feat: chord diagram — piano/guitar diagrams in song detail

app/app/routes/songs.$id.tsx

@@ -1,11 +1,15 @@
-import { useEffect, useState } from "react";
+import { useEffect, useState, useRef, useCallback } from "react";
 import { data, Link } from "react-router";
 import type { Route } from "./+types/songs.$id";
 import { TransposeBar } from "~/components/transpose-bar";
 import { ChordChart } from "~/components/chord-chart";
+import { ChordGrid } from "~/components/chord-diagram/chord-grid";
+import { ChordDiagram } from "~/components/chord-diagram/chord-diagram";
+import type { Instrument } from "~/components/chord-diagram/chord-diagram";
 import { EditSongSheet } from "~/components/edit-song-sheet";
 import { DeleteSongDialog } from "~/components/delete-song-dialog";
 import { transposeSong } from "~/lib/transpose";
+import { extractUniqueChords } from "~/lib/song-utils";
 import { getSong } from "~/lib/api";
 import type { Song, SongSummary } from "~/lib/types";
 
@@ -41,6 +45,14 @@ function initFontSize(): FontSize {
   return 'sm';
 }
 
+function initInstrument(): Instrument {
+  try {
+    const v = localStorage.getItem('chordDiagramInstrument');
+    if (v === 'piano' || v === 'guitar') return v;
+  } catch { /* noop */ }
+  return 'piano';
+}
+
 export default function SongDetail({ loaderData }: Route.ComponentProps) {
   const { song: initialSong, id } = loaderData;
   const [baseSong, setBaseSong] = useState<Song | null>(initialSong ?? null);
@@ -62,6 +74,9 @@ export default function SongDetail({ loaderData }: Route.ComponentProps) {
   const [fontSize, setFontSize] = useState<FontSize>(initFontSize);
   const [editOpen, setEditOpen] = useState(false);
   const [deleteOpen, setDeleteOpen] = useState(false);
+  const [activeChord, setActiveChord] = useState<string | null>(null);
+  const [instrument, setInstrument] = useState<Instrument>(initInstrument);
+  const scrollRef = useRef<HTMLDivElement>(null);
 
   useEffect(() => {
     if (applyCapo && baseSong?.meta.capo) {
@@ -81,6 +96,13 @@ export default function SongDetail({ loaderData }: Route.ComponentProps) {
     try { localStorage.setItem('fontSize', size); } catch { /* noop */ }
   }
 
+  function handleInstrumentChange(i: Instrument) {
+    setInstrument(i);
+    try { localStorage.setItem('chordDiagramInstrument', i); } catch { /* noop */ }
+  }
+
+  const handleScroll = useCallback(() => setActiveChord(null), []);
+
   if (!baseSong || !displayedSong) {
     return (
       <div className="flex flex-col items-center justify-center h-full gap-4">
@@ -93,6 +115,8 @@ export default function SongDetail({ loaderData }: Route.ComponentProps) {
   }
 
   const displayed = transposeSong(displayedSong, offset);
+  const uniqueChords = extractUniqueChords(displayed.sections);
+  const handleChordClick = (chord: string) => setActiveChord(chord);
 
   function handleUpdated(summary: SongSummary) {
     setBaseSong((prev) => prev ? { ...prev, meta: summary.meta } : prev);
@@ -100,7 +124,7 @@ export default function SongDetail({ loaderData }: Route.ComponentProps) {
   }
 
   return (
-    <div className="flex flex-col h-full max-w-lg mx-auto">
+    <div className="flex flex-col h-full">
       <TransposeBar
         meta={baseSong.meta}
         offset={offset}
@@ -113,9 +137,56 @@ export default function SongDetail({ loaderData }: Route.ComponentProps) {
         applyCapo={applyCapo}
         onToggleCapo={() => setApplyCapo((v) => !v)}
       />
-      <div className="flex-1 overflow-y-auto">
-        <ChordChart sections={displayed.sections} fontSize={fontSize} />
+
+      {/* Body: single column on mobile, two columns on desktop */}
+      <div className="flex-1 overflow-hidden flex flex-col lg:flex-row">
+        {/* Left / main column */}
+        <div
+          className="flex-1 overflow-y-auto"
+          ref={scrollRef}
+          onScroll={handleScroll}
+        >
+          <div className="max-w-lg mx-auto lg:max-w-none">
+            <ChordChart
+              sections={displayed.sections}
+              fontSize={fontSize}
+              onChordClick={handleChordClick}
+            />
+
+            {/* Mobile bottom chord grid (hidden on desktop) */}
+            <div className="lg:hidden border-t border-border">
+              <ChordGrid
+                chords={uniqueChords}
+                instrument={instrument}
+                onInstrumentChange={handleInstrumentChange}
+              />
             </div>
+          </div>
+        </div>
+
+        {/* Desktop side column (hidden on mobile) */}
+        <div className="hidden lg:block w-72 overflow-y-auto border-l border-border shrink-0">
+          <ChordGrid
+            chords={uniqueChords}
+            instrument={instrument}
+            onInstrumentChange={handleInstrumentChange}
+          />
+        </div>
+      </div>
+
+      {/* Mobile inline popup — fixed bottom, dismissed on scroll */}
+      {activeChord && (
+        <div className="lg:hidden fixed bottom-0 left-0 right-0 z-50 border-t border-border bg-background shadow-lg p-3 flex items-center gap-3">
+          <ChordDiagram chord={activeChord} instrument={instrument} />
+          <button
+            className="ml-auto text-muted-foreground text-xs underline-offset-4 hover:underline"
+            onClick={() => setActiveChord(null)}
+          >
+            close
+          </button>
+        </div>
+      )}
+
       <EditSongSheet
         id={id}
         meta={baseSong.meta}