//! 函数声明语句 emit：`emit_function_declaration_statement` 创建闭包并绑定函数名。

use crate::{CompileCtx, Emitter, ParamSpec};
use oxide_bytecode::opcode::OpCode;
use oxide_ir::inst::Inst;
use oxide_ir::operand::Operand;
use oxide_parser::Statement;

impl Emitter {
    pub(crate) fn emit_function_declaration_statement(
        &self, stmt: &Statement, ctx: &mut CompileCtx,
    ) -> Result<Option<u32>, String> {
        let Statement::FunctionDeclaration(fd) = stmt else {
            return Err("FunctionDeclaration without name".into());
        };
        self.emit_function_declaration(fd, ctx)
    }

    /// 函数声明本体：供 export 声明复用（导出声明先按普通声明 emit，再就地注册导出值）。
    pub(crate) fn emit_function_declaration(
        &self, fd: &oxide_parser::Function, ctx: &mut CompileCtx,
    ) -> Result<Option<u32>, String> {
        let name = if let Some(id) = &fd.id {
            id.name.to_string()
        } else {
            return Err("FunctionDeclaration without name".into());
        };
        let mut param_names = Vec::new();
        for (idx, param) in fd.params.items.iter().enumerate() {
            match &param.pattern {
                oxide_parser::BindingPattern::BindingIdentifier(bi) => param_names.push(ParamSpec::Identifier {
                    name: bi.name.to_string(),
                    initializer: param.initializer.as_deref(),
                }),
                pattern => param_names.push(ParamSpec::Pattern {
                    synthetic_name: format!("@@param_{idx}"),
                    pattern,
                    initializer: param.initializer.as_deref(),
                }),
            }
        }
        if let Some(rest) = &fd.params.rest {
            self.push_rest_param(&rest.rest.argument, &mut param_names)?;
        }
        let body_stmts: &[Statement] = if let Some(body) = &fd.body { &body.statements } else { &[] };
        let own_strict = fd.has_use_strict_directive();
        let mut sub_module = if fd.generator && fd.r#async {
            self.compile_async_generator_body(&param_names, body_stmts, ctx, own_strict)?
        } else if fd.generator {
            self.compile_generator_body(&param_names, body_stmts, ctx, own_strict)?
        } else if fd.r#async {
            self.compile_async_body(&param_names, body_stmts, ctx, false, false, own_strict)?
        } else {
            self.compile_function_body(&param_names, body_stmts, ctx, false, false, own_strict)?
        };
        sub_module.function_name = Some(name.clone());
        ctx.nested.push(sub_module);
        let var_reg = ctx.lookup(&name)?;
        ctx.reserve_reg(var_reg);
        ctx.inst(Inst::create_closure(Operand::Reg(var_reg), ctx.nested.len() as u16));
        if let Some(&cell_idx) = ctx.captured_bindings.get(&name) {
            ctx.inst(Inst::new(
                OpCode::MAKE_CELL,
                Operand::Reg(var_reg),
                Operand::Imm(cell_idx as u16),
                Operand::None,
            ));
        } else {
            ctx.inst(Inst::new(OpCode::STORE_VAR, Operand::Reg(var_reg), Operand::Reg(var_reg), Operand::None));
        }
        // 脚本顶层（非块内）函数声明：同步写全局对象，使 globalThis 可反射函数名。
        // 块内函数声明是块级绑定，不得落全局对象（作用域隔离，块外不可见）。
        if ctx.is_global_scope && ctx.scopes.symbols.scopes.len() == 1 {
            self.emit_global_prop_write(&name, var_reg, ctx);
        }
        Ok(None)
    }
}