//! One instance's rust-link sidecar: its config, and asking the installed binary about it.
//!
//! **The installer writes each instance's `sidecar.toml` itself, once.** ServUO's sidecar is one per
//! host and its defaults are right as shipped; a Rust host runs several, and every one of them needs
//! its own game port, web port and database, which no default can give it. So the first run writes
//! the file with those three decided and the token blank, and `--print-config` then generates the
//! token and saves it into that same file — the sidecar still owns the secret, exactly as for ServUO.
//! An existing file is never rewritten: after the first run it is the operator's, and the ports it
//! names are the ones recorded.
//!
//! The same rule as `crate::sidecar` holds for the token: it crosses one process boundary, here,
//! and goes to the terminal and nowhere else.

use std::path::Path;

use anyhow::{bail, Context, Result};
use serde::Deserialize;

/// What `rust-link-sidecar --print-config` prints (Rust-Link `sidecar/src/config.rs::describe`).
#[derive(Debug, Clone, Deserialize)]
pub struct ConfigDoc {
    pub component: String,
    pub version: String,
    pub protocol: u32,
    pub config_path: String,
    pub token_generated: bool,
    pub game: GameDoc,
    pub web: WebDoc,
    pub store: StoreDoc,
}

#[derive(Debug, Clone, Deserialize)]
pub struct GameDoc {
    pub bind: String,
    #[serde(default)]
    pub server_id: String,
}

#[derive(Debug, Clone, Deserialize)]
pub struct WebDoc {
    pub bind: String,
    /// **A secret.** Printed in the handoff and recorded nowhere.
    pub auth_token: String,
}

#[derive(Debug, Clone, Deserialize)]
pub struct StoreDoc {
    pub path: String,
}

/// The first `sidecar.toml` for an instance. Pure, so its content is a test.
///
/// Paths are TOML **literal** strings (single quotes): a Windows path is all backslashes, and a basic
/// string would read each one as an escape. A literal string cannot hold a single quote, and neither
/// a server id nor any path this installer builds contains one.
pub fn instance_config(server_id: &str, game_port: u16, web_port: u16, db: &Path) -> String {
    format!(
        "# rust-link sidecar for Rust server {server_id:?}.\n\
         #\n\
         # Written once by the Runic Gateway installer, which decided the ports and the database\n\
         # below; it is never rewritten, so it is yours to edit from here. The token is generated\n\
         # by the sidecar on first start and saved into this file.\n\
         \n\
         [game]\n\
         # Where the plugin dials in. Loopback: there is no token on this link.\n\
         bind = '127.0.0.1:{game_port}'\n\
         # Cross-checked against the serverId the plugin announces.\n\
         server_id = '{server_id}'\n\
         \n\
         [web]\n\
         # Where the website reaches this sidecar. Put a TLS proxy in front to reach it from\n\
         # another machine (docs/rust-link/INSTALL.md).\n\
         bind = '127.0.0.1:{web_port}'\n\
         auth_token = \"\"\n\
         \n\
         [store]\n\
         path = '{db}'\n",
        db = db.display(),
    )
}

/// Runs the installed binary's `--print-config` against one instance's config, provisioning the
/// token on first use. **Must not print or attach the child's stdout** — it holds the token.
pub fn print_config(binary: &Path, config: &Path) -> Result<ConfigDoc> {
    let output = std::process::Command::new(binary)
        .arg("--print-config")
        .arg("--config")
        .arg(config)
        // An operator's shell may export RUSTLINK_* while testing; an installed instance is
        // described by its file alone, so none of them may leak into this read.
        .env_remove("RUSTLINK_CONFIG")
        .env_remove("RUSTLINK_GAME_BIND")
        .env_remove("RUSTLINK_WEB_BIND")
        .env_remove("RUSTLINK_WEB_TOKEN")
        .env_remove("RUSTLINK_DB_PATH")
        .env_remove("RUSTLINK_SERVER_ID")
        .output()
        .with_context(|| {
            format!(
                "cannot run {} --print-config — the binary cannot execute here",
                binary.display()
            )
        })?;
    if !output.status.success() {
        let reason = String::from_utf8_lossy(&output.stderr)
            .lines()
            .map(str::trim)
            .find(|l| !l.is_empty())
            .unwrap_or("(nothing on stderr)")
            .to_string();
        bail!(
            "{} --print-config --config {} failed: {reason}",
            binary.display(),
            config.display()
        );
    }
    let doc: ConfigDoc = serde_json::from_slice(&output.stdout).context(
        "the rust-link sidecar's --print-config output is not the document this installer \
         expects. It is not shown here because it contains the auth token.",
    )?;
    if doc.component != "rust-link-sidecar" {
        bail!(
            "the binary at {} identifies itself as {:?}, not rust-link-sidecar",
            binary.display(),
            doc.component
        );
    }
    if doc.web.auth_token.trim().is_empty() {
        bail!(
            "the sidecar reported an empty auth token from {}; refusing to continue",
            doc.config_path
        );
    }
    Ok(doc)
}

/// The port half of a bind.
pub fn port_of(bind: &str) -> Option<u16> {
    bind.rsplit_once(':').and_then(|(_, p)| p.parse().ok())
}

/// The lowest port from `start` that no recorded instance holds and nothing on this host is bound
/// to. `keep`, when given, is the port this instance already has, which is always kept.
pub fn choose_port(start: u16, held: &[u16], keep: Option<u16>) -> Result<u16> {
    if let Some(port) = keep {
        return Ok(port);
    }
    (start..=u16::MAX)
        .take(1000)
        .find(|p| !held.contains(p) && std::net::TcpListener::bind(("127.0.0.1", *p)).is_ok())
        .ok_or_else(|| anyhow::anyhow!("no free port found in the 1000 from {start}"))
}

/// The end-of-run block for one instance: what `/admin/rust/servers` asks for.
///
/// It says what the run did, not what it hopes: nothing here has seen the plugin connect — on a
/// stopped server it has not even loaded — so the first line never claims a link. `doctor` is the
/// command that checks one (D156).
pub fn handoff(
    server_id: &str,
    doc: &ConfigDoc,
    host: &str,
    site_url: Option<&str>,
    registered: bool,
    running: bool,
) -> String {
    let port = port_of(&doc.web.bind)
        .map(|p| p.to_string())
        .unwrap_or_else(|| doc.web.bind.clone());
    let site = site_url
        .map(|s| s.trim_end_matches('/').to_string())
        .unwrap_or_else(|| "https://<your-site>".to_string());
    let loopback = doc.web.bind.starts_with("127.") || doc.web.bind.starts_with("[::1]");
    format!(
        "\nRust server {server_id:?} is set up. {when}\n\n\
         One manual step remains — add it to the website:\n\n  \
         Server id         {server_id}\n  \
         Sidecar URL       http://{host}:{port}\n  \
         Auth token        {token}\n                    \
         (also in {config})\n  \
         Protocol          {protocol}\n\n\
         Add these at      {site}/admin/rust/servers\n{loopback_note}{service_note}",
        token = doc.web.auth_token,
        config = doc.config_path,
        protocol = doc.protocol,
        when = if running {
            format!(
                "The plugin loads now; `doctor --game rust --server-id {server_id}` confirms it                  connected."
            )
        } else {
            "The plugin connects when the server next starts.".to_string()
        },
        loopback_note = if loopback {
            format!(
                "\nThe sidecar listens on {} only. If the website runs on another machine, put a \
                 TLS proxy in\nfront of it and give the site the proxy's URL \
                 (docs/rust-link/INSTALL.md).\n",
                doc.web.bind
            )
        } else {
            String::new()
        },
        service_note = if registered {
            ""
        } else {
            "\nNo service was registered, so nothing is listening yet — see the steps above.\n"
        },
    )
}

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

    #[test]
    fn the_instance_config_parses_and_keeps_a_windows_path_intact() {
        let db = Path::new(r"C:\ProgramData\RunicGateway\rust\alpha\rust-link.db");
        let text = instance_config("alpha", 7800, 8091, db);
        let value: toml_lite::Doc = toml_lite::parse(&text);
        assert_eq!(value.get("game", "bind"), Some("127.0.0.1:7800"));
        assert_eq!(value.get("game", "server_id"), Some("alpha"));
        assert_eq!(value.get("web", "bind"), Some("127.0.0.1:8091"));
        assert_eq!(value.get("web", "auth_token"), Some(""));
        assert_eq!(
            value.get("store", "path"),
            Some(r"C:\ProgramData\RunicGateway\rust\alpha\rust-link.db")
        );
    }

    #[test]
    fn the_print_config_document_parses() {
        // What Rust-Link v0.1.0 prints (sidecar/src/config.rs::describe).
        let doc: ConfigDoc = serde_json::from_str(
            r#"{ "component": "rust-link-sidecar", "version": "0.1.0", "protocol": 12,
                 "config_path": "/etc/runicgateway/rust/alpha.toml", "config_created": false,
                 "token_generated": true,
                 "game": { "bind": "127.0.0.1:7800", "server_id": "alpha" },
                 "web": { "bind": "127.0.0.1:8091", "ws_path": "/ws", "auth_required": true,
                          "auth_token": "t0k" },
                 "store": { "path": "/var/lib/runicgateway/rust/alpha/rust-link.db" } }"#,
        )
        .unwrap();
        assert_eq!(port_of(&doc.web.bind), Some(8091));
        let text = handoff("alpha", &doc, "rust.example", None, true, false);
        for needle in [
            "alpha",
            "http://rust.example:8091",
            "t0k",
            "/admin/rust/servers",
            "12",
        ] {
            assert!(text.contains(needle), "{needle} missing from:\n{text}");
        }
        assert!(text.contains("TLS proxy"), "{text}");

        // D156: never a claim about a link nothing has seen.
        assert!(!text.contains("is connected"), "{text}");
        assert!(
            text.contains("The plugin connects when the server next starts."),
            "{text}"
        );
        let running = handoff("alpha", &doc, "rust.example", None, true, true);
        assert!(!running.contains("is connected"), "{running}");
        assert!(
            running.contains("doctor --game rust --server-id alpha"),
            "{running}"
        );
    }

    #[test]
    fn a_held_port_is_skipped_and_a_kept_one_is_kept() {
        let port = choose_port(47_990, &[47_990, 47_991], None).unwrap();
        assert!(port >= 47_992);
        assert_eq!(
            choose_port(47_990, &[47_990], Some(47_990)).unwrap(),
            47_990
        );
    }

    /// Enough TOML to read back the file `instance_config` writes — `[section]` and
    /// `key = 'literal'` / `key = "basic"` lines. The installer has no TOML dependency and this
    /// test is the only reader it needs.
    mod toml_lite {
        pub struct Doc(Vec<(String, String, String)>);
        impl Doc {
            pub fn get(&self, section: &str, key: &str) -> Option<&str> {
                self.0
                    .iter()
                    .find(|(s, k, _)| s == section && k == key)
                    .map(|(_, _, v)| v.as_str())
            }
        }
        pub fn parse(text: &str) -> Doc {
            let mut section = String::new();
            let mut out = Vec::new();
            for line in text.lines().map(str::trim) {
                if line.starts_with('#') || line.is_empty() {
                    continue;
                }
                if let Some(name) = line.strip_prefix('[').and_then(|l| l.strip_suffix(']')) {
                    section = name.to_string();
                } else if let Some((k, v)) = line.split_once('=') {
                    let v = v.trim();
                    let v = v
                        .strip_prefix('\'')
                        .and_then(|v| v.strip_suffix('\''))
                        .or_else(|| v.strip_prefix('"').and_then(|v| v.strip_suffix('"')))
                        .unwrap_or(v);
                    out.push((section.clone(), k.trim().to_string(), v.to_string()));
                }
            }
            Doc(out)
        }
    }
}