feat(cli): implement downgrade migration command

migra-cli/src/config.rs

@@ -133,6 +133,16 @@ impl Migration {
 
         Ok(())
     }
+
+    pub fn downgrade(&self, client: &mut Client) -> Result<(), Box<dyn std::error::Error + 'static>> {
+        let content = fs::read_to_string(&self.downgrade_sql)?;
+
+        database::apply_sql(client, &content)?;
+
+        database::delete_migration_info(client, self.name())?;
+
+        Ok(())
+    }
 }
 
 impl Config {

migra-cli/src/database.rs

@@ -40,3 +40,7 @@ pub fn create_migration_table(client: &mut Client) -> Result<(), Error> {
 pub fn insert_migration_info(client: &mut Client, name: &str) -> Result<u64, Error> {
     client.execute("INSERT INTO migrations (name) VALUES ($1)", &[&name])
 }
+
+pub fn delete_migration_info(client: &mut Client, name: &str) -> Result<u64, Error> {
+    client.execute("DELETE FROM migrations WHERE name = $1", &[&name])
+}

migra-cli/src/main.rs

@@ -123,13 +123,25 @@ fn main() -> Result<(), Box<dyn std::error::Error>> {
                     .iter()
                     .filter(|m| !applied_migrations.contains(m.name()))
                 {
-                    println!("{}", m.name());
+                    println!("upgrade {}...", m.name());
                     m.upgrade(&mut client)?;
                 }
             }
         }
         Command::Downgrade => {
-            unimplemented!();
+            let config = Config::read(opt.config)?;
+
+            let mut client = database::connect(&config.database.connection)?;
+
+            let applied_migrations = database::applied_migrations(&mut client)?;
+            let migrations = config.migrations()?;
+
+            if let Some(first_applied_migration) = applied_migrations.first() {
+                if let Some(migration) = migrations.iter().find(|m| m.name() == first_applied_migration) {
+                    println!("downgrade {}...", migration.name());
+                    migration.downgrade(&mut client)?;
+                }
+            }
         }
     }