//! Cached Bitcoin node status for browser UIs.
//!
//! The bitcoin-ui should not poll Bitcoin RPC directly for display state.
//! During container restarts, reindexing, and IBD, direct browser RPC polling
//! turns short RPC gaps into visible UI failures. This module owns the RPC
//! polling loop, caches the last successful snapshot, and serves stale-but-known
//! state while the node is reconnecting.

use anyhow::{Context, Result};
use serde::Serialize;
use std::sync::OnceLock;
use std::time::{Duration, SystemTime, UNIX_EPOCH};
use tokio::sync::RwLock;
use tracing::{debug, warn};

const CACHE_REFRESH_SECS: u64 = 10;
const CACHE_ERROR_BACKOFF_SECS: u64 = 15;

#[derive(Debug, Clone, Serialize)]
pub struct BitcoinNodeStatus {
    pub ok: bool,
    pub stale: bool,
    pub updated_at_ms: u64,
    pub error: Option<String>,
    pub blockchain_info: Option<serde_json::Value>,
    pub network_info: Option<serde_json::Value>,
    pub index_info: Option<serde_json::Value>,
    pub zmq_notifications: Option<serde_json::Value>,
}

impl Default for BitcoinNodeStatus {
    fn default() -> Self {
        Self {
            ok: false,
            stale: false,
            updated_at_ms: 0,
            error: Some("Connecting to Bitcoin node...".to_string()),
            blockchain_info: None,
            network_info: None,
            index_info: None,
            zmq_notifications: None,
        }
    }
}

static STATUS_CACHE: OnceLock<RwLock<BitcoinNodeStatus>> = OnceLock::new();

fn cache() -> &'static RwLock<BitcoinNodeStatus> {
    STATUS_CACHE.get_or_init(|| RwLock::new(BitcoinNodeStatus::default()))
}

fn now_ms() -> u64 {
    SystemTime::now()
        .duration_since(UNIX_EPOCH)
        .unwrap_or_default()
        .as_millis() as u64
}

fn transient_error(err_msg: &str) -> bool {
    let lower = err_msg.to_lowercase();
    lower.contains("connect")
        || lower.contains("reset")
        || lower.contains("refused")
        || lower.contains("timed out")
        || lower.contains("timeout")
        || lower.contains("broken pipe")
        || lower.contains("eof")
        || lower.contains("500 internal server error")
        || lower.contains("503 service unavailable")
        || lower.contains("work queue depth exceeded")
        || lower.contains("decode bitcoin rpc json")
        || lower.contains("error decoding response body")
        || lower.contains("expected value at line 1 column 1")
}

fn friendly_transient_error(has_cached_state: bool, err_msg: &str) -> String {
    let detail = err_msg
        .lines()
        .next()
        .unwrap_or(err_msg)
        .trim()
        .trim_end_matches('.');
    let lower = detail.to_lowercase();
    let state = if lower.contains("verifying blocks") {
        "verifying blocks after restart"
    } else if lower.contains("connection refused") || lower.contains("tcp connect error") {
        "waiting for the Bitcoin RPC listener"
    } else if lower.contains("timed out") || lower.contains("timeout") {
        "busy and not answering RPC before the timeout"
    } else {
        "starting or busy syncing"
    };

    if has_cached_state {
        format!("Bitcoin node is {state}; showing last known state and retrying. Detail: {detail}")
    } else {
        format!("Bitcoin node is {state}; retrying automatically. Detail: {detail}")
    }
}

pub fn spawn_status_cache() {
    tokio::spawn(async {
        loop {
            let fresh = fetch_bitcoin_status().await;
            let mut cached = cache().write().await;
            let mut sleep_secs = CACHE_REFRESH_SECS;
            match fresh {
                Ok(mut status) => {
                    status.ok = true;
                    status.stale = false;
                    status.error = None;
                    *cached = status;
                }
                Err(e) => {
                    let err_msg = format!("{e:#}");
                    if transient_error(&err_msg) {
                        debug!("Bitcoin status: transient RPC failure: {}", err_msg);
                    } else {
                        warn!("Bitcoin status: RPC failure: {}", err_msg);
                    }
                    sleep_secs = CACHE_ERROR_BACKOFF_SECS;

                    if cached.blockchain_info.is_some() {
                        cached.ok = false;
                        cached.stale = true;
                        cached.error = Some(friendly_transient_error(true, &err_msg));
                    } else {
                        *cached = BitcoinNodeStatus {
                            ok: false,
                            stale: false,
                            updated_at_ms: now_ms(),
                            error: Some(friendly_transient_error(false, &err_msg)),
                            ..BitcoinNodeStatus::default()
                        };
                    }
                }
            }
            drop(cached);
            tokio::time::sleep(Duration::from_secs(sleep_secs)).await;
        }
    });
}

pub async fn get_bitcoin_status() -> BitcoinNodeStatus {
    cache().read().await.clone()
}

async fn fetch_bitcoin_status() -> Result<BitcoinNodeStatus> {
    let client = reqwest::Client::builder()
        .timeout(Duration::from_secs(20))
        .build()
        .context("build Bitcoin status HTTP client")?;

    let blockchain_info = bitcoin_rpc_call(&client, "getblockchaininfo", serde_json::json!([]))
        .await
        .context("getblockchaininfo")?;
    let network_info = bitcoin_rpc_call(&client, "getnetworkinfo", serde_json::json!([]))
        .await
        .context("getnetworkinfo")
        .ok();
    let index_info = bitcoin_rpc_call(&client, "getindexinfo", serde_json::json!([]))
        .await
        .context("getindexinfo")
        .ok();
    let zmq_notifications = bitcoin_rpc_call(&client, "getzmqnotifications", serde_json::json!([]))
        .await
        .context("getzmqnotifications")
        .ok();

    Ok(BitcoinNodeStatus {
        ok: true,
        stale: false,
        updated_at_ms: now_ms(),
        error: None,
        blockchain_info: Some(blockchain_info),
        network_info,
        index_info,
        zmq_notifications,
    })
}

async fn bitcoin_rpc_call(
    client: &reqwest::Client,
    method: &str,
    params: serde_json::Value,
) -> Result<serde_json::Value> {
    let (rpc_user, rpc_pass) = crate::bitcoin_rpc::bitcoin_rpc_credentials().await;
    let body = serde_json::json!({
        "jsonrpc": "1.0",
        "id": "bitcoin-status",
        "method": method,
        "params": params,
    });

    let resp = client
        .post(crate::constants::BITCOIN_RPC_URL)
        .basic_auth(rpc_user, Some(rpc_pass))
        .header("Content-Type", "application/json")
        .json(&body)
        .send()
        .await
        .context("Bitcoin RPC request failed")?;

    let status = resp.status();
    let json: serde_json::Value = resp.json().await.context("decode Bitcoin RPC JSON")?;
    if !status.is_success() {
        anyhow::bail!("Bitcoin RPC returned {}: {}", status, json);
    }
    if let Some(error) = json.get("error").filter(|e| !e.is_null()) {
        anyhow::bail!("Bitcoin RPC {} error: {}", method, error);
    }
    json.get("result")
        .cloned()
        .context("missing Bitcoin RPC result")
}

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

    #[test]
    fn explains_verifying_blocks_without_generic_timeout_copy() {
        let msg = friendly_transient_error(
            false,
            r#"getblockchaininfo: Bitcoin RPC returned 500 Internal Server Error: {"error":{"code":-28,"message":"Verifying blocks..."}}"#,
        );

        assert!(msg.contains("verifying blocks after restart"));
        assert!(msg.contains("retrying automatically"));
    }

    #[test]
    fn explains_missing_rpc_listener() {
        let msg = friendly_transient_error(
            true,
            "getblockchaininfo: tcp connect error: Connection refused (os error 111)",
        );

        assert!(msg.contains("waiting for the Bitcoin RPC listener"));
        assert!(msg.contains("showing last known state"));
    }

    #[test]
    fn explains_rpc_timeout() {
        let msg = friendly_transient_error(
            false,
            "getblockchaininfo: Bitcoin RPC request failed: operation timed out",
        );

        assert!(msg.contains("busy and not answering RPC before the timeout"));
    }
}