/* Copyright 2002-2026 CS GROUP
    * Licensed to CS GROUP (CS) under one or more
    * contributor license agreements.  See the NOTICE file distributed with
    * this work for additional information regarding copyright ownership.
    * CS 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
    *
    *   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 org.orekit.files.ccsds.utils.generation;
  
  import java.io.IOException;
  import java.util.ArrayDeque;
  import java.util.Deque;
  import java.util.HashMap;
  import java.util.List;
  import java.util.Map;
  
  import org.hipparchus.fraction.Fraction;
  import org.hipparchus.util.FastMath;
  import org.orekit.errors.OrekitException;
  import org.orekit.errors.OrekitInternalError;
  import org.orekit.errors.OrekitMessages;
  import org.orekit.files.ccsds.definitions.TimeConverter;
  import org.orekit.time.AbsoluteDate;
  import org.orekit.time.DateTimeComponents;
  import org.orekit.utils.Formatter;
  import org.orekit.utils.units.Parser;
  import org.orekit.utils.units.PowerTerm;
  import org.orekit.utils.units.Unit;
  
  /** Base class for both Key-Value Notation and eXtended Markup Language generators for CCSDS messages.
   * @author Luc Maisonobe
   * @since 11.0
   */
  public abstract class AbstractGenerator implements Generator {
  
      /** New line separator for output file. */
      private static final char NEW_LINE = '\n';
  
      /** Destination of generated output. */
      private final Appendable output;
  
      /** Output name for error messages. */
      private final String outputName;
  
      /** Maximum offset for relative dates.
       * @since 12.0
       */
      private final double maxRelativeOffset;
  
      /** Flag for writing units. */
      private final boolean writeUnits;
  
      /** Sections stack. */
      private final Deque<String> sections;
  
      /** Map from SI Units name to CCSDS unit names. */
      private final Map<String, String> siToCcsds;
  
      /** Used to format dates and doubles to string. */
      private final Formatter formatter;
  
      /** Simple constructor.
       * @param output destination of generated output
       * @param outputName output name for error messages
       * @param maxRelativeOffset maximum offset in seconds to use relative dates
       * (if a date is too far from reference, it will be displayed as calendar elements)
       * @param formatter how to format date and double to string.
       * @param writeUnits if true, units must be written
       */
      protected AbstractGenerator(final Appendable output, final String outputName,
                                  final double maxRelativeOffset, final boolean writeUnits,
                                  final Formatter formatter) {
          this.output            = output;
          this.outputName        = outputName;
          this.maxRelativeOffset = maxRelativeOffset;
          this.writeUnits        = writeUnits;
          this.sections          = new ArrayDeque<>();
          this.siToCcsds         = new HashMap<>();
          this.formatter = formatter;
      }
  
      /** {@inheritDoc} */
      @Override
      public String getOutputName() {
          return outputName;
      }
  
      /** {@inheritDoc} */
      @Override
      public Formatter getFormatter() { return formatter; }
 
     /** Check if unit must be written.
      * @param unit entry unit
      * @return true if units must be written
      */
     public boolean writeUnits(final Unit unit) {
         return writeUnits &&
                unit != null &&
                !unit.getName().equals(Unit.NONE.getName()) &&
                !unit.getName().equals(Unit.ONE.getName());
     }
 
     /** {@inheritDoc} */
     @Override
     public void close() throws IOException {
 
         // get out from all sections properly
         while (!sections.isEmpty()) {
             exitSection();
         }
 
     }
 
     /** {@inheritDoc} */
     @Override
     public void newLine() throws IOException {
         output.append(NEW_LINE);
     }
 
     /** {@inheritDoc} */
     @Override
     public void writeEntry(final String key, final List<String> value, final boolean mandatory) throws IOException {
         if (value == null || value.isEmpty()) {
             complain(key, mandatory);
         } else {
             final StringBuilder builder = new StringBuilder();
             boolean first = true;
             for (final String v : value) {
                 if (!first) {
                     builder.append(',');
                 }
                 builder.append(v);
                 first = false;
             }
             writeEntry(key, builder.toString(), null, mandatory);
         }
     }
 
     /** {@inheritDoc} */
     @Override
     public void writeEntry(final String key, final Enum<?> value, final boolean mandatory) throws IOException {
         writeEntry(key, value == null ? null : value.name(), null, mandatory);
     }
 
     /** {@inheritDoc} */
     @Override
     public void writeEntry(final String key, final TimeConverter converter, final AbsoluteDate date,
                            final boolean forceCalendar, final boolean mandatory)
         throws IOException {
         if (date == null) {
             writeEntry(key, (String) null, null, mandatory);
         } else {
             writeEntry(key,
                        forceCalendar ? dateToCalendarString(converter, date) : dateToString(converter, date),
                        null,
                        mandatory);
         }
     }
 
     /** {@inheritDoc} */
     @Override
     public void writeEntry(final String key, final double value, final Unit unit, final boolean mandatory) throws IOException {
         writeEntry(key, doubleToString(unit.fromSI(value)), unit, mandatory);
     }
 
     /** {@inheritDoc} */
     @Override
     public void writeEntry(final String key, final Double value, final Unit unit, final boolean mandatory) throws IOException {
         writeEntry(key, value == null ? null : doubleToString(unit.fromSI(value.doubleValue())), unit, mandatory);
     }
 
     /** {@inheritDoc} */
     @Override
     public void writeEntry(final String key, final char value, final boolean mandatory) throws IOException {
         writeEntry(key, Character.toString(value), null, mandatory);
     }
 
     /** {@inheritDoc} */
     @Override
     public void writeEntry(final String key, final int value, final boolean mandatory) throws IOException {
         writeEntry(key, Integer.toString(value), null, mandatory);
     }
 
     /** {@inheritDoc} */
     @Override
     public void writeRawData(final char data) throws IOException {
         output.append(data);
     }
 
     /** {@inheritDoc} */
     @Override
     public void writeRawData(final CharSequence data) throws IOException {
         output.append(data);
     }
 
     /** {@inheritDoc} */
     @Override
     public void enterSection(final String name) throws IOException {
         sections.offerLast(name);
     }
 
     /** {@inheritDoc} */
     @Override
     public String exitSection() throws IOException {
         return sections.pollLast();
     }
 
     /** Complain about a missing value.
      * @param key the keyword to write
      * @param mandatory if true, triggers en exception, otherwise do nothing
      */
     protected void complain(final String key, final boolean mandatory) {
         if (mandatory) {
             throw new OrekitException(OrekitMessages.CCSDS_MISSING_KEYWORD, key, outputName);
         }
     }
 
     /** {@inheritDoc} */
     @Override
     public String doubleToString(final double value) {
         return Double.isNaN(value) ? null : formatter.toString(value);
     }
 
     /** {@inheritDoc} */
     @Override
     public String dateToString(final TimeConverter converter, final AbsoluteDate date) {
 
         if (converter.getReferenceDate() != null) {
             final double relative = date.durationFrom(converter.getReferenceDate());
             if (FastMath.abs(relative) <= maxRelativeOffset) {
                 // we can use a relative date
                 return formatter.toString(relative);
             }
         }
 
         // display the date as calendar elements
         return dateToCalendarString(converter, date);
 
     }
 
     /** {@inheritDoc} */
     @Override
     public String dateToCalendarString(final TimeConverter converter, final AbsoluteDate date) {
         final DateTimeComponents dt = converter.components(date);
         return dateToString(dt);
     }
 
     /**
      * Convert a date to string value with high precision (attosecond accuracy).
      * @param dt date and time components to write
      * @return date as a string
      * @since 13.1.6
      */
     @Override
     public String dateToString(final DateTimeComponents dt) {
         return formatter.toString(dt);
     }
 
     /** {@inheritDoc} */
     @Override
     public String dateToString(final int year, final int month, final int day,
                                final int hour, final int minute, final double seconds) {
         return formatter.toString(year, month, day, hour, minute, seconds);
     }
 
     /** {@inheritDoc} */
     @Override
     public String unitsListToString(final List<Unit> units) {
 
         if (units == null || units.isEmpty()) {
             // nothing to output
             return null;
         }
 
         final StringBuilder builder = new StringBuilder();
         builder.append('[');
         boolean first = true;
         for (final Unit unit : units) {
             if (!first) {
                 builder.append(',');
             }
             builder.append(siToCcsdsName(unit.getName()));
             first = false;
         }
         builder.append(']');
         return builder.toString();
 
     }
 
     /** {@inheritDoc} */
     @Override
     public String siToCcsdsName(final String siName) {
 
         if (!siToCcsds.containsKey(siName)) {
 
             // build a name using only CCSDS syntax
             final StringBuilder builder = new StringBuilder();
 
             // parse the SI name that may contain fancy features like unicode superscripts, square roots sign…
             final List<PowerTerm> terms = Parser.buildTermsList(siName);
 
             if (terms == null) {
                 builder.append("n/a");
             } else {
 
                 // put the positive exponent first
                 boolean first = true;
                 for (final PowerTerm term : terms) {
                     if (term.getExponent().getNumerator() >= 0) {
                         if (!first) {
                             builder.append('*');
                         }
                         appendScale(builder, term.getScale());
                         appendBase(builder, term.getBase());
                         appendExponent(builder, term.getExponent());
                         first = false;
                     }
                 }
 
                 if (first) {
                     // no positive exponents at all, we add "1" to get something like "1/s"
                     builder.append('1');
                 }
 
                 // put the negative exponents last
                 for (final PowerTerm term : terms) {
                     if (term.getExponent().getNumerator() < 0) {
                         builder.append('/');
                         appendScale(builder, term.getScale());
                         appendBase(builder, term.getBase());
                         appendExponent(builder, term.getExponent().negate());
                     }
                 }
 
             }
 
             // put the converted name in the map for reuse
             siToCcsds.put(siName, builder.toString());
 
         }
 
         return siToCcsds.get(siName);
 
     }
 
     /** Append a scaling factor.
      * @param builder builder to which term must be added
      * @param scale scaling factor
      */
     private void appendScale(final StringBuilder builder, final double scale) {
         final int factor = (int) FastMath.rint(scale);
         if (FastMath.abs(scale - factor) > 1.0e-12) {
             // this should never happen with CCSDS units
             throw new OrekitInternalError(null);
         }
         if (factor != 1) {
             builder.append(factor);
         }
     }
 
     /** Append a base term.
      * @param builder builder to which term must be added
      * @param base base term
      */
     private void appendBase(final StringBuilder builder, final CharSequence base) {
         if ("°".equals(base) || "◦".equals(base)) {
             builder.append("deg");
         } else {
             builder.append(base);
         }
     }
 
     /** Append an exponent.
      * @param builder builder to which term must be added
      * @param exponent exponent to add
      */
     private void appendExponent(final StringBuilder builder, final Fraction exponent) {
         if (!exponent.equals(Fraction.ONE)) {
             builder.append("**");
             if (exponent.equals(Fraction.ONE_HALF)) {
                 builder.append("0.5");
             } else if (exponent.getNumerator() == 3 && exponent.getDenominator() == 2) {
                 builder.append("1.5");
             } else {
                 builder.append(exponent);
             }
         }
     }
 
 }