#![allow(dead_code)]

use futures::future::TryFutureExt;
use pathdiff::diff_paths;
use std::collections::HashMap;
use std::fmt;
use std::path::{Path, PathBuf};
use std::process::Stdio;
use tokio::fs;
use tokio::process::Command;
use tokio::sync::{RwLock, Semaphore};

use crate::fs_utils;

#[derive(Debug)]
pub struct Error {
    pub message: String,
}

impl Error {
    fn new(message: impl Into<String>) -> Self {
        Self {
            message: message.into(),
        }
    }
}

impl fmt::Display for Error {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "{}", self.message)
    }
}

impl std::error::Error for Error {}

pub const EMPTY: &str = "0000000000000000000000000000000000000000";

struct RepoData {
    // Only one fetch at a time, and they should be in queue
    fetch_semaphore: Semaphore,
    config_cache: HashMap<String, String>,
}

pub struct Repository {
    path: PathBuf,
    bare: bool,

    remote: Option<String>,
    project_id: Option<String>,
    socket: Option<PathBuf>,
    githook: Option<PathBuf>,
    ssh_config: Option<PathBuf>,

    // Lock for any repo task, 90% of all tasks are readers but there are some writers
    // where nothing else may be done.
    lock: RwLock<RepoData>,
}

#[allow(dead_code)]
pub struct User {
    pub name: String,
    pub email: String,
    // Part before '@' in email
    pub username: String,
}

#[derive(Debug, PartialEq)]
pub enum ObjectType {
    BLOB,
    COMMIT,
    TREE,
}

#[derive(Debug, PartialEq)]
pub struct TreeEntry {
    pub object_type: ObjectType,
    pub object_name: String,
    pub path: String,
}

fn io_err(action: &str, e: std::io::Error) -> Error {
    Error::new(format!("{action}: {e}"))
}

fn parse_user(output: String) -> User {
    let mut lines = output.split_terminator('\0');
    let name = lines.next().unwrap_or("").to_string();
    let username = lines.next().unwrap_or("").to_string();
    let email = lines.next().unwrap_or("").to_string();
    User {
        name,
        email,
        username,
    }
}

fn parse_tree_entries(output: String) -> Vec<TreeEntry> {
    let mut ret = Vec::new();
    for line in output.split_terminator('\0') {
        let mut parts = line.split_terminator('\t');
        let mut parts2 = parts.next().unwrap_or("").split_terminator(' ');
        parts2.next(); // object mode
        let object_type = match parts2.next() {
            Some(value) => match value {
                "blob" => ObjectType::BLOB,
                "commit" => ObjectType::COMMIT,
                "tree" => ObjectType::TREE,
                _ => continue,
            },
            None => continue,
        };
        if let Some(object_name) = parts2.next() {
            if let Some(path) = parts.next() {
                ret.push(TreeEntry {
                    object_type,
                    object_name: object_name.to_string(),
                    path: path.to_string(),
                });
            }
        }
    }
    ret
}

impl RepoData {
    fn new() -> Self {
        Self {
            fetch_semaphore: Semaphore::new(1),
            config_cache: HashMap::new(),
        }
    }

    async fn fetch(&self, repo: &Repository, branch: String) -> Result<(), Error> {
        if repo.remote.is_none() {
            return Err(Error::new("No remote set"));
        }

        let _permit = self.fetch_semaphore.acquire().await;

        let mut cmd = self.git_cmd(repo);
        cmd.arg("fetch");
        // Use an atomic transaction to update local refs.
        cmd.arg("--atomic");
        // Print the output to standard output in an easy-to-parse format for scripts.
        cmd.arg("--porcelain");
        // This option disables this automatic tag following.
        cmd.arg("--no-tags");
        cmd.arg("origin");
        // <+ force update><remote branch>:<local branch>
        cmd.arg(format!("+{branch}:{branch}"));

        self.output(&mut cmd).await?;

        Ok(())
    }

    async fn init(&mut self, repo: &Repository) -> Result<(), Error> {
        fs_utils::create_dir_allow_existing(repo.path())
            .map_err(|e| Error::new(format!("{e}")))
            .await?;

        let mut cmd = self.git_cmd(repo);
        cmd.arg("init");
        if repo.is_bare() {
            cmd.arg("--bare");
        }

        self.run(&mut cmd).await?;

        Ok(())
    }

    async fn sync_config(&mut self, repo: &Repository) -> Result<(), Error> {
        self.config_fill_cache(repo).await?;

        if let Some(remote) = repo.remote() {
            self.config_set(repo, "remote.origin.url", remote).await?;
        }
        if let Some(socket) = repo.socket() {
            let relative = diff_paths(socket, repo.path()).unwrap();
            self.config_set(repo, "eyeballs.socket", relative.to_str().unwrap())
                .await?;
        }
        if let Some(ssh_config) = repo.ssh_config() {
            let relative = diff_paths(ssh_config, repo.path()).unwrap();
            self.config_set(
                repo,
                "core.sshcommand",
                format!("ssh -F {}", relative.to_str().unwrap()).as_str(),
            )
            .await?;
        }

        // Handled by pre-receive hook, allow fast forwards for reviews that expect it.
        self.config_set(repo, "receive.denyNonFastForwards", "false")
            .await?;
        // Handled by pre-receive hook, allow deletes for non-review branches
        self.config_set(repo, "receive.denyDeletes", "false")
            .await?;

        Ok(())
    }

    async fn sync_hooks(&mut self, repo: &Repository) -> Result<(), Error> {
        let hook = match repo.githook() {
            Some(path) => PathBuf::from(path),
            None => {
                let server_exe =
                    std::env::current_exe().map_err(|e| io_err("unable to get current exe", e))?;
                server_exe.parent().unwrap().join("eyeballs-githook")
            }
        };

        let hooks = if repo.is_bare() {
            repo.path().join("hooks")
        } else {
            repo.path().join(".git/hooks")
        };

        fs_utils::create_dir_allow_existing(&hooks)
            .map_err(|e| io_err("unable to create hooks", e))
            .await?;

        let pre_receive = hooks.join("pre-receive");
        let update = hooks.join("update");
        let post_receive = hooks.join("post-receive");

        fs_utils::remove_file_allow_not_found(update)
            .map_err(|e| io_err("unable to remove update hook", e))
            .await?;

        // Must be hard links, symbolic links doesn't allow the hook
        // the lookup how it's called using std::env::current_exe().
        fs_utils::remove_file_allow_not_found(&pre_receive)
            .map_err(|e| io_err("unable to remove pre-receive hook", e))
            .await?;
        fs::hard_link(hook.as_path(), pre_receive)
            .map_err(|e| io_err("unable to link pre-receive hook", e))
            .await?;
        fs_utils::remove_file_allow_not_found(&post_receive)
            .map_err(|e| io_err("unable to remove post-receive hook", e))
            .await?;
        fs::hard_link(hook.as_path(), post_receive)
            .map_err(|e| io_err("unable to link post-receive hook", e))
            .await
    }

    fn canonical_config_name(name: &str) -> String {
        let mut ret = String::with_capacity(name.len());
        let mut iter = name.splitn(3, '.');
        ret.push_str(iter.next().unwrap());
        ret.as_mut_str().make_ascii_lowercase();
        if let Some(subsection) = iter.next() {
            ret.push('.');
            let offset;
            if let Some(value) = iter.next() {
                ret.push_str(subsection);
                ret.push('.');
                offset = ret.len();
                ret.push_str(value);
            } else {
                offset = ret.len();
                ret.push_str(subsection);
            }
            ret.as_mut_str()
                .get_mut(offset..)
                .unwrap()
                .make_ascii_lowercase();
        }
        ret
    }

    async fn config_get(&self, repo: &Repository, name: &str) -> Result<String, Error> {
        let name = Self::canonical_config_name(name);
        if let Some(value) = self.config_cache.get(&name) {
            return Ok(value.clone());
        }

        // Note, want to keep this method non-mutable so we can't update the cache here, should be
        // edge case to end up here anyway.

        let mut cmd = self.git_cmd(repo);
        cmd.arg("config")
            .arg("get")
            // End value with the null character and use newline as delimiter between key and value
            .arg("--null")
            .arg("--default=")
            .arg(name);
        let data = self.output(&mut cmd).await?;
        match data.as_str().split_once('\0') {
            Some((value, _)) => Ok(value.to_string()),
            None => Err(Error::new("Invalid output from git config get")),
        }
    }

    async fn config_fill_cache(&mut self, repo: &Repository) -> Result<(), Error> {
        self.config_cache.clear();

        let mut cmd = self.git_cmd(repo);
        cmd.arg("config")
            .arg("list")
            // read only from the repository .git/config,
            .arg("--local")
            // End value with the null character and use newline as delimiter between key and value
            .arg("--null");
        let data = self.output(&mut cmd).await?;
        for key_value in data.split_terminator('\0') {
            match key_value.split_once('\n') {
                Some((key, value)) => {
                    self.config_cache.insert(key.to_string(), value.to_string());
                }
                None => return Err(Error::new("Invalid output from git config list")),
            };
        }
        Ok(())
    }

    async fn config_set(
        &mut self,
        repo: &Repository,
        name: &str,
        value: &str,
    ) -> Result<(), Error> {
        let name = Self::canonical_config_name(name);
        if let Some(cached_value) = self.config_cache.get(&name) {
            if cached_value == value {
                return Ok(());
            }
        }

        let mut cmd = self.git_cmd(repo);
        cmd.arg("config").arg("set").arg(&name).arg(value);
        self.run(&mut cmd).await?;

        self.config_cache.insert(name, value.to_string());

        Ok(())
    }

    async fn is_ancestor(
        &self,
        repo: &Repository,
        ancestor: &str,
        commit: &str,
    ) -> Result<bool, Error> {
        let mut cmd = self.git_cmd(repo);
        cmd.arg("merge-base")
            .arg("--is-ancestor")
            .arg(ancestor)
            .arg(commit);
        self.check(&mut cmd).await
    }

    async fn is_equal_content(
        &self,
        repo: &Repository,
        commit1: &str,
        commit2: &str,
    ) -> Result<bool, Error> {
        let mut cmd = self.git_cmd(repo);
        cmd.arg("diff")
            .arg("--quiet")
            .arg("--no-renames")
            .arg(commit1)
            .arg(commit2);
        self.check(&mut cmd).await
    }

    async fn get_author(&self, repo: &Repository, commit: &str) -> Result<User, Error> {
        self.get_log_format(repo, commit, "%an%x00%al%x00%ae")
            .map_ok(parse_user)
            .await
    }

    async fn get_commiter(&self, repo: &Repository, commit: &str) -> Result<User, Error> {
        self.get_log_format(repo, commit, "%cn%x00%cl%x00%ce")
            .map_ok(parse_user)
            .await
    }

    async fn delete_branch(&self, repo: &Repository, branch: &str) -> Result<(), Error> {
        let mut cmd = self.git_cmd(repo);
        cmd.arg("branch").arg("--delete").arg("--force").arg(branch);
        self.run(&mut cmd).await
    }

    async fn ls_tree(
        &self,
        repo: &Repository,
        commit: &str,
        recursive: bool,
    ) -> Result<Vec<TreeEntry>, Error> {
        let mut cmd = self.git_cmd(repo);
        cmd.arg("ls-tree").arg("-z");
        if recursive {
            cmd.arg("-r");
        }
        cmd.arg(commit);
        self.output(&mut cmd).map_ok(parse_tree_entries).await
    }

    async fn get_log_format(
        &self,
        repo: &Repository,
        commit: &str,
        format: &str,
    ) -> Result<String, Error> {
        let mut cmd = self.git_cmd(repo);
        cmd.arg("log")
            .arg("-1")
            .arg("--no-decorate")
            .arg("--no-mailmap")
            .arg(format!("--pretty=format:{format}"))
            .arg(commit);
        self.output(&mut cmd).await
    }

    fn git_cmd(&self, repo: &Repository) -> Command {
        let mut cmd = Command::new("git");
        // Run as if git was started in <path> instead of the current working directory.
        cmd.arg("-C").arg(repo.path().to_str().unwrap());
        // Disable all advice hints from being printed.
        cmd.arg("--no-advice");
        // Do not pipe Git output into a pager.
        cmd.arg("--no-pager");
        // Do not perform optional operations that require locks.
        cmd.arg("--no-optional-locks");

        cmd
    }

    async fn run(&self, cmd: &mut Command) -> Result<(), Error> {
        cmd.stdin(Stdio::null())
            .stdout(Stdio::null())
            .stderr(Stdio::piped());

        let child = cmd
            .spawn()
            .map_err(|e| Error::new(format!("git command failed to start: {e}")))?;

        let output = child
            .wait_with_output()
            .map_err(|e| Error::new(format!("git command failed to execute: {e}")))
            .await?;

        if output.status.success() {
            Ok(())
        } else {
            Err(Error::new(format!(
                "git command failed with exitcode: {}\n{:?}\n{}",
                output.status,
                cmd.as_std().get_args(),
                std::str::from_utf8(output.stderr.as_slice()).unwrap_or(""),
            )))
        }
    }

    async fn check(&self, cmd: &mut Command) -> Result<bool, Error> {
        cmd.stdin(Stdio::null())
            .stdout(Stdio::null())
            .stderr(Stdio::piped());

        let child = cmd
            .spawn()
            .map_err(|e| Error::new(format!("git command failed to start: {e}")))?;

        let output = child
            .wait_with_output()
            .map_err(|e| Error::new(format!("git command failed to execute: {e}")))
            .await?;

        if output.status.success() {
            Ok(true)
        } else {
            match output.status.code() {
                Some(1) => Ok(false),
                _ => Err(Error::new(format!(
                    "git command failed with exitcode: {}\n{:?}\n{}",
                    output.status,
                    cmd.as_std().get_args(),
                    std::str::from_utf8(output.stderr.as_slice()).unwrap_or(""),
                ))),
            }
        }
    }

    async fn output(&self, cmd: &mut Command) -> Result<String, Error> {
        cmd.stdin(Stdio::null())
            .stdout(Stdio::piped())
            .stderr(Stdio::piped());

        let child = cmd
            .spawn()
            .map_err(|e| Error::new(format!("git command failed to start: {e}")))?;

        let output = child
            .wait_with_output()
            .map_err(|e| Error::new(format!("git command failed to execute: {e}")))
            .await?;

        if output.status.success() {
            let output_utf8 = String::from_utf8(output.stdout)
                .map_err(|e| Error::new(format!("git command had invalid output: {e}")))?;
            Ok(output_utf8)
        } else {
            Err(Error::new(format!(
                "git command failed with exitcode: {}\n{:?}\n{}",
                output.status,
                cmd.as_std().get_args(),
                std::str::from_utf8(output.stderr.as_slice()).unwrap_or(""),
            )))
        }
    }
}

#[allow(dead_code)]
impl Repository {
    pub fn new(
        path: impl Into<PathBuf>,
        bare: bool,
        remote: Option<impl Into<String>>,
        project_id: Option<impl Into<String>>,
        githook: Option<impl Into<PathBuf>>,
        ssh_config: Option<impl Into<PathBuf>>,
    ) -> Self {
        let path = path.into();
        let project_id = project_id.map(|x| x.into());
        let githook = githook.map(|x| x.into());
        let ssh_config = ssh_config.map(|x| x.into());
        let socket: Option<PathBuf>;
        if let Some(project_id) = &project_id {
            socket = Some(
                path.parent()
                    .unwrap()
                    .join(format!("{}.socket", project_id)),
            );
        } else {
            socket = None;
        }

        Self {
            remote: remote.map(|x| x.into()),
            project_id,
            path,
            socket,
            githook,
            ssh_config,
            bare,
            lock: RwLock::new(RepoData::new()),
        }
    }

    pub fn remote(&self) -> Option<&str> {
        self.remote.as_deref()
    }

    pub fn project_id(&self) -> Option<&str> {
        self.project_id.as_deref()
    }

    pub fn path(&self) -> &Path {
        self.path.as_path()
    }

    pub fn socket(&self) -> Option<&Path> {
        self.socket.as_deref()
    }

    fn githook(&self) -> Option<&Path> {
        self.githook.as_deref()
    }

    pub fn ssh_config(&self) -> Option<&Path> {
        self.ssh_config.as_deref()
    }

    pub fn is_bare(&self) -> bool {
        self.bare
    }

    pub async fn setup(&self) -> Result<(), Error> {
        let mut data = self.lock.write().await;

        data.init(self).await?;
        data.sync_config(self).await?;
        if self.socket.is_some() {
            data.sync_hooks(self).await?;
        }

        Ok(())
    }

    pub async fn fetch(&self, branch: impl Into<String>) -> Result<(), Error> {
        let branch = branch.into();
        let data = self.lock.read().await;

        data.fetch(self, branch).await
    }

    pub async fn config_get(&self, name: impl Into<String>) -> Result<String, Error> {
        let name = name.into();
        let data = self.lock.read().await;

        data.config_get(self, name.as_str()).await
    }

    pub async fn is_ancestor(
        &self,
        ancestor: impl Into<String>,
        commit: impl Into<String>,
    ) -> Result<bool, Error> {
        let ancestor = ancestor.into();
        let commit = commit.into();

        let data = self.lock.read().await;

        data.is_ancestor(self, ancestor.as_str(), commit.as_str())
            .await
    }

    pub async fn is_equal_content(
        &self,
        commit1: impl Into<String>,
        commit2: impl Into<String>,
    ) -> Result<bool, Error> {
        let commit1 = commit1.into();
        let commit2 = commit2.into();
        let data = self.lock.read().await;

        data.is_equal_content(self, commit1.as_str(), commit2.as_str())
            .await
    }

    pub async fn get_author(&self, commit: impl Into<String>) -> Result<User, Error> {
        let commit = commit.into();
        let data = self.lock.read().await;

        data.get_author(self, commit.as_str()).await
    }

    pub async fn get_commiter(&self, commit: impl Into<String>) -> Result<User, Error> {
        let commit = commit.into();
        let data = self.lock.read().await;

        data.get_commiter(self, commit.as_str()).await
    }

    pub async fn delete_branch(&self, branch: impl Into<String>) -> Result<(), Error> {
        let branch = branch.into();
        let data = self.lock.read().await;

        data.delete_branch(self, branch.as_str()).await
    }

    pub async fn ls_tree(
        &self,
        commit: impl Into<String>,
        recursive: bool,
    ) -> Result<Vec<TreeEntry>, Error> {
        let commit = commit.into();
        let data = self.lock.read().await;

        data.ls_tree(self, commit.as_str(), recursive).await
    }
}