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

#[derive(Debug, Clone)]
struct LocalInfo {
    addr: Address,
    identity: Identity,
    // 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>,
}

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

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
enum ScopeKind {
    Root,
    Local,
}

struct FunctionCompiler {
    identity: Identity,
    scopes: Vec<CompilerScope>,
    slot_count: u32,
    upvalues: Vec<Address>,
    kind: ScopeKind,
}

impl FunctionCompiler {
    fn new(kind: ScopeKind, identity: Identity) -> Self {
        Self {
            identity,
            scopes: vec![CompilerScope::new()],
            slot_count: 0,
            upvalues: Vec::new(),
            kind,
        }
    }

    fn push_scope(&mut self) {
        self.scopes.push(CompilerScope::new());
    }

    fn pop_scope(&mut self) {
        self.scopes.pop();
    }

    fn define_variable(
        &mut self,
        name: &Symbol,
        identity: Identity,
        globals: &Rc<RefCell<HashMap<Symbol, (GlobalIdx, Identity)>>>,
    ) -> Result<Address, String> {
        match self.kind {
            ScopeKind::Root => {
                let current_scope = self.scopes.last_mut().unwrap();
                if current_scope.locals.contains_key(name) {
                    return Err(format!(
                        "Variable '{}' is already defined in this scope level.",
                        name.name
                    ));
                }

                let mut globals_map = globals.borrow_mut();
                let addr = if let Some((idx, existing_id)) = globals_map.get(name) {
                    if *existing_id != identity {
                        return Err(format!("Variable '{}' is already defined in global scope.", name.name));
                    }
                    Address::Global(*idx)
                } else {
                    let idx = GlobalIdx(globals_map.len() as u32);
                    globals_map.insert(name.clone(), (idx, identity.clone()));
                    Address::Global(idx)
                };

                current_scope.locals.insert(
                    name.clone(),
                    LocalInfo {
                        addr,
                        identity,
                        _ty: StaticType::Any,
                    },
                );
                Ok(addr)
            }
            ScopeKind::Local => {
                let current_scope = self.scopes.last_mut().unwrap();
                if current_scope.locals.contains_key(name) {
                    return Err(format!(
                        "Variable '{}' is already defined in this scope level.",
                        name.name
                    ));
                }
                let slot = LocalSlot(self.slot_count);
                current_scope.locals.insert(
                    name.clone(),
                    LocalInfo {
                        addr: Address::Local(slot),
                        identity,
                        _ty: StaticType::Any,
                    },
                );
                self.slot_count += 1;
                Ok(Address::Local(slot))
            }
        }
    }

    fn resolve_local(&self, sym: &Symbol) -> Option<LocalInfo> {
        for scope in self.scopes.iter().rev() {
            if let Some(info) = scope.locals.get(sym) {
                return Some(info.clone());
            }
        }
        None
    }

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

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum ExprContext {
    Expression,
    Statement,
}

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

impl Binder {
    pub fn new(globals: Rc<RefCell<HashMap<Symbol, (GlobalIdx, Identity)>>>) -> Self {
        let mut binder = Self {
            functions: Vec::new(),
            globals,
            capture_map: HashMap::new(),
        };
        binder.functions.push(FunctionCompiler::new(
            ScopeKind::Root,
            crate::ast::types::NodeIdentity::new(crate::ast::types::SourceLocation {
                line: 0,
                col: 0,
            }),
        ));
        binder
    }

    pub fn bind_root(
        globals: Rc<RefCell<HashMap<Symbol, (GlobalIdx, Identity)>>>,
        node: &Node<UntypedKind>,
        diagnostics: &mut Diagnostics,
    ) -> Result<(BoundNode, HashMap<Identity, Vec<Identity>>), String> {
        let mut binder = Self::new(globals);
        let bound = binder.bind(node, ExprContext::Expression, diagnostics);

        // Convert HashSet to sorted Vec
        let final_captures = binder
            .capture_map
            .into_iter()
            .map(|(k, v)| (k, v.into_iter().collect()))
            .collect();

        Ok((bound, final_captures))
    }

    fn declare_variable(
        &mut self,
        name: &Symbol,
        identity: Identity,
        _kind: crate::ast::compiler::bound_nodes::DeclarationKind,
        diag: &mut Diagnostics,
    ) -> Option<Address> {
        let current_fn = self.functions.last_mut().unwrap();
        match current_fn.define_variable(name, identity, &self.globals) {
            Ok(addr) => Some(addr),
            Err(e) => {
                diag.push_error(e, None);
                None
            }
        }
    }

    pub fn bind(&mut self, node: &Node<UntypedKind>, ctx: ExprContext, diag: &mut Diagnostics) -> BoundNode {
        match &node.kind {
            UntypedKind::Nop => self.make_node(node.identity.clone(), BoundKind::Nop),
            UntypedKind::Constant(v) => {
                self.make_node(node.identity.clone(), BoundKind::Constant(v.clone()))
            }

            UntypedKind::Identifier(sym) => {
                if let Some(addr) = self.resolve_variable(sym, diag, &node.identity) {
                    self.make_node(
                        node.identity.clone(),
                        BoundKind::Get {
                            addr,
                            name: sym.clone(),
                        },
                    )
                } else {
                    self.make_node(node.identity.clone(), BoundKind::Error)
                }
            }

            UntypedKind::FieldAccessor(k) => {
                self.make_node(node.identity.clone(), BoundKind::FieldAccessor(*k))
            }

            UntypedKind::If {
                cond,
                then_br,
                else_br,
            } => {
                let cond = self.bind(cond, ExprContext::Expression, diag);

                self.functions.last_mut().unwrap().push_scope();
                let then_br = self.bind(then_br, ctx, diag);
                self.functions.last_mut().unwrap().pop_scope();

                let mut else_br_bound = None;
                if let Some(e) = else_br {
                    self.functions.last_mut().unwrap().push_scope();
                    else_br_bound = Some(Rc::new(self.bind(e, ctx, diag)));
                    self.functions.last_mut().unwrap().pop_scope();
                }

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

            UntypedKind::Def { target, value } => {
                if ctx == ExprContext::Expression {
                    diag.push_error(
                        "Statement 'def' cannot be used as an expression.",
                        Some(node.identity.clone()),
                    );
                }
                // Special case: Single identifier (to support recursion)
                if let UntypedKind::Identifier(ref name) = target.kind {
                    let addr_opt = self.declare_variable(
                        name,
                        node.identity.clone(), // Identity of the Def node
                        crate::ast::compiler::bound_nodes::DeclarationKind::Variable,
                        diag,
                    );
                    let val_node = self.bind(value, ExprContext::Expression, diag);

                    if let Some(addr) = addr_opt {
                        self.make_node(
                            node.identity.clone(),
                            BoundKind::Define {
                                name: name.clone(),
                                addr,
                                kind: crate::ast::compiler::bound_nodes::DeclarationKind::Variable,
                                value: Rc::new(val_node),
                                captured_by: Vec::new(), // Will be filled by post-pass
                            },
                        )
                    } else {
                        self.make_node(node.identity.clone(), BoundKind::Error)
                    }
                } else {
                    // Complex Destructuring Pattern
                    // NOTE: Destructuring definitions are NOT recursive by default
                    // (the variables are only available AFTER the definition)
                    let val_node = self.bind(value, ExprContext::Expression, diag);
                    let target_node = self.bind_pattern(target, DeclarationKind::Variable, diag);

                    self.make_node(
                        node.identity.clone(),
                        BoundKind::Destructure {
                            pattern: Rc::new(target_node),
                            value: Rc::new(val_node),
                        },
                    )
                }
            }

            UntypedKind::Assign { target, value } => {
                let val_node = self.bind(value, ExprContext::Expression, diag);

                if let UntypedKind::Identifier(sym) = &target.kind {
                    if let Some(addr) = self.resolve_variable(sym, diag, &target.identity) {
                        self.make_node(
                            node.identity.clone(),
                            BoundKind::Set {
                                addr,
                                value: Rc::new(val_node),
                            },
                        )
                    } else {
                        self.make_node(node.identity.clone(), BoundKind::Error)
                    }
                } else {
                    let target_node = self.bind_assign_pattern(target, diag);
                    self.make_node(
                        node.identity.clone(),
                        BoundKind::Destructure {
                            pattern: Rc::new(target_node),
                            value: Rc::new(val_node),
                        },
                    )
                }
            }

            UntypedKind::Pipe { inputs, lambda } => {
                let mut bound_inputs = Vec::with_capacity(inputs.len());
                for input in inputs {
                    bound_inputs.push(Rc::new(self.bind(input, ExprContext::Expression, diag)));
                }
                let bound_lambda = Rc::new(self.bind(lambda.as_ref(), ExprContext::Expression, diag));
                self.make_node(
                    node.identity.clone(),
                    BoundKind::Pipe {
                        inputs: bound_inputs,
                        lambda: bound_lambda,
                        out_type: crate::ast::types::StaticType::Any,
                    },
                )
            }

            UntypedKind::Lambda { params, body } => {
                let identity = node.identity.clone();
                self.functions
                    .push(FunctionCompiler::new(ScopeKind::Local, identity.clone()));

                // 1. Bind the parameter pattern/tuple
                let params_bound = self.bind_pattern(params, DeclarationKind::Parameter, diag);

                // 2. Bind the body
                let body_bound = self.bind(body, ExprContext::Expression, diag);

                let compiled_fn = self.functions.pop().unwrap();

                // 3. Static optimization: count total parameters needed in flat argument list
                fn count_params(node: &BoundNode) -> Option<u32> {
                    match &node.kind {
                        BoundKind::Define {
                            kind: DeclarationKind::Parameter,
                            ..
                        } => Some(1),
                        BoundKind::Tuple { elements } => {
                            let mut total = 0;
                            for e in elements {
                                total += count_params(e)?;
                            }
                            Some(total)
                        }
                        BoundKind::Nop => Some(0),
                        _ => None,
                    }
                }

                let positional_count = count_params(&params_bound);

                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, ExprContext::Expression, diag);
                let args = self.bind(args, ExprContext::Expression, diag);

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

            UntypedKind::Again { args } => {
                if self.functions.len() <= 1 {
                    diag.push_error(
                        "'again' is only allowed inside a function or lambda.",
                        Some(node.identity.clone()),
                    );
                    return self.make_node(node.identity.clone(), BoundKind::Error);
                }
                let args = self.bind(args, ExprContext::Expression, diag);
                self.make_node(
                    node.identity.clone(),
                    BoundKind::Again {
                        args: Rc::new(args),
                    },
                )
            }

            UntypedKind::Block { exprs } => {
                self.functions.last_mut().unwrap().push_scope();
                let mut bound_exprs = Vec::new();
                for (i, expr) in exprs.iter().enumerate() {
                    let expr_ctx = if i == exprs.len() - 1 { ctx } else { ExprContext::Statement };
                    bound_exprs.push(Rc::new(self.bind(expr, expr_ctx, diag)));
                }
                self.functions.last_mut().unwrap().pop_scope();
                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(Rc::new(self.bind(e, ExprContext::Expression, diag)));
                }
                self.make_node(
                    node.identity.clone(),
                    BoundKind::Tuple {
                        elements: bound_elems,
                    },
                )
            }

            UntypedKind::Record { fields } => {
                let mut bound_values = Vec::new();
                let mut layout_fields = Vec::new();

                for (k, v) in fields {
                    let key_node = self.bind(k, ExprContext::Expression, diag);
                    let val_node = self.bind(v, ExprContext::Expression, diag);

                    if let BoundKind::Constant(crate::ast::types::Value::Keyword(kw)) =
                        key_node.kind
                    {
                        layout_fields.push((kw, crate::ast::types::StaticType::Any));
                    } else {
                        diag.push_error(
                            format!(
                                "Record keys must be keywords, found at {:?}",
                                key_node.identity.location
                            ),
                            Some(key_node.identity.clone()),
                        );
                    }
                    bound_values.push(Rc::new(val_node));
                }

                let layout = crate::ast::types::RecordLayout::get_or_create(layout_fields);

                self.make_node(
                    node.identity.clone(),
                    BoundKind::Record {
                        layout,
                        values: bound_values,
                    },
                )
            }

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

            UntypedKind::Template(_)
            | UntypedKind::Placeholder(_)
            | UntypedKind::Splice(_)
            | UntypedKind::MacroDecl { .. } => {
                diag.push_error(format!("Macro construct {:?} found in Binder. Macros must be expanded before binding.", node.kind), Some(node.identity.clone()));
                self.make_node(node.identity.clone(), BoundKind::Error)
            }

            UntypedKind::Extension(_) => {
                diag.push_error(
                    "Custom extensions not supported in Binder yet",
                    Some(node.identity.clone()),
                );
                self.make_node(node.identity.clone(), BoundKind::Error)
            }
            UntypedKind::Error => crate::ast::compiler::bound_nodes::BoundNode {
                identity: node.identity.clone(),
                kind: crate::ast::compiler::bound_nodes::BoundKind::Error,
                ty: (),
            },
        }
    }

    fn resolve_variable(
        &mut self,
        sym: &Symbol,
        diag: &mut Diagnostics,
        identity: &Identity,
    ) -> Option<Address> {
        let current_fn_idx = self.functions.len() - 1;

        // 1. Try local in current function
        if let Some(info) = self.functions[current_fn_idx].resolve_local(sym) {
            return Some(info.addr);
        }

        // 2. Try enclosing scopes (capture chain)
        for i in (0..current_fn_idx).rev() {
            if let Some(info) = self.functions[i].resolve_local(sym) {
                // If the resolved address is Global, we don't need to capture it as an upvalue
                if let Address::Global(_) = info.addr {
                    return Some(info.addr);
                }
                
                let mut addr = info.addr;

                // Record the capture for each lambda level in between
                for k in (i + 1)..=current_fn_idx {
                    let lambda_id = self.functions[k].identity.clone();
                    self.capture_map
                        .entry(info.identity.clone())
                        .or_default()
                        .insert(lambda_id);
                    addr = Address::Upvalue(self.functions[k].add_upvalue(addr));
                }
                return Some(addr);
            }
        }

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

        diag.push_error(
            format!("Undefined variable '{}'", sym.name),
            Some(identity.clone()),
        );
        None
    }

    fn bind_pattern(
        &mut self,
        node: &Node<UntypedKind>,
        kind: DeclarationKind,
        diag: &mut Diagnostics,
    ) -> BoundNode {
        match &node.kind {
            UntypedKind::Identifier(sym) => {
                if let Some(addr) = self.declare_variable(sym, node.identity.clone(), kind, diag) {
                    self.make_node(
                        node.identity.clone(),
                        BoundKind::Define {
                            name: sym.clone(),
                            addr,
                            kind,
                            value: Rc::new(self.make_node(node.identity.clone(), BoundKind::Nop)),
                            captured_by: Vec::new(), // Filled by post-pass
                        },
                    )
                } else {
                    self.make_node(node.identity.clone(), BoundKind::Error)
                }
            }
            UntypedKind::Tuple { elements } => {
                let mut bound_elems = Vec::new();
                for e in elements {
                    bound_elems.push(Rc::new(self.bind_pattern(e, kind, diag)));
                }
                self.make_node(
                    node.identity.clone(),
                    BoundKind::Tuple {
                        elements: bound_elems,
                    },
                )
            }
            _ => {
                diag.push_error(
                    format!("Invalid node in pattern: {:?}", node.kind),
                    Some(node.identity.clone()),
                );
                self.make_node(node.identity.clone(), BoundKind::Error)
            }
        }
    }

    fn bind_assign_pattern(
        &mut self,
        node: &Node<UntypedKind>,
        diag: &mut Diagnostics,
    ) -> BoundNode {
        match &node.kind {
            UntypedKind::Identifier(sym) => {
                if let Some(addr) = self.resolve_variable(sym, diag, &node.identity) {
                    self.make_node(
                        node.identity.clone(),
                        BoundKind::Set {
                            addr,
                            value: Rc::new(self.make_node(node.identity.clone(), BoundKind::Nop)),
                        },
                    )
                } else {
                    self.make_node(node.identity.clone(), BoundKind::Error)
                }
            }
            UntypedKind::Tuple { elements } => {
                let mut bound_elems = Vec::new();
                for e in elements {
                    bound_elems.push(Rc::new(self.bind_assign_pattern(e, diag)));
                }
                self.make_node(
                    node.identity.clone(),
                    BoundKind::Tuple {
                        elements: bound_elems,
                    },
                )
            }
            _ => {
                diag.push_error(
                    format!("Invalid node in assignment pattern: {:?}", node.kind),
                    Some(node.identity.clone()),
                );
                self.make_node(node.identity.clone(), BoundKind::Error)
            }
        }
    }

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

#[cfg(test)]
mod tests {
    use super::*;
    use crate::ast::diagnostics::Diagnostics;
    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);
        let untyped = parser.parse_expression();

        let globals = Rc::new(RefCell::new(HashMap::new()));
        let mut diagnostics = Diagnostics::new();
        let (bound, captures) = Binder::bind_root(globals, &untyped, &mut diagnostics).unwrap();

        // Structure: Lambda -> Block -> [ Define(x), Define(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::Define { addr, .. } = &x_decl.kind {
                    assert!(matches!(addr, Address::Local(_)));
                    assert!(
                        captures.contains_key(&x_decl.identity),
                        "Variable 'x' should have capturers because it is used in lambda 'f'"
                    );
                } else {
                    panic!(
                        "First expression in block should be Define, 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);
        let untyped = parser.parse_expression();

        let globals = Rc::new(RefCell::new(HashMap::new()));
        let mut diagnostics = Diagnostics::new();
        let (bound, captures) = Binder::bind_root(globals, &untyped, &mut diagnostics).unwrap();

        if let BoundKind::Lambda { body, .. } = &bound.kind {
            if let BoundKind::Block { exprs } = &body.kind {
                let x_decl = &exprs[0];
                if let BoundKind::Define { addr, .. } = &x_decl.kind {
                    assert!(matches!(addr, Address::Local(_)));
                    assert!(
                        !captures.contains_key(&x_decl.identity),
                        "Variable 'x' should NOT have any capturers"
                    );
                } else {
                    panic!("First expression should be Define");
                }
            } 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);
        let untyped = parser.parse_expression();

        let globals = Rc::new(RefCell::new(HashMap::new()));
        let mut diagnostics = Diagnostics::new();
        let _ = Binder::bind_root(globals, &untyped, &mut diagnostics);

        assert!(diagnostics.has_errors());
        assert!(diagnostics.items[0].message.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).parse_expression();
        let mut diagnostics = Diagnostics::new();
        assert!(Binder::bind_root(globals.clone(), &untyped1, &mut diagnostics).is_ok());

        // Second run: attempts to redefine 'x' in the same global environment
        let source2 = "(def x 2)";
        let untyped2 = Parser::new(source2).parse_expression();
        let mut diagnostics2 = Diagnostics::new();
        let _ = Binder::bind_root(globals.clone(), &untyped2, &mut diagnostics2);

        assert!(diagnostics2.has_errors());
        assert!(diagnostics2.items[0].message.contains("already defined"));
    }
}