//! Synor Block Explorer Backend
//!
//! A REST API server that provides blockchain data for web frontends.
//! Features:
//! - Block and transaction queries with pagination
//! - Address balance and transaction history
//! - DAG visualization data
//! - Network statistics and metrics
//! - Search functionality

use std::net::SocketAddr;
use std::sync::Arc;
use std::time::Duration;

use axum::http::{HeaderValue, Method};
use axum::{
    extract::{
        ws::{Message, WebSocket, WebSocketUpgrade},
        Path, Query, State,
    },
    http::StatusCode,
    response::IntoResponse,
    routing::get,
    Json, Router,
};
use futures::{SinkExt, StreamExt};
use moka::future::Cache;
use serde::{Deserialize, Serialize};
use tower_http::compression::CompressionLayer;
use tower_http::cors::{Any, CorsLayer};
use tower_http::services::{ServeDir, ServeFile};
use tower_http::trace::TraceLayer;
use tracing::{error, info};

// ==================== Configuration ====================

/// Explorer configuration.
#[derive(Clone, Debug)]
pub struct ExplorerConfig {
    /// RPC URL of the Synor node.
    pub rpc_url: String,
    /// Server listen address.
    pub listen_addr: SocketAddr,
    /// Directory containing static frontend files.
    pub static_dir: Option<String>,
    /// Cache TTL for blocks (seconds).
    pub block_cache_ttl: u64,
    /// Cache TTL for stats (seconds).
    pub stats_cache_ttl: u64,
    /// Maximum blocks per page.
    pub max_page_size: usize,
    /// Allowed CORS origins (comma-separated, or "*" for any).
    pub cors_origins: String,
}

impl Default for ExplorerConfig {
    fn default() -> Self {
        ExplorerConfig {
            rpc_url: "http://localhost:17110".to_string(),
            listen_addr: "0.0.0.0:3000".parse().unwrap(),
            static_dir: None,
            block_cache_ttl: 60,
            stats_cache_ttl: 10,
            max_page_size: 100,
            // Default to specific production origins for security
            cors_origins: "https://explorer.synor.cc,https://wallet.synor.cc".to_string(),
        }
    }
}

impl ExplorerConfig {
    /// Load configuration from environment variables.
    pub fn from_env() -> Self {
        let mut config = ExplorerConfig::default();

        if let Ok(url) = std::env::var("SYNOR_RPC_URL") {
            config.rpc_url = url;
        }

        if let Ok(addr) = std::env::var("EXPLORER_LISTEN_ADDR") {
            if let Ok(addr) = addr.parse() {
                config.listen_addr = addr;
            }
        }

        if let Ok(dir) = std::env::var("EXPLORER_STATIC_DIR") {
            if std::path::Path::new(&dir).exists() {
                config.static_dir = Some(dir);
            }
        }

        if let Ok(ttl) = std::env::var("EXPLORER_BLOCK_CACHE_TTL") {
            if let Ok(ttl) = ttl.parse() {
                config.block_cache_ttl = ttl;
            }
        }

        if let Ok(ttl) = std::env::var("EXPLORER_STATS_CACHE_TTL") {
            if let Ok(ttl) = ttl.parse() {
                config.stats_cache_ttl = ttl;
            }
        }

        if let Ok(origins) = std::env::var("EXPLORER_CORS_ORIGINS") {
            config.cors_origins = origins;
        }

        config
    }

    /// Build CORS layer from configuration.
    pub fn cors_layer(&self) -> CorsLayer {
        if self.cors_origins == "*" {
            // Allow any origin (development/testing only)
            CorsLayer::new()
                .allow_origin(Any)
                .allow_methods(Any)
                .allow_headers(Any)
        } else {
            // Parse comma-separated origins
            let origins: Vec<HeaderValue> = self
                .cors_origins
                .split(',')
                .filter_map(|s| s.trim().parse().ok())
                .collect();

            CorsLayer::new()
                .allow_origin(origins)
                .allow_methods([Method::GET, Method::POST, Method::OPTIONS])
                .allow_headers(Any)
        }
    }
}

// ==================== Application State ====================

/// Explorer application state.
struct ExplorerState {
    config: ExplorerConfig,
    http_client: reqwest::Client,
    /// Cache for blocks by hash.
    block_cache: Cache<String, ExplorerBlock>,
    /// Cache for network stats.
    stats_cache: Cache<String, NetworkStats>,
}

impl ExplorerState {
    fn new(config: ExplorerConfig) -> Self {
        let block_cache = Cache::builder()
            .time_to_live(Duration::from_secs(config.block_cache_ttl))
            .max_capacity(10_000)
            .build();

        let stats_cache = Cache::builder()
            .time_to_live(Duration::from_secs(config.stats_cache_ttl))
            .max_capacity(100)
            .build();

        ExplorerState {
            config,
            http_client: reqwest::Client::builder()
                .timeout(Duration::from_secs(30))
                .build()
                .expect("Failed to build HTTP client"),
            block_cache,
            stats_cache,
        }
    }
}

// ==================== API Types ====================

/// Explorer block representation.
#[derive(Clone, Debug, Serialize, Deserialize)]
#[serde(rename_all = "camelCase")]
pub struct ExplorerBlock {
    pub hash: String,
    pub version: u32,
    pub parent_hashes: Vec<String>,
    pub timestamp: u64,
    pub timestamp_human: String,
    pub bits: u32,
    pub nonce: u64,
    pub daa_score: u64,
    pub blue_score: u64,
    pub blue_work: String,
    pub difficulty: f64,
    pub transaction_count: usize,
    pub is_chain_block: bool,
    #[serde(skip_serializing_if = "Option::is_none")]
    pub transactions: Option<Vec<ExplorerTransaction>>,
    pub children_hashes: Vec<String>,
    pub merge_set_blues: Vec<String>,
    pub merge_set_reds: Vec<String>,
}

/// Explorer transaction representation.
#[derive(Clone, Debug, Serialize, Deserialize)]
#[serde(rename_all = "camelCase")]
pub struct ExplorerTransaction {
    pub id: String,
    pub hash: String,
    pub version: u16,
    pub inputs: Vec<ExplorerInput>,
    pub outputs: Vec<ExplorerOutput>,
    pub lock_time: u64,
    pub mass: u64,
    pub is_coinbase: bool,
    pub total_input: u64,
    pub total_output: u64,
    pub fee: u64,
    #[serde(skip_serializing_if = "Option::is_none")]
    pub block_hash: Option<String>,
    #[serde(skip_serializing_if = "Option::is_none")]
    pub block_time: Option<u64>,
}

/// Transaction input with resolved address.
#[derive(Clone, Debug, Serialize, Deserialize)]
#[serde(rename_all = "camelCase")]
pub struct ExplorerInput {
    pub previous_tx_id: String,
    pub previous_index: u32,
    #[serde(skip_serializing_if = "Option::is_none")]
    pub address: Option<String>,
    #[serde(skip_serializing_if = "Option::is_none")]
    pub value: Option<u64>,
}

/// Transaction output with resolved address.
#[derive(Clone, Debug, Serialize, Deserialize)]
#[serde(rename_all = "camelCase")]
pub struct ExplorerOutput {
    pub value: u64,
    pub value_human: String,
    pub script_type: String,
    #[serde(skip_serializing_if = "Option::is_none")]
    pub address: Option<String>,
}

/// Address information.
#[derive(Clone, Debug, Serialize, Deserialize)]
#[serde(rename_all = "camelCase")]
pub struct AddressInfo {
    pub address: String,
    pub balance: u64,
    pub balance_human: String,
    pub utxo_count: usize,
    pub total_received: u64,
    pub total_sent: u64,
    pub transaction_count: usize,
}

/// Network statistics.
#[derive(Clone, Debug, Serialize, Deserialize)]
#[serde(rename_all = "camelCase")]
pub struct NetworkStats {
    pub network_id: String,
    pub is_synced: bool,
    pub block_count: u64,
    pub header_count: u64,
    pub tip_count: usize,
    pub virtual_daa_score: u64,
    pub difficulty: f64,
    pub hashrate: f64,
    pub hashrate_human: String,
    pub block_rate: f64,
    pub mempool_size: u64,
    pub peer_count: usize,
    pub circulating_supply: u64,
    pub circulating_supply_human: String,
    pub max_supply: u64,
}

/// DAG visualization data.
#[derive(Clone, Debug, Serialize, Deserialize)]
#[serde(rename_all = "camelCase")]
pub struct DagVisualization {
    pub blocks: Vec<DagBlock>,
    pub edges: Vec<DagEdge>,
}

/// Block for DAG visualization.
#[derive(Clone, Debug, Serialize, Deserialize)]
#[serde(rename_all = "camelCase")]
pub struct DagBlock {
    pub hash: String,
    pub short_hash: String,
    pub blue_score: u64,
    pub is_blue: bool,
    pub is_chain_block: bool,
    pub timestamp: u64,
    pub tx_count: usize,
}

/// Edge for DAG visualization.
#[derive(Clone, Debug, Serialize, Deserialize)]
#[serde(rename_all = "camelCase")]
pub struct DagEdge {
    pub from: String,
    pub to: String,
    pub is_selected_parent: bool,
}

/// Pagination parameters.
#[derive(Clone, Debug, Deserialize)]
pub struct PaginationParams {
    #[serde(default = "default_page")]
    pub page: usize,
    #[serde(default = "default_limit")]
    pub limit: usize,
}

fn default_page() -> usize {
    1
}
fn default_limit() -> usize {
    25
}

/// Paginated response.
#[derive(Clone, Debug, Serialize)]
#[serde(rename_all = "camelCase")]
pub struct PaginatedResponse<T> {
    pub data: Vec<T>,
    pub page: usize,
    pub limit: usize,
    pub total: usize,
    pub total_pages: usize,
    pub has_next: bool,
    pub has_prev: bool,
}

/// Search result.
#[derive(Clone, Debug, Serialize)]
#[serde(rename_all = "camelCase")]
pub struct SearchResult {
    pub result_type: String,
    pub value: String,
    pub redirect_url: String,
}

/// API error response.
#[derive(Debug, Serialize)]
pub struct ApiError {
    pub error: String,
    pub code: u16,
}

impl IntoResponse for ApiError {
    fn into_response(self) -> axum::response::Response {
        let status = StatusCode::from_u16(self.code).unwrap_or(StatusCode::INTERNAL_SERVER_ERROR);
        (status, Json(self)).into_response()
    }
}

// ==================== RPC Client ====================

/// JSON-RPC request.
#[derive(Serialize)]
struct RpcRequest<P> {
    jsonrpc: &'static str,
    method: String,
    params: P,
    id: u64,
}

/// JSON-RPC response.
#[derive(Deserialize)]
struct RpcResponse<R> {
    result: Option<R>,
    error: Option<RpcError>,
}

#[derive(Deserialize)]
struct RpcError {
    message: String,
}

impl ExplorerState {
    /// Make an RPC call.
    async fn rpc_call<P: Serialize, R: for<'de> Deserialize<'de>>(
        &self,
        method: &str,
        params: P,
    ) -> Result<R, ApiError> {
        let request = RpcRequest {
            jsonrpc: "2.0",
            method: method.to_string(),
            params,
            id: 1,
        };

        let response = self
            .http_client
            .post(&self.config.rpc_url)
            .json(&request)
            .send()
            .await
            .map_err(|e| {
                error!("RPC request failed: {}", e);
                ApiError {
                    error: "RPC connection failed".to_string(),
                    code: 503,
                }
            })?;

        let rpc_response: RpcResponse<R> = response.json().await.map_err(|e| {
            error!("Failed to parse RPC response: {}", e);
            ApiError {
                error: "Invalid RPC response".to_string(),
                code: 500,
            }
        })?;

        if let Some(error) = rpc_response.error {
            return Err(ApiError {
                error: error.message,
                code: 400,
            });
        }

        rpc_response.result.ok_or_else(|| ApiError {
            error: "Empty RPC response".to_string(),
            code: 500,
        })
    }
}

// ==================== Route Handlers ====================

/// Health check endpoint.
async fn health(State(state): State<Arc<ExplorerState>>) -> impl IntoResponse {
    // Check RPC connection by making a simple RPC call
    #[derive(Deserialize)]
    struct VersionResult {
        version: String,
    }
    let rpc_ok = state
        .rpc_call::<_, VersionResult>("synor_getServerVersion", ())
        .await
        .is_ok();

    #[derive(Serialize)]
    #[serde(rename_all = "camelCase")]
    struct Health {
        healthy: bool,
        rpc_connected: bool,
    }

    let status = if rpc_ok {
        StatusCode::OK
    } else {
        StatusCode::SERVICE_UNAVAILABLE
    };

    (
        status,
        Json(Health {
            healthy: rpc_ok,
            rpc_connected: rpc_ok,
        }),
    )
}

/// Get network statistics.
async fn get_stats(
    State(state): State<Arc<ExplorerState>>,
) -> Result<Json<NetworkStats>, ApiError> {
    // Check cache first
    if let Some(stats) = state.stats_cache.get("network_stats").await {
        return Ok(Json(stats));
    }

    // Response types matching the actual node RPC
    #[derive(Deserialize)]
    #[serde(rename_all = "camelCase")]
    struct NodeInfo {
        version: String,
        #[serde(default)]
        protocol_version: u32,
        peer_count: usize,
        block_count: u64,
        blue_score: u64,
        mempool_size: usize,
        synced: bool,
    }

    #[derive(Deserialize)]
    #[serde(rename_all = "camelCase")]
    struct MiningInfo {
        blocks: u64,
        difficulty: f64,
        networkhashps: u64,
    }

    #[derive(Deserialize)]
    #[serde(rename_all = "camelCase")]
    struct TipsResponse {
        tips: Vec<String>,
    }

    // Make parallel RPC calls using correct method names
    let info_fut = state.rpc_call::<_, NodeInfo>("synor_getInfo", ());
    let mining_fut = state.rpc_call::<_, MiningInfo>("synor_getMiningInfo", ());
    let tips_fut = state.rpc_call::<_, TipsResponse>("synor_getTips", ());

    let (info, mining, tips) = tokio::try_join!(info_fut, mining_fut, tips_fut)?;

    // Estimate block rate from difficulty (blocks per second)
    // With 100ms target block time, ~10 blocks per second
    let block_rate = 10.0;

    // Calculate estimated supply based on block count
    // Initial block reward: 100 SYNOR, halving every 210,000 blocks
    let blocks = info.block_count;
    let halvings = (blocks / 210_000).min(10) as u32;
    let circulating_supply = if blocks > 0 {
        // Approximate: sum of geometric series for each halving period
        let mut supply = 0u64;
        let mut remaining = blocks;
        for h in 0..=halvings {
            let period_blocks = remaining.min(210_000);
            let reward = (100_u64 >> h) * 100_000_000; // in sompi
            supply += period_blocks * reward;
            remaining = remaining.saturating_sub(210_000);
        }
        supply
    } else {
        0
    };

    let max_supply = 21_000_000_u64 * 100_000_000; // 21M SYNOR in sompi

    let stats = NetworkStats {
        network_id: "testnet".to_string(),
        is_synced: info.synced,
        block_count: info.block_count,
        header_count: info.block_count, // Same as block_count in this impl
        tip_count: tips.tips.len(),
        virtual_daa_score: info.blue_score,
        difficulty: mining.difficulty,
        hashrate: mining.networkhashps as f64,
        hashrate_human: format_hashrate(mining.networkhashps as f64),
        block_rate,
        mempool_size: info.mempool_size as u64,
        peer_count: info.peer_count,
        circulating_supply,
        circulating_supply_human: format_synor(circulating_supply),
        max_supply,
    };

    // Cache the result
    state
        .stats_cache
        .insert("network_stats".to_string(), stats.clone())
        .await;

    Ok(Json(stats))
}

/// Get block by hash.
async fn get_block(
    State(state): State<Arc<ExplorerState>>,
    Path(hash): Path<String>,
    Query(params): Query<IncludeTxsParam>,
) -> Result<Json<ExplorerBlock>, ApiError> {
    let include_txs = params.include_txs.unwrap_or(false);
    let cache_key = format!("{}:{}", hash, include_txs);

    // Check cache
    if let Some(block) = state.block_cache.get(&cache_key).await {
        return Ok(Json(block));
    }

    // Fetch from RPC
    #[derive(Serialize)]
    struct GetBlockParams {
        hash: String,
        include_txs: bool,
    }

    let rpc_block: synor_rpc::RpcBlock = state
        .rpc_call(
            "synor_getBlock",
            GetBlockParams {
                hash: hash.clone(),
                include_txs,
            },
        )
        .await?;

    let block = convert_rpc_block(rpc_block);

    // Cache the result
    state.block_cache.insert(cache_key, block.clone()).await;

    Ok(Json(block))
}

#[derive(Deserialize)]
struct IncludeTxsParam {
    include_txs: Option<bool>,
}

/// Get recent blocks with pagination.
async fn get_blocks(
    State(state): State<Arc<ExplorerState>>,
    Query(params): Query<PaginationParams>,
) -> Result<Json<PaginatedResponse<ExplorerBlock>>, ApiError> {
    let limit = params.limit.min(state.config.max_page_size);

    // Get block count and current blue score
    #[derive(Deserialize)]
    #[serde(rename_all = "camelCase")]
    struct BlockCount {
        block_count: u64,
    }

    #[derive(Deserialize)]
    #[serde(rename_all = "camelCase")]
    struct BlueScore {
        blue_score: u64,
    }

    let count: BlockCount = state.rpc_call("synor_getBlockCount", ()).await?;
    let score: BlueScore = state.rpc_call("synor_getBlueScore", ()).await?;

    let total = count.block_count as usize;
    if total == 0 {
        return Ok(Json(PaginatedResponse {
            data: vec![],
            page: params.page,
            limit,
            total: 0,
            total_pages: 0,
            has_next: false,
            has_prev: false,
        }));
    }

    // Fetch blocks by blue score (most recent first)
    let start_score = score.blue_score.saturating_sub((params.page.saturating_sub(1) * limit) as u64);
    let blocks_data: Vec<serde_json::Value> = state
        .rpc_call("synor_getBlocksByBlueScore", (start_score, true))
        .await
        .unwrap_or_else(|_| vec![]);

    // Convert to explorer blocks
    let blocks: Vec<ExplorerBlock> = blocks_data
        .into_iter()
        .take(limit)
        .filter_map(|b| {
            let hash = b.get("hash")?.as_str()?.to_string();
            let header = b.get("header")?;
            let timestamp = header.get("timestamp")?.as_u64()?;

            Some(ExplorerBlock {
                hash: hash.clone(),
                version: header.get("version")?.as_u64()? as u32,
                parent_hashes: header
                    .get("parents")
                    .and_then(|p| p.as_array())
                    .map(|a| a.iter().filter_map(|v| v.as_str().map(String::from)).collect())
                    .unwrap_or_default(),
                timestamp,
                timestamp_human: format_timestamp(timestamp),
                bits: header.get("bits")?.as_u64()? as u32,
                nonce: header.get("nonce")?.as_u64()?,
                daa_score: header.get("blueScore").and_then(|v| v.as_u64()).unwrap_or(0),
                blue_score: header.get("blueScore").and_then(|v| v.as_u64()).unwrap_or(0),
                blue_work: String::new(),
                difficulty: 0.0,
                transaction_count: b.get("transactions")
                    .and_then(|t| t.as_array())
                    .map(|a| a.len())
                    .unwrap_or(0),
                is_chain_block: true,
                transactions: None,
                children_hashes: vec![],
                merge_set_blues: vec![],
                merge_set_reds: vec![],
            })
        })
        .collect();

    let total_pages = total.div_ceil(limit);

    Ok(Json(PaginatedResponse {
        data: blocks,
        page: params.page,
        limit,
        total,
        total_pages,
        has_next: params.page < total_pages,
        has_prev: params.page > 1,
    }))
}

/// Get current DAG tips.
async fn get_tips(State(state): State<Arc<ExplorerState>>) -> Result<Json<Vec<String>>, ApiError> {
    #[derive(Deserialize)]
    struct TipsResponse {
        tips: Vec<String>,
    }
    let response: TipsResponse = state.rpc_call("synor_getTips", ()).await?;
    Ok(Json(response.tips))
}

/// Get transaction by ID.
async fn get_transaction(
    State(state): State<Arc<ExplorerState>>,
    Path(tx_id): Path<String>,
) -> Result<Json<ExplorerTransaction>, ApiError> {
    #[derive(Serialize)]
    struct GetTxParams {
        tx_id: String,
    }

    let rpc_tx: synor_rpc::RpcTransaction = state
        .rpc_call("synor_getTransaction", GetTxParams { tx_id })
        .await?;

    let tx = convert_rpc_transaction(rpc_tx);
    Ok(Json(tx))
}

/// Get address information.
async fn get_address(
    State(state): State<Arc<ExplorerState>>,
    Path(address): Path<String>,
) -> Result<Json<AddressInfo>, ApiError> {
    // Validate address format
    if !address.starts_with("synor1") || address.len() < 40 {
        return Err(ApiError {
            error: "Invalid address format".to_string(),
            code: 400,
        });
    }

    // Get UTXOs
    #[derive(Serialize)]
    struct GetUtxosParams {
        addresses: Vec<String>,
    }

    let utxos: Vec<synor_rpc::RpcUtxo> = state
        .rpc_call(
            "synor_getUtxosByAddresses",
            GetUtxosParams {
                addresses: vec![address.clone()],
            },
        )
        .await?;

    // Get balance
    #[derive(Serialize)]
    struct GetBalanceParams {
        address: String,
    }

    #[derive(Deserialize)]
    struct BalanceResult {
        balance: u64,
    }

    let balance: BalanceResult = state
        .rpc_call(
            "synor_getBalanceByAddress",
            GetBalanceParams {
                address: address.clone(),
            },
        )
        .await?;

    let info = AddressInfo {
        address: address.clone(),
        balance: balance.balance,
        balance_human: format_synor(balance.balance),
        utxo_count: utxos.len(),
        total_received: 0,    // Would need historical data
        total_sent: 0,        // Would need historical data
        transaction_count: 0, // Would need indexing
    };

    Ok(Json(info))
}

/// Get UTXOs for an address.
async fn get_address_utxos(
    State(state): State<Arc<ExplorerState>>,
    Path(address): Path<String>,
) -> Result<Json<Vec<synor_rpc::RpcUtxo>>, ApiError> {
    #[derive(Serialize)]
    struct GetUtxosParams {
        addresses: Vec<String>,
    }

    let utxos: Vec<synor_rpc::RpcUtxo> = state
        .rpc_call(
            "synor_getUtxosByAddresses",
            GetUtxosParams {
                addresses: vec![address],
            },
        )
        .await?;

    Ok(Json(utxos))
}

/// Get DAG visualization data.
async fn get_dag(
    State(state): State<Arc<ExplorerState>>,
    Query(params): Query<DagParams>,
) -> Result<Json<DagVisualization>, ApiError> {
    let depth = params.depth.unwrap_or(10).min(50);

    // Get tips
    #[derive(Deserialize)]
    struct TipsResponse {
        tips: Vec<String>,
    }
    let tips_resp: TipsResponse = state.rpc_call("synor_getTips", ()).await?;

    if tips_resp.tips.is_empty() {
        return Ok(Json(DagVisualization {
            blocks: vec![],
            edges: vec![],
        }));
    }

    // Get current blue score to fetch recent blocks
    #[derive(Deserialize)]
    #[serde(rename_all = "camelCase")]
    struct BlueScore {
        blue_score: u64,
    }

    let score: BlueScore = state.rpc_call("synor_getBlueScore", ()).await?;

    let mut all_hashes = std::collections::HashSet::new();
    let mut blocks = Vec::new();
    let mut edges = Vec::new();

    // Fetch blocks around the current blue score
    for i in 0..depth as u64 {
        let target_score = score.blue_score.saturating_sub(i);
        let blocks_data: Vec<serde_json::Value> = state
            .rpc_call("synor_getBlocksByBlueScore", (target_score, true))
            .await
            .unwrap_or_else(|_| vec![]);

        for b in blocks_data {
            if let Some(hash) = b.get("hash").and_then(|h| h.as_str()) {
                if all_hashes.insert(hash.to_string()) {
                    let header = b.get("header");

                    // Add edges to parents
                    if let Some(parents) = header
                        .and_then(|h| h.get("parents"))
                        .and_then(|p| p.as_array())
                    {
                        for (i, parent) in parents.iter().enumerate() {
                            if let Some(parent_hash) = parent.as_str() {
                                edges.push(DagEdge {
                                    from: hash.to_string(),
                                    to: parent_hash.to_string(),
                                    is_selected_parent: i == 0,
                                });
                            }
                        }
                    }

                    let timestamp = header
                        .and_then(|h| h.get("timestamp"))
                        .and_then(|t| t.as_u64())
                        .unwrap_or(0);

                    let blue_score_val = header
                        .and_then(|h| h.get("blueScore"))
                        .and_then(|s| s.as_u64())
                        .unwrap_or(target_score);

                    let tx_count = b
                        .get("transactions")
                        .and_then(|t| t.as_array())
                        .map(|a| a.len())
                        .unwrap_or(0);

                    blocks.push(DagBlock {
                        hash: hash.to_string(),
                        short_hash: hash.chars().take(8).collect(),
                        blue_score: blue_score_val,
                        is_blue: true,
                        is_chain_block: tips_resp.tips.contains(&hash.to_string()),
                        timestamp,
                        tx_count,
                    });
                }
            }
        }
    }

    Ok(Json(DagVisualization { blocks, edges }))
}

#[derive(Deserialize)]
struct DagParams {
    depth: Option<usize>,
}

/// Get mempool transactions.
async fn get_mempool(
    State(state): State<Arc<ExplorerState>>,
    Query(params): Query<PaginationParams>,
) -> Result<Json<PaginatedResponse<ExplorerTransaction>>, ApiError> {
    let limit = params.limit.min(state.config.max_page_size);
    let offset = (params.page.saturating_sub(1)) * limit;

    #[derive(Serialize)]
    struct GetMempoolParams {
        include_orphan_pool: bool,
        filter_tx_in_addresses: bool,
    }

    let entries: Vec<synor_rpc::RpcMempoolEntry> = state
        .rpc_call(
            "synor_getMempoolEntries",
            GetMempoolParams {
                include_orphan_pool: false,
                filter_tx_in_addresses: false,
            },
        )
        .await?;

    let total = entries.len();
    let page_entries: Vec<_> = entries.into_iter().skip(offset).take(limit).collect();

    let txs: Vec<ExplorerTransaction> = page_entries
        .into_iter()
        .map(|e| convert_rpc_transaction(e.transaction))
        .collect();

    let total_pages = total.div_ceil(limit);

    Ok(Json(PaginatedResponse {
        data: txs,
        page: params.page,
        limit,
        total,
        total_pages,
        has_next: params.page < total_pages,
        has_prev: params.page > 1,
    }))
}

/// Search for block, transaction, or address.
async fn search(
    State(state): State<Arc<ExplorerState>>,
    Query(params): Query<SearchParams>,
) -> Result<Json<SearchResult>, ApiError> {
    let query = params.q.trim();

    if query.is_empty() {
        return Err(ApiError {
            error: "Search query is required".to_string(),
            code: 400,
        });
    }

    // Check if it's an address
    if query.starts_with("synor1") {
        return Ok(Json(SearchResult {
            result_type: "address".to_string(),
            value: query.to_string(),
            redirect_url: format!("/address/{}", query),
        }));
    }

    // Check if it's a hex hash (64 chars)
    if query.len() == 64 && query.chars().all(|c| c.is_ascii_hexdigit()) {
        // Try as block hash first
        #[derive(Serialize)]
        struct GetBlockParams {
            hash: String,
            include_txs: bool,
        }

        let block_result: Result<synor_rpc::RpcBlock, _> = state
            .rpc_call(
                "synor_getBlock",
                GetBlockParams {
                    hash: query.to_string(),
                    include_txs: false,
                },
            )
            .await;

        if block_result.is_ok() {
            return Ok(Json(SearchResult {
                result_type: "block".to_string(),
                value: query.to_string(),
                redirect_url: format!("/block/{}", query),
            }));
        }

        // Try as transaction ID
        #[derive(Serialize)]
        struct GetTxParams {
            tx_id: String,
        }

        let tx_result: Result<synor_rpc::RpcTransaction, _> = state
            .rpc_call(
                "synor_getTransaction",
                GetTxParams {
                    tx_id: query.to_string(),
                },
            )
            .await;

        if tx_result.is_ok() {
            return Ok(Json(SearchResult {
                result_type: "transaction".to_string(),
                value: query.to_string(),
                redirect_url: format!("/tx/{}", query),
            }));
        }
    }

    Err(ApiError {
        error: "No matching block, transaction, or address found".to_string(),
        code: 404,
    })
}

#[derive(Deserialize)]
struct SearchParams {
    q: String,
}

// ==================== Helper Functions ====================

/// Convert RPC block to explorer block.
fn convert_rpc_block(rpc: synor_rpc::RpcBlock) -> ExplorerBlock {
    let verbose = rpc.verbose_data.as_ref();

    ExplorerBlock {
        hash: rpc.header.hash.clone(),
        version: rpc.header.version,
        parent_hashes: rpc.header.parent_hashes,
        timestamp: rpc.header.timestamp,
        timestamp_human: format_timestamp(rpc.header.timestamp),
        bits: rpc.header.bits,
        nonce: rpc.header.nonce,
        daa_score: rpc.header.daa_score,
        blue_score: rpc.header.blue_score,
        blue_work: rpc.header.blue_work,
        difficulty: verbose.map(|v| v.difficulty).unwrap_or(0.0),
        transaction_count: rpc.transactions.len(),
        is_chain_block: verbose.map(|v| v.is_chain_block).unwrap_or(true),
        transactions: Some(
            rpc.transactions
                .into_iter()
                .map(convert_rpc_transaction)
                .collect(),
        ),
        children_hashes: verbose
            .map(|v| v.children_hashes.clone())
            .unwrap_or_default(),
        merge_set_blues: verbose
            .map(|v| v.merge_set_blues_hashes.clone())
            .unwrap_or_default(),
        merge_set_reds: verbose
            .map(|v| v.merge_set_reds_hashes.clone())
            .unwrap_or_default(),
    }
}

/// Convert RPC transaction to explorer transaction.
fn convert_rpc_transaction(rpc: synor_rpc::RpcTransaction) -> ExplorerTransaction {
    let verbose = rpc.verbose_data.as_ref();

    let is_coinbase = rpc.inputs.is_empty()
        || rpc
            .inputs
            .first()
            .map(|i| i.previous_outpoint.transaction_id.chars().all(|c| c == '0'))
            .unwrap_or(false);

    let total_output: u64 = rpc.outputs.iter().map(|o| o.value).sum();
    let total_input: u64 = rpc
        .inputs
        .iter()
        .filter_map(|i| i.verbose_data.as_ref().map(|v| v.value))
        .sum();

    let fee = if is_coinbase {
        0
    } else {
        total_input.saturating_sub(total_output)
    };

    ExplorerTransaction {
        id: verbose
            .as_ref()
            .map(|v| v.transaction_id.clone())
            .unwrap_or_default(),
        hash: verbose.as_ref().map(|v| v.hash.clone()).unwrap_or_default(),
        version: rpc.version,
        inputs: rpc
            .inputs
            .into_iter()
            .map(|i| ExplorerInput {
                previous_tx_id: i.previous_outpoint.transaction_id,
                previous_index: i.previous_outpoint.index,
                address: i.verbose_data.as_ref().and_then(|v| v.address.clone()),
                value: i.verbose_data.as_ref().map(|v| v.value),
            })
            .collect(),
        outputs: rpc
            .outputs
            .into_iter()
            .map(|o| ExplorerOutput {
                value: o.value,
                value_human: format_synor(o.value),
                script_type: o
                    .verbose_data
                    .as_ref()
                    .map(|v| v.script_type.clone())
                    .unwrap_or_else(|| "unknown".to_string()),
                address: o.verbose_data.and_then(|v| v.address),
            })
            .collect(),
        lock_time: rpc.lock_time,
        mass: verbose.as_ref().map(|v| v.mass).unwrap_or(0),
        is_coinbase,
        total_input,
        total_output,
        fee,
        block_hash: verbose.as_ref().map(|v| v.block_hash.clone()),
        block_time: verbose.as_ref().map(|v| v.block_time),
    }
}

/// Format sompi as SYNOR.
fn format_synor(sompi: u64) -> String {
    let synor = sompi as f64 / 100_000_000.0;
    format!("{:.8} SYNOR", synor)
}

/// Format hashrate.
fn format_hashrate(hashrate: f64) -> String {
    if hashrate >= 1e18 {
        format!("{:.2} EH/s", hashrate / 1e18)
    } else if hashrate >= 1e15 {
        format!("{:.2} PH/s", hashrate / 1e15)
    } else if hashrate >= 1e12 {
        format!("{:.2} TH/s", hashrate / 1e12)
    } else if hashrate >= 1e9 {
        format!("{:.2} GH/s", hashrate / 1e9)
    } else if hashrate >= 1e6 {
        format!("{:.2} MH/s", hashrate / 1e6)
    } else if hashrate >= 1e3 {
        format!("{:.2} KH/s", hashrate / 1e3)
    } else {
        format!("{:.2} H/s", hashrate)
    }
}

/// Format timestamp as human-readable.
fn format_timestamp(ts: u64) -> String {
    chrono::DateTime::from_timestamp_millis(ts as i64)
        .map(|dt| dt.format("%Y-%m-%d %H:%M:%S UTC").to_string())
        .unwrap_or_else(|| "Unknown".to_string())
}

// ==================== WebSocket ====================

/// WebSocket upgrade handler.
async fn ws_handler(
    ws: WebSocketUpgrade,
    State(state): State<Arc<ExplorerState>>,
) -> impl IntoResponse {
    ws.on_upgrade(move |socket| handle_websocket(socket, state))
}

/// Handle WebSocket connection with real-time updates.
async fn handle_websocket(socket: WebSocket, state: Arc<ExplorerState>) {
    let (mut sender, mut receiver) = socket.split();

    // Track last known values for change detection
    let mut last_block_count: u64 = 0;
    let mut last_blue_score: u64 = 0;

    // Spawn a task to send periodic updates
    let state_clone = state.clone();
    let send_task = tokio::spawn(async move {
        let mut interval = tokio::time::interval(Duration::from_secs(1));

        loop {
            interval.tick().await;

            // Get current stats
            #[derive(Deserialize)]
            #[serde(rename_all = "camelCase")]
            struct NodeInfo {
                block_count: u64,
                blue_score: u64,
                mempool_size: usize,
                peer_count: usize,
                synced: bool,
            }

            #[derive(Deserialize)]
            #[serde(rename_all = "camelCase")]
            struct MiningInfo {
                difficulty: f64,
                networkhashps: u64,
            }

            // Fetch current state
            let info_result = state_clone
                .rpc_call::<_, NodeInfo>("synor_getInfo", ())
                .await;
            let mining_result = state_clone
                .rpc_call::<_, MiningInfo>("synor_getMiningInfo", ())
                .await;

            if let (Ok(info), Ok(mining)) = (info_result, mining_result) {
                // Send stats update
                let stats_event = serde_json::json!({
                    "type": "stats_update",
                    "blockCount": info.block_count,
                    "virtualDaaScore": info.blue_score,
                    "difficulty": mining.difficulty,
                    "mempoolSize": info.mempool_size,
                    "hashrate": mining.networkhashps as f64,
                    "hashrateHuman": format_hashrate(mining.networkhashps as f64),
                });

                if sender
                    .send(Message::Text(stats_event.to_string().into()))
                    .await
                    .is_err()
                {
                    break;
                }

                // Check for new blocks
                if info.block_count > last_block_count {
                    // New block detected
                    let block_event = serde_json::json!({
                        "type": "new_block",
                        "hash": format!("{:064x}", info.blue_score), // Placeholder hash
                        "blueScore": info.blue_score,
                        "timestamp": chrono::Utc::now().timestamp_millis(),
                        "txCount": 1,
                        "isChainBlock": true,
                    });

                    if sender
                        .send(Message::Text(block_event.to_string().into()))
                        .await
                        .is_err()
                    {
                        break;
                    }

                    last_block_count = info.block_count;
                }

                // Check for tip updates
                if info.blue_score != last_blue_score {
                    #[derive(Deserialize)]
                    struct TipsResponse {
                        tips: Vec<String>,
                    }

                    if let Ok(tips_resp) = state_clone
                        .rpc_call::<_, TipsResponse>("synor_getTips", ())
                        .await
                    {
                        let tip_event = serde_json::json!({
                            "type": "tip_update",
                            "tips": tips_resp.tips,
                            "tipCount": tips_resp.tips.len(),
                        });

                        if sender
                            .send(Message::Text(tip_event.to_string().into()))
                            .await
                            .is_err()
                        {
                            break;
                        }
                    }

                    last_blue_score = info.blue_score;
                }
            }
        }
    });

    // Handle incoming messages (for potential future subscriptions)
    let recv_task = tokio::spawn(async move {
        while let Some(msg) = receiver.next().await {
            match msg {
                Ok(Message::Close(_)) => break,
                Ok(Message::Ping(data)) => {
                    // Pong is handled automatically by axum
                    let _ = data;
                }
                _ => {}
            }
        }
    });

    // Wait for either task to complete
    tokio::select! {
        _ = send_task => {},
        _ = recv_task => {},
    }

    info!("WebSocket connection closed");
}

// ==================== Main ====================

#[tokio::main]
async fn main() -> anyhow::Result<()> {
    // Initialize logging
    tracing_subscriber::fmt()
        .with_env_filter(
            tracing_subscriber::EnvFilter::from_default_env()
                .add_directive("synor_explorer=info".parse()?)
                .add_directive("tower_http=debug".parse()?),
        )
        .init();

    // Load configuration
    dotenvy::dotenv().ok();
    let config = ExplorerConfig::from_env();

    info!("Starting Synor Block Explorer Backend...");
    info!("RPC URL: {}", config.rpc_url);
    info!("Listen address: {}", config.listen_addr);
    if let Some(ref dir) = config.static_dir {
        info!("Static files: {}", dir);
    }

    // Create application state
    let state = Arc::new(ExplorerState::new(config.clone()));

    // Build API router
    let api_router = Router::new()
        // Health & Info
        .route("/health", get(health))
        .route("/api/v1/stats", get(get_stats))
        // WebSocket for real-time updates
        .route("/ws", get(ws_handler))
        // Blocks
        .route("/api/v1/blocks", get(get_blocks))
        .route("/api/v1/blocks/:hash", get(get_block))
        .route("/api/v1/tips", get(get_tips))
        // Transactions
        .route("/api/v1/tx/:tx_id", get(get_transaction))
        .route("/api/v1/mempool", get(get_mempool))
        // Addresses
        .route("/api/v1/address/:address", get(get_address))
        .route("/api/v1/address/:address/utxos", get(get_address_utxos))
        // DAG
        .route("/api/v1/dag", get(get_dag))
        // Search
        .route("/api/v1/search", get(search))
        .with_state(state);

    // Build full app with optional static file serving
    let app = if let Some(ref static_dir) = config.static_dir {
        // Serve static files with SPA fallback (index.html for client-side routing)
        let index_path = format!("{}/index.html", static_dir);
        let serve_dir = ServeDir::new(static_dir)
            .not_found_service(ServeFile::new(&index_path));

        api_router
            .fallback_service(serve_dir)
            .layer(TraceLayer::new_for_http())
            .layer(CompressionLayer::new())
            .layer(config.cors_layer())
    } else {
        // API-only mode
        api_router
            .layer(TraceLayer::new_for_http())
            .layer(CompressionLayer::new())
            .layer(config.cors_layer())
    };

    // Start server
    let listener = tokio::net::TcpListener::bind(&config.listen_addr).await?;
    info!("Explorer server listening on {}", config.listen_addr);

    axum::serve(listener, app).await?;

    Ok(())
}

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

    #[test]
    fn test_format_synor() {
        assert_eq!(format_synor(100_000_000), "1.00000000 SYNOR");
        assert_eq!(format_synor(50_000_000), "0.50000000 SYNOR");
        assert_eq!(format_synor(1), "0.00000001 SYNOR");
    }

    #[test]
    fn test_format_hashrate() {
        assert_eq!(format_hashrate(1000.0), "1.00 KH/s");
        assert_eq!(format_hashrate(1_000_000.0), "1.00 MH/s");
        assert_eq!(format_hashrate(1_000_000_000.0), "1.00 GH/s");
        assert_eq!(format_hashrate(1_000_000_000_000.0), "1.00 TH/s");
    }

    #[test]
    fn test_pagination() {
        let params = PaginationParams { page: 2, limit: 25 };
        let offset = (params.page.saturating_sub(1)) * params.limit;
        assert_eq!(offset, 25);
    }
}