import db from '@adonisjs/lucid/services/db'
import logger from '@adonisjs/core/services/logger'

/** Ids per partition (as the migration that partitioned files: …150). */
export const FILE_PARTITION_SIZE = 4_000_000
/** Ids kept covered beyond the newest file: two partitions. */
const AHEAD = 2 * FILE_PARTITION_SIZE

/**
 * `files` is partitioned by id (CONCEPT.md D39). An insert with an id no
 * partition covers fails, so gc:scheduler calls ensure() every sweep to keep
 * two partitions ready ahead of the newest id. Each new partition gets its
 * own unique index on file_key (FileStore.insert checks the older ones),
 * in the parent's tablespace (the HDD on homelab).
 */
class FilePartitions {
  async ensure(): Promise<string[]> {
    const created: string[] = []
    while (true) {
      const { rows } = await db.rawQuery(
        `SELECT (SELECT coalesce(max(id), 0) FROM files) AS max_id,
                -- ''{0,1}, not ''?: knex reads ? as a binding.
                max((regexp_match(pg_get_expr(c.relpartbound, c.oid), 'TO \\(''{0,1}(\\d+)''{0,1}\\)'))[1]::bigint) AS upper
         FROM pg_inherits i JOIN pg_class c ON c.oid = i.inhrelid
         WHERE i.inhparent = 'files'::regclass`
      )
      const maxId = Number(rows[0].max_id)
      const upper = Number(rows[0].upper)
      if (upper - maxId >= AHEAD) return created
      const name = `files_p${upper}`
      await db.rawQuery(`CREATE TABLE ${name} PARTITION OF files FOR VALUES FROM (${upper}) TO (${upper + FILE_PARTITION_SIZE})`)
      await db.rawQuery(`ALTER TABLE ${name} ADD CONSTRAINT ${name}_file_key_unique UNIQUE (file_key)`)
      logger.info(`files: partition ${name} created (ids ${upper}–${upper + FILE_PARTITION_SIZE - 1}).`)
      created.push(name)
    }
  }
}

export default new FilePartitions()