Complain if PRs don't reference regions correctly

We want to be able to rely on regions for filtering, e.g. when showing
things in dashboards.

Ideally we would have a source of truth of which region each trainee is
in, but we don't, so in the mean time check that the title claims to be
in some region.

Hard-code the known regions for now - ideally an API will provide these
in the future.

Author: illicitonion

src/bin/pr-metadata-validator.rs

@@ -1,4 +1,4 @@
-use std::process::exit;
+use std::{collections::BTreeMap, process::exit};
 
 use chrono::NaiveDate;
 use indexmap::IndexMap;
@@ -39,6 +39,16 @@ async fn main() {
         }
     };
 
+    // TODO: Fetch this from classplanner or somewhere when we have access to a useful API.
+    let known_region_aliases = KnownRegions(btreemap! {
+        "Cape Town" => vec!["South Africa", "SouthAfrica", "ZA", "ZA Cape Town"],
+        "Glasgow" => vec!["Scotland"],
+        "London" => vec![],
+        "North West" => vec!["NW", "Manchester"],
+        "Sheffield" => vec![],
+        "West Midlands" => vec!["WM", "WestMidlands", "West-Midlands", "Birmingham"],
+    });
+
     let github_token =
         std::env::var("GH_TOKEN").expect("GH_TOKEN wasn't set - must be set to a GitHub API token");
     let octocrab = octocrab_for_token(github_token).expect("Failed to get octocrab");
@@ -56,6 +66,7 @@ async fn main() {
         module_name.clone(),
         github_org_name.clone(),
         pr_number,
+        &known_region_aliases,
     )
     .await
     .expect("Failed to validate PR");
@@ -79,6 +90,15 @@ async fn main() {
                 .expect("Failed to create comment with validation error");
             exit(2);
         }
+        ValidationResult::UnknownRegion => {
+            eprintln!("Validation error: Could not find region in PR title");
+            octocrab
+                .issues(github_org_name, module_name.clone())
+                .create_comment(pr_number, UNKNOWN_REGION_COMMENT)
+                .await
+                .expect("Failed to create comment with validation error");
+            exit(2);
+        }
     }
 }
 
@@ -90,14 +110,19 @@ If this PR is not coursework, please add the NotCoursework label (and message on
 
 const BAD_TITLE_COMMENT_PREFIX: &'static str = r#"Your PR's title isn't in the expected format.
 
-Please check its title is in the correct format, and update it.
+Please check the expected title format, and update yours to match.
 
 Reason: "#;
 
+const UNKNOWN_REGION_COMMENT: &'static str = r#"Your PR's title didn't contain a known region.
+
+Please check the expected title format, and make sure your region is in the correct place and spelled correctly."#;
+
 enum ValidationResult {
     Ok,
     CouldNotMatch,
     BadTitleFormat { reason: String },
+    UnknownRegion,
 }
 
 async fn validate_pr(
@@ -106,6 +131,7 @@ async fn validate_pr(
     module_name: String,
     github_org_name: String,
     pr_number: u64,
+    known_region_aliases: &KnownRegions,
 ) -> Result<ValidationResult, Error> {
     let course = course_schedule
         .with_assignments(&octocrab, github_org_name.clone())
@@ -134,7 +160,7 @@ async fn validate_pr(
         &course.modules[&module_name],
         user_prs,
         Vec::new(),
-        &Region("London".to_owned()),
+        &ARBITRARY_REGION,
     )
     .map_err(|err| err.context("Failed to match PRs to assignments"))?;
 
@@ -150,7 +176,11 @@ async fn validate_pr(
             reason: "Wrong number of parts separated by |s".to_owned(),
         });
     }
-    // TODO: Validate Regions when they're known (0)
+
+    if !known_region_aliases.is_known_ignoring_case(&title_sections[0].trim()) {
+        return Ok(ValidationResult::UnknownRegion);
+    }
+
     // TODO: Validate cohorts when they're known (1)
     let sprint_regex = Regex::new(r"^(S|s)print \d+$").unwrap();
     let sprint_section = title_sections[3].trim();
@@ -167,6 +197,25 @@ async fn validate_pr(
     Ok(ValidationResult::Ok)
 }
 
+struct KnownRegions(BTreeMap<&'static str, Vec<&'static str>>);
+
+impl KnownRegions {
+    fn is_known_ignoring_case(&self, possible_region: &str) -> bool {
+        let possible_region_lower = possible_region.to_ascii_lowercase();
+        for (known_region, known_region_aliases) in &self.0 {
+            if known_region.to_ascii_lowercase() == possible_region_lower {
+                return true;
+            }
+            for known_region_alias in known_region_aliases {
+                if known_region_alias.to_ascii_lowercase() == possible_region_lower {
+                    return true;
+                }
+            }
+        }
+        false
+    }
+}
+
 fn make_fake_course_schedule(module_name: String) -> CourseSchedule {
     let fixed_date = NaiveDate::from_ymd_opt(2030, 1, 1).unwrap();
     let mut sprints = IndexMap::new();