mailks/email_build.rs

use lettre::{
    Address, AsyncSmtpTransport, Message, Tokio1Executor,
    message::{
        Attachment as LettreAttachment, Body, Mailbox, MultiPart, SinglePart,
        header::{ContentType, HeaderName, HeaderValue},
    },
    transport::smtp::{self, authentication::Credentials, extension::ClientId},
};

use crate::{
    config::{SmtpConfig, SmtpTls},
    error::EmailError,
    pb::email::v1::{Attachment, EmailAddress, EmailPriority, SendEmailRequest},
};

pub(crate) fn build_mailer(
    config: &SmtpConfig,
) -> Result<AsyncSmtpTransport<Tokio1Executor>, EmailError> {
    let mut builder = match config.tls {
        SmtpTls::None => {
            smtp::AsyncSmtpTransport::<Tokio1Executor>::builder_dangerous(&config.host)
        }
        SmtpTls::StartTls => {
            smtp::AsyncSmtpTransport::<Tokio1Executor>::starttls_relay(&config.host)
                .map_err(|e| EmailError::BuildTransport(e.to_string()))?
        }
        SmtpTls::Tls => smtp::AsyncSmtpTransport::<Tokio1Executor>::relay(&config.host)
            .map_err(|e| EmailError::BuildTransport(e.to_string()))?,
    }
    .port(config.port)
    .timeout(Some(config.timeout));

    match (&config.username, &config.password) {
        (Some(u), Some(p)) => {
            builder = builder.credentials(Credentials::new(u.clone(), p.clone()));
        }
        (None, None) => {}
        _ => return Err(EmailError::IncompleteCredentials),
    }

    if let Some(name) = config.helo_name.as_deref().and_then(non_empty) {
        builder = builder.hello_name(ClientId::Domain(name.to_owned()));
    }
    Ok(builder.build())
}

pub(crate) fn build_body(
    builder: lettre::message::MessageBuilder,
    request: &SendEmailRequest,
) -> Result<Message, EmailError> {
    match select_body_multipart(request) {
        BodyKind::Both(mp) => builder
            .multipart(mp)
            .map_err(|e| EmailError::BuildMessage(e.to_string())),
        BodyKind::Html(sp) => builder
            .singlepart(sp)
            .map_err(|e| EmailError::BuildMessage(e.to_string())),
        BodyKind::Plain(sp) => builder
            .singlepart(sp)
            .map_err(|e| EmailError::BuildMessage(e.to_string())),
    }
}

pub(crate) fn build_mixed_body(request: &SendEmailRequest) -> MultiPart {
    let mixed = MultiPart::mixed();
    match select_body_multipart(request) {
        BodyKind::Both(mp) => mixed.multipart(mp),
        BodyKind::Html(sp) => mixed.singlepart(sp),
        BodyKind::Plain(sp) => mixed.singlepart(sp),
    }
}

enum BodyKind {
    Both(MultiPart),
    Html(SinglePart),
    Plain(SinglePart),
}

fn select_body_multipart(request: &SendEmailRequest) -> BodyKind {
    if !request.text_body.is_empty() && !request.html_body.is_empty() {
        BodyKind::Both(MultiPart::alternative_plain_html(
            request.text_body.clone(),
            request.html_body.clone(),
        ))
    } else if !request.html_body.is_empty() {
        BodyKind::Html(SinglePart::html(request.html_body.clone()))
    } else {
        BodyKind::Plain(SinglePart::plain(request.text_body.clone()))
    }
}

pub(crate) fn build_single_attachment(
    index: usize,
    att: &Attachment,
) -> Result<SinglePart, EmailError> {
    let filename = if att.filename.trim().is_empty() {
        format!("attachment-{index}")
    } else {
        att.filename.clone()
    };

    if att.data.is_empty() && !att.url.trim().is_empty() {
        return Err(EmailError::UnsupportedAttachmentUrl {
            filename,
            url: att.url.clone(),
        });
    }
    let ct: ContentType = if att.content_type.trim().is_empty() {
        "application/octet-stream"
            .parse()
            .expect("valid static mime")
    } else {
        att.content_type
            .parse()
            .map_err(|e: lettre::message::header::ContentTypeErr| {
                EmailError::InvalidContentType {
                    filename: filename.clone(),
                    value: att.content_type.clone(),
                    reason: e.to_string(),
                }
            })?
    };
    Ok(LettreAttachment::new(filename).body(Body::new(att.data.clone()), ct))
}

pub(crate) fn mailbox_from_email_address(
    field: &'static str,
    value: &EmailAddress,
) -> Result<Mailbox, EmailError> {
    mailbox_from_parts(field, &value.email, non_empty(&value.name))
}

pub(crate) fn mailbox_from_parts(
    field: &'static str,
    email: &str,
    name: Option<&str>,
) -> Result<Mailbox, EmailError> {
    let address = email
        .trim()
        .parse::<Address>()
        .map_err(|e| EmailError::InvalidAddress {
            field,
            value: email.to_owned(),
            reason: e.to_string(),
        })?;
    Ok(Mailbox::new(name.map(ToOwned::to_owned), address))
}

pub(crate) fn apply_custom_headers(
    mut builder: lettre::message::MessageBuilder,
    request: &SendEmailRequest,
) -> Result<lettre::message::MessageBuilder, EmailError> {
    for (name, value) in &request.headers {
        if non_empty(name).is_none() {
            continue;
        }
        if is_managed_header(name) {
            return Err(EmailError::ForbiddenHeader { name: name.clone() });
        }
        if value.contains(['\r', '\n']) {
            return Err(EmailError::InvalidHeader {
                name: name.clone(),
                reason: "header value must not contain CR or LF".to_owned(),
            });
        }
        let hn =
            HeaderName::new_from_ascii(name.clone()).map_err(|e| EmailError::InvalidHeader {
                name: name.clone(),
                reason: e.to_string(),
            })?;
        builder = builder.raw_header(HeaderValue::new(hn, value.clone()));
    }
    Ok(builder)
}

pub(crate) fn apply_priority_headers(
    builder: lettre::message::MessageBuilder,
    priority: i32,
) -> lettre::message::MessageBuilder {
    match EmailPriority::try_from(priority).unwrap_or(EmailPriority::Unspecified) {
        EmailPriority::High => builder
            .raw_header(hv("X-Priority", "1"))
            .raw_header(hv("Importance", "high")),
        EmailPriority::Low => builder
            .raw_header(hv("X-Priority", "5"))
            .raw_header(hv("Importance", "low")),
        EmailPriority::Normal | EmailPriority::Unspecified => builder,
    }
}

fn hv(name: &'static str, value: &str) -> HeaderValue {
    HeaderValue::new(HeaderName::new_from_ascii_str(name), value.to_owned())
}

fn is_managed_header(name: &str) -> bool {
    matches!(
        name.trim().to_ascii_lowercase().as_str(),
        "from"
            | "to"
            | "cc"
            | "bcc"
            | "subject"
            | "reply-to"
            | "date"
            | "mime-version"
            | "content-type"
            | "content-transfer-encoding"
            | "content-disposition"
    )
}

pub(crate) fn non_empty(value: &str) -> Option<&str> {
    let v = value.trim();
    (!v.is_empty()).then_some(v)
}

pub fn build_message_from_parts(
    config: &SmtpConfig,
    request: &SendEmailRequest,
) -> Result<Message, EmailError> {
    if request.to.is_empty() {
        return Err(EmailError::MissingRecipients);
    }
    if request.text_body.is_empty() && request.html_body.is_empty() {
        return Err(EmailError::BuildMessage(
            "email must have at least a text or HTML body".to_owned(),
        ));
    }

    let from = resolve_sender(config, request)?;
    let mut builder = Message::builder()
        .from(from)
        .subject(request.subject.clone());

    for r in &request.to {
        builder = builder.to(mailbox_from_email_address("to", r)?);
    }
    for r in &request.cc {
        builder = builder.cc(mailbox_from_email_address("cc", r)?);
    }
    for r in &request.bcc {
        builder = builder.bcc(mailbox_from_email_address("bcc", r)?);
    }
    if let Some(reply_to) = resolve_reply_to(config, request)? {
        builder = builder.reply_to(reply_to);
    }

    builder = apply_custom_headers(builder, request)?;
    builder = apply_priority_headers(builder, request.priority);

    if request.attachments.is_empty() {
        return build_body(builder, request);
    }
    let mut mixed = build_mixed_body(request);
    for (i, att) in request.attachments.iter().enumerate() {
        mixed = mixed.singlepart(build_single_attachment(i, att)?);
    }
    builder
        .multipart(mixed)
        .map_err(|e| EmailError::BuildMessage(e.to_string()))
}

fn resolve_sender(config: &SmtpConfig, request: &SendEmailRequest) -> Result<Mailbox, EmailError> {
    if let Some(from) = &request.from
        && !from.email.trim().is_empty()
    {
        if !config.allow_request_from {
            return Err(EmailError::RequestSenderDisabled);
        }
        return mailbox_from_email_address("from", from);
    }
    let email = config
        .from_email
        .as_deref()
        .filter(|v| !v.trim().is_empty())
        .ok_or(EmailError::MissingSender)?;
    mailbox_from_parts("from", email, config.from_name.as_deref())
}

fn resolve_reply_to(
    config: &SmtpConfig,
    request: &SendEmailRequest,
) -> Result<Option<Mailbox>, EmailError> {
    let email = non_empty(&request.reply_to).or(config.reply_to.as_deref());
    email
        .map(|v| mailbox_from_parts("reply_to", v, None))
        .transpose()
}