rlox/src/backend/interpreter.rs

use crate::{
    backend::environment::Environment,
    frontend::{
        ast::{AstNode, AstNodeKind, Expr, Stmt},
        source_registry::SourceSlice,
        tokens::{LiteralValue, TokenType},
    },
    result::{LoxError, LoxResult},
};
use std::{
    fmt::{format, Debug, Display},
    ops::{Add, Div, Mul, Neg, Not, Rem, Sub},
};

fn error(message: String) -> LoxError {
    LoxError::RuntimeError {
        source_slice: SourceSlice::default(), // todo change this with the actual source slice
        message: message,
    }
}

fn error_at(source_slice: SourceSlice, message: String) -> LoxError {
    LoxError::RuntimeError {
        source_slice,
        message,
    }
}

impl Not for LiteralValue {
    type Output = LiteralValue;

    fn not(self) -> Self::Output {
        match self {
            LiteralValue::Boolean(b) => LiteralValue::Boolean(!b),
            LiteralValue::Number(n) => LiteralValue::Boolean(n == 0.0),
            _ => LiteralValue::Boolean(false),
        }
    }
}

pub trait Truthy {
    fn is_truthy(&self) -> bool;
}

impl Truthy for LiteralValue {
    fn is_truthy(&self) -> bool {
        match self {
            LiteralValue::Boolean(b) => *b,
            LiteralValue::Number(n) => *n != 0.0,
            LiteralValue::String(s) => !s.is_empty(),
            _ => false,
        }
    }
}

impl Neg for LiteralValue {
    type Output = LoxResult<LiteralValue>;

    fn neg(self) -> Self::Output {
        Ok(LiteralValue::Boolean(!self.is_truthy()))
    }
}

impl Add for LiteralValue {
    type Output = LoxResult<LiteralValue>;

    fn add(self, other: LiteralValue) -> Self::Output {
        match (self, other) {
            (LiteralValue::Number(a), LiteralValue::Number(b)) => Ok(LiteralValue::Number(a + b)),
            (LiteralValue::String(a), LiteralValue::String(b)) => {
                Ok(LiteralValue::String(format!("{}{}", a, b)))
            }
            _ => Err(error("Cannot add non-numeric values".to_string())),
        }
    }
}

impl LiteralValue {
    pub fn add_with_source(
        self,
        other: LiteralValue,
        source_slice: SourceSlice,
    ) -> LoxResult<LiteralValue> {
        match (self, other) {
            (LiteralValue::Number(a), LiteralValue::Number(b)) => Ok(LiteralValue::Number(a + b)),
            (LiteralValue::String(a), LiteralValue::String(b)) => {
                Ok(LiteralValue::String(format!("{}{}", a, b)))
            }
            _ => Err(error_at(
                source_slice,
                "Cannot add non-numeric values".to_string(),
            )),
        }
    }
}

impl Sub for LiteralValue {
    type Output = LoxResult<LiteralValue>;

    fn sub(self, other: LiteralValue) -> Self::Output {
        match (self, other) {
            (LiteralValue::Number(a), LiteralValue::Number(b)) => Ok(LiteralValue::Number(a - b)),
            _ => Err(error("Cannot subtract non-numeric values".to_string())),
        }
    }
}

impl Div for LiteralValue {
    type Output = LoxResult<LiteralValue>;

    fn div(self, other: LiteralValue) -> Self::Output {
        match (self, other) {
            (LiteralValue::Number(a), LiteralValue::Number(b)) => {
                if b == 0.0 {
                    Err(error("Division by zero".to_string()))
                } else {
                    Ok(LiteralValue::Number(a / b))
                }
            }
            _ => Err(error("Cannot divide non-numeric values".to_string())),
        }
    }
}

impl Mul for LiteralValue {
    type Output = LoxResult<LiteralValue>;

    fn mul(self, other: LiteralValue) -> Self::Output {
        match (self, other) {
            (LiteralValue::Number(a), LiteralValue::Number(b)) => Ok(LiteralValue::Number(a * b)),
            _ => Err(error("Cannot multiply non-numeric values".to_string())),
        }
    }
}

impl Rem for LiteralValue {
    type Output = LoxResult<LiteralValue>;

    fn rem(self, other: LiteralValue) -> Self::Output {
        match (self, other) {
            (LiteralValue::Number(a), LiteralValue::Number(b)) => {
                if b == 0.0 {
                    Err(error("Division by zero".to_string()))
                } else {
                    Ok(LiteralValue::Number(a % b))
                }
            }
            _ => Err(error("Cannot divide non-numeric values".to_string())),
        }
    }
}

impl PartialOrd for LiteralValue {
    fn partial_cmp(&self, other: &Self) -> Option<std::cmp::Ordering> {
        match (self, other) {
            (LiteralValue::Number(a), LiteralValue::Number(b)) => a.partial_cmp(b),
            _ => None,
        }
    }
}

impl From<LiteralValue> for bool {
    fn from(value: LiteralValue) -> Self {
        match value {
            LiteralValue::Boolean(b) => b,
            LiteralValue::Number(n) => n != 0.0,
            _ => false,
        }
    }
}

pub struct Interpreter<'a> {
    enviorment: &'a mut Environment<'a>,
}

impl<'a> Interpreter<'a> {
    pub fn new(env: &'a mut Environment<'a>) -> Self {
        Self { enviorment: env }
    }

    fn interpret_binary(
        &mut self,
        left: AstNode<Expr>,
        operator: TokenType,
        right: AstNode<Expr>,
        source_slice: SourceSlice,
    ) -> LoxResult<LiteralValue> {
        let left_value = self.interpret(left)?;
        let right_value = self.interpret(right)?;
        match operator {
            TokenType::Minus => left_value - right_value,
            TokenType::Plus => left_value.add_with_source(right_value, source_slice.clone()),
            TokenType::Slash => left_value / right_value,
            TokenType::Star => left_value * right_value,
            TokenType::EqualEqual => Ok(LiteralValue::Boolean(left_value == right_value)),
            TokenType::BangEqual => Ok(LiteralValue::Boolean(left_value != right_value)),
            TokenType::Greater => Ok(LiteralValue::Boolean(left_value > right_value)),
            TokenType::GreaterEqual => Ok(LiteralValue::Boolean(left_value >= right_value)),
            TokenType::Less => Ok(LiteralValue::Boolean(left_value < right_value)),
            TokenType::LessEqual => Ok(LiteralValue::Boolean(left_value <= right_value)),
            TokenType::Percent => left_value % right_value,

            TokenType::And => Ok(LiteralValue::Boolean(
                left_value.is_truthy() && right_value.is_truthy(),
            )),
            TokenType::Or => Ok(LiteralValue::Boolean(
                left_value.is_truthy() || right_value.is_truthy(),
            )),
            _ => Err(LoxError::RuntimeError {
                source_slice: SourceSlice::default(), // todo change this to the actual source slice
                message: format!("Unsupported binary operator {}", operator),
            }),
        }
    }
}

pub trait EvaluateInterpreter<T> {
    fn interpret(&mut self, stmt: T) -> LoxResult<LiteralValue>;
}

impl<'a, R: AstNodeKind + Clone + Debug + Display> EvaluateInterpreter<AstNode<R>>
    for Interpreter<'a>
where
    Interpreter<'a>: EvaluateInterpreter<R>,
{
    fn interpret(&mut self, stmt: AstNode<R>) -> LoxResult<LiteralValue> {
        match self.interpret(stmt.node.clone()) {
            Ok(value) => Ok(value),
            Err(err) => Err(LoxError::RuntimeError {
                source_slice: stmt.source_slice,
                message: err.get_message(),
            }),
        }
    }
}

// Direct Expr evaluation to avoid infinite recursion
impl<'a> EvaluateInterpreter<Expr> for Interpreter<'a> {
    fn interpret(&mut self, expr: Expr) -> LoxResult<LiteralValue> {
        match expr {
            Expr::Literal { value } => Ok(value),
            Expr::Variable { name } => self.enviorment.get(&name),
            Expr::Binary {
                left,
                operator,
                right,
            } => {
                let left_val = self.interpret(*left)?;
                let right_val = self.interpret(*right)?;
                self.evaluate_binary(left_val, operator, right_val)
            }
            Expr::Unary { operator, operand } => {
                let operand_val = self.interpret(*operand)?;
                self.evaluate_unary(operator, operand_val)
            }
            Expr::Grouping { expression } => self.interpret(*expression),
        }
    }
}

impl<'a> EvaluateInterpreter<AstNode<Stmt>> for Interpreter<'a> {
    fn interpret(&mut self, node: AstNode<Stmt>) -> LoxResult<LiteralValue> {
        let stmt = node.node;
        let _source_slice = node.source_slice;
        self.interpret_stmt_inner(stmt)
    }
}

impl<'a> Interpreter<'a> {
    fn evaluate_binary(
        &mut self,
        left: LiteralValue,
        operator: TokenType,
        right: LiteralValue,
    ) -> LoxResult<LiteralValue> {
        match operator {
            TokenType::Plus => left + right,
            TokenType::Minus => left - right,
            TokenType::Star => left * right,
            TokenType::Slash => left / right,
            TokenType::Greater => Ok(LiteralValue::Boolean(left > right)),
            TokenType::GreaterEqual => Ok(LiteralValue::Boolean(left >= right)),
            TokenType::Less => Ok(LiteralValue::Boolean(left < right)),
            TokenType::LessEqual => Ok(LiteralValue::Boolean(left <= right)),
            TokenType::EqualEqual => Ok(LiteralValue::Boolean(left == right)),
            TokenType::BangEqual => Ok(LiteralValue::Boolean(left != right)),
            _ => Err(error(format!(
                "Unsupported binary operator: {:?}",
                operator
            ))),
        }
    }

    fn evaluate_unary(
        &mut self,
        operator: TokenType,
        operand: LiteralValue,
    ) -> LoxResult<LiteralValue> {
        match operator {
            TokenType::Minus => -operand,
            TokenType::Bang => Ok(!operand),
            _ => Err(error(format!("Unsupported unary operator: {:?}", operator))),
        }
    }

    fn interpret_stmt_inner(&mut self, stmt: Stmt) -> LoxResult<LiteralValue> {
        match stmt {
            Stmt::Expression { expression } => self.interpret(*expression),
            Stmt::Print { expression } => {
                let value = self.interpret(*expression)?;
                println!("print interpreter: \t{}", value);
                Ok(LiteralValue::Nil)
            }
            Stmt::Block { statements } => {
                let (elements, final_expr) = match statements.split_last() {
                    Some((stmt, body)) => match &stmt.node {
                        Stmt::Expression { expression } => (body, Some(expression)),
                        Stmt::Return { expression } => (body, Some(expression)),
                        _ => (statements.as_slice(), None),
                    },

                    None => {
                        (&[][..], None) // Blocco vuoto
                    }
                };

                // Ora elements è sempre disponibile
                for statement in elements.iter() {
                    self.interpret((*statement).clone())?;
                }

                // Gestisci l'espressione finale se presente
                match final_expr {
                    Some(expr) => self.interpret(*expr.clone()),
                    None => Ok(LiteralValue::Nil),
                }
            }
            Stmt::Stmt { expression } => self.interpret(*expression.clone()),
            Stmt::Return { expression } => self.interpret(*expression),
            Stmt::Var { name, initializer } => {
                let value = if let Some(expr) = initializer {
                    self.interpret(*expr)?
                } else {
                    LiteralValue::Nil
                };
                self.enviorment.set(name.clone(), value);
                return Ok(LiteralValue::Nil);
            }
            Stmt::Assign { name, value } => {
                let result = self.interpret(*value)?;
                self.enviorment.set(name.clone(), result);
                Ok(LiteralValue::Nil)
            }
            Stmt::If {
                condition,
                then_branch,
                elif_branch,
                else_branch,
            } => {
                let condition = self.interpret(*condition)?;
                match condition {
                    LiteralValue::Boolean(true) => self.interpret(*then_branch),
                    LiteralValue::Boolean(false) => {
                        for (elif_condition, elif_then_branch) in elif_branch {
                            let condition = self.interpret(*elif_condition)?;
                            match condition {
                                LiteralValue::Boolean(true) => {
                                    return self.interpret(*elif_then_branch);
                                }
                                LiteralValue::Boolean(false) => continue,
                                _ => {
                                    return Err(LoxError::TypeMismatch {
                                        source_slice: SourceSlice::default(), // todo change this to the actual source slice
                                        expected: "boolean".to_string(),
                                        found: condition.to_string(),
                                    });
                                }
                            };
                        }
                        if let Some(else_block) = else_branch {
                            self.interpret(*else_block)
                        } else {
                            Ok(LiteralValue::Nil)
                        }
                    }
                    _ => Err(LoxError::TypeMismatch {
                        source_slice: SourceSlice::default(), // todo change this to the actual source slice
                        expected: "boolean".to_string(),
                        found: condition.to_string(),
                    }),
                }
            }
            Stmt::While { condition, body } => {
                while self.interpret(*condition.clone())?.is_truthy() {
                    self.interpret(*body.clone())?;
                }
                Ok(LiteralValue::Nil)
            }
            Stmt::For {
                variable,
                iterable,
                body,
            } => todo!(),
        }
    }
}