defmodule Crawler.Linker.PathExpander do
@moduledoc """
Expands the path by expanding any `.` and `..` characters.
See [this pull request](https://github.com/elixir-lang/elixir/pull/6486).
"""
@doc """
Expands the path by expanding any `.` and `..` characters.
Note this function only expands any `.` and `..` characters within the given
path, and it does not take into account the absolute or relative nature of
the path itself, for that please use `expand/1` or `expand/2`.
## Examples
### Intended use case
iex> PathExpander.expand_dot("foo/bar/../baz")
"foo/baz"
iex> PathExpander.expand_dot("/foo/bar/../baz")
"/foo/baz"
### Non-intended use cases are ignored
iex> PathExpander.expand_dot("foo/bar/./baz")
"foo/bar/baz"
iex> PathExpander.expand_dot("../foo/bar")
"foo/bar"
"""
def expand_dot(<<"/", rest::binary>>),
do: "/" <> do_expand_dot(rest)
def expand_dot(path),
do: do_expand_dot(path)
defp do_expand_dot(path),
do: do_expand_dot(:binary.split(path, "/", [:global]), [])
defp do_expand_dot([".." | t], [_, _ | acc]),
do: do_expand_dot(t, acc)
defp do_expand_dot([".." | t], []),
do: do_expand_dot(t, [])
defp do_expand_dot(["." | t], acc),
do: do_expand_dot(t, acc)
defp do_expand_dot([h | t], acc),
do: do_expand_dot(t, ["/", h | acc])
defp do_expand_dot([], []),
do: ""
defp do_expand_dot([], ["/" | acc]),
do: IO.iodata_to_binary(:lists.reverse(acc))
end