duster/src/renderer/walking.rs

use crate::renderer::breadcrumb_tree::BreadcrumbTreeElement;
use crate::renderer::context_element::IntoContextElement;
use crate::renderer::WalkError;
use std::borrow::Borrow;

enum WalkResult<'a> {
    NoWalk,
    PartialWalk,
    FullyWalked(&'a dyn IntoContextElement),
}

fn walk_path_from_single_level<'a, P>(
    context: &'a dyn IntoContextElement,
    path: &[P],
) -> WalkResult<'a>
where
    P: Borrow<str>,
{
    if path.is_empty() {
        return WalkResult::FullyWalked(context);
    }

    let mut walk_failure = WalkResult::NoWalk;
    let mut output = context;
    for elem in path.iter() {
        match output.walk(elem.borrow()) {
            Err(WalkError::CantWalk { .. }) => {
                return walk_failure;
            }
            Ok(new_val) => {
                walk_failure = WalkResult::PartialWalk;
                output = new_val;
            }
        }
    }

    WalkResult::FullyWalked(output)
}

fn get_first_non_pseudo_element<'a>(
    breadcrumbs: &'a Vec<BreadcrumbTreeElement<'a>>,
) -> Option<&'a BreadcrumbTreeElement<'a>> {
    breadcrumbs
        .iter()
        .rev()
        .filter(|b| {
            !std::borrow::Borrow::<dyn IntoContextElement + 'a>::borrow(*b).is_pseudo_element()
        })
        .next()
}

pub fn walk_path<'a, P>(
    breadcrumbs: &'a Vec<BreadcrumbTreeElement<'a>>,
    path: &Vec<P>,
) -> Result<&'a dyn IntoContextElement, WalkError>
where
    P: Borrow<str>,
{
    match (breadcrumbs.last(), path.first()) {
        (None, _) => return Err(WalkError::CantWalk),
        (Some(last_elem), None) => return Ok(last_elem.borrow()),
        (Some(_), Some(path_first)) if path_first.borrow() == "." => {
            let first_non_pseudo_element = get_first_non_pseudo_element(breadcrumbs);
            return match first_non_pseudo_element {
                None => Err(WalkError::CantWalk),
                Some(current_context) => {
                    match walk_path_from_single_level(current_context.borrow(), &path[1..]) {
                        // If no walking was done at all or we partially walked
                        // then stop trying to find anything because '.' restricts
                        // us to the current scope
                        WalkResult::NoWalk | WalkResult::PartialWalk => Err(WalkError::CantWalk),
                        WalkResult::FullyWalked(new_context) => Ok(new_context),
                    }
                }
            };
        }
        (Some(_), Some(_path_first)) => {
            for context in breadcrumbs.iter().rev() {
                match walk_path_from_single_level(context.borrow(), path) {
                    // If no walking was done at all, keep looping
                    WalkResult::NoWalk => {}
                    // If we partially walked then stop trying to find
                    // anything
                    WalkResult::PartialWalk => {
                        return Err(WalkError::CantWalk);
                    }
                    WalkResult::FullyWalked(new_context) => return Ok(new_context),
                }
            }
        }
    }

    Err(WalkError::CantWalk)
}