Sort reminders lists by drag-and-drop (#40)

* Proof-of-concept: manual list sorting.

* wip

* wip

* wip

---------

Co-authored-by: Stephen Celis <stephen@stephencelis.com>

Author: mbrandonw

Examples/Reminders/RemindersLists.swift

@@ -5,6 +5,7 @@ struct RemindersListsView: View {
   @FetchAll(
     RemindersList
       .group(by: \.id)
+      .order(by: \.position)
       .leftJoin(Reminder.all) { $0.id.eq($1.remindersListID) && !$1.isCompleted }
       .select {
         ReminderListState.Columns(remindersCount: $1.id.count(), remindersList: $0)
@@ -129,7 +130,10 @@ struct RemindersListsView: View {
                 remindersCount: state.remindersCount,
                 remindersList: state.remindersList
               )
-            }
+          }
+          }
+          .onMove { indexSet, index in
+            move(from: indexSet, to: index)
           }
         } header: {
           Text("My Lists")
@@ -210,6 +214,27 @@ struct RemindersListsView: View {
       RemindersListDetailView(detailType: detailType)
     }
   }
+
+  func move(from source: IndexSet, to destination: Int) {
+    withErrorReporting {
+      try database.write { db in
+        var ids = remindersLists.map(\.remindersList.id)
+        ids.move(fromOffsets: source, toOffset: destination)
+        try RemindersList
+          .where { $0.id.in(ids) }
+          .update {
+            let ids = Array(ids.enumerated())
+            let (first, rest) = (ids.first!, ids.dropFirst())
+            $0.position = rest
+              .reduce(Case($0.id).when(first.element, then: first.offset)) { cases, id in
+                cases.when(id.element, then: id.offset)
+              }
+              .else($0.position)
+          }
+          .execute(db)
+      }
+    }
+  }
 }
 
 private struct ReminderGridCell: View {

Examples/Reminders/Schema.swift

@@ -9,6 +9,7 @@ struct RemindersList: Hashable, Identifiable {
   var id: Int
   @Column(as: Color.HexRepresentation.self)
   var color = Color(red: 0x4a / 255, green: 0x99 / 255, blue: 0xef / 255)
+  var position = 0
   var title = ""
 }
 
@@ -107,7 +108,7 @@ func appDatabase() throws -> any DatabaseWriter {
   #if DEBUG
     migrator.eraseDatabaseOnSchemaChange = true
   #endif
-  migrator.registerMigration("Add reminders lists table") { db in
+  migrator.registerMigration("Create initial tables") { db in
     try #sql(
       """
       CREATE TABLE "remindersLists" (
@@ -118,8 +119,6 @@ func appDatabase() throws -> any DatabaseWriter {
       """
     )
     .execute(db)
-  }
-  migrator.registerMigration("Add reminders table") { db in
     try #sql(
       """
       CREATE TABLE "reminders" (
@@ -137,8 +136,6 @@ func appDatabase() throws -> any DatabaseWriter {
       """
     )
     .execute(db)
-  }
-  migrator.registerMigration("Add tags table") { db in
     try #sql(
       """
       CREATE TABLE "tags" (
@@ -161,6 +158,27 @@ func appDatabase() throws -> any DatabaseWriter {
     )
     .execute(db)
   }
+  migrator.registerMigration("Add 'position' column to 'remindersLists'") { db in
+    try #sql(
+      """
+      ALTER TABLE "remindersLists"
+      ADD COLUMN "position" INTEGER NOT NULL DEFAULT 0
+      """
+    )
+    .execute(db)
+    try #sql(
+      """
+      CREATE TRIGGER "default_position_reminders_lists" 
+      AFTER INSERT ON "remindersLists"
+      FOR EACH ROW BEGIN
+        UPDATE "remindersLists"
+        SET "position" = (SELECT max("position") + 1 FROM "remindersLists")
+        WHERE "id" = NEW."id";
+      END
+      """
+    )
+    .execute(db)
+  }
   #if DEBUG && targetEnvironment(simulator)
     if context != .test {
       migrator.registerMigration("Seed sample data") { db in