use crate::utils::{match_def_path, paths, qpath_res, span_lint};
use if_chain::if_chain;
use rustc::hir::{Expr, ExprKind, Item, ItemKind, Node};
use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
use rustc::{declare_lint_pass, declare_tool_lint};

declare_clippy_lint! {
    /// **What it does:** `exit()`  terminates the program and doesn't provide a
    /// stack trace.
    ///
    /// **Why is this bad?** Ideally a program is terminated by finishing
    /// the main function.
    ///
    /// **Known problems:** None.
    ///
    /// **Example:**
    /// ```ignore
    /// std::process::exit(0)
    /// ```
    pub EXIT,
    restriction,
    "`std::process::exit` is called, terminating the program"
}

declare_lint_pass!(Exit => [EXIT]);

impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Exit {
    fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx Expr) {
        if_chain! {
            if let ExprKind::Call(ref path_expr, ref _args) = e.kind;
            if let ExprKind::Path(ref path) = path_expr.kind;
            if let Some(def_id) = qpath_res(cx, path, path_expr.hir_id).opt_def_id();
            if match_def_path(cx, def_id, &paths::EXIT);
            then {
                let mut parent = cx.tcx.hir().get_parent_item(e.hir_id);
                // We have to traverse the parents upwards until we find a function
                // otherwise a exit in a let or if in main would still trigger this
                loop{
                    match cx.tcx.hir().find(parent) {
                        Some(Node::Item(Item{ident, kind: ItemKind::Fn(..), ..})) => {
                            // If we found a function we check it's name if it is
                            // `main` we emit a lint.
                            if ident.name.as_str() != "main" {
                                span_lint(cx, EXIT, e.span, "usage of `process::exit`");
                            }
                            // We found any kind of function and can end our loop
                            break;
                        }
                        // If we found anything but a funciton we continue with the
                        // loop and go one parent up
                        Some(_) => {
                            cx.tcx.hir().get_parent_item(parent);
                        },
                        // If we found nothing we break.
                        None => break,
                    }
                }
            }

        }
    }
}