// Copyright (c) 2017-present PyO3 Project and Contributors
//
// based on Daniel Grunwald's https://github.com/dgrunwald/rust-cpython

//! Python argument parsing
use ffi;
use err::PyResult;
use python::Python;
use conversion::PyTryFrom;
use objects::{PyObjectRef, PyTuple, PyDict, PyString, exc};

#[derive(Debug)]
/// Description of a python parameter; used for `parse_args()`.
pub struct ParamDescription<'a> {
    /// The name of the parameter.
    pub name: &'a str,
    /// Whether the parameter is optional.
    pub is_optional: bool,
    /// Whether the parameter is optional.
    pub kw_only: bool,
}

/// Parse argument list
///
/// * fname:  Name of the current function
/// * params: Declared parameters of the function
/// * args:   Positional arguments
/// * kwargs: Keyword arguments
/// * output: Output array that receives the arguments.
///           Must have same length as `params` and must be initialized to `None`.
pub fn parse_args<'p>(fname: Option<&str>, params: &[ParamDescription],
                      args: &'p PyTuple, kwargs: Option<&'p PyDict>,
                      accept_args: bool, accept_kwargs: bool,
                      output: &mut[Option<&'p PyObjectRef>]) -> PyResult<()>
{
    let nargs = args.len();
    let nkeywords = kwargs.map_or(0, |d| d.len());
    if !accept_args && (nargs + nkeywords > params.len()) {
        return Err(exc::TypeError::new(
            format!("{}{} takes at most {} argument{} ({} given)",
                    fname.unwrap_or("function"),
                    if fname.is_some() { "()" } else { "" },
                    params.len(),
                    if params.len() == 1 { "s" } else { "" },
                    nargs + nkeywords
            )));
    }
    let mut used_keywords = 0;
    // Iterate through the parameters and assign values to output:
    for (i, (p, out)) in params.iter().zip(output).enumerate() {
        match kwargs.and_then(|d| d.get_item(p.name)) {
            Some(kwarg) => {
                *out = Some(kwarg);
                used_keywords += 1;
                if i < nargs {
                    return Err(exc::TypeError::new(
                        format!("Argument given by name ('{}') and position ({})", p.name, i+1)));
                }
            },
            None => {
                if p.kw_only {
                    if !p.is_optional {
                        return Err(exc::TypeError::new(
                            format!("Required argument ('{}') is keyword only argument", p.name)));
                    }
                    *out = None;
                }
                else if i < nargs {
                    *out = Some(args.get_item(i));
                } else {
                    *out = None;
                    if !p.is_optional {
                        return Err(exc::TypeError::new(
                            format!("Required argument ('{}') (pos {}) not found", p.name, i+1)));
                    }
                }
            }
        }
    }
    if !accept_kwargs && used_keywords != nkeywords {
        // check for extraneous keyword arguments
        for item in kwargs.unwrap().items().iter() {
            let item = PyTuple::try_from(item)?;
            let key = PyString::try_from(item.get_item(0))?.to_string()?;
            if !params.iter().any(|p| p.name == key) {
                return Err(exc::TypeError::new(
                    format!("'{}' is an invalid keyword argument for this function", key)));
            }
        }
    }
    Ok(())
}

#[inline]
#[doc(hidden)]
pub unsafe fn get_kwargs(py: Python, ptr: *mut ffi::PyObject) -> Option<&PyDict> {
    if ptr.is_null() {
        None
    } else {
        Some(py.from_borrowed_ptr::<PyDict>(ptr))
    }
}