"""V006 - scheduler reservation metadata (wrong-database no-op).

Adds persisted reservation fields to ``scheduler_jobs`` so cron execution can
claim a job durably before handler execution.

``scheduler_jobs`` lives in ``scheduler.db`` (``JobStore`` opened from
``gateway/boot.py``), NOT in ``sessions.db`` — and ``apply_pending`` only
ever runs against ``sessions.db``. On real split-database deployments the
table is absent from the migration connection and this step no-ops,
recorded in the sessions.db ledger without touching scheduler data. The
real in-place upgrade is ``JobStore._migrate``'s connect-time ADD COLUMN
pass (``scheduler/persistence.py``); the guards below keep this step
harmless where the table does share a file with the session store (e.g.
ad-hoc test setups).
"""

from __future__ import annotations

from yoyo import step

__depends__: set[str] = {"V005__agent_tasks"}

TABLE = "scheduler_jobs"
COLUMNS = [
    ("reservation_token", "TEXT NOT NULL DEFAULT ''"),
    ("reserved_at", "TEXT"),
    ("reserved_by", "TEXT NOT NULL DEFAULT ''"),
    ("reservation_source", "TEXT NOT NULL DEFAULT ''"),
    ("scheduled_run_at", "TEXT"),
]


def _table_exists(conn, table: str) -> bool:
    cur = conn.cursor()
    cur.execute(
        "SELECT 1 FROM sqlite_master WHERE type='table' AND name=?",
        (table,),
    )
    return cur.fetchone() is not None


def _has_column(conn, table: str, column: str) -> bool:
    cur = conn.cursor()
    cur.execute(f"PRAGMA table_info({table})")
    return any(row[1] == column for row in cur.fetchall())


def apply_step(conn) -> None:
    if not _table_exists(conn, TABLE):
        return
    cur = conn.cursor()
    for column, ddl in COLUMNS:
        if not _has_column(conn, TABLE, column):
            cur.execute(f"ALTER TABLE {TABLE} ADD COLUMN {column} {ddl}")


def rollback_step(conn) -> None:
    if not _table_exists(conn, TABLE):
        return
    cur = conn.cursor()
    for column, _ddl in reversed(COLUMNS):
        if _has_column(conn, TABLE, column):
            cur.execute(f"ALTER TABLE {TABLE} DROP COLUMN {column}")


steps = [step(apply_step, rollback_step)]