#!/usr/bin/env python3

import collections
import asyncio
import sys


class AsyncSubProcess:
    def __init__(self, program, *args, env={}, output=True, cwd=None):
        self.proc = None
        self.program = program
        self.args = args
        self.env = env
        self.cwd = cwd
        self.callback_stdout = output and (lambda x: print(x, end=""))
        self.callback_stderr = output and (lambda x: print(x, end="", file=sys.stderr))
        self.tasks = {}

    async def exec(self):
        self.proc = await asyncio.create_subprocess_exec(
            self.program,
            *self.args,
            stdout=asyncio.subprocess.PIPE,
            stderr=asyncio.subprocess.PIPE,
            env=self.env,
            cwd=self.cwd
        )

    @staticmethod
    async def read_stream(stream, callback=None):
        output = collections.deque(maxlen=50000)
        while not stream.at_eof():
            line = await stream.readline()
            output.append(line.decode("UTF-8"))
            if line and callback:
                callback(output[-1])
        return output

    def create_tasks(self):
        self.tasks["stdout"] = asyncio.create_task(
            self.read_stream(self.proc.stdout, self.callback_stdout)
        )
        self.tasks["stderr"] = asyncio.create_task(
            self.read_stream(self.proc.stderr, self.callback_stderr)
        )

    async def wait(self):
        self.create_tasks()
        await asyncio.wait(self.tasks.values())
        return (
            self.proc.returncode,
            "".join(self.tasks["stdout"].result()),
            "".join(self.tasks["stderr"].result()),
        )

    @classmethod
    async def main(self, *cmd, **kw):
        runner = self(*cmd, **kw)
        await runner.exec()
        return await runner.wait()


def run(*cmd, **kw):
    return asyncio.run(AsyncSubProcess.main(*cmd, **kw))