//! Encrypted peer-discovery handshake via Nostr NIP-44.
//!
//! Goals:
//! - A node can opt in to being *discoverable* on Nostr by publishing a
//!   minimal presence event (DID + nostr pubkey, NIP-33 kind 30078). The
//!   presence event NEVER contains the onion address, the federation list,
//!   the app inventory, or anything beyond a DID + nostr pubkey + version.
//! - Another node that sees the presence event can send an encrypted
//!   `PeerRequest` (NIP-44 DM, kind 4) asking to peer. The request also
//!   does NOT contain the requester's onion — it carries only the DID
//!   the requester claims, an optional friendly name, and an optional
//!   one-line message.
//! - The recipient does NOT auto-accept and does NOT auto-respond.
//!   Instead, the request is queued in `federation::pending` for the
//!   user to manually approve or reject in the Federation UI.
//! - On approval, the recipient generates a one-shot federation invite
//!   code (which contains *their* onion + pubkey) and ships it back via
//!   NIP-44 encrypted to the requester's nostr pubkey. The requester's
//!   poll loop receives the invite, applies it via the existing
//!   `federation.join` flow, and the two boxes complete the trust
//!   exchange over Tor — never over a public relay.
//!
//! Result: the only thing ever visible on a public Nostr relay is the
//! presence event (a DID + a npub + a version). Everything actionable
//! lives inside NIP-44 ciphertext addressed to a specific nostr pubkey.

use anyhow::{Context, Result};
use nostr_sdk::prelude::*;
use serde::{Deserialize, Serialize};
use std::net::SocketAddr;
use std::path::Path;
use std::time::Duration;
use tokio::fs;
use tracing::warn;

const NOSTR_SECRET_FILE: &str = "nostr_secret";

/// Message types exchanged inside NIP-44 encrypted DMs (kind 4).
///
/// Note: NONE of these variants carry an onion address. The onion is only
/// transmitted as part of a `PeerInvite { invite_code }`, where the invite
/// code is generated by the local approval flow and points at the local
/// federation hidden service. The legacy `connect-request` / `connect-response`
/// variants from earlier development are preserved on the deserialize side
/// (`#[serde(other)]`-style fallback via untagged Unknown) so that an old
/// peer that hasn't been upgraded yet can't crash the parser, but we no
/// longer construct or act on them.
#[derive(Debug, Clone, Serialize, Deserialize)]
#[serde(tag = "type")]
pub enum HandshakeMessage {
    /// Inbound peer-discovery request. The sender proves they hold the
    /// nostr secret key by signing the kind-4 envelope (Nostr does this
    /// at the protocol layer). They claim a `from_did` here, but we do
    /// not trust it until the federation invite round-trip completes.
    #[serde(rename = "peer-request")]
    PeerRequest {
        from_did: String,
        version: String,
        name: Option<String>,
        message: Option<String>,
    },
    /// Approval reply: contains a one-shot federation invite code
    /// generated by the approver. The invite code embeds the approver's
    /// onion + pubkey, but the whole envelope is NIP-44 encrypted to the
    /// requester's nostr pubkey, so only the requester can read it.
    #[serde(rename = "peer-invite")]
    PeerInvite { invite_code: String },
    /// Rejection reply. Optional one-line reason for the user.
    #[serde(rename = "peer-reject")]
    PeerReject { reason: Option<String> },
    /// Cancellation of a previously-sent `PeerRequest`. Sent by the
    /// original requester to withdraw the handshake before the target
    /// has approved/rejected it. The recipient removes the matching
    /// inbound pending row so it no longer shows in their UI.
    #[serde(rename = "peer-cancel")]
    PeerCancel {
        /// Optional one-line reason (shown in the target's UI if they
        /// still have the row). Typically empty.
        reason: Option<String>,
    },
}

/// Result of polling for incoming handshake messages
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct IncomingHandshake {
    /// Sender's Nostr public key in hex
    pub from_nostr_pubkey: String,
    /// Sender's Nostr public key in bech32 npub format (NIP-19)
    pub from_nostr_npub: String,
    pub message: HandshakeMessage,
    pub timestamp: String,
}

/// Parse "host:port" to SocketAddr.
fn parse_proxy_addr(s: &str) -> Option<SocketAddr> {
    s.trim().parse().ok()
}

/// Load existing Nostr keys (secp256k1). Returns None if no keys exist.
async fn load_nostr_keys(identity_dir: &Path) -> Result<Option<Keys>> {
    let secret_path = identity_dir.join(NOSTR_SECRET_FILE);
    if !secret_path.exists() {
        return Ok(None);
    }
    let hex_secret = fs::read_to_string(&secret_path)
        .await
        .context("Failed to read Nostr secret")?;
    let keys = Keys::parse(hex_secret.trim()).context("Invalid Nostr secret")?;
    Ok(Some(keys))
}

/// Build a Nostr client with optional Tor proxy.
fn build_client(keys: Keys, tor_proxy: Option<&str>) -> Result<Client> {
    let client = if let Some(proxy_str) = tor_proxy {
        let addr = parse_proxy_addr(proxy_str)
            .ok_or_else(|| anyhow::anyhow!("Invalid Nostr Tor proxy: {}", proxy_str))?;
        let connection = Connection::new().proxy(addr).target(ConnectionTarget::All);
        let opts = ClientOptions::new().connection(connection);
        Client::builder().signer(keys).opts(opts).build()
    } else {
        Client::new(keys)
    };
    Ok(client)
}

/// Publish a presence-only event to Nostr relays.
/// Content: { did, nostr_pubkey, version } — NO onion address.
/// Uses NIP-33 replaceable events (kind 30078) with d-tag "archipelago-node".
pub async fn publish_presence(
    identity_dir: &Path,
    did: &str,
    version: &str,
    relays: &[String],
    tor_proxy: Option<&str>,
) -> Result<()> {
    if relays.is_empty() {
        anyhow::bail!("No relays configured");
    }

    let keys = load_nostr_keys(identity_dir)
        .await?
        .ok_or_else(|| anyhow::anyhow!("No Nostr keys — generate them first"))?;

    let nostr_pubkey = keys.public_key().to_hex();
    let nostr_npub = keys.public_key().to_bech32().unwrap_or_default();
    let client = build_client(keys, tor_proxy)?;

    let content = serde_json::json!({
        "did": did,
        "nostr_pubkey": nostr_pubkey,
        "nostr_npub": nostr_npub,
        "version": version,
        // No onion address — exchanged only via encrypted DM
    })
    .to_string();

    for url in relays {
        let _ = client.add_relay(url).await;
    }
    if tokio::time::timeout(Duration::from_secs(10), client.connect())
        .await
        .is_err()
    {
        warn!("Nostr relay connection timed out after 10s, continuing anyway");
    }

    let builder =
        EventBuilder::new(Kind::Custom(30078), content).tag(Tag::identifier("archipelago-node"));
    let _ = client.send_event_builder(builder).await;
    client.disconnect().await;

    tracing::info!(
        "📡 Published presence (no onion) to {} relays",
        relays.len()
    );
    Ok(())
}

/// Discover other Archipelago nodes (presence-only — no onion addresses).
/// Returns Nostr pubkeys and DIDs of discoverable nodes.
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct DiscoverableNode {
    /// Nostr secp256k1 public key in hex
    pub nostr_pubkey: String,
    /// Nostr public key in bech32 npub format (NIP-19)
    pub nostr_npub: String,
    pub did: String,
    pub version: String,
}

pub async fn discover_nodes(
    _identity_dir: &Path,
    relays: &[String],
    tor_proxy: Option<&str>,
) -> Result<Vec<DiscoverableNode>> {
    if relays.is_empty() {
        return Ok(Vec::new());
    }

    let anon_keys = Keys::generate();
    let client = build_client(anon_keys, tor_proxy)?;
    for url in relays {
        let _ = client.add_relay(url).await;
    }
    if tokio::time::timeout(Duration::from_secs(10), client.connect())
        .await
        .is_err()
    {
        warn!("Nostr relay connection timed out after 10s, continuing anyway");
    }

    let filter = Filter::new()
        .kind(Kind::Custom(30078))
        .identifier("archipelago-node")
        .limit(50);
    let events = client
        .fetch_events(filter, std::time::Duration::from_secs(15))
        .await
        .map(|e| e.to_vec())
        .unwrap_or_default();
    client.disconnect().await;

    let mut nodes = Vec::new();
    for event in events {
        if let Ok(content) = serde_json::from_str::<serde_json::Value>(&event.content) {
            let nostr_pubkey = content
                .get("nostr_pubkey")
                .and_then(|v| v.as_str())
                .unwrap_or("")
                .to_string();
            let did = content
                .get("did")
                .and_then(|v| v.as_str())
                .unwrap_or("")
                .to_string();
            let version = content
                .get("version")
                .and_then(|v| v.as_str())
                .unwrap_or("0.1")
                .to_string();

            // Skip entries that still have node_address (legacy public format)
            if content.get("node_address").is_some() {
                continue;
            }

            if !nostr_pubkey.is_empty() {
                // Derive npub (bech32 NIP-19) from hex
                let nostr_npub = nostr_sdk::PublicKey::from_hex(&nostr_pubkey)
                    .ok()
                    .and_then(|pk| pk.to_bech32().ok())
                    .unwrap_or_default();
                nodes.push(DiscoverableNode {
                    nostr_pubkey,
                    nostr_npub,
                    did,
                    version,
                });
            }
        }
    }
    Ok(nodes)
}

/// Encrypt and publish a `HandshakeMessage` to a recipient's nostr pubkey.
/// Used by both the request-side (PeerRequest) and the approver-side
/// (PeerInvite / PeerReject) flows. The message is wrapped in a NIP-44 v2
/// ciphertext addressed to `recipient_nostr_pubkey` and posted as a kind-4
/// encrypted DM, so only the holder of that nostr secret key can decrypt
/// the contents. Relays only ever see the ciphertext.
async fn send_handshake_message(
    identity_dir: &Path,
    recipient_nostr_pubkey: &str,
    msg: &HandshakeMessage,
    relays: &[String],
    tor_proxy: Option<&str>,
) -> Result<()> {
    if relays.is_empty() {
        anyhow::bail!("No relays configured");
    }

    let keys = load_nostr_keys(identity_dir)
        .await?
        .ok_or_else(|| anyhow::anyhow!("No Nostr keys"))?;
    let recipient_pk =
        PublicKey::from_hex(recipient_nostr_pubkey).context("Invalid recipient Nostr pubkey")?;

    let plaintext = serde_json::to_string(msg).context("Failed to serialize handshake")?;
    let encrypted = nip44::encrypt(
        keys.secret_key(),
        &recipient_pk,
        &plaintext,
        nip44::Version::V2,
    )
    .map_err(|e| anyhow::anyhow!("NIP-44 encrypt failed: {}", e))?;

    let client = build_client(keys, tor_proxy)?;
    for url in relays {
        let _ = client.add_relay(url).await;
    }
    if tokio::time::timeout(Duration::from_secs(10), client.connect())
        .await
        .is_err()
    {
        warn!("Nostr relay connection timed out after 10s, continuing anyway");
    }

    let builder = EventBuilder::new(Kind::EncryptedDirectMessage, encrypted)
        .tag(Tag::public_key(recipient_pk));
    let _ = client.send_event_builder(builder).await;
    client.disconnect().await;
    Ok(())
}

/// Send a `PeerRequest` to a discovered node's nostr pubkey. We never
/// include an onion address — the recipient learns nothing that would let
/// them dial us directly. They learn only our claimed DID, version,
/// optional friendly name, and the optional message.
pub async fn send_peer_request(
    identity_dir: &Path,
    recipient_nostr_pubkey: &str,
    our_did: &str,
    our_version: &str,
    our_name: Option<&str>,
    message: Option<&str>,
    relays: &[String],
    tor_proxy: Option<&str>,
) -> Result<()> {
    let msg = HandshakeMessage::PeerRequest {
        from_did: our_did.to_string(),
        version: our_version.to_string(),
        name: our_name.map(String::from),
        message: message.map(String::from),
    };
    send_handshake_message(
        identity_dir,
        recipient_nostr_pubkey,
        &msg,
        relays,
        tor_proxy,
    )
    .await?;
    tracing::info!(
        "🤝 Sent peer-request to {}...{}",
        &recipient_nostr_pubkey[..8.min(recipient_nostr_pubkey.len())],
        &recipient_nostr_pubkey[recipient_nostr_pubkey.len().saturating_sub(4)..]
    );
    Ok(())
}

/// Send a `PeerInvite` reply containing a one-shot federation invite code.
/// The code embeds our onion + pubkey, but the entire envelope is NIP-44
/// encrypted to the requester's nostr pubkey, so the onion is only ever
/// readable by them.
pub async fn send_peer_invite(
    identity_dir: &Path,
    recipient_nostr_pubkey: &str,
    invite_code: &str,
    relays: &[String],
    tor_proxy: Option<&str>,
) -> Result<()> {
    let msg = HandshakeMessage::PeerInvite {
        invite_code: invite_code.to_string(),
    };
    send_handshake_message(
        identity_dir,
        recipient_nostr_pubkey,
        &msg,
        relays,
        tor_proxy,
    )
    .await?;
    tracing::info!(
        "🤝 Sent peer-invite to {}...{}",
        &recipient_nostr_pubkey[..8.min(recipient_nostr_pubkey.len())],
        &recipient_nostr_pubkey[recipient_nostr_pubkey.len().saturating_sub(4)..]
    );
    Ok(())
}

/// Send a `PeerReject` reply with an optional reason.
pub async fn send_peer_reject(
    identity_dir: &Path,
    recipient_nostr_pubkey: &str,
    reason: Option<&str>,
    relays: &[String],
    tor_proxy: Option<&str>,
) -> Result<()> {
    let msg = HandshakeMessage::PeerReject {
        reason: reason.map(String::from),
    };
    send_handshake_message(
        identity_dir,
        recipient_nostr_pubkey,
        &msg,
        relays,
        tor_proxy,
    )
    .await?;
    tracing::info!(
        "🚫 Sent peer-reject to {}...{}",
        &recipient_nostr_pubkey[..8.min(recipient_nostr_pubkey.len())],
        &recipient_nostr_pubkey[recipient_nostr_pubkey.len().saturating_sub(4)..]
    );
    Ok(())
}

/// Send a `PeerCancel` notice to withdraw a previously-sent PeerRequest.
/// The recipient will drop their matching inbound pending row.
pub async fn send_peer_cancel(
    identity_dir: &Path,
    recipient_nostr_pubkey: &str,
    reason: Option<&str>,
    relays: &[String],
    tor_proxy: Option<&str>,
) -> Result<()> {
    let msg = HandshakeMessage::PeerCancel {
        reason: reason.map(String::from),
    };
    send_handshake_message(
        identity_dir,
        recipient_nostr_pubkey,
        &msg,
        relays,
        tor_proxy,
    )
    .await?;
    tracing::info!(
        "↩️  Sent peer-cancel to {}...{}",
        &recipient_nostr_pubkey[..8.min(recipient_nostr_pubkey.len())],
        &recipient_nostr_pubkey[recipient_nostr_pubkey.len().saturating_sub(4)..]
    );
    Ok(())
}

/// Poll relays for incoming encrypted handshake DMs addressed to us.
/// Returns new handshake messages since `since` timestamp.
pub async fn poll_handshakes(
    identity_dir: &Path,
    relays: &[String],
    tor_proxy: Option<&str>,
    since: Option<Timestamp>,
) -> Result<Vec<IncomingHandshake>> {
    if relays.is_empty() {
        return Ok(Vec::new());
    }

    let keys = load_nostr_keys(identity_dir)
        .await?
        .ok_or_else(|| anyhow::anyhow!("No Nostr keys"))?;

    let our_pk = keys.public_key();
    let client = build_client(keys.clone(), tor_proxy)?;
    for url in relays {
        let _ = client.add_relay(url).await;
    }
    if tokio::time::timeout(Duration::from_secs(10), client.connect())
        .await
        .is_err()
    {
        warn!("Nostr relay connection timed out after 10s, continuing anyway");
    }

    // Query for encrypted DMs addressed to us
    let mut filter = Filter::new()
        .kind(Kind::EncryptedDirectMessage)
        .pubkey(our_pk)
        .limit(50);
    if let Some(ts) = since {
        filter = filter.since(ts);
    }

    let events = client
        .fetch_events(filter, std::time::Duration::from_secs(15))
        .await
        .map(|e| e.to_vec())
        .unwrap_or_default();
    client.disconnect().await;

    let mut handshakes = Vec::new();
    for event in events {
        // Skip our own events
        if event.pubkey == our_pk {
            continue;
        }

        // Try NIP-44 decryption
        let plaintext = match nip44::decrypt(keys.secret_key(), &event.pubkey, &event.content) {
            Ok(pt) => pt,
            Err(_) => continue, // Not a handshake message or wrong key
        };

        // Try to parse as HandshakeMessage
        if let Ok(msg) = serde_json::from_str::<HandshakeMessage>(&plaintext) {
            let from_npub = event.pubkey.to_bech32().unwrap_or_default();
            handshakes.push(IncomingHandshake {
                from_nostr_pubkey: event.pubkey.to_hex(),
                from_nostr_npub: from_npub,
                message: msg,
                timestamp: event.created_at.to_human_datetime(),
            });
        }
    }

    Ok(handshakes)
}