vomit-config 0.4.0

//! This crate provides a unified config file for all tools that are part of the
//! [Vomit project](https://sr.ht/~bitfehler/vomit).
//!
//! It aims to provide configuration options for various aspects of email
//! accounts. Most tools will only need a subset of the available options, but
//! once an account is fully configured, all tools will be able to work with it.
//!
//! While written for the Vomit project, this is essentially a generic email
//! account configuration library. If you think it might be useful for you feel
//! free to use outside of Vomit.
//!
//! ## File format
//!
//! Previously, the TOML file format was used. This is still supported, but
//! deprecated in favor of [scfg](https://codeberg.org/emersion/scfg). The
//! library will print a warning to stderr when loading a TOML file. To migrate
//! over, simply change the filename extension from `.toml` to `.scfg` and
//! convert it to the format described below.
//!
//! The standard location is `$XDG_CONFIG_DIR/vomit/config.scfg`, which usually
//! means `~/.config/vomit/config.scfg`.
//!
//! Projects using this will have their own documentation about which values
//! they require. Here is a sample with all available options (though some
//! commented out), including comments on their usage:
//!
//! ```scfg
//! # This section defines one account named "example". Most tools
//! # support multiple accounts. If not specified, tools should default
//! # to the first account in the config file.
//! account example {
//!
//!     # `local` defaults to "~/.maildir", but is best set explicitly:
//!     local '/home/test/.mail'
//!
//!     # The mail server. Must support IMAPS
//!     remote 'imap.example.com'
//!
//!     # Login name for the mail server
//!     user 'johndoe'
//!
//!     # Password for the mail server. Can be set explicitly:
//!     #password 'hunter1'
//!     # but that's not great for security. Instead use a command,
//!     # e.g. to interact with your password manager
//!     pass-cmd 'pass show mail/example.com'
//!
//!     # This section defines settings relevant only for sending mail.
//!     send {
//!         # Override the mail server for sending.
//!         # Defaults to the account-level remote if not set.
//!         remote 'smtp.example.com'
//!
//!         # Some mail setups have different credentials for sending,
//!         # so those can be overridden, too.
//!         # Defaults to the account-level user if not set.
//!         user 'johndoe@example.com'
//!
//!         # See password and pass-cmd above.
//!         # If neither are set, account-level credentials will be used.
//!         #password 's3cr3t'
//!         pass-cmd 'pass show mail/smtp.example.com'
//!
//!         # The From header of outgoing emails. Defaults to the configured
//!         # user, but this will only work if the username is a valid email
//!         # address.
//!         from 'John Doe <johndoe@example.com>'
//!     }
//! }
//! ```

use std::io;
use std::path::{Path, PathBuf};
use std::process::Command;

use dirs::{config_dir, home_dir};
use shellexpand::tilde;
use thiserror::Error;

mod tomlcfg;

mod scfg;

const DEFAULT_MAILDIR: &str = "~/.maildir";

/// An error that can occur while reading the config file.
#[derive(Error, Debug)]
pub enum ConfigError {
    /// Error determining the user's home directory.
    #[error("error getting default config file location")]
    DirError,
    /// IO error while trying to read the config file.
    #[error("error reading config file: {0}")]
    IOError(#[from] io::Error),
    /// Error executing the "pass-cmd".
    #[error("error executing pass-cmd: {0}")]
    PassExecError(String),
    /// An invalid UTF-8 string was encountered.
    #[error("UTF-8 error: {0}")]
    UTF8Error(#[from] std::string::FromUtf8Error),
    /// The TOML parser failed.
    #[error("error parsing config file: {0}")]
    TOMLError(#[from] toml::de::Error),
    /// The scfg parser failed.
    #[error("error parsing config file: {0}")]
    ScfgError(#[from] derpscfg::Error),
    /// Other generic error, details in the message.
    #[error("config error: {0}")]
    Error(&'static str),
}

enum AccountImpl<'a> {
    Toml(tomlcfg::TomlAccount<'a>),
    Scfg(&'a scfg::ScfgAccount),
}

/// Represents the configuration of a specific account.
pub struct Account<'a> {
    name: String,
    // Keep a copy of this, as it is potentially computed (tilde expansion)
    local: String,
    acc: AccountImpl<'a>,
}

// TODO remove TOML and rip out the level of indirection here.
enum ConfigImpl {
    Toml(tomlcfg::TomlConfig),
    Scfg(scfg::ScfgConfig),
}

/// Represents a complete config file, which can hold multiple
/// [Accounts](Account).
pub struct Config {
    cfg: ConfigImpl,
}

impl Config {
    /// Returns a specific account's configuration.
    ///
    /// If `name` is some string and matches the name of a configured account
    /// returns the corresponding [`Account`]. If `name` is `None`, returns the
    /// configuration of the first account in the config file. The latter can be
    /// expected to never return `None` as loading a configuration file fails if
    /// it does not configure at least one account.
    pub fn for_account(&self, name: Option<&str>) -> Option<Account<'_>> {
        match &self.cfg {
            ConfigImpl::Toml(t) => t.for_account(name).map(|a| {
                let local = a.local().to_string();
                Account {
                    name: a.name().clone(),
                    acc: AccountImpl::Toml(a),
                    local,
                }
            }),
            ConfigImpl::Scfg(s) => s.for_account(name).map(|(n, a)| {
                let l = a.local.as_deref();
                let local = tilde(l.unwrap_or(DEFAULT_MAILDIR)).to_string();
                Account {
                    name: n.clone(),
                    acc: AccountImpl::Scfg(a),
                    local,
                }
            }),
        }
    }
}

impl Account<'_> {
    /// The name of the account.
    pub fn name(&self) -> &str {
        &self.name
    }

    /// The directory where mail is stored locally.
    pub fn local(&self) -> &str {
        &self.local
    }

    /// The remote IMAP server.
    pub fn remote(&self) -> Option<&str> {
        match &self.acc {
            AccountImpl::Toml(t) => t.remote(),
            AccountImpl::Scfg(s) => s.remote.as_deref(),
        }
    }

    /// The username to log in to the remote server.
    pub fn user(&self) -> Option<&str> {
        match &self.acc {
            AccountImpl::Toml(t) => t.user(),
            AccountImpl::Scfg(s) => s.user.as_deref(),
        }
    }

    /// The "From" address to use when sending mail.
    ///
    /// Can be just an email address or "Some Name <name@example.com>". Falls
    /// back to [send_user()](Self::send_user), which falls back to
    /// [user()](Self::user).
    pub fn send_from(&self) -> Option<&str> {
        match &self.acc {
            AccountImpl::Toml(t) => t.send_from(),
            AccountImpl::Scfg(s) => s
                .send
                .as_ref()
                .and_then(|s| s.from.as_ref())
                .map(|f| f.as_str())
                .or_else(|| self.send_user()),
        }
    }

    /// The username to log in when sending mail.
    ///
    /// If not explicitly configured, this returns the value of
    /// [user()](Account::user).
    pub fn send_user(&self) -> Option<&str> {
        match &self.acc {
            AccountImpl::Toml(t) => t.send_user(),
            AccountImpl::Scfg(s) => s
                .send
                .as_ref()
                .and_then(|s| s.user.as_ref())
                .map(|u| u.as_str())
                .or_else(|| self.user()),
        }
    }

    /// The remote SMTP server.
    ///
    /// If not explicitly configured, this returns the value of
    /// [remote()](Account::remote).
    pub fn send_remote(&self) -> Option<&str> {
        match &self.acc {
            AccountImpl::Toml(t) => t.send_remote(),
            AccountImpl::Scfg(s) => s
                .send
                .as_ref()
                .and_then(|s| s.remote.as_ref())
                .map(|r| r.as_str())
                .or_else(|| self.remote()),
        }
    }

    fn pass_cmd(cmd: &str) -> Result<Option<String>, ConfigError> {
        let out = Command::new("sh").arg("-c").arg(cmd).output();
        match out {
            Ok(mut output) => {
                let newline: u8 = 10;
                if Some(&newline) == output.stdout.last() {
                    _ = output.stdout.pop(); // remove trailing newline
                }
                Ok(Some(String::from_utf8(output.stdout)?))
            }
            Err(e) => Err(ConfigError::PassExecError(e.to_string())),
        }
    }

    /// The password to log in to the remote server.
    ///
    /// Potentially executes a configured command to retrieve the password.
    /// Returns an error if the password command has to be executed and fails.
    /// Can return `Ok(None)` if neither a password nor a password command are
    /// configured. Otherwise, returns the password.
    pub fn password(&self) -> Result<Option<String>, ConfigError> {
        match &self.acc {
            AccountImpl::Toml(t) => t.password(),
            AccountImpl::Scfg(s) => {
                if let Some(p) = s.password.as_ref() {
                    Ok(Some(String::from(p)))
                } else if let Some(cmd) = s.pass_cmd.as_ref() {
                    Account::pass_cmd(cmd)
                } else {
                    Ok(None)
                }
            }
        }
    }

    /// The password to log in to the remote server for sending mail.
    ///
    /// Potentially executes a configured command to retrieve the password.
    /// Returns an error if the password command has to be executed and fails.
    /// Can return `Ok(None)` if neither a password nor a password command are
    /// configured. Otherwise, returns the password.
    ///
    /// Unless explicitly configured by the user, this returns the value of
    /// [password()](Account::password).
    pub fn send_password(&self) -> Result<Option<String>, ConfigError> {
        match &self.acc {
            AccountImpl::Toml(t) => t.send_password(),
            AccountImpl::Scfg(s) => {
                let pass = s.send.as_ref().and_then(|s| s.password.as_ref());
                let pcmd = s.send.as_ref().and_then(|s| s.pass_cmd.as_ref());

                if let Some(p) = pass {
                    Ok(Some(String::from(p)))
                } else if let Some(cmd) = pcmd {
                    Account::pass_cmd(cmd)
                } else {
                    self.password()
                }
            }
        }
    }
}

/// Returns the (system dependent) default path to the configuration file.
///
/// The standard location is `$XDG_CONFIG_DIR`/vomit/config.scfg (which usually
/// means `~/.config/vomit/config.scfg`). If no `$XDG_CONFIG_DIR` can be
/// determined, `~/.vomitrc` is used as fallback. Fails if the user's home
/// directory cannot be determined.
pub fn default_path() -> Result<PathBuf, ConfigError> {
    if let Some(mut path) = config_dir() {
        path.push("vomit");
        path.push("config.scfg");
        return Ok(path);
    };
    if let Some(mut path) = home_dir() {
        path.push(".vomitrc");
        return Ok(path);
    }
    Err(ConfigError::DirError)
}

fn default_path_toml() -> Result<PathBuf, ConfigError> {
    if let Some(mut path) = config_dir() {
        path.push("vomit");
        path.push("config.toml");
        return Ok(path);
    };
    if let Some(mut path) = home_dir() {
        path.push(".vomitrc");
        return Ok(path);
    }
    Err(ConfigError::DirError)
}

/// Load a configuration file.
///
/// If `path` is `None`, load it from the default location (see [default_path]).
///
/// For backwards compatibility, if `path` has a `.toml` filename extension it
/// will be parsed as TOML. If it has an extension other than `.toml` or
/// `.scfg`, or none at all, it will be parsed as both scfg and TOML, using
/// whichever one succeeds. If both fails, the returned error will be that from
/// the attempt to parse it as scfg.
pub fn load<P: AsRef<Path>>(path: Option<P>) -> Result<Config, ConfigError> {
    let ps = default_path()?;
    let pt = default_path_toml()?;
    let p = path.map(|p| p.as_ref().to_path_buf()).unwrap_or_else(|| {
        if ps.exists() {
            ps
        } else if pt.exists() {
            pt
        } else {
            // If both don't exist, at least make the error message about the desired one
            ps
        }
    });
    if let Some("scfg") = p.extension().and_then(|e| e.to_str()) {
        Ok(Config {
            cfg: ConfigImpl::Scfg(scfg::load_scfg_file(&p)?),
        })
    } else if let Some("toml") = p.extension().and_then(|e| e.to_str()) {
        eprintln!("WARNING: loading deprecated TOML config, switch to scfg: https://docs.rs/vomit-config/");
        Ok(Config {
            cfg: ConfigImpl::Toml(tomlcfg::load_toml(&p)?),
        })
    } else {
        let r = tomlcfg::load_toml(&p);
        if let Ok(t) = r {
            eprintln!("WARNING: loading deprecated TOML config, switch to scfg: https://docs.rs/vomit-config/");
            Ok(Config {
                cfg: ConfigImpl::Toml(t),
            })
        } else {
            Ok(Config {
                cfg: ConfigImpl::Scfg(scfg::load_scfg_file(&p)?),
            })
        }
    }
}

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

    #[test]
    fn test_load() {
        let d = PathBuf::from_iter([env!("CARGO_MANIFEST_DIR"), "testdata"]);

        let ext_scfg = PathBuf::from_iter([&d, &PathBuf::from("config.scfg")]);
        let r = load(Some(&ext_scfg));
        assert!(matches!(
            r,
            Ok(Config {
                cfg: ConfigImpl::Scfg(_)
            })
        ));

        let ext_toml = PathBuf::from_iter([&d, &PathBuf::from("config.toml")]);
        let r = load(Some(&ext_toml));
        assert!(matches!(
            r,
            Ok(Config {
                cfg: ConfigImpl::Toml(_)
            })
        ));

        let noext_scfg = PathBuf::from_iter([&d, &PathBuf::from("scfg.vomitrc")]);
        let r = load(Some(&noext_scfg));
        assert!(matches!(
            r,
            Ok(Config {
                cfg: ConfigImpl::Scfg(_)
            })
        ));

        let noext_toml = PathBuf::from_iter([&d, &PathBuf::from("toml.vomitrc")]);
        let r = load(Some(&noext_toml));
        assert!(matches!(
            r,
            Ok(Config {
                cfg: ConfigImpl::Toml(_)
            })
        ));
    }
}