix(prefix);
        setVariableSuffix(suffix);
        setEscapeChar(escape);
        setValueDelimiter(valueDelimiter);
    }

    /**
     * Creates a new instance and initializes it.
     *
     * @param variableResolver  The variable resolver, may be null.
     * @param prefixMatcher  The prefix for variables, not null.
     * @param suffixMatcher  The suffix for variables, not null.
     * @param escape  The escape character.
     * @throws IllegalArgumentException Thrown if the prefix or suffix is null.
     */
    public StrSubstitutor(final StrLookup<?> variableResolver, final StrMatcher prefixMatcher, final StrMatcher suffixMatcher, final char escape) {
        this(variableResolver, prefixMatcher, suffixMatcher, escape, DEFAULT_VALUE_DELIMITER);
    }

    /**
     * Creates a new instance and initializes it.
     *
     * @param variableResolver  The variable resolver, may be null.
     * @param prefixMatcher  The prefix for variables, not null.
     * @param suffixMatcher  The suffix for variables, not null.
     * @param escape  The escape character.
     * @param valueDelimiterMatcher  The variable default value delimiter matcher, may be null.
     * @throws IllegalArgumentException Thrown if the prefix or suffix is null.
     * @since 3.2
     */
    public StrSubstitutor(final StrLookup<?> variableResolver, final StrMatcher prefixMatcher, final StrMatcher suffixMatcher, final char escape,
            final StrMatcher valueDelimiterMatcher) {
        setVariableResolver(variableResolver);
        setVariablePrefixMatcher(prefixMatcher);
        setVariableSuffixMatcher(suffixMatcher);
        setEscapeChar(escape);
        setValueDelimiterMatcher(valueDelimiterMatcher);
    }

    /**
     * Checks if the specified variable is already in the stack (list) of variables.
     *
     * @param varName  The variable name to check.
     * @param priorVariables  The list of prior variables.
     */
    private void checkCyclicSubstitution(final String varName, final List<String> priorVariables) {
        if (!priorVariables.contains(varName)) {
            return;
        }
        final StrBuilder buf = new StrBuilder(256);
        buf.append("Infinite loop in property interpolation of ");
        buf.append(priorVariables.remove(0));
        buf.append(": ");
        buf.appendWithSeparators(priorVariables, "->");
        throw new IllegalStateException(buf.toString());
    }

    /**
     * Gets the escape character.
     *
     * @return The character used for escaping variable references
     */
    public char getEscapeChar() {
        return this.escapeChar;
    }

    /**
     * Gets the variable default value delimiter matcher currently in use.
     * <p>
     * The variable default value delimiter is the character or characters that delimit the
     * variable name and the variable default value. This delimiter is expressed in terms of a matcher
     * allowing advanced variable default value delimiter matches.
     * </p>
     * <p>
     * If it returns null, then the variable default value resolution is disabled.
     * </p>
     *
     * @return The variable default value delimiter matcher in use, may be null.
     * @since 3.2
     */
    public StrMatcher getValueDelimiterMatcher() {
        return valueDelimiterMatcher;
    }

    /**
     * Gets the variable prefix matcher currently in use.
     * <p>
     * The variable prefix is the character or characters that identify the
     * start of a variable. This prefix is expressed in terms of a matcher
     * allowing advanced prefix matches.
     * </p>
     *
     * @return The prefix matcher in use.
     */
    public StrMatcher getVariablePrefixMatcher() {
        return prefixMatcher;
    }

    /**
     * Gets the VariableResolver that is used to lookup variables.
     *
     * @return The VariableResolver.
     */
    public StrLookup<?> getVariableResolver() {
        return this.variableResolver;
    }

    /**
     * Gets the variable suffix matcher currently in use.
     * <p>
     * The variable suffix is the character or characters that identify the
     * end of a variable. This suffix is expressed in terms of a matcher
     * allowing advanced suffix matches.
     * </p>
     *
     * @return The suffix matcher in use.
     */
    public StrMatcher getVariableSuffixMatcher() {
        return suffixMatcher;
    }

    /**
     * Tests whether substitution is done in variable names.
     *
     * @return The substitution in variable names flag.
     * @since 3.0
     */
    public boolean isEnableSubstitutionInVariables() {
        return enableSubstitutionInVariables;
    }

    /**
     * Tests whether escapes are preserved during substitution.
     *
     * @return The preserve escape flag.
     * @since 3.5
     */
    public boolean isPreserveEscapes() {
        return preserveEscapes;
    }

    /**
     * Replaces all the occurrences of variables with their matching values
     * from the resolver using the given source array as a template.
     * The array is not altered by this method.
     *
     * @param source  The character array to replace in, not altered, null returns null.
     * @return The result of the replace operation.
     */
    public String replace(final char[] source) {
        if (source == null) {
            return null;
        }
        final StrBuilder buf = new StrBuilder(source.length).append(source);
        substitute(buf, 0, source.length);
        return buf.toString();
    }

    /**
     * Replaces all the occurrences of variables with their matching values
     * from the resolver using the given source array as a template.
     * The array is not altered by this method.
     * <p>
     * Only the specified portion of the array will be processed.
     * The rest of the array is not processed, and is not returned.
     * </p>
     *
     * @param source  The character array to replace in, not altered, null returns null.
     * @param offset  The start offset within the array, must be valid.
     * @param length  The length within the array to be processed, must be valid.
     * @return The result of the replace operation.
     */
    public String replace(final char[] source, final int offset, final int length) {
        if (source == null) {
            return null;
        }
        final StrBuilder buf = new StrBuilder(length).append(source, offset, length);
        substitute(buf, 0, length);
        return buf.toString();
    }

    /**
     * Replaces all the occurrences of variables with their matching values
     * from the resolver using the given source as a template.
     * The source is not altered by this method.
     *
     * @param source  The buffer to use as a template, not changed, null returns null.
     * @return The result of the replace operation.
     * @since 3.2
     */
    public String replace(final CharSequence source) {
        if (source == null) {
            return null;
        }
        return replace(source, 0, source.length());
    }

    /**
     * Replaces all the occurrences of variables with their matching values
     * from the resolver using the given source as a template.
     * The source is not altered by this method.
     * <p>
     * Only the specified portion of the buffer will be processed.
     * The rest of the buffer is not processed, and is not returned.
     * </p>
     *
     * @param source  The buffer to use as a template, not changed, null returns null.
     * @param offset  The start offset within the array, must be valid.
     * @param length  The length within the array to be processed, must be valid.
     * @return The result of the replace operation.
     * @since 3.2
     */
    public String replace(final CharSequence source, final int offset, final int length) {
        if (source == null) {
            return null;
        }
        final StrBuilder buf = new StrBuilder(length).append(source, offset, length);
        substitute(buf, 0, length);
        return buf.toString();
    }

    /**
     * Replaces all the occurrences of variables in the given source object with
     * their matching values from the resolver. The input source object is
     * converted to a string using {@code toString} and is not altered.
     *
     * @param source  The source to replace in, null returns null.
     * @return The result of the replace operation.
     */
    public String replace(final Object source) {
        if (source == null) {
            return null;
        }
        final StrBuilder buf = new StrBuilder().append(source);
        substitute(buf, 0, buf.length());
        return buf.toString();
    }

    /**
     * Replaces all the occurrences of variables with their matching values
     * from the resolver using the given source builder as a template.
     * The builder is not altered by this method.
     *
     * @param source  The builder to use as a template, not changed, null returns null.
     * @return The result of the replace operation.
     */
    public String replace(final StrBuilder source) {
        if (source == null) {
            return null;
        }
        final StrBuilder buf = new StrBuilder(source.length()).append(source);
        substitute(buf, 0, buf.length());
        return buf.toString();
    }

    /**
     * Replaces all the occurrences of variables with their matching values
     * from the resolver using the given source builder as a template.
     * The builder is not altered by this method.
     * <p>
     * Only the specified portion of the builder will be processed.
     * The rest of the builder is not processed, and is not returned.
     * </p>
     *
     * @param source  The builder to use as a template, not changed, null returns null.
     * @param offset  The start offset within the array, must be valid.
     * @param length  The length within the array to be processed, must be valid.
     * @return The result of the replace operation.
     */
    public String replace(final StrBuilder source, final int offset, final int length) {
        if (source == null) {
            return null;
        }
        final StrBuilder buf = new StrBuilder(length).append(source, offset, length);
        substitute(buf, 0, length);
        return buf.toString();
    }

    /**
     * Replaces all the occurrences of variables with their matching values
     * from the resolver using the given source string as a template.
     *
     * @param source  The string to replace in, null returns null.
     * @return The result of the replace operation.
     */
    public String replace(final String source) {
        if (source == null) {
            return null;
        }
        final StrBuilder buf = new StrBuilder(source);
        if (!substitute(buf, 0, source.length())) {
            return source;
        }
        return buf.toString();
    }

    /**
     * Replaces all the occurrences of variables with their matching values
     * from the resolver using the given source string as a template.
     * <p>
     * Only the specified portion of the string will be processed.
     * The rest of the string is not processed, and is not returned.
     * </p>
     *
     * @param source  The string to replace in, null returns null.
     * @param offset  The start offset within the array, must be valid.
     * @param length  The length within the array to be processed, must be valid.
     * @return The result of the replace operation.
     */
    public String replace(final String source, final int offset, final int length) {
        if (source == null) {
            return null;
        }
        final StrBuilder buf = new StrBuilder(length).append(source, offset, length);
        if (!substitute(buf, 0, length)) {
            return source.substring(offset, offset + length);
        }
        return buf.toString();
    }

    /**
     * Replaces all the occurrences of variables with their matching values
     * from the resolver using the given source buffer as a template.
     * The buffer is not altered by this method.
     *
     * @param source  The buffer to use as a template, not changed, null returns null.
     * @return The result of the replace operation.
     */
    public String replace(final StringBuffer source) {
        if (source == null) {
            return null;
        }
        final StrBuilder buf = new StrBuilder(source.length()).append(source);
        substitute(buf, 0, buf.length());
        return buf.toString();
    }

    /**
     * Replaces all the occurrences of variables with their matching values
     * from the resolver using the given source buffer as a template.
     * The buffer is not altered by this method.
     * <p>
     * Only the specified portion of the buffer will be processed.
     * The rest of the buffer is not processed, and is not returned.
     * </p>
     *
     * @param source  The buffer to use as a template, not changed, null returns null.
     * @param offset  The start offset within the array, must be valid.
     * @param length  The length within the array to be processed, must be valid.
     * @return The result of the replace operation.
     */
    public String replace(final StringBuffer source, final int offset, final int length) {
        if (source == null) {
            return null;
        }
        final StrBuilder buf = new StrBuilder(length).append(source, offset, length);
        substitute(buf, 0, length);
        return buf.toString();
    }

    /**
     * Replaces all the occurrences of variables within the given source
     * builder with their matching values from the resolver.
     *
     * @param source  The builder to replace in, updated, null returns zero.
     * @return true if altered.
     */
    public boolean replaceIn(final StrBuilder source) {
        if (source == null) {
            return false;
        }
        return substitute(source, 0, source.length());
    }

    /**
     * Replaces all the occurrences of variables within the given source
     * builder with their matching values from the resolver.
     * <p>
     * Only the specified portion of the builder will be processed.
     * The rest of the builder is not processed, but it is not deleted.
     * </p>
     *
     * @param source  The builder to replace in, null returns zero.
     * @param offset  The start offset within the array, must be valid.
     * @param length  The length within the builder to be processed, must be valid.
     * @return true if altered.
     */
    public boolean replaceIn(final StrBuilder source, final int offset, final int length) {
        if (source == null) {
            return false;
        }
        return substitute(source, offset, length);
    }

    /**
     * Replaces all the occurrences of variables within the given source buffer
     * with their matching values from the resolver.
     * The buffer is updated with the result.
     *
     * @param source  The buffer to replace in, updated, null returns zero.
     * @return true if altered.
     */
    public boolean replaceIn(final StringBuffer source) {
        if (source == null) {
            return false;
        }
        return replaceIn(source, 0, source.length());
    }

    /**
     * Replaces all the occurrences of variables within the given source buffer
     * with their matching values from the resolver.
     * The buffer is updated with the result.
     * <p>
     * Only the specified portion of the buffer will be processed.
     * The rest of the buffer is not processed, but it is not deleted.
     * </p>
     *
     * @param source  The buffer to replace in, updated, null returns zero.
     * @param offset  The start offset within the array, must be valid.
     * @param length  The length within the buffer to be processed, must be valid.
     * @return true if altered.
     */
    public boolean replaceIn(final StringBuffer source, final int offset, final int length) {
        if (source == null) {
            return false;
        }
        final StrBuilder buf = new StrBuilder(length).append(source, offset, length);
        if (!substitute(buf, 0, length)) {
            return false;
        }
        source.replace(offset, offset + length, buf.toString());
        return true;
    }

    /**
     * Replaces all the occurrences of variables within the given source buffer
     * with their matching values from the resolver.
     * The buffer is updated with the result.
     *
     * @param source  The buffer to replace in, updated, null returns zero.
     * @return true if altered.
     * @since 3.2
     */
    public boolean replaceIn(final StringBuilder source) {
        if (source == null) {
            return false;
        }
        return replaceIn(source, 0, source.length());
    }

    /**
     * Replaces all the occurrences of variables within the given source builder
     * with their matching values from the resolver.
     * The builder is updated with the result.
     * <p>
     * Only the specified portion of the buffer will be processed.
     * The rest of the buffer is not processed, but it is not deleted.
     * </p>
     *
     * @param source  The buffer to replace in, updated, null returns zero.
     * @param offset  The start offset within the array, must be valid.
     * @param length  The length within the buffer to be processed, must be valid.
     * @return true if altered.
     * @since 3.2
     */
    public boolean replaceIn(final StringBuilder source, final int offset, final int length) {
        if (source == null) {
            return false;
        }
        final StrBuilder buf = new StrBuilder(length).append(source, offset, length);
        if (!substitute(buf, 0, length)) {
            return false;
        }
        source.replace(offset, offset + length, buf.toString());
        return true;
    }

    /**
     * Internal method that resolves the value of a variable.
     * <p>
     * Most users of this class do not need to call this method. This method is
     * called automatically by the substitution process.
     * </p>
     * <p>
     * Writers of subclasses can override this method if they need to alter
     * how each substitution occurs. The method is passed the variable's name
     * and must return the corresponding value. This implementation uses the
     * {@link #getVariableResolver()} with the variable's name as the key.
     * </p>
     *
     * @param variableName  The name of the variable, not null.
     * @param buf  The buffer where the substitution is occurring, not null.
     * @param startPos  The start position of the variable including the prefix, valid.
     * @param endPos  The end position of the variable including the suffix, valid.
     * @return The variable's value or {@code null} if the variable is unknown.
     */
    protected String resolveVariable(final String variableName, final StrBuilder buf, final int startPos, final int endPos) {
        final StrLookup<?> resolver = getVariableResolver();
        if (resolver == null) {
            return null;
        }
        return resolver.lookup(variableName);
    }

    /**
     * Sets a flag whether substitution is done in variable names. If set to
     * <strong>true</strong>, the names of variables can contain other variables which are
     * processed first before the original variable is evaluated, e.g.
     * {@code ${jre-${java.version}}}. The default value is <strong>false</strong>.
     *
     * @param enableSubstitutionInVariables The new value of the flag.
     * @since 3.0
     */
    public void setEnableSubstitutionInVariables(
            final boolean enableSubstitutionInVariables) {
        this.enableSubstitutionInVariables = enableSubstitutionInVariables;
    }

    /**
     * Sets the escape character.
     * If this character is placed before a variable reference in the source
     * text, this variable will be ignored.
     *
     * @param escapeCharacter  The escape character (0 for disabling escaping)
     */
    public void setEscapeChar(final char escapeCharacter) {
        this.escapeChar = escapeCharacter;
    }

    /**
     * Sets a flag controlling whether escapes are preserved during
     * substitution.  If set to <strong>true</strong>, the escape character is retained
     * during substitution (e.g. {@code $${this-is-escaped}} remains
     * {@code $${this-is-escaped}}).  If set to <strong>false</strong>, the escape
     * character is removed during substitution (e.g.
     * {@code $${this-is-escaped}} becomes
     * {@code ${this-is-escaped}}).  The default value is <strong>false</strong>
     *
     * @param preserveEscapes true if escapes are to be preserved.
     * @since 3.5
     */
    public void setPreserveEscapes(final boolean preserveEscapes) {
        this.preserveEscapes = preserveEscapes;
    }

    /**
     * Sets the variable default value delimiter to use.
     * <p>
     * The variable default value delimiter is the character or characters that delimit the
     * variable name and the variable default value. This method allows a single character
     * variable default value delimiter to be easily set.
     * </p>
     *
     * @param valueDelimiter  The variable default value delimiter character to use.
     * @return {@code this} instance.
     * @since 3.2
     */
    public StrSubstitutor setValueDelimiter(final char valueDelimiter) {
        return setValueDelimiterMatcher(StrMatcher.charMatcher(valueDelimiter));
    }

    /**
     * Sets the variable default value delimiter to use.
     * <p>
     * The variable default value delimiter is the character or characters that delimit the
     * variable name and the variable default value. This method allows a string
     * variable default value delimiter to be easily set.
     * </p>
     * <p>
     * If the {@code valueDelimiter} is null or empty string, then the variable default
     * value resolution becomes disabled.
     * </p>
     *
     * @param valueDelimiter  The variable default value delimiter string to use, may be null or empty.
     * @return {@code this} instance.
     * @since 3.2
     */
    public StrSubstitutor setValueDelimiter(final String valueDelimiter) {
        if (StringUtils.isEmpty(valueDelimiter)) {
            setValueDelimiterMatcher(null);
            return this;
        }
        return setValueDelimiterMatcher(StrMatcher.stringMatcher(valueDelimiter));
    }

    /**
     * Sets the variable default value delimiter matcher to use.
     * <p>
     * The variable default value delimiter is the character or characters that delimit the
     * variable name and the variable default value. This delimiter is expressed in terms of a matcher
     * allowing advanced variable default value delimiter matches.
     * </p>
     * <p>
     * If the {@code valueDelimiterMatcher} is null, then the variable default value resolution
     * becomes disabled.
     * </p>
     *
     * @param valueDelimiterMatcher  variable default value delimiter matcher to use, may be null.
     * @return {@code this} instance.
     * @since 3.2
     */
    public StrSubstitutor setValueDelimiterMatcher(final StrMatcher valueDelimiterMatcher) {
        this.valueDelimiterMatcher = valueDelimiterMatcher;
        return this;
    }

    /**
     * Sets the variable prefix to use.
     * <p>
     * The variable prefix is the character or characters that identify the
     * start of a variable. This method allows a single character prefix to
     * be easily set.
     * </p>
     *
     * @param prefix  The prefix character to use.
     * @return {@code this} instance.
     */
    public StrSubstitutor setVariablePrefix(final char prefix) {
        return setVariablePrefixMatcher(StrMatcher.charMatcher(prefix));
    }

    /**
     * Sets the variable prefix to use.
     * <p>
     * The variable prefix is the character or characters that identify the
     * start of a variable. This method allows a string prefix to be easily set.
     * </p>
     *
     * @param prefix  The prefix for variables, not null.
     * @return {@code this} instance.
     * @throws NullPointerException Thrown if the prefix is null.
     */
    public StrSubstitutor setVariablePrefix(final String prefix) {
        return setVariablePrefixMatcher(StrMatcher.stringMatcher(Objects.requireNonNull(prefix, "prefix")));
    }

    /**
     * Sets the variable prefix matcher currently in use.
     * <p>
     * The variable prefix is the character or characters that identify the
     * start of a variable. This prefix is expressed in terms of a matcher
     * allowing advanced prefix matches.
     * </p>
     *
     * @param prefixMatcher  The prefix matcher to use, null ignored.
     * @return {@code this} instance.
     * @throws NullPointerException Thrown if the prefix matcher is null.
     */
    public StrSubstitutor setVariablePrefixMatcher(final StrMatcher prefixMatcher) {
        this.prefixMatcher = Objects.requireNonNull(prefixMatcher, "prefixMatcher");
        return this;
    }

    /**
     * Sets the VariableResolver that is used to lookup variables.
     *
     * @param variableResolver  The VariableResolver
     */
    public void setVariableResolver(final StrLookup<?> variableResolver) {
        this.variableResolver = variableResolver;
    }

    /**
     * Sets the variable suffix to use.
     * <p>
     * The variable suffix is the character or characters that identify the
     * end of a variable. This method allows a single character suffix to
     * be easily set.
     * </p>
     *
     * @param suffix  The suffix character to use.
     * @return {@code this} instance.
     */
    public StrSubstitutor setVariableSuffix(final char suffix) {
        return setVariableSuffixMatcher(StrMatcher.charMatcher(suffix));
    }

    /**
     * Sets the variable suffix to use.
     * <p>
     * The variable suffix is the character or characters that identify the
     * end of a variable. This method allows a string suffix to be easily set.
     * </p>
     *
     * @param suffix  The suffix for variables, not null.
     * @return {@code this} instance.
     * @throws NullPointerException Thrown if the suffix is null.
     */
    public StrSubstitutor setVariableSuffix(final String suffix) {
        return setVariableSuffixMatcher(StrMatcher.stringMatcher(Objects.requireNonNull(suffix, "suffix")));
    }

    /**
     * Sets the variable suffix matcher currently in use.
     * <p>
     * The variable suffix is the character or characters that identify the
     * end of a variable. This suffix is expressed in terms of a matcher
     * allowing advanced suffix matches.
     * </p>
     *
     * @param suffixMatcher  The suffix matcher to use, null ignored.
     * @return {@code this} instance.
     * @throws NullPointerException Thrown if the suffix matcher is null.
     */
    public StrSubstitutor setVariableSuffixMatcher(final StrMatcher suffixMatcher) {
        this.suffixMatcher = Objects.requireNonNull(suffixMatcher, "suffixMatcher");
        return this;
    }

    /**
     * Internal method that substitutes the variables.
     * <p>
     * Most users of this class do not need to call this method. This method will
     * be called automatically by another (public) method.
     * </p>
     * <p>
     * Writers of subclasses can override this method if they need access to
     * the substitution process at the start or end.
     * </p>
     *
     * @param buf  The string builder to substitute into, not null.
     * @param offset  The start offset within the builder, must be valid.
     * @param length  The length within the builder to be processed, must be valid.
     * @return true if altered.
     */
    protected boolean substitute(final StrBuilder buf, final int offset, final int length) {
        return substitute(buf, offset, length, null) > 0;
    }

    /**
     * Recursive handler for multiple levels of interpolation. This is the main
     * interpolation method, which resolves the values of all variable references
     * contained in the passed-in text.
     *
     * @param buf  The string builder to substitute into, not null.
     * @param offset  The start offset within the builder, must be valid.
     * @param length  The length within the builder to be processed, must be valid.
     * @param priorVariables  The stack keeping track of the replaced variables, may be null.
     * @return The length change that occurs, unless priorVariables is null when the int
     *  represents a boolean flag as to whether any change occurred.
     * @throws IllegalStateException Thrown if the interpolation exceeds {@value #MAX_SUBSTITUTION_DEPTH} nesting levels or
     *  emits more than {@value #MAX_SUBSTITUTION_LENGTH} characters. These budgets bound recursive expansion that the
     *  cyclic-substitution check cannot detect (acyclic fan-out, deep nesting). This class is deprecated; the
     *  Apache Commons Text successor {@code StringSubstitutor} should receive any richer treatment.
     */
    private int substitute(final StrBuilder buf, final int offset, final int length, final List<String> priorVariables) {
        if (substitutionDepth == 0) {
            substitutionLength = 0;
        }
        if (substitutionDepth >= MAX_SUBSTITUTION_DEPTH) {
            throw new IllegalStateException("Maximum interpolation depth (" + MAX_SUBSTITUTION_DEPTH + ") exceeded in variable substitution");
        }
        substitutionDepth++;
        try {
            return substituteRecursive(buf, offset, length, priorVariables);
        } finally {
            substitutionDepth--;
        }
    }

    /**
     * Implements {@link #substitute(StrBuilder, int, int, List)}; only that budget-enforcing wrapper may call this.
     *
     * @param buf  The string builder to substitute into, not null.
     * @param offset  The start offset within the builder, must be valid.
     * @param length  The length within the builder to be processed, must be valid.
     * @param priorVariables  The stack keeping track of the replaced variables, may be null.
     * @return The length change that occurs, unless priorVariables is null when the int
     *  represents a boolean flag as to whether any change occurred.
     */
    private int substituteRecursive(final StrBuilder buf, final int offset, final int length, List<String> priorVariables) {
        final StrMatcher pfxMatcher = getVariablePrefixMatcher();
        final StrMatcher suffMatcher = getVariableSuffixMatcher();
        final char escape = getEscapeChar();
        final StrMatcher valueDelimMatcher = getValueDelimiterMatcher();
        final boolean substitutionInVariablesEnabled = isEnableSubstitutionInVariables();
        final boolean top = priorVariables == null;
        boolean altered = false;
        int lengthChange = 0;
        char[] chars = buf.buffer;
        int bufEnd = offset + length;
        int pos = offset;
        // an escape character must come from the text being scanned, not from the end of a substituted value
        int escapeStart = offset;
        while (pos < bufEnd) {
            final int startMatchLen = pfxMatcher.isMatch(chars, pos, offset, bufEnd);
            if (startMatchLen == 0) {
                pos++;
            } else // found variable start marker
            if (pos > escapeStart && chars[pos - 1] == escape) {
                // escaped
                if (preserveEscapes) {
                    pos++;
                    continue;
                }
                buf.deleteCharAt(pos - 1);
                chars = buf.buffer; // in case buffer was altered
                lengthChange--;
                altered = true;
                bufEnd--;
            } else {
                // find suffix
                final int startPos = pos;
                pos += startMatchLen;
                int endMatchLen;
                int nestedVarCount = 0;
                while (pos < bufEnd) {
                    if (substitutionInVariablesEnabled && (endMatchLen = pfxMatcher.isMatch(chars, pos, offset, bufEnd)) != 0) {
                        // found a nested variable start
                        nestedVarCount++;
                        pos += endMatchLen;
                        continue;
                    }
                    endMatchLen = suffMatcher.isMatch(chars, pos, offset, bufEnd);
                    if (endMatchLen == 0) {
                        pos++;
                    } else {
                        // found variable end marker
                        if (nestedVarCount == 0) {
                            String varNameExpr = new String(chars, startPos + startMatchLen, pos - startPos - startMatchLen);
                            if (substitutionInVariablesEnabled) {
                                final StrBuilder bufName = new StrBuilder(varNameExpr);
                                substitute(bufName, 0, bufName.length());
                                varNameExpr = bufName.toString();
                            }
                            pos += endMatchLen;
                            final int endPos = pos;
                            String varName = varNameExpr;
                            String varDefaultValue = null;
                            if (valueDelimMatcher != null) {
                                final char[] varNameExprChars = varNameExpr.toCharArray();
                                int valueDelimiterMatchLen;
                                for (int i = 0; i < varNameExprChars.length; i++) {
                                    // if there's any nested variable when nested variable substitution disabled, then stop resolving name and default value.
                                    if (!substitutionInVariablesEnabled && pfxMatcher.isMatch(varNameExprChars, i, i, varNameExprChars.length) != 0) {
                                        break;
                                    }
                                    if ((valueDelimiterMatchLen = valueDelimMatcher.isMatch(varNameExprChars, i)) != 0) {
                                        varName = varNameExpr.substring(0, i);
                                        varDefaultValue = varNameExpr.substring(i + valueDelimiterMatchLen);
                                        break;
                                    }
                                }
                            }
                            // on the first call initialize priorVariables
                            if (priorVariables == null) {
                                priorVariables = new ArrayList<>();
                                priorVariables.add(new String(chars, offset, length));
                            }
                            // handle cyclic substitution
                            checkCyclicSubstitution(varName, priorVariables);
                            priorVariables.add(varName);
                            // resolve the variable
                            String varValue = resolveVariable(varName, buf, startPos, endPos);
                            if (varValue == null) {
                                varValue = varDefaultValue;
                            }
                            if (varValue != null) {
                                // recursive replace
                                final int varLen = varValue.length();
                                buf.replace(startPos, endPos, varValue);
                                altered = true;
                                substitutionLength += varLen;
                                if (substitutionLength > MAX_SUBSTITUTION_LENGTH) {
                                    throw new IllegalStateException("Maximum interpolation size (" + MAX_SUBSTITUTION_LENGTH
                                            + " characters) exceeded in variable substitution");
                                }
                                int change = substitute(buf, startPos, varLen, priorVariables);
                                change = change + varLen - (endPos - startPos);
                                pos += change;
                                escapeStart = pos;
                                bufEnd += change;
                                lengthChange += change;
                                chars = buf.buffer; // in case buffer was altered
                            }
                            // remove variable from the cyclic stack
                            priorVariables.remove(priorVariables.size() - 1);
                            break;
                        }
                        nestedVarCount--;
                        pos += endMatchLen;
                    }
                }
            }
        }
        if (top) {
            return altered ? 1 : 0;
        }
        return lengthChange;
    }
}