use std::collections::HashMap;
use crate::ast::compiler::bound_nodes::{BoundKind, Address, BoundNode};

/// A pass that collects all global function definitions (lambdas) into a registry.
/// This allows the Specializer to retrieve the original AST of a function for monomorphization.
pub struct LambdaCollector<'a> {
    registry: &'a mut HashMap<u32, BoundNode>,
}

impl<'a> LambdaCollector<'a> {
    /// Performs a full traversal of the AST and populates the provided registry.
    pub fn collect(node: &BoundNode, registry: &'a mut HashMap<u32, BoundNode>) {
        let mut collector = Self { registry };
        collector.visit(node);
    }

    fn visit(&mut self, node: &BoundNode) {
        match &node.kind {
            BoundKind::Block { exprs } => {
                for expr in exprs {
                    self.visit(expr);
                }
            }
            
            BoundKind::DefGlobal { global_index, value, .. } => {
                // If we define a global that is a lambda, register its BODY as the template.
                // This allows the VM to skip the Lambda/Parameter nodes during execution.
                if let BoundKind::Lambda { body, .. } = &value.kind {
                    self.registry.insert(*global_index, (**body).clone());
                }
                self.visit(value);
            }

            BoundKind::Set { addr, value } => {
                // Also track assignments to globals if they hold lambdas.
                if let Address::Global(global_index) = addr 
                    && let BoundKind::Lambda { body, .. } = &value.kind 
                {
                    self.registry.insert(*global_index, (**body).clone());
                }
                self.visit(value);
            }

            BoundKind::If { cond, then_br, else_br } => {
                self.visit(cond);
                self.visit(then_br);
                if let Some(e) = else_br {
                    self.visit(e);
                }
            }

            BoundKind::Lambda { params, body, .. } => {
                self.visit(params);
                self.visit(body);
            }

            BoundKind::DefLocal { value, .. } => {
                self.visit(value);
            }

            BoundKind::Call { callee, args } | BoundKind::TailCall { callee, args } => {
                self.visit(callee);
                self.visit(args);
            }

            BoundKind::Tuple { elements } => {
                for el in elements {
                    self.visit(el);
                }
            }

            BoundKind::Map { entries } => {
                for (k, v) in entries {
                    self.visit(k);
                    self.visit(v);
                }
            }

            BoundKind::Expansion { bound_expanded, .. } => {
                self.visit(bound_expanded);
            }

            _ => {} // Leaf nodes
        }
    }
}