use crate::{make, session::SessionInfo, Metadata, Report, Rule, Suggestion};

use if_chain::if_chain;
use macros::lint;
use rnix::{
    types::{AttrSet, EntryHolder, Lambda, Pattern, TypedNode},
    NodeOrToken, SyntaxElement, SyntaxKind, SyntaxNode,
};

/// ## What it does
/// Checks for an empty variadic pattern: `{...}`, in a function
/// argument.
///
/// ## Why is this bad?
/// The intention with empty patterns is not instantly obvious. Prefer
/// an underscore identifier instead, to indicate that the argument
/// is being ignored.
///
/// ## Example
///
/// ```nix
/// client = { ... }: {
///   services.irmaseal-pkg.enable = true;
/// };
/// ```
///
/// Replace the empty variadic pattern with `_` to indicate that you
/// intend to ignore the argument:
///
/// ```nix
/// client = _: {
///   services.irmaseal-pkg.enable = true;
/// };
/// ```
#[lint(
    name = "empty_pattern",
    note = "Found empty pattern in function argument",
    code = 10,
    match_with = SyntaxKind::NODE_LAMBDA
)]
struct EmptyPattern;

impl Rule for EmptyPattern {
    fn validate(&self, node: &SyntaxElement, _sess: &SessionInfo) -> Option<Report> {
        if_chain! {
            if let NodeOrToken::Node(node) = node;
            if let Some(lambda_expr) = Lambda::cast(node.clone());
            if let Some(arg) = lambda_expr.arg();
            if let Some(body) = lambda_expr.body();

            if let Some(pattern) = Pattern::cast(arg.clone());

            // no patterns within `{ }`
            if pattern.entries().count() == 0;
            // pattern is not bound
            if pattern.at().is_none();

            // not a nixos module
            if !is_module(&body);

            then {
                let at = pattern.node().text_range();
                let message = "This pattern is empty, use `_` instead";
                let replacement = make::ident("_").node().clone();
                Some(self.report().suggest(at, message, Suggestion::new(at, replacement)))
            } else {
                None
            }
        }
    }
}

fn is_module(body: &SyntaxNode) -> bool {
    if_chain! {
        if let Some(attr_set) = AttrSet::cast(body.clone());
        if attr_set
            .entries()
            .map(|e| e.key())
            .flatten()
            .any(|k| k.node().to_string() == "imports");
        then {
            true
        } else {
            false
        }
    }
}