use clippy_utils::diagnostics::span_lint;
use clippy_utils::higher::ForLoop;
use clippy_utils::res::MaybeDef;
use rustc_lint::{LateContext, LateLintPass};
use rustc_session::declare_lint_pass;
use rustc_span::sym;

declare_clippy_lint! {
    /// ### What it does
    /// This is a restriction lint which prevents the use of hash types (i.e., `HashSet` and `HashMap`) in for loops.
    ///
    /// ### Why restrict this?
    /// Because hash types are unordered, when iterated through such as in a `for` loop, the values are returned in
    /// an undefined order. As a result, on redundant systems this may cause inconsistencies and anomalies.
    /// In addition, the unknown order of the elements may reduce readability or introduce other undesired
    /// side effects.
    ///
    /// ### Example
    /// ```no_run
    ///     let my_map = std::collections::HashMap::<i32, String>::new();
    ///     for (key, value) in my_map { /* ... */ }
    /// ```
    /// Use instead:
    /// ```no_run
    ///     let my_map = std::collections::HashMap::<i32, String>::new();
    ///     let mut keys = my_map.keys().clone().collect::<Vec<_>>();
    ///     keys.sort();
    ///     for key in keys {
    ///         let value = &my_map[key];
    ///     }
    /// ```
    #[clippy::version = "1.76.0"]
    pub ITER_OVER_HASH_TYPE,
    restriction,
    "iterating over unordered hash-based types (`HashMap` and `HashSet`)"
}

declare_lint_pass!(IterOverHashType => [ITER_OVER_HASH_TYPE]);

impl LateLintPass<'_> for IterOverHashType {
    fn check_expr(&mut self, cx: &LateContext<'_>, expr: &'_ rustc_hir::Expr<'_>) {
        let hash_iter_tys = [
            sym::HashMap,
            sym::HashSet,
            sym::hashmap_keys_ty,
            sym::hashmap_values_ty,
            sym::hashmap_values_mut_ty,
            sym::hashmap_iter_ty,
            sym::hashmap_iter_mut_ty,
            sym::hashmap_drain_ty,
            sym::hashset_iter_ty,
            sym::hashset_drain_ty,
        ];

        if let Some(for_loop) = ForLoop::hir(expr)
            && !for_loop.body.span.from_expansion()
            && let ty = cx.typeck_results().expr_ty(for_loop.arg).peel_refs()
            && hash_iter_tys.into_iter().any(|sym| ty.is_diag_item(cx, sym))
        {
            span_lint(
                cx,
                ITER_OVER_HASH_TYPE,
                expr.span,
                "iteration over unordered hash-based type",
            );
        }
    }
}
