use nom::{
    branch::alt,
    bytes::complete::tag,
    character::complete::char,
    combinator::map,
    error::context,
    multi::{many1, separated_list0, separated_list1},
    sequence::{delimited, tuple, separated_pair},
};

use crate::parser::{identifier, ws0, expression, Expression, IResult, Span, Assign, assign_statement};

#[derive(Debug)]
pub struct ProcBlock<'a> {
    pub net: Span<'a>,
    pub items: Vec<ProcStatement<'a>>,
}

#[derive(Debug)]
pub enum ProcStatement<'a> {
    IfElse(IfElseBlock),
    Assign(Assign<'a>),
    Match(MatchBlock<'a>),
    Block(Vec<ProcStatement<'a>>),
}

// TODO: postponed because annoying to implement
#[derive(Debug)]
pub struct IfElseBlock {}

#[derive(Debug)]
pub struct MatchBlock<'a> {
    pub expr: Expression<'a>,
    pub arms: Vec<(Expression<'a>, ProcStatement<'a>)>,
}

fn match_arm(input: Span) -> IResult<Span, (Expression, ProcStatement)> {
    separated_pair(ws0(expression), tag("=>"), ws0(proc_statement))(input)
}

fn match_block(input: Span) -> IResult<Span, MatchBlock> {
    context(
        "match block",
        map(
            tuple((
                ws0(tag("match")),
                ws0(delimited(char('('), ws0(expression), char(')'))),
                ws0(delimited(char('{'), separated_list1(char(','), ws0(match_arm)), char('}'))),
            )),
            |(_, expr, arms)| MatchBlock {
                expr,
                arms
            },
        ),
    )(input)
}

fn statement_block(input: Span) -> IResult<Span, Vec<ProcStatement>> {
    delimited(char('{'), separated_list1(char(';'), ws0(proc_statement)), char('}'))(input)
}

/// parse a statement that is valid inside a proc block
fn proc_statement(input: Span) -> IResult<Span, ProcStatement> {
    alt((
        map(match_block, ProcStatement::Match),
        map(statement_block, ProcStatement::Block),
        map(assign_statement, ProcStatement::Assign),
    ))(input)
}

pub fn proc_block(input: Span) -> IResult<Span, ProcBlock> {
    context(
        "proc block",
        map(
            tuple((
                ws0(tag("proc")),
                ws0(delimited(char('('), ws0(identifier), char(')'))),
                ws0(delimited(char('{'), many1(ws0(proc_statement)), char('}'))),
            )),
            |(_, net, items)| ProcBlock { net, items },
        ),
    )(input)
}

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

    #[test]
    fn test_statement() {
        proc_statement(" abc = def ".into()).unwrap();
    }

    #[test]
    fn test_match_arm() {
        match_arm(" 1 => abc = def ".into()).unwrap();
    }

    #[test]
    fn test_match_block() {
        let input = "
        match (asdf) {
            1 => a = 0,
            2 => c = ~d
        }
        ";
        match_block(input.into()).unwrap();
    }
}