manage.cmd.migration: add rudimentary implementation

Also add table changes for future message embeds.

manage/cmd/migration/command.py

@@ -1,10 +1,134 @@
-async def migrate_cmd(app, args):
+import inspect
+from pathlib import Path
+from dataclasses import dataclass
+from collections import namedtuple
+from typing import Dict
+
+import asyncpg
+from logbook import Logger
+
+log = Logger(__name__)
+
+
+Migration = namedtuple('Migration', 'id name path')
+
+
+@dataclass
+class MigrationContext:
+    """Hold information about migration."""
+    migration_folder: Path
+    scripts: Dict[int, Migration]
+
+    @property
+    def latest(self):
+        """Return the latest migration ID."""
+        return max(self.scripts.keys())
+
+
+def make_migration_ctx() -> MigrationContext:
+    """Create the MigrationContext instance."""
+    # taken from https://stackoverflow.com/a/6628348
+    script_path = inspect.stack()[0][1]
+    script_folder = '/'.join(script_path.split('/')[:-1])
+    script_folder = Path(script_folder)
+
+    migration_folder = script_folder / 'scripts'
+
+    mctx = MigrationContext(migration_folder, {})
+
+    for mig_path in migration_folder.glob('*.sql'):
+        mig_path_str = str(mig_path)
+
+        # extract migration script id and name
+        mig_filename = mig_path_str.split('/')[-1].split('.')[0]
+        name_fragments = mig_filename.split('_')
+
+        mig_id = int(name_fragments[0])
+        mig_name = '_'.join(name_fragments[1:])
+
+        mctx.scripts[mig_id] = Migration(
+            mig_id, mig_name, mig_path)
+
+    return mctx
+
+
+async def _ensure_changelog(app, ctx):
+    # make sure we have the migration table up
+
+    try:
+        await app.db.execute("""
+        CREATE TABLE migration_log (
+            change_num bigint NOT NULL,
+
+            apply_ts timestamp without time zone default
+                (now() at time zone 'utc'),
+
+            description text,
+
+            PRIMARY KEY (change_num)
+        );
+        """)
+
+        # if we were able to create the
+        # migration_log table, insert that we are
+        # on the latest version.
+        await app.db.execute("""
+        INSERT INTO migration_log (change_num, description)
+        VALUES ($1, $2)
+        """, ctx.latest, 'migration setup')
+    except asyncpg.DuplicateTableError:
+        log.debug('existing migration table')
+
+
+async def apply_migration(app, migration: Migration):
+    """Apply a single migration."""
+    migration_sql = migration.path.read_text(encoding='utf-8')
+
+    try:
+        await app.db.execute("""
+        INSERT INTO migration_log (change_num, description)
+        VALUES ($1, $2)
+        """, migration.id, f'migration: {migration.name}')
+    except asyncpg.UniqueViolationError:
+        log.warning('already applied {}', migration.id)
+        return
+
+    await app.db.execute(migration_sql)
+    log.info('applied {}', migration.id)
+
+
+async def migrate_cmd(app, _args):
     """Main migration command.
 
     This makes sure the database
     is updated.
     """
-    print('not implemented yet')
+
+    ctx = make_migration_ctx()
+
+    await _ensure_changelog(app, ctx)
+
+    # local point in the changelog
+    local_change = await app.db.fetchval("""
+    SELECT max(change_num)
+    FROM migration_log
+    """)
+
+    local_change = local_change or 0
+    latest_change = ctx.latest
+
+    if local_change == latest_change:
+        print('no changes to do, exiting')
+        return
+
+    # we do local_change + 1 so we start from the
+    # next migration to do, end in latest_change + 1
+    # because of how range() works.
+    for idx in range(local_change + 1, latest_change + 1):
+        migration = ctx.scripts.get(idx)
+
+        print('applying', migration.id, migration.name)
+        await apply_migration(app, migration)
 
 
 def setup(subparser):

manage/cmd/migration/scripts/1_message_embed_type.sql

@@ -0,0 +1,6 @@
+-- unused tables
+DROP TABLE message_embeds;
+DROP TABLE embeds;
+
+ALTER TABLE messages
+    ADD COLUMN embeds jsonb DEFAULT '[]'

schema.sql

@@ -486,11 +486,6 @@ CREATE TABLE IF NOT EXISTS bans (
 );
 
 
-CREATE TABLE IF NOT EXISTS embeds (
-    -- TODO: this table
-    id bigint PRIMARY KEY
-);
-
 CREATE TABLE IF NOT EXISTS messages (
     id bigint PRIMARY KEY,
     channel_id bigint REFERENCES channels (id) ON DELETE CASCADE,
@@ -511,6 +506,8 @@ CREATE TABLE IF NOT EXISTS messages (
     tts bool default false,
     mention_everyone bool default false,
 
+    embeds jsonb DEFAULT '[]',
+
     nonce bigint default 0,
 
     message_type int NOT NULL
@@ -522,12 +519,6 @@ CREATE TABLE IF NOT EXISTS message_attachments (
     PRIMARY KEY (message_id, attachment)
 );
 
-CREATE TABLE IF NOT EXISTS message_embeds (
-    message_id bigint REFERENCES messages (id) UNIQUE,
-    embed_id bigint REFERENCES embeds (id),
-    PRIMARY KEY (message_id, embed_id)
-);
-
 CREATE TABLE IF NOT EXISTS message_reactions (
     message_id bigint REFERENCES messages (id),
     user_id bigint REFERENCES users (id),