1 files changed, 40 insertions, 6 deletions

diff --git a/src/map.rs b/src/map.rs
index 4ed4c7f..ab27164 100644
--- a/src/map.rs
+++ b/src/map.rs
@@ -4,6 +4,11 @@ pub use crate::from_yaml;
 pub use crate::Status;
 pub use crate::Step;
 
+
+/// Error in Roadmap, from parsing or otherwise.
+pub type RoadmapError<T> = Result<T, String>;
+
+
 /// Represent a full project roadmap.
 ///
 /// This stores all the steps needed to reach the end goal. See the
@@ -116,10 +121,41 @@ impl Roadmap {
         self.steps.iter().all(|other| !other.depends_on(step.name()))
     }
 
+
+    // Validate that the parsed, constructed roadmap is valid.
+    pub fn validate(&self) -> RoadmapError<()> {
+        // Is there exactly one goal?
+        match self.count_goals() {
+            0 => return Err(format!("the roadmap doesn't have a goal")),
+            1 => (),
+            _ => return Err(format!("must have exactly one goal for roadmap")),
+        }
+
+        // Does every dependency exist?
+        for step in self.iter() {
+            for depname in step.dependencies() {
+                match self.get_step(depname) {
+                    None => {
+                        return Err(format!(
+                            "step {} depends on missing {}",
+                            step.name(),
+                            depname
+                        ))
+                    }
+                    Some(_) => (),
+                }
+            }
+        }
+
+        Ok(())
+    }
+
     /// Get a Graphviz dot language representation of a roadmap. This
     /// is the textual representation, and the caller needs to use the
     /// Graphviz dot(1) tool to create an image from it.
     pub fn format_as_dot(&self, label_width: usize) -> Result<String, Box<dyn std::error::Error>> {
+        self.validate()?;
+
         let labels = self.steps.iter().map(|step| {
             format!(
                 "{} [label=\"{}\" style=filled fillcolor=\"{}\" shape=\"{}\"];\n",
@@ -237,12 +273,10 @@ blocked:
     #[test]
     fn empty_dot() {
         let roadmap = Roadmap::new();
-        assert_eq!(
-            roadmap.format_as_dot(999).unwrap(),
-            "digraph \"roadmap\" {
-}
-"
-        );
+        match roadmap.format_as_dot(999) {
+            Err(_) => (),
+            _ => panic!("expected error for empty roadmap"),
+        }
     }
 
     #[test]