use rustc::hir::*;
use rustc::hir::intravisit::{walk_expr, NestedVisitorMap, Visitor};
use rustc::lint::*;
use syntax::codemap::Span;
use utils::SpanlessEq;
use utils::{get_item_name, match_type, paths, snippet, span_lint_and_then, walk_ptrs_ty};

/// **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
/// let k = &key;
/// if !m.contains_key(k) { m.insert(k.clone(), v); }
/// ```
///
/// **Example:**
/// ```rust
/// if !m.contains_key(&k) { m.insert(k, v) }
/// ```
/// can be rewritten as:
/// ```rust
/// m.entry(k).or_insert(v);
/// ```
declare_lint! {
    pub MAP_ENTRY,
    Warn,
    "use of `contains_key` followed by `insert` on a `HashMap` or `BTreeMap`"
}

#[derive(Copy, Clone)]
pub struct HashMapLint;

impl LintPass for HashMapLint {
    fn get_lints(&self) -> LintArray {
        lint_array!(MAP_ENTRY)
    }
}

impl<'a, 'tcx> LateLintPass<'a, 'tcx> for HashMapLint {
    fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
        if let ExprIf(ref check, ref then_block, ref else_block) = expr.node {
            if let ExprUnary(UnOp::UnNot, ref check) = check.node {
                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 ExprBlock(ref then_block) = then_block.node {
                            (then_block.expr.is_some() as usize) + then_block.stmts.len() == 1
                        } else {
                            true
                        }
                    };

                    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, 'tcx, 'b>(
    cx: &'a LateContext<'a, 'tcx>,
    check: &'b Expr,
) -> Option<(&'static str, &'b Expr, &'b Expr)> {
    if_chain! {
        if let ExprMethodCall(ref path, _, ref params) = check.node;
        if params.len() >= 2;
        if path.name == "contains_key";
        if let ExprAddrOf(_, ref key) = params[1].node;
        then {
            let map = &params[0];
            let obj_ty = walk_ptrs_ty(cx.tables.expr_ty(map));

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

    None
}

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

impl<'a, 'tcx, 'b> Visitor<'tcx> for InsertVisitor<'a, 'tcx, 'b> {
    fn visit_expr(&mut self, expr: &'tcx Expr) {
        if_chain! {
            if let ExprMethodCall(ref path, _, ref params) = expr.node;
            if params.len() == 3;
            if path.name == "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]);
            then {
                span_lint_and_then(self.cx, MAP_ENTRY, self.span,
                                   &format!("usage of `contains_key` followed by `insert` on a `{}`", self.ty), |db| {
                    if self.sole_expr {
                        let help = format!("{}.entry({}).or_insert({})",
                                           snippet(self.cx, self.map.span, "map"),
                                           snippet(self.cx, params[1].span, ".."),
                                           snippet(self.cx, params[2].span, ".."));

                        db.span_suggestion(self.span, "consider using", help);
                    }
                    else {
                        let help = format!("{}.entry({})",
                                           snippet(self.cx, self.map.span, "map"),
                                           snippet(self.cx, params[1].span, ".."));

                        db.span_suggestion(self.span, "consider using", help);
                    }
                });
            }
        }

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