use itertools::Itertools;
use rnix::{match_ast, ast};
use rowan::ast::AstNode;
use crate::queries::*;
use crate::queries::SyntaxKind::*;

#[derive(Debug)]
pub struct Change {
    pub node: rnix::SyntaxNode,
    pub kind: ChangeKind
}

#[derive(Copy, Clone, Debug)]
pub enum ChangeKind {
    Remove,
    Keep
}

type NixExprs = Box<dyn Iterator<Item = rnix::SyntaxNode>>;
type Pipe = (Vec<Change>, NixExprs);

macro_rules! ast_node {
    ($ast:ident, $kind:ident) => {
        #[derive(PartialEq, Eq, Hash)]
        #[repr(transparent)]
        struct $ast(SyntaxNode);
        impl $ast {
            #[allow(unused)]
            fn cast(node: SyntaxNode) -> Option<Self> {
                if node.kind() == $kind {
                    Some(Self(node))
                } else {
                    None
                }
            }
        }
    };
}

ast_node!(Root, ROOT);
ast_node!(Atom, ATOM);
ast_node!(List, LIST);

#[derive(PartialEq, Eq, Hash, Debug)]
#[repr(transparent)]
struct Qexp(SyntaxNode);

enum QexpKind {
    Atom(Atom),
    List(List),
}

impl Qexp {
    fn cast(node: SyntaxNode) -> Option<Self> {
        if Atom::cast(node.clone()).is_some() || List::cast(node.clone()).is_some() {
            Some(Qexp(node))
        } else {
            None
        }
    }

    fn kind(&self) -> QexpKind {
        Atom::cast(self.0.clone())
            .map(QexpKind::Atom)
            .or_else(|| List::cast(self.0.clone()).map(QexpKind::List))
            .unwrap()
    }

    fn apply(&self, _acc: Pipe) -> Pipe {
        todo!()
    }
}

impl Root {
    fn qexps(&self) -> impl Iterator<Item = Qexp> + '_ {
        self.0.children().filter_map(Qexp::cast)
    }
}

enum Op {
    Down,
    DownRecursive,
    Up,
    UpRecursive,
    NixSyntaxNode(rnix::SyntaxKind),
    Named(String)
}

impl Atom {
    fn eval(&self) -> Option<i64> {
        self.text().parse().ok()
    }
    fn as_op(&self) -> Option<Op> {
        let op = match self.text().as_str() {
            ">" => Op::Down,
            ">>" => Op::DownRecursive,
            "<" => Op::Up,
            "<<" => Op::UpRecursive,
            "Inherit" => Op::NixSyntaxNode(rnix::SyntaxKind::NODE_INHERIT),
            "String" => Op::NixSyntaxNode(rnix::SyntaxKind::NODE_STRING),
            // TODO other syntax nodes
            name => Op::Named(name.to_owned()),
        };
        Some(op)
    }
    fn as_change(&self) -> Option<ChangeKind> {
        let change = match self.text().as_str() {
            "remove" => ChangeKind::Remove,
            "keep" => ChangeKind::Keep,
            _ => return None
        };
        Some(change)
    }
    fn iter_args(&self) -> impl Iterator<Item = Atom>  {
        self.0.children().find_map(List::cast).into_iter().map(|arglist| arglist.iter()).flatten()
    }
    fn text(&self) -> String {
        match self.0.green().children().next() {
            Some(rowan::NodeOrToken::Token(token)) => token.text().to_string(),
            _ => unreachable!(),
        }
    }
    fn apply(&self, (mut changes, acc): Pipe) -> Pipe {
        let mut acc: NixExprs = match self.as_op() {
            Some(Op::Down) => Box::new(acc.map(|s| s.children()).flatten()),
            Some(Op::DownRecursive) => Box::new(acc.map(|s| s.descendants()).flatten()),
            Some(Op::Up) => Box::new(acc.filter_map(|s| s.parent())),
            Some(Op::UpRecursive) => Box::new(acc.map(|s| s.ancestors()).flatten()),
            // TODO: how to select roles relative to previous node?
            Some(Op::NixSyntaxNode(kind)) => Box::new(acc.filter(move |s| s.kind() == kind)),
            Some(Op::Named(name)) =>
                Box::new(acc
                .filter(move |node| match_ast! { match node {
                    ast::AttrpathValue(value) => {
                        name == value.attrpath().unwrap().to_string()
                    },
                    ast::Apply(value) => {
                        // TODO: special case lambda = NODE_SELECT here?
                        name == value.lambda().unwrap().to_string()
                    },
                    // TODO: this is difficult — I want to use free-form names
                    // to select things below, too, but that might not always be
                    // possible. perhaps it is possible to skip over descendants?
                    ast::Ident(value) => {
                        name == value.to_string()
                    },
                    _ => false
                }})),
            _ => todo!()
        };

        if let Ok(arg) = self.iter_args().exactly_one() {
            if let Some(change) = arg.as_change() {
                let (mut nchanges, nacc): (Vec<_>, Vec<_>) = acc
                    .map(|node| (Change { node: node.clone(), kind: change }, node))
                    .unzip();
                acc = Box::new(nacc.into_iter());
                changes.append(&mut nchanges);
            }
        }

        (changes, acc)
    }
}

impl List {
    fn sexps(&self) -> impl Iterator<Item = Qexp> + '_ {
        self.0.children().filter_map(Qexp::cast)
    }

    fn iter(&self) -> impl Iterator<Item = Atom> {
        self.0.children().filter_map(Atom::cast)
    }
}



impl Parse {
    fn root(&self) -> Root {
        Root::cast(self.syntax()).unwrap()
    }

    pub fn apply(&self, _content: &str, nexp: rnix::SyntaxNode) -> anyhow::Result<(Vec<Change>, Vec<rnix::SyntaxNode>)> {

        let mut pipe: Pipe = (Vec::new(), Box::new(std::iter::once(nexp)));

        for qexp in self.root().qexps() {
            match qexp.kind() {
                QexpKind::Atom(filter) => {
                    pipe = filter.apply(pipe);
                }
                _ => panic!("???")
            }
        }

        // let results =
        //     acc.map(|node| content[node.text_range().start().into()..node.text_range().end().into()].to_owned())
        //     .collect();

        Ok((pipe.0, pipe.1.collect()))
    }
}