use syn::{parse, ForeignItemFn, ItemFn, Stmt};

use crate::syntax::parse::util::FilterAttrs;
use crate::syntax::{
    ast::{HardwareTask, HardwareTaskArgs},
    parse::util,
};

impl HardwareTask {
    pub(crate) fn parse(args: HardwareTaskArgs, item: ItemFn) -> parse::Result<Self> {
        let span = item.sig.ident.span();
        let valid_signature = util::check_fn_signature(&item, false)
            && item.sig.inputs.len() == 1
            && util::type_is_unit(&item.sig.output);

        let name = item.sig.ident.to_string();

        if name == "init" || name == "idle" {
            return Err(parse::Error::new(
                span,
                "tasks cannot be named `init` or `idle`",
            ));
        }

        if valid_signature {
            if let Some(context) = util::parse_inputs(item.sig.inputs, &name) {
                let FilterAttrs { cfgs, attrs, .. } = util::filter_attributes(item.attrs);

                return Ok(HardwareTask {
                    args,
                    cfgs,
                    attrs,
                    context,
                    stmts: item.block.stmts,
                    is_extern: false,
                });
            }
        }

        Err(parse::Error::new(
            span,
            format!(
                "this task handler must have type signature `fn({name}::Context)`"
            ),
        ))
    }
}

impl HardwareTask {
    pub(crate) fn parse_foreign(
        args: HardwareTaskArgs,
        item: ForeignItemFn,
    ) -> parse::Result<Self> {
        let span = item.sig.ident.span();
        let valid_signature = util::check_foreign_fn_signature(&item, false)
            && item.sig.inputs.len() == 1
            && util::type_is_unit(&item.sig.output);

        let name = item.sig.ident.to_string();

        if name == "init" || name == "idle" {
            return Err(parse::Error::new(
                span,
                "tasks cannot be named `init` or `idle`",
            ));
        }

        if valid_signature {
            if let Some(context) = util::parse_inputs(item.sig.inputs, &name) {
                let FilterAttrs { cfgs, attrs, .. } = util::filter_attributes(item.attrs);

                return Ok(HardwareTask {
                    args,
                    cfgs,
                    attrs,
                    context,
                    stmts: Vec::<Stmt>::new(),
                    is_extern: true,
                });
            }
        }

        Err(parse::Error::new(
            span,
            format!(
                "this task handler must have type signature `fn({name}::Context)`"
            ),
        ))
    }
}