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use std::borrow::Cow;

use crate::ast::{up_dec_rc, up_var_rc, AnonymousValue, Declaration, Expression, Pattern, Typed};
use crate::check::expr::{check, check_type};
use crate::check::read_back::generate_value;
use crate::check::tcm::{update_gamma_borrow, update_gamma_lazy, Gamma, TCE, TCM, TCS};

macro_rules! try_locate {
    ($err:expr, $pattern:expr) => {
        match $err {
            TCE::Located(_, _) => $err,
            e => TCE::Located(Box::new(e), $pattern.clone()),
        }
    };
}

pub type LiftState<'a> = (Expression, Expression, TCS<'a>);

/// Lift all these `parameters` into the context.<br/>
/// Returning `TCS` to reuse the variable.
///
/// `check_body` is supposed to return `signature`, `body` and `tcs`.
pub fn check_lift_parameters<'a>(
    index: u32,
    tcs: TCS<'a>,
    mut parameters: Vec<Typed>,
    check_body: impl FnOnce(TCS<'a>) -> TCM<LiftState<'a>>,
) -> TCM<LiftState<'a>> {
    if parameters.is_empty() {
        return check_body(tcs);
    }
    let (pattern, expression) = parameters.remove(0);
    let TCS { gamma, context } = check_type(index, tcs, *expression.clone())?;
    let generated = generate_value(index);
    let type_val = expression.clone().eval(context.clone());
    let gamma = update_gamma_borrow(gamma, &pattern, type_val.clone(), &generated)?;

    let tcs = TCS {
        gamma,
        context: up_var_rc(context, pattern.clone(), generated),
    };
    let (signature, body, tcs) = check_lift_parameters(index + 1, tcs, parameters, check_body)?;

    Ok((
        Expression::Pi(
            (pattern.clone(), Box::new(*expression)),
            Box::new(signature),
        ),
        Expression::Lambda(pattern, AnonymousValue::some(type_val), Box::new(body)),
        tcs,
    ))
}

/// Extracted from `checkD` in Mini-TT.<br/>
/// This part deals with recursive declarations, but without prefixed parameters.
pub fn check_recursive_declaration(index: u32, tcs: TCS, declaration: Declaration) -> TCM<Gamma> {
    let pattern = declaration.pattern.clone();
    check_type(index, tcs_borrow!(tcs), declaration.signature.clone())
        .map_err(|err| try_locate!(err, pattern))?;
    let TCS { gamma, context } = tcs;
    let signature = declaration.signature.clone().eval(context.clone());
    let generated = generate_value(index);
    let fake_gamma = update_gamma_borrow(
        Cow::Borrowed(&gamma),
        &pattern,
        signature.clone(),
        &generated,
    )
    .map_err(|err| try_locate!(err, pattern))?;
    let fake_context = up_var_rc(context.clone(), pattern.clone(), generated);
    check(
        index + 1,
        TCS::new(fake_gamma, fake_context),
        declaration.body.clone(),
        signature.clone(),
    )
    .map_err(|err| try_locate!(err, pattern))?;
    update_gamma_lazy(gamma, &pattern, signature, || {
        declaration
            .body
            .clone()
            .eval(up_dec_rc(context, declaration))
    })
    .map_err(|err| try_locate!(err, pattern))
}

/// Extracted from `checkD` in Mini-TT.<br/>
/// This part deals with non-recursive declarations, but without prefixed parameters.
pub fn check_simple_declaration(
    index: u32,
    tcs: TCS,
    pattern: Pattern,
    signature: Expression,
    body: Expression,
) -> TCM<Gamma> {
    check_type(index, tcs_borrow!(tcs), signature.clone())
        .map_err(|err| try_locate!(err, pattern))?;
    let signature = signature.eval(tcs.context());
    check(index, tcs_borrow!(tcs), body.clone(), signature.clone())
        .map_err(|err| try_locate!(err, pattern))?;
    let TCS { gamma, context } = tcs;
    update_gamma_lazy(gamma, &pattern, signature, || body.eval(context))
        .map_err(|err| try_locate!(err, pattern))
}

/// Originally `checkD` in Mini-TT, but now it's not because this implementation supports
/// prefixed parameters :)<br/>
/// Check if a declaration is well-typed and update the context.
pub fn check_declaration(index: u32, tcs: TCS, declaration: Declaration) -> TCM<TCS> {
    use crate::ast::DeclarationType::*;
    if declaration.prefix_parameters.is_empty() {
        let context = tcs.context();
        return match &declaration.declaration_type {
            Simple => check_simple_declaration(
                index,
                tcs,
                declaration.pattern.clone(),
                declaration.signature.clone(),
                declaration.body.clone(),
            ),
            Recursive => check_recursive_declaration(index, tcs, declaration.clone()),
        }
        .map(|gamma| TCS::new(gamma, up_dec_rc(context, declaration)));
    }
    let (pattern, signature, body) = match declaration {
        Declaration {
            pattern,
            prefix_parameters,
            signature,
            body,
            declaration_type: Simple,
        } => check_lift_parameters(index, tcs_borrow!(tcs), prefix_parameters, |tcs| {
            let tcs = check_type(index, tcs, signature.clone())
                .map_err(|err| try_locate!(err, pattern))?;
            let context = tcs.context();
            let tcs = check(index, tcs, body.clone(), signature.clone().eval(context))
                .map_err(|err| try_locate!(err, pattern))?;
            Ok((signature, body, tcs))
        })
        .map(|(signature, body, _)| (pattern, signature, body))?,
        declaration => {
            let pattern = declaration.pattern.clone();
            check_lift_parameters(
                index,
                tcs_borrow!(tcs),
                declaration.prefix_parameters.clone(),
                |tcs| {
                    let TCS { gamma, context } =
                        check_type(index, tcs, declaration.signature.clone())
                            .map_err(|err| try_locate!(err, pattern))?;
                    let pattern = pattern.clone();
                    let generated = generate_value(index);
                    let signature = declaration.signature.clone().eval(context.clone());
                    let fake_gamma = update_gamma_borrow(
                        Cow::Borrowed(&gamma),
                        &pattern,
                        signature.clone(),
                        &generated,
                    )
                    .map_err(|err| try_locate!(err, pattern))?;
                    let fake_context = up_var_rc(context.clone(), pattern.clone(), generated);
                    check(
                        index + 1,
                        TCS::new(fake_gamma, fake_context),
                        declaration.body.clone(),
                        signature,
                    )
                    .map_err(|err| try_locate!(err, pattern))?;
                    Ok((
                        declaration.signature.clone(),
                        declaration.body.clone(),
                        TCS::new(gamma, up_dec_rc(context, declaration)),
                    ))
                },
            )
            .map(|(signature, body, _)| (pattern, signature, body))?
        }
    };

    let TCS { gamma, context } = tcs;
    let body = body.eval(context.clone());
    update_gamma_borrow(gamma, &pattern, signature.eval(context.clone()), &body)
        .map(|gamma| TCS::new(gamma, up_var_rc(context, pattern.clone(), body)))
        .map_err(|err| try_locate!(err, pattern))
}