use std::cell::RefCell;
use std::collections::HashMap;

use crate::top_level::{DefinitionId, TopLevelContext, TopLevelDef};
use crate::typecheck::{
    type_inferencer::PrimitiveStore,
    typedef::{Type, Unifier},
};
use crate::{location::Location, typecheck::typedef::TypeEnum};
use itertools::{chain, izip};
use rustpython_parser::ast::Expr;

#[derive(Clone, PartialEq)]
pub enum SymbolValue {
    I32(i32),
    I64(i64),
    Double(f64),
    Bool(bool),
    Tuple(Vec<SymbolValue>),
    // we should think about how to implement bytes later...
    // Bytes(&'a [u8]),
}

pub trait SymbolResolver {
    // get type of type variable identifier or top-level function type
    fn get_symbol_type(
        &self,
        unifier: &mut Unifier,
        primitives: &PrimitiveStore,
        str: &str,
    ) -> Option<Type>;
    // get the top-level definition of identifiers
    fn get_identifier_def(&self, str: &str) -> Option<DefinitionId>;
    fn get_symbol_value(&self, str: &str) -> Option<SymbolValue>;
    fn get_symbol_location(&self, str: &str) -> Option<Location>;
    // handle function call etc.
}

// convert type annotation into type
pub fn parse_type_annotation<T>(
    resolver: &dyn SymbolResolver,
    top_level: &TopLevelContext,
    unifier: &mut Unifier,
    primitives: &PrimitiveStore,
    expr: &Expr<T>,
) -> Result<Type, String> {
    use rustpython_parser::ast::ExprKind::*;
    match &expr.node {
        Name { id, .. } => match id.as_str() {
            "int32" => Ok(primitives.int32),
            "int64" => Ok(primitives.int64),
            "float" => Ok(primitives.float),
            "bool" => Ok(primitives.bool),
            "None" => Ok(primitives.none),
            x => {
                let obj_id = resolver.get_identifier_def(x);
                if let Some(obj_id) = obj_id {
                    let defs = top_level.definitions.read();
                    let def = defs[obj_id.0].read();
                    if let TopLevelDef::Class { fields, methods, type_vars, .. } = &*def {
                        if !type_vars.is_empty() {
                            return Err(format!(
                                "Unexpected number of type parameters: expected {} but got 0",
                                type_vars.len()
                            ));
                        }
                        let fields = RefCell::new(
                            chain(
                                fields.iter().map(|(k, v)| (k.clone(), *v)),
                                methods.iter().map(|(k, v, _)| (k.clone(), *v)),
                            )
                            .collect(),
                        );
                        Ok(unifier.add_ty(TypeEnum::TObj {
                            obj_id,
                            fields,
                            params: Default::default(),
                        }))
                    } else {
                        Err("Cannot use function name as type".into())
                    }
                } else {
                    // it could be a type variable
                    let ty = resolver
                        .get_symbol_type(unifier, primitives, x)
                        .ok_or_else(|| "Cannot use function name as type".to_owned())?;
                    if let TypeEnum::TVar { .. } = &*unifier.get_ty(ty) {
                        Ok(ty)
                    } else {
                        Err(format!("Unknown type annotation {}", x))
                    }
                }
            }
        },
        Subscript { value, slice, .. } => {
            if let Name { id, .. } = &value.node {
                if id == "virtual" {
                    let ty = parse_type_annotation(resolver, top_level, unifier, primitives, slice)?;
                    Ok(unifier.add_ty(TypeEnum::TVirtual { ty }))
                } else {
                    let types = if let Tuple { elts, .. } = &slice.node {
                        elts.iter()
                            .map(|v| parse_type_annotation(resolver, top_level, unifier, primitives, v))
                            .collect::<Result<Vec<_>, _>>()?
                    } else {
                        vec![parse_type_annotation(resolver, top_level, unifier, primitives, slice)?]
                    };

                    let obj_id = resolver
                        .get_identifier_def(id)
                        .ok_or_else(|| format!("Unknown type annotation {}", id))?;
                    let defs = top_level.definitions.read();
                    let def = defs[obj_id.0].read();
                    if let TopLevelDef::Class { fields, methods, type_vars, .. } = &*def {
                        if types.len() != type_vars.len() {
                            return Err(format!(
                                "Unexpected number of type parameters: expected {} but got {}",
                                type_vars.len(),
                                types.len()
                            ));
                        }
                        let mut subst = HashMap::new();
                        for (var, ty) in izip!(type_vars.iter(), types.iter()) {
                            let id = if let TypeEnum::TVar { id, .. } = &*unifier.get_ty(*var) {
                                *id
                            } else {
                                unreachable!()
                            };
                            subst.insert(id, *ty);
                        }
                        let mut fields = fields
                            .iter()
                            .map(|(attr, ty)| {
                                let ty = unifier.subst(*ty, &subst).unwrap_or(*ty);
                                (attr.clone(), ty)
                            })
                            .collect::<HashMap<_, _>>();
                        fields.extend(methods.iter().map(|(attr, ty, _)| {
                            let ty = unifier.subst(*ty, &subst).unwrap_or(*ty);
                            (attr.clone(), ty)
                        }));
                        Ok(unifier.add_ty(TypeEnum::TObj {
                            obj_id,
                            fields: fields.into(),
                            params: subst.into(),
                        }))
                    } else {
                        Err("Cannot use function name as type".into())
                    }
                }
            } else {
                Err("unsupported type expression".into())
            }
        }
        _ => Err("unsupported type expression".into()),
    }
}

impl dyn SymbolResolver {
    pub fn parse_type_annotation<T>(
        &self,
        top_level: &TopLevelContext,
        unifier: &mut Unifier,
        primitives: &PrimitiveStore,
        expr: &Expr<T>,
    ) -> Result<Type, String> {
        parse_type_annotation(self, top_level, unifier, primitives, expr)
    }
}

impl dyn SymbolResolver + Send {
    pub fn parse_type_annotation<T>(
        &self,
        top_level: &TopLevelContext,
        unifier: &mut Unifier,
        primitives: &PrimitiveStore,
        expr: &Expr<T>,
    ) -> Result<Type, String> {
        parse_type_annotation(self, top_level, unifier, primitives, expr)
    }
}