feat(cli): Add support for rendering to mermaid with vector graph command (#22787)

* Plumb in basic switch between output formats

* Get rendering actually functional

* flowchart appears to be preferred terminology over graph

* comemnt about styling

* add the new code after existing instead

* Add changelog file

* Replace expect with unwrap

* Inline formatter arguments where possible

* Remove code comment, it will move to PR body

* link mermaid docs on format help

Author: Firehed

changelog.d/14082_add_mermaid_support.feature.md

@@ -0,0 +1,3 @@
+Add support for rendering to Mermaid format in `vector graph`
+
+authors: Firehed

src/graph.rs

@@ -47,6 +47,19 @@ pub struct Opts {
         value_delimiter(',')
     )]
     pub config_dirs: Vec<PathBuf>,
+
+    /// Set the output format
+    ///
+    /// See https://mermaid.js.org/syntax/flowchart.html#styling-and-classes for
+    /// information on the `mermaid` format.
+    #[arg(id = "format", long, default_value = "dot")]
+    pub format: OutputFormat,
+}
+
+#[derive(clap::ValueEnum, Debug, Clone, Copy, PartialEq, Eq)]
+pub enum OutputFormat {
+    Dot,
+    Mermaid,
 }
 
 impl Opts {
@@ -96,6 +109,14 @@ pub(crate) fn cmd(opts: &Opts) -> exitcode::ExitCode {
         }
     };
 
+    let format = opts.format;
+    match format {
+        OutputFormat::Dot => render_dot(config),
+        OutputFormat::Mermaid => render_mermaid(config),
+    }
+}
+
+fn render_dot(config: config::Config) -> exitcode::ExitCode {
     let mut dot = String::from("digraph {\n");
 
     for (id, source) in config.sources() {
@@ -165,3 +186,45 @@ pub(crate) fn cmd(opts: &Opts) -> exitcode::ExitCode {
 
     exitcode::OK
 }
+
+fn render_mermaid(config: config::Config) -> exitcode::ExitCode {
+    let mut mermaid = String::from("flowchart TD;\n");
+
+    writeln!(mermaid, "\n  %% Sources").unwrap();
+    for (id, _) in config.sources() {
+        writeln!(mermaid, "  {id}[/{id}/]").unwrap();
+    }
+
+    writeln!(mermaid, "\n  %% Transforms").unwrap();
+    for (id, transform) in config.transforms() {
+        writeln!(mermaid, "  {id}{{{id}}}").unwrap();
+
+        for input in transform.inputs.iter() {
+            if let Some(port) = &input.port {
+                writeln!(mermaid, "  {0} -->|{port}| {id}", input.component).unwrap();
+            } else {
+                writeln!(mermaid, "  {0} --> {id}", input.component).unwrap();
+            }
+        }
+    }
+
+    writeln!(mermaid, "\n  %% Sinks").unwrap();
+    for (id, sink) in config.sinks() {
+        writeln!(mermaid, "  {id}[\\{id}\\]").unwrap();
+
+        for input in &sink.inputs {
+            if let Some(port) = &input.port {
+                writeln!(mermaid, "  {0} -->|{port}| {id}", input.component).unwrap();
+            } else {
+                writeln!(mermaid, "  {0} --> {id}", input.component).unwrap();
+            }
+        }
+    }
+
+    #[allow(clippy::print_stdout)]
+    {
+        println!("{}", mermaid);
+    }
+
+    exitcode::OK
+}