//! Explicit per-vhost response protection. HSTS is never emitted on plaintext.
use anyhow::{ensure, Result};
use http::{HeaderMap, HeaderValue};
use serde::{Deserialize, Serialize};

#[derive(Debug, Clone, Default, Serialize, Deserialize)]
#[serde(default, deny_unknown_fields)]
pub struct SecurityHeaders {
    pub hsts: Hsts,
    pub nosniff: bool,
    pub frame_options: FrameOptions,
    pub referrer_policy: Option<String>,
    pub content_security_policy: Option<String>,
    pub permissions_policy: Option<String>,
}
#[derive(Debug, Clone, Serialize, Deserialize)]
#[serde(default, deny_unknown_fields)]
pub struct Hsts {
    pub enabled: bool,
    pub max_age_seconds: u64,
    pub include_subdomains: bool,
    pub preload: bool,
}
impl Default for Hsts {
    fn default() -> Self {
        Self {
            enabled: false,
            max_age_seconds: 31_536_000,
            include_subdomains: false,
            preload: false,
        }
    }
}
#[derive(Debug, Clone, Copy, Default, Serialize, Deserialize)]
#[serde(rename_all = "snake_case")]
pub enum FrameOptions {
    #[default]
    Preserve,
    Deny,
    Sameorigin,
}
#[derive(Debug, Clone, Default)]
pub struct CompiledSecurity {
    hsts: Option<HeaderValue>,
    headers: Vec<(&'static str, HeaderValue)>,
}
impl SecurityHeaders {
    pub fn compile(&self) -> Result<CompiledSecurity> {
        ensure!(
            self.hsts.max_age_seconds <= 63_072_000,
            "HSTS max_age_seconds must be 0..63072000"
        );
        ensure!(
            !self.hsts.preload
                || (self.hsts.enabled
                    && self.hsts.include_subdomains
                    && self.hsts.max_age_seconds >= 31_536_000),
            "HSTS preload requires enabled, include_subdomains and at least one year"
        );
        let mut result = CompiledSecurity::default();
        if self.hsts.enabled {
            let mut value = format!("max-age={}", self.hsts.max_age_seconds);
            if self.hsts.include_subdomains {
                value.push_str("; includeSubDomains");
            }
            if self.hsts.preload {
                value.push_str("; preload");
            }
            result.hsts = Some(value.parse()?);
        }
        if self.nosniff {
            result.headers.push((
                "x-content-type-options",
                HeaderValue::from_static("nosniff"),
            ));
        }
        let frame = match self.frame_options {
            FrameOptions::Preserve => None,
            FrameOptions::Deny => Some("DENY"),
            FrameOptions::Sameorigin => Some("SAMEORIGIN"),
        };
        if let Some(value) = frame {
            result
                .headers
                .push(("x-frame-options", HeaderValue::from_static(value)));
        }
        for (name, value) in [
            ("referrer-policy", &self.referrer_policy),
            ("content-security-policy", &self.content_security_policy),
            ("permissions-policy", &self.permissions_policy),
        ] {
            if let Some(value) = value {
                ensure!(
                    !value.is_empty() && value.len() <= 8192,
                    "security header must contain 1..8192 bytes"
                );
                result.headers.push((name, value.parse()?));
            }
        }
        Ok(result)
    }
}
impl CompiledSecurity {
    pub fn apply(&self, headers: &mut HeaderMap, tls: bool) {
        for (name, value) in &self.headers {
            headers.insert(*name, value.clone());
        }
        if !tls {
            headers.remove("strict-transport-security");
        } else if let Some(value) = &self.hsts {
            headers.insert("strict-transport-security", value.clone());
        }
    }
}
#[cfg(test)]
mod tests {
    use super::*;
    #[test]
    fn hsts_is_tls_only_and_preload_is_explicit() {
        let mut s = SecurityHeaders::default();
        s.hsts.enabled = true;
        let c = s.compile().unwrap();
        let mut h = HeaderMap::new();
        c.apply(&mut h, true);
        assert_eq!(h["strict-transport-security"], "max-age=31536000");
        c.apply(&mut h, false);
        assert!(!h.contains_key("strict-transport-security"));
        s.hsts.preload = true;
        assert!(s.compile().is_err());
        s.hsts.include_subdomains = true;
        assert!(s.compile().is_ok());
        s.hsts.max_age_seconds = 0;
        assert!(s.compile().is_err());
        s.hsts.preload = false;
        assert!(s.compile().is_ok());
    }
    #[test]
    fn rejects_response_splitting() {
        let s = SecurityHeaders {
            content_security_policy: Some("x\r\ninjected: yes".into()),
            ..Default::default()
        };
        assert!(s.compile().is_err());
    }
}