<?php

namespace App\Model;

use JumPHP\Async\Task;

/**
 * Steps one after the other, each a fn (mixed $previous): Task|mixed; the first failure stops them. Task of the last result.
 * Chain::run([fn () => $c->run(... 'VM.clone' ...), fn (string $vm) => $c->run(... 'VM.provision', [$vm] ...), ...])
 */
final class Chain
{
    /** @param list<\Closure> $steps */
    public static function run(array $steps, mixed $value = null): Task
    {
        $done = new Task();
        $next = function (mixed $value, int $i) use (&$next, $steps, $done): void {
            if (!isset($steps[$i])) {
                $done->settle($value);
                return;
            }
            try {
                $out = $steps[$i]($value);
            } catch (\Throwable $e) {
                $done->settle(null, $e);
                return;
            }
            if ($out instanceof Task) {
                $out->then(fn ($r) => $next($r ?? $value, $i + 1), fn (\Throwable $e) => $done->settle(null, $e));
            } else {
                $next($out ?? $value, $i + 1);
            }
        };
        $next($value, 0);
        return $done;
    }

    /** A Task that gives $value when $task succeeds (a step whose own result is not what the next step needs). */
    public static function keep(Task $task, mixed $value): Task
    {
        $out = new Task();
        $task->then(fn () => $out->settle($value), fn (\Throwable $e) => $out->settle(null, $e));
        return $out;
    }
}