php-promise.php

<?php // I don't know why anybody may need it

class Promise {
	protected $resolvers = [];
	protected $catchers = [];
	protected $value = null;
	protected $error = null;
	protected $status = 'idle';
	
	public function __construct($run, $manualStart = false) {
		try {
			$this->status = 'pending';
			$run([$this, 'resolve'], [$this, 'reject']);
		}
		catch (\Exception $e) {
			$this->reject($e);
		}
	}
	
	public function resolve($value) {
		try {
			if (is_a($value, __CLASS__)) {
				if ($value->status === 'rejected') {
					$this->reject($value->value);
				}
				else if ($value->status === 'resolved') {
					$this->resolve($value->value);
				}
				else {
					$value->then([$this, 'resolve'], [$this, 'reject']);
				}
				return $this;
			}
			$this->value = $value;
			$this->status = 'resolved';
			$resolver = array_shift($this->resolvers);
			if ($resolver) {
				$value = $resolver($this->value);
				$this->resolve($value);
			}
		}
		catch (\Exception $e) {
			$this->reject($e);
		}
		return $this;
	}
	
	public function reject($error) {
		$catcher = array_shift($this->catchers);
		if (!$catcher)
			throw $error;
		
		try {
			$this->status = 'rejected';
			$value = $catcher($error);
			if (is_a($value, __CLASS__)) {
				return $value->then([$this, 'resolve'], [$this, 'reject']);
			}
			else {
				return $this->resolve($value);
			}
		}
		catch (\Exception $e) {
			$this->reject($e);
		}
		return $this;
	}
	
	public function check() {
		if ($this->status === 'resolved') {
			$this->resolve($this->value);
			return true;
		}
		else if ($this->status === 'rejected') {
			$this->reject($this->error);
			return true;
		}
		return false;
	}
	
	public function then($resolver, $catcher = null) {
		$this->resolvers[] = $resolver;
		if ($catcher) {
			$this->catchers[] = $catcher;
		}
		$this->check();
		return $this;
	}
	
	public function catch($catcher) {
		$this->catchers[] = $catcher;
		$this->check();
		return $this;
	}
}