//! Outgoing mail (hub spec §5.1.1, §10): SMTP through lettre, or, for

//! development and tests, `file:///dir`, which writes each message to that

//! directory instead of sending it.

use crate::config::Email;

use crate::Shared;

pub const SETTING_SMTP: &str = "mail.smtp";

pub const SETTING_FROM: &str = "mail.from";

/// The mail settings in force: what the admin page saved (#101), else

/// hub.toml's `[email]`.

pub async fn load(db: &crate::db::Pool, from_config: &Email) -> Email {

    let mut mail = from_config.clone();

    if let Ok(Some(s)) = crate::db::accounts::setting(db, SETTING_SMTP).await {

        mail.smtp = s;

        mail.from = crate::db::accounts::setting(db, SETTING_FROM).await.ok().flatten().unwrap_or_default();

    }

    mail

}

pub fn settings(app: &Shared) -> Email {

    app.mail.read().unwrap_or_else(|p| p.into_inner()).clone()

}

/// Save the settings and use them from now on. An empty URL turns mail

/// off.

pub async fn save(app: &Shared, smtp: &str, from: &str) -> sqlx::Result<()> {

    crate::db::accounts::set_setting(&app.db, SETTING_SMTP, smtp).await?;

    crate::db::accounts::set_setting(&app.db, SETTING_FROM, from).await?;

    *app.mail.write().unwrap_or_else(|p| p.into_inner()) = Email { smtp: smtp.to_string(), from: from.to_string() };

    Ok(())

}

/// The SMTP URL with its password hidden, for the page.

pub fn masked(smtp: &str) -> String {

    let Some((scheme, rest)) = smtp.split_once("://") else { return smtp.to_string() };

    let Some((userinfo, host)) = rest.rsplit_once('@') else { return smtp.to_string() };

    match userinfo.split_once(':') {

        Some((user, _)) => format!("{scheme}://{user}:***@{host}"),

        None => smtp.to_string(),

    }

}

/// Whether the hub can send mail at all.

pub fn enabled(app: &Shared) -> bool {

    let cfg = settings(app);

    !cfg.smtp.is_empty() && !cfg.from.is_empty()

}

/// The one thing a message asks of its reader, shown as its button.

#[derive(Clone, Copy, Debug)]

pub struct Action<'a> {

    pub label: &'a str,

    pub url: &'a str,

}

/// Send a message with no button. The subject gets the site's name in

/// brackets.

pub async fn send(app: &Shared, to_name: &str, to_addr: &str, subject: &str, body: &str) -> Result<(), String> {

    send_letter(app, to_name, to_addr, subject, body, None, None).await

}

/// Send a message as plain text and as HTML in the site's look

/// (oxygenhub#182): the Oxygen mark, `action` as a button, and the site's

/// links (with `unsubscribe`, when given) in the footer. The text part is

/// `body` as written.

pub async fn send_letter(

    app: &Shared,

    to_name: &str,

    to_addr: &str,

    subject: &str,

    body: &str,

    action: Option<Action<'_>>,

    unsubscribe: Option<&str>,

) -> Result<(), String> {

    if !enabled(app) {

        return Err("this hub does not send mail".into());

    }

    let sent = deliver(app, to_name, to_addr, subject, body, action, unsubscribe).await;

    let counter = if sent.is_ok() { &crate::metrics::MAIL_SENT } else { &crate::metrics::MAIL_FAILED };

    counter.fetch_add(1, std::sync::atomic::Ordering::Relaxed);

    sent

}

async fn deliver(

    app: &Shared,

    to_name: &str,

    to_addr: &str,

    subject: &str,

    body: &str,

    action: Option<Action<'_>>,

    unsubscribe: Option<&str>,

) -> Result<(), String> {

    let cfg = settings(app);

    let site = sender_name(&cfg.from).unwrap_or_else(|| app.config.site.name.clone());

    let html = html(&site, app.config.base_url(), subject, body, action, unsubscribe);

    let subject = format!("[{site}] {subject}");

    use lettre::message::header::ContentType;

    use lettre::message::{Attachment, MultiPart, SinglePart};

    use lettre::{AsyncSmtpTransport, AsyncTransport, Message, Tokio1Executor};

    let from = cfg.from.parse().map_err(|e| format!("[email] from: {e}"))?;

    let to = format!("{to_name} <{to_addr}>").parse().or_else(|_| to_addr.parse()).map_err(|e| format!("address {to_addr}: {e}"))?;

    let png = ContentType::parse("image/png").map_err(|e| e.to_string())?;

    let message = Message::builder()

        .from(from)

        .to(to)

        .subject(subject)

        .multipart(

            MultiPart::alternative().singlepart(SinglePart::plain(body.to_string())).multipart(

                MultiPart::related()

                    .singlepart(SinglePart::html(html))

                    .singlepart(Attachment::new_inline("logo".to_string()).body(LOGO.to_vec(), png)),

            ),

        )

        .map_err(|e| e.to_string())?;

    if let Some(dir) = cfg.smtp.strip_prefix("file://") {

        let name = format!("{}-{}.eml", crate::db::now_ms(), crate::auth::random_hex(4));

        return tokio::fs::write(std::path::Path::new(dir).join(name), message.formatted())

            .await

            .map_err(|e| format!("write mail to {dir}: {e}"));

    }

    let transport = AsyncSmtpTransport::<Tokio1Executor>::from_url(&secured(&cfg.smtp)).map_err(|e| format!("[email] smtp: {e}"))?.build();

    transport.send(message).await.map(|_| ()).map_err(|e| format!("sending to {to_addr}: {e}"))

}

/// The name mail goes by: the From address's display name

/// (`OxygenHub <noreply@…>`), in the subject's tag and the footer, so a

/// site's mail can read `[OxygenHub]` while the site keeps its own name

/// (which also names its apt repository, where a change makes every

/// `apt update` ask). `None` without one.

fn sender_name(from: &str) -> Option<String> {

    let (name, _) = from.split_once('<')?;

    let name = name.trim().trim_matches('"').trim();

    (!name.is_empty()).then(|| name.to_string())

}

/// The Oxygen mark, sent inline with each message (`cid:logo`), so it

/// shows without loading anything from the web.

const LOGO: &[u8] = include_bytes!("../../../assets/icons/oxygenhub-mail.png");

fn esc(s: &str) -> String {

    s.replace('&', "&amp;").replace('<', "&lt;").replace('>', "&gt;").replace('"', "&quot;")

}

/// A paragraph's text as HTML: escaped, its web addresses linked.

fn linked(text: &str) -> String {

    let re = regex::Regex::new(r"https?://[^\s<>]+[^\s<>.,;:!?)]").expect("a valid pattern");

    let mut out = String::new();

    let mut last = 0;

    for m in re.find_iter(text) {

        out.push_str(&esc(&text[last..m.start()]));

        let u = esc(m.as_str());

        out.push_str(&format!(r#"<a href="{u}" style="color:#0969da;text-decoration:underline;word-break:break-all;">{u}</a>"#));

        last = m.end();

    }

    out.push_str(&esc(&text[last..]));

    out.replace('\n', "<br>")

}

/// The HTML part of a message (oxygenhub#182): a card on a light ground,

/// the Oxygen band with the mark and wordmark, the subject as its heading,

/// the body's paragraphs, `action` as a button with its link beneath for

/// clients that hide buttons, and a footer of the site's links. Tables

/// and inline styles, as mail clients need; dark-mode clients get their

/// own colours.

pub fn html(site: &str, base: &str, subject: &str, body: &str, action: Option<Action<'_>>, unsubscribe: Option<&str>) -> String {

    let base = base.trim_end_matches('/');

    let host = base.split("://").nth(1).unwrap_or(base);

    let button = action

        .map(|a| {

            let (label, url) = (esc(a.label), esc(a.url));

            format!(

                r#"<table role="presentation" cellpadding="0" cellspacing="0" border="0" style="margin:4px 0 12px;"><tr><td style="border-radius:8px;background-color:#0072FF;background-image:linear-gradient(90deg,#00C8F0,#0072FF);">

<a href="{url}" style="display:inline-block;padding:13px 26px;font-size:15px;font-weight:600;color:#ffffff;text-decoration:none;border-radius:8px;">{label}</a></td></tr></table>

<p style="margin:0 0 20px;font-size:12px;line-height:1.5;color:#6e7781;" class="ox-mute">Or open this link: <a href="{url}" style="color:#0969da;word-break:break-all;">{url}</a></p>"#

            )

        })

        .unwrap_or_default();

    // The action's address becomes its button, where it stood in the text;

    // the footer says how to stop.

    let mut placed = false;

    let mut paras = String::new();

    for p in body.split("\n\n").map(str::trim).filter(|p| !p.is_empty()) {

        if action.is_some_and(|a| p == a.url) {

            if !placed {

                paras.push_str(&button);

                placed = true;

            }

            continue;

        }

        if unsubscribe.is_some_and(|u| p.contains(u)) {

            continue;

        }

        paras.push_str(&format!(

            r#"<p style="margin:0 0 16px;font-size:15px;line-height:1.6;color:#1f2328;" class="ox-text">{}</p>"#,

            linked(p)

        ));

    }

    let button = if placed { String::new() } else { button };

    let stop =

        unsubscribe.map(|u| format!(r#" &middot; <a href="{}" style="color:#6e7781;">Stop these emails</a>"#, esc(u))).unwrap_or_default();

    let (site_e, subject_e, host_e) = (esc(site), esc(subject), esc(host));

    format!(

        r#"<!doctype html>

<html lang="en"><head><meta charset="utf-8"><meta name="viewport" content="width=device-width,initial-scale=1">

<meta name="color-scheme" content="light dark"><meta name="supported-color-schemes" content="light dark">

<title>{subject_e}</title>

<style>

@media (prefers-color-scheme: dark) {{

  .ox-ground {{ background-color:#0b1020 !important; }}

  .ox-card {{ background-color:#111a2e !important; border-color:#22304d !important; }}

  .ox-text, .ox-head {{ color:#e6edf3 !important; }}

  .ox-mute {{ color:#8b98ad !important; }}

}}

@media (max-width:600px) {{ .ox-pad {{ padding-left:20px !important; padding-right:20px !important; }} }}

</style></head>

<body style="margin:0;padding:0;background-color:#eef2f8;" class="ox-ground">

<div style="display:none;max-height:0;overflow:hidden;">{subject_e}</div>

<table role="presentation" width="100%" cellpadding="0" cellspacing="0" border="0" style="background-color:#eef2f8;" class="ox-ground"><tr><td align="center" style="padding:32px 12px;">

<table role="presentation" width="100%" cellpadding="0" cellspacing="0" border="0" style="max-width:720px;background-color:#ffffff;border:1px solid #dfe5ee;border-radius:14px;overflow:hidden;font-family:-apple-system,BlinkMacSystemFont,'Segoe UI',Helvetica,Arial,sans-serif;" class="ox-card">

<tr><td style="background-color:#070c18;padding:20px 32px;" class="ox-pad">

<table role="presentation" cellpadding="0" cellspacing="0" border="0"><tr>

<td style="vertical-align:middle;"><a href="{base}"><img src="cid:logo" width="40" height="40" alt="" style="display:block;border:0;border-radius:9px;"></a></td>

<td style="vertical-align:middle;padding-left:12px;font-size:20px;letter-spacing:0.2px;"><a href="{base}" style="text-decoration:none;color:#ffffff;">Oxygen<span style="color:#00F0FF;font-weight:700;">Hub</span></a></td>

</tr></table></td></tr>

<tr><td style="height:4px;line-height:4px;font-size:0;background-color:#0072FF;background-image:linear-gradient(90deg,#00F0FF,#0072FF);">&nbsp;</td></tr>

<tr><td style="padding:32px 32px 12px;" class="ox-pad">

<h1 style="margin:0 0 18px;font-size:21px;line-height:1.3;font-weight:650;color:#0b1220;" class="ox-head">{subject_e}</h1>

{paras}{button}

</td></tr>

<tr><td style="padding:18px 32px 26px;border-top:1px solid #e6ebf2;" class="ox-pad">

<p style="margin:0 0 6px;font-size:12px;line-height:1.6;color:#6e7781;" class="ox-mute"><a href="{base}" style="color:#6e7781;">{site_e}</a> &middot; <a href="{base}/explore" style="color:#6e7781;">Explore</a> &middot; <a href="{base}/help" style="color:#6e7781;">Help</a> &middot; <a href="{base}/settings/notifications" style="color:#6e7781;">Notification settings</a>{stop}</p>

<p style="margin:0;font-size:12px;line-height:1.6;color:#8b949e;" class="ox-mute">Sent by {site_e} at {host_e}, where your work is signed and yours.</p>

</td></tr>

</table></td></tr></table>

</body></html>

"#

    )

}

#[cfg(test)]

mod html_tests {

    use super::*;

    #[test]

    fn a_message_is_a_card_with_its_button_and_the_site_s_links() {

        let body =

            "Confirm that [email protected] is yours:\n\nhttps://hub.example/verify/abc\n\nThe link works for 48 hours. <b>Not</b> HTML.";

        let h = html(

            "OxygenHub",

            "https://hub.example/",

            "Confirm your email address",

            body,

            Some(Action { label: "Confirm my email address", url: "https://hub.example/verify/abc" }),

            Some("https://hub.example/settings/notifications?unsubscribe=k"),

        );

        assert!(h.contains(r#"<img src="cid:logo""#), "the mark, inline");

        assert!(h.contains(">Confirm my email address</a>") && h.contains(r#"href="https://hub.example/verify/abc""#));

        assert_eq!(

            h.matches("https://hub.example/verify/abc</a>").count(),

            1,

            "the address once, under the button, not as a paragraph too"

        );

        assert!(h.contains("<b>Not</b> HTML."), "the body is escaped");

        assert!(h.contains(r#"href="https://hub.example/explore""#) && h.contains("Stop these emails"));

        assert!(h.contains("at hub.example,"));

    }

}

/// An SMTP URL as it is sent with: `smtp://` that says nothing of TLS

/// requires STARTTLS, so a password never crosses in the clear (lettre's

/// own default is none), except to a relay on this machine. `smtps://`

/// (TLS from the start, port 465) and an explicit `?tls=` stay as written.

pub fn secured(url: &str) -> String {

    let Some(rest) = url.strip_prefix("smtp://") else { return url.to_string() };

    if url.contains("tls=") {

        return url.to_string();

    }

    let host = rest.rsplit('@').next().unwrap_or(rest);

    let host = host.split(['/', '?']).next().unwrap_or(host);

    let host = host.rsplit_once(':').map_or(host, |(h, _)| h).trim_matches(['[', ']']);

    if matches!(host, "localhost" | "127.0.0.1" | "::1") {

        return url.to_string();

    }

    format!("{url}{}tls=required", if url.contains('?') { "&" } else { "?" })

}

#[cfg(test)]

mod secured_tests {

    use super::secured;

    #[test]

    fn smtp_urls_require_starttls_unless_they_say_otherwise() {

        assert_eq!(secured("smtp://resend:[email protected]:587"), "smtp://resend:[email protected]:587?tls=required");

        assert_eq!(secured("smtps://resend:[email protected]:465"), "smtps://resend:[email protected]:465");

        assert_eq!(secured("smtp://relay.example:25?tls=opportunistic"), "smtp://relay.example:25?tls=opportunistic");

        assert_eq!(secured("smtp://localhost:25"), "smtp://localhost:25", "a relay on this machine");

        assert_eq!(secured("smtp://u:[email protected]:1025"), "smtp://u:[email protected]:1025");

        assert_eq!(secured("file:///tmp/mail"), "file:///tmp/mail");

    }

}

/// The services the Mail panel knows (oxygenhub#181): each is SMTP

/// underneath, so the hub stores and sends one standard SMTP URL; the

/// panel only fills in the server and the login a service expects.

pub const SERVICES: &[(&str, &str)] = &[

    ("off", "Off"),

    ("resend", "Resend"),

    ("ses", "Amazon SES"),

    ("mailgun", "Mailgun"),

    ("smtp", "Another SMTP server"),

    ("url", "An SMTP URL (advanced)"),

];

/// A stored SMTP URL read back for the panel: which service, and its parts

/// but the secret.

#[derive(Clone, Debug, Default, PartialEq, Eq)]

pub struct Choice {

    pub service: String,

    /// SES's AWS region, or Mailgun's `us` or `eu`.

    pub region: String,

    pub user: String,

    pub host: String,

    pub port: String,

    /// `tls` (from the start), `starttls` or `none`.

    pub security: String,

    /// Whether a password or key is saved.

    pub has_secret: bool,

}

/// Percent-encoding for a URL's user and password: all but unreserved

/// characters (lettre decodes them).

fn enc(s: &str) -> String {

    s.bytes()

        .map(|b| match b {

            b'A'..=b'Z' | b'a'..=b'z' | b'0'..=b'9' | b'-' | b'_' | b'.' | b'~' => (b as char).to_string(),

            _ => format!("%{b:02X}"),

        })

        .collect()

}

fn dec(s: &str) -> String {

    let b = s.as_bytes();

    let mut out = Vec::new();

    let mut i = 0;

    while i < b.len() {

        if b[i] == b'%' && i + 2 < b.len() {

            if let Ok(v) = u8::from_str_radix(&s[i + 1..i + 3], 16) {

                out.push(v);

                i += 3;

                continue;

            }

        }

        out.push(b[i]);

        i += 1;

    }

    String::from_utf8_lossy(&out).into_owned()

}

/// The parts of an SMTP URL: scheme, user, password (as stored, encoded),

/// host, port, query.

fn parts(url: &str) -> Option<(&str, &str, &str, &str, &str, &str)> {

    let (scheme, rest) = url.split_once("://")?;

    let (rest, query) = rest.split_once('?').unwrap_or((rest, ""));

    let (userinfo, hostport) = rest.rsplit_once('@').unwrap_or(("", rest));

    let (user, pass) = userinfo.split_once(':').unwrap_or((userinfo, ""));

    let hostport = hostport.trim_end_matches('/');

    let (host, port) = hostport.rsplit_once(':').unwrap_or((hostport, ""));

    Some((scheme, user, pass, host, port, query))

}

/// How the panel shows a stored SMTP URL.

pub fn describe(url: &str) -> Choice {

    if url.is_empty() {

        return Choice { service: "off".into(), ..Default::default() };

    }

    let Some((scheme, user, pass, host, port, query)) = parts(url).filter(|p| p.0 == "smtp" || p.0 == "smtps") else {

        return Choice { service: "url".into(), ..Default::default() };

    };

    let mut c = Choice {

        user: dec(user),

        host: host.to_string(),

        port: port.to_string(),

        has_secret: !pass.is_empty(),

        security: if scheme == "smtps" {

            "tls".into()

        } else if query.contains("tls=none") {

            "none".into()

        } else {

            "starttls".into()

        },

        ..Default::default()

    };

    c.service = if host == "smtp.resend.com" {

        "resend".into()

    } else if let Some(region) = host.strip_prefix("email-smtp.").and_then(|h| h.strip_suffix(".amazonaws.com")) {

        c.region = region.to_string();

        "ses".into()

    } else if host == "smtp.mailgun.org" || host == "smtp.eu.mailgun.org" {

        c.region = if host.contains(".eu.") { "eu".into() } else { "us".into() };

        "mailgun".into()

    } else if query.contains("tls=opportunistic") {

        "url".into()

    } else {

        "smtp".into()

    };

    c

}

/// What the panel asks for a service.

#[derive(Clone, Debug, Default)]

pub struct Asked {

    pub service: String,

    pub region: String,

    pub user: String,

    /// A new password or key; empty keeps the saved one where it still

    /// fits (the same service, server and user).

    pub secret: String,

    pub host: String,

    pub port: String,

    pub security: String,

}

/// The SMTP URL for what the panel asked, given the URL saved now; or what

/// is missing, said plainly.

pub fn compose(a: &Asked, current: &str) -> Result<String, String> {

    let region = a.region.trim();

    let (scheme, user, host, port, query): (&str, String, String, String, &str) = match a.service.as_str() {

        "resend" => ("smtps", "resend".into(), "smtp.resend.com".into(), "465".into(), ""),

        "ses" => {

            if region.is_empty() || !region.chars().all(|c| c.is_ascii_lowercase() || c.is_ascii_digit() || c == '-') {

                return Err("Give the SES region, such as eu-west-2.".into());

            }

            if a.user.trim().is_empty() {

                return Err("Give the SES SMTP user name (from SES › SMTP settings; not your AWS access key).".into());

            }

            ("smtps", a.user.trim().to_string(), format!("email-smtp.{region}.amazonaws.com"), "465".into(), "")

        }

        "mailgun" => {

            let host = match region {

                "eu" => "smtp.eu.mailgun.org",

                "us" | "" => "smtp.mailgun.org",

                _ => return Err("Mailgun's region is us or eu.".into()),

            };

            if a.user.trim().is_empty() {

                return Err("Give the Mailgun SMTP login, such as [email protected].".into());

            }

            ("smtps", a.user.trim().to_string(), host.into(), "465".into(), "")

        }

        "smtp" => {

            let host = a.host.trim();

            if host.is_empty() || host.contains(['/', '@', ' ']) {

                return Err("Give the SMTP server's host name.".into());

            }

            let port = a.port.trim();

            if !port.is_empty() && port.parse::<u16>().is_err() {

                return Err("The port is a number, such as 465 or 587.".into());

            }

            match a.security.as_str() {

                "tls" => ("smtps", a.user.trim().to_string(), host.into(), if port.is_empty() { "465".into() } else { port.into() }, ""),

                "none" => {

                    ("smtp", a.user.trim().to_string(), host.into(), if port.is_empty() { "25".into() } else { port.into() }, "tls=none")