#region Apache License 2.0
/*
Nuclex .NET Framework
Copyright (C) 2002-2024 Markus Ewald / Nuclex Development Labs

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.
*/
#endregion // Apache License 2.0

using System;
using System.Collections.Generic;

namespace Nuclex.Support.Parsing {

  partial class CommandLine {

    /// <summary>Parses command line strings</summary>
    private class Parser {

      /// <summary>Initializes a new command line parser</summary>
      /// <param name="windowsMode">Whether the / character initiates an argument</param>
      private Parser(bool windowsMode) {
        this.windowsMode = windowsMode;
        this.arguments = new List<CommandLine.Argument>();
      }

      /// <summary>Parses a string containing command line arguments</summary>
      /// <param name="commandLineString">String that will be parsed</param>
      /// <param name="windowsMode">Whether the / character initiates an argument</param>
      /// <returns>The parsed command line arguments from the string</returns>
      public static List<CommandLine.Argument> Parse(
        string commandLineString, bool windowsMode
      ) {
        Parser theParser = new Parser(windowsMode);
        theParser.parseFullCommandLine(commandLineString);
        return theParser.arguments;
      }

      /// <summary>
      ///   Parses the provided string and adds the parameters found to
      ///   the command line representation
      /// </summary>
      /// <param name="commandLineString">
      ///   String containing the command line arguments that will be parsed
      /// </param>
      private void parseFullCommandLine(string commandLineString) {
        if(commandLineString == null) {
          return;
        }

        // Walk through the command line character by character and gather
        // the parameters and values to build the command line representation from
        for(int index = 0; index < commandLineString.Length; ) {

          // Look for the next non-whitespace character
          index = StringHelper.IndexNotOfAny(
            commandLineString, WhitespaceCharacters, index
          );
          if(index == -1) {
            break;
          }

          // Parse the chunk of characters at this location and advance the index
          // to the next location after the chunk of characters
          parseChunk(commandLineString, ref index);

        }
      }

      /// <summary>
      ///   Parses a chunk of characters and adds it as an option or a loose value to
      ///   the command line representation we're building
      /// </summary>
      /// <param name="commandLineString">
      ///   String containing the chunk of characters that will be parsed
      /// </param>
      /// <param name="index">Index in the string at which to begin parsing</param>
      /// <returns>The number of characters that were consumed</returns>
      private void parseChunk(string commandLineString, ref int index) {
        int startIndex = index;

        char currentCharacter = commandLineString[index];
        switch(currentCharacter) {

          // Unix style argument using either '-' or "--" as its initiator
          case '-': {
            ++index;

            // Does the string end here? Stop parsing.
            if(index >= commandLineString.Length) {
              addValue(new StringSegment(commandLineString, startIndex, 1));
              break;
            }

            // Does another '-' follow? Might be a unix style option or a loose "--"
            if(commandLineString[index] == '-') {
              ++index;
            }

            parsePotentialOption(commandLineString, startIndex, ref index);

            break;
          }

          // Windows style argument using '/' as its initiator
          case '/': {
            // The '/ character is only used to initiate argument on windows and can be
            // toggled off. The application decides whether this is done depending on the
            // operating system or whether uniform behavior across platforms is desired.
            if(!this.windowsMode) {
              goto default;
            }

            ++index;
            parsePotentialOption(commandLineString, startIndex, ref index);
            break;
          }

          // Quoted loose value
          case '"': {
            parseQuotedValue(commandLineString, ref index);
            break;
          }

          // Unquoted loose value
          default: {
            parseNakedValue(commandLineString, ref index);
            break;
          }

        }
      }

      /// <summary>Parses a potential command line option</summary>
      /// <param name="commandLineString">String containing the command line arguments</param>
      /// <param name="initiatorStartIndex">
      ///   Index of the option's initiator ('-' or '--' or '/')
      /// </param>
      /// <param name="index">
      ///   Index at which the option name is supposed start (if it's an actual option)
      /// </param>
      /// <returns>The number of characters consumed</returns>
      private void parsePotentialOption(
        string commandLineString, int initiatorStartIndex, ref int index
      ) {

        // If the string ends here this can only be considered as a loose value
        if(index == commandLineString.Length) {
          addValue(
            new StringSegment(
              commandLineString,
              initiatorStartIndex,
              commandLineString.Length - initiatorStartIndex
            )
          );
          return;
        }

        int nameStartIndex = index;

        // Look for the first character that ends the option. If it is not an actual option,
        // the very first character might be the end
        if(commandLineString[index] != commandLineString[initiatorStartIndex]) {
          index = commandLineString.IndexOfAny(NameEndingCharacters, nameStartIndex);
          if(index == -1) {
            index = commandLineString.Length;
          }
        }

        // If the first character of the supposed option is not valid for an option name,
        // we have to consider this to be a loose value        
        if((index == nameStartIndex)/* && !isAssignmentCharacter(commandLineString[index])*/) {
          index = commandLineString.IndexOfAny(WhitespaceCharacters, index);
          if(index == -1) {
            index = commandLineString.Length;
          }

          addValue(
            new StringSegment(
              commandLineString, initiatorStartIndex, index - initiatorStartIndex
            )
          );
          return;
        }

        parsePotentialOptionAssignment(
          commandLineString, initiatorStartIndex, nameStartIndex, ref index
        );

      }

      /// <summary>Parses the value assignment in a command line option</summary>
      /// <param name="commandLineString">String containing the command line arguments</param>
      /// <param name="initiatorStartIndex">
      ///   Position of the character that started the option
      /// </param>
      /// <param name="nameStartIndex">
      ///   Position of the first character in the option's name
      /// </param>
      /// <param name="index">Index at which the option name ended</param>
      private void parsePotentialOptionAssignment(
        string commandLineString, int initiatorStartIndex, int nameStartIndex, ref int index
      ) {
        int nameEndIndex = index;
        int valueStartIndex;
        int valueEndIndex;

        // See if this is an assignment character. If it is, the assigned value
        // should follow to the right.
        bool isAssignment =
          (index < commandLineString.Length) &&
          isAssignmentCharacter(commandLineString[index]);

        // If it's an assignment, we can proceed parsing the assigned value
        if(isAssignment) {
          ++index;
          parseOptionValue(commandLineString, initiatorStartIndex, nameStartIndex, ref index);
          return;
        } else { // No, it's an option name without an assignment

          bool isModifier =
            (commandLineString[index - 1] == '+') ||
            (commandLineString[index - 1] == '-');

          if(isModifier) {
            valueStartIndex = index - 1;
            valueEndIndex = index;
            --nameEndIndex;
          } else {
            valueStartIndex = -1;
            valueEndIndex = -1;
          }
        }

        int argumentLength = index - initiatorStartIndex;
        this.arguments.Add(
          new Argument(
            new StringSegment(commandLineString, initiatorStartIndex, argumentLength),
            nameStartIndex, nameEndIndex - nameStartIndex,
            valueStartIndex, valueEndIndex - valueStartIndex
          )
        );
      }

      /// <summary>Parses the value assignment in a command line option</summary>
      /// <param name="commandLineString">String containing the command line arguments</param>
      /// <param name="initiatorStartIndex">
      ///   Position of the character that started the option
      /// </param>
      /// <param name="nameStartIndex">
      ///   Position of the first character in the option's name
      /// </param>
      /// <param name="index">Index at which the option name ended</param>
      private void parseOptionValue(
        string commandLineString, int initiatorStartIndex, int nameStartIndex, ref int index
      ) {
        int nameEndIndex = index - 1;
        int valueStartIndex, valueEndIndex;

        // Does the string end after the suspected assignment character?
        bool argumentEndReached = (index == commandLineString.Length);

        if(argumentEndReached) {
          valueStartIndex = -1;
          valueEndIndex = -1;
        } else {
          char nextCharacter = commandLineString[index];

          // Is this a quoted assignment
          if(nextCharacter == '"') {
            ++index;
            valueStartIndex = index;
            index = commandLineString.IndexOf('"', index);
            if(index == -1) {
              index = commandLineString.Length;
              valueEndIndex = index;
            } else {
              valueEndIndex = index;
              ++index;
            }
          } else { // Nope, assuming unquoted assignment or empty assignment
            valueStartIndex = index;
            index = commandLineString.IndexOfAny(WhitespaceCharacters, index);
            if(index == -1) {
              index = commandLineString.Length;
              valueEndIndex = index;
            } else {
              if(index == valueStartIndex) {
                valueStartIndex = -1;
                valueEndIndex = -1;
              } else {
                valueEndIndex = index;
              }
            }
          }
        }

        int argumentLength = index - initiatorStartIndex;
        this.arguments.Add(
          new Argument(
            new StringSegment(commandLineString, initiatorStartIndex, argumentLength),
            nameStartIndex, nameEndIndex - nameStartIndex,
            valueStartIndex, valueEndIndex - valueStartIndex
          )
        );
      }

      /// <summary>Parses a quoted value from the input string</summary>
      /// <param name="commandLineString">String the quoted value is parsed from</param>
      /// <param name="index">Index at which the quoted value begins</param>
      private void parseQuotedValue(string commandLineString, ref int index) {
        int startIndex = index;
        char quoteCharacter = commandLineString[index];
        int valueIndex = startIndex + 1;

        // Search for the closing quote
        index = commandLineString.IndexOf(quoteCharacter, valueIndex);
        if(index == -1) {
          index = commandLineString.Length; // value ends at string end
          this.arguments.Add(
            Argument.ValueOnly(
              new StringSegment(commandLineString, startIndex, index - startIndex),
              valueIndex, index - valueIndex
            )
          );
        } else { // A closing quote was found
          this.arguments.Add(
            Argument.ValueOnly(
              new StringSegment(commandLineString, startIndex, index - startIndex + 1),
              valueIndex, index - valueIndex
            )
          );
          ++index; // Skip the closing quote
        }
      }

      /// <summary>Parses a plain, unquoted value from the input string</summary>
      /// <param name="commandLineString">String containing the value to be parsed</param>
      /// <param name="index">Index at which the value begins</param>
      private void parseNakedValue(string commandLineString, ref int index) {
        int startIndex = index;

        index = commandLineString.IndexOfAny(WhitespaceCharacters, index);
        if(index == -1) {
          index = commandLineString.Length;
        }

        addValue(new StringSegment(commandLineString, startIndex, index - startIndex));
      }

      /// <summary>Adds a loose value to the command line</summary>
      /// <param name="value">Value taht will be added</param>
      private void addValue(StringSegment value) {
        this.arguments.Add(
          Argument.ValueOnly(value, value.Offset, value.Count)
        );
      }

      /// <summary>
      ///   Determines whether the specified character indicates an assignment
      /// </summary>
      /// <param name="character">
      ///   Character that will be checked for being an assignemnt
      /// </param>
      /// <returns>
      ///   True if the specified character indicated an assignment, otherwise false
      /// </returns>
      private static bool isAssignmentCharacter(char character) {
        return (character == ':') || (character == '=');
      }

      /// <summary>Characters which end an option name when they are encountered</summary>
      private static readonly char[] NameEndingCharacters = new char[] {
        ' ', '\t', '=', ':', '"'
      };

      /// <summary>Characters the parser considers to be whitespace</summary>
      private static readonly char[] WhitespaceCharacters = new char[] { ' ', '\t' };

      /// <summary>Argument list being filled by the parser</summary>
      private List<CommandLine.Argument> arguments;
      /// <summary>Whether the '/' character initiates an argument</summary>
      private bool windowsMode;

    }

  }

} // namespace Nuclex.Support.Parsing