warp-runtime 1.4.1

//! The bridge of foreign_call(runtime, module, member, arguments) (warp's lowering/foreign/foreign_modules.rs,
//! notes/stdlib_connectors.md), shared by warp and its executables (card exe-foreign): one long-lived child per runtime
//! and process, started on first use, speaking one JSON line per request and per answer. Python: `python3 -u` running
//! FOREIGN_PYTHON_LOOP (`WARP_PYTHON` names another interpreter); JavaScript: `node` running FOREIGN_JS_LOOP
//! (`WARP_NODE`), a global (`Math`) or a module it requires.
//! A read gives the member itself, a call gives its result (a promise awaited); an exception is an error with the
//! runtime's message. A value without a JSON form stays in its runtime behind an id, a handle: it crosses as the record
//! `{$handle: 7, type: "date", text: "datetime.date(2020, 1, 2)"}` and is that object again when it comes back, as an
//! argument or as the receiver of `d.isoformat()` (the module position). Handles live until the process ends.
//! A warp function given as an argument crosses as `{$warp_function: 0}`, its index among the call's functions; node
//! calls it back with the line `{callback: 0, arguments: […]}` and waits for its `{value}` or `{error}` (card js-callbacks).

use serde_json::Value;
use std::cell::RefCell;
use std::io::{BufRead, BufReader, Write};
use std::process::{Child, ChildStdin, ChildStdout, Command, Stdio};
use std::sync::{Condvar, Mutex};

/// A runtime: its name in `use <runtime> …`, the variable naming its interpreter, the default interpreter, and how it
/// runs its loop script
struct Interpreter {
	runtime: &'static str,
	variable: &'static str,
	default: &'static str,
	arguments: [&'static str; 2],
	script: &'static str,
}

const INTERPRETERS: [Interpreter; 2] = [
	Interpreter {
		runtime: "python",
		variable: "WARP_PYTHON",
		default: "python3",
		arguments: ["-u", "-c"],
		script: FOREIGN_PYTHON_LOOP,
	},
	Interpreter {
		runtime: "js",
		variable: "WARP_NODE",
		default: "node",
		arguments: ["--no-warnings", "-e"],
		script: FOREIGN_JS_LOOP,
	},
];
/// An integer beyond 64 bits, sent as its digits: `{"$int": "15511210043330985984000000"}`
pub const BIG_INTEGER_KEY: &str = "$int";
/// A codepoint (a WIT `char`, P94), which JSON would make a text: `{"$char": "b"}`
pub const CODEPOINT_KEY: &str = "$char";
/// A warp function among a call's arguments: `{"$warp_function": 0}`
pub const WARP_FUNCTION_KEY: &str = "$warp_function";
/// How a call's warp functions are called back: by their index, with the arguments the runtime gave them as a list
pub type Callback<'a> = &'a mut dyn FnMut(usize, Value) -> Result<Value, String>;
thread_local! {
	/// The children this thread's calls hold while they call a warp function back: a foreign call that function makes
	/// goes to the same child, which answers it while it waits
	static HELD: RefCell<Vec<(&'static str, Runtime)>> = const { RefCell::new(Vec::new()) };
}
/// The request loop the child runs: {"module", "member", "arguments"} → {"value"} or {"error"}; the playground's
/// Pyodide runs the same file
const FOREIGN_PYTHON_LOOP: &str = include_str!("foreign_python.py"); // a link to web/playground/foreign_python.py: the packaged crate carries the file

/// The same loop for node: a global (`Math`, `JSON`) or a module it requires or imports; a method keeps its object
const FOREIGN_JS_LOOP: &str = r#"
const handles = [];
const handle = value => (handles.push(value), { "$handle": handles.length, type: value?.constructor?.name ?? typeof value, text: String(value).slice(0, 200) });
const unplain = value => Array.isArray(value) ? value.map(unplain)
	: value !== null && typeof value === "object" ? ("$handle" in value ? handles[value.$handle - 1] : "$warp_function" in value ? warpFunction(value.$warp_function)
		: Object.fromEntries(Object.entries(value).map(([key, item]) => [key, unplain(item)])))
	: value;
const plain = value => {
	if (typeof value === "bigint") return value >= -(2n ** 63n) && value < 2n ** 63n ? Number(value) : { "$int": value.toString() };
	if (value === undefined || value === null || typeof value === "symbol") return null; // ø, not a handle of null
	if (Array.isArray(value)) return value.map(plain);
	const prototype = value !== null && typeof value === "object" ? Object.getPrototypeOf(value) : undefined;
	if (prototype === Object.prototype || prototype === null) return Object.fromEntries(Object.entries(value).map(([key, item]) => [key, plain(item)]));
	if (typeof value === "function" || typeof value === "object") return handle(value); // a Date, a Map, an instance, a function
	return value;
};
// what warp's operators on a value of this runtime forward to (lowering/foreign/foreign_modules.rs)
const operator = { add: (a, b) => a + b, sub: (a, b) => a - b, mul: (a, b) => a * b, truediv: (a, b) => a / b, mod: (a, b) => a % b, pow: (a, b) => a ** b,
	lt: (a, b) => a < b, gt: (a, b) => a > b, le: (a, b) => a <= b, ge: (a, b) => a >= b, eq: (a, b) => a === b, ne: (a, b) => a !== b, neg: a => -a,
	getitem: (a, i) => typeof a.get === "function" ? a.get(i) : a[i], len: a => a.length ?? a.size, list: a => Array.from(a) };
// `use js self` / `use js window`: node mirrors a page, its global object is globalThis
const load = name => name === "operator" ? operator : name === "self" || name === "window" ? globalThis : name in globalThis ? globalThis[name] : (() => { try { return require(name); } catch (failure) { return import(name); } })();
// the answers own stdout: what a module prints (console.log) goes to stderr
const reply = answer => require("fs").writeSync(1, JSON.stringify(answer) + "\n");
process.stdout.write = process.stderr.write.bind(process.stderr);
// stdin read synchronously, so a warp function called back answers before the JavaScript calling it goes on
const decoder = new (require("string_decoder").StringDecoder)("utf8");
let buffered = "";
const readLine = () => {
	const chunk = Buffer.alloc(65536);
	while (!buffered.includes("\n")) {
		let count;
		try { count = require("fs").readSync(0, chunk, 0, chunk.length, null); } catch (failure) { if (failure.code === "EAGAIN") continue; throw failure; }
		if (count === 0) return null;
		buffered += decoder.write(chunk.subarray(0, count));
	}
	const line = buffered.slice(0, buffered.indexOf("\n"));
	buffered = buffered.slice(line.length + 1);
	return line;
};
// a request's answer; each `yield` waits for what may be a promise (lowering/foreign/foreign_modules.rs CONSTRUCTOR_MEMBER: member
// "" constructs the module, `new URL(…)`; SETTER_PREFIX: "set innerHTML" sets the member to the one argument)
const SETTER = /^set (.+)$/;
function* answerOf(request) {
	try {
		let owner = null, value = typeof request.module === "object" ? unplain(request.module) : yield load(request.module);
		const set = request.member.match(SETTER);
		if (request.member === "") value = new value(...unplain(request.arguments));
		else if (set) value = value[set[1]] = unplain(request.arguments)[0];
		else {
			for (const part of request.member.split(".")) {
				if (value?.[part] === undefined) throw new ReferenceError(`${request.module} has no ${request.member}`);
				[owner, value] = [value, value[part]];
			}
			if (request.arguments !== null) value = yield value.apply(owner, unplain(request.arguments));
		}
		return { value: plain(value) };
	} catch (failure) {
		return { error: failure instanceof Error ? failure.name + ": " + failure.message : String(failure) };
	}
}
// a request of the program: its promises awaited
const awaited = async steps => {
	let step = steps.next();
	while (!step.done) step = await Promise.resolve(step.value).then(value => steps.next(value), failure => steps.throw(failure));
	return step.value;
};
// a request of a warp function called back, which the JavaScript calling it waits for: no promise can be awaited there
const immediate = steps => {
	let step = steps.next();
	while (!step.done) {
		const promised = typeof step.value?.then === "function";
		if (promised) step.value.then(undefined, () => {}); // its failure is not the program's: no unhandled rejection
		step = promised ? steps.throw(new Error("gives a promise, which a warp function called back cannot wait for")) : steps.next(step.value);
	}
	return step.value;
};
// a warp function given as an argument: called back through warp, answering the foreign calls it makes meanwhile
const warpFunction = index => (...values) => {
	reply({ callback: index, arguments: values.map(plain) });
	for (let line; (line = readLine()) !== null;) {
		const message = JSON.parse(line);
		if ("module" in message) reply(immediate(answerOf(message)));
		else if ("error" in message) throw new Error(message.error);
		else return unplain(message.value);
	}
	throw new Error("warp ended");
};
(async () => {
	for (let line; (line = readLine()) !== null;) reply(await awaited(answerOf(JSON.parse(line))));
})();
"#;

struct Runtime {
	_child: Child,
	input: ChildStdin,
	output: BufReader<ChildStdout>,
}

/// The running children, by runtime; None while a call holds its child, which another thread waits for (RETURNED)
static RUNNING: Mutex<Vec<(&'static str, Option<Runtime>)>> = Mutex::new(Vec::new());
static RETURNED: Condvar = Condvar::new();

/// Is `runtime` one an interpreter runs (python, js)
pub fn is_interpreted(runtime: &str) -> bool {
	interpreter(runtime).is_some()
}

fn interpreter(runtime: &str) -> Option<&'static Interpreter> {
	INTERPRETERS.iter().find(|interpreter| interpreter.runtime == runtime)
}

/// `runtime.module.member(arguments…)` (arguments null: the member itself, read): the value the runtime answered, or
/// its error as `runtime module.member: error`; `module` is a module's name or a handle, `module_name` how errors name it
pub fn call(
	runtime: &str,
	module_name: &str,
	module: Value,
	member: &str,
	arguments: Value,
	callback: Callback,
) -> Result<Value, String> {
	let interpreter = interpreter(runtime).ok_or_else(|| format!("no foreign runtime {runtime}"))?;
	let request = serde_json::json!({"module": module, "member": member, "arguments": arguments});
	let mut answer =
		exchange(interpreter, &request.to_string(), callback).map_err(|failure| format!("{runtime}: {failure}"))?;
	match (answer.get_mut("value").map(Value::take), answer.get("error")) {
		(_, Some(Value::String(error))) => Err(format!("{runtime} {module_name}.{member}: {error}")),
		(Some(value), _) => Ok(value),
		_ => Err(format!("{runtime} answered neither a value nor an error: {answer}")),
	}
}

/// One request line out, one answer line back, each callback line before it answered; the child is started on first
/// use and again after it ended
fn exchange(interpreter: &'static Interpreter, request: &str, callback: Callback) -> Result<Value, String> {
	let held = take_held(interpreter.runtime);
	let nested = held.is_some();
	let child = match held {
		Some(child) => child,
		None => borrow(interpreter)?,
	};
	let (answer, child) = talk(interpreter.runtime, child, request, callback);
	match (nested, child) {
		(true, Some(child)) => HELD.with_borrow_mut(|held| held.push((interpreter.runtime, child))),
		(true, None) => {}
		(false, child) => give_back(interpreter.runtime, child),
	}
	answer
}

/// The request to the child and its answer; a callback line calls the warp function back meanwhile, the child held by
/// this thread for the foreign calls it makes. The child is gone when it ended
fn talk(
	runtime: &'static str,
	mut child: Runtime,
	request: &str,
	callback: Callback,
) -> (Result<Value, String>, Option<Runtime>) {
	let mut line = request.to_string();
	loop {
		let mut answer = String::new();
		let sent = writeln!(child.input, "{line}").and_then(|_| child.input.flush());
		if sent.is_err() || child.output.read_line(&mut answer).unwrap_or(0) == 0 {
			return (Err("the interpreter ended".into()), None);
		}
		let mut answer: Value = match serde_json::from_str(&answer) {
			Ok(answer) => answer,
			Err(failure) => return (Err(format!("answered no JSON: {failure}")), Some(child)),
		};
		let Some(function) = answer.get("callback").and_then(Value::as_u64) else {
			return (Ok(answer), Some(child));
		};
		HELD.with_borrow_mut(|held| held.push((runtime, child)));
		let arguments = answer.get_mut("arguments").map(Value::take).unwrap_or(Value::Null);
		let result = callback(function as usize, arguments);
		let Some(held) = take_held(runtime) else {
			return (Err("the interpreter ended".into()), None);
		};
		child = held;
		line = match result {
			Ok(value) => serde_json::json!({ "value": value }),
			Err(failure) => serde_json::json!({ "error": failure }),
		}
		.to_string();
	}
}

/// The child of `runtime` this thread holds, while a warp function is called back
fn take_held(runtime: &str) -> Option<Runtime> {
	HELD.with_borrow_mut(|held| held.iter().rposition(|(name, _)| *name == runtime).map(|index| held.remove(index).1))
}

/// The child of the interpreter for one call: started when there is none, waited for while another thread's call holds it
fn borrow(interpreter: &'static Interpreter) -> Result<Runtime, String> {
	let mut running = RUNNING.lock().unwrap_or_else(|poisoned| poisoned.into_inner());
	loop {
		let Some((_, slot)) = running.iter_mut().find(|(runtime, _)| *runtime == interpreter.runtime) else {
			running.push((interpreter.runtime, None));
			drop(running);
			return start(interpreter).inspect_err(|_| give_back(interpreter.runtime, None));
		};
		if let Some(child) = slot.take() {
			return Ok(child);
		}
		running = RETURNED.wait(running).unwrap_or_else(|poisoned| poisoned.into_inner());
	}
}

/// The child back for the next call, or none: it ended, the next call starts another
fn give_back(runtime: &'static str, child: Option<Runtime>) {
	let mut running = RUNNING.lock().unwrap_or_else(|poisoned| poisoned.into_inner());
	match child {
		Some(child) => {
			if let Some((_, slot)) = running.iter_mut().find(|(name, _)| *name == runtime) {
				*slot = Some(child);
			}
		}
		None => running.retain(|(name, _)| *name != runtime),
	}
	RETURNED.notify_all();
}

fn start(interpreter: &Interpreter) -> Result<Runtime, String> {
	let program = std::env::var(interpreter.variable).unwrap_or_else(|_| interpreter.default.to_string());
	let mut child = Command::new(&program)
		.args(interpreter.arguments)
		.arg(interpreter.script)
		.stdin(Stdio::piped())
		.stdout(Stdio::piped())
		.stderr(Stdio::inherit())
		.spawn()
		.map_err(|failure| {
			format!("cannot start {program} ({failure}); set {} to an interpreter", interpreter.variable)
		})?;
	let input = child.stdin.take().ok_or("no stdin")?;
	let output = BufReader::new(child.stdout.take().ok_or("no stdout")?);
	Ok(Runtime { _child: child, input, output })
}