<?php

namespace Amp\Awaitable;

use Interop\Async\Awaitable;
use Interop\Async\Loop;
use Interop\Async\LoopDriver;

/**
 * Return a awaitable using the given value. There are four possible outcomes depending on the type of $value:
 * (1) \Interop\Async\Awaitable: The awaitable is returned without modification.
 * (2) \Generator: The generator is used to create a coroutine.
 * (3) callable: The callable is invoked with no arguments. The return value is pass through this function agian.
 * (4) All other types: A successful awaitable is returned using the given value as the result.
 *
 * @param mixed $value
 *
 * @return \Interop\Async\Awaitable
 */
function resolve($value = null) {
    if ($value instanceof Awaitable) {
        return $value;
    }

    if ($value instanceof \Generator) {
        return new Coroutine($value);
    }

    if (\is_callable($value)) {
        return resolve($value());
    }

    return new Success($value);
}

/**
 * Create a new failed awaitable using the given exception.
 *
 * @param \Throwable|\Exception $reason
 *
 * @return \Interop\Async\Awaitable
 */
function fail($reason) {
    return new Failure($reason);
}

/**
 * Returns a new function that when invoked runs the Generator returned by $worker as a coroutine.
 *
 * @param callable(mixed ...$args): \Generator $worker
 *
 * @return callable(mixed ...$args): \Amp\Awaitable\Coroutine
 */
function coroutine(callable $worker) {
    return function (/* ...$args */) use ($worker) {
        $generator = \call_user_func_array($worker, \func_get_args());

        if (!$generator instanceof \Generator) {
            throw new \LogicException("The callable did not return a Generator");
        }

        return new Coroutine($generator);
    };
}

/**
 * Registers a callback that will forward the failure reason to the Loop error handler if the awaitable fails.
 *
 * @param \Interop\Async\Awaitable $awaitable
 */
function rethrow(Awaitable $awaitable) {
    /**
     * @param \Throwable|\Exception $exception
     * @param mixed $value
     */
    $awaitable->when(function ($exception = null, $value = null) {
        if ($exception) {
            /** @var \Throwable|\Exception $exception */
            throw $exception;
        }
    });
}

/**
 * Runs the event loop until the awaitable is resolved. Should not be called within a running event loop.
 *
 * @param \Interop\Async\Awaitable $awaitable
 * @param \Interop\Async\LoopDriver|null $driver
 *
 * @return mixed Awaitable success value.
 *
 * @throws \Throwable|\Exception Awaitable failure reason.
 */
function wait(Awaitable $awaitable, LoopDriver $driver = null) {
    Loop::execute(function () use (&$value, &$exception, $awaitable) {
        $awaitable->when(function ($e = null, $v = null) use (&$value, &$exception) {
            Loop::stop();
            $exception = $e;
            $value = $v;
        });
    }, $driver);

    if ($exception) {
        throw $exception;
    }

    return $value;
}

/**
 * Pipe the promised value through the specified functor once it resolves.
 *
 * @param \Interop\Async\Awaitable $awaitable
 * @param callable(mixed $value): mixed $functor
 *
 * @return \Interop\Async\Awaitable
 */
function pipe(Awaitable $awaitable, callable $functor) {
    $deferred = new Deferred();

    $awaitable->when(function ($exception = null, $value = null) use ($deferred, $functor) {
        if ($exception) {
            $deferred->fail($exception);
            return;
        }

        try {
            $deferred->resolve($functor($value));
        } catch (\Throwable $exception) {
            $deferred->fail($exception);
        } catch (\Exception $exception) {
            $deferred->fail($exception);
        }
    });

    return $deferred->getAwaitable();
}

/**
 * @param \Interop\Async\Awaitable $awaitable
 * @param callable(\Throwable|\Exception $exception): mixed $functor
 *
 * @return \Interop\Async\Awaitable
 */
function capture(Awaitable $awaitable, callable $functor) {
    $deferred = new Deferred();

    $awaitable->when(function ($exception = null, $value = null) use ($deferred, $functor) {
        if (!$exception) {
            $deferred->resolve($value);
            return;
        }

        try {
            $deferred->resolve($functor($exception));
        } catch (\Throwable $exception) {
            $deferred->fail($exception);
        } catch (\Exception $exception) {
            $deferred->fail($exception);
        }
    });

    return $deferred->getAwaitable();
}

/**
 * Create an artificial timeout for any Awaitable.
 *
 * If the timeout expires before the awaitable is resolved, the returned awaitable fails with an instance of
 * \Amp\Awaitable\Exception\TimeoutException.
 *
 * @param \Interop\Async\Awaitable $awaitable
 * @param int $timeout Timeout in milliseconds.
 *
 * @return \Interop\Async\Awaitable
 */
function timeout(Awaitable $awaitable, $timeout) {
    $deferred = new Deferred();

    $watcher = Loop::delay(function () use ($deferred) {
        $deferred->fail(new Exception\TimeoutException());
    }, $timeout);

    $onResolved = function () use ($awaitable, $deferred, $watcher) {
        Loop::cancel($watcher);
        $deferred->resolve($awaitable);
    };

    $awaitable->when($onResolved);

    return $deferred->getAwaitable();
}

/**
 * Artificially delays the success of an awaitable $delay milliseconds after the awaitable succeeds. If the
 * awaitable fails, the returned awaitable fails immediately.
 *
 * @param \Interop\Async\Awaitable $awaitable
 * @param int $delay Delay in milliseconds.
 *
 * @return \Interop\Async\Awaitable
 */
function delay(Awaitable $awaitable, $delay) {
    $deferred = new Deferred();

    $onResolved = function ($exception = null) use ($awaitable, $deferred, $delay) {
        if ($exception) {
            $deferred->fail($exception);
            return;
        }

        Loop::delay(function () use ($awaitable, $deferred) {
            $deferred->resolve($awaitable);
        }, $delay);
    };

    $awaitable->when($onResolved);

    return $deferred->getAwaitable();
}

/**
 * Returns a awaitable that calls $promisor only when the result of the awaitable is requested (e.g., then() or
 * done() is called on the returned awaitable). $promisor can return a awaitable or any value. If $promisor throws
 * an exception, the returned awaitable is rejected with that exception.
 *
 * @param callable $promisor
 * @param mixed ...$args
 *
 * @return \Interop\Async\Awaitable
 */
function lazy(callable $promisor /* ...$args */) {
    $args = \array_slice(\func_get_args(), 1);

    if (empty($args)) {
        return new Internal\LazyAwaitable($promisor);
    }

    return new Internal\LazyAwaitable(function () use ($promisor, $args) {
        return \call_user_func_array($promisor, $args);
    });
}

/**
 * Transforms a function that takes a callback into a function that returns a awaitable. The awaitable is fulfilled
 * with an array of the parameters that would have been passed to the callback function.
 *
 * @param callable $worker Function that normally accepts a callback.
 * @param int $index Position of callback in $worker argument list (0-indexed).
 *
 * @return callable
 */
function promisify(callable $worker, $index = 0) {
    return function (/* ...$args */) use ($worker, $index) {
        $args = \func_get_args();

        $deferred = new Deferred();

        $callback = function (/* ...$args */) use ($deferred) {
            $deferred->resolve(\func_get_args());
        };

        if (\count($args) < $index) {
            throw new \InvalidArgumentException("Too few arguments given to function");
        }

        \array_splice($args, $index, 0, [$callback]);

        \call_user_func_array($worker, $args);

        return $deferred->getAwaitable();
    };
}

/**
 * Adapts any object with a then(callable $onFulfilled, callable $onRejected) method to a awaitable usable by
 * components depending on placeholders implementing Awaitable.
 *
 * @param object $thenable Object with a then() method.
 *
 * @return \Interop\Async\Awaitable Awaitable resolved by the $thenable object.
 */
function adapt($thenable) {
    if (!\is_object($thenable) || !\method_exists($thenable, "then")) {
        return fail(new \InvalidArgumentException("Must provide an object with a then() method"));
    }

    return new Promise(function (callable $resolve, callable $fail) use ($thenable) {
        $thenable->then($resolve, $fail);
    });
}

/**
 * Wraps the given callable $worker in a awaitable aware function that has the same number of arguments as $worker,
 * but those arguments may be awaitables for the future argument value or just values. The returned function will
 * return a awaitable for the return value of $worker and will never throw. The $worker function will not be called
 * until each awaitable given as an argument is fulfilled. If any awaitable provided as an argument fails, the
 * awaitable returned by the returned function will be failed for the same reason. The awaitable succeeds with
 * the return value of $worker or failed if $worker throws.
 *
 * @param callable $worker
 *
 * @return callable
 */
function lift(callable $worker) {
    /**
     * @param mixed ...$args Awaitables or values.
     *
     * @return \Interop\Async\Awaitable
     */
    return function (/* ...$args */) use ($worker) {
        $args = \func_get_args();

        if (1 === \count($args)) {
            return pipe(resolve($args[0]), $worker);
        }

        return pipe(all($args), function (array $args) use ($worker) {
            return \call_user_func_array($worker, $args);
        });
    };
}

/**
 * Returns a awaitable that is resolved when all awaitables are resolved. The returned awaitable will not fail.
 * Returned awaitable succeeds with an array of resolved awaitables, with keys identical and corresponding to the
 * original given array.
 *
 * @param mixed[] $awaitables Awaitables or values (passed through resolve() to create awaitables).
 *
 * @return \Interop\Async\Awaitable
 */
function settle(array $awaitables) {
    if (empty($awaitables)) {
        return resolve([]);
    }

    $deferred = new Deferred();

    $pending = \count($awaitables);

    $onResolved = function () use (&$awaitables, &$pending, $deferred) {
        if (0 === --$pending) {
            $deferred->resolve($awaitables);
        }
    };

    foreach ($awaitables as &$awaitable) {
        $awaitable = resolve($awaitable);
        $awaitable->when($onResolved);
    }

    return $deferred->getAwaitable();
}

/**
 * Returns a awaitable that succeeds when all awaitables succeed, and fails if any awaitable fails. Returned
 * awaitable succeeds with an array of values used to succeed each contained awaitable, with keys corresponding to
 * the array of awaitables.
 *
 * @param mixed[] $awaitables Awaitables or values (passed through resolve() to create awaitables).
 *
 * @return \Interop\Async\Awaitable
 */
function all(array $awaitables) {
    if (empty($awaitables)) {
        return resolve([]);
    }

    $deferred = new Deferred();

    $pending = \count($awaitables);
    $values = [];

    foreach ($awaitables as $key => $awaitable) {
        $onResolved = function ($exception = null, $value = null) use ($key, &$values, &$pending, $deferred) {
            if ($exception) {
                $deferred->fail($exception);
                return;
            }

            $values[$key] = $value;
            if (0 === --$pending) {
                $deferred->resolve($values);
            }
        };

        resolve($awaitable)->when($onResolved);
    }

    return $deferred->getAwaitable();
}

/**
 * Returns a awaitable that succeeds when any awaitable succeeds, and fails only if all awaitables fail.
 *
 * @param mixed[] $awaitables Awaitables or values (passed through resolve() to create awaitables).
 *
 * @return \Interop\Async\Awaitable
 */
function any(array $awaitables) {
    if (empty($awaitables)) {
        return fail(new \InvalidArgumentException("No awaitables provided"));
    }

    $deferred = new Deferred();

    $pending = \count($awaitables);
    $exceptions = [];

    foreach ($awaitables as $key => $awaitable) {
        $onResolved = function ($exception = null, $value = null) use ($key, &$exceptions, &$pending, $deferred) {
            if (!$exception) {
                $deferred->resolve($value);
                return;
            }

            $exceptions[$key] = $exception;
            if (0 === --$pending) {
                $deferred->fail(new Exception\MultiReasonException($exceptions));
            }
        };

        resolve($awaitable)->when($onResolved);
    }

    return $deferred->getAwaitable();
}

/**
 * Returns a awaitable that succeeds when $required number of awaitables succeed. The awaitable fails if $required
 * number of awaitables can no longer succeed.
 *
 * @param mixed[] $awaitables Awaitables or values (passed through resolve() to create awaitables).
 * @param int $required Number of awaitables that must succeed to succeed the returned awaitable.
 *
 * @return \Interop\Async\Awaitable
 */
function some(array $awaitables, $required) {
    $required = (int) $required;

    if (0 >= $required) {
        return resolve([]);
    }

    $pending = \count($awaitables);

    if ($required > $pending) {
        return fail(new \InvalidArgumentException("Too few awaitables provided"));
    }

    $deferred = new Deferred();

    $required = \min($pending, $required);
    $values = [];
    $exceptions = [];

    foreach ($awaitables as $key => $awaitable) {
        $onResolved = function ($exception = null, $value = null) use (
            &$key, &$values, &$exceptions, &$pending, &$required, $deferred
        ) {
            if ($exception) {
                $exceptions[$key] = $exception;
                if ($required > --$pending) {
                    $deferred->fail(new Exception\MultiReasonException($exceptions));
                }
                return;
            }

            $values[$key] = $value;
            --$pending;
            if (0 === --$required) {
                $deferred->resolve($values);
            }
        };

        resolve($awaitable)->when($onResolved);
    }

    return $deferred->getAwaitable();
}

/**
 * Returns a awaitable that succeeds or fails when the first awaitable succeeds or fails.
 *
 * @param mixed[] $awaitables Awaitables or values (passed through resolve() to create awaitables).
 *
 * @return \Interop\Async\Awaitable
 */
function choose(array $awaitables) {
    if (empty($awaitables)) {
        return fail(new \InvalidArgumentException("No awaitables provided"));
    }

    $deferred = new Deferred();

    foreach ($awaitables as $awaitable) {
        resolve($awaitable)->when(function ($exception = null, $value = null) use ($deferred) {
            if ($exception) {
                $deferred->fail($exception);
                return;
            }

            $deferred->resolve($value);
        });
    }

    return $deferred->getAwaitable();
}

/**
 * Maps the callback to each awaitable as it succeeds. Returns an array of awaitables resolved by the return
 * callback value of the callback function. The callback may return awaitables or throw exceptions to fail
 * awaitables in the array. If a awaitable in the passed array fails, the callback will not be called and the
 * awaitable in the array fails for the same reason. Tip: Use all() or settle() to determine when all
 * awaitables in the array have been resolved.
 *
 * @param callable(mixed $value): mixed $callback
 * @param mixed[] ...$awaitables Awaitables or values (passed through resolve() to create awaitables).
 *
 * @return \Interop\Async\Awaitable[] Array of awaitables resolved with the result of the mapped function.
 */
function map(callable $callback /* array ...$awaitables */) {
    $args = \func_get_args();
    $args[0] = lift($args[0]);

    return \call_user_func_array('array_map', $args);
}