Support unified rich expressions in the configuration file

[jbmorley]

The configuration file currently works at the very coarse granularity of handlers, and handlers may then require their own handler-specific configuration. This can lead to inconsistencies in the way things are expressed in the configuration file.

It might be nice if we can come up with a consistent way to express the configuration for all plugins in a consistent (and perhaps flat) way.

Currently, I think plugins only actually need to do a few things, so it might be possible to do this.

Specifically, given 1-or-more input files (expressed in the settings), plugins need to be able to:

• generate one-or-more documents (dictionaries)
• generate one-or-more files

[jbmorley]

While working on the configuration for the gallery / image handling, I knocked up the following rough ideas for configurations.

Image handler specific configuration block:

- where: glob("*") and metadata(projection="equirectangular")
  transform:
  - resize("large", width=1000, tags=["image"])

More generic approach, using the plugin instance as a key:

- where: glob("*") and metadata(projection="equirectangular")
  import_image(category="instagram"):
  - resize("large", width=1000, tags=["image"])
  - resize("large", width=1000, tags=["image"])

where: glob("*") and metadata(projection="equirectangular")
transform:
   large: resize(width=1000, tags=["image"])
   small: resize(width=480, tags=["thumbnail"])

where: glob("*") and metadata(projection="equirectangular")
transform:
   resize(width=1000, tags=["image"]) as "image"
   resize(width=480, tags=["thumbnail"]) as "small"

What if we were to depart entirely from the idea of YAML for the configuration. The image handler configuration might look like this:

if metadata(projection="equirectangular") {

    resize("large", width=10000, tags=["image"])
    fisheye("preview-small", width=480, tags=["thumbnail", "previews"])
    fisheye("preview-large", width=960, tags=["thumbnail", "previews"])

} else if glob("*.heic") or glob("*.tiff") {

    resize("large", width=1000, format="image/jpeg", tags=["image"])
    resize("small", width=480, format="image/jpeg", tags=["thumbnail"])

} else {

    resize("large", width=1000, tags=["image"])
    resize("small", width=480, tags=["thumbnail"])

}

Or, you can start to stretch the idea and imagine that the whole thing flattens out:

if glob("*.markdown") {
    markdown
} else if glob("*.{jpeg,jpg,tiff,png,gif}") and metadata(projection="equirectangular") {
    image {
        resize("large", width=10000, tags=["image"])
        fisheye("preview-small", width=480, tags=["thumbnail", "previews"])
        fisheye("preview-large", width=960, tags=["thumbnail", "previews"])
    }
} else if glob("*.heic") or glob("*.tiff") {
    image {
        resize("large", width=1000, format="image/jpeg", tags=["image"])
        resize("small", width=480, format="image/jpeg", tags=["thumbnail"])
    }
} else {
    image {
        resize("large", width=1000, tags=["image"])
        resize("small", width=480, tags=["thumbnail"])
    }
}

This still feels clunky, but perhaps it helps set the direction.