use std::hash::BuildHasher;

use bumpalo::Bump;
use gc_arena::{Arena, Rootable};
use ghost_cell::{GhostCell, GhostToken};
use hashbrown::{DefaultHashBuilder, HashMap, HashSet, HashTable};
use rnix::TextRange;
use string_interner::symbol::SymbolU32;
use string_interner::{DefaultStringInterner, Symbol as _};

use crate::codegen::{BytecodeContext, InstructionPtr};
use crate::disassembler::{Disassembler, DisassemblerContext};
use crate::downgrade::{Downgrade as _, DowngradeContext};
use crate::error::{Error, Result, Source};
use crate::ir::{ArgId, Ir, IrKey, IrRef, RawIrRef, StringId, ThunkId, ir_content_eq};
use crate::runtime::builtins::init_builtins;
use crate::runtime::value::StaticValue;
use crate::runtime::vm::{ForceMode, new_gc_root};
use crate::store::{DaemonStore, StoreConfig};
use crate::value::Symbol;

mod builtins;
mod stack;
pub(crate) mod value;
mod vm;
pub(crate) use builtins::{BUILTINS, BuiltinId};
use stack::Stack;
use vm::{ErrorFrame, GcRoot};

pub struct Runtime {
    // global
    sources: Vec<Source>,
    spans: Vec<(usize, TextRange)>,
    store: DaemonStore,
    strings: DefaultStringInterner,
    // FIXME: remove?
    thunk_count: usize,
    bytecode: Vec<u8>,
    pub(crate) constants: Vec<StaticValue>,
    constant_dedup: HashMap<u64, u32>,

    // downgrade
    global_env: HashMap<StringId, Ir<'static, RawIrRef<'static>>>,

    // eval
    pc: usize,
    fuel: usize,
    error_contexts: Stack<8192, ErrorFrame>,
    arena: Arena<Rootable![GcRoot<'_>]>,
    force_mode: ForceMode,
}

impl Runtime {
    const DEFAULT_FUEL_AMOUNT: usize = 2048;

    pub fn new() -> Result<Self> {
        // HACK: what the heck...
        let mut global_env = HashMap::new();
        let mut strings = DefaultStringInterner::new();
        let arena = Arena::new(|mc| {
            let (root, env) = new_gc_root(mc, &mut strings);
            global_env = env;
            root
        });

        let config = StoreConfig::from_env();
        let store = DaemonStore::connect(&config.daemon_socket)?;

        Ok(Self {
            sources: Vec::new(),
            spans: Vec::new(),
            store,
            strings,
            thunk_count: 0,
            bytecode: Vec::new(),
            constants: Vec::new(),
            constant_dedup: HashMap::new(),

            global_env,

            pc: 0,
            fuel: Self::DEFAULT_FUEL_AMOUNT,
            error_contexts: Stack::new(),
            arena,
            force_mode: ForceMode::default(),
        })
    }

    pub fn eval(&mut self, source: Source) -> Result<crate::value::Value> {
        self.do_eval(source, None, ForceMode::AsIs)
    }

    pub fn eval_shallow(&mut self, source: Source) -> Result<crate::value::Value> {
        self.do_eval(source, None, ForceMode::Shallow)
    }

    pub fn eval_deep(&mut self, source: Source) -> Result<crate::value::Value> {
        self.do_eval(source, None, ForceMode::Deep)
    }

    pub fn eval_repl(
        &mut self,
        source: Source,
        scope: &HashSet<StringId>,
    ) -> Result<crate::value::Value> {
        self.do_eval(source, Some(Scope::Repl(scope)), ForceMode::Shallow)
    }

    fn do_eval<'ctx>(
        &'ctx mut self,
        source: Source,
        extra_scope: Option<Scope<'ctx>>,
        force_mode: ForceMode,
    ) -> Result<crate::value::Value> {
        let root = self.downgrade(source, extra_scope)?;
        let ip = crate::codegen::compile_bytecode(root.as_ref(), self);
        self.run(ip, force_mode)
    }

    pub fn add_binding(
        &mut self,
        _ident: &str,
        _expr: &str,
        _scope: &mut HashSet<StringId>,
    ) -> Result<crate::value::Value> {
        todo!()
    }

    pub fn compile_bytecode(&mut self, source: Source) -> Result<InstructionPtr> {
        let root = self.downgrade(source, None)?;
        let ip = crate::codegen::compile_bytecode(root.as_ref(), self);
        Ok(ip)
    }

    pub fn disassemble_colored(&mut self, ip: InstructionPtr) -> String {
        Disassembler::new(ip, self).disassemble_colored()
    }

    pub fn disassemble(&mut self, ip: InstructionPtr) -> String {
        Disassembler::new(ip, self).disassemble()
    }

    fn downgrade_ctx<'a, 'bump, 'id>(
        &'a mut self,
        bump: &'bump Bump,
        token: GhostToken<'id>,
        extra_scope: Option<Scope<'a>>,
    ) -> DowngradeCtx<'a, 'id, 'bump> {
        let Runtime {
            global_env,
            sources,
            thunk_count,
            strings,
            ..
        } = self;
        DowngradeCtx {
            bump,
            token,
            strings,
            source: sources.last().expect("no current source").clone(),
            scopes: [Scope::Global(global_env)]
                .into_iter()
                .chain(extra_scope)
                .collect(),
            with_scope_count: 0,
            arg_count: 0,
            thunk_count,
            thunk_scopes: vec![ThunkScope::new_in(bump)],
        }
    }

    fn downgrade<'a>(
        &'a mut self,
        source: Source,
        extra_scope: Option<Scope<'a>>,
    ) -> Result<OwnedIr> {
        tracing::debug!("Parsing Nix expression");

        self.sources.push(source.clone());

        let root = rnix::Root::parse(&source.src);
        handle_parse_error(root.errors(), source).map_or(Ok(()), Err)?;

        tracing::debug!("Downgrading Nix expression");
        let expr = root
            .tree()
            .expr()
            .ok_or_else(|| Error::parse_error("unexpected EOF".into()))?;
        let bump = Bump::new();
        GhostToken::new(|token| {
            let ir = self
                .downgrade_ctx(&bump, token, extra_scope)
                .downgrade_toplevel(expr)?;
            let ir = unsafe { std::mem::transmute::<RawIrRef<'_>, RawIrRef<'static>>(ir) };
            Ok(OwnedIr { _bump: bump, ir })
        })
    }
}

fn parse_error_span(error: &rnix::ParseError) -> Option<rnix::TextRange> {
    use rnix::ParseError::*;
    match error {
        Unexpected(range)
        | UnexpectedExtra(range)
        | UnexpectedWanted(_, range, _)
        | UnexpectedDoubleBind(range)
        | DuplicatedArgs(range, _) => Some(*range),
        _ => None,
    }
}

fn handle_parse_error<'a>(
    errors: impl IntoIterator<Item = &'a rnix::ParseError>,
    source: Source,
) -> Option<Box<Error>> {
    for err in errors {
        if let Some(span) = parse_error_span(err) {
            return Some(
                Error::parse_error(err.to_string())
                    .with_source(source)
                    .with_span(span),
            );
        }
    }
    None
}

struct DowngradeCtx<'ctx, 'id, 'ir> {
    bump: &'ir Bump,
    token: GhostToken<'id>,
    strings: &'ctx mut DefaultStringInterner,
    source: Source,
    scopes: Vec<Scope<'ctx>>,
    with_scope_count: u32,
    arg_count: u32,
    thunk_count: &'ctx mut usize,
    thunk_scopes: Vec<ThunkScope<'id, 'ir>>,
}

fn should_thunk<'id>(ir: IrRef<'id, '_>, token: &GhostToken<'id>) -> bool {
    !matches!(
        ir.borrow(token),
        Ir::Builtin(_)
            | Ir::Builtins
            | Ir::Int(_)
            | Ir::Float(_)
            | Ir::Bool(_)
            | Ir::Null
            | Ir::Str(_)
            | Ir::Thunk(_)
    )
}

impl<'ctx, 'id, 'ir> DowngradeCtx<'ctx, 'id, 'ir> {
    fn new(
        bump: &'ir Bump,
        token: GhostToken<'id>,
        symbols: &'ctx mut DefaultStringInterner,
        global: &'ctx HashMap<StringId, Ir<'static, RawIrRef<'static>>>,
        extra_scope: Option<Scope<'ctx>>,
        thunk_count: &'ctx mut usize,
        source: Source,
    ) -> Self {
        Self {
            bump,
            token,
            strings: symbols,
            source,
            scopes: std::iter::once(Scope::Global(global))
                .chain(extra_scope)
                .collect(),
            thunk_count,
            arg_count: 0,
            with_scope_count: 0,
            thunk_scopes: vec![ThunkScope::new_in(bump)],
        }
    }
}

impl<'ctx: 'ir, 'id, 'ir> DowngradeContext<'id, 'ir> for DowngradeCtx<'ctx, 'id, 'ir> {
    fn new_expr(&self, expr: Ir<'ir, IrRef<'id, 'ir>>) -> IrRef<'id, 'ir> {
        IrRef::new(self.bump.alloc(GhostCell::new(expr)))
    }

    fn new_arg(&mut self) -> ArgId {
        self.arg_count += 1;
        ArgId(self.arg_count - 1)
    }

    fn maybe_thunk(&mut self, ir: IrRef<'id, 'ir>) -> IrRef<'id, 'ir> {
        if !should_thunk(ir, &self.token) {
            return ir;
        }

        let cached = self
            .thunk_scopes
            .last()
            .expect("no active cache scope")
            .lookup_cache(ir, &self.token);

        if let Some(id) = cached {
            return IrRef::alloc(self.bump, Ir::Thunk(id));
        }

        let id = ThunkId(*self.thunk_count);
        *self.thunk_count = self.thunk_count.checked_add(1).expect("thunk id overflow");
        self.thunk_scopes
            .last_mut()
            .expect("no active cache scope")
            .add_binding(id, ir, &self.token);
        IrRef::alloc(self.bump, Ir::Thunk(id))
    }

    fn new_sym(&mut self, sym: String) -> StringId {
        StringId(self.strings.get_or_intern(sym))
    }

    fn get_sym(&self, id: StringId) -> Symbol<'_> {
        self.strings.resolve(id.0).expect("no symbol found").into()
    }

    fn lookup(&self, sym: StringId, span: TextRange) -> Result<IrRef<'id, 'ir>> {
        for scope in self.scopes.iter().rev() {
            match scope {
                &Scope::Global(global_scope) => {
                    if let Some(expr) = global_scope.get(&sym) {
                        let ir = match expr {
                            Ir::Builtins => Ir::Builtins,
                            Ir::Builtin(s) => Ir::Builtin(*s),
                            Ir::Bool(b) => Ir::Bool(*b),
                            Ir::Null => Ir::Null,
                            _ => unreachable!("globals should only contain leaf IR nodes"),
                        };
                        return Ok(self.new_expr(ir));
                    }
                }
                &Scope::Repl(repl_bindings) => {
                    if repl_bindings.contains(&sym) {
                        return Ok(self.new_expr(Ir::ReplBinding(sym)));
                    }
                }
                Scope::ScopedImport(scoped_bindings) => {
                    if scoped_bindings.contains(&sym) {
                        return Ok(self.new_expr(Ir::ScopedImportBinding(sym)));
                    }
                }
                Scope::Let(let_scope) => {
                    if let Some(&expr) = let_scope.get(&sym) {
                        return Ok(self.new_expr(Ir::Thunk(expr)));
                    }
                }
                &Scope::Param(param_sym, id) => {
                    if param_sym == sym {
                        return Ok(self.new_expr(Ir::Arg(id)));
                    }
                }
            }
        }

        if self.with_scope_count > 0 {
            Ok(self.new_expr(Ir::WithLookup(sym)))
        } else {
            Err(Error::downgrade_error(
                format!("'{}' not found", self.get_sym(sym)),
                self.get_current_source(),
                span,
            ))
        }
    }

    fn get_current_source(&self) -> Source {
        self.source.clone()
    }

    fn with_let_scope<F, R>(&mut self, keys: &[StringId], f: F) -> Result<R>
    where
        F: FnOnce(&mut Self) -> Result<(bumpalo::collections::Vec<'ir, IrRef<'id, 'ir>>, R)>,
    {
        let base = *self.thunk_count;
        *self.thunk_count = self
            .thunk_count
            .checked_add(keys.len())
            .expect("thunk id overflow");
        let iter = keys.iter().enumerate().map(|(offset, &key)| {
            (
                key,
                ThunkId(unsafe { base.checked_add(offset).unwrap_unchecked() }),
            )
        });
        self.scopes.push(Scope::Let(iter.collect()));
        let (vals, ret) = {
            let mut guard = ScopeGuard { ctx: self };
            f(guard.as_ctx())?
        };
        assert_eq!(keys.len(), vals.len());
        let scope = self.thunk_scopes.last_mut().expect("no active thunk scope");
        scope.extend_bindings((base..base + keys.len()).map(ThunkId).zip(vals));
        Ok(ret)
    }

    fn with_param_scope<F, R>(&mut self, param: StringId, arg: ArgId, f: F) -> R
    where
        F: FnOnce(&mut Self) -> R,
    {
        self.scopes.push(Scope::Param(param, arg));
        let mut guard = ScopeGuard { ctx: self };
        f(guard.as_ctx())
    }

    fn with_with_scope<F, R>(&mut self, f: F) -> R
    where
        F: FnOnce(&mut Self) -> R,
    {
        self.with_scope_count += 1;
        let ret = f(self);
        self.with_scope_count -= 1;
        ret
    }

    fn with_thunk_scope<F, R>(
        &mut self,
        f: F,
    ) -> (
        R,
        bumpalo::collections::Vec<'ir, (ThunkId, IrRef<'id, 'ir>)>,
    )
    where
        F: FnOnce(&mut Self) -> R,
    {
        self.thunk_scopes.push(ThunkScope::new_in(self.bump));
        let ret = f(self);
        (
            ret,
            self.thunk_scopes
                .pop()
                .expect("no thunk scope left???")
                .bindings,
        )
    }

    fn bump(&self) -> &'ir bumpalo::Bump {
        self.bump
    }
}

impl<'id, 'ir, 'ctx: 'ir> DowngradeCtx<'ctx, 'id, 'ir> {
    fn downgrade_toplevel(mut self, root: rnix::ast::Expr) -> Result<RawIrRef<'ir>> {
        let body = root.downgrade(&mut self)?;
        let thunks = self
            .thunk_scopes
            .pop()
            .expect("no thunk scope left???")
            .bindings;
        let ir = IrRef::alloc(self.bump, Ir::TopLevel { body, thunks });
        Ok(ir.freeze(self.token))
    }
}

struct ThunkScope<'id, 'ir> {
    bindings: bumpalo::collections::Vec<'ir, (ThunkId, IrRef<'id, 'ir>)>,
    cache: HashTable<(IrRef<'id, 'ir>, ThunkId)>,
    hasher: DefaultHashBuilder,
}

impl<'id, 'ir> ThunkScope<'id, 'ir> {
    fn new_in(bump: &'ir Bump) -> Self {
        Self {
            bindings: bumpalo::collections::Vec::new_in(bump),
            cache: HashTable::new(),
            hasher: DefaultHashBuilder::default(),
        }
    }

    fn lookup_cache(&self, key: IrRef<'id, 'ir>, token: &GhostToken<'id>) -> Option<ThunkId> {
        let hash = self.hasher.hash_one(IrKey(key, token));
        self.cache
            .find(hash, |&(ir, _)| ir_content_eq(key, ir, token))
            .map(|&(_, id)| id)
    }

    fn add_binding(&mut self, id: ThunkId, ir: IrRef<'id, 'ir>, token: &GhostToken<'id>) {
        self.bindings.push((id, ir));
        let hash = self.hasher.hash_one(IrKey(ir, token));
        self.cache.insert_unique(hash, (ir, id), |&(ir, _)| {
            self.hasher.hash_one(IrKey(ir, token))
        });
    }

    fn extend_bindings(&mut self, iter: impl IntoIterator<Item = (ThunkId, IrRef<'id, 'ir>)>) {
        self.bindings.extend(iter);
    }
}

enum Scope<'ctx> {
    Global(&'ctx HashMap<StringId, Ir<'static, RawIrRef<'static>>>),
    Repl(&'ctx HashSet<StringId>),
    ScopedImport(HashSet<StringId>),
    Let(HashMap<StringId, ThunkId>),
    Param(StringId, ArgId),
}

struct ScopeGuard<'a, 'ctx, 'id, 'ir> {
    ctx: &'a mut DowngradeCtx<'ctx, 'id, 'ir>,
}

impl Drop for ScopeGuard<'_, '_, '_, '_> {
    fn drop(&mut self) {
        self.ctx.scopes.pop();
    }
}

impl<'id, 'ir, 'ctx> ScopeGuard<'_, 'ctx, 'id, 'ir> {
    fn as_ctx(&mut self) -> &mut DowngradeCtx<'ctx, 'id, 'ir> {
        self.ctx
    }
}

struct OwnedIr {
    _bump: Bump,
    ir: RawIrRef<'static>,
}

impl OwnedIr {
    unsafe fn new(ir: RawIrRef<'_>, bump: Bump) -> Self {
        Self {
            _bump: bump,
            ir: unsafe { std::mem::transmute::<RawIrRef<'_>, RawIrRef<'static>>(ir) },
        }
    }

    fn as_ref(&self) -> RawIrRef<'_> {
        self.ir
    }
}

impl BytecodeContext for Runtime {
    fn intern_string(&mut self, s: &str) -> StringId {
        StringId(self.strings.get_or_intern(s))
    }

    fn register_span(&mut self, range: TextRange) -> u32 {
        let id = self.spans.len();
        let source_id = self
            .sources
            .len()
            .checked_sub(1)
            .expect("current_source not set");
        self.spans.push((source_id, range));
        id as u32
    }

    fn get_code(&self) -> &[u8] {
        &self.bytecode
    }

    fn get_code_mut(&mut self) -> &mut Vec<u8> {
        &mut self.bytecode
    }

    fn add_constant(&mut self, val: StaticValue) -> u32 {
        let bits = val.to_bits();
        *self.constant_dedup.entry(bits).or_insert_with(|| {
            let idx = self.constants.len() as u32;
            self.constants.push(val);
            idx
        })
    }
}

impl DisassemblerContext for Runtime {
    fn lookup_string(&self, id: u32) -> &str {
        self.strings
            .resolve(SymbolU32::try_from_usize(id as usize).expect("invalid string id"))
            .expect("string not found")
    }
    fn get_code(&self) -> &[u8] {
        &self.bytecode
    }
}

struct WellKnownSymbols {
    // TODO:
}