use std::cell::RefCell;
use std::rc::Rc;

use async_once_cell::OnceCell;
use futures::{StreamExt, stream};
use itertools::Itertools;
use orchid_base::error::{OrcRes, Reporter, mk_errv};
use orchid_base::parse::{
	Comment, ParseCtx, Parsed, Snippet, expect_end, expect_tok, line_items, token_errv,
	try_pop_no_fluff,
};
use orchid_base::tree::{Paren, Token};
use orchid_base::{clone, sym};
use orchid_extension::atom::TAtom;
use orchid_extension::context::i;
use orchid_extension::conv::{ToExpr, TryFromExpr};
use orchid_extension::gen_expr::{atom, call, sym_ref};
use orchid_extension::parser::{PSnippet, ParsCtx, ParsedLine, Parser};

use crate::macros::let_line::{dealias_mac_v, parse_tokv};
use crate::macros::macro_value::{Macro, MacroData, Rule};
use crate::macros::mactree::MacTreeSeq;
use crate::macros::rule::matcher::Matcher;
use crate::{Int, MacTok};

#[derive(Default)]
pub struct MacroLine;
impl Parser for MacroLine {
	const LINE_HEAD: &'static str = "macro";
	async fn parse<'a>(
		ctx: ParsCtx<'a>,
		exported: bool,
		comments: Vec<Comment>,
		line: PSnippet<'a>,
	) -> OrcRes<Vec<ParsedLine>> {
		if exported {
			return Err(mk_errv(
				ctx.i().i("macros are always exported").await,
				"The export keyword is forbidden here to avoid confusion\n\
					because macros are exported by default",
				[line.sr()],
			));
		}
		let module = ctx.module();
		let Parsed { output: prio_or_body, tail } = try_pop_no_fluff(&ctx, line).await?;
		let bad_first_item_err = || {
			token_errv(&ctx, prio_or_body, "Expected priority or block", |s| {
				format!("Expected a priority number or a () block, found {s}")
			})
		};
		let (prio, body) = match &prio_or_body.tok {
			Token::S(Paren::Round, body) => {
				expect_end(&ctx, tail).await?;
				(None, body)
			},
			Token::Handle(expr) => match TAtom::<Int>::try_from_expr(expr.clone()).await {
				Err(e) => {
					return Err(e + bad_first_item_err().await);
				},
				Ok(prio) => {
					let Parsed { output: body, tail } = try_pop_no_fluff(&ctx, tail).await?;
					let Token::S(Paren::Round, block) = &body.tok else {
						return Err(
							token_errv(&ctx, prio_or_body, "Expected () block", |s| {
								format!("Expected a () block, found {s}")
							})
							.await,
						);
					};
					expect_end(&ctx, tail).await?;
					(Some(prio), block)
				},
			},
			_ => return Err(bad_first_item_err().await),
		};
		let lines = line_items(&ctx, Snippet::new(prio_or_body, body)).await;
		let Some((kw_line, rule_lines)) = lines.split_first() else { return Ok(Vec::new()) };
		let mut keywords = Vec::new();
		let Parsed { tail: kw_tail, .. } =
			expect_tok(&ctx, kw_line.tail, ctx.i().i("keywords").await).await?;
		for kw_tok in kw_tail.iter().filter(|kw| !kw.is_fluff()) {
			match kw_tok.as_name() {
				Some(kw) => {
					keywords.push((kw, kw_tok.sr()));
				},
				None => ctx.rep().report(
					token_errv(&ctx, kw_tok, "invalid macro keywords list", |tok| {
						format!("The keywords list must be a sequence of names; received {tok}")
					})
					.await,
				),
			}
		}
		let Some((macro_name, _)) = keywords.first().cloned() else {
			return Err(mk_errv(
				ctx.i().i("macro with no keywords").await,
				"Macros must define at least one macro of their own.",
				[kw_line.tail.sr()],
			));
		};
		let mut rules = Vec::new();
		let mut lines = Vec::new();
		for (idx, line) in rule_lines.iter().enumerate().map(|(n, v)| (n as u32, v)) {
			let sr = line.tail.sr();
			let name = ctx.i().i(&format!("rule::{}::{}", macro_name, idx)).await;
			let Parsed { tail, .. } = expect_tok(&ctx, line.tail, ctx.i().i("rule").await).await?;
			let arrow_token = ctx.i().i("=>").await;
			let Some((pattern, body)) = tail.split_once(|tok| tok.is_kw(arrow_token.clone())) else {
				ctx.rep().report(mk_errv(
					ctx.i().i("Missing => in rule").await,
					"Rule lines are of the form `rule ...pattern => ...body`",
					[line.tail.sr()],
				));
				continue;
			};
			let pattern = parse_tokv(pattern, &ctx).await;
			let mut placeholders = Vec::new();
			pattern.map(&mut false, &mut |tok| {
				if let MacTok::Ph(ph) = tok.tok() {
					placeholders.push((ph.clone(), tok.pos()))
				}
				None
			});
			let mut body_mactree = parse_tokv(body, &ctx).await;
			for (ph, ph_pos) in placeholders.iter().rev() {
				let name = ctx.module().suffix([ph.name.clone()], ctx.i()).await;
				body_mactree =
					MacTreeSeq::new([
						MacTok::Lambda(MacTok::Name(name).at(ph_pos.clone()), body_mactree).at(ph_pos.clone())
					])
			}
			let body_sr = body.sr();
			rules.push((name.clone(), placeholders, pattern));
			lines.push(ParsedLine::cnst(&sr, &line.output, true, name, async move |ctx| {
				let rep = Reporter::new();
				let body = dealias_mac_v(&body_mactree, &ctx, &rep).await;
				let macro_input = MacTok::S(Paren::Round, body).at(body_sr.pos());
				if let Some(e) = rep.errv() {
					return Err(e);
				}
				Ok(call(sym_ref(sym!(macros::resolve; i())), [macro_input.to_gen().await]))
			}))
		}
		let mac_cell = Rc::new(OnceCell::new());
		let rules = Rc::new(RefCell::new(Some(rules)));
		for (kw, sr) in &*keywords {
			clone!(mac_cell, rules, module, prio);
			lines.push(ParsedLine::cnst(&sr.clone(), &comments, true, kw.clone(), async move |cctx| {
				let mac = mac_cell
					.get_or_init(async {
						let rep = Reporter::new();
						let rules = rules.borrow_mut().take().expect("once cell initializer runs");
						let rules = stream::iter(rules)
							.then(|(body_name, placeholders, pattern_rel)| {
								let cctx = &cctx;
								let rep = &rep;
								async move {
									let pattern = dealias_mac_v(&pattern_rel, cctx, rep).await;
									let pattern_res = Matcher::new(pattern.clone()).await;
									let placeholders = placeholders.into_iter().map(|(ph, _)| ph.name).collect_vec();
									match pattern_res {
										Ok(matcher) => Some(Rule { body_name, matcher, pattern, placeholders }),
										Err(e) => {
											rep.report(e);
											None
										},
									}
								}
							})
							.flat_map(stream::iter)
							.collect::<Vec<_>>()
							.await;
						Macro(Rc::new(MacroData { module, prio: prio.map(|i| i.0 as u64), rules }))
					})
					.await;
				atom(mac.clone())
			}))
		}
		Ok(lines)
	}
}