#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;
using System.IO;
using System.Text;

namespace Nuclex.Support.Parsing {

  /// <summary>Parses and stores an application's command line parameters</summary>
  /// <remarks>
  ///   <para>
  ///     At the time of the creation of this component, there are already several command
  ///     line parsing libraries out there. Most of them, however, do way too much at once
  ///     or at the very least rely on huge, untested clutters of classes and methods to
  ///     arrive at their results.
  ///   </para>
  ///   <para>
  ///     This command line parser does nothing more than represent the command line to
  ///     the application through a convenient interface. It parses a command line and
  ///     extracts the arguments, but doesn't interpret them and or check them for validity.
  ///   </para>
  ///   <para>
  ///     This design promotes simplicity and makes is an ideal building block to create
  ///     actual command line interpreters that connect the parameters to program
  ///     instructions and or fill structures in code.
  ///   </para>
  ///   <para>
  ///     Terminology
  ///     <list type="table">
  ///       <item>
  ///         <term>Command line</term>
  ///         <description>
  ///           The entire command line either as a string or as
  ///           an already parsed data structure
  ///         </description>
  ///       </item>
  ///       <item>
  ///         <term>Argument</term>
  ///         <description>
  ///           Either an option or a loose value (see below) being specified on
  ///           the command line
  ///         </description>
  ///       </item>
  ///       <item>
  ///         <term>Option</term>
  ///         <description>
  ///           Can be specified on the command line and typically alters the behavior
  ///           of the application or changes a setting. For example, '--normalize' or
  ///           '/safemode'.
  ///         </description>
  ///       </item>
  ///       <item>
  ///         <term>Value</term>
  ///         <description>
  ///           Can either sit loosely in the command line (eg. 'update' or 'textfile.txt')
  ///           or as assignment to an option (eg. '--width=1280' or '/overwrite:always')
  ///         </description>
  ///       </item>
  ///     </list>
  ///   </para>
  /// </remarks>
  public partial class CommandLine {

    /// <summary>
    ///   Whether the command line should use Windows mode by default
    /// </summary>
    public static readonly bool WindowsModeDefault =
      (Path.DirectorySeparatorChar == '\\');

    /// <summary>Initializes a new command line</summary>
    public CommandLine() :
      this(new List<Argument>(), WindowsModeDefault) { }

    /// <summary>Initializes a new command line</summary>
    /// <param name="windowsMode">Whether the / character initiates an argument</param>
    public CommandLine(bool windowsMode) :
      this(new List<Argument>(), windowsMode) { }

    /// <summary>Initializes a new command line</summary>
    /// <param name="argumentList">List containing the parsed arguments</param>
    private CommandLine(IList<Argument> argumentList) :
      this(argumentList, WindowsModeDefault) { }

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

    /// <summary>Parses the command line arguments from the provided string</summary>
    /// <param name="commandLineString">String containing the command line arguments</param>
    /// <returns>The parsed command line</returns>
    /// <remarks>
    ///   You should always pass Environment.CommandLine to this method to avoid
    ///   some problems with the built-in command line tokenizer in .NET
    ///   (which splits '--test"hello world"/v' into '--testhello world/v')
    /// </remarks>
    public static CommandLine Parse(string commandLineString) {
      bool windowsMode = (Path.DirectorySeparatorChar != '/');
      return Parse(commandLineString, windowsMode);
    }

    /// <summary>Parses the command line arguments from the provided string</summary>
    /// <param name="commandLineString">String containing the command line arguments</param>
    /// <param name="windowsMode">Whether the / character initiates an argument</param>
    /// <returns>The parsed command line</returns>
    /// <remarks>
    ///   You should always pass Environment.CommandLine to this methods to avoid
    ///   some problems with the built-in command line tokenizer in .NET
    ///   (which splits '--test"hello world"/v' into '--testhello world/v')
    /// </remarks>
    public static CommandLine Parse(string commandLineString, bool windowsMode) {
      return new CommandLine(
        Parser.Parse(commandLineString, windowsMode)
      );
    }

    /// <summary>Returns whether an argument with the specified name exists</summary>
    /// <param name="name">Name of the argument whose existence will be checked</param>
    /// <returns>True if an argument with the specified name exists</returns>
    public bool HasArgument(string name) {
      return (indexOfArgument(name) != -1);
    }

    /// <summary>Adds a value to the command line</summary>
    /// <param name="value">Value that will be added</param>
    public void AddValue(string value) {
      int valueLength = (value != null) ? value.Length : 0;

      if(requiresQuotes(value)) {
        StringBuilder builder = new StringBuilder(valueLength + 2);
        builder.Append('"');
        builder.Append(value);
        builder.Append('"');

        this.arguments.Add(
          Argument.ValueOnly(
            new StringSegment(builder.ToString(), 0, valueLength + 2),
            1,
            valueLength
          )
        );
      } else {
        this.arguments.Add(
          Argument.ValueOnly(new StringSegment(value), 0, valueLength)
        );
      }
    }

    /// <summary>Adds an option to the command line</summary>
    /// <param name="name">Name of the option that will be added</param>
    public void AddOption(string name) {
      AddOption("-", name);
    }

    /// <summary>Adds an option to the command line</summary>
    /// <param name="initiator">Initiator that will be used to start the option</param>
    /// <param name="name">Name of the option that will be added</param>
    public void AddOption(string initiator, string name) {
      StringBuilder builder = new StringBuilder(initiator.Length + name.Length);
      builder.Append(initiator);
      builder.Append(name);

      this.arguments.Add(
        Argument.OptionOnly(
          new StringSegment(builder.ToString()),
          initiator.Length,
          name.Length
        )
      );
    }

    /// <summary>Adds an option with an assignment to the command line</summary>
    /// <param name="name">Name of the option that will be added</param>
    /// <param name="value">Value that will be assigned to the option</param>
    public void AddAssignment(string name, string value) {
      AddAssignment("-", name, value);
    }

    /// <summary>Adds an option with an assignment to the command line</summary>
    /// <param name="initiator">Initiator that will be used to start the option</param>
    /// <param name="name">Name of the option that will be added</param>
    /// <param name="value">Value that will be assigned to the option</param>
    public void AddAssignment(string initiator, string name, string value) {
      bool valueContainsSpaces = containsWhitespace(value);
      StringBuilder builder = new StringBuilder(
        initiator.Length + name.Length + 1 + value.Length + (valueContainsSpaces ? 2 : 0)
      );
      builder.Append(initiator);
      builder.Append(name);
      builder.Append('=');
      if(valueContainsSpaces) {
        builder.Append('"');
        builder.Append(value);
        builder.Append('"');
      } else {
        builder.Append(value);
      }

      this.arguments.Add(
        new Argument(
          new StringSegment(builder.ToString()),
          initiator.Length,
          name.Length,
          initiator.Length + name.Length + 1 + (valueContainsSpaces ? 1 : 0),
          value.Length
        )
      );
    }

    /// <summary>Returns a string that contains the entire command line</summary>
    /// <returns>The entire command line as a single string</returns>
    public override string ToString() {
      return Formatter.FormatCommandLine(this);
    }

    /// <summary>Retrieves the index of the argument with the specified name</summary>
    /// <param name="name">Name of the argument whose index will be returned</param>
    /// <returns>
    ///   The index of the indicated argument of -1 if no argument with that name exists
    /// </returns>
    private int indexOfArgument(string name) {
      for(int index = 0; index < this.arguments.Count; ++index) {
        if(this.arguments[index].Name == name) {
          return index;
        }
      }

      return -1;
    }

    /// <summary>Options that were specified on the command line</summary>
    public IList<Argument> Arguments {
      get { return this.arguments; }
    }

    /// <summary>
    ///   Determines whether the string requires quotes to survive the command line
    /// </summary>
    /// <param name="value">Value that will be checked for requiring quotes</param>
    /// <returns>True if the value requires quotes to survive the command line</returns>
    private bool requiresQuotes(string value) {

      // If the value is empty, it needs quotes to become visible as an argument
      // (versus being intepreted as spacing between other arguments)
      if(string.IsNullOrEmpty(value)) {
        return true;
      }

      // Any whitespace characters force us to use quotes, so does a minus sign
      // at the beginning of the value (otherwise, it would become an option argument)
      bool requiresQuotes =
        containsWhitespace(value) ||
        (value[0] == '-');

      // On windows, option arguments can also be starten with the forward slash
      // character, so we require quotes as well if the value starts with one
      if(this.windowsMode) {
        requiresQuotes |= (value[0] == '/');
      }

      return requiresQuotes;

    }

    /// <summary>
    ///   Determines whether the string contains any whitespace characters
    /// </summary>
    /// <param name="value">String that will be scanned for whitespace characters</param>
    /// <returns>True if the provided string contains whitespace characters</returns>
    private static bool containsWhitespace(string value) {
      return
        (value.IndexOf(' ') != -1) ||
        (value.IndexOf('\t') != -1);
    }

    /// <summary>Options that were specified on the command line</summary>
    private IList<Argument> arguments;
    /// <summary>Whether the / character initiates an argument</summary>
    private bool windowsMode;

  }

} // namespace Nuclex.Support.Parsing