Prepending inferred metadata to posts, pages

The current inferred metadata system does not add the inferred metadata to posts and pages, but rather leaves them unaltered, and reinfers metadata at each build.

This has two downsides:

1. It has a time cost; but, more significantly
2. It assigns authorship of each page without embedded metadata to whoever is running the build at the time.

I currently have a version where, is the flag `:write-back-inferred-meta?` is present (and `true`) in `config.edn`

1. Makes a backup of the post or page file;
2. infers the metadata, and then prepends that to the content in the post or page file.

Diff as follows:

```diff
diff --git a/src/cryogen_core/infer_meta.clj b/src/cryogen_core/infer_meta.clj
index 84f3d3d..5061ae3 100644
--- a/src/cryogen_core/infer_meta.clj
+++ b/src/cryogen_core/infer_meta.clj
@@ -11,8 +11,10 @@
trimmed-html-snippet]]
[mikera.image.core :refer [height load-image width]]
[pantomime.mime :refer [mime-type-of]]
- [cc.journeyman.real-name.core :refer [get-real-name]])
+ [cc.journeyman.real-name.core :refer [get-real-name]]
+ [clojure.pprint :refer [pprint]])
(:import [java.util Date Locale]
+ [java.io File]
[java.nio.file Files FileSystems LinkOption]
[java.nio.file.attribute FileOwnerAttributeView]))

@@ -136,10 +138,10 @@
been used to extract meta-data removed."
([dom] (clean dom dom))
([elt dom]
- (cond
- (map? elt) (when-not (redundant? elt dom) (assoc elt :content (clean (:content elt) dom)))
- (coll? elt) (remove nil? (map #(clean % dom) elt))
- :else elt)))
+ (cond
+ (map? elt) (when-not (redundant? elt dom) (assoc elt :content (clean (:content elt) dom)))
+ (coll? elt) (remove nil? (map #(clean % dom) elt))
+ :else elt)))

(def infer-title
"Infer the title of this page, ideally by extracting the first `H1` element from this
@@ -205,24 +207,47 @@
tag-line?
(walk-dom dom))
tags (when tags-p (join ", " (reduce concat (map #(rest (:content %)) tags-p))))]
- (when tags (doall (set (map trim (split tags #",")))))))
+ (when tags (doall (apply vector (set (map trim (split tags #","))))))))

(defn infer-meta
"Infer metadata related to this `page`, assumed to be the name of a file in
this `markup`, given this `config`."
[^java.io.File page config dom]
- (let [metadata (assoc {}
- :author (infer-author page config)
- :date (infer-date page config)
- :description (infer-description page config dom)
- :image (infer-image-data dom config)
- :inferred-meta true
- :tags (infer-tags dom)
- :title (infer-title page config dom))]
- (info (format "Inferred metadata for document %s dated %s."
- (:title metadata)
- (:date metadata)))
- metadata))
+ (let [metadata (assoc {}
+ :author (infer-author page config)
+ :date (infer-date page config)
+ :description (infer-description page config dom)
+ :image (infer-image-data dom config)
+ :inferred-meta true
+ :tags (infer-tags dom)
+ :title (infer-title page config dom))]
+ (info (format "Inferred metadata for document %s dated %s."
+ (:title metadata)
+ (:date metadata)))
+ metadata))
+
+(defn file-extension
+ "Return the extension, if any, of this `file-name`."
+ [file-name]
+ (second (re-find #"(\.[a-zA-Z0-9]+)$" file-name)))
+
+(defn- create-backup
+ [^File file]
+ (let [path (.getPath file)
+ backup-path (File. (str (replace path (file-extension path) ".bak")))]
+ (info (format "Backing up %s to %s" (.getPath file) (.getPath backup-path)))
+ (spit backup-path (slurp file))))
+
+(defn- write-back-inferred-meta
+ "Backup the file indicated by `page` to a new file with the same name but the
+ extension `.bak`, and replace it with a file having the same content but
+ with this `meta-data` prefixed."
+ [^File page meta-data config]
+ (let [content (slurp page)
+ pretty-meta (with-out-str (pprint meta-data))]
+ (warn (format "%s: Prepending meta-data:\n %s" (.getName page) pretty-meta))
+ (create-backup page)
+ (spit page (str pretty-meta "\n\n" content))))

(defn using-inferred-metadata
"An implementation of the guts of `cryogen-core.compiler.page-content` for
@@ -235,6 +260,7 @@
(let [content-dom (trimmed-html-snippet ((render-fn markup) rdr config))
page-meta (infer-meta page config content-dom)
file-name (infer-file-name page page-meta config)]
+ (when (:write-back-inferred-meta? config) (write-back-inferred-meta page page-meta config))
{:file-name file-name
:page-meta page-meta
:content-dom (clean content-dom)})))
```

Would you accept this as a pull request?