//! A set of tree utilities used internally in the tree.rs module

use crate::HashId;
use git2::{Repository, Tree};
use std::{iter::Peekable, path::PathBuf, sync::Arc};

pub(super) trait PairIter<I, K>
where
    I: Iterator<Item = K>,
{
    /// Step through
    fn pairs<'i, F: FnMut(K, Option<&K>)>(&'i mut self, cb: F);

    fn next_pair<'i>(&'i mut self) -> (Option<K>, Option<&K>);
}

impl<I, K> PairIter<I, K> for Peekable<I>
where
    I: Iterator<Item = K>,
{
    fn pairs<'i, F: FnMut(K, Option<&K>)>(&'i mut self, mut cb: F) {
        // Iterate until a->None
        while let (Some(a), b) = self.next_pair() {
            cb(a, b);
        }
    }

    fn next_pair<'i>(&'i mut self) -> (Option<K>, Option<&K>) {
        (self.next(), self.peek())
    }
}

/// Take a vector of path segments, and turn it into a valid offset path
///
/// There are tests to make sure this function works properly.
/// Following are some example transformations.
///
/// * vec![] -> ""
/// * vec!["foo"] -> "foo"
/// * vec!["foo", "bar", "baz"] -> "foo/bar/baz"
pub(super) fn path_segs_join(segments: Vec<&str>) -> String {
    segments
        .into_iter()
        .fold(PathBuf::new(), |buf, seg| buf.join(seg))
        .as_path()
        .to_str()
        .unwrap()
        .to_owned()
}

/// Take an offset path inside the repository and split it into a vec
pub(super) fn path_split(path: &str) -> Vec<&str> {
    path.split("/").filter(|s| s != &"").collect()
}

/// Compare a path and entry to a target buffer
pub(super) fn path_cmp(target: &Vec<&str>, path: &str, entry: &str) -> bool {
    let mut buf = path_split(path);
    buf.push(entry);

    target == &buf
}

/// Open a tree for a particular commit
pub(super) fn open_tree<'r>(repo: &'r Arc<Repository>, c: &HashId) -> Option<Tree<'r>> {
    repo.find_commit(c.to_oid()).unwrap().tree().ok()
}

#[test]
fn empty_path() {
    assert_eq!(path_segs_join(vec![]), String::from(""));
}

#[test]
fn one_path() {
    assert_eq!(path_segs_join(vec!["foo".into()]), String::from("foo"));
}

#[test]
fn nested_path() {
    assert_eq!(
        path_segs_join(vec!["foo".into(), "bar".into(), "baz".into()]),
        String::from("foo/bar/baz")
    );
}

#[test]
fn pair_iterator() {
    // The pair iterator needs access to `peek()`
    let mut i = vec![1, 2, 3, 4].into_iter().peekable();

    assert_eq!(i.next_pair(), (Some(1), Some(&2)));
    assert_eq!(i.next_pair(), (Some(2), Some(&3)));
    assert_eq!(i.next_pair(), (Some(3), Some(&4)));
    assert_eq!(i.next_pair(), (Some(4), None));
}