# `Expresso.Assets`
[🔗](https://github.com/rellen/expresso/blob/main/lib/expresso/assets.ex#L1)

Keeps one copy of each large file that the document holds more than one time

A deck is one file, so an image or a track goes into the document as a data
URI. An SVG file of a diagram or of an icon can also hold an image as a data
URI in an `href` or an `xlink:href` attribute. Each view of the slide holds
its own copy: the present view, each page of the handout view and the
picture in the menu. An image of 250 KB in a slide of two steps was then in
the document six times.

`dedupe/1` runs on the HTML of the document. For each value of a `src`, an
`href` or an `xlink:href` attribute that is a data URI of `1024`
characters or more, and that occurs more than one time:

  * the first element keeps the attribute, and gets `data-asset-N` with the
    name of that attribute, such as `data-asset-0="src"`;
  * each other element loses the attribute, and gets `data-asset-src="0"` or
    `data-asset-href="0"` in its place. An `xlink:href` gets
    `data-asset-href`, because SVG 2 reads `href` in place of `xlink:href`,
    and a selector cannot hold the `:` of the name.

The presenter script copies the value back into each element when the
document loads. `assets/src/assets.ts` gives the rules.

# `dedupe`

```elixir
@spec dedupe(String.t()) :: String.t()
```

Replace each copy of a large data URI after its first with a reference to the first

    iex> uri = "data:image/png;base64," <> String.duplicate("A", 1100)
    iex> html = ~s(<img src="#{uri}"><img src="#{uri}">)
    iex> Expresso.Assets.dedupe(html)
    ~s(<img data-asset-0="src" src="#{uri}"><img data-asset-src="0">)

A data URI that occurs one time, or that is short, stays as it is.

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*Consult [api-reference.md](api-reference.md) for complete listing*