#![allow(clippy::arc_with_non_send_sync)]

use std::sync::Arc;

use oxide_bytecode::module::Constant;

use crate::bindings;
use crate::vm::{native_fn_ptr_to_fn, Vm};
use oxide_kernel::kernel::{KernelConfig, KernelCore, KernelSession};
use oxide_kernel::shape_forge::EMPTY_SHAPE_ID;
use oxide_types::error::JsError;
use oxide_types::mem::{Epoch, P};
use oxide_types::object::{JsObject, PropAttributes};
use oxide_types::value::JsValue;

impl Vm {
    pub fn new() -> Self {
        let core = KernelCore::new(KernelConfig::minimal());
        let mut session = KernelSession::new(&core);
        bindings::init_kernel_builtins(&core, &mut session);
        let obj_proto = P::clone(&session.builtin_world().object_proto);
        Self {
            regs: [JsValue::undefined(); 256],
            pc: 0,
            bytecode: Vec::new(),
            constants: Vec::new(),
            frames: smallvec::SmallVec::new(),
            for_in_iters: Vec::new(),
            kernel_core: core,
            session,
            interned_strings: Vec::new(),
            epoch: Epoch::new(),
            session_epoch: bumpalo::Bump::new(),
            session_gc: crate::session_gc::SessionGc::new(),
            forwarding: std::collections::HashMap::with_hasher(rustc_hash::FxBuildHasher),
            epoch_object_ptrs: Vec::new(),
            session_object_ptrs: Vec::new(),
            session_bytes_allocated: 0,
            object_prototype: obj_proto,
            math_rng_state: 0,
            sub_modules: Vec::new(),
            sub_module_constants: Vec::new(),
            saved_bytecode_stack: Vec::new(),
            saved_constants_stack: Vec::new(),
            try_stack: Vec::new(),
            exception_value: None,
            pending_exception: None,
            pending_error_kind: None,
            symbol_counter: 0,
            symbol_descriptions: Vec::new(),
            symbol_registry: std::collections::HashMap::new(),
            for_of_iters: Vec::new(),
            last_for_of_result: JsValue::undefined(),
            root_reg_limit: 0,
            active_reg_limit: 0,
            native_call_depth: 0,
            accessor_frame_target_reg: None,
            ic_hits: std::cell::Cell::new(0),
            ic_misses: std::cell::Cell::new(0),
            instruction_count: 0,
        }
    }

    pub fn with_kernel_core(core: Arc<KernelCore>) -> Self {
        let mut session = KernelSession::new(&core);
        bindings::init_kernel_builtins(&core, &mut session);
        let obj_proto = P::clone(&session.builtin_world().object_proto);
        Self {
            regs: [JsValue::undefined(); 256],
            pc: 0,
            bytecode: Vec::new(),
            constants: Vec::new(),
            frames: smallvec::SmallVec::new(),
            for_in_iters: Vec::new(),
            kernel_core: core,
            session,
            interned_strings: Vec::new(),
            epoch: Epoch::new(),
            session_epoch: bumpalo::Bump::new(),
            session_gc: crate::session_gc::SessionGc::new(),
            forwarding: std::collections::HashMap::with_hasher(rustc_hash::FxBuildHasher),
            epoch_object_ptrs: Vec::new(),
            session_object_ptrs: Vec::new(),
            session_bytes_allocated: 0,
            object_prototype: obj_proto,
            math_rng_state: 0,
            sub_modules: Vec::new(),
            sub_module_constants: Vec::new(),
            saved_bytecode_stack: Vec::new(),
            saved_constants_stack: Vec::new(),
            try_stack: Vec::new(),
            exception_value: None,
            pending_exception: None,
            pending_error_kind: None,
            symbol_counter: 0,
            symbol_descriptions: Vec::new(),
            symbol_registry: std::collections::HashMap::new(),
            for_of_iters: Vec::new(),
            last_for_of_result: JsValue::undefined(),
            root_reg_limit: 0,
            active_reg_limit: 0,
            native_call_depth: 0,
            accessor_frame_target_reg: None,
            ic_hits: std::cell::Cell::new(0),
            ic_misses: std::cell::Cell::new(0),
            instruction_count: 0,
        }
    }

    pub fn full_reset(&mut self) {
        let dirty = self.session.selective_reset(&self.kernel_core);
        if dirty.any_builtin_dirty() {
            bindings::rebind_dirty_builtins(&self.kernel_core, &mut self.session, Some(&dirty));
        }
        if dirty.global {
            let global_ptr = self.session.global_object().as_ptr() as *mut JsObject;
            let global = unsafe { &mut *global_ptr };
            bindings::bind_global_builtin_slots(&self.kernel_core, &self.session, global);
        }
        self.session.record_snapshot();
        self.object_prototype = P::clone(&self.session.builtin_world().object_proto);
        self.clear_full_reset_state();
    }

    #[doc(hidden)]
    pub fn full_reset_legacy_for_bench(&mut self) {
        self.session = KernelSession::new(&self.kernel_core);
        bindings::init_kernel_builtins(&self.kernel_core, &mut self.session);
        self.object_prototype = P::clone(&self.session.builtin_world().object_proto);
        self.clear_full_reset_state();
    }

    fn clear_full_reset_state(&mut self) {
        self.clear_execution_state();
        self.bytecode.clear();
        self.constants.clear();
        self.free_epoch_object_heap_data();
        self.epoch.reset();
        self.epoch_object_ptrs.clear();
        self.session_epoch.reset();
        self.session_object_ptrs.clear();
        self.session_bytes_allocated = 0;
        self.session_gc = crate::session_gc::SessionGc::new();
        self.interned_strings.clear();
        self.symbol_counter = 0;
        self.symbol_descriptions.clear();
        self.symbol_registry.clear();
        self.root_reg_limit = 0;
        self.active_reg_limit = 0;
    }

    fn free_epoch_object_heap_data(&mut self) {
        let mut freed = 0u64;
        for ptr in self.epoch_object_ptrs.drain(..) {
            freed += crate::session_gc::SessionGc::drop_object_heap_data(ptr, false);
        }
        if freed > 0 {
            self.session_gc.total_bytes_freed = self.session_gc.total_bytes_freed.saturating_add(freed);
            self.session_gc.last_collection_bytes_freed = freed;
        }
    }

    pub(crate) fn clear_execution_state(&mut self) {
        // Reset contract:
        // - Clears register file, pc, frame/iterator stacks, saved execution stacks,
        //   try handlers, pending exceptions, and native call depth.
        // - Leaves kernel-owned shared state intact.
        // - `reset()` additionally clears bytecode/constants and resets epoch ownership.
        self.regs = [JsValue::undefined(); 256];
        self.pc = 0;
        self.frames.clear();
        self.for_in_iters.clear();
        self.for_of_iters.clear();
        self.last_for_of_result = JsValue::undefined();
        self.saved_bytecode_stack.clear();
        self.saved_constants_stack.clear();
        self.try_stack.clear();
        self.exception_value = None;
        self.pending_exception = None;
        self.pending_error_kind = None;
        self.native_call_depth = 0;
    }

    pub fn reset(&mut self) {
        self.clear_execution_state();
        self.maybe_collect_session_gc();
        self.bytecode.clear();
        self.constants.clear();
        self.free_epoch_object_heap_data();
        self.epoch.reset();
        self.epoch_object_ptrs.clear();
        self.interned_strings.clear();
        self.root_reg_limit = 0;
        self.active_reg_limit = 0;
    }

    pub fn intern(&mut self, s: &str) -> JsValue {
        let (idx, hash) = self.kernel_core.string_forge().intern(s);
        self.interned_strings.push(idx);
        JsValue::string(idx, hash)
    }

    /// Create a function JsObject for a BytecodeFunc constant.
    /// When `is_arrow` is true, captures the current `this` (regs[254])
    /// for lexical this binding at call time.
    fn create_function_object(
        &mut self, sub_idx: u32, is_arrow: bool, is_class_constructor: bool, is_derived_constructor: bool,
        needs_home_object: bool,
    ) -> JsValue {
        let func_proto_ptr = self.session.builtin_world().function_proto.as_ptr() as *mut JsObject;
        let proto_val = JsValue::from_js_object(func_proto_ptr);
        let mut obj = JsObject::new_empty(EMPTY_SHAPE_ID, proto_val);
        obj.set_function(true);
        obj.set_sub_module_index(sub_idx);
        obj.set_class_constructor(is_class_constructor);
        obj.set_derived_constructor(is_derived_constructor);
        let _ = needs_home_object;
        if is_arrow {
            obj.set_arrow(true);
            obj.set_captured_this(self.regs[254]);
        }
        let obj_ptr = self.alloc_object(obj);
        let func_val = JsValue::object(obj_ptr as *mut u8);

        if !is_arrow {
            let object_proto_ptr = self.session.builtin_world().object_proto.as_ptr() as *mut JsObject;
            let prototype_obj = self
                .epoch
                .alloc(JsObject::new_empty(EMPTY_SHAPE_ID, JsValue::from_js_object(object_proto_ptr)));
            self.epoch_object_ptrs.push(prototype_obj);
            let prototype_val = JsValue::from_js_object(prototype_obj);

            let constructor_si = self.kernel_core.string_forge().intern("constructor").0;
            let constructor_shape = self.kernel_core.shape_forge().make_shape(EMPTY_SHAPE_ID, constructor_si);
            let prototype = unsafe { &mut *prototype_obj };
            prototype.set_shape_id(constructor_shape);
            let constructor_pos = prototype.push_prop(func_val);
            prototype.set_data_meta(constructor_pos, PropAttributes::new(true, false, true));
            prototype.bump_generation();

            let prototype_si = self.kernel_core.string_forge().intern("prototype").0;
            let func = unsafe { &mut *obj_ptr };
            let prototype_shape = self.kernel_core.shape_forge().make_shape(func.shape_id(), prototype_si);
            func.set_shape_id(prototype_shape);
            func.ensure_hash_props().push(prototype_val);
            func.bump_generation();
        }

        func_val
    }

    pub(crate) fn error_text(&self, val: JsValue) -> String {
        if let Some(s) = self.lookup_str(val) {
            return s;
        }
        if val.is_object() {
            let obj = unsafe { &*val.as_js_object_ptr() };
            let name_si = self.kernel_core.string_forge().intern("name").0;
            let message_si = self.kernel_core.string_forge().intern("message").0;
            let name = self
                .resolve_property(obj, name_si)
                .and_then(|v| self.lookup_str(v))
                .unwrap_or_else(|| "Error".to_string());
            let message = self
                .resolve_property(obj, message_si)
                .and_then(|v| self.lookup_str(v))
                .unwrap_or_default();
            return crate::vm::format_error_message(&name, &message);
        }
        format!("{val}")
    }

    fn convert_constant(&mut self, constant: &Constant) -> Result<JsValue, JsError> {
        match constant {
            Constant::Number(v) => Ok(JsValue::float(*v)),
            Constant::Int(v) => Ok(JsValue::int(*v)),
            Constant::String(s) => Ok(self.intern(s)),
            Constant::Boolean(b) => Ok(JsValue::bool(*b)),
            Constant::Null => Ok(JsValue::null()),
            Constant::Undefined => Ok(JsValue::undefined()),
            Constant::BytecodeFunc(idx) => {
                let sub_idx = *idx as usize;
                let (is_arrow, is_class_constructor, is_derived_constructor, needs_home_object) =
                    if sub_idx > 0 && sub_idx <= self.sub_modules.len() {
                        let sub_module = &self.sub_modules[sub_idx - 1];
                        (
                            sub_module.is_arrow,
                            sub_module.is_class_constructor,
                            sub_module.is_derived_constructor,
                            sub_module.needs_home_object,
                        )
                    } else {
                        (false, false, false, false)
                    };
                Ok(self.create_function_object(
                    *idx,
                    is_arrow,
                    is_class_constructor,
                    is_derived_constructor,
                    needs_home_object,
                ))
            }
            Constant::RegExp(pattern, flags) => {
                let pat_si = self.kernel_core.string_forge().intern(pattern).0;
                let flags_si = self.kernel_core.string_forge().intern(flags).0;
                let pat_val = JsValue::string(pat_si, 0);
                let flags_val = JsValue::string(flags_si, 0);

                let ctor_ptr = self.session.builtin_world().regexp_constructor.as_ptr() as *mut JsObject;
                let ctor = unsafe { &*ctor_ptr };
                let Some(native_fn) = ctor.native_fn() else {
                    return Err(JsError::syntax_error("RegExp constructor unavailable"));
                };

                let saved_0 = self.regs[0];
                let saved_1 = self.regs[1];
                let saved_2 = self.regs[2];
                self.regs[0] = JsValue::undefined();
                self.regs[1] = pat_val;
                self.regs[2] = flags_val;
                let func = unsafe { native_fn_ptr_to_fn(native_fn) };
                let result = func(self, &[0, 1, 2]);
                self.regs[0] = saved_0;
                self.regs[1] = saved_1;
                self.regs[2] = saved_2;
                result.map_err(|err| JsError::syntax_error(self.error_text(err)))
            }
        }
    }

    pub(crate) fn convert_constants(&mut self, constants: &[Constant]) -> Result<Vec<JsValue>, JsError> {
        let mut values = Vec::with_capacity(constants.len());
        for constant in constants {
            values.push(self.convert_constant(constant)?);
        }
        Ok(values)
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    fn global_prop(vm: &Vm, name: &str) -> JsValue {
        global_prop_opt(vm, name).expect("global slot should exist")
    }

    fn global_prop_opt(vm: &Vm, name: &str) -> Option<JsValue> {
        let global = vm.session.global_object();
        let si = vm.kernel_core.string_forge().intern(name).0;
        vm.kernel_core
            .shape_forge()
            .lookup_position(global.shape_id(), si)
            .map(|pos| global.get_prop_at(pos))
    }

    fn run_source(vm: &mut Vm, source: &str) -> JsValue {
        let allocator = oxide_parser::Allocator::default();
        let program = oxide_parser::parse(&allocator, source).expect("parse failed");
        let module = oxide_compiler::compiler::Compiler::new()
            .compile(&program)
            .expect("compile failed");
        vm.run(&module).expect("vm run failed")
    }

    #[test]
    fn full_reset_clean_keeps_session_objects() {
        let mut vm = Vm::new();
        let world_ptr = Arc::as_ptr(&vm.session.builtin_world);
        let global_ptr = vm.session.global_object.as_ptr();
        let object_proto_ptr = vm.session.builtin_world().object_proto.as_ptr();

        vm.full_reset();

        assert!(std::ptr::eq(world_ptr, Arc::as_ptr(&vm.session.builtin_world)));
        assert!(std::ptr::eq(global_ptr, vm.session.global_object.as_ptr()));
        assert!(std::ptr::eq(object_proto_ptr, vm.session.builtin_world().object_proto.as_ptr()));
        assert!(!vm.session.is_dirty_since_snapshot());
    }

    #[test]
    fn full_reset_global_dirty_rebuilds_global_and_restores_slots() {
        let mut vm = Vm::new();
        let world_ptr = Arc::as_ptr(&vm.session.builtin_world);
        let global_ptr = vm.session.global_object.as_ptr();
        let global = unsafe { &mut *(vm.session.global_object.as_ptr() as *mut JsObject) };
        bindings::bind_global_value(&vm.kernel_core, global, "userGlobal", JsValue::int(99));
        unsafe { &mut *(vm.session.global_object.as_ptr() as *mut JsObject) }.bump_generation();

        vm.full_reset();

        assert!(std::ptr::eq(world_ptr, Arc::as_ptr(&vm.session.builtin_world)));
        assert!(!std::ptr::eq(global_ptr, vm.session.global_object.as_ptr()));
        assert!(global_prop_opt(&vm, "userGlobal").is_none());
        assert!(std::ptr::eq(
            global_prop(&vm, "Array").as_js_object_ptr(),
            vm.session.builtin_world().array_constructor.as_ptr() as *mut JsObject
        ));
        assert!(std::ptr::eq(
            global_prop(&vm, "globalThis").as_js_object_ptr(),
            vm.session.global_object.as_ptr() as *mut JsObject
        ));
        assert!(!vm.session.is_dirty_since_snapshot());
    }

    #[test]
    fn full_reset_dirty_builtin_rebinds_global_slot() {
        let mut vm = Vm::new();
        let old_object_proto = vm.session.builtin_world().object_proto.as_ptr();
        let old_array_proto = vm.session.builtin_world().array_proto.as_ptr();
        unsafe { &mut *(old_array_proto as *mut JsObject) }.bump_generation();

        vm.full_reset();

        assert!(std::ptr::eq(old_object_proto, vm.session.builtin_world().object_proto.as_ptr()));
        assert!(!std::ptr::eq(old_array_proto, vm.session.builtin_world().array_proto.as_ptr()));
        assert!(std::ptr::eq(
            global_prop(&vm, "Array").as_js_object_ptr(),
            vm.session.builtin_world().array_constructor.as_ptr() as *mut JsObject
        ));
        let constructor_si = vm.kernel_core.string_forge().intern("constructor").0;
        let array_proto = &*vm.session.builtin_world().array_proto;
        let constructor = vm
            .resolve_property(array_proto, constructor_si)
            .expect("Array.prototype.constructor");
        assert!(std::ptr::eq(
            constructor.as_js_object_ptr(),
            vm.session.builtin_world().array_constructor.as_ptr() as *mut JsObject
        ));
        assert!(!vm.session.is_dirty_since_snapshot());
    }

    #[test]
    fn full_reset_dirty_function_keeps_call_working() {
        let mut vm = Vm::new();
        let function_proto = vm.session.builtin_world().function_proto.as_ptr();
        unsafe { &mut *(function_proto as *mut JsObject) }.bump_generation();

        vm.full_reset();

        let result = run_source(&mut vm, "Array.prototype.push.call([1], 2)");
        assert_eq!(result, JsValue::int(2));
        assert!(!vm.session.is_dirty_since_snapshot());
    }

    #[test]
    fn session_epoch_survives_reset() {
        let mut vm = Vm::new();
        let session_ptr = vm.session_epoch.alloc(123i32) as *mut i32;

        vm.reset();

        assert!(unsafe { *session_ptr } == 123);
    }

    #[test]
    fn session_epoch_reset_is_only_in_full_reset_state_clear() {
        let src = include_str!("vm_support.rs");
        let production = src.split("#[cfg(test)]").next().expect("production source");
        assert_eq!(production.matches("self.session_epoch.reset()").count(), 1);
        assert!(production.contains("fn clear_full_reset_state(&mut self)"));
        assert!(production.contains("self.session_epoch.reset();"));
    }

    #[test]
    fn full_reset_refreshes_object_prototype_after_object_dirty() {
        let mut vm = Vm::new();
        let old_object_proto = vm.session.builtin_world().object_proto.as_ptr();
        unsafe { &mut *(old_object_proto as *mut JsObject) }.bump_generation();

        vm.full_reset();

        assert!(!std::ptr::eq(old_object_proto, vm.session.builtin_world().object_proto.as_ptr()));
        assert!(std::ptr::eq(
            vm.object_prototype.as_ptr(),
            vm.session.builtin_world().object_proto.as_ptr()
        ));
        assert!(!vm.session.is_dirty_since_snapshot());
    }
}