//! Runtime configuration, loaded from an external file — nothing here is compiled into the binary.
//!
//! Precedence: environment variables override the file, the file overrides built-in defaults. On
//! first run, if the file is absent, a default one is written with a freshly generated auth token,
//! so the sidecar is secured out of the box and the operator just copies the token to the website.
//!
//! File path: `--config <PATH>`, else `$RUSTLINK_CONFIG`, else `sidecar.toml` in the working
//! directory.
//!
//! **Paths are anchored to the config file, not the working directory.** A relative `[store].path`
//! resolves against the directory holding `sidecar.toml`, so a service started with
//! `RUSTLINK_CONFIG=/etc/runicgateway/rust-main.toml` keeps its database beside its config instead
//! of wherever the service manager happened to set the working directory.
//!
//! # `server_id`, and why it is here rather than only in the plugin
//!
//! R8 makes the platform multi-server: one sidecar per game server, and every row the module
//! stores carries the server it came from. The plugin declares its own `serverId` in `server.hello`
//! and that is the authority. This setting is a **cross-check**, not a second source of truth: when
//! both are set and they disagree, the sidecar **refuses the plugin** — it closes the connection
//! before the frame is filed, and logs both ids at ERROR (D155). Two servers dialling one sidecar is
//! the mistake this catches, and it is silent in every other design. It was a warning that kept the
//! plugin's id until the phase 18 walk showed what that costs: one server's history filed under
//! another's name, visible on the website. Left blank, nothing is checked.

use std::env;
use std::fs;
use std::path::{Component, Path, PathBuf};

use serde::Deserialize;
use serde_json::json;
use tracing::info;

use crate::PROTOCOL_VERSION;

#[derive(Debug, Default, Deserialize)]
pub struct Config {
    #[serde(default)]
    pub game: GameCfg,
    #[serde(default)]
    pub web: WebCfg,
    #[serde(default)]
    pub store: StoreCfg,
}

#[derive(Debug, Deserialize)]
pub struct GameCfg {
    #[serde(default = "default_game_bind")]
    pub bind: String,
    /// Optional cross-check against the `serverId` the plugin announces. See the module docs.
    #[serde(default)]
    pub server_id: String,
}

#[derive(Debug, Deserialize)]
pub struct WebCfg {
    #[serde(default = "default_web_bind")]
    pub bind: String,
    /// Shared secret the website must present. Never empty in practice — `Config::load` generates
    /// and persists one when it finds none, so the web surface is authenticated from first boot.
    #[serde(default)]
    pub auth_token: String,
}

#[derive(Debug, Deserialize)]
pub struct StoreCfg {
    #[serde(default = "default_db_path")]
    pub path: String,
    /// How many days of event history to keep. `0` keeps everything.
    ///
    /// The store sits on a game host, and protocol 2 gave it a catalogue that produces real volume
    /// — every death, every chat line, every connect. The *permanent* record is the website's:
    /// per-wipe rollups in the module's own tables (R12). So this bounds the sidecar's copy, and
    /// the default is generous enough that nobody needs to think about it and small enough that a
    /// busy month is not a wipe-day outage.
    #[serde(default = "default_retain_days")]
    pub retain_days: i64,
}

/// A loaded configuration plus what loading it *did* — an installer re-running the binary needs to
/// distinguish "read an existing install" from "provisioned a new one", and it cannot tell from the
/// values alone.
#[derive(Debug)]
pub struct Loaded {
    pub cfg: Config,
    /// Absolute path of the config file that was read or written.
    pub path: PathBuf,
    /// The config file did not exist and was created by this run.
    pub config_created: bool,
    /// No usable token was configured, so one was generated and saved.
    pub token_generated: bool,
}

fn default_game_bind() -> String {
    "127.0.0.1:7799".into()
}
fn default_web_bind() -> String {
    "127.0.0.1:8090".into()
}
fn default_db_path() -> String {
    "rust-link.db".into()
}
fn default_retain_days() -> i64 {
    14
}

impl Default for GameCfg {
    fn default() -> Self {
        Self {
            bind: default_game_bind(),
            server_id: String::new(),
        }
    }
}
impl Default for WebCfg {
    fn default() -> Self {
        Self {
            bind: default_web_bind(),
            auth_token: String::new(),
        }
    }
}
impl Default for StoreCfg {
    fn default() -> Self {
        Self {
            path: default_db_path(),
            retain_days: default_retain_days(),
        }
    }
}

impl Config {
    /// Which config file this invocation will use: `--config`, else `$RUSTLINK_CONFIG`, else
    /// `sidecar.toml` beside the working directory. Always returned absolute, so every later
    /// message names a path the operator can act on.
    pub fn resolve_path(cli_override: Option<&str>) -> PathBuf {
        let raw = cli_override
            .map(str::to_string)
            .or_else(|| env::var("RUSTLINK_CONFIG").ok())
            .unwrap_or_else(|| "sidecar.toml".into());
        absolutize(PathBuf::from(raw))
    }

    pub fn load(cli_override: Option<&str>) -> anyhow::Result<Loaded> {
        let path = Self::resolve_path(cli_override);
        let existed = path.exists();

        let mut cfg: Config = if existed {
            let text = fs::read_to_string(&path)?;
            toml::from_str(&text)?
        } else {
            Config::default()
        };

        cfg.apply_env();

        // Authentication is always on. A blank token is never allowed — if none is set (fresh
        // install, or someone cleared it), generate one, save it, and continue. This keeps setup
        // effortless while making it impossible to accidentally run with auth off.
        let token_generated = cfg.web.auth_token.trim().is_empty();
        if token_generated {
            let token = generate_token();

            if existed {
                persist_token(&path, &token)?;
            } else {
                // The parent may not exist yet when an installer points at a fresh
                // /etc/runicgateway; failing here would mean "run me again after mkdir".
                create_parent_dir(&path)?;
                fs::write(&path, default_file(&token))?;
            }

            cfg.web.auth_token = token.clone();

            info!("No auth token configured.");
            info!("Generated new token: {}", token);
            info!("Saved to {}. Authentication is on.", path.display());
        }

        cfg.anchor_store_path(&path);

        Ok(Loaded {
            cfg,
            path,
            config_created: !existed,
            token_generated,
        })
    }

    /// Environment overrides, so a deployment can set secrets without editing the file.
    fn apply_env(&mut self) {
        self.apply_env_from(|key| env::var(key).ok());
    }

    /// [`Self::apply_env`] against any lookup, so the rules below are testable without mutating the
    /// process environment (which the test harness shares across threads).
    ///
    /// **An empty or blank value is the same as an unset one.** A Pterodactyl egg exports every
    /// variable it declares, so an operator who leaves `RUSTLINK_WEB_TOKEN` blank arrives here as
    /// `RUSTLINK_WEB_TOKEN=""`. Honouring that as an override would blank the token saved in
    /// `sidecar.toml` on every boot, and a fresh one would be generated and persisted each time:
    /// the website's copy would go stale at every restart (PLAN.md §34, D152). No variable here has
    /// a meaningful empty value — an empty bind or database path can only fail later, less clearly.
    fn apply_env_from(&mut self, get: impl Fn(&str) -> Option<String>) {
        let get = |key: &str| get(key).filter(|v| !v.trim().is_empty());
        if let Some(v) = get("RUSTLINK_GAME_BIND") {
            self.game.bind = v;
        }
        if let Some(v) = get("RUSTLINK_SERVER_ID") {
            self.game.server_id = v;
        }
        if let Some(v) = get("RUSTLINK_WEB_BIND") {
            self.web.bind = v;
        }
        if let Some(v) = get("RUSTLINK_WEB_TOKEN") {
            self.web.auth_token = v;
        }
        if let Some(v) = get("RUSTLINK_DB_PATH") {
            self.store.path = v;
        }
        if let Some(v) = get("RUSTLINK_RETAIN_DAYS") {
            // A malformed value is ignored rather than fatal: this reaches the process as a panel
            // variable somebody typed (R22), and refusing to start over a stray character would
            // take the bridge down for a setting that has a perfectly good default.
            match v.trim().parse::<i64>() {
                Ok(days) if days >= 0 => self.store.retain_days = days,
                _ => tracing::warn!(value = %v, "ignoring an unreadable RUSTLINK_RETAIN_DAYS"),
            }
        }
    }

    /// Resolves `[store].path` against the config file's directory (see the module docs). Absolute
    /// paths and SQLite's non-filesystem spellings are left exactly as written.
    fn anchor_store_path(&mut self, config_path: &Path) {
        if is_sqlite_special(&self.store.path) {
            return;
        }
        let raw = PathBuf::from(&self.store.path);
        let anchored = if raw.is_absolute() {
            raw
        } else {
            config_dir(config_path).join(raw)
        };
        self.store.path = absolutize(anchored).to_string_lossy().into_owned();
    }

    pub fn auth_required(&self) -> bool {
        // Always true now — load() guarantees a non-empty token.
        !self.web.auth_token.is_empty()
    }
}

/// The `--print-config` document: everything an installer needs to register this sidecar with a
/// website, in one non-interactive read.
///
/// **This includes the auth token in clear text**, which is the point: the manual token hunt is the
/// largest "I installed it and nothing happened" failure mode. The caller prints it to stdout and
/// starts no log subscriber, so the document is the whole output.
pub fn describe(loaded: &Loaded) -> serde_json::Value {
    json!({
        "component": "rust-link-sidecar",
        "version": env!("CARGO_PKG_VERSION"),
        "protocol": PROTOCOL_VERSION,
        "config_path": loaded.path.to_string_lossy(),
        "config_created": loaded.config_created,
        "token_generated": loaded.token_generated,
        "game": {
            "bind": loaded.cfg.game.bind,
            "server_id": loaded.cfg.game.server_id,
        },
        "web": {
            "bind": loaded.cfg.web.bind,
            "ws_path": crate::web::WS_PATH,
            "auth_required": loaded.cfg.auth_required(),
            "auth_token": loaded.cfg.web.auth_token,
        },
        "store": { "path": loaded.cfg.store.path },
    })
}

/// Directory holding the config file. A bare `sidecar.toml` has no parent component, which would
/// join into an empty base — treat it as the current directory.
fn config_dir(config_path: &Path) -> PathBuf {
    match config_path.parent() {
        Some(p) if !p.as_os_str().is_empty() => p.to_path_buf(),
        _ => PathBuf::from("."),
    }
}

/// Prefixes the working directory onto a relative path, then drops the `.` components that
/// joining leaves behind — cosmetic, but these paths are printed and pasted into service units.
fn absolutize(p: PathBuf) -> PathBuf {
    let joined = if p.is_absolute() {
        p
    } else {
        match env::current_dir() {
            Ok(cwd) => cwd.join(p),
            Err(_) => p,
        }
    };
    let cleaned: PathBuf = joined
        .components()
        .filter(|c| !matches!(c, Component::CurDir))
        .collect();
    if cleaned.as_os_str().is_empty() {
        joined
    } else {
        cleaned
    }
}

/// `:memory:` and `file:` URIs are instructions to SQLite, not paths on disk. Anchoring them to a
/// directory would turn a working in-memory store into an attempt to create a file called
/// `:memory:` — which Windows cannot even name.
fn is_sqlite_special(path: &str) -> bool {
    path == ":memory:" || path.starts_with("file:")
}

fn create_parent_dir(path: &Path) -> anyhow::Result<()> {
    if let Some(dir) = path.parent() {
        if !dir.as_os_str().is_empty() && !dir.exists() {
            fs::create_dir_all(dir)?;
        }
    }
    Ok(())
}

/// Rewrites the `auth_token` line in an existing config file, preserving everything else. Falls
/// back to inserting it under `[web]`, or appending a `[web]` section, if the key is absent.
fn persist_token(path: &Path, token: &str) -> anyhow::Result<()> {
    let text = fs::read_to_string(path)?;
    let line = format!("auth_token = \"{token}\"");

    if text
        .lines()
        .any(|l| l.trim_start().starts_with("auth_token"))
    {
        let out: String = text
            .lines()
            .map(|l| {
                if l.trim_start().starts_with("auth_token") {
                    line.clone()
                } else {
                    l.to_string()
                }
            })
            .collect::<Vec<_>>()
            .join("\n");
        fs::write(path, out + "\n")?;
    } else if text.lines().any(|l| l.trim() == "[web]") {
        let out: String = text
            .lines()
            .flat_map(|l| {
                if l.trim() == "[web]" {
                    vec![l.to_string(), line.clone()]
                } else {
                    vec![l.to_string()]
                }
            })
            .collect::<Vec<_>>()
            .join("\n");
        fs::write(path, out + "\n")?;
    } else {
        fs::write(path, format!("{text}\n[web]\n{line}\n"))?;
    }

    Ok(())
}

fn generate_token() -> String {
    let mut buf = [0u8; 24];
    // OS randomness; falls back to a time-seeded token only if the OS RNG is unavailable.
    if getrandom::getrandom(&mut buf).is_err() {
        let nanos = std::time::SystemTime::now()
            .duration_since(std::time::UNIX_EPOCH)
            .map(|d| d.as_nanos())
            .unwrap_or(0);
        return format!("insecure-fallback-{nanos:x}");
    }
    buf.iter().map(|b| format!("{b:02x}")).collect()
}

fn default_file(token: &str) -> String {
    format!(
        r#"# rust-link sidecar configuration.
#
# One sidecar serves one Rust game server. A community running six servers runs
# six of these, each with its own port, its own database and its own token.
#
# Environment variables override every value here.

[game]
# Where the Oxide bridge plugin dials in. The plugin is the client; this is the
# listener, which is why the game server itself opens no extra port.
bind = "127.0.0.1:7799"

# Optional. If set, it is cross-checked against the serverId the plugin
# announces in server.hello; a disagreement is logged and the plugin wins.
server_id = ""

[web]
# Where the website reaches this sidecar. Bind to a LAN or public address only
# behind TLS and a firewall — the token below is the only thing guarding it.
bind = "127.0.0.1:8090"

# Generated on first run. Paste it into the website's Rust server form. It is
# write-only there: the site never shows it back.
auth_token = "{token}"

[store]
# Relative paths resolve against the directory holding THIS FILE, not the
# working directory of whatever started the process.
path = "rust-link.db"

# How many days of event history to keep. 0 keeps everything.
#
# The permanent record is the website's — it holds per-wipe rollups that survive
# a wipe. This database is the recent copy the site reads to catch up, and it
# lives on the game host, so it is bounded.
retain_days = 14
"#
    )
}

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

    #[test]
    fn a_generated_token_is_48_hex_characters() {
        let t = generate_token();
        assert!(!t.starts_with("insecure-fallback-"), "OS RNG unavailable");
        assert_eq!(t.len(), 48);
        assert!(t.chars().all(|c| c.is_ascii_hexdigit()));
    }

    #[test]
    fn sqlite_special_paths_are_not_anchored() {
        let mut cfg = Config::default();
        cfg.store.path = ":memory:".into();
        cfg.anchor_store_path(Path::new("/etc/runicgateway/sidecar.toml"));
        assert_eq!(cfg.store.path, ":memory:");
    }

    /// The whole point of anchoring: a service manager's working directory must not decide where
    /// the database lands.
    #[test]
    fn a_relative_store_path_anchors_to_the_config_directory() {
        let mut cfg = Config::default();
        cfg.store.path = "rust-link.db".into();
        let config_path = absolutize(PathBuf::from("cfgdir/sidecar.toml"));
        cfg.anchor_store_path(&config_path);

        let expected = config_path.parent().unwrap().join("rust-link.db");
        assert_eq!(PathBuf::from(&cfg.store.path), expected);
    }

    /// The written default must be loadable by the loader that wrote it — a template with a typo
    /// in it fails on the second start, not the first.
    #[test]
    fn the_default_file_round_trips() {
        let cfg: Config = toml::from_str(&default_file("deadbeef")).unwrap();
        assert_eq!(cfg.web.auth_token, "deadbeef");
        assert_eq!(cfg.game.bind, default_game_bind());
        assert_eq!(cfg.store.path, default_db_path());
        assert_eq!(cfg.game.server_id, "");
    }

    /// The egg's case (D152): a blank panel variable must not erase the token already saved in the
    /// file, or a new one would be generated on every boot.
    #[test]
    fn an_empty_variable_does_not_override_the_file() {
        let mut cfg: Config = toml::from_str(&default_file("saved-token")).unwrap();
        cfg.apply_env_from(|key| match key {
            "RUSTLINK_WEB_TOKEN" => Some(String::new()),
            "RUSTLINK_WEB_BIND" => Some("   ".into()),
            "RUSTLINK_SERVER_ID" => Some(String::new()),
            _ => None,
        });
        assert_eq!(cfg.web.auth_token, "saved-token");
        assert_eq!(cfg.web.bind, default_web_bind());
        assert_eq!(cfg.game.server_id, "");
    }

    #[test]
    fn a_set_variable_still_overrides_the_file() {
        let mut cfg: Config = toml::from_str(&default_file("saved-token")).unwrap();
        cfg.apply_env_from(|key| match key {
            "RUSTLINK_WEB_TOKEN" => Some("from-env".into()),
            "RUSTLINK_WEB_BIND" => Some("0.0.0.0:21009".into()),
            "RUSTLINK_SERVER_ID" => Some("alpha".into()),
            _ => None,
        });
        assert_eq!(cfg.web.auth_token, "from-env");
        assert_eq!(cfg.web.bind, "0.0.0.0:21009");
        assert_eq!(cfg.game.server_id, "alpha");
    }
}