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use std::mem::swap;

use voile_util::loc::ToLoc;

use crate::syntax::abs::AbsDecl;
use crate::syntax::core::{Neutral, TraverseNeutral, Val, ValInfo, TYPE_OMEGA};

use super::monad::{ValTCM, TCE, TCM, TCS};

/// Checking a list of declarations.
pub fn check_decls(tcs: TCS, decls: Vec<AbsDecl>) -> TCM {
    decls.into_iter().try_fold(tcs, check_decl)
}

fn require_local_emptiness(tcs: &TCS) {
    debug_assert!(tcs.local_env.is_empty());
    debug_assert!(tcs.local_gamma.is_empty());
}

fn unimplemented_to_glob(v: &mut [ValInfo], i: usize) {
    let mut placeholder = Default::default();
    swap(&mut v[i], &mut placeholder);
    placeholder = placeholder.map_ast(|ast| ast.unimplemented_to_glob());
    swap(&mut placeholder, &mut v[i]);
}

fn inline_metas(mut tcs: TCS, val: ValInfo) -> ValTCM {
    use Neutral::*;
    let info = val.loc;
    let val = val.ast.try_map_neutral(&mut |neut| match neut {
        Meta(mi) => tcs
            .meta_context
            .take_meta(mi)
            .ok_or_else(|| TCE::MetaUnsolved(mi)),
        e => Ok(Val::Neut(e)),
    })?;
    Ok((val.into_info(info), tcs))
}

/**
Checking one declaration.
$$
\newcommand{\cdecl}[2]{#1 \vdash_\texttt{d} #2 \ \textbf{ok}}
\newcommand{\Gcdecl}[1]{\cdecl{\Gamma}{#1}}
\newcommand{\infer}[3]{#1 \vdash_\texttt{i} #2 \Leftarrow #3}
\newcommand{\xx}[0]{\texttt{x}}
\newcommand{\tyck}[4]{#1 \vdash_\texttt{c} #2 : #3 \Rightarrow #4}
\newcommand{\Gtyck}[3]{\tyck{\Gamma}{#1}{#2}{#3}}
\newcommand{\ty}[0]{\tau}
\newcommand{\cA}[0]{\mathcal A}
\newcommand{\cB}[0]{\mathcal B}
\cfrac{}{\cdecl{}{}}
\quad
\cfrac{}{
  \infer{
    \Gamma, \textbf{val } \xx' : \cA
  }{\xx'}{\cA}
}
\quad
\cfrac{
  \Gtyck{A}{\ty}{\cA} \quad
  \cdecl{
    \Gamma, \textbf{val } \xx' : \cA
  }{D}
}{
  \Gcdecl{\textbf{val } \xx' : A; D}
}
\\\\ \space \\\\
\cfrac{
  \tyck{
    \Gamma, \xx' : \cA
  }{a}{\cA}{\alpha}
  \quad
  \cdecl{
    \Gamma,
    \textbf{val } \xx' : \cA,
    \textbf{let } \xx' = \alpha
  }{D}
}{
  \cdecl{
    \Gamma, \textbf{val } \xx' : \cA
  }{\textbf{let } \xx' = a; D}
}
$$
*/
fn check_decl(tcs: TCS, decl: AbsDecl) -> TCM {
    debug_assert_eq!(tcs.gamma.len(), tcs.env.len());
    let tcs = match decl {
        AbsDecl::Impl(impl_abs, sign_dbi) => {
            let sign = tcs.glob_type(sign_dbi);
            let sign_cloned = sign.ast.clone();
            let (val_fake, tcs) = tcs.check(&impl_abs, &sign_cloned)?;
            // We generate axioms for lambda parameters during type-checking.
            // Now it's time to change them back to `var` references.
            let val = val_fake.map_ast(|ast| ast.generated_to_var());
            let (val, mut tcs) = inline_metas(tcs, val)?;

            tcs.env[sign_dbi.0] = val;

            // Every references to me are now actually valid (they were axioms before),
            // replace them with a global reference.
            for i in sign_dbi.0..tcs.glob_len() {
                unimplemented_to_glob(&mut tcs.env, i);
            }
            for i in sign_dbi.0 + 1..tcs.glob_len() {
                unimplemented_to_glob(&mut tcs.gamma, i);
            }

            // Err(TCE::DbiOverflow(tcs.env.len(), new_dbi))
            tcs
        }
        AbsDecl::Sign(sign_abs, self_index) => {
            let loc = sign_abs.loc();
            let (sign_fake, tcs) = tcs.check(&sign_abs, &TYPE_OMEGA)?;
            let (sign_fake, mut tcs) = inline_metas(tcs, sign_fake)?;
            let sign = sign_fake.map_ast(|ast| ast.generated_to_var());
            let val_info = Val::fresh_unimplemented(self_index).into_info(loc);
            tcs.env.push(val_info);
            tcs.gamma.push(sign);

            // Give warning on axiom?
            tcs
        }
        AbsDecl::Decl(impl_abs) => {
            let (inferred, tcs) = tcs.infer(&impl_abs)?;
            let (inferred, tcs) = inline_metas(tcs, inferred)?;
            let (compiled, tcs) = tcs.evaluate(impl_abs);
            let (compiled, mut tcs) = inline_metas(tcs, compiled)?;
            let compiled = compiled.map_ast(|ast| ast.generated_to_var());
            let inferred = inferred.map_ast(|ast| ast.generated_to_var());
            tcs.env.push(compiled);
            tcs.gamma.push(inferred);

            tcs
        }
    };

    require_local_emptiness(&tcs);
    Ok(tcs)
}

impl TCS {
    #[inline]
    pub fn check_decls(self, decls: Vec<AbsDecl>) -> TCM {
        check_decls(self, decls)
    }
}