rlox/src/backend/interpreter.rs

use crate::{
    backend::environment::EnvironmentStack,
    common::{
        ast::{AstNode, AstNodeKind, Expr, Stmt},
        base_value::{BaseValue, NativeFunction, Number, Truthy},
        lox_result::{runtime_error, LoxError, LoxResult},
    },
    frontend::{source_registry::SourceSlice, tokens::TokenType},
};
use std::fmt::{Debug, Display};

pub struct Interpreter {
    enviorment: EnvironmentStack,
}

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

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

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

impl EvaluateInterpreter<AstNode<Stmt>> for Interpreter {
    fn evaluate(&mut self, node: AstNode<Stmt>) -> LoxResult<BaseValue> {
        let stmt = node.node;
        let result = self.interpret_stmt_inner(stmt);
        match result {
            Ok(value) => Ok(value),
            Err(LoxError::RuntimeError {
                message,
                source_slice,
            }) if source_slice == SourceSlice::default() => {
                runtime_error(node.source_slice.clone(), message)
            }
            Err(err) => Err(err),
        }
    }
}

impl Interpreter {
    pub fn new() -> Self {
        let mut env = EnvironmentStack::new();
        let _ = env.declare(
            "clock".to_string(),
            BaseValue::NativeFunction(NativeFunction::new(Vec::default(), |_args| {
                BaseValue::Number(Number::U128(
                    std::time::SystemTime::now()
                        .duration_since(std::time::UNIX_EPOCH)
                        .unwrap()
                        .as_millis(),
                ))
            })),
        );
        Self { enviorment: env }
    }
    fn evaluate_call(
        &mut self,
        callee: Box<AstNode<Expr>>,
        arguments: Vec<AstNode<Expr>>,
    ) -> LoxResult<BaseValue> {
        let source_slice = callee.source_slice.clone();

        // Estrai il nome della variabile se il callee è un identificatore
        let function_name = match &callee.node {
            Expr::Identifier { name } => Some(name.clone()),
            _ => None,
        };

        let function = if let Some(name) = function_name {
            // Se abbiamo un nome di variabile, ottieni la funzione dall'ambiente
            self.enviorment.get(&name)?
        } else {
            // Altrimenti valuta l'espressione callee (per casi più complessi)
            self.evaluate(*callee)?
        };

        if !function.is_callable() {
            return runtime_error(source_slice, "Can only call functions");
        }

        let evaluated_arguments = arguments
            .iter()
            .map(|arg| self.evaluate(arg.clone()))
            .collect::<Result<Vec<BaseValue>, LoxError>>()?;

        match function {
            BaseValue::NativeFunction(func) => Ok((func.function)(&evaluated_arguments)),
            BaseValue::Function(func) => {
                func.parameters
                    .iter()
                    .enumerate()
                    .map(|(index, par)| {
                        let value = evaluated_arguments.get(index).unwrap();
                        self.enviorment.declare(par.0.clone(), value.clone())
                    })
                    .collect::<LoxResult<Vec<BaseValue>>>()?;
                self.evaluate(func.body)
            }
            _ => runtime_error(
                source_slice.clone(),
                "This is callable, but apparently is not implemented",
            ),
        }
    }

    fn evaluate_binary(
        &mut self,
        left: BaseValue,
        operator: TokenType,
        right: BaseValue,
    ) -> LoxResult<BaseValue> {
        match operator {
            TokenType::Plus => left + right,
            TokenType::Minus => left - right,
            TokenType::Star => left * right,
            TokenType::Slash => left / right,
            TokenType::Greater => Ok(BaseValue::Boolean(left > right)),
            TokenType::GreaterEqual => Ok(BaseValue::Boolean(left >= right)),
            TokenType::Less => Ok(BaseValue::Boolean(left < right)),
            TokenType::LessEqual => Ok(BaseValue::Boolean(left <= right)),
            TokenType::EqualEqual => Ok(BaseValue::Boolean(left == right)),
            TokenType::BangEqual => Ok(BaseValue::Boolean(left != right)),
            TokenType::And => Ok(BaseValue::Boolean(left.is_truthy() && right.is_truthy())),
            TokenType::Or => Ok(BaseValue::Boolean(left.is_truthy() || right.is_truthy())),
            _ => Err(LoxError::RuntimeError {
                source_slice: SourceSlice::default(),
                message: format!("Unsupported binary operator: {:?}", operator),
            }),
        }
    }

    fn evaluate_unary(&mut self, operator: TokenType, operand: BaseValue) -> LoxResult<BaseValue> {
        match operator {
            TokenType::Minus => match operand {
                BaseValue::Number(n) => Ok(BaseValue::Number(n.neg())),
                _ => Err(LoxError::RuntimeError {
                    source_slice: SourceSlice::default(),
                    message: "Cannot negate non-numeric value".to_string(),
                }),
            },
            TokenType::Bang => Ok(!operand),
            _ => Err(LoxError::RuntimeError {
                source_slice: SourceSlice::default(),
                message: format!("Unsupported unary operator: {:?}", operator),
            }),
        }
    }

    fn interpret_stmt_inner(&mut self, stmt: Stmt) -> LoxResult<BaseValue> {
        match stmt {
            Stmt::Expression { expression, .. } => self.evaluate(*expression),
            Stmt::Print { expression, .. } => {
                let value = self.evaluate(*expression)?;
                println!("{}", value);
                Ok(BaseValue::Nil)
            }
            Stmt::Block { statements, .. } => self.evaluate_block(*statements),
            Stmt::Return { expression, .. } => self.evaluate(*expression),
            Stmt::VarDeclaration {
                name, initializer, ..
            } => {
                let value = match initializer {
                    Some(expr_node) => match &expr_node.node {
                        Expr::Literal { value } => {
                            if value.is_callable() {
                                value.clone()
                            } else {
                                value.clone()
                            }
                        }
                        _ => self.evaluate(*expr_node)?,
                    },
                    None => BaseValue::Nil,
                };
                self.enviorment.declare(name.clone(), value)
            }

            Stmt::VarAssigment { name, value, .. } => {
                let result = self.evaluate(*value)?;
                self.enviorment.set(name.clone(), result)
            }
            Stmt::If {
                condition,
                then_branch,
                elif_branch,
                else_branch,
                ..
            } => self.evaluate_if(condition, then_branch, elif_branch, else_branch),
            Stmt::While {
                condition, body, ..
            } => {
                while self.evaluate(*condition.clone())?.is_truthy() {
                    self.evaluate(*body.clone())?;
                }
                Ok(BaseValue::Nil)
            }
            Stmt::For {
                variable,
                condition,
                increment,
                body,
                ..
            } => {
                self.enviorment.push_new_scope();
                let source_slice = variable.source_slice.clone();
                let val = self.evaluate(*variable)?;
                if !matches!(val, BaseValue::Number(..)) {
                    return runtime_error(source_slice, "Expected number literal");
                }
                let mut ret = BaseValue::Nil;
                while self.evaluate(*condition.clone())?.is_truthy() {
                    ret = self.evaluate(*body.clone())?;
                    self.evaluate(*increment.clone())?;
                }

                Ok(ret)
            }
        }
    }
    fn evaluate_if(
        &mut self,
        condition: Box<AstNode<Expr>>,
        then_branch: Box<AstNode<Stmt>>,
        elif_branch: Vec<(Box<AstNode<Expr>>, Box<AstNode<Stmt>>)>,
        else_branch: Option<Box<AstNode<Stmt>>>,
    ) -> LoxResult<BaseValue> {
        let condition = self.evaluate(*condition)?;
        match condition {
            BaseValue::Boolean(true) => self.evaluate(*then_branch),
            BaseValue::Boolean(false) => {
                for (elif_condition, elif_then_branch) in elif_branch {
                    let condition = self.evaluate(*elif_condition)?;
                    match condition {
                        BaseValue::Boolean(true) => {
                            return self.evaluate(*elif_then_branch);
                        }
                        BaseValue::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.evaluate(*else_block)
                } else {
                    Ok(BaseValue::Nil)
                }
            }
            _ => Err(LoxError::TypeMismatch {
                source_slice: SourceSlice::default(), // todo change this to the actual source slice
                expected: "boolean".to_string(),
                found: condition.to_string(),
            }),
        }
    }

    fn evaluate_block(&mut self, statements: Vec<AstNode<Stmt>>) -> LoxResult<BaseValue> {
        self.enviorment.push_new_scope();
        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.evaluate((*statement).clone())?;
        }

        // Gestisci l'espressione finale se presente
        match final_expr {
            Some(expr) => {
                let res = self.evaluate(*expr.clone());
                self.enviorment.pop_scope();
                res
            }
            None => {
                self.enviorment.pop_scope();
                Ok(BaseValue::Nil)
            }
        }
    }
}