use ::ast::{self, WithLocation};
use super::environment;
use super::types::{self, Ty};

#[derive(Debug)]
pub enum TypeError {
    Unimplemented,
    Mismatch {
        expected: Ty,
        actual: Ty,
    },
    UnboundName,
}

type TypeEnvironment<'a> = environment::Environment<'a, String, Ty>;
pub type Result = ::std::result::Result<Ty, WithLocation<TypeError>>;

pub fn translate(program: &ast::Program) -> Result {
    let mut venv = TypeEnvironment::new(None);
    let mut tenv = TypeEnvironment::new(None);
    tenv.add_binding("int".into(), Ty::Int);
    tenv.add_binding("string".into(), Ty::String);
    trans_exp(&mut venv, &mut tenv, &*program.0)
}

macro_rules! err {
    ($exp: expr, $err: expr) => {
        Err(WithLocation::new($err, $exp.start, $exp.end))
    }
}

fn trans_ty<'a>(
    venv: &mut TypeEnvironment<'a>,
    tenv: &mut TypeEnvironment<'a>,
    ty: &WithLocation<ast::Ty>) -> Result {
    match ty.value {
        ast::Ty::Name(ref name) => {
            tenv.lookup(&name)
                .map(|v| v.clone())
                .ok_or(WithLocation::new(TypeError::UnboundName, ty.start, ty.end))
        }
        ast::Ty::Array(ref inner_ty) => {
            trans_ty(venv, tenv, &inner_ty)
        },
        ast::Ty::Record(ref fields) => {
            let mut result = vec![];
            for field in fields {
                result.push(types::RecordField::new(
                    field.name.clone(),
                    trans_ty(venv, tenv, &field.ty)?));
            }
            Ok(Ty::Record(result))
        },
    }
}

fn trans_decl<'a>(
    venv: &mut TypeEnvironment<'a>,
    tenv: &mut TypeEnvironment<'a>,
    decl: &WithLocation<ast::Declaration>) -> Result {
    match decl.declaration {
        ast::DeclarationBody::Fun { .. } => {
            err!(decl, TypeError::Unimplemented)
        }
        ast::DeclarationBody::Ty { ref ty } => {
            trans_ty(venv, tenv, ty)
        }
        ast::DeclarationBody::Var { ref ty, ref value } => {
            let actual_ty = trans_exp(venv, tenv, &value)?;
            if let &Some(ref ty) = ty {
                let decl_ty = trans_ty(venv, tenv, &ty)?;
                if decl_ty != actual_ty {
                    return err!(ty, TypeError::Mismatch {
                        expected: decl_ty,
                        actual: actual_ty,
                    });
                }
            }
            Ok(actual_ty)
        }
    }
}

fn trans_exp<'a>(
    venv: &mut TypeEnvironment<'a>,
    tenv: &mut TypeEnvironment<'a>,
    exp: &WithLocation<ast::Expression>) -> Result {
    use ast::Expression::*;

    match &exp.value {
        &Let(ref decls, ref body) => {
            let mut new_venv = TypeEnvironment::new(Some(venv));
            let mut new_tenv = TypeEnvironment::new(Some(tenv));
            for decl in decls.iter() {
                let decl_ty = trans_decl(&mut new_venv, &mut new_tenv, decl)?;
                match decl.declaration {
                    ast::DeclarationBody::Fun { .. } | ast::DeclarationBody::Var { .. } => {
                        new_venv.add_binding(decl.name.clone(), decl_ty);
                    }
                    ast::DeclarationBody::Ty { .. } => {
                        new_tenv.add_binding(decl.name.clone(), decl_ty);
                    }
                }
            }
            trans_exp(&mut new_venv, &mut new_tenv, &*body)
        },
        &UnaryOp(ref op, ref operand) => {
            use ast::UnaryOp::*;
            let operand_ty = trans_exp(venv, tenv, operand)?;
            match op {
                &Neg | &Pos => {
                    match operand_ty {
                        Ty::Int => {
                            Ok(Ty::Int)
                        }
                        other => {
                            err!(operand, TypeError::Mismatch {
                                expected: Ty::Int,
                                actual: other,
                            })
                        }
                    }
                }
                &Not => {
                    err!(exp, TypeError::Unimplemented)
                }
            }
        },
        &BinOp(ref op, ref left, ref right) => {
            use ast::BinOp::*;
            let left_ty = trans_exp(venv, tenv, left)?;
            let right_ty = trans_exp(venv, tenv, right)?;
            match op {
                &Add => {
                    match (left_ty, right_ty) {
                        (Ty::Int, Ty::Int) => {
                            Ok(Ty::Int)
                        }
                        (Ty::String, Ty::String) => {
                            Ok(Ty::String)
                        }
                        (Ty::Int, other) => {
                            err!(right, TypeError::Mismatch {
                                expected: Ty::Int,
                                actual: other,
                            })
                        }
                        (Ty::String, other) => {
                            err!(right, TypeError::Mismatch {
                                expected: Ty::String,
                                actual: other,
                            })
                        }
                        _ => {
                            err!(exp, TypeError::Unimplemented)
                        }
                    }
                }
                _ => {
                    err!(exp, TypeError::Unimplemented)
                }
            }
        },
        &Number(_) => Ok(Ty::Int),
        &String(_) => Ok(Ty::String),
        &Name(ref name) => {
            if let Some(ty) = venv.lookup(name) {
                Ok(ty.clone())
            }
            else {
                err!(exp, TypeError::UnboundName)
            }
        },
        &Nil => {
            Err(WithLocation::new(TypeError::Unimplemented, exp.start, exp.end))
        },
    }
}