move entomologist database to new library file

fixes: d3a705245bd69aa56524b80b5ae0bc26

src/database.rs

@@ -0,0 +1,82 @@
+
+/// The main function looks at the command-line arguments and determines
+/// from there where to get the Issues Database to operate on.
+///
+/// * If the user specified `--issues-dir` we use that.
+///
+/// * If the user specified `--issues-branch` we make sure the branch
+///   exists, then use that.
+///
+/// * If the user specified neither, we use the default branch
+///   `entomologist-data` (after ensuring that it exists).
+///
+/// * If the user specified both, it's an operator error and we abort.
+///
+/// The result of that code populates an IssuesDatabaseSource object,
+/// that gets used later to access the database.
+pub enum IssuesDatabaseSource<'a> {
+    Dir(&'a std::path::Path),
+    Branch(&'a str),
+}
+
+
+
+/// The IssuesDatabase type is a "fat path".  It holds a PathBuf pointing
+/// at the issues database directory, and optionally a Worktree object
+/// corresponding to that path.
+///
+/// The worktree field itself is never read: we put its path in `dir`
+/// and that's all that the calling code cares about.
+///
+/// The Worktree object is included here *when* the IssuesDatabaseSource
+/// is a branch.  In this case a git worktree is created to hold the
+/// checkout of the branch.  When the IssueDatabase object is dropped,
+/// the contained/owned Worktree object is dropped, which deletes the
+/// worktree directory from the filesystem and prunes the worktree from
+/// git's worktree list.
+
+pub struct IssuesDatabase {
+    pub dir: std::path::PathBuf,
+
+    #[allow(dead_code)]
+    pub worktree: Option<crate::git::Worktree>,
+}
+
+pub enum IssuesDatabaseAccess {
+    ReadOnly,
+    ReadWrite,
+}
+
+pub fn make_issues_database(
+    issues_database_source: &IssuesDatabaseSource,
+    access_type: IssuesDatabaseAccess,
+) -> anyhow::Result<IssuesDatabase> {
+    match issues_database_source {
+        IssuesDatabaseSource::Dir(dir) => Ok(IssuesDatabase {
+            dir: std::path::PathBuf::from(dir),
+            worktree: None,
+        }),
+        IssuesDatabaseSource::Branch(branch) => {
+            let worktree = match access_type {
+                IssuesDatabaseAccess::ReadOnly => {
+                    crate::git::Worktree::new_detached(branch)?
+                }
+                IssuesDatabaseAccess::ReadWrite => crate::git::Worktree::new(branch)?,
+            };
+            Ok(IssuesDatabase {
+                dir: std::path::PathBuf::from(worktree.path()),
+                worktree: Some(worktree),
+            })
+        }
+    }
+}
+
+pub fn read_issues_database(
+    issues_database_source: &IssuesDatabaseSource,
+) -> anyhow::Result<crate::issues::Issues> {
+    let issues_database =
+        make_issues_database(issues_database_source, IssuesDatabaseAccess::ReadOnly)?;
+    Ok(crate::issues::Issues::new_from_dir(
+        &issues_database.dir,
+    )?)
+}