// Copyright 2021 Citrix
// SPDX-License-Identifier: MIT OR Apache-2.0
// There is NO WARRANTY.

//! Uniform access to github and gitlab
//!
//! Currently, listing and creating merge requests is suppored.
//!
//! Start by creating a `Forge`, probably by initialising a
//! `Config` with `default`-based a literal and calling `Setup::forge`.
//!
//! # Terminology and model
//!
//! * **Repository**.  A single git tree that can contain code, and
//!   has other things associated with it such as issues and merge
//!   requests.  (GitHub, GitLab: **project**.)
//!
//!   Identified in the `gitforge` API by a string, which is typically
//!   the path suffix.
//!
//! * **Merge Request**.  A request to incorporate changes from
//!   a **source** repository and **branch** into a **target**
//!   repository and branch.  Forges typically associate merge
//!   requsts primarily with the *target* repository.  A merge
//!   request typically has an associated discussion.
//!
//!   (GitHub: a **pull request**.)
//!
//! * **Issue**.  A feature request or bug report, associated with
//!   a *repository*, and an associated discussion.  *Not currently
//!   supported by this library.
//!
//! * *Merge request* or *issue* **Number**.  A (usually short)
//!   string which uniquely identifies a merge request or issue
//!   within a *repository*.
//!
//! * **User**.  An individual user, or possibly, organisation.
//!   Represented as a string, being the username (as used, eg,
//!   as a slug in the forge's URLs).
//!
//! * **Branch**.  A git *branch* (on the server), ie a remote
//!   ref named `refs/heads/BRANCH`.  Identified by the string
//!   `BRANCH`.
//!
//! See the individual forge module docs for the mapping.
//!
//! # Non-exhaustive structs
//!
//! Some structs in this api have fields named `_non_exhaustive`.
//! This indicates that the struct may be extended with additional
//! fields in future, and that this won't be considered a semver
//! breaking change.
//!
//! Do not explicitly initialise such a field.  Instead, use
//! `..` syntax to initialise all the fields you are not naming.
//! Typically, you would write `..Default::default()`.
//!
//! This rule is in addition to some (other) structs being marked
//! `#[non_exhaustive]`.
//!
//! # Non-exhaustive enums
//!
//! Some enums have variants named `_NonExhaustive`.  This indicates
//! that the enum may be extended with additional variants in future,
//! and that this won't be considered a semver breaking change.
//!
//! Do not construct such an enum variant.  The library will *panic*
//! if it finds one.
//!
//! This rule is in addition to some (other) enums being marked
//! `#[non_exhaustive]`.

use crate::prelude::*;

/// Errors accessing forges
#[derive(Error,Debug)]
#[non_exhaustive]
pub enum Error {
  /// Forge operation error (unclassified)
  ///
  /// Something went wrong accessing the forge.  The error has not
  /// been more completely classified.
  #[error("error conducting forge operation (unclassified): {0}")]
  UncleassifiedOperationError(anyhow::Error),

  /// Forge operation build failed
  ///
  /// The forge-specific client library rejected the attempted request
  /// or otherwise failed to construct an appropriate query to the
  /// forge.
  ///
  /// This error occured before the actual forge was contacted.
  #[error("forge operation build failed: {0}")]
  OperationBuildFailed(anyhow::Error),

  /// Forge operation result processing failed
  ///
  /// The principal forge operation completed successfully (at least
  /// as far as the forge-specific client library was concerned) but
  /// error occurred processing the results.
  #[error("forge results processing failed: {0}")]
  ResultsProcessingFailed(anyhow::Error),

  /// Forge ancillary operation failed
  ///
  /// An error occurred while conducting operations ancillary to the
  /// principally-requested operation.
  #[error("forge ancillary operation failed: {0}")]
  AncillaryOperationFailed(anyhow::Error),

  /// Forge client creation error
  ///
  /// The operation to construct a forge client instance failed.
  /// Perhaps the forge-kind-specific library did not like the
  /// `Config`.
  #[error("forge client creation failed (bad config?): {0}")]
  ClientCreationFailed(anyhow::Error),

  /// Forge kind must be specified
  ///
  /// `Config` contains `Option<Kind>` so that it `impl Default` and
  /// for future compatibility.  But the kind must, currently, always
  /// be specified.
  #[error("forge kind must be specified")]
  KindMustBeSpecified,

  /// Forge kind disabled in this build
  ///
  /// This build of the `gitforge` library has been compiled without
  /// support for the specified forge type.
  #[error("forge kind {0:?} disnabled (cargo feature)")]
  KindDisabled(Kind),

  /// Async runtime failed
  ///
  /// The asynchronous runtimee failed
  #[error("async runtime error: {0}")] Async(anyhow::Error),

  /// Token always required for this forge kind
  ///
  /// Some forges (eg gitlab) always need a token and do not support
  /// anonymous API access.
  #[error("token always required for {0}")]
  TokenAlwaysRequired(Kind),

  /// Search query had too many results.
  ///
  /// See the discussion of *Searching and limits* by
  /// `ForgeMethods::request`.  Narrow your search by providing more
  /// parametsrs.
  #[error("request returned too many results (API limit)")]
  TooManyResults,

  /// Unsupported operation
  ///
  /// The operation is not supported on this kind of forge.
  #[error("unsupporrted operation: {0}")]
  UnsupportedOperation(anyhow::Error),

  /// Unsupported state in this context
  ///
  /// A state or status field value in a request was not supported.
  /// Whether a particular state or status is supported might depend on
  /// the request.
  #[error("{0}: state not supported (in this context): {1:?}")]
  UnsupportedState(RemoteObjectKind, String),

  /// Name refers to nonexistent remote object
  #[error("{0}: name not found: {1:?}")]
  NameNotFound(RemoteObjectKind,String),

  /// Id or number refers to nonexistent remote object
  #[error("{0}: id not found: {1}")]
  IdNotFound(RemoteObjectKind,String),

  /// Invalid object syntax
  #[error("invalid {0} syntax: {2:?}: {1}")]
  InvalidObjectSyntax(RemoteObjectKind,String,String),

  /// Invalid id or number syntax
  #[error("{0}: invalid id syntax: {2:?}: {1}")]
  InvalidIdSyntax(RemoteObjectKind,String,String),

  /// Unsupported remote URL format
  #[error("unsupported remote URL format: {1:?}: {0}")]
  UnsupportedRemoteUrlSyntax(String,String),

  /// Remote URL does not match the forge hsotname
  #[error("remote URL host {url:?} does not match forge host {forge:?}")]
  UrlHostMismatch { url: String, forge: String },
}

/// Kind of a thing on a forge.  Used mostly in errors.
#[derive(Debug,Error,Clone,Copy,Eq,PartialEq,Hash)]
pub enum RemoteObjectKind {
  #[error("user")]      User,
  #[error("repo")]      Repo,
  #[error("merge req")] MergeReq,
  #[error("issue")]     Issue,
}

#[derive(Debug,Error,Clone,Copy,Eq,PartialEq,Hash)]
#[derive(Serialize,Deserialize)]
#[serde(rename_all="snake_case")]
#[derive(Display,EnumString)]
#[strum(serialize_all = "lowercase")]
/// What protocol to use to access a forge.  Don't hardcode.
///
/// Please do not hardcode this.  Instead, read it, along with your
/// forge hostname, from a config file, or your command line.
///
/// You can parse this from a string.  The `FromStr` implementation
/// expects lowercase strings: **`gitlab`** or **`github`**.
pub enum Kind {
  GitLab,
  GitHub,
}

/// Secret access token.
#[derive(Clone,From,FromStr,Serialize,Deserialize)]
#[serde(transparent)]
pub struct Token(pub String);

impl Debug for Token {
  #[throws(fmt::Error)]
  fn fmt(&self, f: &mut fmt::Formatter) { write!(f,"forge::Token(..)")? }
}

pub(crate) type Constructor = fn(&Config) -> Result<
    Box<dyn Forge + 'static>,
    FE,
  >;

pub(crate) type ForgeEntry = (Kind, Constructor);
pub(crate) const FORGES: &[ForgeEntry] = &[
  #[cfg(feature="gitlab")] (Kind::GitLab, crate::lab::Lab::new),
  #[cfg(feature="github")] (Kind::GitHub, crate::hub::Hub::new),
];

/// Instructions for how to connect to a forge
#[derive(Default,Clone,Debug,Serialize,Deserialize)]
pub struct Config {
  /// Access token (secret).
  ///
  /// If left as `None`, `Config::forge()` will do the work
  /// of `load_default_token`.
  #[serde(default)]
  pub token: Option<TokenConfig>,

  /// The kind of forge (ie, the protocol to speak).
  ///
  /// Currently, `None` is not supported.  In the future omitting
  /// `kind` might result in auto-guessing from `host`.
  #[serde(default)]
  pub kind: Option<Kind>,

  /// Hostname.
  ///
  /// Eg, `gitlab.com`, `github.com`, `salsa.debian.org`.
  #[serde(default)]
  pub host: String,

  /// Do not specify this field.  Instead, say `..Default::default()`.
  /// New fields may be added and this will not be considered a semver break.
  #[serde(skip)]
  pub _non_exhaustive: (),
}

/// Instructions for how to obtain an access token
#[derive(Clone,Debug,Serialize,Deserialize)]
pub enum TokenConfig {
  /** Use anonymous access, do not authenticate. */ Anonymous,
  /** Read the token from this file.             */ Path(PathBuf),
  /** Use this token.                            */ Value(Token),
}

impl Config {
  /// Main constructor for a `Forge`
  #[throws(FE)]
  pub fn forge(&self) -> Box<dyn Forge + 'static> {
    let kind = self.kind.ok_or_else(|| FE::KindMustBeSpecified)?;

    let entry = FORGES.iter().find(|c| c.0 == kind)
      .ok_or_else(|| FE::KindDisabled(kind))?;
    entry.1(&self)?
  }
}

impl TokenConfig {
  #[throws(AE)]
  fn get_token(&self) -> Option<Token> {
    match self {
      TokenConfig::Anonymous => None,
      TokenConfig::Value(v) => Some(v).cloned(),
      TokenConfig::Path(path) => {
        let token = Token::load(path)?
          .ok_or_else(|| anyhow!("specified token file does not exist"))
          .with_context(|| format!("{:?}", &path))?;
        Some(token)
      }
    }
  }
}

impl Token {
  /// Load a secret token from a specified file.
  ///
  /// If the file does not exist (as opposed to other errors trying to
  /// read it), returns None.
  ///
  /// On Unix, will return an error if the file is world-readable.
  #[throws(anyhow::Error)]
  pub fn load(path: &Path) -> Option<Token> { (|| {
    let mut f = match File::open(&path) {
      Err(e) if e.kind() == ErrorKind::NotFound => {
        info!("forge token file {:?} does not exist", path);
        return Ok(None);
      },
      Err(e) => throw!(anyhow::Error::from(e).context("open")),
      Ok(f) => f,
    };

    #[cfg(unix)] {
      use std::os::unix::fs::MetadataExt;
      let m = f.metadata().context("stat")?;
      if m.mode() & 0o004 != 0 {
        throw!(anyhow!("token file is world-readable! refusing to use"))
      }
    }

    let mut buf = String::new();
    f.read_to_string(&mut buf).context("read")?;
    let token = Token(buf.trim().into());

    info!("forge token file {:?}", path);

    Ok::<_,anyhow::Error>(Some(token))
  })()
    .with_context(|| format!("{:?}", path))
    .context("git forge auth token file")?
  }
}

impl Config {
  /// Calculate the default path for finding a secret token.
  ///
  /// On Unix this is `~/.config/gitforge/FORGE_EXAMPLE_ORG.KIND-token`
  /// where `FORGE_EXAMPLE_ORG` is `host` with dots replaced with
  /// underscores.
  #[throws(anyhow::Error)]
  pub fn default_token_path(&self) -> PathBuf {
    let chk = |s: &str, what| if {
      s.chars().all(|c| c=='-' || c=='.' || c.is_ascii_alphanumeric()) &&
      s.chars().next().map(|c| c.is_ascii_alphanumeric()) == Some(true)
    } { Ok(()) } else { Err(anyhow!(
      "{} contains, or starts with, bad character(s)", what
    )) };

    let kind = self.kind.ok_or_else(|| FE::KindMustBeSpecified)?;

    let host: &str = &self.host;
    chk(host, "hostname")?;

    let mut path =
      directories::ProjectDirs::from("","","GitForge")
      .ok_or_else(|| anyhow!("could not find home directory"))?
      .config_dir().to_owned();

    path.push(format!(
      "{}.{}-token",
      host.replace('.',"_"),
      kind,
    ));

    path
  }

  #[throws(AE)]
  pub(crate) fn get_token_or_default(&self) -> Option<Token> {
    match &self.token {
      Some(c) => {
        c.get_token()?
      },
      None => {
        let path = self.default_token_path()?;
        let token = Token::load(&path)?;
        token
      },
    }

  }

  /// Load the default token, updating this Config.
  ///
  /// It is not normally necessary to call this, because `Config::new()`
  /// will automatically laod and use the appropriate token anyway,
  /// according to the same algorithm.
  ///
  /// Arranges that `self.token` is either `Anonymous` or `Value`,
  /// by establishing a suitable default, and loading the token from
  /// a file, as necessary.
  #[throws(anyhow::Error)]
  pub fn load_default_token(&mut self) -> &mut Self {
    (||{
      self.token = Some(match self.get_token_or_default()? {
        None => TokenConfig::Anonymous,
        Some(v) => TokenConfig::Value(v),
      });
      Ok::<_,AE>(())
    })().context("load default token")?;
    self
  }

  #[throws(FE)]
  pub(crate) fn get_token(&self) -> Option<Token> {
    self.get_token_or_default()
      .map_err(FE::ClientCreationFailed)?
  }
}

/// Main entrypoints once a `Forge` has been constructed.
///
/// All `Forge` opbjects implement this trait.
pub trait ForgeMethods {
  /// Make a request.  This could be a read or write request.
  ///
  /// # General rules
  ///
  /// ## Searching and `Option`
  ///
  /// Searching and listing is done with requests which specify
  /// the kind of thing to search for, and some fields for filtering
  /// the returned results.  Where a field is not `Option`, it is
  /// mandatory (and there is no way to specify a wildcard).  Where
  /// a field is an `Option(VALUE)`, it must match exactly; `None`
  /// is a wildcard.
  ///
  /// ## Searching and limits
  ///
  /// Search operations (ie, requests which return a list of objects
  /// matching various criteria) need careful use.
  ///
  /// Most forges apply a limit to the number of results from any
  /// search operation.  Therefore, we have to make searches producing
  /// (at the forge API level) no more results than fit into the
  /// result limit.
  ///
  /// It is therefore necessary to make sure that the search operation
  /// parameters are sufficient to limit the results.  Unfortunately
  /// the search criteria actually implemented by each forge's public
  /// API are different.  We resolve this as follows:
  ///
  /// *Each search operation in this library gives minimum guarantees
  /// for server-side result filtering*.  When making a search
  /// operation, you should try to ensure that you can make the
  /// server-side-filtered result set sufficiently small; typically,
  /// less than 100 results.
  ///
  /// If the search succeds, the `gitforge` library will then do
  /// client-side filtering to make sure to only return results
  /// matching your actual query.
  ///
  /// (The `gitforge` library does not make multiple requests for
  /// successive "pages" of results.  This is because forges do not
  /// provide a way to maintain a snapshot of results which can be
  /// retreived over multiple requets.  Consequently pages results are
  /// impossible to use reliably For example, if a the set of matching
  /// items changes, an already-existing item might be imagined by the
  /// forge to be on page 2 for our request for page 1, but be
  /// promoted to page 1 for our request for page 2 - so we would miss
  /// it entirely.0
  fn request(&mut self, req: &Req) -> Result<Resp, forge::Error>;

  /// Clear any cached id lookups.
  ///
  /// Some forges need to cache various id lookups (for example,
  /// project and user names).  When these mappings may have changed,
  /// call this methods.
  ///
  /// This is necessary to pick up changes to:
  ///   * users (and organisations)
  ///   * repositories (or projects)
  ///
  /// It is not necessary for routine objects such as merge requests,
  /// issues, discussion commonets, etc.
  fn clear_id_caches(&mut self);

  /// Get the repo name string from a URL
  ///
  /// For example, `https://salsa.debian.org/iwj/otter` => `iwj/otter`.
  ///
  /// Correct results are not guaranteed if the url is not a valid url
  /// at this forge.  The host might or might not be checked against
  /// the configured/ host.
  ///
  /// Not all git URL formats are supported, but the usual ones are.
  #[throws(FE)]
  fn remote_url_to_repo(&self, url: &str) -> String {
    parse_git_remote_url(url, Some(self.host()))?.path.to_owned()
  }

  /// Inspect forge's hostname
  fn host(&self) -> &str;

  /// Inspect forge's hostname
  fn kind(&self) -> Kind;
}

/// Main trait; forge objects are `Box<dyn Forge>`
///
/// This is just an alias for `ForgeMethods` with various
/// conventional supertraits.
///
/// Look at `ForgeMethods`.
pub trait Forge: ForgeMethods + Debug + Send + Sync + 'static { }
impl<T> Forge for T where T: ForgeMethods + Debug + Send + Sync + 'static { }

/// Search for merge requests.
///
/// Server-side filtering guaranteed on:
///  * `target_repo`
///  * `author`
///  * `statuses` but only if it contains exactly one entry
///  * `source_branch` but only if source_repo provided
#[derive(Debug,Default,Clone,Eq,PartialEq,Serialize,Deserialize)]
#[allow(non_camel_case_types)]
pub struct Req_MergeRequests {
  pub target_repo:   String,
  pub number:        Option<String>,
  pub author:        Option<String>,
  pub source_repo:   Option<String>,
  pub target_branch: Option<String>,
  pub source_branch: Option<String>,
  pub statuses:      Option<HashSet<IssueMrStatus>>,
  #[serde(skip)] pub _non_exhaustive: (),
}

/// Create a new merge request.
#[derive(Debug,Default,Clone,Eq,PartialEq,Serialize,Deserialize)]
#[allow(non_camel_case_types)]
pub struct Req_CreateMergeRequest {
  pub target:        RepoBranch,
  pub source:        RepoBranch,
  pub title:         String,
  /// markdown, in forge's own format
  pub description:   String,
  #[serde(skip)] pub _non_exhaustive: (),
}

/// Issue or Merge Request status
///
/// The `Ord` implementation orders, roughly, "open-ness"
///
/// `Unrepresentable` covers states which can be present on the forge
/// but which cannot be represented in the `gitforge` API.
#[derive(Debug,Clone,Copy,Hash,Serialize,Deserialize)]
#[derive(Eq,PartialEq,Ord,PartialOrd)]
pub enum IssueMrStatus {
  Closed, Merged, Open, Unrepresentable,
}

/// Whether an Issue or Merge Request is locked
///
/// **Locked** means that contributions to the discussion, and/or
/// state changes, are restricted.  Typically locking is used as a
/// moderation tool for controversial discussions, and prevents
/// strangers from commenting.
#[derive(Debug,Clone,Copy,Hash,Serialize,Deserialize)]
#[derive(Eq,PartialEq,Ord,PartialOrd)] // ordered by "open-ness"
pub enum IssueMrLocked {
  Unlocked, Locked,
}

/// Overall state of an Issue or Merge Request
#[derive(Debug,Clone,Copy,Hash,Serialize,Deserialize)]
#[derive(Eq,PartialEq,Ord,PartialOrd)] // ordered by "open-ness"
#[non_exhaustive]
pub struct IssueMrState {
  pub status: IssueMrStatus,
  pub locked: IssueMrLocked,
}

/// Request (command) to a forge
#[derive(Debug,Clone,Eq,PartialEq,Serialize,Deserialize)]
pub enum Req {
  /** Merge Requests: search */ MergeRequests(Req_MergeRequests),
  /** Merge Request: create */ CreateMergeRequest(Req_CreateMergeRequest),
  #[allow(non_camel_case_types)] _NonExhaustive(),
}

/// Response from a forge
#[derive(Debug,Clone,Hash,Eq,PartialEq,Serialize,Deserialize)]
pub enum Resp {
  #[non_exhaustive] MergeRequests      { mrs: Vec<Resp_MergeRequest>, },
  #[non_exhaustive] CreateMergeRequest { number: String,              },
  #[allow(non_camel_case_types)] _NonExhaustive(),
}

/// Repository and branch
///
/// Convenience structure for cases where these come together
#[derive(Debug,Clone,Default,Hash,Eq,PartialEq,Serialize,Deserialize)]
pub struct RepoBranch {
  pub repo: String,
  pub branch: String,
}

/// Merge request, in a response
#[derive(Debug,Clone,Hash,Eq,PartialEq,Serialize,Deserialize)]
#[allow(non_camel_case_types)]
#[non_exhaustive]
pub struct Resp_MergeRequest {
  pub number: String,
  pub author: String,
  pub state:  IssueMrState,
  pub source: RepoBranch,
  pub target: RepoBranch,
}