RustAst/src/ast/compiler/binder.rs

use std::collections::HashMap;
use std::rc::Rc;
use std::cell::RefCell;
use crate::ast::nodes::{Node, UntypedKind, Symbol};
use crate::ast::compiler::bound_nodes::{BoundKind, Address, BoundNode};
use crate::ast::types::{Identity, StaticType};

#[derive(Debug, Clone)]
struct LocalInfo {
    slot: u32,
    // Note: Binder doesn't strictly need the type anymore, 
    // but it might be useful for built-ins during resolution.
    // For now we keep it as Any or Unknown.
    _ty: StaticType, 
}

#[derive(Debug, Clone)]
struct CompilerScope {
    locals: HashMap<Symbol, LocalInfo>,
    slot_count: u32,
}

impl CompilerScope {
    fn new() -> Self {
        Self {
            locals: HashMap::new(),
            slot_count: 0,
        }
    }

    fn define(&mut self, sym: &Symbol) -> Result<u32, String> {
        if self.locals.contains_key(sym) {
            return Err(format!("Variable '{}' is already defined in this scope level.", sym.name));
        }
        let slot = self.slot_count;
        self.locals.insert(sym.clone(), LocalInfo { slot, _ty: StaticType::Any });
        self.slot_count += 1;
        Ok(slot)
    }

    fn resolve(&self, sym: &Symbol) -> Option<LocalInfo> {
        self.locals.get(sym).cloned()
    }
}

struct FunctionCompiler {
    scope: CompilerScope,
    upvalues: Vec<Address>,
}

impl FunctionCompiler {
    fn new() -> Self {
        Self {
            scope: CompilerScope::new(),
            upvalues: Vec::new(),
        }
    }

    fn add_upvalue(&mut self, addr: Address) -> u32 {
        if let Some(idx) = self.upvalues.iter().position(|&a| a == addr) {
            return idx as u32;
        }
        let idx = self.upvalues.len() as u32;
        self.upvalues.push(addr);
        idx
    }
}

pub struct Binder {
    functions: Vec<FunctionCompiler>,
    // Globals mapping: Symbol -> Index
    globals: Rc<RefCell<HashMap<Symbol, u32>>>,
    // Map of Declaration Identity -> List of Lambda Identities that capture it
    capture_map: HashMap<Identity, Vec<Identity>>,
}

impl Binder {
    pub fn new(globals: Rc<RefCell<HashMap<Symbol, u32>>>) -> Self {
        Self::with_boxed(globals, HashMap::new())
    }

    fn with_boxed(globals: Rc<RefCell<HashMap<Symbol, u32>>>, captures: HashMap<Identity, Vec<Identity>>) -> Self {
        let mut binder = Self {
            functions: Vec::new(),
            globals,
            capture_map: captures,
        };
        binder.functions.push(FunctionCompiler::new());
        binder
    }

    pub fn bind_root(globals: Rc<RefCell<HashMap<Symbol, u32>>>, node: &Node<UntypedKind>) -> Result<BoundNode, String> {
        let captures = crate::ast::compiler::upvalues::UpvalueAnalyzer::analyze(node);
        let mut binder = Self::with_boxed(globals, captures);
        binder.bind(node)
    }

    pub fn bind(&mut self, node: &Node<UntypedKind>) -> Result<BoundNode, String> {
        match &node.kind {
            UntypedKind::Nop => Ok(self.make_node(node.identity.clone(), BoundKind::Nop)),
            UntypedKind::Constant(v) => {
                Ok(self.make_node(node.identity.clone(), BoundKind::Constant(v.clone())))
            },
            
            UntypedKind::Identifier(sym) => {
                let addr = self.resolve_variable(sym)?;
                Ok(self.make_node(node.identity.clone(), BoundKind::Get { 
                    addr, 
                    name: sym.clone() 
                }))
            },

            UntypedKind::Parameter(sym) => {
                // Parameters are ONLY allowed if we are inside a function (Binder stack > 1)
                if self.functions.len() <= 1 {
                    return Err(format!("Parameter '{}' is not allowed in root scope.", sym.name));
                }
                let current_fn = self.functions.last_mut().unwrap();
                let slot = current_fn.scope.define(sym)?;
                Ok(self.make_node(node.identity.clone(), BoundKind::Parameter { 
                    name: sym.clone(), 
                    slot 
                }))
            },

            UntypedKind::If { cond, then_br, else_br } => {
                let cond = self.bind(cond)?;
                let then_br = self.bind(then_br)?;
                let mut else_br_bound = None;
                if let Some(e) = else_br {
                    else_br_bound = Some(Box::new(self.bind(e)?));
                }

                Ok(self.make_node(node.identity.clone(), BoundKind::If { 
                    cond: Box::new(cond), 
                    then_br: Box::new(then_br), 
                    else_br: else_br_bound 
                }))
            },

            UntypedKind::Def { name, value } => {
                // 1. Pre-declare name to support recursion
                let slot_or_idx = if self.functions.len() == 1 {
                    let mut globals = self.globals.borrow_mut();
                    if globals.contains_key(name) {
                        return Err(format!("Global variable '{}' is already defined.", name.name));
                    }
                    let idx = globals.len() as u32;
                    globals.insert(name.clone(), idx);
                    idx
                } else {
                    let current_fn = self.functions.last_mut().unwrap();
                    current_fn.scope.define(name)?
                };

                // 2. Bind Value (now 'name' is visible)
                let val_node = self.bind(value)?;

                // 3. Return Node
                if self.functions.len() == 1 {
                    Ok(self.make_node(node.identity.clone(), BoundKind::DefGlobal { 
                        name: name.clone(),
                        global_index: slot_or_idx, 
                        value: Box::new(val_node) 
                    }))
                } else {
                    let captured_by = self.capture_map.get(&node.identity).cloned().unwrap_or_default();
                    Ok(self.make_node(node.identity.clone(), BoundKind::DefLocal { 
                        name: name.clone(),
                        slot: slot_or_idx, 
                        value: Box::new(val_node) ,
                        captured_by
                    }))
                }
            },

            UntypedKind::Assign { target, value } => {
                let val_node = self.bind(value)?;
                
                if let UntypedKind::Identifier(sym) = &target.kind {
                    let addr = self.resolve_variable(sym)?;
                    Ok(self.make_node(node.identity.clone(), BoundKind::Set { 
                        addr, 
                        value: Box::new(val_node) 
                    }))
                } else {
                    Err("Assignment target must be an identifier".to_string())
                }
            },

            UntypedKind::Lambda { params, body } => {
                let identity = node.identity.clone();
                self.functions.push(FunctionCompiler::new());
                
                // 1. Bind the parameter pattern/tuple
                let params_bound = self.bind(params)?;
                
                // 2. Bind the body
                let body_bound = self.bind(body)?;
                
                let compiled_fn = self.functions.pop().unwrap();

                // 3. Static optimization: check if parameters are purely positional
                let positional_count = match &params_bound.kind {
                    BoundKind::Tuple { elements } => {
                        let mut count = 0;
                        let mut all_params = true;
                        for e in elements {
                            if matches!(e.kind, BoundKind::Parameter { .. }) {
                                count += 1;
                            } else {
                                all_params = false;
                                break;
                            }
                        }
                        if all_params { Some(count) } else { None }
                    }
                    BoundKind::Parameter { .. } => Some(1),
                    _ => None,
                };

                Ok(self.make_node(identity, BoundKind::Lambda {
                    params: Rc::new(params_bound),
                    upvalues: compiled_fn.upvalues,
                    body: Rc::new(body_bound),
                    positional_count,
                }))
            },

            UntypedKind::Call { callee, args } => {
                let callee = self.bind(callee)?;
                let args = self.bind(args)?;

                Ok(self.make_node(node.identity.clone(), BoundKind::Call { 
                    callee: Box::new(callee), 
                    args: Box::new(args) 
                }))
            },

            UntypedKind::Block { exprs } => {
                let mut bound_exprs = Vec::new();
                for expr in exprs {
                    bound_exprs.push(self.bind(expr)?);
                }
                Ok(self.make_node(node.identity.clone(), BoundKind::Block { exprs: bound_exprs }))
            },

            UntypedKind::Tuple { elements } => {
                let mut bound_elems = Vec::new();
                for e in elements {
                    bound_elems.push(self.bind(e)?);
                }
                Ok(self.make_node(node.identity.clone(), BoundKind::Tuple { elements: bound_elems }))
            },

            UntypedKind::Record { fields } => {
                let mut bound_fields = Vec::new();
                for (k, v) in fields {
                    bound_fields.push((self.bind(k)?, self.bind(v)?));
                }
                Ok(self.make_node(node.identity.clone(), BoundKind::Record { fields: bound_fields }))
            },

            UntypedKind::Expansion { call, expanded } => {
                let bound_expanded = self.bind(expanded)?;
                Ok(self.make_node(node.identity.clone(), BoundKind::Expansion {
                    original_call: Rc::from(call.as_ref().clone()),
                    bound_expanded: Box::new(bound_expanded),
                }))
            },

            UntypedKind::Template(_) | UntypedKind::Placeholder(_) | UntypedKind::Splice(_) | UntypedKind::MacroDecl { .. } => {
                Err(format!("Macro construct {:?} found in Binder. Macros must be expanded before binding.", node.kind))
            }
            
            UntypedKind::Extension(_) => {
                // Future: Delegate to extension binder
                Err("Custom extensions not supported in Binder yet".to_string())
            }
        }
    }

    fn resolve_variable(&mut self, sym: &Symbol) -> Result<Address, String> {
        let current_fn_idx = self.functions.len() - 1;

        // 1. Try local in current function
        if let Some(info) = self.functions[current_fn_idx].scope.resolve(sym) {
            return Ok(Address::Local(info.slot));
        }

        // 2. Try enclosing scopes (capture chain)
        for i in (0..current_fn_idx).rev() {
            if let Some(info) = self.functions[i].scope.resolve(sym) {
                let mut addr = Address::Local(info.slot);
                
                for k in (i + 1)..=current_fn_idx {
                    addr = Address::Upvalue(self.functions[k].add_upvalue(addr));
                }
                return Ok(addr);
            }
        }

        // 3. Try Global
        let globals = self.globals.borrow();
        if let Some(idx) = globals.get(sym) {
            return Ok(Address::Global(*idx));
        }

        // 4. Global Fallback
        if sym.context.is_some() {
            let fallback_sym = Symbol { name: sym.name.clone(), context: None };
            if let Some(idx) = globals.get(&fallback_sym) {
                return Ok(Address::Global(*idx));
            }
        }

        Err(format!("Undefined variable '{}'", sym.name))
    }

    fn make_node(&self, identity: Identity, kind: BoundKind<()>) -> BoundNode {
        Node { identity, kind, ty: () }
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::ast::parser::Parser;

    #[test]
    fn test_upvalue_capture_sets_is_boxed() {
        // Wrap in a lambda to ensure 'x' is a local variable, not a global
        let source = "(fn [] (do (def x 10) (def f (fn [] x)) x))";
        let mut parser = Parser::new(source).unwrap();
        let untyped = parser.parse_expression().unwrap();
        
        let globals = Rc::new(RefCell::new(HashMap::new()));
        let bound = Binder::bind_root(globals, &untyped).unwrap();
        
        // Structure: Lambda -> Block -> [ DefLocal(x), DefLocal(f), Get(x) ]
        if let BoundKind::Lambda { body, .. } = &bound.kind {
            if let BoundKind::Block { exprs } = &body.kind {
                let x_decl = &exprs[0];
                if let BoundKind::DefLocal { captured_by, .. } = &x_decl.kind {
                    assert!(!captured_by.is_empty(), "Variable 'x' should have capturers because it is used in lambda 'f'");
                } else {
                    panic!("First expression in block should be DefLocal, got {:?}", x_decl.kind);
                }
            } else {
                panic!("Lambda body should be a Block, got {:?}", body.kind);
            }
        } else {
            panic!("Root should be a Lambda, got {:?}", bound.kind);
        }
    }

    #[test]
    fn test_no_capture_not_boxed() {
        let source = "(fn [] (do (def x 10) x))";
        let mut parser = Parser::new(source).unwrap();
        let untyped = parser.parse_expression().unwrap();
        
        let globals = Rc::new(RefCell::new(HashMap::new()));
        let bound = Binder::bind_root(globals, &untyped).unwrap();
        
        if let BoundKind::Lambda { body, .. } = &bound.kind {
            if let BoundKind::Block { exprs } = &body.kind {
                let x_decl = &exprs[0];
                if let BoundKind::DefLocal { captured_by, .. } = &x_decl.kind {
                    assert!(captured_by.is_empty(), "Variable 'x' should NOT have any capturers");
                } else {
                    panic!("First expression should be DefLocal");
                }
            } else {
                panic!("Lambda body should be a Block");
            }
        } else {
            panic!("Root should be a Lambda");
        }
    }

    #[test]
    fn test_redefinition_error() {
        let source = "(do (def x 1) (def x 2))";
        let mut parser = Parser::new(source).unwrap();
        let untyped = parser.parse_expression().unwrap();
        
        let globals = Rc::new(RefCell::new(HashMap::new()));
        let result = Binder::bind_root(globals, &untyped);
        
        assert!(result.is_err());
        assert!(result.unwrap_err().contains("already defined"));
    }

    #[test]
    fn test_repro_global_redefinition() {
        let globals = Rc::new(RefCell::new(HashMap::new()));
        
        // First run: defines 'x'
        let source1 = "(def x 1)";
        let untyped1 = Parser::new(source1).unwrap().parse_expression().unwrap();
        assert!(Binder::bind_root(globals.clone(), &untyped1).is_ok());

        // Second run: attempts to redefine 'x' in the same global environment
        let source2 = "(def x 2)";
        let untyped2 = Parser::new(source2).unwrap().parse_expression().unwrap();
        let result = Binder::bind_root(globals.clone(), &untyped2);
        
        assert!(result.is_err());
        assert!(result.unwrap_err().contains("already defined"));
    }
}