duster/src/renderer/walking.rs

use crate::renderer::context_element::ContextElement;
use crate::renderer::WalkError;

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

fn walk_path_from_single_level<'a>(
    context: &'a dyn ContextElement,
    path: &[&str],
) -> WalkResult<'a> {
    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) {
            Err(WalkError::CantWalk { .. }) => {
                return walk_failure;
            }
            Ok(new_val) => {
                walk_failure = WalkResult::PartialWalk;
                output = new_val;
            }
        }
    }

    WalkResult::FullyWalked(output)
}

pub fn walk_path<'a>(
    breadcrumbs: &Vec<&'a dyn ContextElement>,
    path: &'a Vec<&str>,
) -> Result<&'a dyn ContextElement, WalkError> {
    if path.is_empty() {
        return Ok(*breadcrumbs
            .last()
            .expect("Breadcrumbs should never be empty"));
    }
    if *path.first().expect("Already proved path is not empty") == "." {
        return match walk_path_from_single_level(
            *breadcrumbs
                .last()
                .expect("Breadcrumbs should never be empty"),
            &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),
        };
    }
    for context in breadcrumbs.iter().rev() {
        match walk_path_from_single_level(*context, 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)
}

pub fn owned_walk_path<'a>(
    breadcrumbs: &'a Vec<Box<dyn ContextElement>>,
    path: &Vec<String>,
) -> Result<&'a dyn ContextElement, WalkError> {
    let path_reference: Vec<&str> = path.iter().map(|p| &p[..]).collect();
    for context in breadcrumbs.iter().rev() {
        match walk_path_from_single_level(context.as_ref(), &path_reference) {
            // 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)
}