refactor: move policy on whether to back up a file into a module

This commit also splits up the src/cmd/backup.rs module into other,
smaller, more cohesive modules that are easier to understand and use.

1 files changed, 64 insertions, 0 deletions

diff --git a/src/policy.rs b/src/policy.rs
new file mode 100644
index 0000000..032b851
--- /dev/null
+++ b/src/policy.rs
@@ -0,0 +1,64 @@
+use crate::backup_reason::Reason;
+use crate::fsentry::FilesystemEntry;
+use crate::generation::LocalGeneration;
+use log::{debug, warn};
+
+pub struct BackupPolicy {
+    new: bool,
+    old_if_changed: bool,
+}
+
+impl BackupPolicy {
+    pub fn new() -> Self {
+        Self {
+            new: true,
+            old_if_changed: true,
+        }
+    }
+
+    pub fn needs_backup(&self, old: &LocalGeneration, new_entry: &FilesystemEntry) -> Reason {
+        let new_name = new_entry.pathbuf();
+        let reason = match old.get_file(&new_name) {
+            Ok(None) => {
+                if self.new {
+                    Reason::IsNew
+                } else {
+                    Reason::Skipped
+                }
+            }
+            Ok(Some(old_entry)) => {
+                if self.old_if_changed {
+                    if file_has_changed(&old_entry, new_entry) {
+                        Reason::Changed
+                    } else {
+                        Reason::Unchanged
+                    }
+                } else {
+                    Reason::Skipped
+                }
+            }
+            Err(err) => {
+                warn!(
+                    "needs_backup: lookup in old generation returned error, ignored: {:?}: {}",
+                    new_name, err
+                );
+                Reason::Error
+            }
+        };
+        debug!(
+            "needs_backup: file {:?}: policy decision: {}",
+            new_name, reason
+        );
+        reason
+    }
+}
+
+fn file_has_changed(old: &FilesystemEntry, new: &FilesystemEntry) -> bool {
+    let unchanged = old.kind() == new.kind()
+        && old.len() == new.len()
+        && old.mode() == new.mode()
+        && old.mtime() == new.mtime()
+        && old.mtime_ns() == new.mtime_ns()
+        && old.symlink_target() == new.symlink_target();
+    !unchanged
+}