OXYGENHUB
# 99ca93d60bca oxygenhub / crates / hub / src / render / graph.rs
4.4 KiB · Rust · last changed Milestone 0.1: browse 1 month ago source blame history raw
d23464c0 Andy McCall ↶ 1 
//! Lane layout for the history graph (hub spec §6.7): each change takes a
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//! lane, its first dependency continues that lane, other dependencies
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//! take free lanes, so edges flow downward from a change to what it
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//! depends on. Ported from the VS Code extension's webview.
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use std::collections::HashMap;
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/// A row of the graph: the change's lane and the edges to the rows below.
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#[derive(Clone, Debug, PartialEq, Eq)]
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pub struct Row {
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    pub lane: usize,
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    /// `(from_lane, to_lane)` for each dependency drawn from this row.
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    pub edges: Vec<(usize, usize)>,
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    /// Lanes that pass through this row without touching it.
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    pub through: Vec<usize>,
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}
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/// `changes` newest first as `(hash, deps)`. Dependencies outside the list
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/// end their lane at the bottom.
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pub fn layout(changes: &[(String, Vec<String>)]) -> Vec<Row> {
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    let mut active: Vec<Option<String>> = Vec::new();
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    let mut rows = Vec::with_capacity(changes.len());
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    let known: std::collections::HashSet<&str> = changes.iter().map(|(h, _)| h.as_str()).collect();
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    let mut lanes: HashMap<String, usize> = HashMap::new();
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    for (hash, deps) in changes {
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        let lane = match active.iter().position(|a| a.as_deref() == Some(hash)) {
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            Some(l) => l,
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            None => match active.iter().position(|a| a.is_none()) {
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                Some(l) => {
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                    active[l] = Some(hash.clone());
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                    l
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                }
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                None => {
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                    active.push(Some(hash.clone()));
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                    active.len() - 1
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                }
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            },
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        };
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        lanes.insert(hash.clone(), lane);
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        let mut edges = Vec::new();
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        let deps: Vec<&String> = deps.iter().filter(|d| known.contains(d.as_str())).collect();
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        active[lane] = None;
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        for (i, d) in deps.iter().enumerate() {
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            let target = match active.iter().position(|a| a.as_deref() == Some(d.as_str())) {
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                Some(l) => l,
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                None => {
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                    let l = if i == 0 && active[lane].is_none() {
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                        lane
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                    } else {
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                        match active.iter().position(|a| a.is_none()) {
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                            Some(l) => l,
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                            None => {
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                                active.push(None);
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                                active.len() - 1
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                            }
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                        }
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                    };
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                    active[l] = Some((*d).clone());
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                    l
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                }
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            };
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            edges.push((lane, target));
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        }
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        let through: Vec<usize> = active
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            .iter()
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            .enumerate()
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            .filter(|(l, a)| a.is_some() && *l != lane && !edges.iter().any(|e| e.1 == *l))
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            .map(|(l, _)| l)
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            .collect();
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        rows.push(Row { lane, edges, through });
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        // Trim trailing free lanes so the graph stays narrow.
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        while active.last().is_some_and(|a| a.is_none()) {
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            active.pop();
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        }
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    }
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    rows
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}
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pub fn width(rows: &[Row]) -> usize {
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    rows.iter()
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        .map(|r| r.lane.max(r.edges.iter().map(|e| e.1).max().unwrap_or(0)).max(r.through.iter().copied().max().unwrap_or(0)))
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        .max()
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        .map(|m| m + 1)
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        .unwrap_or(1)
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}
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#[cfg(test)]
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mod tests {
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    use super::*;
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    fn c(h: &str, deps: &[&str]) -> (String, Vec<String>) {
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        (h.into(), deps.iter().map(|d| d.to_string()).collect())
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    }
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    #[test]
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    fn linear_history_is_one_lane() {
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        let rows = layout(&[c("c", &["b"]), c("b", &["a"]), c("a", &[])]);
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        assert!(rows.iter().all(|r| r.lane == 0), "{rows:?}");
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        assert_eq!(rows[0].edges, vec![(0, 0)]);
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        assert_eq!(width(&rows), 1);
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    }
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    #[test]
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    fn independent_changes_take_lanes_and_rejoin() {
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        // d depends on b and c, which both depend on a: a diamond.
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        let rows = layout(&[c("d", &["b", "c"]), c("b", &["a"]), c("c", &["a"]), c("a", &[])]);
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        assert_eq!(rows[0].lane, 0);
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        assert_eq!(rows[0].edges, vec![(0, 0), (0, 1)]);
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        assert_eq!(rows[1].lane, 0);
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        assert_eq!(rows[2].lane, 1);
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        assert_eq!(rows[2].edges, vec![(1, 0)], "c joins a's lane");
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        assert_eq!(rows[3].lane, 0);
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        assert_eq!(width(&rows), 2);
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        // Two heads with no common change: two lanes throughout.
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        let rows = layout(&[c("x", &[]), c("y", &[])]);
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        assert_eq!((rows[0].lane, rows[1].lane), (0, 0), "a lane is reused once its change is drawn");
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    }
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}