// Copyright (c) 2022 Marceline Cramer
// SPDX-License-Identifier: GPL-3.0-or-later

use crate::parse::ast;
use cranelift::prelude::*;

pub struct FunctionTranslator<'a> {
    pub int: types::Type,
    pub builder: FunctionBuilder<'a>,
    pub locals: Vec<Local>,
    pub variable_index: usize,
}

pub struct Local {
    pub name: String,
    pub var: Variable,
    pub mutable: bool,
}

impl<'a> FunctionTranslator<'a> {
    pub fn new(int: types::Type, builder: FunctionBuilder<'a>) -> Self {
        Self {
            int,
            builder,
            locals: Vec::new(),
            variable_index: 0,
        }
    }

    pub fn translate(mut self, fn_impl: &ast::FnImpl) {
        let signature = &fn_impl.def.signature;

        let return_info = if let Some(tail_expr) = &fn_impl.body.tail_expr {
            match signature.return_type {
                Some(t) => Some((tail_expr, t)),
                None => panic!("Function has tail expression but no return type"),
            }
        } else if let Some(_) = signature.return_type {
            panic!("Function has return type but no tail expression");
        } else {
            None
        };

        for ast::FnArg { type_name, .. } in signature.args.iter() {
            if type_name != &"i64" {
                unimplemented!("Non-i64 function arg types are unimplemented");
            }

            self.builder
                .func
                .signature
                .params
                .push(AbiParam::new(self.int));
        }

        if let Some((_, _return_type)) = return_info {
            self.builder
                .func
                .signature
                .returns
                .push(AbiParam::new(self.int));
        }

        let entry_block = self.builder.create_block();
        self.builder
            .append_block_params_for_function_params(entry_block);
        self.builder.switch_to_block(entry_block);
        self.builder.seal_block(entry_block);

        for (i, arg) in signature.args.iter().enumerate() {
            if let Some(name) = arg.name {
                let val = self.builder.block_params(entry_block)[i];
                let var = self.add_local(self.int, name, false);
                self.builder.def_var(var, val);
            }
        }

        for stmt in fn_impl.body.statements.iter() {
            self.translate_statement(stmt);
        }

        if let Some((tail_expr, _)) = return_info {
            let return_value = self.translate_expr(tail_expr);
            self.builder.ins().return_(&[return_value]);
        }

        println!("{}", self.builder.func.display());
        self.builder.finalize();
    }

    pub fn translate_statement(&mut self, stmt: &ast::Statement) {
        use ast::Statement::*;
        match stmt {
            Expr(expr) => {
                self.translate_expr(expr);
            }
            While {
                test_expr,
                loop_body,
            } => self.translate_while_stmt(test_expr, loop_body),
            Let { var, mutable, expr } => {
                let val = self.translate_expr(expr);
                let var = self.add_local(self.int, var, *mutable);
                self.builder.def_var(var, val);
            }
            If(if_stmt) => self.translate_if_stmt(if_stmt),
        }
    }

    pub fn translate_expr(&mut self, expr: &ast::Expr) -> Value {
        use ast::Expr::*;
        match expr {
            If(if_expr) => self.translate_if_expr(if_expr),
            Local(name) => {
                let var = self
                    .get_local(name)
                    .expect(&format!("Unrecognized local {}", name))
                    .var;
                self.builder.use_var(var)
            }
            Literal(ast::Literal::DecimalInteger(literal)) => {
                // TODO parse integers while building ast so that codegen doesn't have to
                let val: i64 = literal.parse().unwrap();
                self.builder.ins().iconst(self.int, val)
            }
            BinaryOp(op, terms) => self.translate_binary_op(op, &terms.0, &terms.1),
            // TODO the AST doesn't need this either
            Group(expr) => self.translate_expr(expr),
            _ => unimplemented!("Expression: {:#?}", expr),
        }
    }

    pub fn translate_if_expr(&mut self, if_expr: &ast::IfExpr) -> Value {
        let ast::IfExpr {
            test_expr,
            then_body,
            else_body,
        } = if_expr;

        let test_val = self.translate_expr(test_expr);

        let then_block = self.builder.create_block();
        let else_block = self.builder.create_block();
        let merge_block = self.builder.create_block();

        self.builder.append_block_param(merge_block, self.int);

        self.builder.ins().brz(test_val, else_block, &[]);
        self.builder.ins().jump(then_block, &[]);

        let mut translate_branch = |block, body| {
            self.builder.switch_to_block(block);
            self.builder.seal_block(block);
            let val = self.translate_branch_body(body).unwrap();
            self.builder.ins().jump(merge_block, &[val]);
        };

        translate_branch(then_block, then_body);
        translate_branch(else_block, else_body);

        self.builder.switch_to_block(merge_block);
        self.builder.seal_block(merge_block);

        self.builder.block_params(merge_block)[0]
    }

    pub fn translate_if_stmt(&mut self, if_stmt: &ast::IfStmt) {
        let ast::IfStmt {
            test_expr,
            then_body,
            else_body,
        } = if_stmt;

        let test_val = self.translate_expr(test_expr);

        let then_block = self.builder.create_block();
        let else_info = else_body.as_ref().map(|b| (b, self.builder.create_block()));
        let merge_block = self.builder.create_block();

        let else_jump = else_info.map(|b| b.1).unwrap_or(merge_block);
        self.builder.ins().brz(test_val, else_jump, &[]);
        self.builder.ins().jump(then_block, &[]);

        let mut translate_branch = |block, body| {
            self.builder.switch_to_block(block);
            self.builder.seal_block(block);
            let val = self.translate_branch_body(body);
            assert_eq!(val, None, "If statement branch has tail expression");
            self.builder.ins().jump(merge_block, &[]);
        };

        translate_branch(then_block, then_body);

        if let Some((else_body, else_block)) = else_info {
            translate_branch(else_block, else_body);
        }

        self.builder.switch_to_block(merge_block);
        self.builder.seal_block(merge_block);
    }

    pub fn translate_while_stmt(&mut self, test_expr: &ast::Expr, loop_body: &ast::BranchBody) {
        let header_block = self.builder.create_block();
        let body_block = self.builder.create_block();
        let exit_block = self.builder.create_block();

        self.builder.ins().jump(header_block, &[]);
        self.builder.switch_to_block(header_block);

        let test_val = self.translate_expr(test_expr);
        self.builder.ins().brz(test_val, exit_block, &[]);
        self.builder.ins().jump(body_block, &[]);

        self.builder.switch_to_block(body_block);
        self.builder.seal_block(body_block);
        let val = self.translate_branch_body(loop_body);
        assert_eq!(val, None, "While statement body has tail expression");
        self.builder.ins().jump(header_block, &[]);

        self.builder.switch_to_block(exit_block);
        self.builder.seal_block(header_block);
        self.builder.seal_block(exit_block);
    }

    pub fn translate_branch_body(&mut self, branch_body: &ast::BranchBody) -> Option<Value> {
        let scope_size = self.locals.len();

        for stmt in branch_body.statements.iter() {
            self.translate_statement(stmt);
        }

        let tail_val = if let Some(tail_expr) = &branch_body.tail_expr {
            Some(self.translate_expr(tail_expr))
        } else {
            None
        };

        self.locals.truncate(scope_size);

        tail_val
    }

    pub fn translate_binary_op(
        &mut self,
        op: &ast::BinaryOp,
        lhs: &ast::Expr,
        rhs: &ast::Expr,
    ) -> Value {
        let rhs = self.translate_expr(rhs);

        if *op == ast::BinaryOp::Assign {
            if let ast::Expr::Local(var) = lhs {
                let local = self
                    .get_local(var)
                    .expect(&format!("Unrecognized local {}", var));

                if !local.mutable {
                    panic!("Attempted to assign to immutable variable {}", var);
                }

                let var = local.var;
                self.builder.def_var(var, rhs);
                return rhs;
            } else {
                unimplemented!("Assign to non-local lhs");
            }
        }

        let lhs = self.translate_expr(lhs);

        // TODO refactor ast to separate binary ops into types
        if let Some(val) = self.translate_bool_op(op, lhs, rhs) {
            val
        } else {
            use ast::BinaryOp::*;
            let ins = self.builder.ins();
            match op {
                Add => ins.iadd(lhs, rhs),
                Sub => ins.isub(lhs, rhs),
                Mul => ins.imul(lhs, rhs),
                Div => ins.udiv(lhs, rhs),
                _ => unimplemented!("Binary operation: {:#?}", op),
            }
        }
    }

    pub fn translate_bool_op(
        &mut self,
        op: &ast::BinaryOp,
        lhs: Value,
        rhs: Value,
    ) -> Option<Value> {
        use ast::BinaryOp::*;
        if let Some(cmp) = match op {
            Eq => Some(IntCC::Equal),
            Neq => Some(IntCC::NotEqual),
            Less => Some(IntCC::SignedLessThan),
            LessEq => Some(IntCC::SignedLessThanOrEqual),
            Greater => Some(IntCC::SignedGreaterThan),
            GreaterEq => Some(IntCC::SignedGreaterThanOrEqual),
            _ => None,
        } {
            let val = self.builder.ins().icmp(cmp, lhs, rhs);
            Some(self.builder.ins().bint(self.int, val))
        } else {
            None
        }
    }

    pub fn get_local(&self, name: &str) -> Option<&Local> {
        self.locals.iter().rev().find(|l| &l.name == name)
    }

    pub fn add_local(&mut self, var_type: types::Type, name: &str, mutable: bool) -> Variable {
        let name = name.to_string();
        let var = Variable::new(self.variable_index);
        self.builder.declare_var(var, var_type);
        self.locals.push(Local { name, var, mutable });
        self.variable_index += 1;
        var
    }
}