Add Last.fm import support

Users can import their top tracks from Last.fm by entering their username.
No OAuth required - uses the public Last.fm API with user.getTopTracks and
user.getInfo endpoints. Includes a preview feature to verify the username
and see sample tracks before importing. Supports configurable time periods
(all time, 7 days, 1/3/6/12 months). Free tier playlist limit enforced.

backend/app/api/endpoints/lastfm.py

@@ -0,0 +1,147 @@
+from fastapi import APIRouter, Depends, HTTPException, Query
+from pydantic import BaseModel
+from sqlalchemy import select
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from app.core.config import settings
+from app.core.database import get_db
+from app.core.security import get_current_user
+from app.models.user import User
+from app.models.playlist import Playlist
+from app.models.track import Track
+from app.services.lastfm import get_user_info, get_top_tracks
+from app.services.recommender import build_taste_profile
+from app.schemas.playlist import PlaylistDetailResponse
+
+router = APIRouter(prefix="/lastfm", tags=["lastfm"])
+
+
+class ImportLastfmRequest(BaseModel):
+    username: str
+    period: str = "overall"
+
+
+class LastfmPreviewTrack(BaseModel):
+    title: str
+    artist: str
+    playcount: int
+    image_url: str | None = None
+
+
+class LastfmPreviewResponse(BaseModel):
+    display_name: str
+    track_count: int
+    sample_tracks: list[LastfmPreviewTrack]
+
+
+@router.get("/preview", response_model=LastfmPreviewResponse)
+async def preview_lastfm(
+    username: str = Query(..., min_length=1),
+    user: User = Depends(get_current_user),
+):
+    """Preview a Last.fm user's top tracks without importing."""
+    if not settings.LASTFM_API_KEY:
+        raise HTTPException(status_code=500, detail="Last.fm API key not configured")
+
+    info = await get_user_info(username.strip())
+    if not info:
+        raise HTTPException(status_code=404, detail="Last.fm user not found")
+
+    try:
+        tracks = await get_top_tracks(username.strip(), period="overall", limit=50)
+    except ValueError as e:
+        raise HTTPException(status_code=400, detail=str(e))
+
+    sample = tracks[:5]
+    return LastfmPreviewResponse(
+        display_name=info["display_name"],
+        track_count=len(tracks),
+        sample_tracks=[LastfmPreviewTrack(**t) for t in sample],
+    )
+
+
+@router.post("/import", response_model=PlaylistDetailResponse)
+async def import_lastfm(
+    data: ImportLastfmRequest,
+    user: User = Depends(get_current_user),
+    db: AsyncSession = Depends(get_db),
+):
+    """Import top tracks from a Last.fm user as a playlist."""
+    if not settings.LASTFM_API_KEY:
+        raise HTTPException(status_code=500, detail="Last.fm API key not configured")
+
+    username = data.username.strip()
+    if not username:
+        raise HTTPException(status_code=400, detail="Username is required")
+
+    # Free tier limit
+    if not user.is_pro:
+        result = await db.execute(
+            select(Playlist).where(Playlist.user_id == user.id)
+        )
+        existing = list(result.scalars().all())
+        if len(existing) >= settings.FREE_MAX_PLAYLISTS:
+            raise HTTPException(
+                status_code=403,
+                detail="Free tier limited to 1 playlist. Upgrade to Pro for unlimited.",
+            )
+
+    # Verify user exists
+    info = await get_user_info(username)
+    if not info:
+        raise HTTPException(status_code=404, detail="Last.fm user not found")
+
+    # Fetch top tracks
+    try:
+        raw_tracks = await get_top_tracks(username, period=data.period, limit=50)
+    except ValueError as e:
+        raise HTTPException(status_code=400, detail=str(e))
+
+    if not raw_tracks:
+        raise HTTPException(
+            status_code=400,
+            detail="No top tracks found for this user and time period.",
+        )
+
+    # Build playlist name from period
+    period_labels = {
+        "overall": "All Time",
+        "7day": "Last 7 Days",
+        "1month": "Last Month",
+        "3month": "Last 3 Months",
+        "6month": "Last 6 Months",
+        "12month": "Last Year",
+    }
+    period_label = period_labels.get(data.period, "All Time")
+    playlist_name = f"{info['display_name']}'s Top Tracks ({period_label})"
+
+    # Create playlist
+    playlist = Playlist(
+        user_id=user.id,
+        name=playlist_name,
+        platform_source="lastfm",
+        external_id=f"lastfm:{username}:{data.period}",
+        track_count=len(raw_tracks),
+    )
+    db.add(playlist)
+    await db.flush()
+
+    # Create tracks (no audio features from Last.fm)
+    tracks = []
+    for rt in raw_tracks:
+        track = Track(
+            playlist_id=playlist.id,
+            title=rt["title"],
+            artist=rt["artist"],
+            image_url=rt.get("image_url"),
+        )
+        db.add(track)
+        tracks.append(track)
+
+    await db.flush()
+
+    # Build taste profile
+    playlist.taste_profile = build_taste_profile(tracks)
+    playlist.tracks = tracks
+
+    return playlist