# Page Parameters

All the data LiterateCS will pass to the theme is contained inside a PageParams object. This class defines the built-in parameters that are always available, and the custom parameters specified in front matter.

namespace LiterateCS.Theme
{
using System.Collections.Generic;
using System.IO;

public class PageParams
{


## Custom Parameters

You can specify any parameters inside front matter. How these will be used is up to the theme. The parameters are simple key-value pairs with string both as the key and value type. The parameters are stored in a dictionary that is initialized when a PageParams object is created.

		private Dictionary<string, string> _parameters;

public PageParams ()
{
_parameters = new Dictionary<string, string> ();
}


The parameters are converted to lowercase before they are added to the dictionary. Parameter names are case-insensitive, so we need to do this in all the methods accessing the dictionary. If a parameter with the same name already exists in the dictionary, its value is updated.

		public void Add (string name, string value)
{
name = name.ToLower ();
if (_parameters.ContainsKey (name))
_parameters[name] = value;
else
}


Removing a parameter is also possible, although themes should not generally do so.

		public void Remove (string name)
{
_parameters.Remove (name.ToLower ());
}


Two indexer methods can be used to access the custom parameters. The first one takes two arguments: name and default value. If a parameter with a given name is not found, the default value is returned.

		public string this[string name, string defaultValue]
{
get
{
return _parameters.TryGetValue (name.ToLower (), out string result) ?
result : defaultValue;
}
}


The second version takes just name of the parameter, and returns it back, if the parameter is not found.

		public string this[string name] =>
this[name, name];


## Built-in Properties

The rest of the properties defined in the PageParams class are updated for each generated page. These are page-level parameters which are always available.

The Root property gives the relative path from the page location to the root directory of the website. For example, if the page we are generating resides under directory source\code\, then Root would contain path ..\..\. Say you want to add a link to another page which resides under directory doc\. Now you can to refer to it by adding the value of the Root property at the beginning of the path. The resulting path would be ..\..\doc\.

So, the Root property allows us to create relative links between pages that work regardless of where the site resides on disk. This is quite handy since now the links work correctly when pages are viewed locally from disk as well as when they are accessed from a web server.

		public string Root { get; set; }


The name of the currently processed file is stored in the property below. The name does not include a file extension.

		public string Filename { get; set; }


Perhaps the most important data passed to the theme is the contents of the page which is provided in the property below. The property contains the documentation extracted from the source file in HTML format. Typically the theme will just insert this in the appropriate place on a page.

		public string Contents { get; set; }


The table of contents object is accessible through the Toc property. This object is always initialized, even when the user does not provide a TOC file. In that case the TOC is empty, and there are no sections in it.

		public Toc Toc { get; set; }


When a TOC file is provided, and the current page can be found in it, then the following property contains a reference to the Section object we are on currently. This information can be used to highlight which section in the TOC we are viewing.

		public Section CurrentSection { get; set; }


The SectionPath helper function returns the relative path to section in the TOC from the current page. It is handy in generating links to TOC. The method also changes the source file path to a relative URL by changing the extension to "html" and replacing backslashes with forward slashes.

		public string SectionPath (Section entry) =>
entry.File == null ?
null :
Path.Combine (Root, Path.ChangeExtension (entry.File, "html"))
.Replace ('\\', '/');
}
}