use std::cell::{OnceCell, RefCell};
use std::rc::Rc;

use derive_more::Unwrap;
use hashbrown::{HashMap, HashSet};
use itertools::Itertools;
use petgraph::graph::{DiGraph, NodeIndex};

use nixjit_builtins::{
    Builtins, BuiltinsContext,
    builtins::{CONSTS_LEN, GLOBAL_LEN, SCOPED_LEN},
};
use nixjit_error::{Error, Result};
use nixjit_eval::{EvalContext, Evaluate, Value};
use nixjit_hir::{Downgrade, DowngradeContext, Hir};
use nixjit_ir::{ArgIdx, Const, ExprId, Param, PrimOp, PrimOpId};
use nixjit_lir::{Lir, LookupResult, Resolve, ResolveContext};

use nixjit_jit::{JITCompiler, JITContext, JITFunc};
use replace_with::replace_with_and_return;

enum Scope {
    With,
    Let(HashMap<String, ExprId>),
    Arg(Option<String>),
}

#[derive(Debug, Unwrap)]
enum Ir {
    Hir(Hir),
    Lir(Lir),
}

impl Ir {
    unsafe fn unwrap_hir_ref_unchecked(&self) -> &Hir {
        if let Self::Hir(hir) = self {
            hir
        } else {
            unsafe { core::hint::unreachable_unchecked() }
        }
    }

    unsafe fn unwrap_hir_mut_unchecked(&mut self) -> &mut Hir {
        #[cfg(debug_assertions)]
        if let Self::Hir(hir) = self {
            hir
        } else {
            unsafe { core::hint::unreachable_unchecked() }
        }
        #[cfg(not(debug_assertions))]
        if let Self::Hir(hir) = self {
            hir
        } else {
            unsafe { core::hint::unreachable_unchecked() }
        }
    }

    unsafe fn unwrap_hir_unchecked(self) -> Hir {
        if cfg!(debug_assertions) {
            self.unwrap_hir()
        } else if let Self::Hir(hir) = self {
            hir
        } else {
            unsafe { core::hint::unreachable_unchecked() }
        }
    }

    unsafe fn unwrap_lir_ref_unchecked(&self) -> &Lir {
        #[cfg(debug_assertions)]
        if let Self::Lir(lir) = self {
            lir
        } else {
            unsafe { core::hint::unreachable_unchecked() }
        }
        #[cfg(not(debug_assertions))]
        if let Self::Lir(lir) = self {
            lir
        } else {
            panic!()
        }
    }
}

pub struct Context {
    irs: Vec<RefCell<Ir>>,
    resolved: Vec<bool>,
    scopes: Vec<Scope>,
    args_count: usize,
    primops: Vec<fn(&mut Context, Vec<Value>) -> Result<Value>>,
    funcs: HashMap<ExprId, Param>,
    graph: DiGraph<ExprId, ()>,
    nodes: Vec<NodeIndex>,

    stack: Vec<Vec<Value>>,
    with_scopes: Vec<Rc<HashMap<String, Value>>>,

    jit: JITCompiler<Self>,
    compiled: Vec<OnceCell<JITFunc<Self>>>,
}

impl Default for Context {
    fn default() -> Self {
        let Builtins {
            consts,
            global,
            scoped,
        } = Builtins::new();
        let global_scope = Scope::Let(
            consts
                .iter()
                .enumerate()
                .map(|(id, (k, _))| (k.to_string(), unsafe { ExprId::from(id) }))
                .chain(global.iter().enumerate().map(|(idx, (k, _, _))| {
                    (k.to_string(), unsafe {
                        ExprId::from(idx + CONSTS_LEN)
                    })
                }))
                .chain(core::iter::once(("builtins".to_string(), unsafe {
                    ExprId::from(CONSTS_LEN + GLOBAL_LEN + SCOPED_LEN)
                })))
                .collect(),
        );
        let primops = global
            .iter()
            .map(|&(_, _, f)| f)
            .chain(scoped.iter().map(|&(_, _, f)| f))
            .collect();
        let irs = consts
            .into_iter()
            .map(|(_, val)| Ir::Lir(Lir::Const(Const { val })))
            .chain(
                global
                    .into_iter()
                    .enumerate()
                    .map(|(idx, (name, arity, _))| {
                        Ir::Lir(Lir::PrimOp(PrimOp {
                            name,
                            arity,
                            id: unsafe { PrimOpId::from(idx) },
                        }))
                    }),
            )
            .map(RefCell::new)
            .collect();
        Self {
            irs,
            resolved: Vec::new(),
            scopes: vec![global_scope],
            args_count: 0,
            primops,
            funcs: HashMap::new(),
            graph: DiGraph::new(),
            nodes: Vec::new(),

            stack: Vec::new(),
            with_scopes: Vec::new(),

            jit: JITCompiler::new(),
            compiled: Vec::new(),
        }
    }
}

impl Context {
    pub fn new() -> Self {
        Self::default()
    }

    pub fn eval(mut self, expr: &str) -> Result<nixjit_value::Value> {
        let root = rnix::Root::parse(expr);
        if !root.errors().is_empty() {
            return Err(Error::ParseError(
                root.errors().iter().map(|err| err.to_string()).join(";"),
            ));
        }
        let root = root.tree().expr().unwrap().downgrade(&mut self)?;
        self.resolve(&root)?;
        Ok(EvalContext::eval(&mut self, &root)?.to_public(&mut HashSet::new()))
    }
}

impl DowngradeContext for Context {
    fn new_expr(&mut self, expr: Hir) -> ExprId {
        let id = unsafe { ExprId::from(self.irs.len()) };
        self.irs.push(Ir::Hir(expr).into());
        self.nodes.push(self.graph.add_node(unsafe { id.clone() }));
        self.resolved.push(false);
        self.compiled.push(OnceCell::new());
        id
    }
    fn with_expr<T>(&self, id: ExprId, f: impl FnOnce(&Hir, &Self) -> T) -> T {
        unsafe {
            let idx = id.raw();
            f(&self.irs[idx].borrow().unwrap_hir_ref_unchecked(), self)
        }
    }
    fn with_expr_mut<T>(&mut self, id: &ExprId, f: impl FnOnce(&mut Hir, &mut Self) -> T) -> T {
        unsafe {
            let idx = id.clone().raw();
            let self_mut = &mut *(self as *mut Self);
            f(
                &mut self
                    .irs
                    .get_unchecked_mut(idx)
                    .borrow_mut()
                    .unwrap_hir_mut_unchecked(),
                self_mut,
            )
        }
    }
}

impl ResolveContext for Context {
    fn lookup(&self, name: &str) -> LookupResult {
        let mut arg_idx = 0;
        for scope in self.scopes.iter().rev() {
            match scope {
                Scope::Let(scope) => {
                    if let Some(expr) = scope.get(name) {
                        return LookupResult::Expr(unsafe { expr.clone() });
                    }
                }
                Scope::Arg(ident) => {
                    if ident.as_deref() == Some(name) {
                        return LookupResult::Arg(unsafe { ArgIdx::from(arg_idx) });
                    }
                    arg_idx += 1;
                }
                Scope::With => return LookupResult::Unknown,
            }
        }
        LookupResult::NotFound
    }

    fn new_dep(&mut self, expr: &ExprId, dep: ExprId) {
        unsafe {
            let expr = expr.clone().raw();
            let dep = dep.raw();
            let expr = *self.nodes.get_unchecked(expr);
            let dep = *self.nodes.get_unchecked(dep);
            self.graph.add_edge(expr, dep, ());
        }
    }

    fn resolve(&mut self, expr: &ExprId) -> Result<()> {
        unsafe {
            let idx = expr.clone().raw();
            let self_mut = &mut *(self as *mut Self);
            replace_with_and_return(
                &mut *self.irs.get_unchecked(idx).borrow_mut(),
                || {
                    Ir::Hir(Hir::Const(Const {
                        val: nixjit_value::Const::Null,
                    }))
                },
                |ir| {
                    let hir = ir.unwrap_hir_unchecked();
                    match hir.resolve(self_mut) {
                        Ok(lir) => (Ok(()), Ir::Lir(lir)),
                        Err(err) => (
                            Err(err),
                            Ir::Hir(Hir::Const(Const {
                                val: nixjit_value::Const::Null,
                            })),
                        ),
                    }
                },
            )?;
        }
        Ok(())
    }

    fn new_func(&mut self, body: &ExprId, param: Param) {
        self.funcs.insert(unsafe { body.clone() }, param);
    }

    fn with_let_env<'a, T>(
        &mut self,
        bindings: impl Iterator<Item = (&'a String, &'a ExprId)>,
        f: impl FnOnce(&mut Self) -> T,
    ) -> T {
        let mut scope = HashMap::new();
        for (name, expr) in bindings {
            scope.insert(name.clone(), unsafe { expr.clone() });
        }
        self.scopes.push(Scope::Let(scope));
        let res = f(self);
        self.scopes.pop();
        res
    }

    fn with_with_env<T>(&mut self, f: impl FnOnce(&mut Self) -> T) -> (bool, T) {
        self.scopes.push(Scope::With);
        let res = f(self);
        self.scopes.pop();
        (true, res)
    }

    fn with_param_env<T>(&mut self, ident: Option<String>, f: impl FnOnce(&mut Self) -> T) -> T {
        self.scopes.push(Scope::Arg(ident));
        self.args_count += 1;
        let res = f(self);
        self.args_count -= 1;
        self.scopes.pop();
        res
    }
}

impl EvalContext for Context {
    fn eval(&mut self, expr: &ExprId) -> Result<nixjit_eval::Value> {
        let idx = unsafe { expr.clone().raw() };
        let lir = unsafe {
            &*(self
                .irs
                .get_unchecked(idx)
                .borrow()
                .unwrap_lir_ref_unchecked() as *const Lir)
        };
        println!("{:#?}", self.irs);
        lir.eval(self)
    }

    fn pop_frame(&mut self) -> Vec<nixjit_eval::Value> {
        self.stack.pop().unwrap()
    }

    fn lookup_with<'a>(&'a self, ident: &str) -> Option<&'a nixjit_eval::Value> {
        for scope in self.with_scopes.iter().rev() {
            if let Some(val) = scope.get(ident) {
                return Some(val);
            }
        }
        None
    }

    fn lookup_arg<'a>(&'a self, idx: ArgIdx) -> &'a Value {
        unsafe {
            let values = self.stack.last().unwrap_unchecked();
            dbg!(values, idx);
            &values[values.len() - idx.raw() - 1]
        }
    }

    fn with_with_env<T>(
        &mut self,
        namespace: std::rc::Rc<HashMap<String, nixjit_eval::Value>>,
        f: impl FnOnce(&mut Self) -> T,
    ) -> T {
        self.with_scopes.push(namespace);
        let res = f(self);
        self.with_scopes.pop();
        res
    }

    fn with_args_env<T>(
        &mut self,
        args: Vec<nixjit_eval::Value>,
        f: impl FnOnce(&mut Self) -> T,
    ) -> (Vec<Value>, T) {
        self.stack.push(args);
        let res = f(self);
        let frame = self.stack.pop().unwrap();
        (frame, res)
    }

    fn call_primop(&mut self, id: nixjit_ir::PrimOpId, args: Vec<Value>) -> Result<Value> {
        unsafe {
            (self.primops.get_unchecked(id.raw()))(self, args)
        }
    }
}

impl JITContext for Context {
    fn lookup_arg(&self, offset: usize) -> &nixjit_eval::Value {
        let values = self.stack.last().unwrap();
        &values[values.len() - offset - 1]
    }

    fn lookup_stack(&self, offset: usize) -> &nixjit_eval::Value {
        todo!()
    }

    fn enter_with(&mut self, namespace: std::rc::Rc<HashMap<String, nixjit_eval::Value>>) {
        self.with_scopes.push(namespace);
    }

    fn exit_with(&mut self) {
        self.with_scopes.pop();
    }
}

impl BuiltinsContext for Context {}