//! FIXME: write short doc here
mod lower;

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

use hir_expand::{either::Either, HirFileId, MacroDefId, Source};
use ra_arena::{map::ArenaMap, Arena};
use ra_syntax::{ast, AstPtr};
use rustc_hash::FxHashMap;

use crate::{
    db::DefDatabase2,
    expr::{Expr, ExprId, Pat, PatId},
    nameres::CrateDefMap,
    path::Path,
    ModuleId,
};

pub struct Expander {
    crate_def_map: Arc<CrateDefMap>,
    current_file_id: HirFileId,
    module: ModuleId,
}

impl Expander {
    pub fn new(db: &impl DefDatabase2, current_file_id: HirFileId, module: ModuleId) -> Expander {
        let crate_def_map = db.crate_def_map(module.krate);
        Expander { crate_def_map, current_file_id, module }
    }

    fn resolve_path_as_macro(&self, db: &impl DefDatabase2, path: &Path) -> Option<MacroDefId> {
        self.crate_def_map.resolve_path(db, self.module.module_id, path).0.get_macros()
    }
}

/// The body of an item (function, const etc.).
#[derive(Debug, Eq, PartialEq)]
pub struct Body {
    exprs: Arena<ExprId, Expr>,
    pats: Arena<PatId, Pat>,
    /// 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.
    params: Vec<PatId>,
    /// The `ExprId` of the actual body expression.
    body_expr: ExprId,
}

pub type ExprPtr = Either<AstPtr<ast::Expr>, AstPtr<ast::RecordField>>;
pub type ExprSource = Source<ExprPtr>;

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

/// 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<ExprPtr, ExprId>,
    expr_map_back: ArenaMap<ExprId, ExprSource>,
    pat_map: FxHashMap<PatPtr, PatId>,
    pat_map_back: ArenaMap<PatId, PatSource>,
    field_map: FxHashMap<(ExprId, usize), AstPtr<ast::RecordField>>,
}

impl Body {
    pub fn new(
        db: &impl DefDatabase2,
        expander: Expander,
        params: Option<ast::ParamList>,
        body: Option<ast::Expr>,
    ) -> (Body, BodySourceMap) {
        lower::lower(db, expander, params, body)
    }

    pub fn params(&self) -> &[PatId] {
        &self.params
    }

    pub fn body_expr(&self) -> ExprId {
        self.body_expr
    }

    pub fn exprs(&self) -> impl Iterator<Item = (ExprId, &Expr)> {
        self.exprs.iter()
    }

    pub fn pats(&self) -> impl Iterator<Item = (PatId, &Pat)> {
        self.pats.iter()
    }
}

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 BodySourceMap {
    pub fn expr_syntax(&self, expr: ExprId) -> Option<ExprSource> {
        self.expr_map_back.get(expr).copied()
    }

    pub fn node_expr(&self, node: &ast::Expr) -> Option<ExprId> {
        self.expr_map.get(&Either::A(AstPtr::new(node))).cloned()
    }

    pub fn pat_syntax(&self, pat: PatId) -> Option<PatSource> {
        self.pat_map_back.get(pat).copied()
    }

    pub fn node_pat(&self, node: &ast::Pat) -> Option<PatId> {
        self.pat_map.get(&Either::A(AstPtr::new(node))).cloned()
    }

    pub fn field_syntax(&self, expr: ExprId, field: usize) -> AstPtr<ast::RecordField> {
        self.field_map[&(expr, field)]
    }
}