cacheing and mb wrapper

src/sh/mb.sh

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+# The only IDs uses here are MusicBrainz IDs
+
+__mb_artist_cache_or_fetch() {
+  mbartist="$(cache_get_artist_mb "$1" || true)"
+  if [ ! "$mbartist" ]; then
+    __api_mb_get_artist "$1" | cache_put_artist_mb "$1"
+    mbartist="$(cache_get_artist_mb "$1")"
+  fi
+  echo "$mbartist"
+}
+
+# Get MusicBrainz json for artist
+# @argument $1: MusicBrainz Artist ID
+mb_artist() {
+  __mb_artist_cache_or_fetch "$1"
+}
+
+# Get Wikidata json for artist
+# @argument $1: MusicBrainz Artist ID
+mb_artist_wikidata() {
+  wikidata=$(cache_get_artist_wikidata "$1" || true)
+  if [ ! "$wikidata" ] || [ "$wikidata" = "null" ]; then
+    wikidataid=$(mb_artist "$1" |
+      $JQ -r '.relations |
+      map(select(.type=="wikidata")) |
+      .[0].url.resource' |
+      awk -F "/" '{print $NF}')
+    [ ! "$wikidataid" ] || [ "$wikidataid" != "null" ] || return
+    __api_wikidata_get_sitelinks "$wikidataid" | cache_put_artist_wikidata "$1"
+    wikidata=$(cache_get_artist_wikidata "$1")
+  fi
+  echo "$wikidata"
+}
+
+# Get Wikipedia (English) summary json for artist
+# @argument $1: MusicBrainz Artist ID
+mb_artist_enwikipedia() {
+  enwiki="$(cache_get_artist_enwikipedia "$1" || true)"
+  if [ ! "$enwiki" ] || [ "$enwiki" = "null" ]; then
+    # To fetch the wikipedia data, we need the wikipedia URL
+    # There are two possibly ways to get the wikipedia URL
+    # 1. From the website relations in MB (MB artists donw have wiki rels)
+    # 2. MB website relations -> Wikidata -> Wikipedia
+    # Lately, Wikipedia pages are not stored in the MB artist url relations.
+    # For obvious reasons it is recommended to link to wikidata only. So, we
+    # take the second route.
+    wikidata=$(mb_artist_wikidata "$1" || true)
+    wikiid=$(echo "$wikidata" |
+      $JQ -r '.enwiki.url' |
+      awk -F "/" '{print $NF}')
+    [ ! "$wikiid" ] || [ "$wikiid" != "null" ] || return
+    __api_wikipedia_en_get_summary "$wikiid" | cache_put_artist_enwikipedia "$1"
+    enwiki="$(cache_get_artist_enwikipedia "$1")"
+  fi
+  echo "$enwiki"
+}