add browser warning

src/lib/chords/coverage.ts

@@ -0,0 +1,23 @@
+import type {Chord} from "$lib/serial/chord"
+import {KEYMAP_CODES} from "$lib/serial/keymap-codes"
+
+interface Language {
+  name: string
+  noLazyMode?: boolean
+  orderedByFrequency?: boolean
+  words: string[]
+}
+
+export async function calculateChordCoverage(chords: Chord[]) {
+  const language: Language = await fetch("/languages/english.json").then(it => it.json())
+
+  const words = new Set(language.words)
+  for (const chord of chords) {
+    words.delete(chord.phrase.map(it => KEYMAP_CODES[it].id!).join(""))
+  }
+
+  return {
+    coverage: words.size / language.words.length,
+    missing: [...words.values()],
+  }
+}