// Copyright 2020 Google LLC
//
// 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.

use crate::store::{CommitId, Timestamp};
use std::collections::HashSet;
use std::fmt::{Debug, Error, Formatter};

#[derive(PartialEq, Eq, PartialOrd, Ord, Clone, Hash)]
pub struct ViewId(pub Vec<u8>);

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

impl ViewId {
    pub fn hex(&self) -> String {
        hex::encode(&self.0)
    }
}

#[derive(PartialEq, Eq, PartialOrd, Ord, Clone, Hash)]
pub struct OperationId(pub Vec<u8>);

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

impl OperationId {
    pub fn hex(&self) -> String {
        hex::encode(&self.0)
    }
}

/// Represents the way the repo looks at a given time, just like how a Tree
/// object represents how the file system looks at a given time.
#[derive(Clone)]
pub struct View {
    /// All head commits
    pub head_ids: HashSet<CommitId>,
    // The commit that *should be* checked out in the (default) working copy. Note that the
    // working copy (.jj/working_copy/) has the source of truth about which commit *is* checked out
    // (to be precise: the commit to which we most recently completed a checkout to).
    // TODO: Allow multiple working copies
    pub checkout: CommitId,
}

impl View {
    pub fn new(checkout: CommitId) -> Self {
        Self {
            head_ids: HashSet::new(),
            checkout,
        }
    }
}

/// Represents an operation (transaction) on the repo view, just like how a
/// Commit object represents an operation on the tree.
///
/// Operations and views are not meant to be exchanged between repos or users;
/// they represent local state and history.
///
/// The operation history will almost always be linear. It will only have
/// forks when parallel operations occurred. The parent is determined when
/// the transaction starts. When the transaction commits, a lock will be
/// taken and it will be checked that the current head of the operation
/// graph is unchanged. If the current head has changed, there has been
/// concurrent operation.
#[derive(Clone)]
pub struct Operation {
    pub view_id: ViewId,
    pub parents: Vec<OperationId>,
    pub metadata: OperationMetadata,
}

#[derive(Clone)]
pub struct OperationMetadata {
    pub start_time: Timestamp,
    pub end_time: Timestamp,
    // Whatever is useful to the user, such as exact command line call
    pub description: String,
    pub hostname: String,
    pub username: String,
}

impl OperationMetadata {
    pub fn new(description: String) -> Self {
        let timestamp = Timestamp::now();
        let hostname = whoami::hostname();
        let username = whoami::username();
        OperationMetadata {
            start_time: timestamp.clone(),
            end_time: timestamp,
            description,
            hostname,
            username,
        }
    }
}

#[derive(Debug)]
pub enum OpStoreError {
    NotFound,
    Other(String),
}

pub type OpStoreResult<T> = Result<T, OpStoreError>;

pub trait OpStore: Send + Sync + Debug {
    fn read_view(&self, id: &ViewId) -> OpStoreResult<View>;

    fn write_view(&self, contents: &View) -> OpStoreResult<ViewId>;

    fn read_operation(&self, id: &OperationId) -> OpStoreResult<Operation>;

    fn write_operation(&self, contents: &Operation) -> OpStoreResult<OperationId>;
}
