use crate::utils::SpanlessEq;
use crate::utils::{get_item_name, higher, is_type_diagnostic_item, match_type, paths, snippet, snippet_opt};
use crate::utils::{snippet_with_applicability, span_lint_and_then};
use if_chain::if_chain;
use rustc_errors::Applicability;
use rustc_hir::intravisit::{walk_expr, NestedVisitorMap, Visitor};
use rustc_hir::{BorrowKind, Expr, ExprKind, UnOp};
use rustc_lint::{LateContext, LateLintPass};
use rustc_middle::hir::map::Map;
use rustc_session::{declare_lint_pass, declare_tool_lint};
use rustc_span::source_map::Span;

declare_clippy_lint! {
    /// **What it does:** Checks for uses of `contains_key` + `insert` on `HashMap`
    /// or `BTreeMap`.
    ///
    /// **Why is this bad?** Using `entry` is more efficient.
    ///
    /// **Known problems:** Some false negatives, eg.:
    /// ```rust
    /// # use std::collections::HashMap;
    /// # let mut map = HashMap::new();
    /// # let v = 1;
    /// # let k = 1;
    /// if !map.contains_key(&k) {
    ///     map.insert(k.clone(), v);
    /// }
    /// ```
    ///
    /// **Example:**
    /// ```rust
    /// # use std::collections::HashMap;
    /// # let mut map = HashMap::new();
    /// # let k = 1;
    /// # let v = 1;
    /// if !map.contains_key(&k) {
    ///     map.insert(k, v);
    /// }
    /// ```
    /// can both be rewritten as:
    /// ```rust
    /// # use std::collections::HashMap;
    /// # let mut map = HashMap::new();
    /// # let k = 1;
    /// # let v = 1;
    /// map.entry(k).or_insert(v);
    /// ```
    pub MAP_ENTRY,
    perf,
    "use of `contains_key` followed by `insert` on a `HashMap` or `BTreeMap`"
}

declare_lint_pass!(HashMapPass => [MAP_ENTRY]);

impl<'tcx> LateLintPass<'tcx> for HashMapPass {
    fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
        if let Some((ref check, ref then_block, ref else_block)) = higher::if_block(&expr) {
            if let ExprKind::Unary(UnOp::UnNot, ref check) = check.kind {
                if let Some((ty, map, key)) = check_cond(cx, check) {
                    // in case of `if !m.contains_key(&k) { m.insert(k, v); }`
                    // we can give a better error message
                    let sole_expr = {
                        else_block.is_none()
                            && if let ExprKind::Block(ref then_block, _) = then_block.kind {
                                (then_block.expr.is_some() as usize) + then_block.stmts.len() == 1
                            } else {
                                true
                            }
                        // XXXManishearth we can also check for if/else blocks containing `None`.
                    };

                    let mut visitor = InsertVisitor {
                        cx,
                        span: expr.span,
                        ty,
                        map,
                        key,
                        sole_expr,
                    };

                    walk_expr(&mut visitor, &**then_block);
                }
            } else if let Some(ref else_block) = *else_block {
                if let Some((ty, map, key)) = check_cond(cx, check) {
                    let mut visitor = InsertVisitor {
                        cx,
                        span: expr.span,
                        ty,
                        map,
                        key,
                        sole_expr: false,
                    };

                    walk_expr(&mut visitor, else_block);
                }
            }
        }
    }
}

fn check_cond<'a>(cx: &LateContext<'_>, check: &'a Expr<'a>) -> Option<(&'static str, &'a Expr<'a>, &'a Expr<'a>)> {
    if_chain! {
        if let ExprKind::MethodCall(ref path, _, ref params, _) = check.kind;
        if params.len() >= 2;
        if path.ident.name == sym!(contains_key);
        if let ExprKind::AddrOf(BorrowKind::Ref, _, ref key) = params[1].kind;
        then {
            let map = &params[0];
            let obj_ty = cx.typeck_results().expr_ty(map).peel_refs();

            return if match_type(cx, obj_ty, &paths::BTREEMAP) {
                Some(("BTreeMap", map, key))
            }
            else if is_type_diagnostic_item(cx, obj_ty, sym!(hashmap_type)) {
                Some(("HashMap", map, key))
            }
            else {
                None
            };
        }
    }

    None
}

struct InsertVisitor<'a, 'tcx, 'b> {
    cx: &'a LateContext<'tcx>,
    span: Span,
    ty: &'static str,
    map: &'b Expr<'b>,
    key: &'b Expr<'b>,
    sole_expr: bool,
}

impl<'a, 'tcx, 'b> Visitor<'tcx> for InsertVisitor<'a, 'tcx, 'b> {
    type Map = Map<'tcx>;

    fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
        if_chain! {
            if let ExprKind::MethodCall(ref path, _, ref params, _) = expr.kind;
            if params.len() == 3;
            if path.ident.name == sym!(insert);
            if get_item_name(self.cx, self.map) == get_item_name(self.cx, &params[0]);
            if SpanlessEq::new(self.cx).eq_expr(self.key, &params[1]);
            if snippet_opt(self.cx, self.map.span) == snippet_opt(self.cx, params[0].span);
            then {
                span_lint_and_then(self.cx, MAP_ENTRY, self.span,
                                   &format!("usage of `contains_key` followed by `insert` on a `{}`", self.ty), |diag| {
                    if self.sole_expr {
                        let mut app = Applicability::MachineApplicable;
                        let help = format!("{}.entry({}).or_insert({});",
                                           snippet_with_applicability(self.cx, self.map.span, "map", &mut app),
                                           snippet_with_applicability(self.cx, params[1].span, "..", &mut app),
                                           snippet_with_applicability(self.cx, params[2].span, "..", &mut app));

                        diag.span_suggestion(
                            self.span,
                            "consider using",
                            help,
                            Applicability::MachineApplicable, // snippet
                        );
                    }
                    else {
                        let help = format!("consider using `{}.entry({})`",
                                           snippet(self.cx, self.map.span, "map"),
                                           snippet(self.cx, params[1].span, ".."));

                        diag.span_label(
                            self.span,
                            &help,
                        );
                    }
                });
            }
        }

        if !self.sole_expr {
            walk_expr(self, expr);
        }
    }
    fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
        NestedVisitorMap::None
    }
}
