Fix table drop order during backup import.

Fixes #12671

app/src/test/java/org/thoughtcrime/securesms/backup/FullBackupImporterTest.kt

@@ -0,0 +1,162 @@
+package org.thoughtcrime.securesms.backup
+
+import org.junit.Assert.assertEquals
+import org.junit.Test
+
+class FullBackupImporterTest {
+
+  @Test
+  fun `computeTableOrder - empty`() {
+    val order = FullBackupImporter.computeTableDropOrder(mapOf())
+
+    assertEquals(listOf<String>(), order)
+  }
+
+  /**
+   * A B C
+   */
+  @Test
+  fun `computeTableOrder - no dependencies`() {
+    val order = FullBackupImporter.computeTableDropOrder(
+      mapOf(
+        "A" to setOf(),
+        "B" to setOf(),
+        "C" to setOf(),
+      )
+    )
+
+    assertEquals(listOf("A", "B", "C"), order)
+  }
+
+  /**
+   * A
+   * |
+   * B
+   * |
+   * C
+   */
+  @Test
+  fun `computeTableOrder - single chain`() {
+    val order = FullBackupImporter.computeTableDropOrder(
+      mapOf(
+        "A" to setOf("B"),
+        "B" to setOf("C"),
+      )
+    )
+
+    assertEquals(listOf("A", "B", "C"), order)
+  }
+
+  /**
+   *   ┌──A──┐    B   C
+   * ┌─D   ┌─E─┐
+   * F     G   H
+   */
+  @Test
+  fun `computeTableOrder - complex 1`() {
+    val order = FullBackupImporter.computeTableDropOrder(
+      mapOf(
+        "A" to setOf("D", "E"),
+        "B" to setOf(),
+        "C" to setOf(),
+        "D" to setOf("F"),
+        "E" to setOf("G", "H"),
+        "F" to setOf(),
+        "G" to setOf(),
+        "H" to setOf(),
+      )
+    )
+
+    assertEquals(listOf("A", "B", "C", "D", "E", "F", "G", "H"), order)
+  }
+
+  /**
+   *   ┌────A────┐
+   *   │    |    │
+   * ┌─B─┐  C  ┌─D─┐
+   * │   │  |  │   │
+   * E   F  G  H   I
+   */
+  @Test
+  fun `computeTableOrder - complex 2`() {
+    val order = FullBackupImporter.computeTableDropOrder(
+      mapOf(
+        "A" to setOf("B", "C", "D"),
+        "B" to setOf("E", "F"),
+        "C" to setOf("G"),
+        "D" to setOf("H", "I"),
+        "E" to setOf(),
+        "F" to setOf(),
+        "G" to setOf(),
+        "H" to setOf(),
+        "I" to setOf(),
+      )
+    )
+
+    assertEquals(listOf("A", "B", "C", "D", "E", "F", "G", "H", "I"), order)
+  }
+
+  /**
+   * ┌─A─┐  B  ┌─C─┐
+   * │   │  |  │   │
+   * D   E  F  G   H
+   */
+  @Test
+  fun `computeTableOrder - multiple roots`() {
+    val order = FullBackupImporter.computeTableDropOrder(
+      mapOf(
+        "A" to setOf("D", "E"),
+        "B" to setOf("F"),
+        "C" to setOf("G", "H"),
+        "D" to setOf(),
+        "E" to setOf(),
+        "F" to setOf(),
+        "G" to setOf(),
+        "H" to setOf(),
+      )
+    )
+
+    assertEquals(listOf("A", "B", "C", "D", "E", "F", "G", "H"), order)
+  }
+
+  /**
+   * ┌─A─┐  B  ┌─C─┐
+   * │   │  |  │   │
+   * D   E  D  D   E
+   */
+  @Test
+  fun `computeTableOrder - multiple roots, dupes across graphs`() {
+    val order = FullBackupImporter.computeTableDropOrder(
+      mapOf(
+        "A" to setOf("D", "E"),
+        "B" to setOf("D"),
+        "C" to setOf("D", "E"),
+        "D" to setOf(),
+        "E" to setOf(),
+      )
+    )
+
+    assertEquals(listOf("A", "B", "C", "D", "E"), order)
+  }
+
+  /**
+   * A  B
+   * │  │
+   * D  C
+   *    │
+   *    D
+   */
+  @Test
+  fun `computeTableOrder - multiple roots, new dependencies across roots`() {
+    val order = FullBackupImporter.computeTableDropOrder(
+      mapOf(
+        "A" to setOf("D"),
+        "B" to setOf("C"),
+        "C" to setOf("D"),
+        "D" to setOf(),
+      )
+    )
+
+    assertEquals(listOf("A", "B", "C", "D"), order)
+  }
+}