1 files changed, 49 insertions, 0 deletions
diff --git a/src/prune.rs b/src/prune.rs
new file mode 100644
index 0000000..dd7a5fb
--- /dev/null
+++ b/src/prune.rs
@@ -0,0 +1,49 @@
+use std::path::Path;
+use std::fs::File;
+use std::io::prelude::*;
+use chrono::{NaiveDate, Duration};
+
+use crate::parse::*;
+
+pub fn prune_week_from_file(week: NaiveDate, file_str: &str) -> String {
+    let path = Path::new(file_str);
+    let display = path.display();
+
+    // Open the path in read-only mode, returns `io::Result<File>`
+    let mut file = match File::open(&path) {
+        Err(why) => panic!("Error opening {}: {}", display, why),
+        Ok(file) => file,
+    };
+
+    // Read the file contents into a string, returns `io::Result<usize>`
+    let mut s = String::new();
+    match file.read_to_string(&mut s) {
+        Err(why) => panic!("Couldn't read {}: {}", display, why),
+        Ok(_) => return prune_week_from_str(week, &s),
+    }
+}
+
+fn prune_week_from_str(week: NaiveDate, file_str: &str) -> String {
+    let mut new_contents = "\n".to_string();
+    let mut ghost = false;
+    let ghost_start = week - Duration::days(6);
+    let ghost_end = week + Duration::days(6);
+    for l in file_str.split('\n') {
+        if l.starts_with("# ") {
+            // '# 12/27/21', starts a new week block
+            let start_date = parse_date_line(l).expect("Couldn't parse '# ' header.");
+            ghost = ghost_start <= start_date && start_date <= ghost_end;
+            if ghost && start_date != week {
+                panic!("generate currently assumes `# ` headers always start on Mondays.");
+            }
+        }
+        if !ghost {
+            new_contents.push_str(l);
+            new_contents.push('\n');
+        }
+    }
+    // Remove leading & trailing newlines.
+    new_contents.remove(0);
+    new_contents.pop();
+    return new_contents;
+}