//! This module is responsible for resolving paths within rules.

use crate::errors::error;
use crate::{parsing, SsrError};
use parsing::Placeholder;
use ra_syntax::{ast, SmolStr, SyntaxKind, SyntaxNode, SyntaxToken};
use rustc_hash::{FxHashMap, FxHashSet};
use test_utils::mark;

pub(crate) struct ResolvedRule {
    pub(crate) pattern: ResolvedPattern,
    pub(crate) template: Option<ResolvedPattern>,
    pub(crate) index: usize,
}

pub(crate) struct ResolvedPattern {
    pub(crate) placeholders_by_stand_in: FxHashMap<SmolStr, parsing::Placeholder>,
    pub(crate) node: SyntaxNode,
    // Paths in `node` that we've resolved.
    pub(crate) resolved_paths: FxHashMap<SyntaxNode, ResolvedPath>,
}

pub(crate) struct ResolvedPath {
    pub(crate) resolution: hir::PathResolution,
    pub(crate) depth: u32,
}

impl ResolvedRule {
    pub(crate) fn new(
        rule: parsing::ParsedRule,
        scope: &hir::SemanticsScope,
        hygiene: &hir::Hygiene,
        index: usize,
    ) -> Result<ResolvedRule, SsrError> {
        let resolver =
            Resolver { scope, hygiene, placeholders_by_stand_in: rule.placeholders_by_stand_in };
        let resolved_template = if let Some(template) = rule.template {
            Some(resolver.resolve_pattern_tree(template)?)
        } else {
            None
        };
        Ok(ResolvedRule {
            pattern: resolver.resolve_pattern_tree(rule.pattern)?,
            template: resolved_template,
            index,
        })
    }

    pub(crate) fn get_placeholder(&self, token: &SyntaxToken) -> Option<&Placeholder> {
        if token.kind() != SyntaxKind::IDENT {
            return None;
        }
        self.pattern.placeholders_by_stand_in.get(token.text())
    }
}

struct Resolver<'a, 'db> {
    scope: &'a hir::SemanticsScope<'db>,
    hygiene: &'a hir::Hygiene,
    placeholders_by_stand_in: FxHashMap<SmolStr, parsing::Placeholder>,
}

impl Resolver<'_, '_> {
    fn resolve_pattern_tree(&self, pattern: SyntaxNode) -> Result<ResolvedPattern, SsrError> {
        let mut resolved_paths = FxHashMap::default();
        self.resolve(pattern.clone(), 0, &mut resolved_paths)?;
        Ok(ResolvedPattern {
            node: pattern,
            resolved_paths,
            placeholders_by_stand_in: self.placeholders_by_stand_in.clone(),
        })
    }

    fn resolve(
        &self,
        node: SyntaxNode,
        depth: u32,
        resolved_paths: &mut FxHashMap<SyntaxNode, ResolvedPath>,
    ) -> Result<(), SsrError> {
        use ra_syntax::ast::AstNode;
        if let Some(path) = ast::Path::cast(node.clone()) {
            // Check if this is an appropriate place in the path to resolve. If the path is
            // something like `a::B::<i32>::c` then we want to resolve `a::B`. If the path contains
            // a placeholder. e.g. `a::$b::c` then we want to resolve `a`.
            if !path_contains_type_arguments(path.qualifier())
                && !self.path_contains_placeholder(&path)
            {
                let resolution = self
                    .resolve_path(&path)
                    .ok_or_else(|| error!("Failed to resolve path `{}`", node.text()))?;
                resolved_paths.insert(node, ResolvedPath { resolution, depth });
                return Ok(());
            }
        }
        for node in node.children() {
            self.resolve(node, depth + 1, resolved_paths)?;
        }
        Ok(())
    }

    /// Returns whether `path` contains a placeholder, but ignores any placeholders within type
    /// arguments.
    fn path_contains_placeholder(&self, path: &ast::Path) -> bool {
        if let Some(segment) = path.segment() {
            if let Some(name_ref) = segment.name_ref() {
                if self.placeholders_by_stand_in.contains_key(name_ref.text()) {
                    return true;
                }
            }
        }
        if let Some(qualifier) = path.qualifier() {
            return self.path_contains_placeholder(&qualifier);
        }
        false
    }

    fn resolve_path(&self, path: &ast::Path) -> Option<hir::PathResolution> {
        let hir_path = hir::Path::from_src(path.clone(), self.hygiene)?;
        // First try resolving the whole path. This will work for things like
        // `std::collections::HashMap`, but will fail for things like
        // `std::collections::HashMap::new`.
        if let Some(resolution) = self.scope.resolve_hir_path(&hir_path) {
            return Some(resolution);
        }
        // Resolution failed, try resolving the qualifier (e.g. `std::collections::HashMap` and if
        // that succeeds, then iterate through the candidates on the resolved type with the provided
        // name.
        let resolved_qualifier = self.scope.resolve_hir_path_qualifier(&hir_path.qualifier()?)?;
        if let hir::PathResolution::Def(hir::ModuleDef::Adt(adt)) = resolved_qualifier {
            adt.ty(self.scope.db).iterate_path_candidates(
                self.scope.db,
                self.scope.module()?.krate(),
                &FxHashSet::default(),
                Some(hir_path.segments().last()?.name),
                |_ty, assoc_item| Some(hir::PathResolution::AssocItem(assoc_item)),
            )
        } else {
            None
        }
    }
}

/// Returns whether `path` or any of its qualifiers contains type arguments.
fn path_contains_type_arguments(path: Option<ast::Path>) -> bool {
    if let Some(path) = path {
        if let Some(segment) = path.segment() {
            if segment.type_arg_list().is_some() {
                mark::hit!(type_arguments_within_path);
                return true;
            }
        }
        return path_contains_type_arguments(path.qualifier());
    }
    false
}