//! Parser for `docker://` URLs.
//!
//! This module provides support for parsing image references.
//!
//! ## Example
//!
//! ```rust
//! # fn main() {
//! # fn run() -> docker_registry::errors::Result<()> {
//! #
//! use std::str::FromStr;
//!
//! use docker_registry::reference::Reference;
//!
//! // Parse an image reference
//! let dkref = Reference::from_str("docker://busybox")?;
//! assert_eq!(dkref.registry(), "registry-1.docker.io");
//! assert_eq!(dkref.repository(), "library/busybox");
//! assert_eq!(dkref.version(), "latest");
//! #
//! # Ok(())
//! # };
//! # run().unwrap();
//! # }
//! ```

// The `docker://` schema is not officially documented, but has a reference implementation:
// https://github.com/docker/distribution/blob/v2.6.1/reference/reference.go

use std::{collections::VecDeque, fmt, str, str::FromStr};

use regex_lite::Regex;

pub static DEFAULT_REGISTRY: &str = "registry-1.docker.io";
static DEFAULT_TAG: &str = "latest";
static DEFAULT_SCHEME: &str = "docker";

/// Image version, either a tag or a digest.
#[derive(Clone)]
pub enum Version {
  Tag(String),
  Digest(String, String),
}

#[derive(thiserror::Error, Debug)]
pub enum VersionParseError {
  #[error("wrong digest format: checksum missing")]
  WrongDigestFormat,
  #[error("unknown prefix: digest must start from : or @")]
  UnknownPrefix,
  #[error("empty string is invalid digest")]
  Empty,
}

impl str::FromStr for Version {
  type Err = VersionParseError;
  fn from_str(s: &str) -> Result<Self, Self::Err> {
    let v = match s.chars().next() {
      Some(':') => Version::Tag(s.trim_start_matches(':').to_string()),
      Some('@') => {
        let r: Vec<&str> = s.trim_start_matches('@').splitn(2, ':').collect();
        if r.len() != 2 {
          return Err(VersionParseError::WrongDigestFormat);
        };
        Version::Digest(r[0].to_string(), r[1].to_string())
      }
      Some(_) => return Err(VersionParseError::UnknownPrefix),
      None => return Err(VersionParseError::Empty),
    };
    Ok(v)
  }
}

impl Default for Version {
  fn default() -> Self {
    Version::Tag("latest".to_string())
  }
}

impl fmt::Debug for Version {
  fn fmt(&self, f: &mut fmt::Formatter) -> Result<(), fmt::Error> {
    let v = match *self {
      Version::Tag(ref s) => ":".to_string() + s,
      Version::Digest(ref t, ref d) => "@".to_string() + t + ":" + d,
    };
    write!(f, "{}", v)
  }
}

impl fmt::Display for Version {
  fn fmt(&self, f: &mut fmt::Formatter) -> Result<(), fmt::Error> {
    let v = match *self {
      Version::Tag(ref s) => s.to_string(),
      Version::Digest(ref t, ref d) => t.to_string() + ":" + d,
    };
    write!(f, "{}", v)
  }
}

/// A registry image reference.
#[derive(Clone, Debug, Default)]
pub struct Reference {
  raw_input: String,
  registry: String,
  repository: String,
  version: Version,
}

impl Reference {
  pub fn new(registry: Option<String>, repository: String, version: Option<Version>) -> Self {
    let reg = registry.unwrap_or_else(|| DEFAULT_REGISTRY.to_string());
    let ver = version.unwrap_or_else(|| Version::Tag(DEFAULT_TAG.to_string()));
    Self {
      raw_input: "".into(),
      registry: reg,
      repository,
      version: ver,
    }
  }

  pub fn registry(&self) -> String {
    self.registry.clone()
  }

  pub fn repository(&self) -> String {
    self.repository.clone()
  }

  pub fn version(&self) -> String {
    self.version.to_string()
  }

  pub fn to_raw_string(&self) -> String {
    self.raw_input.clone()
  }

  //TODO(lucab): move this to a real URL type
  pub fn to_url(&self) -> String {
    format!(
      "{}://{}/{}{:?}",
      DEFAULT_SCHEME, self.registry, self.repository, self.version
    )
  }
}

impl fmt::Display for Reference {
  fn fmt(&self, f: &mut fmt::Formatter) -> Result<(), fmt::Error> {
    write!(f, "{}/{}{:?}", self.registry, self.repository, self.version)
  }
}

impl str::FromStr for Reference {
  type Err = ReferenceParseError;
  fn from_str(s: &str) -> Result<Self, Self::Err> {
    parse_url(s)
  }
}

#[derive(thiserror::Error, Debug)]
pub enum ReferenceParseError {
  #[error("missing image name")]
  MissingImageName,
  #[error("version parse error")]
  VersionParse(#[from] VersionParseError),
  #[error("empty image name")]
  EmptyImageName,
  #[error("component '{component}' does not conform to regex '{regex}'")]
  RegexViolation { regex: &'static str, component: String },
  #[error("empty repository name")]
  EmptyRepositoryName,
  #[error("repository name too long")]
  RepositoryNameTooLong,
}

fn parse_url(input: &str) -> Result<Reference, ReferenceParseError> {
  // TODO(lucab): investigate using a grammar-based parser.
  let mut rest = input;

  // Detect and remove schema.
  let has_schema = rest.starts_with("docker://");
  if has_schema {
    rest = input.trim_start_matches("docker://");
  };

  // Split path components apart and retain non-empty ones.
  let mut components: VecDeque<String> = rest.split('/').filter(|s| !s.is_empty()).map(String::from).collect();

  // Figure out if the first component is a registry String, and assume the
  // default registry if it's not.
  let first = components.pop_front().ok_or(ReferenceParseError::MissingImageName)?;

  let registry = if Regex::new(
    r"(?x)
        ^
        # hostname
        (([a-zA-Z0-9]|[a-zA-Z0-9][a-zA-Z0-9\-]*[a-zA-Z0-9])\.)+([A-Za-z0-9]|[A-Za-z0-9][A-Za-z0-9\-]*[A-Za-z0-9])

        # optional port
        ([:][0-9]{1,6})?
        $
    ",
  )
  .expect("hardcoded regex is invalid")
  .is_match(&first)
  {
    first
  } else {
    components.push_front(first);
    DEFAULT_REGISTRY.to_string()
  };

  // Take image name and extract tag or digest-ref, if any.
  let last = components.pop_back().ok_or(ReferenceParseError::MissingImageName)?;
  let (image_name, version) = match (last.rfind('@'), last.rfind(':')) {
    (Some(i), _) | (None, Some(i)) => {
      let s = last.split_at(i);
      (String::from(s.0), Version::from_str(s.1)?)
    }
    (None, None) => (last, Version::default()),
  };
  if image_name.is_empty() {
    return Err(ReferenceParseError::EmptyImageName);
  }

  // Handle images in default library namespace, that is:
  // `ubuntu` -> `library/ubuntu`
  if components.is_empty() && registry == DEFAULT_REGISTRY {
    components.push_back("library".to_string());
  }
  components.push_back(image_name);

  // Check if all path components conform to the regex at
  // https://docs.docker.com/registry/spec/api/#overview.
  const REGEX: &str = "^[a-z0-9]+(?:[._-][a-z0-9]+)*$";
  let path_re = Regex::new(REGEX).expect("hardcoded regex is invalid");
  components.iter().try_for_each(|component| {
    if !path_re.is_match(component) {
      return Err(ReferenceParseError::RegexViolation {
        component: component.clone(),
        regex: REGEX,
      });
    };

    Ok(())
  })?;

  // Re-assemble repository name.
  let repository = components.into_iter().collect::<Vec<_>>().join("/");
  if repository.is_empty() {
    return Err(ReferenceParseError::EmptyRepositoryName);
  }
  if repository.len() > 127 {
    return Err(ReferenceParseError::RepositoryNameTooLong);
  }

  Ok(Reference {
    raw_input: input.to_string(),
    registry,
    repository,
    version,
  })
}