cacheing and mb wrapper

src/sh/cache.sh

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+CACHEDIR="$HOME/.cache/$APP_NAME"
+[ -d "$CACHEDIR" ] || mkdir "$CACHEDIR"
+
+artist_mb_filename="musicbrainz.json"
+artist_discogs_filename="discogs.json"
+artist_wikidata_filename="wikidata.json"
+artist_enwikipedia_filename="enwikipedia.json"
+
+# Super wrapper
+# argument $1: MusicBrainz Artist ID
+# argument $2: Filename of json file
+__get_artist_json() {
+  f="$CACHEDIR/$1/$2"
+  [ -f "$f" ] || return
+  cat "$f"
+}
+
+# Super wrapper
+# argument $1: MusicBrainz Artist ID
+# argument $2: Filename of json file
+__put_artist_json() {
+  artistdir="$CACHEDIR/$1"
+  [ -d "$artistdir" ] || mkdir "$artistdir"
+  f="$artistdir/$2"
+  tmpf=$(mktemp)
+  cat >"$tmpf"
+  [ -s "$tmpf" ] && mv "$tmpf" "$f" || echo "{}" >"$f"
+}
+
+# Returns the cached MusicBrainz data for the artist given by the MusicBrainz
+# Artist ID in $1
+cache_get_artist_mb() {
+  __get_artist_json "$1" "$artist_mb_filename"
+}
+
+# Returns the cached Discogs data for the artist given by the MusicBrainz
+# Artist ID in $1
+cache_get_artist_discogs() {
+  __get_artist_json "$1" "$artist_discogs_filename"
+}
+
+# Returns the cached Wikipedia (English) data for the artist given by the
+# MusicBrainz Artist ID in $1
+cache_get_artist_enwikipedia() {
+  __get_artist_json "$1" "$artist_enwikipedia_filename"
+}
+
+cache_get_artist_wikidata() {
+  __get_artist_json "$1" "$artist_wikidata_filename"
+}
+
+# Read from stdin the MusicBrainz data for the artist given by the MusicBrainz
+# Artist ID in $1, and cache it.
+cache_put_artist_mb() {
+  cat | __put_artist_json "$1" "$artist_mb_filename"
+}
+
+# Read from stdin the Discogs data for the artist given by the MusicBrainz
+# Artist ID in $1, and cache it.
+cache_put_artist_discogs() {
+  cat | __put_artist_json "$1" "$artist_discogs_filename"
+}
+
+# Read from stdin the Wikipedia data (English) for the artist given by the
+# MusicBrainz Artist ID in $1, and cache it.
+cache_put_artist_enwikipedia() {
+  cat | __put_artist_json "$1" "$artist_enwikipedia_filename"
+}
+
+cache_put_artist_wikidata() {
+  cat | __put_artist_json "$1" "$artist_wikidata_filename"
+}