use std::ops::{Add, Range};

use futures::FutureExt;
use hashbrown::{HashMap, HashSet};
use itertools::Itertools;
use orchid_base::{NameLike, Paren, Pos, VPath, fmt, is, log, mk_errv, report};
use orchid_extension::gen_expr::{call_v, new_atom};
use orchid_extension::{ExecHandle, ReflMemKind, TAtom, refl};
use subslice_offset::SubsliceOffset;

use crate::macros::macro_value::{Macro, Rule};
use crate::macros::mactree::MacTreeSeq;
use crate::macros::rule::state::{MatchState, StateEntry};
use crate::{MacTok, MacTree};

pub async fn resolve(h: &mut ExecHandle<'_>, val: MacTree) -> MacTree {
	writeln!(log("debug"), "Macro-resolving {}", fmt(&val).await).await;
	let root = refl();
	let mut macros = HashMap::new();
	for n in val.glossary() {
		let (foot, body) = n.split_last_seg();
		let new_name = VPath::new(body.iter().cloned())
			.name_with_suffix(is(&format!("__macro__{foot}")).await)
			.to_sym()
			.await;
		if let Ok(ReflMemKind::Const) = root.get_by_path(&new_name).await.map(|m| m.kind()) {
			let Ok(mac) = h.exec::<TAtom<Macro>>(new_name).await else { continue };
			let mac = mac.own().await;
			macros.entry(mac.0.canonical_name.clone()).or_insert(mac);
		}
	}
	let mut exclusive = Vec::new();
	let mut prios = Vec::<u64>::new();
	let mut priod = Vec::<FilteredMacroRecord>::new();
	for (_, mac) in macros.iter() {
		let mut record = FilteredMacroRecord { mac, rules: Vec::new() };
		for (rule_i, rule) in mac.0.rules.iter().enumerate() {
			if rule.pattern.glossary.is_subset(val.glossary()) {
				record.rules.push(rule_i);
			}
		}
		if !record.rules.is_empty() {
			match mac.0.prio {
				None => exclusive.push(record),
				Some(prio) => {
					let i = prios.partition_point(|p| *p > prio);
					prios.insert(i, prio);
					priod.insert(i, record);
				},
			}
		}
	}
	let mut rctx = ResolveCtx { exclusive, priod, h: &mut *h };
	let gex = resolve_one(&mut rctx, &val).await.unwrap_or(val.clone());
	writeln!(log("debug"), "Macro-resolution over {} yielded {}", fmt(&val).await, fmt(&gex).await)
		.await;
	gex
}

/// Rules belonging to one macro that passed a particular filter
pub struct FilteredMacroRecord<'a> {
	mac: &'a Macro,
	/// The rules in increasing order of index
	rules: Vec<usize>,
}

struct ResolveCtx<'a, 'b> {
	/// If these overlap, that's a compile-time error
	pub exclusive: Vec<FilteredMacroRecord<'a>>,
	/// If these overlap, the priorities decide the order. In case of a tie, the
	/// order is unspecified
	pub priod: Vec<FilteredMacroRecord<'a>>,
	pub h: &'a mut ExecHandle<'b>,
}

async fn resolve_one(ctx: &mut ResolveCtx<'_, '_>, value: &MacTree) -> Option<MacTree> {
	match value.tok() {
		MacTok::Ph(_) | MacTok::Slot => panic!("Forbidden element in value mactree"),
		MacTok::Bottom(_) | MacTok::Value(_) | MacTok::Name(_) | MacTok::Resolved(_) => None,
		MacTok::Lambda(arg, body) => {
			let new_arg = resolve_one(ctx, arg).boxed_local().await;
			let new_body = resolve_seq(ctx, body, value.pos()).boxed_local().await;
			if new_arg.is_none() && new_body.is_none() {
				return None;
			}
			let tok = MacTok::Lambda(
				new_arg.unwrap_or_else(|| arg.clone()),
				new_body.unwrap_or_else(|| body.clone()),
			);
			Some(tok.at(value.pos()))
		},
		MacTok::S(pty, body) => (resolve_seq(ctx, body, value.pos()).boxed_local().await)
			.map(|body| MacTok::S(*pty, body).at(value.pos())),
	}
}

type XMatches<'a> = Vec<(Range<usize>, &'a Macro, &'a Rule, MatchState<'a>)>;

/// find the subsection of the slice that satisfies both the lower and upper
/// limit.
fn subsection<T>(
	slice: &[T],
	lower_limit: impl FnMut(&T) -> bool,
	mut upper_limit: impl FnMut(&T) -> bool,
) -> Range<usize> {
	let start = slice.partition_point(lower_limit);
	let len = slice[start..].partition_point(|t| !upper_limit(t));
	start..start + len
}

async fn resolve_seq(
	ctx: &mut ResolveCtx<'_, '_>,
	val: &MacTreeSeq,
	fallback_pos: Pos,
) -> Option<MacTreeSeq> {
	if val.items.is_empty() {
		return None;
	}
	// A sorted collection of overlapping but non-nested matches to exclusive
	// macros
	let mut x_matches: XMatches = Vec::new();
	let top_glossary = val.top_glossary.clone();
	let mut new_val = val.items.to_vec();
	'x_macros: for x in &ctx.exclusive {
		let mut rules_iter = x.rules.iter();
		let ((before, state, after), rule) = 'rules: loop {
			let Some(ridx) = rules_iter.next() else { continue 'x_macros };
			let rule = &x.mac.0.rules[*ridx];
			if rule.pattern.top_glossary.is_subset(&top_glossary)
				&& let Some(record) = rule.matcher.apply(&val.items[..], &|_| true).await
			{
				break 'rules (record, rule);
			};
		};
		let new_r = (before.len()..new_val.len() - after.len(), x.mac, rule, state);
		// elements that overlap with us
		let overlap =
			subsection(&x_matches[..], |r| new_r.0.start < r.0.end, |r| r.0.start < new_r.0.end);
		let overlapping = &x_matches[overlap.clone()];
		// elements that fully contain us
		let geq_range =
			subsection(overlapping, |r| r.0.start <= new_r.0.start, |r| new_r.0.end <= r.0.end);
		let geq = &overlapping[geq_range.clone()];
		// if any of these is equal to us, all of them must be, otherwise the larger
		// ranges would have overridden the smaller ones
		if let Some(example) = geq.first() {
			// if they are equal to us, record the conflict.
			if example.0 == new_r.0 {
				let idx = (x_matches.subslice_offset(geq))
					.expect("this slice is statically derived from x_matches");
				x_matches.insert(idx, new_r);
			}
			// either way, we matched so no further rules can run.
			continue 'x_macros;
		}
		// elements we fully contain. Equal ranges have been handled above
		let lt_range =
			subsection(overlapping, |r| new_r.0.start <= r.0.start, |r| r.0.end <= new_r.0.end);
		let lt = &overlapping[lt_range.clone()];
		if lt.is_empty() {
			// an empty range
			let i = x_matches.partition_point(|r| r.0.start < new_r.0.start);
			x_matches.insert(i, new_r);
		} else {
			let lt_start =
				x_matches.subslice_offset(overlapping).expect("Slice statically derived from x_matches");
			x_matches.splice(lt_start..lt_start + lt_range.len(), [new_r]);
		}
	}
	let mut any_match = !x_matches.is_empty();
	// apply exclusive matches
	if !x_matches.is_empty() {
		// ranges of indices into x_matches which setwise conflict with each other.
		// Pairwise conflict reporting is excess noise, but a single conflict error
		// doesn't reveal where within the parenthesized block to look, so it's easiest
		// to group them setwise even if these sets may associate macros which don't
		// directly conflict.
		let conflict_sets = (0..x_matches.len()).map(|x| x..x + 1).coalesce(|lran, rran| {
			// each index was mapped to a range that contains only itself. Now we check if
			// the last match in the first range overlaps the first match in the second
			// range, and combine them if this is the case.
			if x_matches[rran.start].0.start < x_matches[lran.end].0.end {
				Ok(lran.start..rran.end)
			} else {
				Err((lran, rran))
			}
		});
		let mac_conflict_tk = is("Macro conflict").await;
		let error = conflict_sets
			.filter(|r| 1 < r.len())
			.map(|set| {
				mk_errv(
					mac_conflict_tk.clone(),
					"Multiple partially overlapping syntax elements detected. \n\
							Try parenthesizing whichever side is supposed to be the subexpression.",
					x_matches[set].iter().flat_map(|rec| rec.3.names()).flat_map(|name| name.1).cloned(),
				)
			})
			.reduce(|l, r| l + r);
		if let Some(error) = error {
			report(error.clone());
			return Some(MacTreeSeq::new([MacTok::Bottom(error).at(fallback_pos)]));
		}
		// no conflicts, apply all exclusive matches
		for (range, mac, rule, state) in x_matches.into_iter().rev() {
			// backwards so that the non-overlapping ranges remain valid
			let pos = (state.names().flat_map(|r| r.1).cloned().reduce(Pos::add))
				.expect("All macro rules must contain at least one locally defined name");
			let subex = call_body(ctx.h, mac, rule, &state, pos.clone()).await;
			new_val.splice(range, [subex]);
		}
	};
	// TODO: Does this glossary refresh actually pay off?
	let top_glossary = (new_val.iter())
		.flat_map(|t| if let MacTok::Name(t) = t.tok() { Some(t.clone()) } else { None })
		.collect::<HashSet<_>>();
	for FilteredMacroRecord { mac, rules } in &ctx.priod {
		for ridx in rules {
			let rule = &mac.0.rules[*ridx];
			if !rule.pattern.top_glossary.is_subset(&top_glossary) {
				continue;
			}
			let Some((pre, state, suf)) = rule.matcher.apply(&new_val, &|_| true).await else { continue };
			any_match = true;
			let range = pre.len()..new_val.len() - suf.len();
			let pos = (state.names().flat_map(|pair| pair.1).cloned().reduce(Pos::add))
				.expect("All macro rules must contain at least one locally defined name");
			let subex = call_body(ctx.h, mac, rule, &state, pos.clone()).await;
			std::mem::drop(state);
			new_val.splice(range, [subex]);
		}
	}
	for item in new_val.iter_mut() {
		let Some(new) = resolve_one(ctx, item).await else { continue };
		*item = new;
		any_match = true;
	}
	any_match.then_some(MacTreeSeq::new(new_val))
}

async fn call_body(
	h: &mut ExecHandle<'_>,
	mac: &Macro,
	rule: &Rule,
	state: &MatchState<'_>,
	pos: Pos,
) -> MacTree {
	let mut call_args = vec![];
	for name in rule.ph_names.iter() {
		call_args.push(match state.get(name).expect("Missing state entry for placeholder") {
			StateEntry::Scalar(scal) => new_atom((**scal).clone()),
			StateEntry::Vec(vec) =>
				new_atom(MacTok::S(Paren::Round, MacTreeSeq::new(vec.iter().cloned())).at(Pos::None)),
		});
	}
	let f_name = mac.0.module.suffix([rule.body.clone()]).await;
	match h.exec::<TAtom<MacTree>>(call_v(f_name, call_args)).await {
		Err(e) => MacTok::Bottom(e).at(pos),
		Ok(mt) => MacTok::Resolved(mt.own().await).at(mt.pos()),
	}
}