manager: Add first version of the techtree manager

The techtree manager is a CI tool that derives the techtree graph from
the forgejo issues in this repository.  It then adds graph
visualizations to each issue and the wiki, to give an overview of the
tree.

techtree-manager/src/event_meta.rs

@@ -0,0 +1,57 @@
+use anyhow::Context as _;
+
+#[derive(serde::Deserialize, Debug, Clone, PartialEq, Eq)]
+pub struct IssueEventMeta {
+    pub action: IssueAction,
+    pub issue: IssueMeta,
+}
+
+#[derive(serde::Deserialize, Debug, Clone, Copy, PartialEq, Eq)]
+#[serde(rename_all = "lowercase")]
+pub enum IssueAction {
+    Opened,
+    Reopened,
+    Closed,
+    Assigned,
+    Unassigned,
+    Edited,
+    #[serde(rename = "label_updated")]
+    LabelUpdated,
+    Labeled,
+    #[serde(rename = "label_cleared")]
+    LabelCleared,
+    Unlabeled,
+}
+
+#[derive(serde::Deserialize, Debug, Clone, PartialEq, Eq)]
+pub struct IssueMeta {
+    pub number: u64,
+    pub repository: RepoMeta,
+}
+
+#[derive(serde::Deserialize, Debug, Clone, PartialEq, Eq)]
+pub struct RepoMeta {
+    pub name: String,
+    pub owner: String,
+}
+
+pub fn get_issue_event_meta_from_env() -> anyhow::Result<IssueEventMeta> {
+    let path = std::env::var_os("GITHUB_EVENT_PATH")
+        .context("Could not get event description file path (GITHUB_EVENT_PATH)")?;
+    let f = std::fs::File::open(path).context("Could not open GITHUB_EVENT_PATH file")?;
+    let meta: IssueEventMeta = serde_json::de::from_reader(f).context("Failed to parse")?;
+    Ok(meta)
+}
+
+pub fn fake() -> IssueEventMeta {
+    IssueEventMeta {
+        action: IssueAction::Edited,
+        issue: IssueMeta {
+            number: 1337,
+            repository: RepoMeta {
+                name: "techtree-poc".to_owned(),
+                owner: "rahix".to_owned(),
+            },
+        },
+    }
+}