apollo-federation 2.13.1

Apollo Federation
Documentation 
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// Output module for query graphs
// - Corresponds to the `graphviz` and `mermaid` modules from the JS federation.

use std::fmt::Write;
use std::sync::Arc;

use petgraph::dot::Config;
use petgraph::dot::Dot;
use petgraph::graph::EdgeIndex;
use petgraph::stable_graph::StableGraph;

use crate::query_graph::QueryGraph;
use crate::query_graph::QueryGraphEdge;
use crate::query_graph::QueryGraphNode;

type StableInnerGraph = StableGraph<QueryGraphNode, QueryGraphEdge>;

//////////////////////////////////////////////////////////////////////////////
// GraphViz output for QueryGraph

fn label_edge(edge: &QueryGraphEdge) -> String {
    let label = edge.to_string();
    if label.is_empty() {
        String::new()
    } else {
        format!("label=\"{edge}\"")
    }
}

fn label_node(node: &QueryGraphNode) -> String {
    format!("label=\"{}\"", node.type_)
}

pub fn to_dot(graph: &QueryGraph) -> String {
    if graph.sources.len() > 1 {
        return to_dot_federated(graph).expect("Failed to generate the federated graph");
    }

    // Note: Use label_edge/label_node as `attr_getters` in order to create custom label
    //       strings, instead of the default labeling.
    let config = [Config::NodeNoLabel, Config::EdgeNoLabel];
    Dot::with_attr_getters(
        &graph.graph,
        &config,
        &(|_, er| label_edge(er.weight())),
        &(|_, (_, node)| label_node(node)),
    )
    .to_string()
}

fn to_dot_federated(graph: &QueryGraph) -> Result<String, std::fmt::Error> {
    fn edge_within_cluster(
        graph: &StableInnerGraph,
        cluster_name: &Arc<str>,
        edge_index: EdgeIndex,
    ) -> bool {
        graph.edge_endpoints(edge_index).is_some_and(|(n1, n2)| {
            graph[n1].source == *cluster_name && graph[n2].source == *cluster_name
        })
    }

    fn edge_across_clusters(graph: &StableInnerGraph, edge_index: EdgeIndex) -> bool {
        graph
            .edge_endpoints(edge_index)
            .is_some_and(|(n1, n2)| graph[n1].source != graph[n2].source)
    }

    fn label_cluster_node(node: &QueryGraphNode) -> String {
        let provide_id = match node.provide_id {
            Some(id) => format!("#{id}"),
            None => String::new(),
        };
        format!(r#"label="{}{}@{}""#, node.type_, provide_id, node.source)
    }

    // Build a stable graph, so we can derive subgraph clusters with the same indices.
    let stable_graph = StableGraph::from(graph.graph.clone());
    let cluster_dot_config = [
        Config::NodeNoLabel,
        Config::EdgeNoLabel,
        Config::GraphContentOnly,
    ];

    let mut dot_str = String::new();
    writeln!(dot_str, r#"digraph "{}" {{"#, graph.name())?;

    // Subgraph clusters
    for (cluster_name, _) in graph.sources.iter() {
        if cluster_name == graph.name() {
            continue; // skip non-subgraph nodes
        }

        let filtered_graph: StableInnerGraph = stable_graph.filter_map(
            |_i, n| {
                if n.source == *cluster_name {
                    Some(n.clone())
                } else {
                    None
                }
            },
            |i, e| {
                if edge_within_cluster(&stable_graph, cluster_name, i) {
                    Some(e.clone())
                } else {
                    None
                }
            },
        );
        let s = Dot::with_attr_getters(
            &filtered_graph,
            &cluster_dot_config,
            &(|_, er| label_edge(er.weight())),
            &(|_, (_, node)| label_cluster_node(node)),
        )
        .to_string();

        writeln!(dot_str, r#"  subgraph "cluster_{}" {{"#, &cluster_name)?;
        writeln!(dot_str, r#"    label = "Subgraph \"{}\"";"#, &cluster_name)?;
        writeln!(dot_str, r#"    color = "black";"#)?;
        writeln!(dot_str, r#"    style = "";"#)?;
        dot_str.push_str(&s);
        writeln!(dot_str, "  }}")?;
    }

    // Supergraph nodes
    for i in stable_graph.node_indices() {
        let node = &stable_graph[i];
        if node.source == *graph.name() {
            writeln!(dot_str, "  {} [{}]", i.index(), label_node(node))?;
        }
    }

    // Supergraph edges
    for i in stable_graph.edge_indices() {
        if edge_across_clusters(&stable_graph, i)
            && let Some((n1, n2)) = stable_graph.edge_endpoints(i)
        {
            let edge = &stable_graph[i];
            writeln!(
                dot_str,
                "  {} -> {} [{}]",
                n1.index(),
                n2.index(),
                label_edge(edge)
            )?;
        }
    }

    writeln!(dot_str, "}}")?;
    Ok(dot_str)
}