use std::{collections::HashMap, convert::From};

use crate::{
    ast::{TypeIdentifier, AST},
    identifier::{define_id_kind, Id, IdStore},
};

define_id_kind!(TypeItem);
pub type TypeId = Id<TypeItem>;

pub struct TypeContext {
    defined_types: HashMap<TypeId, DefinedType>,
    type_id_store: IdStore<TypeItem>,
}

impl TypeContext {
    pub fn new() -> Self {
        Self { defined_types: HashMap::new(), type_id_store: IdStore::new() }
    }

    pub fn register_type(&mut self, builder: TypeBuilder) -> TypeId {
        let type_id = self.type_id_store.fresh();

        let mut pending_variants = vec![];
        for variant_builder in builder.variants.into_iter() {
            let members = variant_builder.members;
            if members.is_empty() {
                pending_variants.push(Variant { name: variant_builder.name, members: VariantMembers::Unit });
                continue;
            }
            let record_variant = matches!(members.get(0).unwrap(), VariantMemberBuilder::KeyVal(..));

            if record_variant {
                let pending_members = members.into_iter().map(|var| match var {
                    VariantMemberBuilder::KeyVal(name, ty) => (name, ty),
                    _ => panic!("Compiler internal error: variant mismatch"),
                });

                //TODO make this mapping meaningful
                let type_ids = pending_members
                    .into_iter()
                    .map(|(name, _ty_id)| (name, self.type_id_store.fresh()))
                    .collect();
                pending_variants
                    .push(Variant { name: variant_builder.name, members: VariantMembers::Record(type_ids) });
            } else {
                let pending_members = members.into_iter().map(|var| match var {
                    VariantMemberBuilder::Pending(pending_type) => pending_type,
                    _ => panic!("Compiler internal error: variant mismatch"),
                });

                //TODO make this mapping meaningful
                let type_ids = pending_members.into_iter().map(|_ty_id| self.type_id_store.fresh()).collect();

                pending_variants
                    .push(Variant { name: variant_builder.name, members: VariantMembers::Tuple(type_ids) });
            }
        }

        // Eventually, I will want to have a better way of determining which numeric tag goes with
        // which variant. For now, just sort them alphabetically.
        pending_variants.sort_unstable_by(|a, b| a.name.cmp(&b.name));

        let defined = DefinedType { name: builder.name, variants: pending_variants };

        self.defined_types.insert(type_id, defined);
        type_id
    }

    pub fn variant_local_name(&self, type_id: &TypeId, tag: u32) -> Option<&str> {
        self.defined_types
            .get(type_id)
            .and_then(|defined| defined.variants.get(tag as usize))
            .map(|variant| variant.name.as_ref())
    }

    pub fn lookup_variant_arity(&self, type_id: &TypeId, tag: u32) -> Option<u32> {
        self.defined_types.get(type_id).and_then(|defined| defined.variants.get(tag as usize)).map(
            |variant| match &variant.members {
                VariantMembers::Unit => 0,
                VariantMembers::Tuple(items) => items.len() as u32,
                VariantMembers::Record(items) => items.len() as u32,
            },
        )
    }

    pub fn lookup_record_members(&self, type_id: &TypeId, tag: u32) -> Option<&[(String, TypeId)]> {
        self.defined_types.get(type_id).and_then(|defined| defined.variants.get(tag as usize)).and_then(
            |variant| match &variant.members {
                VariantMembers::Record(items) => Some(items.as_ref()),
                _ => None,
            },
        )
    }

    pub fn lookup_type(&self, type_id: &TypeId) -> Option<&DefinedType> {
        self.defined_types.get(type_id)
    }

    //TODO return some kind of overall type later?
    pub fn typecheck(&mut self, ast: &AST) -> Result<(), TypeError> {
        Ok(())
    }
}

/// A type defined in program source code, as opposed to a builtin.
#[allow(dead_code)]
#[derive(Debug)]
pub struct DefinedType {
    pub name: String,

    // the variants are in this list according to tag order
    pub variants: Vec<Variant>,
}

#[derive(Debug)]
pub struct Variant {
    pub name: String,
    pub members: VariantMembers,
}

#[derive(Debug)]
pub enum VariantMembers {
    Unit,
    // Should be non-empty
    Tuple(Vec<TypeId>),
    Record(Vec<(String, TypeId)>),
}

/// Represents a type mentioned as a member of another type during the type registration process.
/// It may not have been registered itself in the relevant context.
#[allow(dead_code)]
#[derive(Debug)]
pub struct PendingType {
    inner: TypeIdentifier,
}

impl From<&TypeIdentifier> for PendingType {
    fn from(type_identifier: &TypeIdentifier) -> Self {
        Self { inner: type_identifier.clone() }
    }
}

#[derive(Debug)]
pub struct TypeBuilder {
    name: String,
    variants: Vec<VariantBuilder>,
}

impl TypeBuilder {
    pub fn new(name: &str) -> Self {
        Self { name: name.to_string(), variants: vec![] }
    }

    pub fn add_variant(&mut self, vb: VariantBuilder) {
        self.variants.push(vb);
    }
}

#[derive(Debug)]
pub struct VariantBuilder {
    name: String,
    members: Vec<VariantMemberBuilder>,
}

impl VariantBuilder {
    pub fn new(name: &str) -> Self {
        Self { name: name.to_string(), members: vec![] }
    }

    pub fn add_member(&mut self, member_ty: PendingType) {
        self.members.push(VariantMemberBuilder::Pending(member_ty));
    }

    // You can't call this and `add_member` on the same fn, there should be a runtime error when
    // that's detected.
    pub fn add_record_member(&mut self, name: &str, ty: PendingType) {
        self.members.push(VariantMemberBuilder::KeyVal(name.to_string(), ty));
    }
}

#[derive(Debug)]
enum VariantMemberBuilder {
    Pending(PendingType),
    KeyVal(String, PendingType),
}

#[derive(Debug, Clone)]
pub struct TypeError {
    pub msg: String,
}

#[allow(dead_code)]
#[derive(Debug, Clone, PartialEq, Eq)]
pub enum TypeConst {
    Unit,
    Nat,
    Int,
    Float,
    StringT,
    Bool,
    Ordering,
}

#[allow(dead_code)]
#[derive(Debug, Clone, PartialEq)]
pub enum Type {
    Const(TypeConst),
    //Var(TypeVar),
    Arrow { params: Vec<Type>, ret: Box<Type> },
    Compound { ty_name: String, args: Vec<Type> },
}

macro_rules! ty {
    ($type_name:ident) => {
        Type::Const(crate::type_inference::TypeConst::$type_name)
    };
    ($t1:ident -> $t2:ident) => {
        Type::Arrow { params: vec![ty!($t1)], ret: box ty!($t2) }
    };
    ($t1:ident -> $t2:ident -> $t3:ident) => {
        Type::Arrow { params: vec![ty!($t1), ty!($t2)], ret: box ty!($t3) }
    };
    ($type_list:ident, $ret_type:ident) => {
        Type::Arrow { params: $type_list, ret: box $ret_type }
    };
}