// Copyright 2019-2021 Tauri Programme within The Commons Conservancy
// SPDX-License-Identifier: Apache-2.0
// SPDX-License-Identifier: MIT

//! Platform helper functions.

use std::path::{PathBuf, MAIN_SEPARATOR};

use crate::{Env, PackageInfo};

mod starting_binary;

/// Retrieves the currently running binary's path, taking into account security considerations.
///
/// The path is cached as soon as possible (before even `main` runs) and that value is returned
/// repeatedly instead of fetching the path every time. It is possible for the path to not be found,
/// or explicitly disabled (see following macOS specific behavior).
///
/// # Platform-specific behavior
///
/// On `macOS`, this function will return an error if the original path contained any symlinks
/// due to less protection on macOS regarding symlinks. This behavior can be disabled by setting the
/// `process-relaunch-dangerous-allow-symlink-macos` feature, although it is *highly discouraged*.
///
/// # Security
///
/// If the above platform-specific behavior does **not** take place, this function uses the
/// following resolution.
///
/// We canonicalize the path we received from [`std::env::current_exe`] to resolve any soft links.
/// This avoids the usual issue of needing the file to exist at the passed path because a valid
/// current executable result for our purpose should always exist. Notably,
/// [`std::env::current_exe`] also has a security section that goes over a theoretical attack using
/// hard links. Let's cover some specific topics that relate to different ways an attacker might
/// try to trick this function into returning the wrong binary path.
///
/// ## Symlinks ("Soft Links")
///
/// [`std::path::Path::canonicalize`] is used to resolve symbolic links to the original path,
/// including nested symbolic links (`link2 -> link1 -> bin`). On macOS, any results that include
/// a symlink are rejected by default due to lesser symlink protections. This can be disabled,
/// **although discouraged**, with the `process-relaunch-dangerous-allow-symlink-macos` feature.
///
/// ## Hard Links
///
/// A [Hard Link] is a named entry that points to a file in the file system.
/// On most systems, this is what you would think of as a "file". The term is
/// used on filesystems that allow multiple entries to point to the same file.
/// The linked [Hard Link] Wikipedia page provides a decent overview.
///
/// In short, unless the attacker was able to create the link with elevated
/// permissions, it should generally not be possible for them to hard link
/// to a file they do not have permissions to - with exception to possible
/// operating system exploits.
///
/// There are also some platform-specific information about this below.
///
/// ### Windows
///
/// Windows requires a permission to be set for the user to create a symlink
/// or a hard link, regardless of ownership status of the target. Elevated
/// permissions users have the ability to create them.
///
/// ### macOS
///
/// macOS allows for the creation of symlinks and hard links to any file.
/// Accessing through those links will fail if the user who owns the links
/// does not have the proper permissions on the original file.
///
/// ### Linux
///
/// Linux allows for the creation of symlinks to any file. Accessing the
/// symlink will fail if the user who owns the symlink does not have the
/// proper permissions on the original file.
///
/// Linux additionally provides a kernel hardening feature since version
/// 3.6 (30 September 2012). Most distributions since then have enabled
/// the protection (setting `fs.protected_hardlinks = 1`) by default, which
/// means that a vast majority of desktop Linux users should have it enabled.
/// **The feature prevents the creation of hardlinks that the user does not own
/// or have read/write access to.** [See the patch that enabled this].
///
/// [Hard Link]: https://en.wikipedia.org/wiki/Hard_link
/// [See the patch that enabled this]: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=800179c9b8a1e796e441674776d11cd4c05d61d7
pub fn current_exe() -> std::io::Result<PathBuf> {
  self::starting_binary::STARTING_BINARY.cloned()
}

/// Try to determine the current target triple.
///
/// Returns a target triple (e.g. `x86_64-unknown-linux-gnu` or `i686-pc-windows-msvc`) or an
/// `Error::Config` if the current config cannot be determined or is not some combination of the
/// following values:
/// `linux, mac, windows` -- `i686, x86, armv7` -- `gnu, musl, msvc`
///
/// * Errors:
///     * Unexpected system config
pub fn target_triple() -> crate::Result<String> {
  let arch = if cfg!(target_arch = "x86") {
    "i686"
  } else if cfg!(target_arch = "x86_64") {
    "x86_64"
  } else if cfg!(target_arch = "arm") {
    "armv7"
  } else if cfg!(target_arch = "aarch64") {
    "aarch64"
  } else {
    return Err(crate::Error::Architecture);
  };

  let os = if cfg!(target_os = "linux") {
    "unknown-linux"
  } else if cfg!(target_os = "macos") {
    "apple-darwin"
  } else if cfg!(target_os = "windows") {
    "pc-windows"
  } else if cfg!(target_os = "freebsd") {
    "unknown-freebsd"
  } else {
    return Err(crate::Error::Os);
  };

  let os = if cfg!(target_os = "macos") || cfg!(target_os = "freebsd") {
    String::from(os)
  } else {
    let env = if cfg!(target_env = "gnu") {
      "gnu"
    } else if cfg!(target_env = "musl") {
      "musl"
    } else if cfg!(target_env = "msvc") {
      "msvc"
    } else {
      return Err(crate::Error::Environment);
    };

    format!("{}-{}", os, env)
  };

  Ok(format!("{}-{}", arch, os))
}

/// Computes the resource directory of the current environment.
///
/// On Windows, it's the path to the executable.
///
/// On Linux, when running in an AppImage the `APPDIR` variable will be set to
/// the mounted location of the app, and the resource dir will be
/// `${APPDIR}/usr/lib/${exe_name}`. If not running in an AppImage, the path is
/// `/usr/lib/${exe_name}`.  When running the app from
/// `src-tauri/target/(debug|release)/`, the path is
/// `${exe_dir}/../lib/${exe_name}`.
///
/// On MacOS, it's `${exe_dir}../Resources` (inside .app).
#[allow(unused_variables)]
pub fn resource_dir(package_info: &PackageInfo, env: &Env) -> crate::Result<PathBuf> {
  let exe = current_exe()?;
  let exe_dir = exe.parent().expect("failed to get exe directory");
  let curr_dir = exe_dir.display().to_string();

  if curr_dir.ends_with(format!("{S}target{S}debug", S = MAIN_SEPARATOR).as_str())
    || curr_dir.ends_with(format!("{S}target{S}release", S = MAIN_SEPARATOR).as_str())
    || cfg!(target_os = "windows")
  {
    // running from the out dir or windows
    return Ok(exe_dir.to_path_buf());
  }

  #[allow(unused_mut, unused_assignments)]
  let mut res = Err(crate::Error::UnsupportedPlatform);

  #[cfg(target_os = "linux")]
  {
    res = if curr_dir.ends_with("/data/usr/bin") {
      // running from the deb bundle dir
      Ok(exe_dir.join(format!("../lib/{}", package_info.package_name())))
    } else if let Some(appdir) = &env.appdir {
      let appdir: &std::path::Path = appdir.as_ref();
      Ok(PathBuf::from(format!(
        "{}/usr/lib/{}",
        appdir.display(),
        package_info.package_name()
      )))
    } else {
      // running bundle
      Ok(PathBuf::from(format!(
        "/usr/lib/{}",
        package_info.package_name()
      )))
    };
  }

  #[cfg(target_os = "macos")]
  {
    res = Ok(exe_dir.join("../Resources"));
  }

  res
}