use rustc_hir::{Expr, ExprKind};
use rustc_span::sym;

use crate::LateContext;

/// Given an expression, peel all of casts (`<expr> as ...`, `<expr>.cast{,_mut,_const}()`,
/// `ptr::from_ref(<expr>)`, ...) and init expressions.
///
/// Returns the innermost expression and a boolean representing if one of the casts was
/// `UnsafeCell::raw_get(<expr>)`
pub(crate) fn peel_casts<'tcx>(
    cx: &LateContext<'tcx>,
    mut e: &'tcx Expr<'tcx>,
) -> (&'tcx Expr<'tcx>, bool) {
    let mut gone_trough_unsafe_cell_raw_get = false;

    loop {
        e = e.peel_blocks();
        // <expr> as ...
        e = if let ExprKind::Cast(expr, _) = e.kind {
            expr
        // <expr>.cast(), <expr>.cast_mut() or <expr>.cast_const()
        } else if let ExprKind::MethodCall(_, expr, [], _) = e.kind
            && let Some(def_id) = cx.typeck_results().type_dependent_def_id(e.hir_id)
            && matches!(
                cx.tcx.get_diagnostic_name(def_id),
                Some(sym::ptr_cast | sym::const_ptr_cast | sym::ptr_cast_mut | sym::ptr_cast_const)
            )
        {
            expr
        // ptr::from_ref(<expr>), UnsafeCell::raw_get(<expr>) or mem::transmute<_, _>(<expr>)
        } else if let ExprKind::Call(path, [arg]) = e.kind
            && let ExprKind::Path(ref qpath) = path.kind
            && let Some(def_id) = cx.qpath_res(qpath, path.hir_id).opt_def_id()
            && matches!(
                cx.tcx.get_diagnostic_name(def_id),
                Some(sym::ptr_from_ref | sym::unsafe_cell_raw_get | sym::transmute)
            )
        {
            if cx.tcx.is_diagnostic_item(sym::unsafe_cell_raw_get, def_id) {
                gone_trough_unsafe_cell_raw_get = true;
            }
            arg
        } else {
            let init = cx.expr_or_init(e);
            if init.hir_id != e.hir_id {
                init
            } else {
                break;
            }
        };
    }

    (e, gone_trough_unsafe_cell_raw_get)
}