use nom::{
    branch::alt,
    bytes::complete::tag,
    character::complete::{char, multispace1},
    combinator::{consumed, map},
    error::context,
    multi::{many1, separated_list0},
    sequence::{delimited, tuple, terminated},
};

use crate::parser::{
    assign_statement, declaration, identifier, ws0, Assign, IResult,
    NetDecl, Span, proc::{proc_block, ProcBlock},
};

#[derive(Debug)]
pub enum PortDirection {
    Input,
    Output,
}

#[derive(Debug)]
pub struct PortDecl<'a> {
    pub pos: Span<'a>,
    pub direction: PortDirection,
    pub net: NetDecl<'a>,
}

#[derive(Debug)]
pub struct Module<'a> {
    pub name: &'a str,
    pub ports: Vec<PortDecl<'a>>,
    pub items: Vec<ModuleItem<'a>>,
}

#[derive(Debug)]
pub enum ModuleItem<'a> {
    Assign(Assign<'a>),
    Proc(ProcBlock<'a>),
}

fn port_decl(i: Span) -> IResult<Span, PortDecl> {
    map(
        consumed(tuple((
            alt((
                map(tag("input"), |_| PortDirection::Input),
                map(tag("output"), |_| PortDirection::Output),
            )),
            declaration,
        ))),
        |(pos, (direction, net))| PortDecl {
            pos,
            direction,
            net,
        },
    )(i)
}

fn ports_list(input: Span) -> IResult<Span, Vec<PortDecl>> {
    separated_list0(ws0(char(',')), ws0(port_decl))(input)
}

fn assign_item(input: Span) -> IResult<Span, Assign> {
    context(
        "assignment",
        delimited(
            ws0(terminated(tag("assign"), multispace1)),
            ws0(assign_statement),
            ws0(char(';')),
        ),
    )(input)
}

fn module_item(input: Span) -> IResult<Span, ModuleItem> {
    alt((
        map(assign_item, ModuleItem::Assign),
        map(proc_block, ModuleItem::Proc),
    ))(input)
}

/// parse a top-level module declaration
pub fn module(input: Span) -> IResult<Span, Module> {
    context(
        "module",
        map(
            tuple((
                tag("module"),
                ws0(identifier),
                ws0(delimited(char('('), ws0(ports_list), char(')'))),
                ws0(delimited(char('{'), many1(ws0(module_item)), char('}'))),
            )),
            |(_, name, ports, items)| Module {
                name: (*name.fragment()),
                ports,
                items,
            },
        ),
    )(input)
}

#[cfg(test)]
mod test {
    use super::*;
    use nom::combinator::all_consuming;

    #[test]
    fn test_decl() {
        declaration("reg abcd".into()).unwrap();
    }

    #[test]
    fn test_assignment_item() {
        all_consuming(assign_item)(" assign a = b ; ".into()).unwrap();
        all_consuming(assign_item)(" assign a = b | c ; ".into()).unwrap();
    }

    #[test]
    fn test_module_item() {
        all_consuming(module_item)(" assign a = b ;".into()).unwrap();
    }
}