// postgres's admin client — postgres's own code, living in the module (novox/hq ADR 0039). Both this
// module's tools and its provisioner import it, and nothing outside postgres does.
//
// SQL is executed through `psql`, not a wire-protocol driver: the module may take NO npm dependency
// beyond @novox/mesh-sdk, and hand-rolling startup + SCRAM auth + the query protocol is more surface
// than this should carry — so it shells out to the client the postgres tools ship, the same way
// minio drives itself through `mc` and mailu through doveadm. One boundary, `query()`, and every
// method is built on it.

import { randomBytes } from "node:crypto";
import { readFileSync } from "node:fs";
import { execFile } from "node:child_process";
import { promisify } from "node:util";

const run = promisify(execFile);

export interface QueryResult {
  /** The command tag postgres returns, e.g. "SELECT", "CREATE DATABASE". */
  readonly command: string;
  readonly rows: Record<string, unknown>[];
}

export interface PgConn {
  readonly host: string;
  readonly port: number;
  readonly user: string;
  readonly password: string;
}


export class PostgresClient {
  constructor(private readonly conn: PgConn) {}

  /**
   * Build from the module's resolved environment. Reads MESH_POSTGRES_* first (the documented
   * names), falling back to the MESH_PROVISION_* keys the manifest already sets on the provisioner
   * container. Throws if it cannot find a host and an admin password.
   */
  static fromEnv(env: NodeJS.ProcessEnv = process.env): PostgresClient {
    const url = env.MESH_PROVISION_POSTGRES ? safeUrl(env.MESH_PROVISION_POSTGRES) : undefined;
    const host = env.MESH_POSTGRES_HOST ?? url?.hostname;
    const port = Number(env.MESH_POSTGRES_PORT ?? url?.port ?? "5432") || 5432;
    const user = env.MESH_POSTGRES_USER ?? url?.username ?? "postgres";
    const password = env.MESH_POSTGRES_PASSWORD ?? readSecretFile(env.MESH_PROVISION_PASSWORD_FILE);
    if (!host || !password) {
      throw new Error("postgres host or admin password is not set — postgres's own code cannot reach the server");
    }
    return new PostgresClient({ host, port, user, password });
  }

  get host(): string {
    return this.conn.host;
  }

  get port(): number {
    return this.conn.port;
  }

  /** Execute SQL against a database as the admin and return its rows, through `psql` (see header). */
  async query(sql: string, database = "postgres"): Promise<QueryResult> {
    // Executed through `psql`, the way minio drives itself through `mc` and mailu through doveadm:
    // node has no postgres wire client without an npm dependency, and the module owns its own code
    // (ADR 0039), so it shells out to the client the postgres tools ship. CSV so the rows come back
    // structured; ON_ERROR_STOP so a failed statement is an error here, not a success with a warning.
    const { stdout } = await run(
      "psql",
      ["-h", this.conn.host, "-p", String(this.conn.port), "-U", this.conn.user, "-d", database,
        "-v", "ON_ERROR_STOP=1", "--no-psqlrc", "--csv", "-c", sql],
      { env: { ...process.env, PGPASSWORD: this.conn.password }, maxBuffer: 16 << 20 },
    );
    const rows = parseCsvRows(stdout);
    return { command: sql.trimStart().split(/\s+/)[0]?.toUpperCase() ?? "", rows };
  }

  /**
   * Create a login role and a database it owns, idempotently. The DDL is the full, correct shape, run through query(). Extensions can be requested per
   * database and are created as the admin (a plain owner cannot install most of them).
   */
  async createDatabaseAndRole(database: string, role: string, password: string): Promise<void> {
    const roles = await this.query("SELECT 1 FROM pg_roles WHERE rolname = " + literal(role));
    if (roles.rows.length === 0) {
      await this.query(`CREATE ROLE ${ident(role)} WITH LOGIN PASSWORD ${literal(password)}`);
    } else {
      await this.query(`ALTER ROLE ${ident(role)} WITH LOGIN PASSWORD ${literal(password)}`);
    }
    const dbs = await this.query("SELECT 1 FROM pg_database WHERE datname = " + literal(database));
    if (dbs.rows.length === 0) {
      await this.query(`CREATE DATABASE ${ident(database)} OWNER ${ident(role)}`);
    }
    await this.query(`GRANT ALL PRIVILEGES ON DATABASE ${ident(database)} TO ${ident(role)}`);
  }

  /** Drop a database and its owning role, idempotently, after evicting live connections. */
  async dropDatabaseAndRole(database: string, role: string): Promise<void> {
    await this.query(
      "SELECT pg_terminate_backend(pid) FROM pg_stat_activity WHERE datname = " +
        literal(database) + " AND pid <> pg_backend_pid()",
    );
    await this.query(`DROP DATABASE IF EXISTS ${ident(database)}`);
    await this.query(`DROP ROLE IF EXISTS ${ident(role)}`);
  }

  /** List the non-template databases, with size, for the postgres_list_databases tool. */
  async listDatabases(): Promise<{ name: string; sizeBytes: number }[]> {
    const res = await this.query(
      "SELECT datname, pg_database_size(datname) AS size FROM pg_database WHERE datistemplate = false ORDER BY datname",
    );
    return res.rows.map((r) => ({ name: String(r.datname), sizeBytes: Number(r.size) }));
  }

  /** Run a read-only SQL statement against a named database, for the postgres_query tool. */
  async readOnlyQuery(database: string, sql: string): Promise<QueryResult> {
    // The read-only guarantee is a wrapping transaction the server honours.
    return this.query(`BEGIN TRANSACTION READ ONLY; ${sql}; ROLLBACK;`, database);
  }
}

/** Generate a URL-safe password. */
export function generatePassword(): string {
  return randomBytes(24).toString("base64url");
}

/** Quote a SQL identifier (double quotes, doubled internal quotes). */
export function ident(id: string): string {
  return '"' + id.replace(/"/g, '""') + '"';
}

/** Quote a SQL string literal (single quotes, doubled internal quotes). */
export function literal(val: string): string {
  return "'" + val.replace(/'/g, "''") + "'";
}

function readSecretFile(path: string | undefined): string | undefined {
  if (!path) return undefined;
  try {
    return readFileSync(path, "utf8").trim();
  } catch {
    return undefined;
  }
}

function safeUrl(raw: string): URL | undefined {
  try {
    return new URL(raw);
  } catch {
    return undefined;
  }
}

/** Parse psql --csv output into row objects. RFC-4180: fields may be quoted, an embedded quote is
 *  doubled, and a quoted field may span newlines. Empty output (a DDL statement) yields no rows. */
function parseCsvRows(csv: string): Record<string, unknown>[] {
  const records = parseCsv(csv);
  if (records.length === 0) return [];
  const [header, ...rows] = records;
  return rows.map((cells) => {
    const row: Record<string, unknown> = {};
    header.forEach((name, i) => (row[name] = cells[i] ?? null));
    return row;
  });
}

function parseCsv(text: string): string[][] {
  const records: string[][] = [];
  let field = "";
  let record: string[] = [];
  let inQuotes = false;
  let started = false;
  const endRecord = (): void => {
    if (started || field.length > 0 || record.length > 0) {
      record.push(field);
      records.push(record);
    }
    field = "";
    record = [];
    started = false;
  };
  for (let i = 0; i < text.length; i++) {
    const c = text[i];
    if (inQuotes) {
      if (c === '"') {
        if (text[i + 1] === '"') { field += '"'; i++; } else inQuotes = false;
      } else field += c;
    } else if (c === '"') { inQuotes = true; started = true; }
    else if (c === ",") { record.push(field); field = ""; started = true; }
    else if (c === "\n" || c === "\r") {
      if (c === "\r" && text[i + 1] === "\n") i++;
      endRecord();
    } else { field += c; started = true; }
  }
  endRecord();
  return records;
}