Save path ./photos/YYYY/YYYY-MM/YYYY-MM-DD/YYYY-MM-DD.fileID.ext; download() from the cache first (closes #143)

Originals are saved at `{downloadDirectory}/YYYY/YYYY-MM/YYYY-MM-DD/YYYY-MM-DD.{fileID}{ext}`. The date is the photo's `takenAt` in local time, and `downloadDirectory` defaults to `./photos`, resolved when the library opens. The old `originals/` layout is gone.

`photo.download()` writes the original to `savePath`. It copies from the cache when the cache holds the original, and fetches otherwise. `lib.backup()` uses the same path and rule, and every album in `collections/` links to it. `isLocal` is true only when the original is at `savePath`.

For a file in several albums, one rule picks the copy everything uses: the most recently synced, with the lowest album ID breaking a tie.

Model: opus-5-5

src/library/records.ts

@@ -86,6 +86,10 @@ export interface LibraryChange {
 export interface DerivedRecords {
     albums: Map<number, AlbumRecord>;
     photos: Map<number, PhotoRecord>;
+    // The membership each photo's record is read from, for its `Photo`'s save
+    // path. It holds the file's key, so it stays in this process: no snapshot
+    // or change carries it.
+    files: Map<number, EnteFile>;
 }
 
 const asString = (v: unknown): string | undefined =>
@@ -101,18 +105,19 @@ const microsToMillis = (micros: number): number => Math.floor(micros / 1000);
 const byNewestPhoto = (a: PhotoRecord, b: PhotoRecord): number =>
     b.takenAt - a.takenAt || b.fileID - a.fileID;
 
-// Build one PhotoRecord from every membership of a file. The memberships share
-// the same underlying file, so metadata is read from a single representative
-// (the most recently synced, lowest collection id to break ties); `albumIDs`
-// gathers them all.
-const toPhotoRecord = (
-    fileID: number,
-    memberships: EnteFile[],
-): PhotoRecord => {
-    const albumIDs = memberships
-        .map((m) => m.collectionID)
-        .sort((a, b) => a - b);
-    const rep = memberships.reduce((best, m) =>
+// A photo's `takenAt` in milliseconds: `pubMagicMetadata.editedTime` when the
+// user edited the date, else basic-metadata `creationTime`.
+export const takenAtOf = (file: EnteFile): number =>
+    microsToMillis(
+        asNumber(file.pubMagicMetadata?.editedTime) ??
+            file.metadata.creationTime,
+    );
+
+// The membership a file's record is read from: the most recently synced, lowest
+// collection id to break ties. Whatever dates a file's save path takes this
+// membership too, so the path always carries the record's `takenAt`.
+export const representative = (memberships: EnteFile[]): EnteFile =>
+    memberships.reduce((best, m) =>
         m.updationTime > best.updationTime ||
         (m.updationTime === best.updationTime &&
             m.collectionID < best.collectionID)
@@ -120,17 +125,28 @@ const toPhotoRecord = (
             : best,
     );
 
+// Build one PhotoRecord from every membership of a file. The memberships share
+// the same underlying file, so metadata is read from a single representative;
+// `albumIDs` gathers them all.
+const toPhotoRecord = (
+    fileID: number,
+    memberships: EnteFile[],
+): PhotoRecord => {
+    const albumIDs = memberships
+        .map((m) => m.collectionID)
+        .sort((a, b) => a - b);
+    const rep = representative(memberships);
+
     const pub = rep.pubMagicMetadata ?? {};
     const priv = rep.magicMetadata ?? {};
 
-    const takenAtMicros = asNumber(pub.editedTime) ?? rep.metadata.creationTime;
     const visibility = asNumber(priv.visibility);
 
     const record: PhotoRecord = {
         fileID,
         albumIDs,
         title: asString(pub.editedName) ?? rep.metadata.title,
-        takenAt: microsToMillis(takenAtMicros),
+        takenAt: takenAtOf(rep),
         modifiedAt: microsToMillis(rep.metadata.modificationTime),
         fileType: rep.metadata.fileType,
         isArchived: visibility === VISIBILITY_ARCHIVED,
@@ -198,6 +214,7 @@ export const deriveRecords = (
     }
 
     const photos = new Map<number, PhotoRecord>();
+    const photoFiles = new Map<number, EnteFile>();
     const takenAtByFile = new Map<number, number>();
     for (const [fileID, memberships] of byFileID) {
         const record = toPhotoRecord(fileID, memberships);
@@ -209,6 +226,7 @@ export const deriveRecords = (
                 record.thumbnailPath = paths.thumbnailPath;
         }
         photos.set(fileID, record);
+        photoFiles.set(fileID, representative(memberships));
         takenAtByFile.set(fileID, record.takenAt);
     }
 
@@ -217,7 +235,7 @@ export const deriveRecords = (
         albums.set(c.id, toAlbumRecord(c, files, takenAtByFile));
     }
 
-    return { albums, photos };
+    return { albums, photos, files: photoFiles };
 };
 
 // Sorted, GUI-ready arrays: albums newest updated first, photos newest first.