"""Incremental schema migration register for SQLite single-host installations.

Legacy tables are created by their existing setup functions. This new ledger
tracks newly introduced migrations and verifies their SQL checksums. Do not
mistake this for a completed migration of all legacy PostgreSQL structures.
"""
from __future__ import annotations
import hashlib
from datetime import datetime,timezone

# Each migration has separately executable (single statement) DDL entries.
# Never rewrite an already applied migration: add a new sequence instead.
MIGRATIONS=(
    ('20261022_001_p1_limits',(
        'CREATE TABLE IF NOT EXISTS platform_limit_overrides (name TEXT PRIMARY KEY, value INTEGER NOT NULL CHECK (value > 0), updated_at TEXT NOT NULL)',
    )),
)

def ensure(conn):
    conn.execute('''CREATE TABLE IF NOT EXISTS schema_migrations (
        version TEXT PRIMARY KEY, checksum TEXT NOT NULL, applied_at TEXT NOT NULL)''')
    for version,statements in MIGRATIONS:
        checksum=hashlib.sha256('\n'.join(statements).encode()).hexdigest()
        row=conn.execute('SELECT checksum FROM schema_migrations WHERE version=?',(version,)).fetchone()
        if row:
            if row[0]!=checksum:raise RuntimeError('Schema migration checksum mismatch: '+version)
            continue
        # The caller owns a single transaction. DDL and ledger entry commit together.
        for sql in statements:conn.execute(sql)
        conn.execute('INSERT INTO schema_migrations VALUES (?,?,?)',(
            version,checksum,datetime.now(timezone.utc).isoformat(timespec='seconds')))