import type Database from 'better-sqlite3';

/** Keep metadata ahead of overflow pages, preserving IDs and all references. */
export function migrateVersionLayout(handle: Database.Database): void {
    const columns = handle.pragma('table_info(script_versions)') as { name: string }[];
    if (!columns.some((column) => column.name === 'content') || columns.at(-1)?.name === 'content')
        return;
    const { sql } = handle
        .prepare("SELECT sql FROM sqlite_master WHERE name='script_versions'")
        .get() as { sql: string };
    const content = /\bcontent\s+BLOB\s+NOT\s+NULL\s*,/i;
    if (!content.test(sql)) throw new Error('Unrecognized script version content layout');
    const replacement = sql
        .replace(content, '')
        .replace(/,\s*UNIQUE\s*\(/i, ', content BLOB NOT NULL, UNIQUE(')
        .replace('script_versions', 'script_versions_metadata');
    const dependents = handle
        .prepare(
            "SELECT sql FROM sqlite_master WHERE tbl_name='script_versions' AND type IN ('index','trigger') AND sql IS NOT NULL"
        )
        .all() as { sql: string }[];
    const sequence = handle
        .prepare("SELECT seq FROM sqlite_sequence WHERE name='script_versions'")
        .get() as { seq: number } | undefined;
    handle.pragma('foreign_keys = OFF');
    try {
        handle.transaction(() => {
            handle.exec(replacement);
            const names = columns.map((column) => `"${column.name}"`).join(',');
            handle.exec(`INSERT INTO script_versions_metadata (${names}) SELECT ${names} FROM script_versions;
                DROP TABLE script_versions; ALTER TABLE script_versions_metadata RENAME TO script_versions;`);
            if (sequence)
                handle
                    .prepare(
                        "UPDATE sqlite_sequence SET seq=MAX(seq,?) WHERE name='script_versions'"
                    )
                    .run(sequence.seq);
            for (const dependent of dependents) handle.exec(dependent.sql);
            if ((handle.pragma('foreign_key_check') as unknown[]).length)
                throw new Error('Version layout migration found broken references');
        })();
    } finally {
        handle.pragma('foreign_keys = ON');
    }
}