//! Who is who (spec §8): the owner, the instance, and agents, each an Oxygen
//! identity; an agent is valid while the owner's current identity delegates
//! to its key (oxygen spec §14.2). Everything here is derived from the
//! ledger, and every claim in it was proven when it was recorded:
//!
//! - `identity.owner` and `identity.rotated` are signed by the identity they
//!   record, so only the holder of its secret key can name it the owner.
//!   A successor must keep the key pair and chain back, by `previous`, to
//!   the owner already known; a fresh key pair needs `oxy identity rotate`'s
//!   attestation, which 0.1 does not accept yet.
//! - `identity.instance` is signed by the instance key.
//! - `agent.added` and `agent.disabled` are signed by the owner, and an
//!   agent is added only while the owner's identity delegates to it.
//!
//! [`Principals`] replays these in ledger order, so `spectra admin verify`
//! checks every signed event against who was who at that moment.

use crate::event::{Event, Method};
use crate::identity::Identity;
use crate::identity::KeyId;
use crate::ledger::KeyResolver;
use crate::proof::Proof;
use serde_json::Value as Json;
use sqlx::SqliteConnection;
use std::collections::HashMap;

/// The scopes a new agent gets (spec §8.4).
pub const DEFAULT_SCOPES: &[&str] = &["read", "say", "tasks", "claims", "decisions", "status", "search", "schedule:self"];

/// Who caused something.
#[derive(Clone, Debug, PartialEq, Eq)]
pub enum Principal {
    Owner { key: KeyId, name: String },
    Agent { name: String, key: KeyId, owner_name: String, uid: Option<u32>, learn_uid: bool, project: String, scopes: Vec<String> },
    Instance { key: KeyId },
}

impl Principal {
    /// The `actor` events carry: `human`, `agent:NAME` or `system`.
    pub fn actor(&self) -> String {
        match self {
            Principal::Owner { .. } => "human".into(),
            Principal::Agent { name, .. } => format!("agent:{name}"),
            Principal::Instance { .. } => "system".into(),
        }
    }
    /// How it is shown to people: `claude-oxygen · Andy McCall's agent`.
    pub fn display(&self) -> String {
        match self {
            Principal::Owner { name, .. } => name.clone(),
            Principal::Agent { name, owner_name, .. } => format!("{name} · {owner_name}'s agent"),
            Principal::Instance { .. } => "Spectra".into(),
        }
    }
}

#[derive(Clone, Debug)]
struct AgentRec {
    name: String,
    identity: Identity,
    owner_name: String,
    uid: Option<u32>,
    learn_uid: bool,
    project: String,
    scopes: Vec<String>,
    disabled: bool,
}

/// The principals as of some point in the ledger.
#[derive(Clone, Debug, Default)]
pub struct Principals {
    /// The owner's identities, oldest first; the last is current.
    owner: Vec<Identity>,
    instance: Option<Identity>,
    agents: HashMap<KeyId, AgentRec>,
    by_name: HashMap<String, KeyId>,
}

impl Principals {
    /// Replay every identity and agent event of the ledger.
    pub async fn load(ledger: &crate::ledger::Ledger) -> anyhow::Result<Principals> {
        let mut p = Principals::default();
        let mut from = 1;
        loop {
            let rows = ledger
                .events_of_kinds(
                    from,
                    &["identity.owner", "identity.rotated", "identity.instance", "agent.added", "agent.disabled", "agent.scoped"],
                    1000,
                )
                .await?;
            if rows.is_empty() {
                break;
            }
            for e in &rows {
                // Recorded facts were checked when written; `verify` checks them again.
                let _ = p.observe(e);
            }
            from = rows.last().map(|e| e.seq + 1).unwrap_or(from);
        }
        Ok(p)
    }

    /// The owner's current identity.
    pub fn owner(&self) -> Option<&Identity> {
        self.owner.last()
    }

    pub fn instance(&self) -> Option<&Identity> {
        self.instance.as_ref()
    }

    /// The agent named `name`, whatever its state.
    pub fn agent_key(&self, name: &str) -> Option<KeyId> {
        self.by_name.get(name).copied()
    }

    /// Who `key` is at `at_ms`, if anyone may act with it then: the owner
    /// (any of its identities' KeyIds), the instance, or an agent that is
    /// not disabled and that the owner's current identity delegates to.
    pub fn principal(&self, key: &KeyId, at_ms: u64) -> Result<Principal, String> {
        if let Some(owner) = self.owner.iter().rev().find(|i| &i.hash() == key) {
            return Ok(Principal::Owner { key: *key, name: owner.name.clone() });
        }
        if self.instance.as_ref().is_some_and(|i| &i.hash() == key) {
            return Ok(Principal::Instance { key: *key });
        }
        let a = self.agents.get(key).ok_or("an unknown key")?;
        if a.disabled {
            return Err(format!("agent {} is disabled", a.name));
        }
        let owner = self.owner().ok_or("no owner is recorded")?;
        if !owner.delegates_to(key, at_ms) {
            return Err(match owner.delegate(key) {
                Some(d) if d.expires.is_some_and(|x| at_ms > x) => format!("agent {}'s delegation from {} has expired", a.name, owner.name),
                Some(_) => format!("{}'s delegation to agent {} does not include `changes`", owner.name, a.name),
                None => format!("{}'s current identity does not delegate to agent {}", owner.name, a.name),
            });
        }
        Ok(Principal::Agent {
            name: a.name.clone(),
            key: *key,
            owner_name: a.owner_name.clone(),
            uid: a.uid,
            learn_uid: a.learn_uid,
            project: a.project.clone(),
            scopes: a.scopes.clone(),
        })
    }

    /// The identity behind `key`, for checking its signatures.
    pub fn identity(&self, key: &KeyId) -> Option<&Identity> {
        self.owner
            .iter()
            .find(|i| &i.hash() == key)
            .or_else(|| self.instance.as_ref().filter(|i| &i.hash() == key))
            .or_else(|| self.agents.get(key).map(|a| &a.identity))
    }

    /// Take one event into account, checking what it claims first.
    pub fn observe(&mut self, e: &Event) -> Result<(), String> {
        let p = e.json();
        match e.kind.as_str() {
            "identity.owner" => {
                if !self.owner.is_empty() {
                    return Err("an owner is already recorded".into());
                }
                let id = identity_of(&p)?;
                self_signed(e, &id)?;
                self.owner.push(id);
            }
            "identity.rotated" => {
                let new = identity_of(&p)?;
                let cur = self.owner().ok_or("no owner to succeed")?.clone();
                accept_successor(&cur, &new, &p)?;
                self_signed(e, &new)?;
                self.owner.push(new);
            }
            "identity.instance" => {
                let id = identity_of(&p)?;
                self_signed(e, &id)?;
                self.instance = Some(id);
            }
            "agent.added" => {
                let id = identity_of(&p)?;
                let key = id.hash();
                let owner = self.owner_signed(e)?;
                if !owner.delegates_to(&key, e.hlc.wall_ms) {
                    return Err("added without the owner's delegation to its key".into());
                }
                let name = text(&p, "name")?;
                if self.by_name.get(&name).is_some_and(|k| *k != key) {
                    return Err(format!("agent {name} already exists with another key"));
                }
                self.by_name.insert(name.clone(), key);
                self.agents.insert(
                    key,
                    AgentRec {
                        name,
                        identity: id,
                        owner_name: owner.name.clone(),
                        uid: p.get("uid").and_then(Json::as_u64).map(|u| u as u32),
                        learn_uid: p.get("learn_uid").and_then(Json::as_bool).unwrap_or(false),
                        project: text(&p, "project")?,
                        scopes: p
                            .get("scopes")
                            .and_then(Json::as_array)
                            .map(|a| a.iter().filter_map(|s| s.as_str().map(String::from)).collect())
                            .unwrap_or_default(),
                        disabled: false,
                    },
                );
            }
            "agent.uid_bound" => {
                // The daemon binds a learning agent to the uid of its first
                // signed connection; covered by the next checkpoint.
                let name = text(&p, "name")?;
                let uid = p.get("uid").and_then(Json::as_u64).ok_or("no uid")? as u32;
                let key = *self.by_name.get(&name).ok_or("an unknown agent")?;
                if let Some(a) = self.agents.get_mut(&key) {
                    if a.uid.is_none() {
                        a.uid = Some(uid);
                    }
                }
            }
            "agent.disabled" => {
                self.owner_signed(e)?;
                let name = text(&p, "name")?;
                let key = *self.by_name.get(&name).ok_or("an unknown agent")?;
                if let Some(a) = self.agents.get_mut(&key) {
                    a.disabled = true;
                }
            }
            // The owner grants or takes back one scope (spec §8.4), such
            // as `channel:NAME` to post in another project's channel.
            "agent.scoped" => {
                self.owner_signed(e)?;
                let name = text(&p, "name")?;
                let scope = text(&p, "scope")?;
                if !grantable(&scope) {
                    return Err(format!("{scope} is not a scope an agent may be given"));
                }
                let grant = p.get("grant").and_then(Json::as_bool).unwrap_or(true);
                let key = *self.by_name.get(&name).ok_or("an unknown agent")?;
                if let Some(a) = self.agents.get_mut(&key) {
                    a.scopes.retain(|s| s != &scope);
                    if grant {
                        a.scopes.push(scope);
                    }
                }
            }
            _ => {}
        }
        Ok(())
    }

    /// Check that `e` is signed by the owner's current identity; returns it.
    fn owner_signed(&self, e: &Event) -> Result<Identity, String> {
        let owner = self.owner().ok_or("no owner is recorded")?.clone();
        if e.auth.key != Some(owner.hash().0) {
            return Err("not signed by the owner's current identity".into());
        }
        check_proof(e, &owner)?;
        Ok(owner)
    }

    /// An event from a Radar session: its proof is the owner's signed
    /// request for the sign-in link, so it must verify against the owner,
    /// and only the owner acts this way.
    pub fn check_session(&self, e: &Event) -> Result<(), String> {
        let key = crate::identity::KeyId(e.auth.key.ok_or("a session event names no key")?);
        if !matches!(self.principal(&key, e.hlc.wall_ms)?, Principal::Owner { .. }) || e.actor != "human" {
            return Err("only the owner acts through a Radar session".into());
        }
        let identity = self.identity(&key).ok_or("an unknown key")?;
        let proof = Proof::decode(e.auth.proof.as_deref().ok_or("no proof")?)?;
        if proof.key() != key.0 || proof.method != "POST /radar/link" {
            return Err("the session's proof is not the owner's sign-in request".into());
        }
        proof.verify(identity, None)
    }

    /// Check a signed event's proof against the principal its key was at
    /// the event's time.
    pub fn check_signed(&self, e: &Event) -> Result<(), String> {
        let key = crate::identity::KeyId(e.auth.key.ok_or("signed, but names no key")?);
        let who = self.principal(&key, e.hlc.wall_ms)?;
        // The actor an event names must be the principal that signed it:
        // an agent's key never makes an event in another's name.
        if who.actor() != e.actor {
            return Err(format!("names {} as its actor but is signed by {}", e.actor, who.display()));
        }
        let identity = self.identity(&key).ok_or("an unknown key")?;
        check_proof(e, identity)
    }
}

impl KeyResolver for Principals {
    fn check(&mut self, e: &Event) -> Result<(), String> {
        match e.kind.as_str() {
            "identity.owner" | "identity.rotated" | "identity.instance" | "agent.added" | "agent.disabled" | "agent.scoped" => {
                if e.auth.method != Method::Signature {
                    return Err(format!("{} must be signed", e.kind));
                }
                self.observe(e)
            }
            "agent.uid_bound" => self.observe(e),
            _ if matches!(e.auth.method, Method::Signature | Method::Passkey) => self.check_signed(e),
            _ if e.auth.method == Method::Session => self.check_session(e),
            _ => Ok(()),
        }
    }
}

/// Apply identity and agent events to the projection tables.
pub async fn project(conn: &mut SqliteConnection, e: &Event) -> sqlx::Result<()> {
    if e.kind == "agent.uid_bound" {
        let p = e.json();
        sqlx::query("UPDATE agents SET uid = ? WHERE name = ? AND uid IS NULL")
            .bind(p.get("uid").and_then(Json::as_i64))
            .bind(p.get("name").and_then(Json::as_str))
            .execute(&mut *conn)
            .await?;
        return Ok(());
    }
    // Who is who is only ever said by a signature; `verify` checks which.
    if e.auth.method != Method::Signature {
        return Ok(());
    }
    let p = e.json();
    let id = |p: &Json| identity_of(p).ok();
    match e.kind.as_str() {
        "identity.owner" | "identity.rotated" | "identity.instance" => {
            let Some(identity) = id(&p) else { return Ok(()) };
            let role = if e.kind == "identity.instance" { "instance" } else { "owner" };
            sqlx::query("UPDATE identities SET current = 0 WHERE role = ?").bind(role).execute(&mut *conn).await?;
            sqlx::query(
                "INSERT OR REPLACE INTO identities (key, role, name, identity, previous, current, seq) VALUES (?, ?, ?, ?, ?, 1, ?)",
            )
            .bind(identity.hash().to_hex())
            .bind(role)
            .bind(&identity.name)
            .bind(identity.encode())
            .bind(identity.previous.map(|k| k.to_hex()))
            .bind(e.seq as i64)
            .execute(&mut *conn)
            .await?;
        }
        "agent.added" => {
            let Some(identity) = id(&p) else { return Ok(()) };
            if p.get("name").and_then(Json::as_str).is_none_or(str::is_empty) {
                return Ok(());
            }
            let s = |k: &str| p.get(k).and_then(Json::as_str).unwrap_or("").to_string();
            sqlx::query(
                "INSERT OR REPLACE INTO agents (name, key, owner, owner_name, kind, project, home, uid, learn_uid, scopes, created_ms, disabled_ms, seq) \
                 VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, NULL, ?)",
            )
            .bind(s("name"))
            .bind(identity.hash().to_hex())
            .bind(s("owner"))
            .bind(s("owner_name"))
            .bind(s("kind"))
            .bind(s("project"))
            .bind(s("home"))
            .bind(p.get("uid").and_then(Json::as_i64))
            .bind(p.get("learn_uid").and_then(Json::as_bool).unwrap_or(false))
            .bind(p.get("scopes").map(|v| v.to_string()).unwrap_or_else(|| "[]".into()))
            .bind(e.at_ms as i64)
            .bind(e.seq as i64)
            .execute(&mut *conn)
            .await?;
            sqlx::query(
                "INSERT OR REPLACE INTO identities (key, role, name, identity, previous, current, seq) VALUES (?, 'agent', ?, ?, ?, 1, ?)",
            )
            .bind(identity.hash().to_hex())
            .bind(&identity.name)
            .bind(identity.encode())
            .bind(identity.previous.map(|k| k.to_hex()))
            .bind(e.seq as i64)
            .execute(&mut *conn)
            .await?;
        }
        "agent.disabled" => {
            sqlx::query("UPDATE agents SET disabled_ms = ? WHERE name = ?")
                .bind(e.at_ms as i64)
                .bind(p.get("name").and_then(Json::as_str))
                .execute(&mut *conn)
                .await?;
        }
        "agent.scoped" if e.actor == "human" => {
            let (Some(name), Some(scope)) = (p.get("name").and_then(Json::as_str), p.get("scope").and_then(Json::as_str)) else {
                return Ok(());
            };
            if !grantable(scope) {
                return Ok(());
            }
            let grant = p.get("grant").and_then(Json::as_bool).unwrap_or(true);
            let current: Option<String> =
                sqlx::query_scalar("SELECT scopes FROM agents WHERE name = ?").bind(name).fetch_optional(&mut *conn).await?;
            let mut scopes: Vec<String> = current.and_then(|s| serde_json::from_str(&s).ok()).unwrap_or_default();
            scopes.retain(|s| s != scope);
            if grant {
                scopes.push(scope.to_string());
            }
            sqlx::query("UPDATE agents SET scopes = ? WHERE name = ?")
                .bind(serde_json::to_string(&scopes).unwrap_or_default())
                .bind(name)
                .execute(&mut *conn)
                .await?;
        }
        _ => {}
    }
    Ok(())
}

/// A scope the owner may give an agent (spec §8.4): never the owner's own
/// authority, only reach.
pub fn grantable(scope: &str) -> bool {
    match scope.strip_prefix("channel:") {
        Some(ch) => !ch.is_empty() && ch.len() <= 64 && ch.bytes().all(|b| b.is_ascii_lowercase() || b.is_ascii_digit() || b == b'-'),
        None => matches!(scope, "projects:all" | "schedule:any" | "webhooks:read"),
    }
}

/// The payload of an identity event for `identity`.
pub fn identity_payload(identity: &Identity) -> Json {
    serde_json::json!({ "key": identity.hash().to_hex(), "name": identity.name, "identity": hex::encode(identity.encode()) })
}

fn identity_of(p: &Json) -> Result<Identity, String> {
    let b = p.get("identity").and_then(Json::as_str).and_then(|h| hex::decode(h).ok()).ok_or("no identity in the event")?;
    Identity::decode(&b).map_err(|e| format!("malformed identity: {e}"))
}

fn text(p: &Json, k: &str) -> Result<String, String> {
    p.get(k).and_then(Json::as_str).map(String::from).ok_or_else(|| format!("no {k}"))
}

fn self_signed(e: &Event, id: &Identity) -> Result<(), String> {
    if e.auth.key != Some(id.hash().0) {
        return Err("not signed by the identity it records".into());
    }
    check_proof(e, id)
}

/// The event's proof verifies against `identity`, and a CLI proof covers
/// exactly the event's payload.
fn check_proof(e: &Event, identity: &Identity) -> Result<(), String> {
    let proof = Proof::decode(e.auth.proof.as_deref().ok_or("no proof")?)?;
    if proof.key() != identity.hash().0 {
        return Err("the proof is by another key".into());
    }
    let body = (proof.method == "cli").then(|| e.payload.as_deref().unwrap_or(b""));
    proof.verify(identity, body)
}

/// A successor of the owner must keep the key pair and chain back to the
/// current identity through `previous` (the intermediate identities, if
/// any, are carried in the event as `chain`).
fn accept_successor(cur: &Identity, new: &Identity, p: &Json) -> Result<(), String> {
    if new.ed25519_pk != cur.ed25519_pk || new.mldsa65_pk != cur.mldsa65_pk {
        return Err("a successor with a fresh key pair needs `oxy identity rotate`'s attestation, not accepted in 0.1".into());
    }
    let chain: Vec<Identity> = p
        .get("chain")
        .and_then(Json::as_array)
        .map(|a| a.iter().filter_map(|h| h.as_str().and_then(|h| hex::decode(h).ok()).and_then(|b| Identity::decode(&b).ok())).collect())
        .unwrap_or_default();
    let mut at = new.clone();
    for _ in 0..=chain.len() {
        match at.previous {
            Some(prev) if prev == cur.hash() => return Ok(()),
            Some(prev) => match chain.iter().find(|i| i.hash() == prev) {
                Some(i) if i.ed25519_pk == cur.ed25519_pk => at = i.clone(),
                _ => break,
            },
            None => break,
        }
    }
    Err("does not succeed the recorded owner".into())
}

/// An event signed by `pair` from the command line: its proof covers the
/// canonical payload, so the event's content is bound to the signature.
pub fn signed_event(pair: &crate::keys::KeyPair, actor: &str, kind: &str, payload: Json) -> crate::event::NewEvent {
    let body = crate::event::canonical_json(&payload);
    let proof = Proof::sign(pair, "cli", &body);
    crate::event::NewEvent::system(kind, payload)
        .by(actor, crate::event::Auth { key: Some(pair.key.0), method: Method::Signature, assurance: 2, proof: Some(proof.encode()) })
}