/**
 * The per-device instance registry: which autofirmer processes run on this
 * machine, on which ports, against which databases.
 *
 * scripts/instances.json is created and edited by add-instance.sh /
 * remove-instance.sh. When the file is absent the device is a legacy
 * single-instance install and everything behaves exactly as it always has:
 * one PM2 process named `autofirmer` on port 3000 using ./autotrader.sqlite.
 *
 * Entry shape: { "name": "autofirmer-2", "port": 3100, "db": ".data/instance-2/autotrader.sqlite" }
 * `db` is relative to the project root. Instance 1 keeps the legacy
 * name/port/db so the clicker and extension (hardwired to :3000) still work.
 */
import { existsSync, readFileSync } from 'node:fs';
import path from 'node:path';
import { fileURLToPath } from 'node:url';

export const ROOT = path.resolve(path.dirname(fileURLToPath(import.meta.url)), '..');
export const REGISTRY_FILE = path.join(ROOT, 'scripts', 'instances.json');

const LEGACY = [{
    name: 'autofirmer',
    port: Number(process.env.AUTOFIRMER_PORT ?? '3000'),
    db: 'autotrader.sqlite',
}];

export function loadInstances() {
    if (!existsSync(REGISTRY_FILE)) return LEGACY;
    let parsed;
    try {
        parsed = JSON.parse(readFileSync(REGISTRY_FILE, 'utf8'));
    } catch (err) {
        throw new Error(`scripts/instances.json is not valid JSON: ${err.message}`);
    }
    if (!Array.isArray(parsed) || parsed.length === 0) return LEGACY;
    for (const e of parsed) {
        if (typeof e?.name !== 'string' || !e.name
            || !Number.isInteger(e?.port)
            || typeof e?.db !== 'string' || !e.db) {
            throw new Error(`scripts/instances.json entry is malformed: ${JSON.stringify(e)}`);
        }
    }
    return parsed;
}