migrations

migrations.ts

@@ -0,0 +1,63 @@
+import { types as T } from "./mod.ts";
+import { EmVer } from "./emver-lite/mod.ts";
+
+export type MigrationFn = (effects: T.Effects) => Promise<T.MigrationRes>;
+
+export interface Migration {
+  up: MigrationFn;
+  down: MigrationFn;
+}
+
+export interface MigrationMapping {
+  [version: string]: Migration;
+}
+
+export function fromMapping(
+  migrations: MigrationMapping,
+  currentVersion: string,
+): T.ExpectedExports.migration {
+  return async (effects: T.Effects, version: string) => {
+    let configured = true;
+
+    const current = EmVer.parse(currentVersion);
+    const previous = EmVer.parse(version);
+
+    let migrationsToRun: MigrationFn[];
+    switch (previous.compare(current)) {
+      case 0:
+        migrationsToRun = [];
+        break;
+      case 1: // ups
+        migrationsToRun = Object.entries(migrations).map(
+          ([version, migration]) => ({
+            version: EmVer.parse(version),
+            migration,
+          }),
+        ).filter(({ version }) => version.greaterThan(previous)).sort((a, b) =>
+          a.version.compare(b.version)
+        ).map(({ migration }) => migration.up);
+        break;
+      case -1: // downs
+        migrationsToRun = Object.entries(migrations).map(
+          ([version, migration]) => ({
+            version: EmVer.parse(version),
+            migration,
+          }),
+        ).filter(({ version }) => version.lessThanOrEqual(previous)).sort((
+          a,
+          b,
+        ) => b.version.compare(a.version)).map(({ migration }) =>
+          migration.down
+        );
+        break;
+      default:
+        return { error: "unreachable" };
+    }
+
+    for (const migration of migrationsToRun) {
+      configured = (await migration(effects)).configured && configured;
+    }
+
+    return { result: { configured } };
+  };
+}