//! Email related utilities.

use std::io::Write;
use std::process::{Command, Stdio};

use anyhow::{bail, format_err, Error};

/// Sends multi-part mail with text and/or html to a list of recipients
///
/// Includes the header `Auto-Submitted: auto-generated`, so that auto-replies
/// (i.e. OOO replies) won't trigger.
/// ``sendmail`` is used for sending the mail.
pub fn sendmail(
    mailto: &[&str],
    subject: &str,
    text: Option<&str>,
    html: Option<&str>,
    mailfrom: Option<&str>,
    author: Option<&str>,
) -> Result<(), Error> {
    use std::fmt::Write as _;

    if mailto.is_empty() {
        bail!("At least one recipient has to be specified!")
    }
    let mailfrom = mailfrom.unwrap_or("root");
    let recipients = mailto.join(",");
    let author = author.unwrap_or("Proxmox Backup Server");

    let now = proxmox_time::epoch_i64();

    let mut sendmail_process = match Command::new("/usr/sbin/sendmail")
        .arg("-B")
        .arg("8BITMIME")
        .arg("-f")
        .arg(mailfrom)
        .arg("--")
        .args(mailto)
        .stdin(Stdio::piped())
        .spawn()
    {
        Err(err) => bail!("could not spawn sendmail process: {}", err),
        Ok(process) => process,
    };
    let mut is_multipart = false;
    if let (Some(_), Some(_)) = (text, html) {
        is_multipart = true;
    }

    let mut body = String::new();
    let boundary = format!("----_=_NextPart_001_{}", now);
    if is_multipart {
        body.push_str("Content-Type: multipart/alternative;\n");
        let _ = writeln!(body, "\tboundary=\"{}\"", boundary);
        body.push_str("MIME-Version: 1.0\n");
    } else if !subject.is_ascii() {
        body.push_str("MIME-Version: 1.0\n");
    }
    if !subject.is_ascii() {
        let _ = writeln!(body, "Subject: =?utf-8?B?{}?=", base64::encode(subject));
    } else {
        let _ = writeln!(body, "Subject: {}", subject);
    }
    let _ = writeln!(body, "From: {} <{}>", author, mailfrom);
    let _ = writeln!(body, "To: {}", &recipients);
    let rfc2822_date = proxmox_time::epoch_to_rfc2822(now)?;
    let _ = writeln!(body, "Date: {}", rfc2822_date);
    body.push_str("Auto-Submitted: auto-generated;\n");

    if is_multipart {
        body.push('\n');
        body.push_str("This is a multi-part message in MIME format.\n");
        let _ = write!(body, "\n--{}\n", boundary);
    }
    if let Some(text) = text {
        body.push_str("Content-Type: text/plain;\n");
        body.push_str("\tcharset=\"UTF-8\"\n");
        body.push_str("Content-Transfer-Encoding: 8bit\n");
        body.push('\n');
        body.push_str(text);
        if is_multipart {
            let _ = write!(body, "\n--{}\n", boundary);
        }
    }
    if let Some(html) = html {
        body.push_str("Content-Type: text/html;\n");
        body.push_str("\tcharset=\"UTF-8\"\n");
        body.push_str("Content-Transfer-Encoding: 8bit\n");
        body.push('\n');
        body.push_str(html);
        if is_multipart {
            let _ = write!(body, "\n--{}--", boundary);
        }
    }

    if let Err(err) = sendmail_process
        .stdin
        .take()
        .unwrap()
        .write_all(body.as_bytes())
    {
        bail!("couldn't write to sendmail stdin: {}", err)
    };

    // wait() closes stdin of the child
    if let Err(err) = sendmail_process.wait() {
        bail!("sendmail did not exit successfully: {}", err)
    }

    Ok(())
}

/// Forwards an email message to a given list of recipients.
///
/// ``sendmail`` is used for sending the mail, thus `message` must be
/// compatible with that (the message is piped into stdin unmodified).
pub fn forward(
    mailto: &[&str],
    mailfrom: &str,
    message: &[u8],
    uid: Option<u32>,
) -> Result<(), Error> {
    use std::os::unix::process::CommandExt;

    if mailto.is_empty() {
        bail!("At least one recipient has to be specified!")
    }

    let mut builder = Command::new("/usr/sbin/sendmail");

    builder
        .args([
            "-N", "never", // never send DSN (avoid mail loops)
            "-f", mailfrom, "--",
        ])
        .args(mailto)
        .stdin(Stdio::piped())
        .stdout(Stdio::null())
        .stderr(Stdio::null());

    if let Some(uid) = uid {
        builder.uid(uid);
    }

    let mut process = builder
        .spawn()
        .map_err(|err| format_err!("could not spawn sendmail process: {err}"))?;

    process
        .stdin
        .take()
        .unwrap()
        .write_all(message)
        .map_err(|err| format_err!("couldn't write to sendmail stdin: {err}"))?;

    process
        .wait()
        .map_err(|err| format_err!("sendmail did not exit successfully: {err}"))?;

    Ok(())
}

#[cfg(test)]
mod test {
    use crate::email::sendmail;

    #[test]
    fn email_without_recipients() {
        let result = sendmail(
            &[],
            "Subject2",
            None,
            Some("<b>HTML</b>"),
            None,
            Some("test1"),
        );
        assert!(result.is_err());
    }
}