Batch scrobble rule application by type to reduce N queries to 2 (#61)

* Implement optimized batch rule application

- Add apply_all_album_rules/1 to batch apply all album rules in single query
- Add apply_all_artist_rules/1 to batch apply all artist rules in single query
- Update apply_all_rules/0 to use new batch functions
- Add comprehensive tests for batch application
- Use CASE statement in SQL to apply multiple rules efficiently

Co-authored-by: cloud8421 <537608+cloud8421@users.noreply.github.com>

* Add batch application support for track-filtered rules

- Extend apply_all_album_rules/2 to support filtering by tracks
- Extend apply_all_artist_rules/2 to support filtering by tracks
- Update apply_all_rules/1 to use batch functions for track-filtered application
- Remove duplicate function definitions
- Ensures both main use cases (all tracks and specific tracks) are optimized

Co-authored-by: cloud8421 <537608+cloud8421@users.noreply.github.com>

* Add comprehensive documentation for optimization

- Document the problem and solution approach
- Explain SQL generation and performance impact
- Detail trade-offs and backward compatibility
- Include future considerations and scalability notes

Co-authored-by: cloud8421 <537608+cloud8421@users.noreply.github.com>

* Apply credo suggestions and format

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: cloud8421 <537608+cloud8421@users.noreply.github.com>
Co-authored-by: Claudio Ortolina <cloud8421@gmail.com>

docs/scrobble_rule_optimization.md

@@ -0,0 +1,219 @@
+# Scrobble Rule Application Optimization
+
+## Overview
+
+This document describes the optimization made to the scrobble rule application system to improve performance when applying multiple rules.
+
+## Problem
+
+Previously, when applying all enabled scrobble rules, each rule was applied independently with a separate database UPDATE query. With N rules, this resulted in N separate database operations, which became inefficient as the number of rules grew.
+
+### Previous Implementation
+
+```elixir
+def apply_all_rules do
+  list_enabled_rules()
+  |> Enum.map(fn rule ->
+    case apply_rule(rule) do
+      {:ok, count} -> {:ok, {rule.type, rule.match_value, count}}
+      {:error, reason} -> {:error, {rule.type, rule.match_value, reason}}
+    end
+  end)
+end
+```
+
+This approach meant:
+- 10 rules = 10 separate UPDATE queries
+- 100 rules = 100 separate UPDATE queries
+- Each query had to scan the entire `scrobbled_tracks` table
+
+## Solution
+
+The optimization groups rules by type (album/artist) and applies all rules of each type in a single database query using SQLite's CASE statement.
+
+### New Implementation
+
+```elixir
+def apply_all_rules do
+  enabled_rules = list_enabled_rules()
+  
+  # Group rules by type
+  {album_rules, artist_rules} = 
+    Enum.split_with(enabled_rules, fn rule -> rule.type == :album end)
+  
+  # Apply all album rules in one query
+  apply_all_album_rules(album_rules)
+  
+  # Apply all artist rules in one query
+  apply_all_artist_rules(artist_rules)
+end
+```
+
+This approach means:
+- 10 album rules + 10 artist rules = 2 total UPDATE queries (one for albums, one for artists)
+- 100 album rules + 100 artist rules = 2 total UPDATE queries
+- Each query still scans the table once, but updates all matching records in a single pass
+
+## Technical Details
+
+### SQL Generation
+
+The optimization dynamically builds a CASE statement for all rules of the same type:
+
+**Example for 2 album rules:**
+
+```sql
+UPDATE scrobbled_tracks 
+SET album = CASE 
+  WHEN json_extract(album, '$.title') = 'Dark Side of the Moon' 
+    THEN json_set(album, '$.musicbrainz_id', '12345678-1234-1234-1234-123456789012')
+  WHEN json_extract(album, '$.title') = 'Wish You Were Here' 
+    THEN json_set(album, '$.musicbrainz_id', 'abcdef12-3456-7890-abcd-ef1234567890')
+  ELSE album 
+END
+WHERE json_extract(album, '$.title') IN ('Dark Side of the Moon', 'Wish You Were Here')
+```
+
+The WHERE clause uses IN to filter only tracks that match any of the rules, avoiding unnecessary updates.
+
+### Functions Added
+
+#### 1. `apply_all_album_rules/1`
+Applies all album rules in a single query.
+
+```elixir
+@spec apply_all_album_rules([ScrobbleRule.t()]) :: {:ok, non_neg_integer()} | {:error, any()}
+```
+
+#### 2. `apply_all_artist_rules/1`
+Applies all artist rules in a single query.
+
+```elixir
+@spec apply_all_artist_rules([ScrobbleRule.t()]) :: {:ok, non_neg_integer()} | {:error, any()}
+```
+
+#### 3. `apply_all_album_rules/2`
+Applies all album rules to a specific set of tracks in a single query.
+
+```elixir
+@spec apply_all_album_rules([ScrobbleRule.t()], [Track.t()]) :: 
+  {:ok, non_neg_integer()} | {:error, any()}
+```
+
+#### 4. `apply_all_artist_rules/2`
+Applies all artist rules to a specific set of tracks in a single query.
+
+```elixir
+@spec apply_all_artist_rules([ScrobbleRule.t()], [Track.t()]) :: 
+  {:ok, non_neg_integer()} | {:error, any()}
+```
+
+### Use Cases
+
+The optimization handles two main use cases:
+
+#### 1. Periodic Full Application
+The `ApplyScrobbleRules` Oban worker runs every 30 minutes and applies all rules to all tracks:
+
+```elixir
+ScrobbleRules.apply_all_rules()
+```
+
+#### 2. Incremental Application on New Tracks
+When new tracks are inserted via `LastFm.Feed.update/1`, rules are applied to just those tracks:
+
+```elixir
+tracks
+|> ScrobbleRules.apply_all_rules()
+```
+
+Both use cases now benefit from batched rule application.
+
+## Performance Impact
+
+### Expected Improvements
+
+For a database with:
+- 10,000 scrobbled tracks
+- 20 enabled rules (10 album + 10 artist)
+
+**Before:**
+- 20 UPDATE queries
+- Each query scans ~10,000 rows
+- Total: ~200,000 row scans
+
+**After:**
+- 2 UPDATE queries (1 for albums, 1 for artists)
+- Each query scans ~10,000 rows
+- Total: ~20,000 row scans
+
+**Result:** ~10x reduction in database operations for this scenario.
+
+The benefit scales with the number of rules:
+- 5 rules: ~2.5x improvement
+- 10 rules: ~5x improvement
+- 20 rules: ~10x improvement
+- 100 rules: ~50x improvement
+
+## Trade-offs
+
+### Return Value Semantics
+
+With the batched approach, all rules of the same type report the same aggregate count (total rows updated) rather than individual per-rule counts:
+
+```elixir
+# Before: Each rule gets its own count
+[
+  {:ok, {:album, "Album 1", 5}},   # 5 tracks updated
+  {:ok, {:album, "Album 2", 3}},   # 3 tracks updated
+]
+
+# After: Both rules report the total updated
+[
+  {:ok, {:album, "Album 1", 8}},   # 8 total tracks updated
+  {:ok, {:album, "Album 2", 8}},   # 8 total tracks updated
+]
+```
+
+This is an acceptable trade-off because:
+1. The logging still shows how many rules were applied
+2. The total tracks updated is more meaningful for understanding impact
+3. Getting individual counts would require separate queries, negating the optimization
+
+### Backward Compatibility
+
+The API remains fully backward compatible:
+- All existing functions (`apply_rule/1`, `apply_album_rule/1`, etc.) still work
+- Return value format is unchanged: `{:ok, {type, match_value, count}}`
+- Error handling is unchanged
+- Tests continue to pass
+
+## Testing
+
+New tests were added to verify the optimization:
+
+1. `apply_all_album_rules/1` applies multiple album rules in one query
+2. `apply_all_artist_rules/1` applies multiple artist rules in one query  
+3. Empty list handling returns `{:ok, 0}`
+4. `apply_all_rules/0` correctly batches rules by type
+5. All existing tests continue to pass
+
+## Future Considerations
+
+### Potential Enhancements
+
+1. **Parallel Execution**: Album and artist rule applications could run in parallel since they're independent
+2. **Query Optimization**: Could add indexes on `json_extract(album, '$.title')` and `json_extract(artist, '$.name')` if performance is still a concern
+3. **Metrics**: Add telemetry events to track batch sizes and execution times
+4. **Rule Ordering**: If rule priority matters in the future, the CASE statement naturally handles this (first match wins)
+
+### Scalability
+
+The current approach scales well up to ~100 rules per type. Beyond that, consider:
+- SQL query length limits (SQLite's default limit is 1MB, which allows ~10,000 rules)
+- Transaction size and memory usage
+- Potential chunking if needed (apply rules in batches of N)
+
+## Conclusion
+
+This optimization significantly improves the performance of scrobble rule application by reducing database operations from O(N) to O(1) per rule type, where N is the number of rules. The implementation maintains backward compatibility while providing substantial performance benefits that scale with the number of rules.

lib/music_library/scrobble_rules.ex

@@ -326,9 +326,229 @@ defmodule MusicLibrary.ScrobbleRules do
     apply_artist_rule(rule, tracks)
   end
 
+  @doc """
+  Applies all album rules in a single query.
+
+  Uses a CASE statement to update the musicbrainz_id for all matching albums
+  in one database operation, which is more efficient than applying rules individually.
+
+  ## Examples
+
+      iex> apply_all_album_rules([rule1, rule2])
+      {:ok, 15}
+
+  """
+  def apply_all_album_rules([]), do: {:ok, 0}
+
+  def apply_all_album_rules(rules) when is_list(rules) do
+    # Build CASE WHEN clauses dynamically
+    {case_clauses, case_params} =
+      rules
+      |> Enum.reduce({"", []}, fn rule, {sql_acc, params_acc} ->
+        clause =
+          "WHEN json_extract(album, '$.title') = ? THEN json_set(album, '$.musicbrainz_id', ?) "
+
+        {sql_acc <> clause, params_acc ++ [rule.match_value, rule.target_musicbrainz_id]}
+      end)
+
+    # Build complete UPDATE statement
+    case_sql = "CASE #{case_clauses}ELSE album END"
+
+    # Build WHERE IN clause
+    match_values = Enum.map(rules, & &1.match_value)
+    in_placeholders = Enum.map_join(match_values, ", ", fn _ -> "?" end)
+    where_sql = "json_extract(album, '$.title') IN (#{in_placeholders})"
+
+    # Complete SQL
+    sql = """
+    UPDATE scrobbled_tracks 
+    SET album = #{case_sql}
+    WHERE #{where_sql}
+    """
+
+    # All parameters: case params + where params
+    all_params = case_params ++ match_values
+
+    # Execute the query
+    case Repo.query(sql, all_params) do
+      {:ok, %{num_rows: count}} -> {:ok, count}
+      {:error, reason} -> {:error, reason}
+    end
+  end
+
+  @doc """
+  Applies all album rules to a specific set of tracks in a single query.
+
+  Uses a CASE statement to update the musicbrainz_id for all matching albums
+  in one database operation, filtering by the provided tracks.
+
+  ## Examples
+
+      iex> apply_all_album_rules([rule1, rule2], tracks)
+      {:ok, 3}
+
+  """
+  def apply_all_album_rules([], _tracks), do: {:ok, 0}
+  def apply_all_album_rules(_rules, []), do: {:ok, 0}
+
+  def apply_all_album_rules(rules, tracks) when is_list(rules) and is_list(tracks) do
+    # Build CASE WHEN clauses dynamically
+    {case_clauses, case_params} =
+      rules
+      |> Enum.reduce({"", []}, fn rule, {sql_acc, params_acc} ->
+        clause =
+          "WHEN json_extract(album, '$.title') = ? THEN json_set(album, '$.musicbrainz_id', ?) "
+
+        {sql_acc <> clause, params_acc ++ [rule.match_value, rule.target_musicbrainz_id]}
+      end)
+
+    # Build complete UPDATE statement
+    case_sql = "CASE #{case_clauses}ELSE album END"
+
+    # Build WHERE IN clause for album titles
+    match_values = Enum.map(rules, & &1.match_value)
+    album_placeholders = Enum.map_join(match_values, ", ", fn _ -> "?" end)
+
+    # Build WHERE IN clause for track timestamps
+    track_scrobbled_at_uts = Enum.map(tracks, & &1.scrobbled_at_uts)
+    track_placeholders = Enum.map_join(track_scrobbled_at_uts, ", ", fn _ -> "?" end)
+
+    where_sql =
+      "json_extract(album, '$.title') IN (#{album_placeholders}) AND " <>
+        "scrobbled_at_uts IN (#{track_placeholders})"
+
+    # Complete SQL
+    sql = """
+    UPDATE scrobbled_tracks 
+    SET album = #{case_sql}
+    WHERE #{where_sql}
+    """
+
+    # All parameters: case params + album match values + track timestamps
+    all_params = case_params ++ match_values ++ track_scrobbled_at_uts
+
+    # Execute the query
+    case Repo.query(sql, all_params) do
+      {:ok, %{num_rows: count}} -> {:ok, count}
+      {:error, reason} -> {:error, reason}
+    end
+  end
+
+  @doc """
+  Applies all artist rules in a single query.
+
+  Uses a CASE statement to update the musicbrainz_id for all matching artists
+  in one database operation, which is more efficient than applying rules individually.
+
+  ## Examples
+
+      iex> apply_all_artist_rules([rule1, rule2])
+      {:ok, 25}
+
+  """
+  def apply_all_artist_rules([]), do: {:ok, 0}
+
+  def apply_all_artist_rules(rules) when is_list(rules) do
+    # Build CASE WHEN clauses dynamically
+    {case_clauses, case_params} =
+      rules
+      |> Enum.reduce({"", []}, fn rule, {sql_acc, params_acc} ->
+        clause =
+          "WHEN json_extract(artist, '$.name') = ? THEN json_set(artist, '$.musicbrainz_id', ?) "
+
+        {sql_acc <> clause, params_acc ++ [rule.match_value, rule.target_musicbrainz_id]}
+      end)
+
+    # Build complete UPDATE statement
+    case_sql = "CASE #{case_clauses}ELSE artist END"
+
+    # Build WHERE IN clause
+    match_values = Enum.map(rules, & &1.match_value)
+    in_placeholders = Enum.map_join(match_values, ", ", fn _ -> "?" end)
+    where_sql = "json_extract(artist, '$.name') IN (#{in_placeholders})"
+
+    # Complete SQL
+    sql = """
+    UPDATE scrobbled_tracks 
+    SET artist = #{case_sql}
+    WHERE #{where_sql}
+    """
+
+    # All parameters: case params + where params
+    all_params = case_params ++ match_values
+
+    # Execute the query
+    case Repo.query(sql, all_params) do
+      {:ok, %{num_rows: count}} -> {:ok, count}
+      {:error, reason} -> {:error, reason}
+    end
+  end
+
+  @doc """
+  Applies all artist rules to a specific set of tracks in a single query.
+
+  Uses a CASE statement to update the musicbrainz_id for all matching artists
+  in one database operation, filtering by the provided tracks.
+
+  ## Examples
+
+      iex> apply_all_artist_rules([rule1, rule2], tracks)
+      {:ok, 7}
+
+  """
+  def apply_all_artist_rules([], _tracks), do: {:ok, 0}
+  def apply_all_artist_rules(_rules, []), do: {:ok, 0}
+
+  def apply_all_artist_rules(rules, tracks) when is_list(rules) and is_list(tracks) do
+    # Build CASE WHEN clauses dynamically
+    {case_clauses, case_params} =
+      rules
+      |> Enum.reduce({"", []}, fn rule, {sql_acc, params_acc} ->
+        clause =
+          "WHEN json_extract(artist, '$.name') = ? THEN json_set(artist, '$.musicbrainz_id', ?) "
+
+        {sql_acc <> clause, params_acc ++ [rule.match_value, rule.target_musicbrainz_id]}
+      end)
+
+    # Build complete UPDATE statement
+    case_sql = "CASE #{case_clauses}ELSE artist END"
+
+    # Build WHERE IN clause for artist names
+    match_values = Enum.map(rules, & &1.match_value)
+    artist_placeholders = Enum.map_join(match_values, ", ", fn _ -> "?" end)
+
+    # Build WHERE IN clause for track timestamps
+    track_scrobbled_at_uts = Enum.map(tracks, & &1.scrobbled_at_uts)
+    track_placeholders = Enum.map_join(track_scrobbled_at_uts, ", ", fn _ -> "?" end)
+
+    where_sql =
+      "json_extract(artist, '$.name') IN (#{artist_placeholders}) AND " <>
+        "scrobbled_at_uts IN (#{track_placeholders})"
+
+    # Complete SQL
+    sql = """
+    UPDATE scrobbled_tracks 
+    SET artist = #{case_sql}
+    WHERE #{where_sql}
+    """
+
+    # All parameters: case params + artist match values + track timestamps
+    all_params = case_params ++ match_values ++ track_scrobbled_at_uts
+
+    # Execute the query
+    case Repo.query(sql, all_params) do
+      {:ok, %{num_rows: count}} -> {:ok, count}
+      {:error, reason} -> {:error, reason}
+    end
+  end
+
   @doc """
   Applies all enabled rules.
 
+  This optimized version groups rules by type and applies all rules of each type
+  in a single database query, which is much more efficient than applying each rule
+  individually.
+
   ## Examples
 
       iex> apply_all_rules()
@@ -337,14 +557,45 @@ defmodule MusicLibrary.ScrobbleRules do
   """
   def apply_all_rules do
     :telemetry.span([:music_library, :scrobble_rules, :apply_all_rules], %{}, fn ->
-      result =
+      enabled_rules = list_enabled_rules()
-        list_enabled_rules()
+
-        |> Enum.map(fn rule ->
+      # Group rules by type
-          case apply_rule(rule) do
+      {album_rules, artist_rules} =
-            {:ok, count} -> {:ok, {rule.type, rule.match_value, count}}
+        Enum.split_with(enabled_rules, fn rule -> rule.type == :album end)
-            {:error, reason} -> {:error, {rule.type, rule.match_value, reason}}
+
-          end
+      # Apply all album rules in one query
-        end)
+      album_result =
+        case apply_all_album_rules(album_rules) do
+          {:ok, count} ->
+            # Return the count for each album rule (total updated)
+            # Note: this returns the same count for each rule since they're applied together
+            Enum.map(album_rules, fn rule ->
+              {:ok, {rule.type, rule.match_value, count}}
+            end)
+
+          {:error, reason} ->
+            Enum.map(album_rules, fn rule ->
+              {:error, {rule.type, rule.match_value, reason}}
+            end)
+        end
+
+      # Apply all artist rules in one query
+      artist_result =
+        case apply_all_artist_rules(artist_rules) do
+          {:ok, count} ->
+            # Return the count for each artist rule (total updated)
+            # Note: this returns the same count for each rule since they're applied together
+            Enum.map(artist_rules, fn rule ->
+              {:ok, {rule.type, rule.match_value, count}}
+            end)
+
+          {:error, reason} ->
+            Enum.map(artist_rules, fn rule ->
+              {:error, {rule.type, rule.match_value, reason}}
+            end)
+        end
+
+      result = album_result ++ artist_result
 
       {result, %{scrobble_track_count: :all}}
     end)
@@ -353,6 +604,9 @@ defmodule MusicLibrary.ScrobbleRules do
   @doc """
   Applies all enabled rules to a specific set of tracks.
 
+  This optimized version groups rules by type and applies all rules of each type
+  in a single database query, filtering by the provided tracks.
+
   ## Examples
 
       iex> apply_all_rules(tracks)
@@ -368,14 +622,41 @@ defmodule MusicLibrary.ScrobbleRules do
 
   def apply_all_rules(tracks) do
     :telemetry.span([:music_library, :scrobble_rules, :apply_all_rules], %{}, fn ->
-      result =
+      enabled_rules = list_enabled_rules()
-        list_enabled_rules()
+
-        |> Enum.map(fn rule ->
+      # Group rules by type
-          case apply_rule(rule, tracks) do
+      {album_rules, artist_rules} =
-            {:ok, count} -> {:ok, {rule.type, rule.match_value, count}}
+        Enum.split_with(enabled_rules, fn rule -> rule.type == :album end)
-            {:error, reason} -> {:error, {rule.type, rule.match_value, reason}}
+
-          end
+      # Apply all album rules in one query
-        end)
+      album_result =
+        case apply_all_album_rules(album_rules, tracks) do
+          {:ok, count} ->
+            Enum.map(album_rules, fn rule ->
+              {:ok, {rule.type, rule.match_value, count}}
+            end)
+
+          {:error, reason} ->
+            Enum.map(album_rules, fn rule ->
+              {:error, {rule.type, rule.match_value, reason}}
+            end)
+        end
+
+      # Apply all artist rules in one query
+      artist_result =
+        case apply_all_artist_rules(artist_rules, tracks) do
+          {:ok, count} ->
+            Enum.map(artist_rules, fn rule ->
+              {:ok, {rule.type, rule.match_value, count}}
+            end)
+
+          {:error, reason} ->
+            Enum.map(artist_rules, fn rule ->
+              {:error, {rule.type, rule.match_value, reason}}
+            end)
+        end
+
+      result = album_result ++ artist_result
 
       {result, %{scrobble_track_count: Enum.count(tracks)}}
     end)

test/music_library/scrobble_rules_test.exs

@@ -287,5 +287,141 @@ defmodule MusicLibrary.ScrobbleRulesTest do
 
       assert ScrobbleRules.count_artist_matches(rule) == 2
     end
+
+    test "apply_all_album_rules/1 applies multiple album rules in one query" do
+      # Create two album rules
+      rule1 = scrobble_rule_fixture(@valid_album_attrs)
+
+      rule2 =
+        scrobble_rule_fixture(%{
+          match_value: "Wish You Were Here",
+          target_musicbrainz_id: "abcdef12-3456-7890-abcd-ef1234567890"
+        })
+
+      # Create tracks matching each rule
+      track1 =
+        scrobbled_track_fixture(%{
+          album: %{musicbrainz_id: "", title: "Dark Side of the Moon"}
+        })
+
+      track2 =
+        scrobbled_track_fixture(%{
+          scrobbled_at_uts: System.system_time(:second) + 1,
+          album: %{musicbrainz_id: "", title: "Wish You Were Here"}
+        })
+
+      # Create a non-matching track
+      _track3 =
+        scrobbled_track_fixture(%{
+          scrobbled_at_uts: System.system_time(:second) + 2,
+          album: %{musicbrainz_id: "", title: "The Wall"}
+        })
+
+      # Apply both rules at once
+      assert {:ok, 2} = ScrobbleRules.apply_all_album_rules([rule1, rule2])
+
+      # Verify both tracks were updated by fetching them again
+      updated_track1 = Repo.get(Track, track1.scrobbled_at_uts)
+      assert updated_track1.album.musicbrainz_id == rule1.target_musicbrainz_id
+
+      updated_track2 = Repo.get(Track, track2.scrobbled_at_uts)
+      assert updated_track2.album.musicbrainz_id == rule2.target_musicbrainz_id
+    end
+
+    test "apply_all_artist_rules/1 applies multiple artist rules in one query" do
+      # Create two artist rules
+      rule1 = scrobble_rule_fixture(@valid_artist_attrs)
+
+      rule2 =
+        scrobble_rule_fixture(%{
+          type: :artist,
+          match_value: "Led Zeppelin",
+          target_musicbrainz_id: "fedcba98-7654-3210-fedc-ba9876543210"
+        })
+
+      # Create tracks matching each rule
+      track1 =
+        scrobbled_track_fixture(%{
+          artist: %{musicbrainz_id: "", name: "Pink Floyd"}
+        })
+
+      track2 =
+        scrobbled_track_fixture(%{
+          scrobbled_at_uts: System.system_time(:second) + 1,
+          artist: %{musicbrainz_id: "", name: "Led Zeppelin"}
+        })
+
+      # Create a non-matching track
+      _track3 =
+        scrobbled_track_fixture(%{
+          scrobbled_at_uts: System.system_time(:second) + 2,
+          artist: %{musicbrainz_id: "", name: "The Beatles"}
+        })
+
+      # Apply both rules at once
+      assert {:ok, 2} = ScrobbleRules.apply_all_artist_rules([rule1, rule2])
+
+      # Verify both tracks were updated by fetching them again
+      updated_track1 = Repo.get(Track, track1.scrobbled_at_uts)
+      assert updated_track1.artist.musicbrainz_id == rule1.target_musicbrainz_id
+
+      updated_track2 = Repo.get(Track, track2.scrobbled_at_uts)
+      assert updated_track2.artist.musicbrainz_id == rule2.target_musicbrainz_id
+    end
+
+    test "apply_all_album_rules/1 with empty list returns 0" do
+      assert {:ok, 0} = ScrobbleRules.apply_all_album_rules([])
+    end
+
+    test "apply_all_artist_rules/1 with empty list returns 0" do
+      assert {:ok, 0} = ScrobbleRules.apply_all_artist_rules([])
+    end
+
+    test "apply_all_rules/0 batches rules by type" do
+      # Create multiple rules of each type
+      _album_rule1 = scrobble_rule_fixture(@valid_album_attrs)
+
+      _album_rule2 =
+        scrobble_rule_fixture(%{
+          match_value: "Wish You Were Here",
+          target_musicbrainz_id: "abcdef12-3456-7890-abcd-ef1234567890"
+        })
+
+      _artist_rule1 = scrobble_rule_fixture(@valid_artist_attrs)
+
+      _artist_rule2 =
+        scrobble_rule_fixture(%{
+          type: :artist,
+          match_value: "Led Zeppelin",
+          target_musicbrainz_id: "fedcba98-7654-3210-fedc-ba9876543210"
+        })
+
+      # Create tracks matching the rules
+      _track1 =
+        scrobbled_track_fixture(%{
+          album: %{musicbrainz_id: "", title: "Dark Side of the Moon"},
+          artist: %{musicbrainz_id: "", name: "Pink Floyd"}
+        })
+
+      _track2 =
+        scrobbled_track_fixture(%{
+          scrobbled_at_uts: System.system_time(:second) + 1,
+          album: %{musicbrainz_id: "", title: "Wish You Were Here"},
+          artist: %{musicbrainz_id: "", name: "Led Zeppelin"}
+        })
+
+      # Apply all rules
+      results = ScrobbleRules.apply_all_rules()
+
+      # Should have 4 results (one for each rule)
+      assert length(results) == 4
+
+      # All results should be successful
+      Enum.each(results, fn result ->
+        assert {:ok, {_type, _match_value, count}} = result
+        # Count should be > 0 since we have matching tracks
+        assert count > 0
+      end)
+    end
   end
 end