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

namespace Nuclex.Support.Settings {

  /// <summary>Represents an ini- or cfg-like configuration file</summary>
  /// <remarks>
  ///   <para>
  ///     This class tries its best to preserve the formatting of configuration files.
  ///     Changing a value will keep the line it appears in intact. The parser also takes
  ///     as much data from a line as it can - anything to the left of an equals sign
  ///     becomes the name, anything to the right (excluding comments) becomes the value.
  ///   </para>
  ///   <para>
  ///     To access the contents of a configuration file, simply parse it and use it like
  ///     you would any other settings store:
  ///   </para>
  ///   <example>
  ///     <code>
  ///       // # Settings.ini
  ///       // message = hello world      ; the usual...
  ///       // show message = true
  ///       ISettingsStore settings;
  ///       using(var reader = new StreamReader("settings.ini")) {
  ///         settings = ConfigurationFile.Parse(reader);
  ///       }
  ///
  ///       if(settings.Get&lt;bool&gt;(null, "show message")) {
  ///         Console.WriteLine(settings.Get&lt;string&gt;(null, "message"));
  ///       }
  ///     </code>
  ///   </example>
  ///   <para>
  ///     It's usually a good idea to keep an application and all of its required files
  ///     together, whether it's code or data, but platforms often have their own conventions:
  ///   </para>
  ///   <list type="bullet">
  ///     <listheader>
  ///       <term>Operating System</term>
  ///       <description>Convention</description>
  ///     </listheader>
  ///     <item>
  ///       <term>Linux</term>
  ///       <description>
  ///         System-wide configuration goes into /etc/&lt;appname&gt;/, user-specific
  ///         configuration goes into ~/.&lt;appname&gt;/ while static configuration that is
  ///         known at build time resides with the application in /opt/&lt;appname&gt;/
  ///       </description>
  ///     </item>
  ///     <item>
  ///       <term>Windows</term>
  ///       <description>
  ///         System-wide configuration goes into %ProgramData%, user-specific configuration
  ///         has no real place (try %AppData%/&lt;appname&gt;/ if you want to hide it from
  ///         the user, %UserProfile%/Documents/&lt;appname&gt; if the user should see it)
  ///         and static configuration resides with your application
  ///         in %ProgramFiles%/&lt;appname&gt;/.
  ///       </description>
  ///     </item>
  ///     <item>
  ///       <term>MacOS</term>
  ///       <description>
  ///         System-wide configuration goes into /etc/&lt;appname&gt;/, user-specific
  ///         configuration goes into /Users/&lt;username&gt;/.&lt;appname&gt;/ while static
  ///         configuration resides with the application in /Applications/&lt;appname&gt;/
  ///       </description>
  ///     </item>
  ///   </list>
  /// </remarks>
  public partial class ConfigurationFileStore : ISettingsStore {

    #region class Category

    /// <summary>Stores informations about a category found in the configuration file</summary>
    private class Category {

      /// <summary>Name of the category as a string</summary>
      public StringSegment CategoryName;

      /// <summary>Lookup table for the options in this category</summary>
      public IDictionary<string, Option> OptionLookup;

      /// <summary>Lines this category and its options consist of</summary>
      public IList<string> Lines;

    }

    #endregion // class Category

    #region class Option

    /// <summary>Stores informations about an option found in the configuration file</summary>
    private class Option {

      /// <summary>Index of the line the option is defined in</summary>
      public int LineIndex;

      /// <summary>Name of the option as a string</summary>
      public StringSegment OptionName;

      /// <summary>Value of the option as a string</summary>
      public StringSegment OptionValue;

    }

    #endregion // class Option

    /// <summary>Initializes a new, empty configuration file</summary>
    public ConfigurationFileStore() {
      this.options = new List<Option>();
      this.categoryLookup = new Dictionary<string, Category>();
      this.rootCategory = new Category() {
        OptionLookup = new Dictionary<string, Option>(),
        Lines = new List<string>()
      };
    }

    /// <summary>Saves the configuration file into the specified writer</summary>
    /// <param name="writer">Writer the configuration file will be saved into</param>
    public void Save(TextWriter writer) {
      for(int index = 0; index < this.rootCategory.Lines.Count; ++index) {
        writer.WriteLine(this.rootCategory.Lines[index]);
      }
      foreach(Category category in this.categoryLookup.Values) {
        for(int index = 0; index < category.Lines.Count; ++index) {
          writer.WriteLine(category.Lines[index]);
        }
      }
    }

    /// <summary>Enumerates the categories defined in the configuration</summary>
    /// <returns>An enumerable list of all used categories</returns>
    public IEnumerable<string> EnumerateCategories() {
      return this.categoryLookup.Keys;
    }

    /// <summary>Enumerates the options stored under the specified category</summary>
    /// <param name="category">Category whose options will be enumerated</param>
    /// <returns>An enumerable list of all options in the category</returns>
    public IEnumerable<OptionInfo> EnumerateOptions(string category = null) {
      Category enumeratedCategory = getCategoryByName(category);
      if(enumeratedCategory == null) {
        yield break;
      }

      foreach(Option option in this.rootCategory.OptionLookup.Values) {
        OptionInfo optionInfo = new OptionInfo() {
          Name = option.OptionName.ToString(),
          OptionType = getBestMatchingType(ref option.OptionValue)
        };
        yield return optionInfo;
      }
    }

    /// <summary>Retrieves the value of the specified option</summary>
    /// <typeparam name="TValue">Type the option will be converted to</typeparam>
    /// <param name="category">Category the option can be found in. Can be null.</param>
    /// <param name="optionName">Name of the option that will be looked up</param>
    /// <returns>The value of the option with the specified name</returns>
    public TValue Get<TValue>(string category, string optionName) {
      TValue value;
      if(TryGet<TValue>(category, optionName, out value)) {
        return value;
      } else {
        if(string.IsNullOrEmpty(category)) {
          throw new KeyNotFoundException(
            "There is no option named '" + optionName + "' in the configuration file"
          );
        } else {
          throw new KeyNotFoundException(
            "There is no option named '" + optionName + "' under the category '" +
            category + "' in the configuration file"
          );
        }
      }
    }

    /// <summary>Tries to retrieve the value of the specified option</summary>
    /// <typeparam name="TValue">Type the option will be converted to</typeparam>
    /// <param name="category">Category the option can be found in. Can be null.</param>
    /// <param name="optionName">Name of the option that will be looked up</param>
    /// <param name="value">Will receive the value of the option, if found</param>
    /// <returns>
    ///   True if the option existed and its value was written into the <paramref name="value" />
    ///   parameter, false otherwise
    /// </returns>
    public bool TryGet<TValue>(string category, string optionName, out TValue value) {
      Category containingCategory = getCategoryByName(category);
      if(containingCategory != null) {
        Option option;
        if(containingCategory.OptionLookup.TryGetValue(optionName, out option)) {
          if(typeof(TValue) == typeof(bool)) {
            bool? boolean = parseBooleanLiteral(ref option.OptionValue);
            if(boolean.HasValue) {
              value = (TValue)(object)boolean.Value;
              return true;
            } else {
              throw new FormatException(
                "The value '" + option.OptionValue.ToString() + "' is not a boolean"
              );
            }
          } else {
            value = (TValue)Convert.ChangeType(option.OptionValue.ToString(), typeof(TValue));
            return true;
          }
        }
      }

      value = default(TValue);
      return false;
    }

    /// <summary>Saves an option in the settings store</summary>
    /// <typeparam name="TValue">Type of value that will be saved</typeparam>
    /// <param name="category">Category the option will be placed in. Can be null.</param>
    /// <param name="optionName">Name of the option that will be saved</param>
    /// <param name="value">The value under which the option will be saved</param>
    public void Set<TValue>(string category, string optionName, TValue value) {
      string valueAsString = (string)Convert.ChangeType(
        value, typeof(string), CultureInfo.InvariantCulture
      );

      Category targetCategory;
      if(string.IsNullOrEmpty(category)) {
        targetCategory = this.rootCategory;
      } else if(!this.categoryLookup.TryGetValue(category, out targetCategory)) {
        targetCategory = createCategory(category);
        createOption(targetCategory, optionName, valueAsString);
        return;
      }

      Option targetOption;
      if(targetCategory.OptionLookup.TryGetValue(optionName, out targetOption)) {
        changeOption(targetCategory, targetOption, valueAsString);
      } else {
        createOption(targetCategory, optionName, valueAsString);
      }
    }

    /// <summary>Removes the option with the specified name</summary>
    /// <param name="category">Category the option is found in. Can be null.</param>
    /// <param name="optionName">Name of the option that will be removed</param>
    /// <returns>True if the option was found and removed</returns>
    public bool Remove(string category, string optionName) {
      Category sourceCategory = getCategoryByName(category);
      if(sourceCategory == null) {
        return false;
      }

      Option option;
      if(!sourceCategory.OptionLookup.TryGetValue(optionName, out option)) {
        return false;
      }

      sourceCategory.Lines.RemoveAt(option.LineIndex);
      sourceCategory.OptionLookup.Remove(optionName);

      foreach(Option shiftedOption in sourceCategory.OptionLookup.Values) {
        if(shiftedOption.LineIndex > option.LineIndex) {
          --shiftedOption.LineIndex;
        }
      }

      return true;
    }

    /// <summary>Looks a category up by its name</summary>
    /// <param name="categoryName">
    ///   Name of the category. Can be null for the root category
    /// </param>
    /// <returns>The category with the specified name</returns>
    private Category getCategoryByName(string categoryName) {
      Category category;

      if(string.IsNullOrEmpty(categoryName)) {
        category = this.rootCategory;
      } else if(!this.categoryLookup.TryGetValue(categoryName, out category)) {
        return null;
      }

      return category;
    }

    /// <summary>Creates a new option</summary>
    /// <param name="category">Category the option will be added to</param>
    /// <param name="name">Name of the option</param>
    /// <param name="value">Value that will be assigned to the option</param>
    private void createOption(Category category, string name, string value) {
      int valueLength;
      if(value == null) {
        valueLength = 0;
      } else {
        valueLength = value.Length;
      }

      // Build the complete line containing the option assignment
      string line;
      {
        StringBuilder builder = new StringBuilder(name.Length + 3 + valueLength);

        builder.Append(name);
        builder.Append(" = ");
        if(valueLength > 0) {
          builder.Append(value);
        }

        line = builder.ToString();
      }

      Option newOption = new Option() {
        OptionName = new StringSegment(line, 0, name.Length),
        OptionValue = new StringSegment(line, name.Length + 3, valueLength)
      };

      // Figure out which line the new option should be put in
      int lastLineIndex = category.Lines.Count - 1;
      if((lastLineIndex > 0) && (category.Lines[lastLineIndex].Length == 0)) {
        newOption.LineIndex = lastLineIndex;
        category.Lines.Insert(lastLineIndex, line);
      } else {
        newOption.LineIndex = category.Lines.Count;
        category.Lines.Add(line);
        category.Lines.Add(string.Empty);
      }

      category.OptionLookup.Add(name, newOption);
    }

    /// <summary>Changes the value of an option</summary>
    /// <param name="category">Category that holds the option</param>
    /// <param name="option">Option whose value will be changed</param>
    /// <param name="newValue">New value that will be assigned to the option</param>
    private void changeOption(Category category, Option option, string newValue) {
      int newValueLength;
      if(newValue == null) {
        newValueLength = 0;
      } else {
        newValueLength = newValue.Length;
      }

      // Form the new line
      string line = option.OptionValue.Text;
      {
        StringBuilder builder = new StringBuilder(
          line.Length - option.OptionValue.Count + newValueLength
        );

        // Stuff before the value
        if(option.OptionValue.Offset > 0) {
          builder.Append(line, 0, option.OptionValue.Offset);
        }

        // The value itself
        if(newValueLength > 0) {
          builder.Append(newValue);
        }

        // Stuff after the value
        int endIndex = option.OptionValue.Offset + option.OptionValue.Count;
        if(endIndex < line.Length) {
          builder.Append(line, endIndex, line.Length - endIndex);
        }

        line = builder.ToString();
      }

      option.OptionValue = new StringSegment(line, option.OptionValue.Offset, newValueLength);
      category.Lines[option.LineIndex] = line;
    }

    /// <summary>Creates a new category in the configuration file</summary>
    /// <param name="category">Name of the new category</param>
    /// <returns>The category that was created</returns>
    private Category createCategory(string category) {
      string categoryDefinition;
      {
        StringBuilder builder = new StringBuilder(category.Length + 2);
        builder.Append('[');
        builder.Append(category);
        builder.Append(']');
        categoryDefinition = builder.ToString();
      }

      Category newCategory = new Category() {
        CategoryName = new StringSegment(categoryDefinition, 1, category.Length),
        OptionLookup = new Dictionary<string, Option>(),
        Lines = new List<string>()
      };

      newCategory.Lines.Add(categoryDefinition);
      newCategory.Lines.Add(string.Empty);

      this.categoryLookup.Add(category, newCategory);

      return newCategory;
    }

    /// <summary>Records where options are stored in the configuration file</summary>
    private IList<Option> options;

    /// <summary>Root category where options above any category definition go</summary>
    private Category rootCategory;
    /// <summary>Lookup table for all categories by their name</summary>
    private IDictionary<string, Category> categoryLookup;

  }

} // namespace Nuclex.Support.Settings