/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
use crate::{
    error::{FMLError, Result},
    SUPPORT_URL_LOADING,
};

use anyhow::anyhow;
use reqwest::blocking::{Client, ClientBuilder};
use std::{
    collections::{hash_map::DefaultHasher, BTreeMap},
    env,
    fmt::Display,
    hash::{Hash, Hasher},
    path::{Path, PathBuf},
};
use url::Url;

pub(crate) const GITHUB_USER_CONTENT_DOTCOM: &str = "https://raw.githubusercontent.com";
pub(crate) const API_GITHUB_DOTCOM: &str = "https://api.github.com";

#[derive(Clone)]
pub struct LoaderConfig {
    pub cwd: PathBuf,
    pub repo_files: Vec<String>,
    pub cache_dir: Option<PathBuf>,
    pub refs: BTreeMap<String, String>,
}

impl LoaderConfig {
    pub(crate) fn repo_and_path(f: &str) -> Option<(String, String)> {
        if f.starts_with('@') {
            let parts = f.splitn(3, '/').collect::<Vec<&str>>();
            match parts.as_slice() {
                [user, repo, path] => Some((format!("{user}/{repo}"), path.to_string())),
                _ => None,
            }
        } else {
            None
        }
    }
}

impl Default for LoaderConfig {
    fn default() -> Self {
        Self {
            repo_files: Default::default(),
            cache_dir: None,
            cwd: env::current_dir().expect("Current Working Directory is not set"),
            refs: Default::default(),
        }
    }
}

/// A FilePath for a file hosted in a GitHub repository with a specified ref.
#[derive(Clone, Debug)]
pub struct GitHubRepoFilePath {
    /// The repository id, i.e,. `owner/repo`.
    repo_id: String,

    /// The Git ref.
    git_ref: String,

    /// A Url, which is only used so that we can re-use Url::join for paths
    /// inside the repository.
    ///
    /// The URL scheme and host should not be referenced.
    ///
    /// Instead of this, you probably want [`Self::path()`] or
    /// [`Self::default_download_url()`].
    url: Url,
}

impl GitHubRepoFilePath {
    pub fn new(repo_id: &str, git_ref: &str) -> Self {
        Self {
            repo_id: repo_id.into(),
            git_ref: git_ref.into(),
            url: Url::parse("invalid://do-not-use/").expect("This is a constant, valid URL"),
        }
    }

    /// Return the repository ID.
    pub fn repo_id(&self) -> &str {
        &self.repo_id
    }

    /// Return the Git ref.
    pub fn git_ref(&self) -> &str {
        &self.git_ref
    }

    /// Return the path of the file in the GitHub repository.
    pub fn path(&self) -> &str {
        self.url.path()
    }

    pub fn join(&self, file: &str) -> Result<Self> {
        Ok(Self {
            repo_id: self.repo_id.clone(),
            git_ref: self.git_ref.clone(),
            url: self.url.join(file)?,
        })
    }

    /// Return the default download URL, without a token, as a string.
    ///
    /// [`Self::default_download_url()`] can return an error, so this is
    /// provided as a convenience for situations where an actual valid URL is
    /// not required, such as in Display impls.
    pub(crate) fn default_download_url_as_str(&self) -> String {
        format!(
            "{}/{}/{}{}",
            GITHUB_USER_CONTENT_DOTCOM,
            self.repo_id,
            self.git_ref,
            self.path() // begins with a /
        )
    }

    /// Return the default download URL, without a token.
    ///
    /// This URL can only be used to download files from public repositories.
    ///
    /// Otherwise, the URL must be retrieved via the GitHub repository contents
    /// API.
    pub fn default_download_url(&self) -> Result<Url> {
        Url::parse(&self.default_download_url_as_str()).map_err(Into::into)
    }

    pub fn contents_api_url(&self) -> Result<Url> {
        // https://docs.github.com/en/rest/repos/contents?apiVersion=2022-11-28#get-repository-content
        Url::parse(&format!(
            "{}/repos/{}/contents{}?ref={}",
            API_GITHUB_DOTCOM,
            self.repo_id,
            self.path(), // begins with a /
            self.git_ref
        ))
        .map_err(Into::into)
    }
}

/// A small enum for working with URLs and relative files
#[derive(Clone, Debug)]
pub enum FilePath {
    Local(PathBuf),
    Remote(Url),
    GitHub(GitHubRepoFilePath),
}

impl FilePath {
    pub fn new(cwd: &Path, file: &str) -> Result<Self> {
        Ok(if file.contains("://") {
            FilePath::Remote(Url::parse(file)?)
        } else {
            FilePath::Local(cwd.join(file))
        })
    }

    /// Appends a suffix to a path.
    /// If the `self` is a local file and the suffix is an absolute URL,
    /// then the return is the URL.
    pub fn join(&self, file: &str) -> Result<Self> {
        if file.contains("://") {
            return Ok(FilePath::Remote(Url::parse(file)?));
        }
        Ok(match self {
            Self::Local(p) => Self::Local(
                // We implement a join similar to Url::join.
                // If the root is a directory, we append;
                // if not we take the parent, then append.
                if is_dir(p) {
                    p.join(file)
                } else {
                    p.parent()
                        .expect("a file within a parent directory")
                        .join(file)
                },
            ),
            Self::Remote(u) => Self::Remote(u.join(file)?),
            Self::GitHub(p) => Self::GitHub(p.join(file)?),
        })
    }

    pub fn canonicalize(&self) -> Result<Self> {
        Ok(match self {
            Self::Local(p) => Self::Local(p.canonicalize().map_err(|e| {
                // We do this map_err here because the IO Error message that comes out of `canonicalize`
                // doesn't include the problematic file path.
                FMLError::InvalidPath(format!("{}: {}", e, p.as_path().display()))
            })?),
            _ => self.clone(),
        })
    }

    pub fn extension(&self) -> Option<&str> {
        Some(match self {
            Self::Local(p) => {
                let ext = p.extension()?;
                ext.to_str()?
            }
            Self::GitHub(GitHubRepoFilePath { url, .. }) | Self::Remote(url) => {
                let file = url.path_segments()?.last()?;
                let (_, ext) = file.rsplit_once('.')?;
                ext
            }
        })
    }
}

impl Display for FilePath {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        match self {
            Self::Local(p) => p.display().fmt(f),
            Self::Remote(u) => u.fmt(f),
            Self::GitHub(p) => p.default_download_url_as_str().fmt(f),
        }
    }
}

impl From<&Path> for FilePath {
    fn from(path: &Path) -> Self {
        Self::Local(path.into())
    }
}

#[cfg(not(test))]
fn is_dir(path_buf: &Path) -> bool {
    path_buf.is_dir()
}

// In tests, the directories don't always exist on-disk, so we cannot use the
// `.is_dir()` method, which would call `stat` (or equivalent) on a non-existent
// file. Instead, we check for the presence of a trailing slash, so all tests
// that need to treat a path like a directory *must* append trailing slashes to
// those paths.
#[cfg(test)]
fn is_dir(path_buf: &Path) -> bool {
    path_buf.display().to_string().ends_with('/')
}

static USER_AGENT: &str = concat!(env!("CARGO_PKG_NAME"), "/", env!("CARGO_PKG_VERSION"),);

/// Utility class to abstract away the differences between loading from file and network.
///
/// With a nod to offline developer experience, files which come from the network
/// are cached on disk.
///
/// The cache directory should be in a directory that will get purged on a clean build.
///
/// This allows us to import files from another repository (via https) or include files
/// from a local files.
///
/// The loader is able to resolve a shortcut syntax similar to other package managers.
///
/// By default a prefix of `@XXXX/YYYY`: resolves to the `main` branch `XXXX/YYYY` Github repo.
///
/// The config is a map of repository names to paths, URLs or branches.
///
/// Config files can be loaded
#[derive(Clone, Debug)]
pub struct FileLoader {
    cache_dir: Option<PathBuf>,
    fetch_client: Client,

    /// A mapping of repository IDs (without the leading @) to the git refs that
    /// should be used to download files.
    repo_refs: BTreeMap<String, FilePath>,

    // This is used for resolving relative paths when no other path
    // information is available.
    cwd: PathBuf,
}

impl TryFrom<&LoaderConfig> for FileLoader {
    type Error = FMLError;

    fn try_from(loader_config: &LoaderConfig) -> Result<Self, Self::Error> {
        let cache_dir = loader_config.cache_dir.clone();
        let cwd = loader_config.cwd.clone();

        let mut file_loader = Self::new(cwd, cache_dir, Default::default())?;

        for (repo_id, git_ref) in &loader_config.refs {
            file_loader.add_repo(repo_id, git_ref)?;
        }

        for f in &loader_config.repo_files {
            let path = file_loader.file_path(f)?;
            file_loader.add_repo_file(&path)?;
        }

        Ok(file_loader)
    }
}

impl FileLoader {
    pub fn new(
        cwd: PathBuf,
        cache_dir: Option<PathBuf>,
        repo_refs: BTreeMap<String, FilePath>,
    ) -> Result<Self> {
        let http_client = ClientBuilder::new()
            .https_only(true)
            .user_agent(USER_AGENT)
            .build()?;

        Ok(Self {
            cache_dir,
            fetch_client: http_client,
            cwd,
            repo_refs,
        })
    }

    #[allow(clippy::should_implement_trait)]
    #[cfg(test)]
    pub fn default() -> Result<Self> {
        let cwd = std::env::current_dir()?;
        let cache_path = cwd.join("build/app/fml-cache");
        Self::new(
            std::env::current_dir().expect("Current Working Directory not set"),
            Some(cache_path),
            Default::default(),
        )
    }

    /// Load a file containing mapping of repo names to `FilePath`s.
    /// Repo files can be JSON or YAML in format.
    /// Files are simple key value pair mappings of `repo_id` to repository locations,
    /// where:
    ///
    /// - a repo id is of the format used on Github: `$ORGANIZATION/$PROJECT`, and
    /// - location can be
    ///     - a path to a directory on disk, or
    ///     - a ref/branch/tag/commit hash in the repo stored on Github.
    ///
    /// Relative paths to on disk directories will be taken as relative to this file.
    pub fn add_repo_file(&mut self, file: &FilePath) -> Result<()> {
        let config: BTreeMap<String, String> = self.read(file)?;

        for (k, v) in config {
            self.add_repo_relative(file, &k, &v)?;
        }

        Ok(())
    }

    /// Add a repo and version/tag/ref/location.
    /// `repo_id` is the github `$ORGANIZATION/$PROJECT` string, e.g. `mozilla/application-services`.
    /// The `loc` string can be a:
    /// 1. A branch, commit hash or release tag on a remote repository, hosted on Github
    /// 2. A URL
    /// 3. A relative path (to the current working directory) to a directory on the local disk.
    /// 4. An absolute path to a directory on the local disk.
    pub fn add_repo(&mut self, repo_id: &str, loc: &str) -> Result<()> {
        self.add_repo_relative(&FilePath::Local(self.cwd.clone()), repo_id, loc)
    }

    fn add_repo_relative(&mut self, cwd: &FilePath, repo_id: &str, loc: &str) -> Result<()> {
        // We're building up a mapping of repo_ids to `FilePath`s; recall: `FilePath` is an enum that is an
        // absolute path or URL.

        // Standardize the form of repo id. We accept `@user/repo` or `user/repo`, but store it as
        // `user/repo`.
        let repo_id = repo_id.strip_prefix('@').unwrap_or(repo_id);

        // We construct the FilePath. We want to be able to tell the difference between a what `FilePath`s
        // can already reason about (relative file paths, absolute file paths and URLs) and what git knows about (refs, tags, versions).
        let file_path = if loc.starts_with('.')
            || loc.starts_with('/')
            || loc.contains(":\\")
            || loc.contains("://")
        {
            // The `loc`, whatever the current working directory, is going to end up as a part of a path.
            // A trailing slash ensures it gets treated like a directory, rather than a file.
            // See Url::join.
            let loc = if loc.ends_with('/') {
                loc.to_string()
            } else {
                format!("{}/", loc)
            };

            // URLs, relative file paths, absolute paths.
            cwd.join(&loc)?
        } else {
            // refs, commit hashes, tags, branches.
            self.remote_file_path(repo_id, loc)
        };

        // Finally, add the absolute path that we use every time the user refers to @user/repo.
        self.repo_refs.insert(repo_id.into(), file_path);
        Ok(())
    }

    fn remote_file_path(&self, repo: &str, branch_or_tag: &str) -> FilePath {
        FilePath::GitHub(GitHubRepoFilePath::new(repo, branch_or_tag))
    }

    fn default_remote_path(&self, key: String) -> FilePath {
        self.remote_file_path(&key, "main")
    }

    /// This loads a text file from disk or the network.
    ///
    /// If it's coming from the network, then cache the file to disk (based on the URL).
    ///
    /// We don't worry about cache invalidation, because a clean build should blow the cache
    /// away.
    pub fn read_to_string(&self, file: &FilePath) -> Result<String> {
        Ok(match file {
            FilePath::Local(path) => std::fs::read_to_string(path)?,
            FilePath::Remote(url) => self.fetch_and_cache(url)?,
            FilePath::GitHub(p) => {
                // If there is a GITHUB_BEARER_TOKEN environment variable
                // present, we will use that to get the download URL from the
                // GitHub contents API.
                let api_key = match env::var("GITHUB_BEARER_TOKEN") {
                    Ok(api_key) => Some(api_key),
                    Err(env::VarError::NotPresent) => None,
                    Err(env::VarError::NotUnicode(_)) => Err(FMLError::InvalidApiToken)?,
                };

                let download_url = if let Some(api_key) = api_key {
                    let contents_api_url = p.contents_api_url()?;

                    // The response format is documented here:
                    // https://docs.github.com/en/rest/repos/contents?apiVersion=2022-11-28#get-repository-content
                    self.fetch_client
                        .get(contents_api_url)
                        .bearer_auth(api_key)
                        .send()?
                        .error_for_status()?
                        .json::<serde_json::Value>()?
                        .get("download_url")
                        .and_then(serde_json::Value::as_str)
                        .ok_or_else(|| {
                            anyhow!(
                                "GitHub API did not return a download_url for @{}/{} at ref {}",
                                p.repo_id(),
                                p.path(),
                                p.git_ref()
                            )
                        })
                        .and_then(|u| Url::parse(u).map_err(Into::into))?
                } else {
                    p.default_download_url()?
                };

                self.fetch_and_cache(&download_url)?
            }
        })
    }

    pub fn read<T: serde::de::DeserializeOwned>(&self, file: &FilePath) -> Result<T> {
        let string = self
            .read_to_string(file)
            .map_err(|e| FMLError::InvalidPath(format!("{file}: {e}")))?;

        Ok(serde_yaml::from_str(&string)?)
    }

    fn fetch_and_cache(&self, url: &Url) -> Result<String> {
        if !SUPPORT_URL_LOADING {
            unimplemented!("Loading manifests from URLs is not yet supported ({})", url);
        }
        let path_buf = self.create_cache_path_buf(url);
        Ok(if path_buf.exists() {
            std::fs::read_to_string(path_buf)?
        } else {
            let res = self.fetch_client.get(url.clone()).send()?;
            let text = res.text()?;

            let parent = path_buf.parent().expect("Cache directory is specified");
            if !parent.exists() {
                std::fs::create_dir_all(parent)?;
            }

            std::fs::write(path_buf, &text)?;
            text
        })
    }

    fn create_cache_path_buf(&self, url: &Url) -> PathBuf {
        // Method to look after the cache directory.
        // We can organize this how we want: in this case we use a flat structure
        // with a hash of the URL as a prefix of the directory.
        let mut hasher = DefaultHasher::new();
        url.hash(&mut hasher);
        let checksum = hasher.finish();
        let filename = match url.path_segments() {
            Some(segments) => segments.last().unwrap_or("unknown.txt"),
            None => "unknown.txt",
        };
        // Take the last 16 bytes of the hash to make sure our prefixes are still random, but
        // not crazily long.
        let filename = format!("{:x}_{}", (checksum & 0x000000000000FFFF) as u16, filename,);

        self.cache_dir().join(filename)
    }

    fn cache_dir(&self) -> &Path {
        match &self.cache_dir {
            Some(d) => d,
            _ => self.tmp_cache_dir(),
        }
    }

    fn tmp_cache_dir<'a>(&self) -> &'a Path {
        use std::time::SystemTime;
        lazy_static::lazy_static! {
            static ref CACHE_DIR_NAME: String = format!("nimbus-fml-manifests-{:x}", match SystemTime::now().duration_since(SystemTime::UNIX_EPOCH) {
                Ok(n) => n.as_micros() & 0x00ffffff,
                Err(_) => 0,
            });

            static ref TMP_CACHE_DIR: PathBuf = std::env::temp_dir().join(CACHE_DIR_NAME.as_str());
        }
        &TMP_CACHE_DIR
    }

    /// Joins a path to a string, to make a new path.
    ///
    /// We want to be able to support local and remote files.
    /// We also want to be able to support a configurable short cut format.
    /// Following a pattern common in other package managers, `@XXXX/YYYY`
    /// is used as short hand for the main branch in github repos.
    ///
    /// If `f` is a relative path, the result is relative to `base`.
    pub fn join(&self, base: &FilePath, f: &str) -> Result<FilePath> {
        Ok(if let Some(u) = self.resolve_url_shortcut(f)? {
            u
        } else {
            base.join(f)?
        })
    }

    /// Make a new path.
    ///
    /// We want to be able to support local and remote files.
    /// We also want to be able to support a configurable short cut format.
    /// Following a pattern common in other package managers, `@XXXX/YYYY`
    /// is used as short hand for the main branch in github repos.
    ///
    /// If `f` is a relative path, the result is relative to `self.cwd`.
    pub fn file_path(&self, f: &str) -> Result<FilePath> {
        Ok(if let Some(u) = self.resolve_url_shortcut(f)? {
            u
        } else {
            FilePath::new(&self.cwd, f)?
        })
    }

    /// Checks that the given string has a @organization/repo/ prefix.
    /// If it does, then use that as a `repo_id` to look up the `FilePath` prefix
    /// if it exists in the `repo_refs`, and use the `main` branch of the github repo if it
    /// doesn't exist.
    fn resolve_url_shortcut(&self, f: &str) -> Result<Option<FilePath>> {
        if f.starts_with('@') {
            let f = f.replacen('@', "", 1);
            let parts = f.splitn(3, '/').collect::<Vec<&str>>();
            match parts.as_slice() {
                [user, repo, path] => {
                    let key = format!("{}/{}", user, repo);
                    Ok(if let Some(repo) = self.lookup_repo_path(user, repo) {
                        Some(repo.join(path)?)
                    } else {
                        let repo = self.default_remote_path(key);
                        Some(repo.join(path)?)
                    })
                }
                _ => Err(FMLError::InvalidPath(format!(
                    "'{}' needs to include a username, a repo and a filepath",
                    f
                ))),
            }
        } else {
            Ok(None)
        }
    }

    fn lookup_repo_path(&self, user: &str, repo: &str) -> Option<&FilePath> {
        let key = format!("{}/{}", user, repo);
        self.repo_refs.get(&key)
    }
}

impl Drop for FileLoader {
    fn drop(&mut self) {
        if self.cache_dir.is_some() {
            return;
        }
        let cache_dir = self.tmp_cache_dir();
        if cache_dir.exists() {
            _ = std::fs::remove_dir_all(cache_dir);
        }
    }
}

#[cfg(test)]
mod unit_tests {
    use std::fs;

    use crate::util::{build_dir, pkg_dir};

    use super::*;

    #[test]
    fn test_relative_paths() -> Result<()> {
        let tmp = std::env::temp_dir();

        let file = tmp.join("foo/bar.txt");
        let obs = FilePath::from(file.as_path());

        assert!(matches!(obs, FilePath::Local(_)));
        assert!(obs.to_string().ends_with("foo/bar.txt"));

        let obs = obs.join("baz.txt")?;
        assert!(obs.to_string().ends_with("foo/baz.txt"));

        let obs = obs.join("./bam.txt")?;
        // We'd prefer it to be like this:
        // assert!(obs.to_string().ends_with("foo/bam.txt"));
        // But there's no easy way to get this (because symlinks).
        // This is most likely the correct thing for us to do.
        // We put this test here for documentation purposes, and to
        // highlight that with URLs, ../ and ./ do what you might
        // expect.
        assert!(obs.to_string().ends_with("foo/./bam.txt"));

        let obs = obs.join("https://example.com/foo/bar.txt")?;
        assert!(matches!(obs, FilePath::Remote(_)));
        assert_eq!(obs.to_string(), "https://example.com/foo/bar.txt");

        let obs = obs.join("baz.txt")?;
        assert_eq!(obs.to_string(), "https://example.com/foo/baz.txt");

        let obs = obs.join("./bam.txt")?;
        assert_eq!(obs.to_string(), "https://example.com/foo/bam.txt");

        let obs = obs.join("../brum/bram.txt")?;
        assert_eq!(obs.to_string(), "https://example.com/brum/bram.txt");

        Ok(())
    }

    #[test]
    fn test_at_shorthand_with_no_at() -> Result<()> {
        let files = create_loader()?;
        let cwd = FilePath::Local(files.cwd.clone());
        let src_file = cwd.join("base/old.txt")?;

        // A source file asks for a destination file relative to it.
        let obs = files.join(&src_file, "a/file.txt")?;
        assert!(matches!(obs, FilePath::Local(_)));
        assert_eq!(
            obs.to_string(),
            format!("{}/base/a/file.txt", remove_trailing_slash(&cwd))
        );
        Ok(())
    }

    #[test]
    fn test_at_shorthand_default_branch() -> Result<()> {
        let files = create_loader()?;
        let cwd = FilePath::Local(files.cwd.clone());
        let src_file = cwd.join("base/old.txt")?;

        // A source file asks for a file in another repo. We haven't any specific configuration
        // for this repo, so we default to the `main` branch.
        let obs = files.join(&src_file, "@repo/unspecified/a/file.txt")?;
        assert!(
            matches!(obs, FilePath::GitHub(ref gh) if gh.repo_id() == "repo/unspecified" && gh.git_ref() == "main" && gh.path() == "/a/file.txt")
        );
        assert_eq!(
            obs.to_string(),
            "https://raw.githubusercontent.com/repo/unspecified/main/a/file.txt"
        );
        Ok(())
    }

    #[test]
    fn test_at_shorthand_absolute_url() -> Result<()> {
        let mut files = create_loader()?;
        let cwd = FilePath::Local(files.cwd.clone());
        let src_file = cwd.join("base/old.txt")?;

        // A source file asks for a file in another repo. The loader uses an absolute
        // URL as the base URL.
        files.add_repo("@repos/url", "https://example.com/remote/directory/path")?;

        let obs = files.join(&src_file, "@repos/url/a/file.txt")?;
        assert!(matches!(obs, FilePath::Remote(_)));
        assert_eq!(
            obs.to_string(),
            "https://example.com/remote/directory/path/a/file.txt"
        );

        let obs = files.file_path("@repos/url/b/file.txt")?;
        assert!(matches!(obs, FilePath::Remote(_)));
        assert_eq!(
            obs.to_string(),
            "https://example.com/remote/directory/path/b/file.txt"
        );
        Ok(())
    }

    #[test]
    fn test_at_shorthand_specified_branch() -> Result<()> {
        let mut files = create_loader()?;
        let cwd = FilePath::Local(files.cwd.clone());
        let src_file = cwd.join("base/old.txt")?;

        // A source file asks for a file in another repo. The loader uses the branch/tag/ref
        // specified.
        files.add_repo("@repos/branch", "develop")?;
        let obs = files.join(&src_file, "@repos/branch/a/file.txt")?;
        assert!(
            matches!(obs, FilePath::GitHub(ref gh) if gh.repo_id() == "repos/branch" && gh.git_ref() == "develop" && gh.path() == "/a/file.txt")
        );
        assert_eq!(
            obs.to_string(),
            "https://raw.githubusercontent.com/repos/branch/develop/a/file.txt"
        );

        let obs = files.file_path("@repos/branch/b/file.txt")?;
        assert!(
            matches!(obs, FilePath::GitHub(ref gh) if gh.repo_id() == "repos/branch" && gh.git_ref() == "develop" && gh.path() == "/b/file.txt")
        );
        assert_eq!(
            obs.to_string(),
            "https://raw.githubusercontent.com/repos/branch/develop/b/file.txt"
        );
        Ok(())
    }

    #[test]
    fn test_at_shorthand_local_development() -> Result<()> {
        let mut files = create_loader()?;
        let cwd = FilePath::Local(files.cwd.clone());
        let src_file = cwd.join("base/old.txt")?;

        // A source file asks for a file in another repo. The loader is configured to
        // give a file in a directory on the local filesystem.
        let rel_dir = "../directory/path";
        files.add_repo("@repos/local", rel_dir)?;

        let obs = files.join(&src_file, "@repos/local/a/file.txt")?;
        assert!(matches!(obs, FilePath::Local(_)));
        assert_eq!(
            obs.to_string(),
            format!("{}/{}/a/file.txt", remove_trailing_slash(&cwd), rel_dir)
        );

        let obs = files.file_path("@repos/local/b/file.txt")?;
        assert!(matches!(obs, FilePath::Local(_)));
        assert_eq!(
            obs.to_string(),
            format!("{}/{}/b/file.txt", remove_trailing_slash(&cwd), rel_dir)
        );

        Ok(())
    }

    fn create_loader() -> Result<FileLoader, FMLError> {
        let cache_dir = PathBuf::from(format!("{}/cache", build_dir()));
        let repo_refs = Default::default();
        let cwd = PathBuf::from(format!("{}/fixtures/", pkg_dir()));
        let loader = FileLoader::new(cwd, Some(cache_dir), repo_refs)?;
        Ok(loader)
    }

    #[test]
    fn test_at_shorthand_from_config_file() -> Result<()> {
        let cwd = PathBuf::from(pkg_dir());

        let config = &LoaderConfig {
            cwd,
            cache_dir: None,
            repo_files: vec![
                "fixtures/loaders/config_files/remote.json".to_string(),
                "fixtures/loaders/config_files/local.yaml".to_string(),
            ],
            refs: Default::default(),
        };

        let files: FileLoader = config.try_into()?;
        let cwd = FilePath::Local(files.cwd.clone());

        // This is a remote repo, specified in remote.json.
        let tfr = files.file_path("@my/remote/file.txt")?;
        assert_eq!(
            tfr.to_string(),
            "https://example.com/repo/branch/file.txt".to_string()
        );

        // This is a local file, specified in local.yaml
        let tf1 = files.file_path("@test/nested1/test-file.txt")?;
        assert_eq!(
            tf1.to_string(),
            format!(
                "{}/fixtures/loaders/config_files/./nested-1/test-file.txt",
                &cwd
            )
        );

        // This is a remote repo, specified in remote.json, but overridden in local.yaml
        let tf2 = files.file_path("@test/nested2/test-file.txt")?;
        assert_eq!(
            tf2.to_string(),
            format!(
                "{}/fixtures/loaders/config_files/./nested-2/test-file.txt",
                &cwd
            )
        );

        let tf1 = files.read_to_string(&tf1)?;
        let tf2 = files.read_to_string(&tf2)?;

        assert_eq!("test-file/1".to_string(), tf1);
        assert_eq!("test-file/2".to_string(), tf2);

        Ok(())
    }

    fn remove_trailing_slash(cwd: &FilePath) -> String {
        let s = cwd.to_string();
        let mut chars = s.chars();
        if s.ends_with('/') {
            chars.next_back();
        }
        chars.as_str().to_string()
    }

    #[test]
    fn test_at_shorthand_override_via_cli() -> Result<()> {
        let cwd = PathBuf::from(pkg_dir());

        let config = &LoaderConfig {
            cwd,
            cache_dir: None,
            repo_files: Default::default(),
            refs: BTreeMap::from([("@my-remote/repo".to_string(), "cli-branch".to_string())]),
        };

        let files: FileLoader = config.try_into()?;

        // This is a file from the remote repo
        let tfr = files.file_path("@my-remote/repo/path/to/file.txt")?;
        assert_eq!(
            tfr.to_string(),
            // We're going to fetch it from the `cli-branch` of the repo.
            "https://raw.githubusercontent.com/my-remote/repo/cli-branch/path/to/file.txt"
                .to_string()
        );

        Ok(())
    }

    #[test]
    fn test_dropping_tmp_cache_dir() -> Result<()> {
        let cwd = PathBuf::from(pkg_dir());
        let config = &LoaderConfig {
            cwd,
            cache_dir: None,
            repo_files: Default::default(),
            refs: Default::default(),
        };

        let files: FileLoader = config.try_into()?;
        let cache_dir = files.tmp_cache_dir();
        fs::create_dir_all(cache_dir)?;

        assert!(cache_dir.exists());
        drop(files);

        assert!(!cache_dir.exists());
        Ok(())
    }

    #[test]
    fn test_github_repo_file_path() -> Result<()> {
        let gh = GitHubRepoFilePath::new("owner/repo-name", "ref").join("a/file.txt")?;
        assert_eq!(
            gh.contents_api_url()?.to_string(),
            "https://api.github.com/repos/owner/repo-name/contents/a/file.txt?ref=ref",
        );
        assert_eq!(
            gh.default_download_url()?.to_string(),
            "https://raw.githubusercontent.com/owner/repo-name/ref/a/file.txt"
        );

        let gh = gh.join("/b/file.txt")?;
        assert_eq!(
            gh.contents_api_url()?.to_string(),
            "https://api.github.com/repos/owner/repo-name/contents/b/file.txt?ref=ref",
        );
        assert_eq!(
            gh.default_download_url()?.to_string(),
            "https://raw.githubusercontent.com/owner/repo-name/ref/b/file.txt"
        );

        let gh = gh.join("/c/")?.join("file.txt")?;
        assert_eq!(
            gh.contents_api_url()?.to_string(),
            "https://api.github.com/repos/owner/repo-name/contents/c/file.txt?ref=ref",
        );
        assert_eq!(
            gh.default_download_url()?.to_string(),
            "https://raw.githubusercontent.com/owner/repo-name/ref/c/file.txt"
        );

        let gh = gh.join("d/")?.join("file.txt")?;
        assert_eq!(
            gh.contents_api_url()?.to_string(),
            "https://api.github.com/repos/owner/repo-name/contents/c/d/file.txt?ref=ref",
        );
        assert_eq!(
            gh.default_download_url()?.to_string(),
            "https://raw.githubusercontent.com/owner/repo-name/ref/c/d/file.txt"
        );

        Ok(())
    }

    #[test]
    fn test_extension() -> Result<()> {
        let path = FilePath::Local("file.json".into());
        assert_eq!(path.extension(), Some("json"));

        let path = FilePath::Local("file.fml.yaml".into());
        assert_eq!(path.extension(), Some("yaml"));

        let path = FilePath::Local("file".into());
        assert_eq!(path.extension(), None);

        // Remote paths
        let path = FilePath::Remote("https://example.com/file.json".try_into()?);
        assert_eq!(path.extension(), Some("json"));

        let path = FilePath::Remote("https://example.com/file.fml.yaml".try_into()?);
        assert_eq!(path.extension(), Some("yaml"));

        let path = FilePath::Remote("https://example.com/".try_into()?);
        assert_eq!(path.extension(), None);

        let path = FilePath::Remote("https://example.com/file".try_into()?);
        assert_eq!(path.extension(), None);

        let path = FilePath::Remote("https://example.com/path/".try_into()?);
        assert_eq!(path.extension(), None);

        let path = FilePath::GitHub(GitHubRepoFilePath::new("example", "main"));
        assert_eq!(path.extension(), None);

        let path = path.join("./file.json")?;
        assert_eq!(path.extension(), Some("json"));

        let path = path.join("./file.fml.yaml")?;
        assert_eq!(path.extension(), Some("yaml"));

        Ok(())
    }
}