use std::{convert::TryInto, iter::once};

use crate::top_level::{CodeGenContext, TopLevelDef};
use crate::typecheck::typedef::{Type, TypeEnum};
use inkwell::{types::BasicType, values::BasicValueEnum};
use itertools::{chain, izip, zip, Itertools};
use rustpython_parser::ast::{self, Boolop, Constant, Expr, ExprKind, Operator};

impl<'ctx> CodeGenContext<'ctx> {
    fn get_attr_index(&mut self, ty: Type, attr: &str) -> usize {
        let obj_id = match &*self.unifier.get_ty(ty) {
            TypeEnum::TObj { obj_id, .. } => *obj_id,
            // we cannot have other types, virtual type should be handled by function calls
            _ => unreachable!(),
        };
        let def = &self.top_level.definitions.read()[obj_id];
        let index = if let TopLevelDef::Class { fields, .. } = &*def.read() {
            fields.iter().find_position(|x| x.0 == attr).unwrap().0
        } else {
            unreachable!()
        };
        index
    }

    fn gen_const(&mut self, value: &Constant, ty: Type) -> BasicValueEnum<'ctx> {
        match value {
            Constant::Bool(v) => {
                assert!(self.unifier.unioned(ty, self.top_level.primitives.bool));
                let ty = self.ctx.bool_type();
                ty.const_int(if *v { 1 } else { 0 }, false).into()
            }
            Constant::Int(v) => {
                let ty = if self.unifier.unioned(ty, self.top_level.primitives.int32) {
                    self.ctx.i32_type()
                } else if self.unifier.unioned(ty, self.top_level.primitives.int64) {
                    self.ctx.i64_type()
                } else {
                    unreachable!();
                };
                ty.const_int(v.try_into().unwrap(), false).into()
            }
            Constant::Float(v) => {
                assert!(self.unifier.unioned(ty, self.top_level.primitives.float));
                let ty = self.ctx.f64_type();
                ty.const_float(*v).into()
            }
            Constant::Tuple(v) => {
                let ty = self.unifier.get_ty(ty);
                let types =
                    if let TypeEnum::TTuple { ty } = &*ty { ty.clone() } else { unreachable!() };
                let values = zip(types.into_iter(), v.iter())
                    .map(|(ty, v)| self.gen_const(v, ty))
                    .collect_vec();
                let types = values.iter().map(BasicValueEnum::get_type).collect_vec();
                let ty = self.ctx.struct_type(&types, false);
                ty.const_named_struct(&values).into()
            }
            _ => unimplemented!(),
        }
    }

    fn gen_int_ops(
        &mut self,
        op: &Operator,
        lhs: BasicValueEnum<'ctx>,
        rhs: BasicValueEnum<'ctx>,
    ) -> BasicValueEnum<'ctx> {
        let (lhs, rhs) =
            if let (BasicValueEnum::IntValue(lhs), BasicValueEnum::IntValue(rhs)) = (lhs, rhs) {
                (lhs, rhs)
            } else {
                unreachable!()
            };
        match op {
            Operator::Add => self.builder.build_int_add(lhs, rhs, "add").into(),
            Operator::Sub => self.builder.build_int_sub(lhs, rhs, "sub").into(),
            Operator::Mult => self.builder.build_int_mul(lhs, rhs, "mul").into(),
            Operator::Div => {
                let float = self.ctx.f64_type();
                let left = self.builder.build_signed_int_to_float(lhs, float, "i2f");
                let right = self.builder.build_signed_int_to_float(rhs, float, "i2f");
                self.builder.build_float_div(left, right, "fdiv").into()
            }
            Operator::Mod => self.builder.build_int_signed_rem(lhs, rhs, "mod").into(),
            Operator::BitOr => self.builder.build_or(lhs, rhs, "or").into(),
            Operator::BitXor => self.builder.build_xor(lhs, rhs, "xor").into(),
            Operator::BitAnd => self.builder.build_and(lhs, rhs, "and").into(),
            Operator::LShift => self.builder.build_left_shift(lhs, rhs, "lshift").into(),
            Operator::RShift => self.builder.build_right_shift(lhs, rhs, true, "rshift").into(),
            Operator::FloorDiv => self.builder.build_int_signed_div(lhs, rhs, "floordiv").into(),
            // special implementation?
            Operator::Pow => unimplemented!(),
            Operator::MatMult => unreachable!(),
        }
    }

    fn gen_float_ops(
        &mut self,
        op: &Operator,
        lhs: BasicValueEnum<'ctx>,
        rhs: BasicValueEnum<'ctx>,
    ) -> BasicValueEnum<'ctx> {
        let (lhs, rhs) = if let (BasicValueEnum::FloatValue(lhs), BasicValueEnum::FloatValue(rhs)) =
            (lhs, rhs)
        {
            (lhs, rhs)
        } else {
            unreachable!()
        };
        match op {
            Operator::Add => self.builder.build_float_add(lhs, rhs, "fadd").into(),
            Operator::Sub => self.builder.build_float_sub(lhs, rhs, "fsub").into(),
            Operator::Mult => self.builder.build_float_mul(lhs, rhs, "fmul").into(),
            Operator::Div => self.builder.build_float_div(lhs, rhs, "fdiv").into(),
            Operator::Mod => self.builder.build_float_rem(lhs, rhs, "fmod").into(),
            Operator::FloorDiv => {
                let div = self.builder.build_float_div(lhs, rhs, "fdiv");
                let floor_intrinsic =
                    self.module.get_function("llvm.floor.f64").unwrap_or_else(|| {
                        let float = self.ctx.f64_type();
                        let fn_type = float.fn_type(&[float.into()], false);
                        self.module.add_function("llvm.floor.f64", fn_type, None)
                    });
                self.builder
                    .build_call(floor_intrinsic, &[div.into()], "floor")
                    .try_as_basic_value()
                    .left()
                    .unwrap()
            }
            // special implementation?
            _ => unimplemented!(),
        }
    }

    pub fn gen_expr(&mut self, expr: &Expr<Option<Type>>) -> BasicValueEnum<'ctx> {
        let zero = self.ctx.i32_type().const_int(0, false);
        let primitives = &self.top_level.primitives;
        match &expr.node {
            ExprKind::Constant { value, .. } => {
                let ty = expr.custom.clone().unwrap();
                self.gen_const(value, ty)
            }
            ExprKind::Name { id, .. } => {
                let ptr = self.var_assignment.get(id).unwrap();
                self.builder.build_load(*ptr, "load")
            }
            ExprKind::List { elts, .. } => {
                // this shall be optimized later for constant primitive lists...
                let elements = elts.iter().map(|x| self.gen_expr(x)).collect_vec();
                let ty = if elements.is_empty() {
                    self.ctx.i32_type().into()
                } else {
                    elements[0].get_type()
                };
                // this length includes the leading length element
                let arr_ty = self.ctx.struct_type(
                    &[self.ctx.i32_type().into(), ty.array_type(elements.len() as u32).into()],
                    false,
                );
                let arr_ptr = self.builder.build_alloca(arr_ty, "tmparr");
                unsafe {
                    let len_ptr = arr_ptr
                        .const_in_bounds_gep(&[zero, self.ctx.i32_type().const_int(0u64, false)]);
                    self.builder.build_store(
                        len_ptr,
                        self.ctx.i32_type().const_int(elements.len() as u64, false),
                    );
                    let arr_offset = self.ctx.i32_type().const_int(1, false);
                    for (i, v) in elements.iter().enumerate() {
                        let ptr = self.builder.build_in_bounds_gep(
                            arr_ptr,
                            &[zero, arr_offset, self.ctx.i32_type().const_int(i as u64, false)],
                            "arr_element",
                        );
                        self.builder.build_store(ptr, *v);
                    }
                }
                arr_ptr.into()
            }
            ExprKind::Tuple { elts, .. } => {
                let element_val = elts.iter().map(|x| self.gen_expr(x)).collect_vec();
                let element_ty = element_val.iter().map(BasicValueEnum::get_type).collect_vec();
                let tuple_ty = self.ctx.struct_type(&element_ty, false);
                let tuple_ptr = self.builder.build_alloca(tuple_ty, "tuple");
                for (i, v) in element_val.into_iter().enumerate() {
                    unsafe {
                        let ptr = tuple_ptr.const_in_bounds_gep(&[
                            zero,
                            self.ctx.i32_type().const_int(i as u64, false),
                        ]);
                        self.builder.build_store(ptr, v);
                    }
                }
                tuple_ptr.into()
            }
            ExprKind::Attribute { value, attr, .. } => {
                // note that we would handle class methods directly in calls
                let index = self.get_attr_index(value.custom.unwrap(), attr);
                let val = self.gen_expr(value);
                let ptr = if let BasicValueEnum::PointerValue(v) = val {
                    v
                } else {
                    unreachable!();
                };
                unsafe {
                    let ptr = ptr.const_in_bounds_gep(&[
                        zero,
                        self.ctx.i32_type().const_int(index as u64, false),
                    ]);
                    self.builder.build_load(ptr, "field")
                }
            }
            ExprKind::BoolOp { op, values } => {
                // requires conditional branches for short-circuiting...
                let left = if let BasicValueEnum::IntValue(left) = self.gen_expr(&values[0]) {
                    left
                } else {
                    unreachable!()
                };
                let current = self.builder.get_insert_block().unwrap().get_parent().unwrap();
                let a_bb = self.ctx.append_basic_block(current, "a");
                let b_bb = self.ctx.append_basic_block(current, "b");
                let cont_bb = self.ctx.append_basic_block(current, "cont");
                self.builder.build_conditional_branch(left, a_bb, b_bb);
                let (a, b) = match op {
                    Boolop::Or => {
                        self.builder.position_at_end(a_bb);
                        let a = self.ctx.bool_type().const_int(1, false);
                        self.builder.build_unconditional_branch(cont_bb);
                        self.builder.position_at_end(b_bb);
                        let b = if let BasicValueEnum::IntValue(b) = self.gen_expr(&values[1]) {
                            b
                        } else {
                            unreachable!()
                        };
                        self.builder.build_unconditional_branch(cont_bb);
                        (a, b)
                    }
                    Boolop::And => {
                        self.builder.position_at_end(a_bb);
                        let a = if let BasicValueEnum::IntValue(a) = self.gen_expr(&values[1]) {
                            a
                        } else {
                            unreachable!()
                        };
                        self.builder.build_unconditional_branch(cont_bb);
                        self.builder.position_at_end(b_bb);
                        let b = self.ctx.bool_type().const_int(0, false);
                        self.builder.build_unconditional_branch(cont_bb);
                        (a, b)
                    }
                };
                self.builder.position_at_end(cont_bb);
                let phi = self.builder.build_phi(self.ctx.bool_type(), "phi");
                phi.add_incoming(&[(&a, a_bb), (&b, b_bb)]);
                phi.as_basic_value()
            }
            ExprKind::BinOp { op, left, right } => {
                let ty1 = self.unifier.get_representative(left.custom.unwrap());
                let ty2 = self.unifier.get_representative(left.custom.unwrap());
                let left = self.gen_expr(left);
                let right = self.gen_expr(right);

                // we can directly compare the types, because we've got their representatives
                // which would be unchanged until further unification, which we would never do
                // when doing code generation for function instances
                if ty1 != ty2 {
                    unimplemented!()
                } else if [primitives.int32, primitives.int64].contains(&ty1) {
                    self.gen_int_ops(op, left, right)
                } else if primitives.float == ty1 {
                    self.gen_float_ops(op, left, right)
                } else {
                    unimplemented!()
                }
            }
            ExprKind::UnaryOp { op, operand } => {
                let ty = self.unifier.get_representative(operand.custom.unwrap());
                let val = self.gen_expr(operand);
                if ty == primitives.bool {
                    let val =
                        if let BasicValueEnum::IntValue(val) = val { val } else { unreachable!() };
                    match op {
                        ast::Unaryop::Invert | ast::Unaryop::Not => {
                            self.builder.build_not(val, "not").into()
                        }
                        _ => val.into(),
                    }
                } else if [primitives.int32, primitives.int64].contains(&ty) {
                    let val =
                        if let BasicValueEnum::IntValue(val) = val { val } else { unreachable!() };
                    match op {
                        ast::Unaryop::USub => self.builder.build_int_neg(val, "neg").into(),
                        ast::Unaryop::Invert => self.builder.build_not(val, "not").into(),
                        ast::Unaryop::Not => self
                            .builder
                            .build_int_compare(
                                inkwell::IntPredicate::EQ,
                                val,
                                val.get_type().const_zero(),
                                "not",
                            )
                            .into(),
                        _ => val.into(),
                    }
                } else if ty == primitives.float {
                    let val = if let BasicValueEnum::FloatValue(val) = val {
                        val
                    } else {
                        unreachable!()
                    };
                    match op {
                        ast::Unaryop::USub => self.builder.build_float_neg(val, "neg").into(),
                        ast::Unaryop::Not => self
                            .builder
                            .build_float_compare(
                                inkwell::FloatPredicate::OEQ,
                                val,
                                val.get_type().const_zero(),
                                "not",
                            )
                            .into(),
                        _ => val.into(),
                    }
                } else {
                    unimplemented!()
                }
            }
            ExprKind::Compare { left, ops, comparators } => {
                izip!(
                    chain(once(left.as_ref()), comparators.iter()),
                    comparators.iter(),
                    ops.iter(),
                )
                .fold(None, |prev, (lhs, rhs, op)| {
                    let ty = lhs.custom.unwrap();
                    let current = if [primitives.int32, primitives.int64, primitives.bool]
                        .contains(&ty)
                    {
                        let (lhs, rhs) =
                            if let (BasicValueEnum::IntValue(lhs), BasicValueEnum::IntValue(rhs)) =
                                (self.gen_expr(lhs), self.gen_expr(rhs))
                            {
                                (lhs, rhs)
                            } else {
                                unreachable!()
                            };
                        let op = match op {
                            ast::Cmpop::Eq | ast::Cmpop::Is => inkwell::IntPredicate::EQ,
                            ast::Cmpop::NotEq => inkwell::IntPredicate::NE,
                            ast::Cmpop::Lt => inkwell::IntPredicate::SLT,
                            ast::Cmpop::LtE => inkwell::IntPredicate::SLE,
                            ast::Cmpop::Gt => inkwell::IntPredicate::SGT,
                            ast::Cmpop::GtE => inkwell::IntPredicate::SGE,
                            _ => unreachable!(),
                        };
                        self.builder.build_int_compare(op, lhs, rhs, "cmp")
                    } else if ty == primitives.float {
                        let (lhs, rhs) = if let (
                            BasicValueEnum::FloatValue(lhs),
                            BasicValueEnum::FloatValue(rhs),
                        ) = (self.gen_expr(lhs), self.gen_expr(rhs))
                        {
                            (lhs, rhs)
                        } else {
                            unreachable!()
                        };
                        let op = match op {
                            ast::Cmpop::Eq | ast::Cmpop::Is => inkwell::FloatPredicate::OEQ,
                            ast::Cmpop::NotEq => inkwell::FloatPredicate::ONE,
                            ast::Cmpop::Lt => inkwell::FloatPredicate::OLT,
                            ast::Cmpop::LtE => inkwell::FloatPredicate::OLE,
                            ast::Cmpop::Gt => inkwell::FloatPredicate::OGT,
                            ast::Cmpop::GtE => inkwell::FloatPredicate::OGE,
                            _ => unreachable!(),
                        };
                        self.builder.build_float_compare(op, lhs, rhs, "cmp")
                    } else {
                        unimplemented!()
                    };
                    prev.map(|v| self.builder.build_and(v, current, "cmp")).or(Some(current))
                })
                .unwrap()
                .into() // as there should be at least 1 element, it should never be none
            }
            _ => unimplemented!(),
        }
    }
}