use std::path::{Path, PathBuf};
use std::time::*;
use std::str::from_utf8;
use std::process::Output;
use std::num::NonZeroU32;

use clap::Parser;
use serde::Deserialize;
use tracing::{debug, info, warn, error};
use tracing_subscriber::filter::EnvFilter;
use futures::stream::StreamExt;
use tokio::io::AsyncBufReadExt;
use governor::prelude::*;
use governor::{Quota, RateLimiter};
use reqwest::header::{CONTENT_TYPE, AUTHORIZATION, ACCEPT};

type AnyError = Box<dyn std::error::Error>;

/// type representing the schema of the config.json file
/// placed at the root of the crate index repo.
///
/// e.g.
///
/// ```json,ignore
/// {
///   "dl": "https://crates.shipyard.rs/api/v1/crates",
///   "api": "https://crates.shipyard.rs",
///   "allowed-registries": ["https://github.com/rust-lang/crates.io-index"]
/// }
/// ```
#[derive(Debug, Clone, Deserialize)]
#[serde(rename_all = "kebab-case")]
pub struct RegistryConfig {
    pub dl: String,
    pub api: String,
    #[serde(default)]
    pub allowed_registries: Vec<String>,
    #[serde(default)]
    pub auth_required: Option<bool>,
}

/// One version per line in the index metadata files.
#[derive(Debug, Clone, Deserialize)]
pub struct CrateVersion {
    pub name: String,
    pub vers: String,
}

/// Configuration for where to save the downloaded .crate files, and
/// using what syntax for the output filenames.
#[derive(Deserialize, Debug, Parser)]
#[serde(rename_all = "kebab-case")]
pub struct OutputConfig {
    /// Directory where downloaded .crate files will be saved to.
    #[clap(short, long = "output-path", default_value = DEFAULT_OUTPUT_PATH)]
    #[serde(default = "default_output_path")]
    pub path: PathBuf,
    // /// What format to use for the output filenames. Works the same as
    // /// Cargo's registry syntax for the "dl" key in the `config.json`
    // /// file in a reigstry index. See [Cargo
    // /// docs](https://doc.rust-lang.org/cargo/reference/registries.html#index-format)
    // /// for additional details. Not specifying this field is equivalent
    // /// to specifying "/{crate}/{version}/download", the default.
    // #[clap(long = "output-format")]
    // pub format: Option<String>,
    // /// Use whatever output filename syntax is specified in the target
    // /// registry's `config.json` file. Conflicts with --output-format.
    // #[serde(default)]
    // #[clap(long)]
    // pub mirror_registry_format: bool,
}

#[derive(Deserialize, Debug, Parser)]
#[serde(rename_all = "kebab-case")]
pub struct HttpConfig {
    /// Value of user-agent HTTP header
    #[serde(default = "default_user_agent")]
    #[clap(short, long, default_value = DEFAULT_USER_AGENT)]
    pub user_agent: String,
    /// Requests to registry server will not exceed this rate
    #[serde(default = "default_requests_per_second")]
    #[clap(long, default_value_t = default_requests_per_second())]
    pub requests_per_second: NonZeroU32,
    /// Independent of the requests per second rate limit, no more
    /// than `max_concurrent_requests` will be in flight at any given
    /// moment.
    #[serde(default = "default_max_concurrent_requests")]
    #[clap(long, default_value_t = default_max_concurrent_requests())]
    pub max_concurrent_requests: NonZeroU32,
}

/// Download all .crate files from a registry server.
#[derive(Deserialize, Parser)]
#[serde(rename_all = "kebab-case")]
#[clap(
    author,
    version,
    about,
    global_setting(clap::AppSettings::DeriveDisplayOrder)
)]
pub struct Config {
    /// URL of the registry index we are downloading .crate files from. The
    /// program expects that it will be able to clone the index to a local
    /// temporary directory; the user must handle authentication if needed.
    #[serde(default)]
    #[clap(long)]
    pub index_url: Option<String>,
    /// instead of an index url, just point to a local path where the index
    /// is already cloned.
    #[serde(default)]
    #[clap(long, conflicts_with = "index_url")]
    pub index_path: Option<PathBuf>,
    /// Where to save the downloaded files
    #[clap(flatten)]
    pub output: OutputConfig,
    /// Download settings
    #[clap(flatten)]
    pub http: HttpConfig,
    /// If registry requires authorization (i.e. "auth-required" key is
    /// set to `true` in the `config.json` file), the token to include
    /// using the Authorization HTTP header.
    #[clap(short, long, alias = "token")]
    #[serde(default)]
    pub auth_token: Option<String>,
    /// Specify configuration values using the provided TOML file, instead of
    /// via command line flags. The values in the config file will override
    /// any values passed as command line flags. See config.toml.sample for
    /// syntax of the config file.
    #[serde(default)]
    #[clap(short, long, exclusive(true))]
    pub config_file: Option<PathBuf>,

    // TODO: offer some way to specify you want to use an existing
    // path as the index, instead of cloning it
}

const DEFAULT_OUTPUT_PATH: &str = "output";
const DEFAULT_USER_AGENT: &str = concat!("registry-backup/v", clap::crate_version!());

// const DEFAULT_INDEX: &str = "https://github.com/rust-lang/crates.io-index.git";
// fn default_index() -> String {
//     DEFAULT_INDEX.to_string()
// }

fn default_output_path() -> PathBuf {
    PathBuf::from(DEFAULT_OUTPUT_PATH)
}

fn default_user_agent() -> String {
    DEFAULT_USER_AGENT.to_string()
}

const fn default_requests_per_second() -> NonZeroU32 {
    unsafe { NonZeroU32::new_unchecked(25) }
}

const fn default_max_concurrent_requests() -> NonZeroU32 {
    unsafe { NonZeroU32::new_unchecked(10) }
}

impl std::fmt::Debug for Config {
    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
        f.debug_struct("Config")
            .field("index_url", &self.index_url)
            .field("index_path", &self.index_path)
            .field("output", &self.output)
            .field("http", &self.http)
            .field("auth_token", &"***") // hide sensitive data
            .field("config_file", &self.config_file)
            .finish()
    }
}

async fn popen(
    cmd: &str,
    args: &[&str],
    envs: &[(&str, &str)],
) -> Result<Output, AnyError> {
    let args: Vec<String> = args.iter()
        .map(|x| x.to_string())
        .collect();

    let output = tokio::process::Command::new(cmd)
        .args(args.iter().map(|x| x.as_str()))
        .envs(envs.iter().map(|(k,v)| (k.to_string(), v.to_string())))
        .output()
        .await
        .map_err(|e| {
            error!("Command `{}` failed to execute at all: {:?}", cmd, e);
            e
        })?;

    debug!("finished executing `{}` Command with status {:?}\n\
            STDOUT (length={}):\n{}\n\
            STDERR (length={}):\n{}\n",
        cmd,
        output.status,
        output.stdout.len(),
        from_utf8(&output.stdout)?,
        output.stderr.len(),
        from_utf8(&output.stderr)?,
    );

    if ! output.status.success() {
        error!("finished executing `{}` Command with status {:?}\n\
                STDOUT (length={}):\n{}\n\
                STDERR (length={}):\n{}\n",
            cmd,
            output.status,
            output.stdout.len(),
            from_utf8(&output.stdout)?,
            output.stderr.len(),
            from_utf8(&output.stderr)?,
        );

        return Err(format!("git clone commnad failed with error code {:?}", output.status).into())
    }

    Ok(output)
}

async fn git_clone(
    src: &str,
    dst: &Path,
    envs: &[(&str, &str)],
) -> Result<(), AnyError> {
    let begin = Instant::now();
    popen(
        "git",
        &[
            "clone",
            src,
            dst.to_str().expect("dst path .to_str() failed"),
        ][..],
        envs,
    )
        .await
        .map_err(|e| -> AnyError {
            error!(%src, ?dst, ?e, "in git_clone, Command failed");
            e
        })?;

    info!(%src, ?dst, "cloned repo in {:?}", begin.elapsed());

    Ok(())
}

fn setup_logger() {
    let env_filter = EnvFilter::from_default_env();
    let builder = tracing_subscriber::fmt()
        .with_env_filter(env_filter)
        .with_ansi(true);
    builder.init();
}

async fn load_config_file(config: Config) -> Result<Config, AnyError> {
    match config.config_file.as_ref() {
        Some(path) => {
            debug!(?path, "loading config file");
            let toml = tokio::fs::read_to_string(&path).await?;
            let config: Config = toml::from_str(&toml)?;
            Ok(config)
        }

        None => Ok(config),
    }
}

async fn load_registry_config(clone_dir: &Path) -> Result<RegistryConfig, AnyError> {
    let json = tokio::fs::read_to_string(clone_dir.join("config.json")).await?;
    let parsed = serde_json::from_str(&json)?;
    Ok(parsed)
}

fn is_hidden(entry: &walkdir::DirEntry) -> bool {
    entry.file_name()
         .to_str()
         .map(|s| s.starts_with('.'))
         .unwrap_or(false)
}

async fn get_crate_versions(clone_dir: &Path) -> Result<Vec<CrateVersion>, AnyError> {
    let files: Vec<PathBuf> = walkdir::WalkDir::new(clone_dir)
        .max_depth(3)
        .into_iter()
        .filter_entry(|e| !is_hidden(e))
        .filter_map(|res| {
            match res {
                Ok(entry) => {
                    if entry.file_type().is_file() && entry.depth() >= 2 && entry.depth() <= 3 {
                        let path = entry.into_path();
                        debug!(?path, "found crate metadata file to parse");
                        Some(path)
                    } else {
                        None
                    }
                }
                Err(e) => {
                    warn!(error = ?e, "walkdir result is error");
                    None
                }
            }
        }).collect();

    info!("found {} crate metadata files to parse", files.len());

    let crate_versions: Vec<Result<Vec<CrateVersion>, AnyError>> = futures::stream::iter(
        files.into_iter().map(|path| {
            async move {
                let file = tokio::fs::File::open(&path)
                    .await
                    .map_err(|e| { error!(err = ?e, ?path, "failed to open file"); e })?;
                let buf = tokio::io::BufReader::new(file);
                let mut out = Vec::new();
                let mut lines = buf.lines();
                while let Some(line) = lines.next_line().await? {
                    let vers: CrateVersion = serde_json::from_str(&line)
                        .map_err(|e| { error!(err = ?e, ?path, "failed to parse line"); e })?;
                    out.push(vers);
                }
                debug!(crate_name = %out.first().map(|x| x.name.as_str()).unwrap_or("na"),
                    "parsed {} crate versions from metadata file", out.len()
                );

                Ok(out)
            }
        })
    )
        .buffer_unordered(num_cpus::get())
        .collect()
        .await;

    let crate_versions: Vec<CrateVersion> = crate_versions.into_iter()
        .flat_map(|result| {
            match result {
                Ok(xs) => xs.into_iter().filter(|x| x.name != "vst").collect(),
                Err(e) => {
                    error!(err = ?e, "parsing metadata failed, skipping file");
                    vec![]
                }
            }
        }).collect();

    info!("collected {} total crate versions to download", crate_versions.len());
    
    Ok(crate_versions)
}

async fn ensure_dir_exists<P: AsRef<std::path::Path>>(path: P) -> Result<(), AnyError> {
    match tokio::fs::metadata(path.as_ref()).await {
        Ok(meta) if meta.is_dir() => Ok(()),

        Ok(meta) /* if ! meta.is_dir() */ => {
            debug_assert!( ! meta.is_dir());
            Err(format!("path exists, but is not a directory: {:?}", path.as_ref()).into())
        }

        Err(e) if e.kind() == std::io::ErrorKind::NotFound => {
            tokio::fs::create_dir_all(&path).await?;
            Ok(())
        }

        Err(e) => Err(e.into()),
    }
}

async fn ensure_file_parent_dir_exists<P: AsRef<std::path::Path>>(path: P) -> Result<(), AnyError> {
    if let Some(parent_dir) = path.as_ref().parent() {
        ensure_dir_exists(parent_dir).await
    } else {
        Ok(())
    }
}

macro_rules! megabytes {
    ($x:expr) => {{
        use pretty_toa::ThousandsSep;
        let mb = $x as f64 / 1024.0 /1024.0;
        if mb > 2048.0 {
            format!("{}G", (((mb / 1024.0) * 100.0).round() / 100.0).thousands_sep())
        } else if mb < 0.75 {
            let kb = $x as f64 / 1024.0;
            format!("{}K", ((kb * 10.0).round() / 10.0).thousands_sep())
        } else {
            format!("{}M", ((mb * 10.0).round() / 10.0).thousands_sep())
        }
    }}
}

async fn download_versions(config: &Config, registry_config: &RegistryConfig, versions: Vec<CrateVersion>) -> Result<(), AnyError> {
    let begin = Instant::now();
    ensure_dir_exists(&config.output.path).await?;

    let rate_limit = RateLimiter::direct(
        Quota::per_second(config.http.requests_per_second)
    );

    let http_client = reqwest::Client::builder()
        .user_agent(&config.http.user_agent)
        .build()?;

    let inner_stream = futures::stream::iter(
        versions.into_iter().map(|vers| {
            let req_begin = Instant::now();
            let http_client = http_client.clone();
            async move {
                // TODO actually parse and use the format
                let vers_path = format!("{}/{}/download", vers.name, vers.vers);
                let url = format!("{}/{}", registry_config.dl, vers_path);
                debug!(?url, "downloading...");
                let req = http_client.get(url)
                    .header(CONTENT_TYPE, "application/json")
                    .header(ACCEPT, "application/json");

                let req = if let Some(token) = config.auth_token.as_deref() {
                    req.header(AUTHORIZATION, token)

                } else {
                    req
                };

                let resp = req.send().await?;
                let status = resp.status();
                let body = resp.bytes().await?;
                if ! status.is_success() {
                    error!(status = ?status, "download failed");
                    debug!("response body:\n{}\n", from_utf8(&body.slice(..))?);
                    Err::<_, AnyError>(format!("error response {:?} from server", status).into())
                } else {
                    // TODO: check if this path exists already before downloading
                    let output_path = config.output.path.join(vers_path);
                    ensure_file_parent_dir_exists(&output_path)
                        .await
                        .map_err(|e| {
                            error!(?output_path, err = ?e, "ensure parent dir exists failed");
                            e
                        })?;
                    tokio::fs::write(&output_path, body.slice(..))
                        .await
                        .map_err(|e| { error!(err = ?e, "writing file failed"); e })?;
                    info!(
                        filesize = megabytes!(body.len()),
                        crate_name = %vers.name,
                        version = %vers.vers,
                        "downloaded .crate file in {:?}", req_begin.elapsed());
                    debug!(?output_path, "wrote {} bytes to file", body.len());
                    Ok(output_path)
                }
            }
        })
    )
        .buffer_unordered(config.http.max_concurrent_requests.get() as usize);

    let outer_stream = inner_stream.ratelimit_stream(&rate_limit);

    let results: Vec<Result<PathBuf, AnyError>> =
        outer_stream
            .collect()
            .await;

    let mut ret = Ok(());

    let n = results.len();
    let mut n_err = 0;
    for result in results {
        if let Err(e) = result {
            n_err += 1;
            error!(err = ?e, "download failed");
            ret = Err(e);
        }
    }

    let n_ok = n - n_err;
    info!(n_ok, n_err, "finished downloading {} files in {:?}", n_ok, begin.elapsed());

    ret
}

async fn run(config: Config) -> Result<(), AnyError> {
    let config = load_config_file(config).await?;
    debug!("config:\n{:#?}\n", config);

    assert!(config.index_url.is_some() || config.index_path.is_some(),
        "one of index-url or index-path is required",
    );

    let tmpdir = tempdir::TempDir::new("registry-backup-index")?;

    let index_path = match (&config.index_url, &config.index_path) {
        (Some(url), _) => {
            let tmp = tmpdir.path();
            git_clone(url, tmp, &[][..]).await?;
            tmp
        }

        (_, Some(path)) => path,

        _ => unreachable!(),
    };

    let registry_config = load_registry_config(index_path).await?;

    let versions = get_crate_versions(index_path).await?;

    download_versions(&config, &registry_config, versions).await?;
    Ok(())
}

fn main() {
    let begin = Instant::now();

    setup_logger();

    info!("initializing...");

    let config = Config::parse();

    let rt = tokio::runtime::Builder::new_multi_thread()
        .enable_all()
        .build()
        .unwrap();

    rt.block_on(run(config)).unwrap();

    info!("finished in {:?}", begin.elapsed());
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn parse_sample_config() {
        const TOML: &str = include_str!("../config.toml.sample");
        let _config: Config = toml::from_str(TOML).unwrap();
    }
}