// Copyright 2021 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 std::fs::File;
use std::io::{self, Read, Write};
use std::path::{Path, PathBuf};
use std::sync::Arc;

use thiserror::Error;

use crate::backend::Backend;
use crate::git_backend::GitBackend;
use crate::local_backend::LocalBackend;
use crate::op_store::WorkspaceId;
use crate::repo::{BackendFactories, IoResultExt, PathError, ReadonlyRepo, RepoLoader};
use crate::settings::UserSettings;
use crate::working_copy::WorkingCopy;

#[derive(Error, Debug)]
pub enum WorkspaceInitError {
    #[error("The destination repo ({0}) already exists")]
    DestinationExists(PathBuf),
    #[error("Repo path could not be interpreted as Unicode text")]
    NonUnicodePath,
    #[error(transparent)]
    Path(#[from] PathError),
}

#[derive(Error, Debug)]
pub enum WorkspaceLoadError {
    #[error("The repo appears to no longer be at {0}")]
    RepoDoesNotExist(PathBuf),
    #[error("There is no Jujutsu repo in {0}")]
    NoWorkspaceHere(PathBuf),
    #[error("Repo path could not be interpreted as Unicode text")]
    NonUnicodePath,
    #[error(transparent)]
    Path(#[from] PathError),
}

/// Represents a workspace, i.e. what's typically the .jj/ directory and its
/// parent.
pub struct Workspace {
    // Path to the workspace root (typically the parent of a .jj/ directory), which is where
    // working copy files live.
    workspace_root: PathBuf,
    repo_loader: RepoLoader,
    working_copy: WorkingCopy,
}

fn create_jj_dir(workspace_root: &Path) -> Result<PathBuf, WorkspaceInitError> {
    let jj_dir = workspace_root.join(".jj");
    match std::fs::create_dir(&jj_dir).context(&jj_dir) {
        Ok(()) => Ok(jj_dir),
        Err(ref e) if e.error.kind() == io::ErrorKind::AlreadyExists => {
            Err(WorkspaceInitError::DestinationExists(jj_dir))
        }
        Err(e) => Err(e.into()),
    }
}

fn init_working_copy(
    user_settings: &UserSettings,
    repo: &Arc<ReadonlyRepo>,
    workspace_root: &Path,
    jj_dir: &Path,
    workspace_id: WorkspaceId,
) -> Result<(WorkingCopy, Arc<ReadonlyRepo>), WorkspaceInitError> {
    let working_copy_state_path = jj_dir.join("working_copy");
    std::fs::create_dir(&working_copy_state_path).context(&working_copy_state_path)?;

    let mut tx = repo.start_transaction(
        user_settings,
        &format!("add workspace '{}'", workspace_id.as_str()),
    );
    tx.mut_repo().check_out(
        workspace_id.clone(),
        user_settings,
        &repo.store().root_commit(),
    );
    let repo = tx.commit();

    let working_copy = WorkingCopy::init(
        repo.store().clone(),
        workspace_root.to_path_buf(),
        working_copy_state_path,
        repo.op_id().clone(),
        workspace_id,
    );
    Ok((working_copy, repo))
}

impl Workspace {
    fn new(
        workspace_root: &Path,
        working_copy: WorkingCopy,
        repo_loader: RepoLoader,
    ) -> Result<Workspace, PathError> {
        let workspace_root = workspace_root.canonicalize().context(workspace_root)?;
        Ok(Workspace {
            workspace_root,
            repo_loader,
            working_copy,
        })
    }

    pub fn init_local(
        user_settings: &UserSettings,
        workspace_root: &Path,
    ) -> Result<(Self, Arc<ReadonlyRepo>), WorkspaceInitError> {
        Self::init_with_backend(user_settings, workspace_root, |store_path| {
            Box::new(LocalBackend::init(store_path))
        })
    }

    /// Initializes a workspace with a new Git backend in .jj/git/ (bare Git
    /// repo)
    pub fn init_internal_git(
        user_settings: &UserSettings,
        workspace_root: &Path,
    ) -> Result<(Self, Arc<ReadonlyRepo>), WorkspaceInitError> {
        Self::init_with_backend(user_settings, workspace_root, |store_path| {
            Box::new(GitBackend::init_internal(store_path))
        })
    }

    /// Initializes a workspace with an existing Git backend at the specified
    /// path
    pub fn init_external_git(
        user_settings: &UserSettings,
        workspace_root: &Path,
        git_repo_path: &Path,
    ) -> Result<(Self, Arc<ReadonlyRepo>), WorkspaceInitError> {
        Self::init_with_backend(user_settings, workspace_root, |store_path| {
            Box::new(GitBackend::init_external(store_path, git_repo_path))
        })
    }

    pub fn init_with_backend(
        user_settings: &UserSettings,
        workspace_root: &Path,
        backend_factory: impl FnOnce(&Path) -> Box<dyn Backend>,
    ) -> Result<(Self, Arc<ReadonlyRepo>), WorkspaceInitError> {
        let jj_dir = create_jj_dir(workspace_root)?;
        let repo_dir = jj_dir.join("repo");
        std::fs::create_dir(&repo_dir).context(&repo_dir)?;
        let repo = ReadonlyRepo::init(user_settings, &repo_dir, backend_factory)?;
        let (working_copy, repo) = init_working_copy(
            user_settings,
            &repo,
            workspace_root,
            &jj_dir,
            WorkspaceId::default(),
        )?;
        let repo_loader = repo.loader();
        let workspace = Workspace::new(workspace_root, working_copy, repo_loader)?;
        Ok((workspace, repo))
    }

    pub fn init_workspace_with_existing_repo(
        user_settings: &UserSettings,
        workspace_root: &Path,
        repo: &Arc<ReadonlyRepo>,
        workspace_id: WorkspaceId,
    ) -> Result<(Self, Arc<ReadonlyRepo>), WorkspaceInitError> {
        let jj_dir = create_jj_dir(workspace_root)?;

        let repo_dir = repo.repo_path().canonicalize().context(repo.repo_path())?;
        let repo_file_path = jj_dir.join("repo");
        let mut repo_file = File::create(&repo_file_path).context(&repo_file_path)?;
        repo_file
            .write_all(
                repo_dir
                    .to_str()
                    .ok_or(WorkspaceInitError::NonUnicodePath)?
                    .as_bytes(),
            )
            .context(&repo_file_path)?;

        let (working_copy, repo) =
            init_working_copy(user_settings, repo, workspace_root, &jj_dir, workspace_id)?;
        let workspace = Workspace::new(workspace_root, working_copy, repo.loader())?;
        Ok((workspace, repo))
    }

    pub fn load(
        user_settings: &UserSettings,
        workspace_path: &Path,
        backend_factories: &BackendFactories,
    ) -> Result<Self, WorkspaceLoadError> {
        let jj_dir = find_jj_dir(workspace_path)
            .ok_or_else(|| WorkspaceLoadError::NoWorkspaceHere(workspace_path.to_owned()))?;
        let workspace_root = jj_dir
            .parent()
            .ok_or(WorkspaceLoadError::NonUnicodePath)?
            .to_owned();
        let mut repo_dir = jj_dir.join("repo");
        // If .jj/repo is a file, then we interpret its contents as a relative path to
        // the actual repo directory (typically in another workspace).
        if repo_dir.is_file() {
            let mut repo_file = File::open(&repo_dir).context(&repo_dir)?;
            let mut buf = Vec::new();
            repo_file.read_to_end(&mut buf).context(&repo_dir)?;
            let repo_path_str =
                String::from_utf8(buf).map_err(|_| WorkspaceLoadError::NonUnicodePath)?;
            repo_dir = jj_dir
                .join(&repo_path_str)
                .canonicalize()
                .context(&repo_path_str)?;
            if !repo_dir.is_dir() {
                return Err(WorkspaceLoadError::RepoDoesNotExist(repo_dir));
            }
        }
        let repo_loader = RepoLoader::init(user_settings, &repo_dir, backend_factories);
        let working_copy_state_path = jj_dir.join("working_copy");
        let working_copy = WorkingCopy::load(
            repo_loader.store().clone(),
            workspace_root.clone(),
            working_copy_state_path,
        );
        Ok(Workspace::new(&workspace_root, working_copy, repo_loader)?)
    }

    pub fn workspace_root(&self) -> &PathBuf {
        &self.workspace_root
    }

    pub fn workspace_id(&self) -> &WorkspaceId {
        self.working_copy.workspace_id()
    }

    pub fn repo_path(&self) -> &PathBuf {
        self.repo_loader.repo_path()
    }

    pub fn repo_loader(&self) -> &RepoLoader {
        &self.repo_loader
    }

    pub fn working_copy(&self) -> &WorkingCopy {
        &self.working_copy
    }

    pub fn working_copy_mut(&mut self) -> &mut WorkingCopy {
        &mut self.working_copy
    }
}

fn find_jj_dir(mut workspace_root: &Path) -> Option<PathBuf> {
    loop {
        let jj_path = workspace_root.join(".jj");
        if jj_path.is_dir() {
            return Some(jj_path);
        }
        workspace_root = workspace_root.parent()?;
    }
}