// Flags array-spread of things that are not arrays.
//
//   npm run check:spreads
//
// The engine's build transpiles `[...a, ...b]` to `[].concat(a, b)`. That is
// correct for arrays, but `Array.prototype.concat` does NOT expand an arbitrary
// iterable — it appends it as a single element. So
//
//     for (const view of [...this._views.values()])   // Map iterator
//
// silently loops once, over the iterator object itself, and every property
// access on it is undefined. It type-checks, it reads perfectly, and it only
// fails at runtime on a real build. That cost a debugging session; hence this
// check. Use `Array.from(...)` instead, which transpiles safely.
import { readdirSync, readFileSync, statSync } from 'node:fs';
import { join } from 'node:path';

const ROOT = 'assets/scripts';

/** Spreads of an iterator or collection, rather than an array. */
const HAZARDS = [
    { pattern: /\.\.\.[\w.$]*\.values\(\)/, what: '.values()' },
    { pattern: /\.\.\.[\w.$]*\.keys\(\)/, what: '.keys()' },
    { pattern: /\.\.\.[\w.$]*\.entries\(\)/, what: '.entries()' },
    { pattern: /\.\.\.new (?:Map|Set)\b/, what: 'a new Map/Set' },
    { pattern: /\.\.\.[\w.$]*(?:Map|Set)\b(?!\s*\()/, what: 'something named like a Map/Set' },
];

const offenders = [];

function walk(dir) {
    for (const entry of readdirSync(dir)) {
        const path = join(dir, entry);
        if (statSync(path).isDirectory()) walk(path);
        else if (path.endsWith('.ts')) inspect(path);
    }
}

function inspect(path) {
    readFileSync(path, 'utf8').split('\n').forEach((line, index) => {
        const code = line.trim();
        if (code.startsWith('*') || code.startsWith('//')) return;

        for (const { pattern, what } of HAZARDS) {
            if (pattern.test(code)) {
                offenders.push(`${path}:${index + 1}  spreads ${what} — use Array.from(...)\n      ${code}`);
                return;
            }
        }
    });
}

walk(ROOT);

if (offenders.length > 0) {
    console.error(
        'Array spread of a non-array. The build turns [...x] into [].concat(x),\n'
        + 'which appends an iterator instead of expanding it:\n - '
        + offenders.join('\n - '),
    );
    process.exit(1);
}

console.log('spreads OK');