use crate::{files::FileTree, Diff, HashId};
use git2::Repository;
use std::{
    fmt::{self, Debug, Formatter},
    sync::Arc,
};

/// Represent a commit on a repository
///
/// When creating a commit object, it is guaranteed that it exists in
/// the repository.
#[derive(Clone)]
pub struct Commit {
    pub id: HashId,
    repo: Arc<Repository>,
}

impl Debug for Commit {
    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
        write!(f, "{}", self.id)
    }
}

impl Commit {
    /// Create a commit object and check if it exists in the repo
    pub(crate) fn new(r: &Arc<Repository>, id: HashId) -> Option<Self> {
        r.find_commit(id.to_oid()).ok().map(|_| Self {
            id,
            repo: Arc::clone(r),
        })
    }

    /// Get a utf-8 string representation of the commit ID
    pub fn id_str(&self) -> String {
        self.id.to_string()
    }

    /// Get the summary line as a utf-8 string
    pub fn summary(&self) -> String {
        self.find().summary().unwrap().into()
    }

    /// Get the number of parents
    pub fn parent_count(&self) -> usize {
        self.repo
            .find_commit(self.id.to_oid())
            .unwrap()
            .parent_count()
    }

    /// Return the first parent, if it exists
    pub fn first_parent(&self) -> Option<Self> {
        self.find()
            .parent(0)
            .ok()
            .and_then(|c| Self::new(&self.repo, c.id().into()))
    }

    /// Get a specific parent, if it exists
    pub fn parent(&self, num: usize) -> Option<Self> {
        self.find()
            .parent(num)
            .ok()
            .and_then(|c| Self::new(&self.repo, c.id().into()))
    }

    /// Get the set of parents as a vector
    ///
    /// Use this function if you suspect a commit has more than one
    /// parent.
    pub fn parents(&self) -> Vec<Commit> {
        self.find()
            .parents()
            .map(|c| Self::new(&self.repo, c.id().into()).unwrap())
            .collect()
    }

    /// Get the file tree for this commit
    pub fn tree(&self) -> FileTree {
        FileTree::new(Arc::clone(&self.repo), self.id.clone())
    }

    /// Get the list of paths in the repository touched by this commit
    ///
    /// Using this function directly is often not what you want.
    /// Instead, use the `get_history(...)` function on `FileTree`,
    /// which uses this function.
    pub fn get_paths(&self) -> Vec<String> {
        self.get_diff()
            .map(|d| Diff::from(d))
            .map_or(vec![], |d| d.get_paths())
    }

    /// Utility function to get a merged diff from all parents
    fn get_diff(&self) -> Option<git2::Diff> {
        // Get all diffs with parents
        let stree = self.find().tree().unwrap();
        let mut vec = self
            .parents()
            .into_iter()
            .filter_map(|p| {
                self.repo
                    .diff_tree_to_tree(Some(&stree), Some(p.find().tree().as_ref().unwrap()), None)
                    .ok()
            })
            .collect::<Vec<_>>();

        // If there are no parents
        if vec.len() == 0 {
            vec = vec![self.repo.diff_tree_to_tree(Some(&stree), None, None).ok()?];
        }

        // Take the first and merge onto
        let first = vec.remove(0);
        Some(vec.iter().fold(first, |mut acc, diff| {
            acc.merge(diff).unwrap();
            acc
        }))
    }

    fn find(&self) -> git2::Commit {
        self.repo.find_commit(self.id.to_oid()).unwrap()
    }
}