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//! Graph manipulation code
//!
//! I had hoped to use petgraph, but it is optimized for efficiency over
//! usability, and I got lost in a maze of indices.
use anyhow::{anyhow, Result};
use std::collections::{HashMap, HashSet};
use std::hash::Hash;
/// Given a hashmap representing a binary relationship, compute its transitive closure.
fn transitive_closure<K: Hash + Eq + PartialEq + Clone>(
inp: &HashMap<K, HashSet<K>>,
) -> HashMap<K, HashSet<K>> {
let mut out = inp.clone();
let max_iters = inp.len();
for _ in 0..max_iters {
let mut new_out = out.clone();
for (k, vs) in out.iter() {
let new_vs = new_out
.get_mut(k)
.expect("That key should have been there when I cloned it...");
for v in vs.iter() {
if let Some(vv) = out.get(v) {
new_vs.extend(vv.iter().cloned());
}
}
}
if out == new_out {
break;
} else {
out = new_out;
}
}
out
}
/// Given a hashmap representing a binary relationship, invert it.
fn invert<K: Hash + Eq + PartialEq + Clone>(
inp: &HashMap<K, HashSet<K>>,
) -> HashMap<K, HashSet<K>> {
let mut out: HashMap<K, HashSet<K>> = HashMap::new();
for (k, vs) in inp.iter() {
for v in vs {
out.entry(v.clone())
.or_insert_with(Default::default)
.insert(k.clone());
}
}
out
}
/// A representation of which features depend on what.
#[derive(Clone, Debug, Default)]
pub struct FeatureGraph {
/// List of all features.
all_features: HashSet<String>,
/// Adjacency map: for each feature F, `depends_on[F]` includes G if F
/// directly depends on G.
depends_on: HashMap<String, HashSet<String>>,
/// Inverse adjacency map.
depended_on_by: HashMap<String, HashSet<String>>,
/// Transitive closure of the adjacency map.
reachable_from: HashMap<String, HashSet<String>>,
}
impl FeatureGraph {
/// Convert a toml `[features]` section into a [`FeatureGraph`].
pub fn from_features_table(features: &toml_edit::Table) -> Result<Self> {
let mut depends_on = HashMap::new();
for (k, vs) in features.iter() {
let mut d = HashSet::new();
for v in vs
.as_array()
.ok_or_else(|| anyhow!("features.{} was not an array", k))?
{
let v = v
.as_str()
.ok_or_else(|| anyhow!("features.{} contained a non-string", k))?;
d.insert(v.to_string());
}
depends_on.insert(k.to_string(), d);
}
let all_features = depends_on.keys().cloned().collect();
let reachable_from = transitive_closure(&depends_on);
let depended_on_by = invert(&depends_on);
Ok(Self {
all_features,
depends_on,
depended_on_by,
reachable_from,
})
}
pub fn all_features(&self) -> impl Iterator<Item = String> + '_ {
self.depends_on.keys().cloned()
}
pub fn contains_feature(&self, feature: &str) -> bool {
self.all_features.contains(feature)
}
pub fn contains_edge(&self, from: &str, to: &str) -> bool {
match self.depends_on.get(from) {
Some(fs) => fs.contains(to),
None => false,
}
}
pub fn all_reachable_from(&self, feature: &str) -> impl Iterator<Item = String> + '_ {
match self.reachable_from.get(feature) {
Some(set) => itertools::Either::Left(set.iter().cloned()),
None => itertools::Either::Right(std::iter::empty()),
}
}
/// Return all the features that `feature` depends on. Return an empty iterator if
/// it has no dependencies, or is not in this map.
pub fn edges_from(&self, feature: &str) -> impl Iterator<Item = String> + '_ {
match self.depends_on.get(feature) {
Some(set) => itertools::Either::Left(set.iter().cloned()),
None => itertools::Either::Right(std::iter::empty()),
}
}
/// Return all the features that depend on `feature` directly. Return an empty iterator if
/// it has no dependencies, or is not in this map.
pub fn edges_to(&self, feature: &str) -> impl Iterator<Item = String> + '_ {
match self.depended_on_by.get(feature) {
Some(set) => itertools::Either::Left(set.iter().cloned()),
None => itertools::Either::Right(std::iter::empty()),
}
}
}
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