// 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::collections::{btree_map, BTreeMap, HashMap, HashSet};
use std::fmt::{Debug, Error, Formatter};
use std::ops::{Deref, DerefMut};
use std::slice;

use thiserror::Error;

use crate::backend::{CommitId, Timestamp};
use crate::content_hash::ContentHash;

content_hash! {
    #[derive(PartialEq, Eq, PartialOrd, Ord, Clone, Hash)]
    pub struct WorkspaceId(String);
}

impl Debug for WorkspaceId {
    fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error> {
        f.debug_tuple("WorkspaceId").field(&self.0).finish()
    }
}

impl Default for WorkspaceId {
    fn default() -> Self {
        Self("default".to_string())
    }
}

impl WorkspaceId {
    pub fn new(value: String) -> Self {
        Self(value)
    }

    pub fn as_str(&self) -> &str {
        &self.0
    }
}

content_hash! {
    #[derive(PartialEq, Eq, PartialOrd, Ord, Clone, Hash)]
    pub struct ViewId(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 new(value: Vec<u8>) -> Self {
        Self(value)
    }

    pub fn from_hex(hex: &str) -> Self {
        Self(hex::decode(hex).unwrap())
    }

    pub fn as_bytes(&self) -> &[u8] {
        &self.0
    }

    pub fn to_bytes(&self) -> Vec<u8> {
        self.0.clone()
    }

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

content_hash! {
    #[derive(PartialEq, Eq, PartialOrd, Ord, Clone, Hash)]
    pub struct OperationId(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 new(value: Vec<u8>) -> Self {
        Self(value)
    }

    pub fn from_hex(hex: &str) -> Self {
        Self(hex::decode(hex).unwrap())
    }

    pub fn as_bytes(&self) -> &[u8] {
        &self.0
    }

    pub fn to_bytes(&self) -> Vec<u8> {
        self.0.clone()
    }

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

#[derive(PartialEq, Eq, Hash, Clone, Debug)]
pub enum RefTarget {
    Normal(CommitId),
    Conflict {
        removes: Vec<CommitId>,
        adds: Vec<CommitId>,
    },
}

impl ContentHash for RefTarget {
    fn hash(&self, state: &mut impl digest::Update) {
        use RefTarget::*;
        match self {
            Normal(id) => {
                state.update(&0u32.to_le_bytes());
                id.hash(state);
            }
            Conflict { removes, adds } => {
                state.update(&1u32.to_le_bytes());
                removes.hash(state);
                adds.hash(state);
            }
        }
    }
}

impl RefTarget {
    /// Creates non-conflicting target pointing to no commit.
    pub fn absent() -> Option<Self> {
        None
    }

    /// Returns non-conflicting target pointing to no commit.
    ///
    /// This will typically be used in place of `None` returned by map lookup.
    pub fn absent_ref() -> Option<&'static Self> {
        // TODO: This will be static ref to Conflict::resolved(None).
        None
    }

    /// Creates non-conflicting target pointing to a commit.
    pub fn normal(id: CommitId) -> Option<Self> {
        Some(RefTarget::Normal(id))
    }

    /// Creates conflicting target from removed/added ids.
    pub fn from_legacy_form(
        removed_ids: impl IntoIterator<Item = CommitId>,
        added_ids: impl IntoIterator<Item = CommitId>,
    ) -> Option<Self> {
        // TODO: This function will create non-conflicting target if there're only one
        // add id and no removed ids.
        let removes = removed_ids.into_iter().collect();
        let adds = added_ids.into_iter().collect();
        Some(RefTarget::Conflict { removes, adds })
    }

    /// Returns id if this target is non-conflicting and points to a commit.
    pub fn as_normal(&self) -> Option<&CommitId> {
        match self {
            RefTarget::Normal(id) => Some(id),
            RefTarget::Conflict { .. } => None,
        }
    }

    pub fn is_conflict(&self) -> bool {
        matches!(self, RefTarget::Conflict { .. })
    }

    pub fn removed_ids(&self) -> slice::Iter<'_, CommitId> {
        let removes: &[_] = match self {
            RefTarget::Normal(_) => &[],
            RefTarget::Conflict { removes, adds: _ } => removes,
        };
        removes.iter()
    }

    pub fn added_ids(&self) -> slice::Iter<'_, CommitId> {
        let adds: &[_] = match self {
            RefTarget::Normal(id) => slice::from_ref(id),
            RefTarget::Conflict { removes: _, adds } => adds,
        };
        adds.iter()
    }
}

// TODO: These methods will be migrate to new Conflict-based RefTarget type.
pub trait RefTargetExt {
    fn as_normal(&self) -> Option<&CommitId>;
    fn is_absent(&self) -> bool;
    fn is_present(&self) -> bool;
    fn is_conflict(&self) -> bool;
    fn removed_ids(&self) -> slice::Iter<'_, CommitId>;
    fn added_ids(&self) -> slice::Iter<'_, CommitId>;
}

impl RefTargetExt for Option<RefTarget> {
    fn as_normal(&self) -> Option<&CommitId> {
        self.as_ref().and_then(|target| target.as_normal())
    }

    fn is_absent(&self) -> bool {
        self.is_none()
    }

    fn is_present(&self) -> bool {
        self.is_some()
    }

    fn is_conflict(&self) -> bool {
        self.as_ref()
            .map(|target| target.is_conflict())
            .unwrap_or(false)
    }

    fn removed_ids(&self) -> slice::Iter<'_, CommitId> {
        self.as_ref()
            .map(|target| target.removed_ids())
            .unwrap_or_else(|| [].iter())
    }

    fn added_ids(&self) -> slice::Iter<'_, CommitId> {
        self.as_ref()
            .map(|target| target.added_ids())
            .unwrap_or_else(|| [].iter())
    }
}

impl RefTargetExt for Option<&RefTarget> {
    fn as_normal(&self) -> Option<&CommitId> {
        self.and_then(|target| target.as_normal())
    }

    fn is_absent(&self) -> bool {
        self.is_none()
    }

    fn is_present(&self) -> bool {
        self.is_some()
    }

    fn is_conflict(&self) -> bool {
        self.map(|target| target.is_conflict()).unwrap_or(false)
    }

    fn removed_ids(&self) -> slice::Iter<'_, CommitId> {
        self.map(|target| target.removed_ids())
            .unwrap_or_else(|| [].iter())
    }

    fn added_ids(&self) -> slice::Iter<'_, CommitId> {
        self.map(|target| target.added_ids())
            .unwrap_or_else(|| [].iter())
    }
}

/// Wrapper to exclude absent `RefTarget` entries from `ContentHash`.
#[derive(Default, PartialEq, Eq, Clone, Debug)]
pub struct RefTargetMap(pub BTreeMap<String, RefTarget>);

impl RefTargetMap {
    pub fn new() -> Self {
        RefTargetMap(BTreeMap::new())
    }
}

// TODO: Update serialization code to preserve absent RefTarget entries, and
// remove this wrapper.
impl ContentHash for RefTargetMap {
    fn hash(&self, state: &mut impl digest::Update) {
        // Derived from content_hash.rs. It's okay for this to produce a different hash
        // value than the inner map, but the value must not be equal to the map which
        // preserves absent RefTarget entries.
        state.update(&(self.0.len() as u64).to_le_bytes());
        for (k, v) in self.0.iter() {
            k.hash(state);
            v.hash(state);
        }
    }
}

// Abuse Deref as this is a temporary workaround. See the comment above.
impl Deref for RefTargetMap {
    type Target = BTreeMap<String, RefTarget>;

    fn deref(&self) -> &Self::Target {
        &self.0
    }
}

impl DerefMut for RefTargetMap {
    fn deref_mut(&mut self) -> &mut Self::Target {
        &mut self.0
    }
}

impl IntoIterator for RefTargetMap {
    type Item = (String, RefTarget);
    type IntoIter = btree_map::IntoIter<String, RefTarget>;

    fn into_iter(self) -> Self::IntoIter {
        self.0.into_iter()
    }
}

impl<'a> IntoIterator for &'a RefTargetMap {
    type Item = (&'a String, &'a RefTarget);
    type IntoIter = btree_map::Iter<'a, String, RefTarget>;

    fn into_iter(self) -> Self::IntoIter {
        self.0.iter()
    }
}

content_hash! {
    #[derive(Default, PartialEq, Eq, Clone, Debug)]
    pub struct BranchTarget {
        /// The commit the branch points to locally. `None` if the branch has been
        /// deleted locally.
        pub local_target: Option<RefTarget>,
        // TODO: Do we need to support tombstones for remote branches? For example, if the branch
        // has been deleted locally and you pull from a remote, maybe it should make a difference
        // whether the branch is known to have existed on the remote. We may not want to resurrect
        // the branch if the branch's state on the remote was just not known.
        pub remote_targets: RefTargetMap,
    }
}

content_hash! {
    /// 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(PartialEq, Eq, Clone, Debug, Default)]
    pub struct View {
        /// All head commits
        pub head_ids: HashSet<CommitId>,
        /// Heads of the set of public commits.
        pub public_head_ids: HashSet<CommitId>,
        pub branches: BTreeMap<String, BranchTarget>,
        pub tags: RefTargetMap,
        pub git_refs: RefTargetMap,
        /// The commit the Git HEAD points to.
        // TODO: Support multiple Git worktrees?
        // TODO: Do we want to store the current branch name too?
        pub git_head: Option<RefTarget>,
        // The commit that *should be* checked out in the workspace. 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 an update to).
        pub wc_commit_ids: HashMap<WorkspaceId, CommitId>,
    }
}

content_hash! {
    /// 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(PartialEq, Eq, Clone, Debug)]
    pub struct Operation {
        pub view_id: ViewId,
        pub parents: Vec<OperationId>,
        pub metadata: OperationMetadata,
    }
}

content_hash! {
    #[derive(PartialEq, Eq, Clone, Debug)]
    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,
        pub tags: HashMap<String, String>,
    }
}

#[derive(Debug, Error)]
pub enum OpStoreError {
    #[error("Operation not found")]
    NotFound,
    #[error("{0}")]
    Other(String),
}

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

pub trait OpStore: Send + Sync + Debug {
    fn name(&self) -> &str;

    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>;
}