//! The daemon's state (spec §7.1): the ledger it alone writes, the
//! principals kept current from the bus, the authenticator, and presence
//! with its timers. HTTP lives elsewhere (`spectra-mcp`, `radar`); this is
//! what they share.

use crate::authn::{Authenticator, Caller, Refusal};
use crate::event::{Auth, Event, Method, NewEvent};
use crate::keys::KeyPair;
use crate::ledger::{KeyResolver, Ledger};
use crate::presence::Presence;
use crate::principals::{Principal, Principals};
use crate::proof::Proof;
use anyhow::{bail, Context, Result};
use serde::{Deserialize, Serialize};
use std::path::{Path, PathBuf};
use std::sync::Arc;
use tokio::sync::{Mutex, RwLock};

/// Kinds the owner's CLI may hand the daemon, already signed over their
/// payload (spec §8.5, "One writer").
pub const OWNER_KINDS: &[&str] = &[
    "identity.rotated",
    "agent.added",
    "agent.disabled",
    "agent.scoped",
    "project.added",
    "project.linked",
    "project.unlinked",
    "brief.set",
];

pub struct Daemon {
    pub data: PathBuf,
    pub ledger: Ledger,
    pub principals: RwLock<Principals>,
    pub authn: Authenticator,
    pub presence: Mutex<Presence>,
    /// Per agent: empty `wait`s in a row, and until when `wait` is refused.
    pub idle_waits: Mutex<std::collections::HashMap<String, (u32, u64)>>,
}

impl Daemon {
    /// Open the data directory's ledger for writing and start the timers.
    pub async fn start(data: &Path) -> Result<Arc<Daemon>> {
        let db = data.join("spectra.db");
        if !db.exists() {
            bail!("no Spectra in {} (run `spectra init`)", data.display());
        }
        let instance = KeyPair::instance(data, "spectra")?;
        let ledger = Ledger::open(&db, Some(instance)).await?;
        let principals = Principals::load(&ledger).await?;
        let d = Arc::new(Daemon {
            data: data.to_path_buf(),
            ledger,
            principals: RwLock::new(principals),
            authn: Authenticator::default(),
            presence: Mutex::new(Presence::default()),
            idle_waits: Mutex::new(Default::default()),
        });
        d.clone().watch_principals();
        d.clone().tick_presence();
        Ok(d)
    }

    /// Reload who is who whenever an identity or agent event is appended.
    fn watch_principals(self: Arc<Self>) {
        let mut rx = self.ledger.subscribe();
        tokio::spawn(async move {
            loop {
                match rx.recv().await {
                    Ok(e)
                        if e.kind.starts_with("identity.")
                            || e.kind.starts_with("agent.") && e.kind != "agent.presence" && e.kind != "agent.status" =>
                    {
                        if let Ok(p) = Principals::load(&self.ledger).await {
                            *self.principals.write().await = p;
                        }
                    }
                    Ok(_) => {}
                    Err(tokio::sync::broadcast::error::RecvError::Lagged(_)) => {
                        if let Ok(p) = Principals::load(&self.ledger).await {
                            *self.principals.write().await = p;
                        }
                    }
                    Err(_) => return,
                }
            }
        });
    }

    /// Record presence changes and quiet sessions every 15 s, and write a
    /// checkpoint when one is due by time.
    fn tick_presence(self: Arc<Self>) {
        tokio::spawn(async move {
            let mut every = tokio::time::interval(std::time::Duration::from_secs(15));
            loop {
                every.tick().await;
                let events = self.presence.lock().await.tick(crate::ids::now_ms());
                if !events.is_empty() {
                    let _ = self.ledger.append(events).await;
                }
                let _ = self.ledger.append(vec![]).await;
            }
        });
    }

    /// Authenticate a request (spec §8.5); an agent used from the wrong Unix
    /// user is recorded as `guard.impersonation`, and a first connection
    /// that binds an agent's uid as `agent.uid_bound`.
    pub async fn authenticate(&self, proof: Option<&Proof>, method: &str, body: &[u8], peer: Option<Peer>) -> Result<Caller, Refusal> {
        let now = crate::ids::now_ms();
        let r = {
            let p = self.principals.read().await;
            if p.owner().is_none() {
                return Err(Refusal::NotAPrincipal("this Spectra has no owner yet: its owner claims it with `spectra connect`".into()));
            }
            self.authn.authenticate(&p, proof, method, body, now, peer.map(|x| x.uid))
        };
        match &r {
            Err(Refusal::WrongUid { agent, bound, from }) => {
                let e = NewEvent::system(
                    "guard.impersonation",
                    serde_json::json!({ "agent": agent, "bound_uid": bound, "from_uid": from, "from_pid": peer.map(|x| x.pid), "method": method }),
                )
                .subject(agent.clone());
                let _ = self.ledger.append_one(e).await;
                tracing::warn!(agent, bound, from, "a key used from the wrong Unix user");
            }
            Err(Refusal::BoundOverNetwork { agent, bound }) => {
                let e = NewEvent::system(
                    "guard.impersonation",
                    serde_json::json!({ "agent": agent, "bound_uid": bound, "from_uid": null, "over": "tcp", "method": method }),
                )
                .subject(agent.clone());
                let _ = self.ledger.append_one(e).await;
                tracing::warn!(agent, bound, "a uid-bound key used over the network");
            }
            Ok(Caller { principal: Principal::Agent { name, .. }, learn_uid: Some(uid), .. }) => {
                let e = NewEvent::system("agent.uid_bound", serde_json::json!({ "name": name, "uid": uid })).subject(name.clone());
                let _ = self.ledger.append_one(e).await;
            }
            _ => {}
        }
        r
    }

    /// Note a request from an agent: its session, and the event that
    /// starts one when this is the first in ten minutes.
    pub async fn touch(&self, who: &Principal, new_session: bool) -> Option<String> {
        let Principal::Agent { name, .. } = who else { return None };
        let (id, started) = self.presence.lock().await.request(name, crate::ids::now_ms(), new_session);
        if let Some(e) = started {
            let _ = self.ledger.append_one(e).await;
        }
        Some(id)
    }

    /// Append events the owner's CLI signed over their payload, after
    /// checking each as `spectra admin verify` would.
    pub async fn accept_owner_events(&self, events: Vec<WireEvent>) -> Result<Vec<u64>> {
        let mut principals = self.principals.read().await.clone();
        let projects: Vec<String> = events
            .iter()
            .filter(|e| e.kind == "project.added")
            .filter_map(|e| e.payload.get("name").and_then(|n| n.as_str()).map(String::from))
            .collect();
        let mut out = Vec::new();
        for w in events {
            let n = w.into_new_event()?;
            if n.kind == "channel.created" {
                // A project's channel comes with its project, unsigned, as `project add` makes it.
                let p = &n.payload;
                let ok = p.get("kind").and_then(|k| k.as_str()) == Some("project")
                    && p.get("name").and_then(|x| x.as_str()).is_some_and(|x| projects.iter().any(|q| q == x));
                if !ok || n.auth.method != Method::System {
                    bail!("a channel is only made with its project");
                }
                out.push(n);
                continue;
            }
            if !OWNER_KINDS.contains(&n.kind.as_str()) {
                bail!("{} cannot be handed to the daemon", n.kind);
            }
            if n.actor != "human" {
                bail!("only the owner hands events to the daemon");
            }
            if n.kind == "brief.set" {
                crate::rules::check(n.payload.get("text").and_then(|t| t.as_str()).unwrap_or(""))?;
            }
            // Check it as verify will, against who is who including the
            // batch so far.
            let probe = probe_event(&n);
            principals.check(&probe).map_err(|why| anyhow::anyhow!("refused {}: {why}", n.kind))?;
            if n.kind != "identity.rotated" {
                let key = crate::identity::KeyId(n.auth.key.context("unsigned")?);
                if !matches!(principals.principal(&key, crate::ids::now_ms()), Ok(Principal::Owner { .. })) {
                    bail!("refused {}: not signed by the owner", n.kind);
                }
            }
            out.push(n);
        }
        let appended = self.ledger.append(out).await?;
        let _ = self.ledger.checkpoint().await;
        // Who is who has changed: know it before the next request arrives.
        *self.principals.write().await = Principals::load(&self.ledger).await?;
        Ok(appended.iter().map(|e| e.seq).collect())
    }

    /// The owner `spectra init --owner` named, while none is recorded.
    pub fn named_owner(&self) -> Option<String> {
        let text = std::fs::read_to_string(self.data.join("spectra.toml")).ok()?;
        let t: toml::Table = text.parse().ok()?;
        t.get("owner")?.get("key")?.as_str().map(|k| k.to_ascii_lowercase())
    }

    /// The owner claims a Spectra set up with `spectra init --owner`
    /// (spec §8.6): the named identity, signed by itself over its payload,
    /// then any successors up to the owner's current identity, each a
    /// rotation as `identity refresh` makes. Accepted only while no owner
    /// is recorded, and only from the key init named.
    pub async fn claim(&self, events: Vec<WireEvent>) -> Result<Vec<u64>> {
        let mut principals = self.principals.read().await.clone();
        if principals.owner().is_some() {
            bail!("this Spectra already has an owner");
        }
        let named = self.named_owner().context("this Spectra names no owner (spectra init --owner)")?;
        let mut out = Vec::new();
        for (i, w) in events.into_iter().enumerate() {
            let n = w.into_new_event()?;
            let want = if i == 0 { "identity.owner" } else { "identity.rotated" };
            if n.kind != want || n.actor != "human" {
                bail!("a claim is the owner's identity.owner, then their rotations");
            }
            if i == 0 {
                let key = n.payload.get("key").and_then(|k| k.as_str()).unwrap_or("").to_ascii_lowercase();
                if key != named || n.auth.key.map(hex::encode) != Some(named.clone()) {
                    bail!("this Spectra was set up for another owner");
                }
            }
            principals.check(&probe_event(&n)).map_err(|why| anyhow::anyhow!("refused the claim: {why}"))?;
            out.push(n);
        }
        if out.is_empty() {
            bail!("an empty claim");
        }
        let appended = self.ledger.append(out).await?;
        let _ = self.ledger.checkpoint().await;
        *self.principals.write().await = Principals::load(&self.ledger).await?;
        Ok(appended.iter().map(|e| e.seq).collect())
    }

    /// Write a checkpoint covering everything (at shutdown).
    pub async fn shutdown(&self) {
        let _ = self.ledger.checkpoint().await;
    }
}

/// The Unix peer of a socket connection.
#[derive(Clone, Copy, Debug, PartialEq, Eq)]
pub struct Peer {
    pub uid: u32,
    pub pid: Option<i32>,
}

/// An event as the CLI hands it to the daemon: signed already.
#[derive(Clone, Debug, Serialize, Deserialize)]
pub struct WireEvent {
    pub kind: String,
    pub actor: String,
    pub subject: Option<String>,
    pub project: Option<String>,
    pub payload: serde_json::Value,
    /// Hex of the auth key and the encoded proof; absent for a project's channel.
    pub key: Option<String>,
    pub proof: Option<String>,
}

impl WireEvent {
    pub fn from_new(n: &NewEvent) -> WireEvent {
        WireEvent {
            kind: n.kind.clone(),
            actor: n.actor.clone(),
            subject: n.subject.clone(),
            project: n.project.clone(),
            payload: n.payload.clone(),
            key: n.auth.key.map(hex::encode),
            proof: n.auth.proof.as_ref().map(hex::encode),
        }
    }

    fn into_new_event(self) -> Result<NewEvent> {
        let auth = match (&self.key, &self.proof) {
            (Some(k), Some(p)) => Auth {
                key: Some(hex::decode(k).ok().and_then(|b| b.try_into().ok()).context("a key is 32 bytes of hex")?),
                method: Method::Signature,
                assurance: 2,
                proof: Some(hex::decode(p).context("a proof is hex")?),
            },
            _ => Auth::system(),
        };
        let mut n = NewEvent::system(&self.kind, self.payload).by(self.actor, auth);
        n.subject = self.subject;
        n.project = self.project;
        Ok(n)
    }
}

/// The event `n` would be, for checking before it is appended.
fn probe_event(n: &NewEvent) -> Event {
    let now = crate::ids::now_ms();
    Event {
        seq: 0,
        id: String::new(),
        at_ms: now,
        hlc: crate::hlc::Hlc { wall_ms: now, logical: 0 },
        prev: [0; 32],
        hash: [0; 32],
        auth: n.auth.clone(),
        kind: n.kind.clone(),
        actor: n.actor.clone(),
        session: n.session.clone(),
        project: n.project.clone(),
        subject: n.subject.clone(),
        payload: Some(crate::event::canonical_json(&n.payload)),
        trace: n.trace.clone(),
    }
}