//! Defines `Body`: a lowered representation of bodies of functions, statics and
//! consts.
mod lower;
#[cfg(test)]
mod tests;
pub mod scope;
mod pretty;

use std::{ops::Index, sync::Arc};

use base_db::CrateId;
use cfg::{CfgExpr, CfgOptions};
use drop_bomb::DropBomb;
use either::Either;
use hir_expand::{
    ast_id_map::AstIdMap, attrs::RawAttrs, hygiene::Hygiene, name::Name, AstId, ExpandError,
    ExpandResult, HirFileId, InFile, MacroCallId,
};
use la_arena::{Arena, ArenaMap};
use limit::Limit;
use once_cell::unsync::OnceCell;
use profile::Count;
use rustc_hash::FxHashMap;
use syntax::{ast, AstPtr, Parse, SyntaxNode, SyntaxNodePtr};

use crate::{
    attr::Attrs,
    db::DefDatabase,
    hir::{
        dummy_expr_id, Binding, BindingId, Expr, ExprId, Label, LabelId, Pat, PatId, RecordFieldPat,
    },
    item_scope::BuiltinShadowMode,
    macro_id_to_def_id,
    nameres::DefMap,
    path::{ModPath, Path},
    src::{HasChildSource, HasSource},
    AsMacroCall, BlockId, DefWithBodyId, HasModule, LocalModuleId, Lookup, MacroId, ModuleId,
    UnresolvedMacro,
};

pub struct LowerCtx<'a> {
    pub db: &'a dyn DefDatabase,
    hygiene: Hygiene,
    ast_id_map: Option<(HirFileId, OnceCell<Arc<AstIdMap>>)>,
}

impl<'a> LowerCtx<'a> {
    pub fn new(db: &'a dyn DefDatabase, hygiene: &Hygiene, file_id: HirFileId) -> Self {
        LowerCtx { db, hygiene: hygiene.clone(), ast_id_map: Some((file_id, OnceCell::new())) }
    }

    pub fn with_file_id(db: &'a dyn DefDatabase, file_id: HirFileId) -> Self {
        LowerCtx {
            db,
            hygiene: Hygiene::new(db.upcast(), file_id),
            ast_id_map: Some((file_id, OnceCell::new())),
        }
    }

    pub fn with_hygiene(db: &'a dyn DefDatabase, hygiene: &Hygiene) -> Self {
        LowerCtx { db, hygiene: hygiene.clone(), ast_id_map: None }
    }

    pub(crate) fn hygiene(&self) -> &Hygiene {
        &self.hygiene
    }

    pub(crate) fn lower_path(&self, ast: ast::Path) -> Option<Path> {
        Path::from_src(ast, self)
    }

    pub(crate) fn ast_id<N: syntax::AstNode>(&self, item: &N) -> Option<AstId<N>> {
        let &(file_id, ref ast_id_map) = self.ast_id_map.as_ref()?;
        let ast_id_map = ast_id_map.get_or_init(|| self.db.ast_id_map(file_id));
        Some(InFile::new(file_id, ast_id_map.ast_id(item)))
    }
}

/// A subset of Expander that only deals with cfg attributes. We only need it to
/// avoid cyclic queries in crate def map during enum processing.
#[derive(Debug)]
pub(crate) struct CfgExpander {
    cfg_options: CfgOptions,
    hygiene: Hygiene,
    krate: CrateId,
}

#[derive(Debug)]
pub struct Expander {
    cfg_expander: CfgExpander,
    def_map: Arc<DefMap>,
    current_file_id: HirFileId,
    module: LocalModuleId,
    /// `recursion_depth == usize::MAX` indicates that the recursion limit has been reached.
    recursion_depth: usize,
}

impl CfgExpander {
    pub(crate) fn new(
        db: &dyn DefDatabase,
        current_file_id: HirFileId,
        krate: CrateId,
    ) -> CfgExpander {
        let hygiene = Hygiene::new(db.upcast(), current_file_id);
        let cfg_options = db.crate_graph()[krate].cfg_options.clone();
        CfgExpander { cfg_options, hygiene, krate }
    }

    pub(crate) fn parse_attrs(&self, db: &dyn DefDatabase, owner: &dyn ast::HasAttrs) -> Attrs {
        Attrs::filter(db, self.krate, RawAttrs::new(db.upcast(), owner, &self.hygiene))
    }

    pub(crate) fn is_cfg_enabled(&self, db: &dyn DefDatabase, owner: &dyn ast::HasAttrs) -> bool {
        let attrs = self.parse_attrs(db, owner);
        attrs.is_cfg_enabled(&self.cfg_options)
    }

    pub(crate) fn hygiene(&self) -> &Hygiene {
        &self.hygiene
    }
}

impl Expander {
    pub fn new(db: &dyn DefDatabase, current_file_id: HirFileId, module: ModuleId) -> Expander {
        let cfg_expander = CfgExpander::new(db, current_file_id, module.krate);
        let def_map = module.def_map(db);
        Expander {
            cfg_expander,
            def_map,
            current_file_id,
            module: module.local_id,
            recursion_depth: 0,
        }
    }

    pub fn enter_expand<T: ast::AstNode>(
        &mut self,
        db: &dyn DefDatabase,
        macro_call: ast::MacroCall,
    ) -> Result<ExpandResult<Option<(Mark, Parse<T>)>>, UnresolvedMacro> {
        // FIXME: within_limit should support this, instead of us having to extract the error
        let mut unresolved_macro_err = None;

        let result = self.within_limit(db, |this| {
            let macro_call = InFile::new(this.current_file_id, &macro_call);

            let resolver =
                |path| this.resolve_path_as_macro(db, &path).map(|it| macro_id_to_def_id(db, it));

            match macro_call.as_call_id_with_errors(db, this.def_map.krate(), resolver) {
                Ok(call_id) => call_id,
                Err(resolve_err) => {
                    unresolved_macro_err = Some(resolve_err);
                    ExpandResult { value: None, err: None }
                }
            }
        });

        if let Some(err) = unresolved_macro_err {
            Err(err)
        } else {
            Ok(result)
        }
    }

    pub fn enter_expand_id<T: ast::AstNode>(
        &mut self,
        db: &dyn DefDatabase,
        call_id: MacroCallId,
    ) -> ExpandResult<Option<(Mark, Parse<T>)>> {
        self.within_limit(db, |_this| ExpandResult::ok(Some(call_id)))
    }

    fn enter_expand_inner(
        db: &dyn DefDatabase,
        call_id: MacroCallId,
        mut error: Option<ExpandError>,
    ) -> ExpandResult<Option<InFile<Parse<SyntaxNode>>>> {
        let file_id = call_id.as_file();
        let ExpandResult { value, err } = db.parse_or_expand_with_err(file_id);

        if error.is_none() {
            error = err;
        }

        let parse = match value {
            Some(it) => it,
            None => {
                // Only `None` if the macro expansion produced no usable AST.
                if error.is_none() {
                    tracing::warn!("no error despite `parse_or_expand` failing");
                }

                return ExpandResult::only_err(error.unwrap_or_else(|| {
                    ExpandError::Other("failed to parse macro invocation".into())
                }));
            }
        };

        ExpandResult { value: Some(InFile::new(file_id, parse)), err: error }
    }

    pub fn exit(&mut self, db: &dyn DefDatabase, mut mark: Mark) {
        self.cfg_expander.hygiene = Hygiene::new(db.upcast(), mark.file_id);
        self.current_file_id = mark.file_id;
        if self.recursion_depth == usize::MAX {
            // Recursion limit has been reached somewhere in the macro expansion tree. Reset the
            // depth only when we get out of the tree.
            if !self.current_file_id.is_macro() {
                self.recursion_depth = 0;
            }
        } else {
            self.recursion_depth -= 1;
        }
        mark.bomb.defuse();
    }

    pub fn ctx<'a>(&self, db: &'a dyn DefDatabase) -> LowerCtx<'a> {
        LowerCtx::new(db, &self.cfg_expander.hygiene, self.current_file_id)
    }

    pub(crate) fn to_source<T>(&self, value: T) -> InFile<T> {
        InFile { file_id: self.current_file_id, value }
    }

    pub(crate) fn parse_attrs(&self, db: &dyn DefDatabase, owner: &dyn ast::HasAttrs) -> Attrs {
        self.cfg_expander.parse_attrs(db, owner)
    }

    pub(crate) fn cfg_options(&self) -> &CfgOptions {
        &self.cfg_expander.cfg_options
    }

    pub fn current_file_id(&self) -> HirFileId {
        self.current_file_id
    }

    fn parse_path(&mut self, db: &dyn DefDatabase, path: ast::Path) -> Option<Path> {
        let ctx = LowerCtx::with_hygiene(db, &self.cfg_expander.hygiene);
        Path::from_src(path, &ctx)
    }

    fn resolve_path_as_macro(&self, db: &dyn DefDatabase, path: &ModPath) -> Option<MacroId> {
        self.def_map.resolve_path(db, self.module, path, BuiltinShadowMode::Other).0.take_macros()
    }

    fn recursion_limit(&self, db: &dyn DefDatabase) -> Limit {
        let limit = db.crate_limits(self.cfg_expander.krate).recursion_limit as _;

        #[cfg(not(test))]
        return Limit::new(limit);

        // Without this, `body::tests::your_stack_belongs_to_me` stack-overflows in debug
        #[cfg(test)]
        return Limit::new(std::cmp::min(32, limit));
    }

    fn within_limit<F, T: ast::AstNode>(
        &mut self,
        db: &dyn DefDatabase,
        op: F,
    ) -> ExpandResult<Option<(Mark, Parse<T>)>>
    where
        F: FnOnce(&mut Self) -> ExpandResult<Option<MacroCallId>>,
    {
        if self.recursion_depth == usize::MAX {
            // Recursion limit has been reached somewhere in the macro expansion tree. We should
            // stop expanding other macro calls in this tree, or else this may result in
            // exponential number of macro expansions, leading to a hang.
            //
            // The overflow error should have been reported when it occurred (see the next branch),
            // so don't return overflow error here to avoid diagnostics duplication.
            cov_mark::hit!(overflow_but_not_me);
            return ExpandResult::only_err(ExpandError::RecursionOverflowPoisoned);
        } else if self.recursion_limit(db).check(self.recursion_depth + 1).is_err() {
            self.recursion_depth = usize::MAX;
            cov_mark::hit!(your_stack_belongs_to_me);
            return ExpandResult::only_err(ExpandError::Other(
                "reached recursion limit during macro expansion".into(),
            ));
        }

        let ExpandResult { value, err } = op(self);
        let Some(call_id) = value else {
            return ExpandResult { value: None, err };
        };

        Self::enter_expand_inner(db, call_id, err).map(|value| {
            value.and_then(|InFile { file_id, value }| {
                let parse = value.cast::<T>()?;

                self.recursion_depth += 1;
                self.cfg_expander.hygiene = Hygiene::new(db.upcast(), file_id);
                let old_file_id = std::mem::replace(&mut self.current_file_id, file_id);
                let mark =
                    Mark { file_id: old_file_id, bomb: DropBomb::new("expansion mark dropped") };
                Some((mark, parse))
            })
        })
    }
}

#[derive(Debug)]
pub struct Mark {
    file_id: HirFileId,
    bomb: DropBomb,
}

/// The body of an item (function, const etc.).
#[derive(Debug, Eq, PartialEq)]
pub struct Body {
    pub exprs: Arena<Expr>,
    pub pats: Arena<Pat>,
    pub bindings: Arena<Binding>,
    pub labels: Arena<Label>,
    /// The patterns for the function's parameters. While the parameter types are
    /// part of the function signature, the patterns are not (they don't change
    /// the external type of the function).
    ///
    /// If this `Body` is for the body of a constant, this will just be
    /// empty.
    pub params: Vec<PatId>,
    /// The `ExprId` of the actual body expression.
    pub body_expr: ExprId,
    /// Block expressions in this body that may contain inner items.
    block_scopes: Vec<BlockId>,
    _c: Count<Self>,
}

pub type ExprPtr = AstPtr<ast::Expr>;
pub type ExprSource = InFile<ExprPtr>;

pub type PatPtr = Either<AstPtr<ast::Pat>, AstPtr<ast::SelfParam>>;
pub type PatSource = InFile<PatPtr>;

pub type LabelPtr = AstPtr<ast::Label>;
pub type LabelSource = InFile<LabelPtr>;

pub type FieldPtr = AstPtr<ast::RecordExprField>;
pub type FieldSource = InFile<FieldPtr>;

/// An item body together with the mapping from syntax nodes to HIR expression
/// IDs. This is needed to go from e.g. a position in a file to the HIR
/// expression containing it; but for type inference etc., we want to operate on
/// a structure that is agnostic to the actual positions of expressions in the
/// file, so that we don't recompute types whenever some whitespace is typed.
///
/// One complication here is that, due to macro expansion, a single `Body` might
/// be spread across several files. So, for each ExprId and PatId, we record
/// both the HirFileId and the position inside the file. However, we only store
/// AST -> ExprId mapping for non-macro files, as it is not clear how to handle
/// this properly for macros.
#[derive(Default, Debug, Eq, PartialEq)]
pub struct BodySourceMap {
    expr_map: FxHashMap<ExprSource, ExprId>,
    expr_map_back: ArenaMap<ExprId, ExprSource>,

    pat_map: FxHashMap<PatSource, PatId>,
    pat_map_back: ArenaMap<PatId, PatSource>,

    label_map: FxHashMap<LabelSource, LabelId>,
    label_map_back: ArenaMap<LabelId, LabelSource>,

    /// We don't create explicit nodes for record fields (`S { record_field: 92 }`).
    /// Instead, we use id of expression (`92`) to identify the field.
    field_map: FxHashMap<FieldSource, ExprId>,
    field_map_back: FxHashMap<ExprId, FieldSource>,

    expansions: FxHashMap<InFile<AstPtr<ast::MacroCall>>, HirFileId>,

    /// Diagnostics accumulated during body lowering. These contain `AstPtr`s and so are stored in
    /// the source map (since they're just as volatile).
    diagnostics: Vec<BodyDiagnostic>,
}

#[derive(Default, Debug, Eq, PartialEq, Clone, Copy)]
pub struct SyntheticSyntax;

#[derive(Debug, Eq, PartialEq)]
pub enum BodyDiagnostic {
    InactiveCode { node: InFile<SyntaxNodePtr>, cfg: CfgExpr, opts: CfgOptions },
    MacroError { node: InFile<AstPtr<ast::MacroCall>>, message: String },
    UnresolvedProcMacro { node: InFile<AstPtr<ast::MacroCall>>, krate: CrateId },
    UnresolvedMacroCall { node: InFile<AstPtr<ast::MacroCall>>, path: ModPath },
    UnreachableLabel { node: InFile<AstPtr<ast::Lifetime>>, name: Name },
    UndeclaredLabel { node: InFile<AstPtr<ast::Lifetime>>, name: Name },
}

impl Body {
    pub(crate) fn body_with_source_map_query(
        db: &dyn DefDatabase,
        def: DefWithBodyId,
    ) -> (Arc<Body>, Arc<BodySourceMap>) {
        let _p = profile::span("body_with_source_map_query");
        let mut params = None;

        let (file_id, module, body, is_async_fn) = match def {
            DefWithBodyId::FunctionId(f) => {
                let data = db.function_data(f);
                let f = f.lookup(db);
                let src = f.source(db);
                params = src.value.param_list().map(|param_list| {
                    let item_tree = f.id.item_tree(db);
                    let func = &item_tree[f.id.value];
                    let krate = f.container.module(db).krate;
                    let crate_graph = db.crate_graph();
                    (
                        param_list,
                        func.params.clone().map(move |param| {
                            item_tree
                                .attrs(db, krate, param.into())
                                .is_cfg_enabled(&crate_graph[krate].cfg_options)
                        }),
                    )
                });
                (
                    src.file_id,
                    f.module(db),
                    src.value.body().map(ast::Expr::from),
                    data.has_async_kw(),
                )
            }
            DefWithBodyId::ConstId(c) => {
                let c = c.lookup(db);
                let src = c.source(db);
                (src.file_id, c.module(db), src.value.body(), false)
            }
            DefWithBodyId::StaticId(s) => {
                let s = s.lookup(db);
                let src = s.source(db);
                (src.file_id, s.module(db), src.value.body(), false)
            }
            DefWithBodyId::VariantId(v) => {
                let e = v.parent.lookup(db);
                let src = v.parent.child_source(db);
                let variant = &src.value[v.local_id];
                (src.file_id, e.container, variant.expr(), false)
            }
        };
        let expander = Expander::new(db, file_id, module);
        let (mut body, source_map) =
            Body::new(db, expander, params, body, module.krate, is_async_fn);
        body.shrink_to_fit();

        (Arc::new(body), Arc::new(source_map))
    }

    pub(crate) fn body_query(db: &dyn DefDatabase, def: DefWithBodyId) -> Arc<Body> {
        db.body_with_source_map(def).0
    }

    /// Returns an iterator over all block expressions in this body that define inner items.
    pub fn blocks<'a>(
        &'a self,
        db: &'a dyn DefDatabase,
    ) -> impl Iterator<Item = (BlockId, Arc<DefMap>)> + '_ {
        self.block_scopes.iter().map(move |&block| (block, db.block_def_map(block)))
    }

    pub fn pretty_print(&self, db: &dyn DefDatabase, owner: DefWithBodyId) -> String {
        pretty::print_body_hir(db, self, owner)
    }

    fn new(
        db: &dyn DefDatabase,
        expander: Expander,
        params: Option<(ast::ParamList, impl Iterator<Item = bool>)>,
        body: Option<ast::Expr>,
        krate: CrateId,
        is_async_fn: bool,
    ) -> (Body, BodySourceMap) {
        lower::lower(db, expander, params, body, krate, is_async_fn)
    }

    fn shrink_to_fit(&mut self) {
        let Self { _c: _, body_expr: _, block_scopes, exprs, labels, params, pats, bindings } =
            self;
        block_scopes.shrink_to_fit();
        exprs.shrink_to_fit();
        labels.shrink_to_fit();
        params.shrink_to_fit();
        pats.shrink_to_fit();
        bindings.shrink_to_fit();
    }

    pub fn walk_bindings_in_pat(&self, pat_id: PatId, mut f: impl FnMut(BindingId)) {
        self.walk_pats(pat_id, &mut |pat| {
            if let Pat::Bind { id, .. } = pat {
                f(*id);
            }
        });
    }

    pub fn walk_pats(&self, pat_id: PatId, f: &mut impl FnMut(&Pat)) {
        let pat = &self[pat_id];
        f(pat);
        match pat {
            Pat::Range { .. }
            | Pat::Lit(..)
            | Pat::Path(..)
            | Pat::ConstBlock(..)
            | Pat::Wild
            | Pat::Missing => {}
            &Pat::Bind { subpat, .. } => {
                if let Some(subpat) = subpat {
                    self.walk_pats(subpat, f);
                }
            }
            Pat::Or(args) | Pat::Tuple { args, .. } | Pat::TupleStruct { args, .. } => {
                args.iter().copied().for_each(|p| self.walk_pats(p, f));
            }
            Pat::Ref { pat, .. } => self.walk_pats(*pat, f),
            Pat::Slice { prefix, slice, suffix } => {
                let total_iter = prefix.iter().chain(slice.iter()).chain(suffix.iter());
                total_iter.copied().for_each(|p| self.walk_pats(p, f));
            }
            Pat::Record { args, .. } => {
                args.iter().for_each(|RecordFieldPat { pat, .. }| self.walk_pats(*pat, f));
            }
            Pat::Box { inner } => self.walk_pats(*inner, f),
        }
    }
}

impl Default for Body {
    fn default() -> Self {
        Self {
            body_expr: dummy_expr_id(),
            exprs: Default::default(),
            pats: Default::default(),
            bindings: Default::default(),
            labels: Default::default(),
            params: Default::default(),
            block_scopes: Default::default(),
            _c: Default::default(),
        }
    }
}

impl Index<ExprId> for Body {
    type Output = Expr;

    fn index(&self, expr: ExprId) -> &Expr {
        &self.exprs[expr]
    }
}

impl Index<PatId> for Body {
    type Output = Pat;

    fn index(&self, pat: PatId) -> &Pat {
        &self.pats[pat]
    }
}

impl Index<LabelId> for Body {
    type Output = Label;

    fn index(&self, label: LabelId) -> &Label {
        &self.labels[label]
    }
}

impl Index<BindingId> for Body {
    type Output = Binding;

    fn index(&self, b: BindingId) -> &Binding {
        &self.bindings[b]
    }
}

// FIXME: Change `node_` prefix to something more reasonable.
// Perhaps `expr_syntax` and `expr_id`?
impl BodySourceMap {
    pub fn expr_syntax(&self, expr: ExprId) -> Result<ExprSource, SyntheticSyntax> {
        self.expr_map_back.get(expr).cloned().ok_or(SyntheticSyntax)
    }

    pub fn node_expr(&self, node: InFile<&ast::Expr>) -> Option<ExprId> {
        let src = node.map(AstPtr::new);
        self.expr_map.get(&src).cloned()
    }

    pub fn node_macro_file(&self, node: InFile<&ast::MacroCall>) -> Option<HirFileId> {
        let src = node.map(AstPtr::new);
        self.expansions.get(&src).cloned()
    }

    pub fn pat_syntax(&self, pat: PatId) -> Result<PatSource, SyntheticSyntax> {
        self.pat_map_back.get(pat).cloned().ok_or(SyntheticSyntax)
    }

    pub fn node_pat(&self, node: InFile<&ast::Pat>) -> Option<PatId> {
        let src = node.map(|it| Either::Left(AstPtr::new(it)));
        self.pat_map.get(&src).cloned()
    }

    pub fn node_self_param(&self, node: InFile<&ast::SelfParam>) -> Option<PatId> {
        let src = node.map(|it| Either::Right(AstPtr::new(it)));
        self.pat_map.get(&src).cloned()
    }

    pub fn label_syntax(&self, label: LabelId) -> LabelSource {
        self.label_map_back[label].clone()
    }

    pub fn node_label(&self, node: InFile<&ast::Label>) -> Option<LabelId> {
        let src = node.map(AstPtr::new);
        self.label_map.get(&src).cloned()
    }

    pub fn field_syntax(&self, expr: ExprId) -> FieldSource {
        self.field_map_back[&expr].clone()
    }

    pub fn node_field(&self, node: InFile<&ast::RecordExprField>) -> Option<ExprId> {
        let src = node.map(AstPtr::new);
        self.field_map.get(&src).cloned()
    }

    pub fn macro_expansion_expr(&self, node: InFile<&ast::MacroExpr>) -> Option<ExprId> {
        let src = node.map(AstPtr::new).map(AstPtr::upcast::<ast::MacroExpr>).map(AstPtr::upcast);
        self.expr_map.get(&src).copied()
    }

    /// Get a reference to the body source map's diagnostics.
    pub fn diagnostics(&self) -> &[BodyDiagnostic] {
        &self.diagnostics
    }
}