import type {
  AppliedMigration,
  AvailableMigration,
  Migrator,
} from "../types/Migrator.js";
import { init, migrations } from "./migrations/index.js";
import { pgToDate } from "./cast.js";
import { WrappedPool } from "./pool.js";
import { sql, toPositional } from "./sql.js";

export class PostgresMigrator implements Migrator {
  #pool: WrappedPool;

  constructor(pool: WrappedPool) {
    this.#pool = pool;
  }

  async #listAppliedMigrations(): Promise<
    { id: number; name: string; applied_at: string }[] | null
  > {
    const client = await this.#pool._pool.connect();
    try {
      const existsResult = await client.query<{ exists: boolean }>(
        `SELECT EXISTS (
          SELECT 1 FROM information_schema.tables
          WHERE table_schema = 'public' AND table_name = '_migrations'
        ) AS "exists"`
      );
      if (!existsResult.rows[0]?.exists) return null;

      const result = await client.query<{
        id: number;
        name: string;
        applied_at: Date;
      }>(
        `SELECT "id", "name", "applied_at" FROM "_migrations" ORDER BY "id" ASC`
      );
      return result.rows.map((x) => ({
        ...x,
        applied_at: pgToDate(x.applied_at),
      }));
    } finally {
      client.release();
    }
  }

  async listAppliedMigrations(): Promise<AppliedMigration[]> {
    return (await this.#listAppliedMigrations()) ?? [];
  }

  listAvailableMigrations(): AvailableMigration[] {
    return migrations.map((m) => ({ id: m.id, name: m.name }));
  }

  async migrateTo(id: number): Promise<void> {
    const target = migrations.find((x) => x.id === id);
    if (!target) throw new Error(`No known migration with id ${id}`);

    let current = await this.#listAppliedMigrations();
    if (!current) {
      const client = await this.#pool._pool.connect();
      try {
        await client.query(init);
      } finally {
        client.release();
      }
      current = [];
    }

    for (const { id, name } of current) {
      const migration = migrations.find((x) => x.id === id);
      if (!migration)
        throw new Error(`Applied migration ${id} (${name}) not known`);
      if (migration.name !== name)
        throw new Error(
          `Applied migration ${id} (${name}) has a different name from expected (${migration.name})`
        );
    }

    const start =
      migrations.findIndex((x) => x.id === current.at(-1)?.id) + 1;
    const end = migrations.indexOf(target) + 1;

    if (end < start) {
      throw new Error(
        `Cannot migrate backward, at ${current.at(-1)?.id ?? 0}, going to ${target.id}`
      );
    }

    const toApply = migrations.slice(start, end);

    if (!toApply.length) {
      console.log("Nothing to do");
      return;
    }

    for (const migration of toApply) {
      console.log(`Applying migration ${migration.id} (${migration.name})`);
      const client = await this.#pool._pool.connect();
      try {
        await client.query("BEGIN");
        for (const part of migration.parts) {
          console.log(`- Applying part ${part.id} (${part.name})`);
          if ("sql" in part) {
            await client.query(part.sql);
          } else {
            await part.apply(this.#pool);
          }
        }
        const recordSql = sql`
          INSERT INTO "_migrations"("id", "name")
          VALUES (${{ int: migration.id }}, ${{ text: migration.name }})
        `;
        await client.query(toPositional(recordSql._sql), recordSql._vars);
        await client.query("COMMIT");
      } catch (e) {
        await client.query("ROLLBACK");
        throw e;
      } finally {
        client.release();
      }
    }

    console.log("Done migrating database");
  }
}