Dave Jarvis' Repositories

/*
 * Copyright 2020 White Magic Software, Ltd.
 *
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 *  o Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 *
 *  o Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 * HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */
package com.scrivenvar.processors;

import com.scrivenvar.Services;
import com.scrivenvar.preferences.UserPreferences;
import com.scrivenvar.service.Options;
import com.scrivenvar.service.events.Notifier;

import javax.script.ScriptEngine;
import javax.script.ScriptEngineManager;
import javax.script.ScriptException;
import java.nio.file.Path;
import java.util.LinkedHashMap;
import java.util.Map;

import static com.scrivenvar.Constants.STATUS_PARSE_ERROR;
import static com.scrivenvar.Messages.get;
import static com.scrivenvar.decorators.RVariableDecorator.PREFIX;
import static com.scrivenvar.decorators.RVariableDecorator.SUFFIX;
import static com.scrivenvar.processors.text.TextReplacementFactory.replace;
import static java.lang.Math.min;

/**
 * Transforms a document containing R statements into Markdown.
 */
public final class InlineRProcessor extends DefinitionProcessor {

  private static final Notifier sNotifier = Services.load( Notifier.class );
  private static final Options sOptions = Services.load( Options.class );

  /**
   * Constrain memory when typing new R expressions into the document.
   */
  private static final int MAX_CACHED_R_STATEMENTS = 512;

  /**
   * Where to put document inline evaluated R expressions.
   */
  private final Map<String, Object> mEvalCache = new LinkedHashMap<>() {
    @Override
    protected boolean removeEldestEntry(
        final Map.Entry<String, Object> eldest ) {
      return size() > MAX_CACHED_R_STATEMENTS;
    }
  };

  /**
   * Only one editor is open at a time.
   */
  private static final ScriptEngine ENGINE =
      (new ScriptEngineManager()).getEngineByName( "Renjin" );

  private static final int PREFIX_LENGTH = PREFIX.length();

  /**
   * Constructs a processor capable of evaluating R statements.
   *
   * @param processor Subsequent link in the processing chain.
   * @param map       Resolved definitions map.
   */
  public InlineRProcessor(
      final Processor<String> processor,
      final Map<String, String> map ) {
    super( processor, map );
    init();
  }

  /**
   * Initialises the R code so that R can find imported libraries.
   */
  private void init() {
    try {
      final Path wd = getWorkingDirectory();
      final String dir = wd.toString().replace( '\\', '/' );
      final Map<String, String> map = getDefinitions();
      map.put( "$application.r.working.directory$", dir );

      final String bootstrap = getBootstrapScript();

      if( !bootstrap.isBlank() ) {
        eval( replace( bootstrap, map ) );
      }
    } catch( final Exception ex ) {
      getNotifier().notify( ex );
    }
  }

  /**
   * Evaluates all R statements in the source document and inserts the
   * calculated value into the generated document.
   *
   * @param text The document text that includes variables that should be
   *             replaced with values when rendered as HTML.
   * @return The generated document with output from all R statements
   * substituted with value returned from their execution.
   */
  @Override
  public String process( final String text ) {
    final int length = text.length();

    // The * 2 is a wild guess at the ratio of R statements to the length
    // of text produced by those statements.
    final StringBuilder sb = new StringBuilder( length * 2 );

    int prevIndex = 0;
    int currIndex = text.indexOf( PREFIX );

    while( currIndex >= 0 ) {
      // Copy everything up to, but not including, an R statement (`r#).
      sb.append( text, prevIndex, currIndex );

      // Jump to the start of the R statement.
      prevIndex = currIndex + PREFIX_LENGTH;

      // Find the statement ending (`), without indexing past the text boundary.
      currIndex = text.indexOf( SUFFIX, min( currIndex + 1, length ) );

      // Only evaluate inline R statements that have end delimiters.
      if( currIndex > 1 ) {
        // Extract the inline R statement to be evaluated.
        final String r = text.substring( prevIndex, currIndex );

        // Pass the R statement into the R engine for evaluation.
        try {
          final Object result = evalText( r );

          // Append the string representation of the result into the text.
          sb.append( result );
        } catch( final Exception e ) {
          // If the string couldn't be parsed using R, append the statement
          // that failed to parse, instead of its evaluated value.
          sb.append( PREFIX ).append( r ).append( SUFFIX );

          // Tell the user that there was a problem.
          getNotifier().notify(
              get( STATUS_PARSE_ERROR, e.getMessage(), currIndex )
          );
        }

        // Retain the R statement's ending position in the text.
        prevIndex = currIndex + 1;
      }

      // Find the start of the next inline R statement.
      currIndex = text.indexOf( PREFIX, min( currIndex + 1, length ) );
    }

    // Copy from the previous index to the end of the string.
    return sb.append( text.substring( min( prevIndex, length ) ) ).toString();
  }

  /**
   * Look up an R expression from the cache then return the resulting object.
   * If the R expression hasn't been cached, it'll first be evaluated.
   *
   * @param r The expression to evaluate.
   * @return The object resulting from the evaluation.
   */
  private Object evalText( final String r ) {
    return mEvalCache.computeIfAbsent( r, v -> eval( r ) );
  }

  /**
   * Evaluate an R expression and return the resulting object.
   *
   * @param r The expression to evaluate.
   * @return The object resulting from the evaluation.
   */
  private Object eval( final String r ) {
    try {
      return getScriptEngine().eval( r );
    } catch( final ScriptException ex ) {
      getNotifier().notify( ex );
      return "";
    }
  }

  /**
   * This will return the given path if not null, otherwise it will return
   * the path to the user's directory.
   *
   * @return A non-null path.
   */
  private Path getWorkingDirectory() {
    return getUserPreferences().getRDirectory().toPath();
  }

  /**
   * Loads the R init script from the application's persisted preferences.
   *
   * @return A non-null String, possibly empty.
   */
  private String getBootstrapScript() {
    return getUserPreferences().getRScript();
  }

  private UserPreferences getUserPreferences() {
    return sOptions.getUserPreferences();
  }

  private ScriptEngine getScriptEngine() {
    return ENGINE;
  }

  private Notifier getNotifier() {
    return sNotifier;
  }
}