feat(core): perceptual hashes for finding similar photos

A 64-bit difference hash of each thumbnail, stored in the new
photos.similar_hash column (schema 34), and the queries the similar-photo
finder needs: what is left to hash, progress, and the sets of shots that
look alike. Sets made only of byte-identical copies are left to the
duplicate finder. A refresh keeps a hash unless the photo's bytes changed.

The daemon pass, the control request and the GUI are not built yet; see
PLAN.md.

crates/pdfs-core/src/db/migrations.rs

@@ -9,7 +9,7 @@ use super::Db;
 use crate::Result;
 
 /// Current schema version. Bump on every forward migration added below.
-pub(super) const SCHEMA_VERSION: i64 = 33;
+pub(super) const SCHEMA_VERSION: i64 = 34;
 
 impl Db {
     pub(super) fn migrate(&self) -> Result<()> {
@@ -300,6 +300,22 @@ impl Db {
                 tx.execute_batch(MIGRATION_V33)?;
             }
         }
+        if current < 34 {
+            // Same guards as V26-V33.
+            let has_column: bool = tx.query_row(
+                "SELECT COUNT(*) FROM pragma_table_info('photos') WHERE name = 'similar_hash'",
+                [],
+                |row| row.get::<_, i64>(0),
+            )? > 0;
+            let has_photos: bool = tx.query_row(
+                "SELECT COUNT(*) FROM sqlite_master WHERE type = 'table' AND name = 'photos'",
+                [],
+                |row| row.get::<_, i64>(0),
+            )? > 0;
+            if has_photos && !has_column {
+                tx.execute_batch(MIGRATION_V34)?;
+            }
+        }
         tx.execute(
             "INSERT INTO sync_state (key, value) VALUES ('schema_version', ?1)
              ON CONFLICT(key) DO UPDATE SET value = excluded.value",
@@ -1006,3 +1022,14 @@ ALTER TABLE photos ADD COLUMN place_id INTEGER;
 CREATE INDEX IF NOT EXISTS idx_photos_place ON photos(place_id);
 UPDATE photos SET resolved_at = NULL;
 ";
+
+/// Schema v34: what each photo looks like, for finding similar ones.
+///
+/// `similar_hash` is a 64-bit difference hash of the photo's thumbnail (see
+/// `crate::similar`): resized and re-encoded copies of one picture land a few
+/// bits apart, where the server's `content_hash` only matches byte-identical
+/// files. `NULL` until the daemon has hashed the thumbnail, which it does as
+/// thumbnails arrive and when the similar-photo finder asks for the rest.
+const MIGRATION_V34: &str = "
+ALTER TABLE photos ADD COLUMN similar_hash INTEGER;
+";

crates/pdfs-core/src/db/photos.rs

@@ -98,6 +98,8 @@ struct Learned {
     content_hash: Option<String>,
     main_uid: Option<String>,
     location: Option<(f64, f64)>,
+    /// What its thumbnail looks like (see [`crate::similar`]).
+    similar_hash: Option<i64>,
     /// When this photo's node was last resolved, kept so a refresh that skips it
     /// does not make it look unresolved again.
     resolved_at: Option<i64>,
@@ -293,7 +295,7 @@ impl Db {
         let learned: HashMap<String, Learned> = {
             let mut stmt = tx.prepare(
                 "SELECT uid, name, ratio, thumb_state, media_type, favorite, content_hash, \
-                 main_uid, resolved_at, latitude, longitude FROM photos",
+                 main_uid, resolved_at, latitude, longitude, similar_hash FROM photos",
             )?;
             let rows = stmt.query_map([], |r| {
                 Ok((
@@ -310,6 +312,7 @@ impl Db {
                         location: r
                             .get::<_, Option<f64>>(9)?
                             .zip(r.get::<_, Option<f64>>(10)?),
+                        similar_hash: r.get(11)?,
                     },
                 ))
             })?;
@@ -332,6 +335,10 @@ impl Db {
                     carried.name = row.name.clone();
                     carried.media_type = row.media_type.clone();
                     carried.favorite = row.favorite.unwrap_or(false);
+                    // New bytes may show another picture: hash it again.
+                    if row.content_hash != carried.content_hash {
+                        carried.similar_hash = None;
+                    }
                     carried.content_hash = row.content_hash.clone();
                     carried.main_uid = row.main_uid.clone();
                     carried.location = row.location;
@@ -373,9 +380,9 @@ impl Db {
                 "INSERT INTO photos
                    (uid, capture_time, name, ratio, thumb_state, seq, media_type, kind, favorite,
                     content_hash, main_uid, group_key, resolved_at, latitude, longitude,
-                    place_id)
+                    place_id, similar_hash)
                  VALUES (?1, ?2, ?3, ?4, ?5, ?6, ?7, ?8, ?9, ?10, ?11, ?12, ?13, ?14, ?15,
-                         ?16)",
+                         ?16, ?17)",
             )?;
             for (seq, ((row, carried, kind), group_key)) in
                 resolved.iter().zip(group_keys.iter()).enumerate()
@@ -400,6 +407,7 @@ impl Db {
                         .location
                         .and_then(|(lat, lon)| crate::places::nearest(lat, lon))
                         .map(|city| city.id),
+                    carried.similar_hash,
                 ])?;
             }
         }
@@ -771,6 +779,106 @@ impl Db {
         Ok(sets)
     }
 
+    /// Shots whose look hasn't been hashed yet, by the uid of the photo the
+    /// grid shows for each, newest first, at most `limit`. Videos, and photos
+    /// with no thumbnail to hash, are left out. A shot counts as hashed once
+    /// any of its files is, since they all show one picture.
+    pub fn photos_unhashed(&self, limit: usize) -> Result<Vec<StoredPhoto>> {
+        let uids: Vec<String> = {
+            let conn = self.read();
+            let mut stmt = conn.prepare(
+                "SELECT COALESCE(group_key, uid) AS k FROM photos \
+                 GROUP BY k \
+                 HAVING MAX(similar_hash) IS NULL \
+                    AND MAX(kind != ?1 AND thumb_state != ?2) \
+                 ORDER BY MAX(capture_time) DESC LIMIT ?3",
+            )?;
+            stmt.query_map(
+                params![
+                    crate::control::PhotoKind::Video.as_i64(),
+                    THUMB_NONE,
+                    limit as i64
+                ],
+                |r| r.get(0),
+            )?
+            .collect::<rusqlite::Result<_>>()?
+        };
+        self.photos_by_uid(&uids)
+    }
+
+    /// Record the look of photo `uid`: its difference hash, or
+    /// [`crate::similar::NO_HASH`] when its thumbnail gave none.
+    pub fn photo_set_similar_hash(&self, uid: &str, hash: u64) -> Result<()> {
+        let conn = self.conn.lock();
+        conn.execute(
+            "UPDATE photos SET similar_hash = ?2 WHERE uid = ?1",
+            params![uid, hash as i64],
+        )?;
+        Ok(())
+    }
+
+    /// How many shots have been hashed, out of how many could be.
+    pub fn similar_progress(&self) -> Result<(usize, usize)> {
+        let conn = self.read();
+        let (hashed, total): (i64, i64) = conn.query_row(
+            "SELECT COUNT(*) FILTER (WHERE hashed), COUNT(*) FROM \
+               (SELECT MAX(similar_hash) IS NOT NULL AS hashed FROM photos \
+                GROUP BY COALESCE(group_key, uid) \
+                HAVING MAX(similar_hash) IS NOT NULL \
+                    OR MAX(kind != ?1 AND thumb_state != ?2))",
+            params![crate::control::PhotoKind::Video.as_i64(), THUMB_NONE],
+            |r| Ok((r.get(0)?, r.get(1)?)),
+        )?;
+        Ok((hashed.max(0) as usize, total.max(0) as usize))
+    }
+
+    /// Sets of shots that look alike (see [`crate::similar`]), one photo per
+    /// shot in capture order, and the sets newest first. A set whose photos
+    /// are all byte-identical copies is left to [`Self::photo_duplicates`].
+    pub fn photo_similar(&self) -> Result<Vec<Vec<StoredPhoto>>> {
+        let rows: Vec<(String, u64, Option<String>)> = {
+            let conn = self.read();
+            let mut stmt = conn.prepare(
+                "SELECT COALESCE(group_key, uid) AS k, MAX(similar_hash), \
+                        MAX(content_hash) FILTER (WHERE uid = COALESCE(group_key, uid)) \
+                 FROM photos GROUP BY k \
+                 HAVING MAX(similar_hash) IS NOT NULL AND MAX(similar_hash) != ?1",
+            )?;
+            stmt.query_map(params![crate::similar::NO_HASH as i64], |r| {
+                Ok((r.get(0)?, r.get::<_, i64>(1)? as u64, r.get(2)?))
+            })?
+            .collect::<rusqlite::Result<_>>()?
+        };
+        let hashes: Vec<u64> = rows.iter().map(|(_, hash, _)| *hash).collect();
+        let found: Vec<Vec<usize>> = crate::similar::sets(&hashes)
+            .into_iter()
+            .filter(|set| {
+                let first = &rows[set[0]].2;
+                first.is_none() || set.iter().any(|&i| rows[i].2 != *first)
+            })
+            .collect();
+        let uids: Vec<String> = found.iter().flatten().map(|&i| rows[i].0.clone()).collect();
+        let mut stored: HashMap<String, StoredPhoto> = self
+            .photos_by_uid(&uids)?
+            .into_iter()
+            .map(|photo| (photo.uid.clone(), photo))
+            .collect();
+        let mut sets: Vec<Vec<StoredPhoto>> = found
+            .iter()
+            .map(|set| {
+                let mut photos: Vec<StoredPhoto> = set
+                    .iter()
+                    .filter_map(|&i| stored.remove(&rows[i].0))
+                    .collect();
+                photos.sort_by_key(|p| p.capture_time);
+                photos
+            })
+            .filter(|set| set.len() > 1)
+            .collect();
+        sets.sort_by_key(|set| std::cmp::Reverse(set.iter().map(|p| p.capture_time).max()));
+        Ok(sets)
+    }
+
     /// Per-tab counts for the Photos page subtitle: `(photos, videos, raw)`.
     pub fn photos_counts(&self) -> Result<(usize, usize, usize)> {
         use crate::control::PhotoKind;

crates/pdfs-core/src/db/tests.rs

@@ -406,6 +406,76 @@ fn duplicates_list_the_copy_to_keep_first() {
     assert_eq!(uids, [vec!["filed", "copy"], vec!["jpeg", "stray"]]);
 }
 
+/// Shots that look alike form a set, one photo per shot, while a set of
+/// byte-identical copies is left to the duplicate finder.
+#[test]
+fn similar_photos_group_by_look_and_skip_exact_copies() {
+    let db = Db::open_in_memory().unwrap();
+    db.photos_replace(&[
+        hashed("big", 500, "IMG_1.JPG", "h1"),
+        hashed("small", 400, "IMG_1-small.JPG", "h2"),
+        hashed("copy", 300, "IMG_2.JPG", "h3"),
+        hashed("copy2", 200, "IMG_2(1).JPG", "h3"),
+        hashed("other", 100, "IMG_3.JPG", "h4"),
+        hashed("flat", 50, "IMG_4.JPG", "h5"),
+    ])
+    .unwrap();
+    let look = 0x0f0f_3c3c_5a5a_9696_u64;
+    db.photo_set_similar_hash("big", look).unwrap();
+    db.photo_set_similar_hash("small", look ^ 0b101).unwrap();
+    db.photo_set_similar_hash("copy", !look).unwrap();
+    db.photo_set_similar_hash("copy2", !look).unwrap();
+    db.photo_set_similar_hash("other", look ^ 0xffff_ffff)
+        .unwrap();
+    db.photo_set_similar_hash("flat", crate::similar::NO_HASH)
+        .unwrap();
+
+    let sets = db.photo_similar().unwrap();
+    let uids: Vec<Vec<&str>> = sets
+        .iter()
+        .map(|set| set.iter().map(|p| p.uid.as_str()).collect())
+        .collect();
+    assert_eq!(uids, [vec!["small", "big"]]);
+    assert_eq!(db.similar_progress().unwrap(), (6, 6));
+}
+
+/// What is left to hash skips videos and hashed shots, and a hash survives a
+/// refresh unless the photo's bytes changed.
+#[test]
+fn similar_hashes_are_kept_until_the_photo_changes() {
+    let db = Db::open_in_memory().unwrap();
+    let resolved = |uid: &str, hash: &str| TimelineRow {
+        resolved_at: Some(1),
+        ..hashed(uid, 100, &format!("{uid}.JPG"), hash)
+    };
+    db.photos_replace(&[
+        resolved("a", "h1"),
+        resolved("b", "h2"),
+        hashed("clip", 50, "clip.mp4", "h3"),
+    ])
+    .unwrap();
+    db.photo_set_similar_hash("a", 7).unwrap();
+    db.photo_set_similar_hash("b", 9).unwrap();
+    let left = |db: &Db| -> Vec<String> {
+        db.photos_unhashed(10)
+            .unwrap()
+            .into_iter()
+            .map(|p| p.uid)
+            .collect()
+    };
+    assert!(left(&db).is_empty());
+    assert_eq!(db.similar_progress().unwrap(), (2, 2));
+
+    db.photos_replace(&[
+        resolved("a", "h1"),
+        resolved("b", "h2-edited"),
+        hashed("clip", 50, "clip.mp4", "h3"),
+    ])
+    .unwrap();
+    assert_eq!(left(&db), ["b"]);
+    assert_eq!(db.similar_progress().unwrap(), (1, 2));
+}
+
 /// Trashing the file a group is shown as leaves the rest of the group on the
 /// timeline instead of pointing at a photo that is gone.
 #[test]