use ra_db::{FileId, Cancelable, SyntaxDatabase};
use ra_syntax::{TextRange, AstNode, ast, SyntaxKind::{NAME, MODULE}};

use ra_editor::find_node_at_offset;

use crate::{FilePosition, NavigationTarget, db::RootDatabase};

pub(crate) fn goto_defenition(
    db: &RootDatabase,
    position: FilePosition,
) -> Cancelable<Option<Vec<NavigationTarget>>> {
    let file = db.source_file(position.file_id);
    let syntax = file.syntax();
    if let Some(name_ref) = find_node_at_offset::<ast::NameRef>(syntax, position.offset) {
        return Ok(Some(reference_defenition(db, position.file_id, name_ref)?));
    }
    if let Some(name) = find_node_at_offset::<ast::Name>(syntax, position.offset) {
        return name_defenition(db, position.file_id, name);
    }
    Ok(None)
}

fn reference_defenition(
    db: &RootDatabase,
    file_id: FileId,
    name_ref: ast::NameRef,
) -> Cancelable<Vec<NavigationTarget>> {
    if let Some(fn_descr) =
        hir::source_binder::function_from_child_node(db, file_id, name_ref.syntax())?
    {
        let scope = fn_descr.scopes(db);
        // First try to resolve the symbol locally
        if let Some(entry) = scope.resolve_local_name(name_ref) {
            let nav = NavigationTarget {
                file_id,
                name: entry.name().to_string().into(),
                range: entry.ptr().range(),
                kind: NAME,
                ptr: None,
            };
            return Ok(vec![nav]);
        };
    }
    // If that fails try the index based approach.
    let navs = db
        .index_resolve(name_ref)?
        .into_iter()
        .map(NavigationTarget::from_symbol)
        .collect();
    Ok(navs)
}

fn name_defenition(
    db: &RootDatabase,
    file_id: FileId,
    name: ast::Name,
) -> Cancelable<Option<Vec<NavigationTarget>>> {
    if let Some(module) = name.syntax().parent().and_then(ast::Module::cast) {
        if module.has_semi() {
            if let Some(child_module) =
                hir::source_binder::module_from_declaration(db, file_id, module)?
            {
                let file_id = child_module.file_id();
                let name = match child_module.name() {
                    Some(name) => name.to_string().into(),
                    None => "".into(),
                };
                let nav = NavigationTarget {
                    file_id,
                    name,
                    range: TextRange::offset_len(0.into(), 0.into()),
                    kind: MODULE,
                    ptr: None,
                };
                return Ok(Some(vec![nav]));
            }
        }
    }
    Ok(None)
}