1 files changed, 55 insertions, 0 deletions
diff --git a/src/content/util/getChronologyRelations.js b/src/content/util/getChronologyRelations.js
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index 0000000..67d6d5f
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+++ b/src/content/util/getChronologyRelations.js
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+export default function getChronologyRelations(thing, {
+  contributions,
+  linkArtist,
+  linkThing,
+  getThings,
+}) {
+  // One call to getChronologyRelations is considered "lumping" together all
+  // contributions as carrying equivalent meaning (for example, "artist"
+  // contributions and "contributor" contributions are bunched together in
+  // one call to getChronologyRelations, while "cover artist" contributions
+  // are a separate call). getChronologyRelations prevents duplicates that
+  // carry the same meaning by only using the first instance of each artist
+  // in the contributions array passed to it. It's expected that the string
+  // identifying which kind of contribution ("track" or "cover art") is
+  // shared and applied to all contributions, as providing them together
+  // in one call to getChronologyRelations implies they carry the same
+  // meaning.
+
+  const artistsSoFar = new Set();
+
+  contributions = contributions.filter(({who}) => {
+    if (artistsSoFar.has(who)) {
+      return false;
+    } else {
+      artistsSoFar.add(who);
+      return true;
+    }
+  });
+
+  return contributions.map(({who}) => {
+    const things = Array.from(new Set(getThings(who)));
+
+    // Don't show a line if this contribution isn't part of the artist's
+    // chronology at all (usually because this thing isn't dated).
+    const index = things.indexOf(thing);
+    if (index === -1) {
+      return;
+    }
+
+    // Don't show a line if this contribution is the *only* item in the
+    // artist's chronology (since there's nothing to navigate there).
+    const previous = things[index - 1];
+    const next = things[index + 1];
+    if (!previous && !next) {
+      return;
+    }
+
+    return {
+      index: index + 1,
+      artistLink: linkArtist(who),
+      previousLink: previous ? linkThing(previous) : null,
+      nextLink: next ? linkThing(next) : null,
+    };
+  }).filter(Boolean);
+}