use hashbrown::HashMap;
use mappable_rc::Mrc;

use crate::{ast::{Expr, Clause}, utils::{iter::{box_once, into_boxed_iter}, to_mrc_slice, one_mrc_slice}, unwrap_or};
use super::{super::RuleError, state::{State, Entry}, slice_matcher::SliceMatcherDnC};

fn verify_scalar_vec(pattern: &Expr, is_vec: &mut HashMap<String, bool>)
-> Result<(), String> {
    let verify_clause = |clause: &Clause, is_vec: &mut HashMap<String, bool>| -> Result<(), String> {
        match clause {
            Clause::Placeh{key, vec} => {
                if let Some(known) = is_vec.get(key) {
                    if known != &vec.is_some() { return Err(key.to_string()) }
                } else {
                    is_vec.insert(key.clone(), vec.is_some());
                }
            }
            Clause::Auto(name, typ, body) => {
                if let Some(key) = name.as_ref().and_then(|key| key.strip_prefix('$')) {
                    if is_vec.get(key) == Some(&true) { return Err(key.to_string()) }
                }
                typ.iter().try_for_each(|e| verify_scalar_vec(e, is_vec))?;
                body.iter().try_for_each(|e| verify_scalar_vec(e, is_vec))?;
            }
            Clause::Lambda(name, typ, body) => {
                if let Some(key) = name.strip_prefix('$') {
                    if is_vec.get(key) == Some(&true) { return Err(key.to_string()) }
                }
                typ.iter().try_for_each(|e| verify_scalar_vec(e, is_vec))?;
                body.iter().try_for_each(|e| verify_scalar_vec(e, is_vec))?;
            }
            Clause::S(_, body) => {
                body.iter().try_for_each(|e| verify_scalar_vec(e, is_vec))?;
            }
            _ => ()
        };
        Ok(())
    };
    let Expr(val, typ) = pattern;
    verify_clause(val, is_vec)?;
    for typ in typ.as_ref() {
        verify_clause(typ, is_vec)?;
    }
    Ok(())
}


fn slice_to_vec(src: &mut Mrc<[Expr]>, tgt: &mut Mrc<[Expr]>) {
    let prefix_expr = Expr(Clause::Placeh{key: "::prefix".to_string(), vec: Some((0, false))}, to_mrc_slice(vec![]));
    let postfix_expr = Expr(Clause::Placeh{key: "::postfix".to_string(), vec: Some((0, false))}, to_mrc_slice(vec![]));
    // Prefix or postfix to match the full vector
    let head_multi = matches!(src.first().expect("Src can never be empty!").0, Clause::Placeh{vec: Some(_), ..});
    let tail_multi = matches!(src.last().expect("Impossible branch!").0, Clause::Placeh{vec: Some(_), ..});
    let prefix_vec = if head_multi {vec![]} else {vec![prefix_expr]};
    let postfix_vec = if tail_multi {vec![]} else {vec![postfix_expr]};
    *src = to_mrc_slice(prefix_vec.iter().chain(src.iter()).chain(postfix_vec.iter()).cloned().collect());
    *tgt = to_mrc_slice(prefix_vec.iter().chain(tgt.iter()).chain(postfix_vec.iter()).cloned().collect());
}

/// Traverse the tree, calling pred on every sibling list until it returns some vec
/// then replace the sibling list with that vec and return true
/// return false if pred never returned some
fn update_first_seq_rec<F>(input: Mrc<[Expr]>, pred: &mut F) -> Option<Mrc<[Expr]>>
where F: FnMut(Mrc<[Expr]>) -> Option<Mrc<[Expr]>> {
    if let o@Some(_) = pred(Mrc::clone(&input)) {o} else {
        for Expr(cls, _) in input.iter() {
            if let Some(t) = cls.typ() {
                if let o@Some(_) = update_first_seq_rec(t, pred) {return o}
            }
            if let Some(b) = cls.body() {
                if let o@Some(_) = update_first_seq_rec(b, pred) {return o}
            }
        }
        None
    }
}

/// keep re-probing the input with pred until it stops matching
fn update_all_seqs<F>(input: Mrc<[Expr]>, pred: &mut F) -> Option<Mrc<[Expr]>>
where F: FnMut(Mrc<[Expr]>) -> Option<Mrc<[Expr]>> {
    let mut tmp = update_first_seq_rec(input, pred);
    while let Some(xv) = tmp {
        tmp = update_first_seq_rec(Mrc::clone(&xv), pred);
        if tmp.is_none() {return Some(xv)}
    }
    None
}

/// Fill in a template from a state as produced by a pattern
fn write_slice(state: &State, tpl: &Mrc<[Expr]>) -> Mrc<[Expr]> {
    eprintln!("Writing {tpl:?} with state {state:?}");
    tpl.iter().flat_map(|Expr(clause, xpr_typ)| match clause {
        Clause::Auto(name_opt, typ, body) => box_once(Expr(Clause::Auto(
            name_opt.as_ref().and_then(|name| {
                if let Some(state_key) = name.strip_prefix('$') {
                    match &state[state_key] {
                        Entry::NameOpt(name) => name.as_ref().map(|s| s.as_ref().to_owned()),
                        Entry::Name(name) => Some(name.as_ref().to_owned()),
                        _ => panic!("Auto template name may only be derived from Auto or Lambda name")
                    }
                } else {
                    Some(name.to_owned())
                }
            }),
            write_slice(state, typ),
            write_slice(state, body)
        ), xpr_typ.to_owned())),
        Clause::Lambda(name, typ, body) => box_once(Expr(Clause::Lambda(
            if let Some(state_key) = name.strip_prefix('$') {
                if let Entry::Name(name) = &state[state_key] {
                    name.as_ref().to_owned()
                } else {panic!("Lambda template name may only be derived from Lambda name")}
            } else {
                name.to_owned()
            },
            write_slice(state, typ),
            write_slice(state, body)
        ), xpr_typ.to_owned())),
        Clause::S(c, body) => box_once(Expr(Clause::S(
            *c,
            write_slice(state, body)
        ), xpr_typ.to_owned())),
        Clause::Placeh{key, vec: None} => {
            let real_key = unwrap_or!(key.strip_prefix('_'); key);
            match &state[real_key] {
                Entry::Scalar(x) => box_once(x.as_ref().to_owned()),
                Entry::Name(n) => box_once(Expr(Clause::Name {
                    local: Some(n.as_ref().to_owned()),
                    qualified: one_mrc_slice(n.as_ref().to_owned())
                }, to_mrc_slice(vec![]))),
                _ => panic!("Scalar template may only be derived from scalar placeholder"),
            }
        },
        Clause::Placeh{key, vec: Some(_)} => if let Entry::Vec(v) = &state[key] {
            into_boxed_iter(v.as_ref().to_owned())
        } else {panic!("Vectorial template may only be derived from vectorial placeholder")},
        // Explicit base case so that we get an error if Clause gets new values
        c@Clause::Literal(_) | c@Clause::Name { .. } | c@Clause::ExternFn(_) | c@Clause::Atom(_) =>
            box_once(Expr(c.to_owned(), xpr_typ.to_owned()))
    }).collect()
}

/// Apply a rule (a pair of pattern and template) to an expression
pub fn execute(mut src: Mrc<[Expr]>, mut tgt: Mrc<[Expr]>, input: Mrc<[Expr]>)
-> Result<Option<Mrc<[Expr]>>, RuleError> {
    // Dimension check
    let mut is_vec_db = HashMap::new();
    src.iter().try_for_each(|e| verify_scalar_vec(e, &mut is_vec_db))
        .map_err(RuleError::ScalarVecMismatch)?;
    tgt.iter().try_for_each(|e| verify_scalar_vec(e, &mut is_vec_db))
        .map_err(RuleError::ScalarVecMismatch)?;
    // Padding
    slice_to_vec(&mut src, &mut tgt);
    // Generate matcher
    let matcher = SliceMatcherDnC::new(src);
    let matcher_cache = SliceMatcherDnC::get_matcher_cache();
    Ok(update_all_seqs(Mrc::clone(&input), &mut |p| {
        let state = matcher.match_range_cached(p, &matcher_cache)?;
        Some(write_slice(&state, &tgt))
    }))
}