// Copyright 2020 The Jujutsu Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

#![allow(missing_docs)]

use std::cmp::Ordering;
use std::fmt::{Debug, Error, Formatter};
use std::hash::{Hash, Hasher};
use std::sync::Arc;

use crate::backend;
use crate::backend::{BackendError, ChangeId, CommitId, MergedTreeId, Signature};
use crate::merged_tree::MergedTree;
use crate::repo_path::RepoPath;
use crate::store::Store;
use crate::tree::Tree;

#[derive(Clone)]
pub struct Commit {
    store: Arc<Store>,
    id: CommitId,
    data: Arc<backend::Commit>,
}

impl Debug for Commit {
    fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error> {
        f.debug_struct("Commit").field("id", &self.id).finish()
    }
}

impl PartialEq for Commit {
    fn eq(&self, other: &Self) -> bool {
        self.id == other.id
    }
}

impl Eq for Commit {}

impl Ord for Commit {
    fn cmp(&self, other: &Self) -> Ordering {
        self.id.cmp(&other.id)
    }
}

impl PartialOrd for Commit {
    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
        Some(self.cmp(other))
    }
}

impl Hash for Commit {
    fn hash<H: Hasher>(&self, state: &mut H) {
        self.id.hash(state)
    }
}

impl Commit {
    pub fn new(store: Arc<Store>, id: CommitId, data: Arc<backend::Commit>) -> Self {
        Commit { store, id, data }
    }

    pub fn store(&self) -> &Arc<Store> {
        &self.store
    }

    pub fn id(&self) -> &CommitId {
        &self.id
    }

    pub fn parent_ids(&self) -> &[CommitId] {
        &self.data.parents
    }

    pub fn parents(&self) -> Vec<Commit> {
        self.data
            .parents
            .iter()
            .map(|id| self.store.get_commit(id).unwrap())
            .collect()
    }

    pub fn predecessor_ids(&self) -> &[CommitId] {
        &self.data.predecessors
    }

    pub fn predecessors(&self) -> Vec<Commit> {
        self.data
            .predecessors
            .iter()
            .map(|id| self.store.get_commit(id).unwrap())
            .collect()
    }

    // TODO(#1624): Delete when all callers use `merged_tree()`
    pub fn tree(&self) -> Tree {
        self.store
            .get_tree(&RepoPath::root(), self.data.root_tree.as_legacy_tree_id())
            .unwrap()
    }

    pub fn merged_tree(&self) -> Result<MergedTree, BackendError> {
        self.store.get_root_tree(&self.data.root_tree)
    }

    pub fn merged_tree_id(&self) -> &MergedTreeId {
        &self.data.root_tree
    }

    pub fn change_id(&self) -> &ChangeId {
        &self.data.change_id
    }

    pub fn store_commit(&self) -> &backend::Commit {
        &self.data
    }

    pub fn description(&self) -> &str {
        &self.data.description
    }

    pub fn author(&self) -> &Signature {
        &self.data.author
    }

    pub fn committer(&self) -> &Signature {
        &self.data.committer
    }

    /// A commit is discardable if it has one parent, no change from its
    /// parent, and an empty description.
    pub fn is_discardable(&self) -> bool {
        if self.description().is_empty() {
            if let [parent_commit] = &*self.parents() {
                return self.merged_tree_id() == parent_commit.merged_tree_id();
            }
        }
        false
    }
}

/// Wrapper to sort `Commit` by committer timestamp.
#[derive(Clone, Debug, Eq, Hash, PartialEq)]
pub(crate) struct CommitByCommitterTimestamp(pub Commit);

impl Ord for CommitByCommitterTimestamp {
    fn cmp(&self, other: &Self) -> Ordering {
        let self_timestamp = &self.0.committer().timestamp.timestamp;
        let other_timestamp = &other.0.committer().timestamp.timestamp;
        self_timestamp
            .cmp(other_timestamp)
            .then_with(|| self.0.cmp(&other.0)) // to comply with Eq
    }
}

impl PartialOrd for CommitByCommitterTimestamp {
    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
        Some(self.cmp(other))
    }
}