//! This example show cases a very simple REPL.
//! While a much better REPL can be found in ../src/shell,
//! This much smaller REPL is still a useful example because it showcases inserting
//! values and functions into the Python runtime's scope, and showcases use
//! of the compilation mode "Single".

use rustpython_vm as vm;
// these are needed for special memory shenanigans to let us share a variable with Python and Rust
use std::sync::atomic::{AtomicBool, Ordering};

// This has to be a macro because it uses the py_compile macro,
// which compiles python source to optimized bytecode at compile time, so that
// the program you're embedding this into doesn't take longer to start up.
macro_rules! add_python_function {
    ( $scope:ident, $vm:ident, $src:literal $(,)? ) => {{
        // compile the code to bytecode
        let code = vm::py_compile!(source = $src);
        // convert the rustpython_compiler_core::CodeObject to a PyRef<PyCode>
        let code = $vm.ctx.new_code(code);

        // run the python code in the scope to store the function
        $vm.run_code_obj(code, $scope.clone())
    }};
}

static ON: AtomicBool = AtomicBool::new(true);

fn on(b: bool) {
    ON.store(b, Ordering::Relaxed);
}

fn main() -> vm::PyResult<()> {
    vm::Interpreter::without_stdlib(Default::default()).enter(run)
}

fn run(vm: &vm::VirtualMachine) -> vm::PyResult<()> {
    let mut input = String::with_capacity(50);
    let stdin = std::io::stdin();

    let scope: vm::scope::Scope = vm.new_scope_with_builtins();

    // typing `quit()` is too long, let's make `on(False)` work instead.
    scope
        .globals
        .set_item("on", vm.new_function("on", on).into(), vm)?;

    // let's include a fibonacci function, but let's be lazy and write it in Python
    add_python_function!(
        scope,
        vm,
        // a fun line to test this with is
        // ''.join( l * fib(i) for i, l in enumerate('supercalifragilistic') )
        r#"\
def fib(n):
    return n if n <= 1 else fib(n - 1) + fib(n - 2)
"#
    )?;

    while ON.load(Ordering::Relaxed) {
        input.clear();
        stdin
            .read_line(&mut input)
            .expect("Failed to read line of input");

        // this line also automatically prints the output
        // (note that this is only the case when compiler::Mode::Single is passed to vm.compile)
        match vm
            .compile(&input, vm::compiler::Mode::Single, "<embedded>")
            .map_err(|err| err.into_pyexception(vm, Some(&input)))
            .and_then(|code_obj| vm.run_code_obj(code_obj, scope.clone()))
        {
            Ok(output) => {
                // store the last value in the "last" variable
                if !vm.is_none(&output) {
                    scope.globals.set_item("last", output, vm)?;
                }
            }
            Err(exc) => {
                vm.print_exception(exc);
            }
        }
    }

    Ok(())
}
