Checks whether we have a file in our cache.

If we do, we return its contents.

Generates a file name for a tuple (module, recipe).

We want to simplify the SVG that Graphviz generates so we can embed it in our HTML.

Formats the error message, if any.

@spec file(:cache | :temp, binary(), binary()) :: binary()

Creates a file name for a temporary file.

Ths may be a cache file or a proper temporary file.

If you need mode than one file, you should encode it in the extensions.

Given a recipe recipe for a graph, first tries a cache and then call a "builder" function to create it.

So if the SVG was already generated, we load it from disk - if not, we build it again.

builder

Builder

It returns {:ok, svg_text} or {:error, reason} that will be used to display a result.

Runs an external command.

It returns a binary that captures STDOUT+STDERR if all went well, or a tuple {:error, e} if something went bonkers.

If it's trying to call a command that does not exist on your local environment, returns {:error, :cmd_not_found}.

Computes a printable SHA for a string.

Creates a temporary file with the contents given, returning the filename.

iex > Provider.to_temp_file("hello", "example")
"/temp/SayCheezImg_AAF4C61DDCC54D_tmp_example"

We make it unique based on the contents, and we require a reason (for example one may have an input file and an output file to generate the contents that will be cached).

The only significant advantage of this HTTP client is that it only uses things that are in Erlang itself.

https://stackoverflow.com/questions/20108421/using-the-httpc-erlang-module-from-elixir

Earmark says that "A HTML Block defined by a tag starting a line and the same tag starting a different line is parsed as one HTML AST node, marked with %{verbatim: true}" (see https://hexdocs.pm/earmark_parser/EarmarkParser.html )

So we wrap everything in a DIV and call it a day.

Write a file to its right cache.