use crate::ast::*;
use crate::checker_state::*;

use std::iter::zip;
use tracing::instrument;

impl CheckerState {
    #[instrument(skip(self), level = "debug", fields(%set))]
    pub fn check_set(&self, set: Set) -> Result<Set, CheckerError> {
        match set {
            Set::BuiltIn(_) => Ok(set.clone()),
            Set::Record(fields) => {
                let mut ctx = self.clone();
                let fields = fields
                    .into_iter()
                    .map(|RecordField { name, set }| {
                        let set = ctx.check_set(set)?;
                        ctx.add_element(
                            name.clone(),
                            Value::Hypothetical(set.clone()),
                            set.clone(),
                        )?;
                        Ok(RecordField { name, set })
                    })
                    .collect::<Result<Vec<_>, _>>()?;
                Ok(Set::Record(fields))
            }
            Set::Variant(fields) => {
                let fields = fields
                    .into_iter()
                    .map(|VariantField { name, set }| {
                        let set = self.check_set(set)?;
                        Ok(VariantField {
                            name: name.clone(),
                            set,
                        })
                    })
                    .collect::<Result<Vec<_>, _>>()?;
                Ok(Set::Variant(fields))
            }
            Set::ClaimedSet(_) => Err(CheckerError::Unimplemented("instances as sets".to_string())),
            Set::Var(v) => {
                let deref = self.lookup_set(&v)?;
                Ok(deref.clone())
            }
        }
    }

    fn _check_literal_set_helper(
        &self,
        value: Element,
        claimed: &Set,
        should_be: Set,
    ) -> Result<(), CheckerError> {
        if !self.equal(claimed, &should_be) {
            Err(CheckerError::WrongSetForElement {
                value: value.clone().into(),
                claimed: claimed.clone(),
                real: should_be,
            })
        } else {
            Ok(())
        }
    }

    #[instrument(skip(self), level = "debug", fields(%element, %set))]
    pub fn check_element(&self, element: Element, set: &Set) -> Result<Element, CheckerError> {
        match element {
            Element::Literal(ref lit) => {
                let value = element.clone();
                // we may infer the type from the element
                match lit {
                    Literal::Int(_) => {
                        self._check_literal_set_helper(value, set, Set::BuiltIn(BuiltIn::Int))?;
                    }
                    Literal::Nat(_) => {
                        self._check_literal_set_helper(value, set, Set::BuiltIn(BuiltIn::Nat))?;
                    }
                    Literal::Str(_) => {
                        self._check_literal_set_helper(value, set, Set::BuiltIn(BuiltIn::Str))?;
                    }
                    Literal::Bool(_) => {
                        self._check_literal_set_helper(value, set, Set::BuiltIn(BuiltIn::Bool))?;
                    }
                    Literal::Float(_) => {
                        self._check_literal_set_helper(value, set, Set::BuiltIn(BuiltIn::Float))?;
                    }
                }
                Ok(element.clone().into())
            }
            Element::Var(ref v) => {
                let lookup = self.lookup_element(&v)?;
                // we have previously done the work to discover the type of
                // this element, so what we're claiming now must match!
                if !self.equal(set, &lookup.container) {
                    return Err(CheckerError::WrongSetForElement {
                        value: element.clone().into(),
                        claimed: set.clone(),
                        real: lookup.container.clone(),
                    });
                }
                // If we found a formal binding, we have no value to report.
                // This is the ONLY source of Var as a return value for
                // check_element, so in other branches we condition our logic
                // for formal bindings on finding Var after recursing.
                if let ElementValue::Concrete(ref deref) = lookup.value {
                    Ok(deref.clone())
                } else {
                    Ok(Element::Var(v.clone()))
                }
            }
            Element::Record(ref assignations) => {
                let rej = |reason| CheckerError::ElementDoesNotBelong {
                    element: element.clone(),
                    claimed: set.clone(),
                    reason,
                };

                // make sure we are filling a record
                let fields = if let Set::Record(fields) = set {
                    Ok(fields)
                } else {
                    Err(rej("element is a record instance".to_string()))
                }?;

                let (set_fnames, set_fsets): (Vec<String>, Vec<Set>) = fields
                    .iter()
                    .map(|RecordField { name, set }| (name.clone(), set.clone()))
                    .unzip();
                let mut set_fnames_sorted = set_fnames.clone();
                set_fnames_sorted.sort();

                let (element_fnames, element_felements): (Vec<String>, Vec<&Element>) =
                    assignations
                        .iter()
                        .map(|ElemAssign { name, element }| (name.clone(), element))
                        .unzip();

                let mut element_fnames_sorted = element_fnames.clone();
                element_fnames_sorted.sort();

                if set_fnames_sorted != element_fnames_sorted {
                    return Err(rej(format!(
                        "expected [{}] but found [{}]",
                        set_fnames.join(", "),
                        element_fnames.join(", "),
                    )));
                }

                // recurse, sets have already been completely expanded
                let sub_els = zip(element_felements, set_fsets)
                    .map(|(e_f, e_s)| self.check_element(e_f.clone().into(), &e_s))
                    .collect::<Result<Vec<_>, _>>()?;
                // rebuild
                let assignations = zip(element_fnames, sub_els)
                    .map(|(name, element)| ElemAssign { name, element })
                    .collect();
                // resign?
                Ok(Element::Record(assignations))
            }
            Element::Project {
                element: ref inner,
                ref field,
            } => {
                // globally unique projections mean we know what the sets going
                // in and out must be
                let Field {
                    field: field_set,
                    owner: owner_set,
                } = self.lookup_record_field(&field)?;

                // enforce the correct typing of the claimed result
                if !self.equal(set, field_set) {
                    return Err(CheckerError::WrongSetForElement {
                        value: element.clone().into(),
                        claimed: set.clone(),
                        real: field_set.clone(),
                    });
                }

                // enforce the correct typing of the element
                let inner = self.check_element(*inner.clone(), owner_set)?;

                // Unfortunately we still have to do something nasty here to
                // obtain the data
                match inner {
                    // We're stuck on something that bottoms out in a binding
                    // blocking computation, nothing to be done here
                    Element::Var(_) | Element::Project { .. } | Element::Case { .. } => {
                        Ok(Element::Project {
                            element: Box::new(inner),
                            field: field.clone(),
                        })
                    }
                    Element::Record(assignations) => {
                        let sub_element = assignations
                            .into_iter()
                            .find(|a| a.name == *field)
                            .expect(
                                "invariant violation: record missing field that was type-checked",
                            )
                            .element;
                        Ok(sub_element)
                    }
                    _ => panic!(
                        "invariant violation: check_element returned neither a record or stuck computation for record set"
                    ),
                }
            }
            Element::Inject {
                element: ref inner,
                ref field,
            } => {
                // globally unique injections mean that we know what the sets
                // going in and out must be, but compared to projections their
                // roles are here interchanged
                let Field {
                    field: field_set,
                    owner: owner_set,
                } = self.lookup_variant_field(&field)?;

                // enforce the correct typing of the claimed result
                if !self.equal(set, owner_set) {
                    return Err(CheckerError::WrongSetForElement {
                        value: element.clone().into(),
                        claimed: set.clone(),
                        real: owner_set.clone(),
                    });
                }

                // enforce the correct typing of the element
                let element = self.check_element(*inner.clone(), field_set)?;
                Ok(Element::Inject {
                    element: Box::new(element),
                    field: field.clone(),
                })
            }

            Element::Case {
                ref arms,
                ref scrutinee,
            } => {
                // TODO: do we allow mapping out of bottom?
                if arms.is_empty() {
                    return Err(CheckerError::Unimplemented(
                        "mapping out of bottom types".to_string(),
                    ));
                }

                // 1. Syntactic checks
                // -------------------
                // arms agree on the set to which the scrutinee should belong
                let arm_owners = arms
                    .iter()
                    .map(|ca| self.lookup_variant_field(&ca.tag).map(|sf| &sf.owner))
                    .collect::<Result<Vec<_>, _>>()?;
                let owner = arm_owners[0]; // safe because of the above decision about bottom
                if !arm_owners.into_iter().all(|o| self.equal(owner, o)) {
                    return Err(CheckerError::IncosistentCaseScrutineeSet(element.clone()));
                }

                // all cases are handled
                let Set::Variant(fields) = owner else {
                    panic!(
                        "invariant violation: looking up the owner of a variant field resulted in a non-variant set",
                    )
                };
                let mut required_field_names_sorted: Vec<String> =
                    fields.iter().map(|vf| vf.name.clone()).collect();
                required_field_names_sorted.sort();
                let mut covered_field_names_sorted: Vec<String> =
                    arms.iter().map(|ca| ca.tag.clone()).collect();
                covered_field_names_sorted.sort();
                if required_field_names_sorted != covered_field_names_sorted {
                    return Err(CheckerError::IncompleteCaseAnalysis {
                        found: covered_field_names_sorted,
                        required: required_field_names_sorted,
                    });
                }

                // 2. semantic checks
                // ------------------

                // scrutinee must be of the same set that all the arms are
                // implying, in particular this implies that the following holds
                // `inner : self.lookup_variant_field(field).field_set`
                let scrutinee = self.check_element(*scrutinee.clone(), owner)?;

                // which variant are we, if any

                let matching: Option<(String, Element)> = match scrutinee {
                    Element::Inject {
                        ref field,
                        element: ref inner,
                    } => Some((field.clone(), *inner.clone())),
                    // These are all the cases which could become stuck on a
                    // formal binding
                    Element::Var(_) | Element::Project { .. } | Element::Case { .. } => None,
                    Element::Literal(_) | Element::Record(_) => panic!(
                        "invariant violation: scrutinee is a non-variant value at variant set"
                    ),
                };

                // for each arm, recurse with a concrete value (if we have one)
                // otherwise fall back to hypothetical elements; in the former
                // case record the end result
                let mut computed_output = None;
                let mut processed_arms = Vec::new();
                for arm in arms {
                    let Field {
                        field: field_set, ..
                    } = self.lookup_variant_field(&arm.tag)?;

                    let mut new_context = self.clone();
                    let binding_name = arm.bound.clone();
                    let binding_set = field_set.clone();

                    let body = if let Some((tag, inner)) = &matching
                        && *tag == arm.tag
                    {
                        new_context.add_element(
                            binding_name.clone(),
                            inner.clone().into(),
                            binding_set,
                        )?;
                        let output = new_context.check_element(arm.body.clone().into(), set)?;
                        if matches!(computed_output, Some(_)) {
                            panic!(
                                "invariant violation: we somehow matched multiple arms in case analysis"
                            )
                        }
                        computed_output = Some(output.clone());
                        output
                    } else {
                        new_context.add_element(
                            binding_name.clone(),
                            Value::Hypothetical(field_set.clone()),
                            binding_set,
                        )?;
                        new_context.check_element(arm.body.clone().into(), set)?
                    };

                    processed_arms.push(CaseArm {
                        tag: arm.tag.clone(),
                        bound: binding_name,
                        body,
                    });
                }
                Ok(computed_output.unwrap_or(Element::Case {
                    scrutinee: Box::new(scrutinee),
                    arms: processed_arms,
                }))
            }
        }
    }
}