feat(app): add AddSongSheet component

app/app/components/add-song-sheet.tsx

@@ -0,0 +1,155 @@
+import { useRef, useState } from "react";
+import { useNavigate } from "react-router";
+import {
+  Sheet,
+  SheetContent,
+  SheetHeader,
+  SheetTitle,
+} from "~/components/ui/sheet";
+import { Input } from "~/components/ui/input";
+import { Button } from "~/components/ui/button";
+import type { Song, SongSummary } from "~/lib/types";
+
+interface Props {
+  open: boolean;
+  onOpenChange: (open: boolean) => void;
+  onSongAdded: (summary: SongSummary) => void;
+}
+
+function previewChords(song: Song): string[] {
+  const seen = new Set<string>();
+  const result: string[] = [];
+  for (const section of song.sections) {
+    for (const line of section.lines) {
+      for (const cp of line.chords) {
+        if (!seen.has(cp.chord)) {
+          seen.add(cp.chord);
+          result.push(cp.chord);
+        }
+      }
+    }
+    if (result.length >= 5) break;
+  }
+  return result.slice(0, 5);
+}
+
+export function AddSongSheet({ open, onOpenChange, onSongAdded }: Props) {
+  const navigate = useNavigate();
+  const [url, setUrl] = useState("");
+  const [loading, setLoading] = useState(false);
+  const [error, setError] = useState<string | null>(null);
+  const fileRef = useRef<HTMLInputElement>(null);
+
+  async function handleSubmit(e: React.FormEvent) {
+    e.preventDefault();
+    setError(null);
+
+    const file = fileRef.current?.files?.[0];
+    if (!url.trim() && !file) {
+      setError("Provide a URL or pick a file.");
+      return;
+    }
+
+    setLoading(true);
+    try {
+      if (file) {
+        // File paths can't be sent from the browser — the API expects a file:// URI
+        // which only works when running locally. Show a helpful error.
+        throw new Error("File upload requires running the app locally with direct file paths. Use a URL instead.");
+      }
+
+      const resp = await fetch("http://localhost:8000/tabs/parse", {
+        method: "POST",
+        headers: { "Content-Type": "application/json" },
+        body: JSON.stringify({ source: url.trim() }),
+      });
+
+      if (!resp.ok) {
+        const data = await resp.json().catch(() => ({}));
+        throw new Error((data as { error?: string }).error ?? `HTTP ${resp.status}`);
+      }
+
+      const song: Song = await resp.json();
+      const id = `new-${Date.now()}`;
+      sessionStorage.setItem(id, JSON.stringify(song));
+
+      const summary: SongSummary = {
+        id,
+        meta: song.meta,
+        preview_chords: previewChords(song),
+      };
+      onSongAdded(summary);
+      onOpenChange(false);
+      setUrl("");
+      navigate(`/songs/${id}`);
+    } catch (err) {
+      setError(err instanceof Error ? err.message : "Something went wrong.");
+    } finally {
+      setLoading(false);
+    }
+  }
+
+  return (
+    <Sheet open={open} onOpenChange={onOpenChange}>
+      <SheetContent side="bottom" className="rounded-t-xl">
+        <SheetHeader className="mb-4">
+          <SheetTitle>Add Song</SheetTitle>
+        </SheetHeader>
+        <form onSubmit={handleSubmit} className="flex flex-col gap-4">
+          <div className="flex flex-col gap-1">
+            <label className="text-xs text-muted-foreground uppercase tracking-wide">
+              From URL
+            </label>
+            <Input
+              placeholder="https://tabs.ultimate-guitar.com/..."
+              value={url}
+              onChange={(e) => setUrl(e.target.value)}
+              disabled={loading}
+            />
+          </div>
+
+          <div className="flex items-center gap-3">
+            <div className="flex-1 h-px bg-border" />
+            <span className="text-xs text-muted-foreground">or</span>
+            <div className="flex-1 h-px bg-border" />
+          </div>
+
+          <div className="flex flex-col gap-1">
+            <label className="text-xs text-muted-foreground uppercase tracking-wide">
+              From File
+            </label>
+            <Button
+              type="button"
+              variant="outline"
+              className="w-full border-dashed"
+              onClick={() => fileRef.current?.click()}
+              disabled={loading}
+            >
+              📂 Choose HTML file
+            </Button>
+            <input ref={fileRef} type="file" accept=".html" className="hidden" />
+          </div>
+
+          {error && (
+            <p className="text-sm text-destructive">{error}</p>
+          )}
+
+          <div className="flex gap-2 pt-1">
+            <Button
+              type="button"
+              variant="outline"
+              className="flex-1"
+              onClick={() => onOpenChange(false)}
+              disabled={loading}
+            >
+              Cancel
+            </Button>
+            <Button type="submit" className="flex-1" disabled={loading}>
+              {loading ? "Importing..." : "Import"}
+            </Button>
+          </div>
+        </form>
+      </SheetContent>
+    </Sheet>
+  );
+}