// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this
// file, You can obtain one at https://mozilla.org/MPL/2.0/.

//! Message templates. A plain-text primary and a minimal HTML alternative are
//! rendered from the same data, with the instance name and URL interpolated.

/// Why an invite was sent.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum Purpose {
    /// A new-account activation link.
    Activate,
    /// A password-reset link.
    Reset,
    /// An email-address verification link.
    VerifyEmail,
}

impl Purpose {
    /// The `invites.purpose` token.
    #[must_use]
    pub fn as_str(self) -> &'static str {
        match self {
            Self::Activate => "activate",
            Self::Reset => "reset",
            Self::VerifyEmail => "verify-email",
        }
    }
}

/// A rendered message: subject plus the two body alternatives.
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct Rendered {
    /// The `Subject:` header.
    pub subject: String,
    /// The plain-text body (primary).
    pub plain: String,
    /// The HTML body (alternative).
    pub html: String,
}

/// Render the invite message for `purpose`, interpolating the instance name/URL
/// and the activation `link`.
#[must_use]
pub fn render(instance_name: &str, link: &str, purpose: Purpose) -> Rendered {
    let (subject, lead, action) = match purpose {
        Purpose::Activate => (
            format!("Activate your {instance_name} account"),
            format!("An account has been created for you on {instance_name}."),
            "set your password and activate your account",
        ),
        Purpose::Reset => (
            format!("Reset your {instance_name} password"),
            format!("A password reset was requested for your {instance_name} account."),
            "choose a new password",
        ),
        Purpose::VerifyEmail => (
            format!("Verify your email for {instance_name}"),
            format!("Confirm this email address to use it on {instance_name}."),
            "verify this email address",
        ),
    };

    let plain = format!(
        "{lead}\n\nOpen this link to {action}:\n\n    {link}\n\n\
         If you did not expect this email, you can safely ignore it.\n"
    );
    let html = format!(
        "<p>{}</p>\n<p>Open this link to {}:</p>\n<p><a href=\"{}\">{}</a></p>\n\
         <p>If you did not expect this email, you can safely ignore it.</p>\n",
        escape(&lead),
        escape(action),
        escape(link),
        escape(link),
    );

    Rendered {
        subject,
        plain,
        html,
    }
}

/// Minimal HTML escaping for the interpolated values.
fn escape(s: &str) -> String {
    s.replace('&', "&amp;")
        .replace('<', "&lt;")
        .replace('>', "&gt;")
        .replace('"', "&quot;")
}

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

    #[test]
    fn activate_body_contains_link_and_name() {
        let r = render(
            "Forge",
            "https://git.example.com/invite/abc123",
            Purpose::Activate,
        );
        assert!(r.subject.contains("Forge"));
        assert!(r.plain.contains("https://git.example.com/invite/abc123"));
        assert!(
            r.html
                .contains("href=\"https://git.example.com/invite/abc123\"")
        );
        assert!(r.plain.contains("activate your account"));
    }

    #[test]
    fn reset_uses_reset_wording() {
        let r = render("Forge", "https://x/invite/t", Purpose::Reset);
        assert!(r.subject.to_lowercase().contains("reset"));
        assert!(r.plain.contains("new password"));
    }

    #[test]
    fn html_escapes_interpolated_values() {
        let r = render("A&B", "https://x/?a=1&b=2", Purpose::Activate);
        assert!(r.html.contains("&amp;"));
        assert!(!r.html.contains("a=1&b=2"), "raw ampersand must be escaped");
    }
}