use git_hash::ObjectId;
use git_object::{bstr::BStr, TreeRefIter};
use git_odb::FindExt;

use crate::{object::find, Id, Tree};

/// Initialization
impl<'repo> Tree<'repo> {
    /// Obtain a tree instance by handing in all components that it is made up of.
    pub fn from_data(id: impl Into<ObjectId>, data: Vec<u8>, repo: &'repo crate::Repository) -> Self {
        Tree {
            id: id.into(),
            data,
            repo,
        }
    }
}

/// Access
impl<'repo> Tree<'repo> {
    /// Return this tree's identifier.
    pub fn id(&self) -> Id<'repo> {
        Id::from_id(self.id, self.repo)
    }

    // TODO: move implementation to git-object, tests.
    /// Follow a sequence of `path` components starting from this instance, and look them up one by one until the last component
    /// is looked up and its tree entry is returned.
    ///
    /// # Performance Notes
    ///
    /// Searching tree entries is currently done in sequence, which allows to the search to be allocation free. It would be possible
    /// to re-use a vector and use a binary search instead, which might be able to improve performance over all.
    /// However, a benchmark should be created first to have some data and see which trade-off to choose here.
    pub fn lookup_path<I, P>(mut self, path: I) -> Result<Option<git_object::tree::Entry>, find::existing::OdbError>
    where
        I: IntoIterator<Item = P>,
        P: PartialEq<BStr>,
    {
        // let mut out = None;
        let mut path = path.into_iter().peekable();
        while let Some(component) = path.next() {
            match TreeRefIter::from_bytes(&self.data)
                .filter_map(Result::ok)
                .find(|entry| component.eq(entry.filename))
            {
                Some(entry) => {
                    if path.peek().is_none() {
                        return Ok(Some(entry.into()));
                    } else {
                        let next_id = entry.oid.to_owned();
                        let handle = self.repo;
                        drop(self);
                        self = match handle.find_object(next_id)?.try_into_tree() {
                            Ok(tree) => tree,
                            Err(_) => return Ok(None),
                        };
                    }
                }
                None => return Ok(None),
            }
        }
        Ok(None)
    }

    /// Obtain a platform for initiating a variety of traversals.
    pub fn traverse(&self) -> Traversal<'_, 'repo> {
        Traversal {
            root: self,
            breadthfirst: BreadthFirstTraversalPresets { root: self },
        }
    }
}

/// An intermediate object to start traversing the parent tree from.
pub struct Traversal<'a, 'repo> {
    root: &'a Tree<'repo>,
    /// TODO: EXPLAIN
    pub breadthfirst: BreadthFirstTraversalPresets<'a, 'repo>,
}

/// TODO: explain THIS!
#[derive(Copy, Clone)]
pub struct BreadthFirstTraversalPresets<'a, 'repo> {
    root: &'a Tree<'repo>,
}

impl<'a, 'repo> BreadthFirstTraversalPresets<'a, 'repo> {
    /// Returns all entries and their file paths, recursively, as reachable from this tree.
    pub fn files(&self) -> Result<Vec<git_traverse::tree::recorder::Entry>, git_traverse::tree::breadthfirst::Error> {
        let mut recorder = git_traverse::tree::Recorder::default();
        Traversal {
            root: self.root,
            breadthfirst: *self,
        }
        .breadthfirst(&mut recorder)?;
        Ok(recorder.records)
    }
}

impl<'a, 'repo> Traversal<'a, 'repo> {
    /// Start a breadth-first traversal with a delegate, note that it's not sorted.
    /// TODO: more docs or links to git-traverse
    pub fn breadthfirst<V>(&self, delegate: &mut V) -> Result<(), git_traverse::tree::breadthfirst::Error>
    where
        V: git_traverse::tree::Visit,
    {
        let root = git_object::TreeRefIter::from_bytes(&self.root.data);
        let state = git_traverse::tree::breadthfirst::State::default();
        git_traverse::tree::breadthfirst(
            root,
            state,
            |oid, buf| self.root.repo.objects.find_tree_iter(oid, buf).ok(),
            delegate,
        )
    }
}

pub use iter::EntryRef;

///
mod iter {
    use super::Tree;
    use crate::Repository;

    /// An entry within a tree
    pub struct EntryRef<'repo, 'a> {
        /// The actual entry ref we are wrapping.
        pub inner: git_object::tree::EntryRef<'a>,

        repo: &'repo Repository,
    }

    impl<'repo, 'a> EntryRef<'repo, 'a> {
        /// The kind of object to which [`id()`][Self::id()] is pointing.
        pub fn mode(&self) -> git_object::tree::EntryMode {
            self.inner.mode
        }

        /// The name of the file in the parent tree.
        pub fn filename(&self) -> &git_object::bstr::BStr {
            self.inner.filename
        }

        /// Return the entries id, connected to the underlying repository.
        pub fn id(&self) -> crate::Id<'repo> {
            crate::Id::from_id(self.inner.oid, self.repo)
        }
    }

    impl<'repo, 'a> std::fmt::Display for EntryRef<'repo, 'a> {
        fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
            write!(
                f,
                "{:06o} {:>6} {}\t{}",
                self.mode() as u32,
                self.mode().as_str(),
                self.id().shorten_or_id(),
                self.filename()
            )
        }
    }

    impl<'repo> Tree<'repo> {
        /// Return an iterator over tree entries.
        pub fn iter(&self) -> impl Iterator<Item = Result<EntryRef<'repo, '_>, git_object::decode::Error>> {
            let repo = self.repo;
            git_object::TreeRefIter::from_bytes(&self.data).map(move |e| e.map(|entry| EntryRef { inner: entry, repo }))
        }
    }
}

impl<'r> std::fmt::Debug for Tree<'r> {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        write!(f, "Tree({})", self.id)
    }
}