# SplitPath Structure

LiterateCS operates on three base directories:

• input directory which contains the files to be processed,
• output directory where the generated documentation will be placed, and
• theme directory which stores the HTML rendering library and its auxiliary files.

When accessing files in these directories it is often necessary to segregate the base directory and the relative path inside that directory. For this purpose, we define a helper data structure that encapsulates a file path, but stores it in two parts: base path and file path. We call this data structure SplitPath and define it as follows.

namespace LiterateCS
{
using System;
using System.IO;
using System.Linq;
using System.Text;

public struct SplitPath
{


## Two Parts of SplitPath

One benefit of splitting a path is that we can make sure that the parts are always in correct format. The base part is extended so that it contains an absolute folder path, and it is ensured that the last character is a backslash. Conversely, the file path is checked to be relative path without a root folder. If that is not the case, the constructor throws an exception.

		public SplitPath (string basePath, string filePath)
{
if (filePath != null && Path.IsPathRooted (filePath))
throw new ArgumentException ("filePath has to be a relative path.");
BasePath = WithLastBackslash (
string.IsNullOrEmpty (basePath) ?
Environment.CurrentDirectory :
Path.GetFullPath (basePath));
FilePath = filePath;
}

private static string WithLastBackslash (string dirPath) =>
dirPath[dirPath.Length - 1] != Path.DirectorySeparatorChar ?
dirPath + Path.DirectorySeparatorChar : dirPath;


## Constructing a SplitPath

There is a handful of constructor methods that help building a SplitPath in various ways.

First of all, it is possible to create a partial SplitPath by omitting either part of the path. Partial paths can be later glued together to create a valid path. The following two methods create a SplitPath given either just a base path or a file path.

		public static SplitPath Base (string basePath) =>
new SplitPath (basePath, null);

public static SplitPath File (string file) =>
new SplitPath (null, file);


Another way to construct a SplitPath is to give a complete file path and a base path. The base path will be excluded from the full path to create the relative file path.

		public static SplitPath Split (string basePath, string fullPath) =>
new SplitPath (basePath, fullPath.Substring (basePath.Length));


Changing either part is also easy. Note that the structure is immutable, so it is never modified in-place. Instead a new structure is returned.

		public SplitPath WithBase (string basePath) =>
new SplitPath (basePath, FilePath);

public SplitPath WithFile (string filePath) =>
new SplitPath (BasePath, filePath);


It is possible to change the file extension as well.

		public SplitPath ChangeExtension (string newExtension) =>
new SplitPath (BasePath, Path.ChangeExtension (FilePath, newExtension));


## SplitPath Features

If both parts of a SplitPath are null, it is considered to be empty.

		public bool IsEmpty =>
BasePath == null && FilePath == null;


The following properties can be used to test if one part of the path is missing.

		public bool IsBase =>
BasePath != null && FilePath == null;

public bool IsFile =>
BasePath == null && FilePath != null;


We are also wrapping some of the methods defined in System.IO.Path class to access other parts of the path: file name, extension, or directory name.

		public string FileName =>
Path.GetFileName (FilePath);

public string FileNameWithoutExtension =>
Path.GetFileNameWithoutExtension (FilePath);

public string Extension =>
Path.GetExtension (FilePath);

public string DirectoryName =>
Path.GetDirectoryName (ToString ());


In some cases it is necessary to know how deep the file path part is; for example, to create a relative file path inside a base directory. The method below counts how many directory separator characters there are in a file path, thus returning its depth.

		public int FilePathDepth =>
FilePath.Count (c => c == Path.DirectorySeparatorChar);


When we know the depth of a file path, we can construct a relative path pointing from the file to the base directory. This comes in handy when we are creating links between generated HTML files.

The following code just concatenates as many parent directory pointers (../) together as the depth of the file path indicates to construct a relative path to the base directory.

		public string RelativePathToRoot
{
get
{
var depth = FilePathDepth;
var result = new StringBuilder ();
for (int i = 0; i < depth; i++)
result.Append (@"../");
return result.ToString ();
}
}


The overloaded ! operator is a shorthand to the ToString method which concatenates the two parts of a SplitPath to form a full path as a string.

		public override string ToString () =>
BasePath + FilePath;

public static string operator ! (SplitPath splitPath) =>
splitPath.ToString ();


Finally, we can combine two SplitPaths by taking the base path from the first one and the file path from the second one. To make this operation more convenient to use it is implemented as the + operator.

		public static SplitPath operator + (SplitPath basePath, SplitPath filePath)
{
return new SplitPath (basePath.BasePath, filePath.FilePath);
}
}
}