//! 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: `$UOLINK_CONFIG`, else `sidecar.toml` in the working directory.

use std::env;
use std::fs;
use std::path::Path;

use serde::Deserialize;
use tracing::info;

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

#[derive(Debug, Deserialize)]
pub struct ShardCfg {
    #[serde(default = "default_shard_bind")]
    pub bind: String,
}

#[derive(Debug, Deserialize)]
pub struct WebCfg {
    #[serde(default = "default_web_bind")]
    pub bind: String,
    /// Shared secret the website must present. Empty means the web surface is unauthenticated —
    /// only acceptable when `bind` is loopback; refused otherwise (see `Config::validate`).
    #[serde(default)]
    pub auth_token: String,
}

#[derive(Debug, Deserialize)]
pub struct StoreCfg {
    #[serde(default = "default_db_path")]
    pub path: String,
}

fn default_shard_bind() -> String {
    "127.0.0.1:7788".into()
}
fn default_web_bind() -> String {
    "127.0.0.1:8080".into()
}
fn default_db_path() -> String {
    "uo-link.db".into()
}

impl Default for ShardCfg {
    fn default() -> Self {
        Self {
            bind: default_shard_bind(),
        }
    }
}
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(),
        }
    }
}

impl Config {
    pub fn load() -> anyhow::Result<Self> {
        let path = env::var("UOLINK_CONFIG").unwrap_or_else(|_| "sidecar.toml".into());
        let existed = Path::new(&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.
        if cfg.web.auth_token.trim().is_empty() {
            let token = generate_token();

            if existed {
                persist_token(&path, &token)?;
            } else {
                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);
        }

        Ok(cfg)
    }

    /// Environment overrides, so a deployment can set secrets without editing the file.
    fn apply_env(&mut self) {
        if let Ok(v) = env::var("UOLINK_SHARD_BIND") {
            self.shard.bind = v;
        }
        if let Ok(v) = env::var("UOLINK_WEB_BIND") {
            self.web.bind = v;
        }
        if let Ok(v) = env::var("UOLINK_WEB_TOKEN") {
            self.web.auth_token = v;
        }
        if let Ok(v) = env::var("UOLINK_DB_PATH") {
            self.store.path = v;
        }
    }

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

/// 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: &str, 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#"# uo-link sidecar configuration.
# Read at startup. Nothing here is compiled into the binary. Environment variables
# (UOLINK_SHARD_BIND, UOLINK_WEB_BIND, UOLINK_WEB_TOKEN, UOLINK_DB_PATH) override these.

[shard]
# Loopback address the shard dials out to. Keep this on localhost — the game must
# not be reachable from anywhere else.
bind = "127.0.0.1:7788"

[web]
# Address the website connects to (WebSocket + REST).
#   127.0.0.1:8080  -> same host only
#   0.0.0.0:8080    -> accept remote clients (then auth_token is mandatory)
bind = "127.0.0.1:8080"

# Shared secret the website must present on every request:
#   REST:      Authorization: Bearer <token>     (or  X-Api-Key: <token>)
#   WebSocket: add  ?token=<token>  to the connect URL
# Authentication is always on: if this is left blank, the sidecar generates a new
# token here on startup. Rotate by changing this value and restarting.
auth_token = "{token}"

[store]
path = "uo-link.db"
"#
    )
}