// Copyright (C) 2026 Doan Luu Duc Tai <doan@luuduct.ai>
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU Affero General Public License as
// published by the Free Software Foundation, either version 3 of the
// License, or (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU Affero General Public License for more details.
//
// You should have received a copy of the GNU Affero General Public License
// along with this program.  If not, see <https://www.gnu.org/licenses/>.

#![doc = "Validated root environment configuration and public-only template rendering."]

use anyhow::{Context, Result, ensure};
use std::collections::BTreeMap;
use std::fmt;
use std::fs;
use std::io::Write;
use std::net::SocketAddr;
use std::os::unix::fs::PermissionsExt;
use std::path::{Component, Path};

const EXAMPLE: &str = include_str!("../../../.env.example");
const HOSTS: &[&str] = &[
    "BASE_DOMAIN",
    "SITE_HOST",
    "GIT_HOST",
    "SEARCH_HOST",
    "WKD_HOST",
    "CHAT_HOST",
    "CHAT_LOCAL_HOST",
];
const PUBLIC: &[&str] = &[
    "BASE_DOMAIN",
    "SITE_HOST",
    "GIT_HOST",
    "SEARCH_HOST",
    "WKD_HOST",
    "CHAT_HOST",
    "CHAT_LOCAL_HOST",
    "WEB_BIND",
    "CHAT_UPSTREAM",
    "HTTP_PORT",
    "HTTPS_PORT",
    "LOCAL_HTTP_PORT",
    "CGIT_UPSTREAM",
    "SEARXNG_UPSTREAM",
    "CHAT_BIND",
    "CHAT_ORIGIN",
    "BACKUP_RECIPIENT",
    "BACKUP_PUBLIC_KEY",
];

#[doc = "One installation's configuration; formatting deliberately excludes all values."]
pub struct Config {
    values: BTreeMap<String, String>,
    explicit: BTreeMap<String, String>,
}

impl fmt::Debug for Config {
    fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
        formatter.debug_struct("Config").finish_non_exhaustive()
    }
}

fn defaults() -> Result<BTreeMap<String, String>> {
    Ok(dotenvy::from_read_iter(EXAMPLE.as_bytes()).collect::<std::result::Result<_, _>>()?)
}

fn hostname(value: &str) -> bool {
    value.len() <= 253
        && value.split('.').all(|label| {
            !label.is_empty()
                && label.len() <= 63
                && !label.starts_with('-')
                && !label.ends_with('-')
                && label
                    .bytes()
                    .all(|byte| byte.is_ascii_alphanumeric() || byte == b'-')
        })
}

fn endpoint(value: &str) -> bool {
    if value.parse::<SocketAddr>().is_ok() {
        return true;
    }
    value.rsplit_once(':').is_some_and(|(host, port)| {
        hostname(host) && port.parse::<u16>().is_ok_and(|number| number > 0)
    })
}

impl Config {
    #[doc = "Loads the single root .env over public defaults from the published example."]
    #[doc = "# Errors"]
    #[doc = "Rejects malformed files and invalid public deployment values without printing secrets."]
    pub fn load(root: &Path) -> Result<Self> {
        let path = root.join(".env");
        let explicit: BTreeMap<String, String> = if path.exists() {
            dotenvy::from_path_iter(path)
                .context("Cannot parse root .env")?
                .collect::<std::result::Result<_, _>>()
                .map_err(|_| anyhow::anyhow!("Cannot parse root .env"))?
        } else {
            BTreeMap::new()
        };
        Self::from_values(explicit)
    }

    #[doc = "Loads only declared public settings and the chat token from a container environment."]
    #[doc = "# Errors"]
    #[doc = "Rejects invalid configuration without importing unrelated host secrets."]
    pub fn from_environment() -> Result<Self> {
        let mut explicit = BTreeMap::new();
        for key in PUBLIC
            .iter()
            .copied()
            .chain(std::iter::once("CHAT_SETUP_TOKEN"))
        {
            if let Some(value) = std::env::var_os(key) {
                explicit.insert(
                    key.to_owned(),
                    value
                        .into_string()
                        .map_err(|_| anyhow::anyhow!("Invalid {key} environment value"))?,
                );
            }
        }
        Self::from_values(explicit)
    }

    fn from_values(explicit: BTreeMap<String, String>) -> Result<Self> {
        let mut values = defaults()?;
        values.retain(|key, _| PUBLIC.contains(&key.as_str()));
        values.extend(explicit.clone());
        let config = Self { values, explicit };
        config.validate()?;
        Ok(config)
    }

    #[doc = "Returns a configured value; callers must not log private values."]
    #[doc = "# Errors"]
    #[doc = "Returns only the missing key name when a value is unavailable."]
    pub fn value(&self, key: &str) -> Result<&str> {
        self.values
            .get(key)
            .map(String::as_str)
            .with_context(|| format!("Missing {key} in root .env"))
    }

    #[doc = "Returns whether a setting is present in the installation file rather than defaults."]
    #[must_use]
    pub fn is_explicit(&self, key: &str) -> bool {
        self.explicit.contains_key(key)
    }

    #[doc = "Reads a nonzero TCP/UDP port."]
    #[doc = "# Errors"]
    #[doc = "Rejects invalid ports without displaying their raw values."]
    pub fn port(&self, key: &str) -> Result<u16> {
        let port = self
            .value(key)?
            .parse::<u16>()
            .with_context(|| format!("Invalid {key} in root .env"))?;
        ensure!(port > 0, "Invalid {key} in root .env");
        Ok(port)
    }

    #[doc = "Reads the configured local chat socket address."]
    #[doc = "# Errors"]
    #[doc = "Rejects malformed socket addresses."]
    pub fn chat_bind(&self) -> Result<SocketAddr> {
        self.value("CHAT_BIND")?
            .parse()
            .context("Invalid CHAT_BIND in root .env")
    }

    fn validate(&self) -> Result<()> {
        for key in HOSTS {
            ensure!(hostname(self.value(key)?), "Invalid {key} in root .env");
        }
        ensure!(
            self.port("HTTP_PORT")? != self.port("HTTPS_PORT")?,
            "HTTP_PORT and HTTPS_PORT must differ"
        );
        ensure!(
            (1024..=65_534).contains(&self.port("LOCAL_HTTP_PORT")?),
            "LOCAL_HTTP_PORT must be between 1024 and 65534"
        );
        for key in ["CGIT_UPSTREAM", "SEARXNG_UPSTREAM", "CHAT_UPSTREAM"] {
            ensure!(endpoint(self.value(key)?), "Invalid {key} in root .env");
        }
        self.value("WEB_BIND")?
            .parse::<std::net::IpAddr>()
            .context("Invalid WEB_BIND")?;
        ensure!(
            self.value("CHAT_LOCAL_HOST")?.ends_with(".localhost"),
            "CHAT_LOCAL_HOST must be a dedicated .localhost name"
        );
        self.chat_bind()?;
        let origin = self.value("CHAT_ORIGIN")?;
        ensure!(
            origin.len() <= 256
                && (origin.starts_with("http://") || origin.starts_with("https://"))
                && origin
                    .bytes()
                    .all(|byte| byte.is_ascii_alphanumeric() || b":/.-[]".contains(&byte)),
            "Invalid CHAT_ORIGIN in root .env"
        );
        let recipient = self.value("BACKUP_RECIPIENT")?;
        ensure!(
            [40, 64].contains(&recipient.len())
                && recipient.bytes().all(|byte| byte.is_ascii_hexdigit()),
            "Invalid BACKUP_RECIPIENT in root .env"
        );
        let key = Path::new(self.value("BACKUP_PUBLIC_KEY")?);
        ensure!(
            !key.as_os_str().is_empty()
                && self
                    .value("BACKUP_PUBLIC_KEY")?
                    .bytes()
                    .all(|byte| byte.is_ascii_alphanumeric() || b"/._-".contains(&byte))
                && key
                    .components()
                    .all(|part| matches!(part, Component::Normal(_))),
            "BACKUP_PUBLIC_KEY must be project-relative"
        );
        Ok(())
    }

    #[doc = "Builds the explicit public-only template map for production or a local HTTP port."]
    #[doc = "# Errors"]
    #[doc = "Rejects invalid configuration or port arithmetic overflow."]
    pub fn public_values(&self, local: Option<u16>) -> Result<BTreeMap<String, String>> {
        let mut values = PUBLIC
            .iter()
            .map(|key| Ok(((*key).to_owned(), self.value(key)?.to_owned())))
            .collect::<Result<BTreeMap<_, _>>>()?;
        let https = self.port("HTTPS_PORT")?;
        let suffix = if https == 443 {
            String::new()
        } else {
            format!(":{https}")
        };
        for (name, key) in [
            ("SITE_ORIGIN", "SITE_HOST"),
            ("GIT_ORIGIN", "GIT_HOST"),
            ("SEARCH_ORIGIN", "SEARCH_HOST"),
            ("WKD_ORIGIN", "WKD_HOST"),
            ("CHAT_PUBLIC_ORIGIN", "CHAT_HOST"),
        ] {
            values.insert(name.into(), format!("https://{}{suffix}", self.value(key)?));
        }
        if let Some(port) = local {
            values.insert("SITE_ORIGIN".into(), format!("http://localhost:{port}"));
            values.insert("GIT_ORIGIN".into(), "/git".into());
            values.insert("SEARCH_ORIGIN".into(), "/search".into());
            values.insert("WKD_ORIGIN".into(), String::new());
            values.insert("LOCAL_HTTP_PORT".into(), port.to_string());
            values.insert(
                "CHAT_PUBLIC_ORIGIN".into(),
                format!("http://{}:{port}", self.value("CHAT_LOCAL_HOST")?),
            );
        }
        Ok(values)
    }

    #[doc = "Renders only whitelisted public variables; private or unknown placeholders fail closed."]
    #[doc = "# Errors"]
    #[doc = "Rejects unknown placeholders without substituting private configuration."]
    pub fn render(&self, source: &str, local: Option<u16>) -> Result<String> {
        render(source, &self.public_values(local)?)
    }
}

#[doc = "Substitutes a previously filtered public configuration map into a source template."]
#[doc = "# Errors"]
#[doc = "Rejects remaining unknown placeholders."]
pub fn render(source: &str, public: &BTreeMap<String, String>) -> Result<String> {
    let mut result = source.to_owned();
    for (key, value) in public {
        result = result.replace(&format!("{{{{{key}}}}}"), value);
    }
    ensure!(
        !result.contains("{{"),
        "Unknown or private configuration placeholder"
    );
    Ok(result)
}

#[doc = "Appends missing public settings to the same root .env, preserving existing values."]
#[doc = "# Errors"]
#[doc = "Returns a filesystem/configuration error without printing environment contents."]
pub fn initialize_public(root: &Path) -> Result<()> {
    let path = root.join(".env");
    let existing = if path.exists() {
        fs::read_to_string(&path)?
    } else {
        String::new()
    };
    let config = Config::load(root)?;
    let mut appended = String::new();
    for (key, value) in defaults()? {
        if PUBLIC.contains(&key.as_str()) && !config.is_explicit(&key) {
            use std::fmt::Write as _;
            writeln!(appended, "{key}={value}")?;
        }
    }
    if path.exists() {
        fs::set_permissions(&path, fs::Permissions::from_mode(0o600))?;
    }
    if appended.is_empty() {
        return Ok(());
    }
    let mut file = tempfile::NamedTempFile::new_in(root)?;
    file.as_file()
        .set_permissions(fs::Permissions::from_mode(0o600))?;
    write!(file, "{existing}\n{appended}")?;
    file.as_file().sync_all()?;
    file.persist(path).map_err(|error| error.error)?;
    Ok(())
}

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

    #[test]
    fn public_rendering_rejects_secrets_and_host_injection() -> Result<()> {
        let root = tempfile::tempdir()?;
        fs::write(
            root.path().join(".env"),
            "CHAT_SETUP_TOKEN=\"private-malformed-sentinel\n",
        )?;
        let error = Config::load(root.path())
            .err()
            .context("Malformed secret must fail")?;
        assert!(!format!("{error:#}").contains("private-malformed-sentinel"));
        fs::write(
            root.path().join(".env"),
            "SITE_HOST=home.example.net\nGIT_HOST=source.example.net\nHTTPS_PORT=8443\nLOCAL_HTTP_PORT=8180\nCHAT_SETUP_TOKEN=private-token-sentinel\nSEARXNG_SECRET=private-search-sentinel\n",
        )?;
        let config = Config::load(root.path())?;
        assert_eq!(
            config.render("{{SITE_ORIGIN}} {{GIT_ORIGIN}}", None)?,
            "https://home.example.net:8443 https://source.example.net:8443"
        );
        assert_eq!(
            config.render("{{SITE_ORIGIN}} {{GIT_ORIGIN}}", Some(8180))?,
            "http://localhost:8180 /git"
        );
        assert!(config.render("{{CHAT_SETUP_TOKEN}}", None).is_err());
        assert!(!format!("{config:?}").contains("private-token"));
        initialize_public(root.path())?;
        assert_eq!(
            Config::load(root.path())?.value("SITE_HOST")?,
            "home.example.net"
        );
        assert_eq!(
            Config::load(root.path())?.value("CHAT_SETUP_TOKEN")?,
            "private-token-sentinel"
        );
        fs::write(
            root.path().join(".env"),
            "SITE_HOST=\"valid.example { respond bad }\"\n",
        )?;
        assert!(Config::load(root.path()).is_err());
        Ok(())
    }
}