use async_std::fs::{create_dir_all, read_dir, read_to_string, remove_file, File};
use sdk_common::sp_client::bitcoin::hex::{DisplayHex, FromHex};
use serde::{Deserialize, Serialize};
use std::time::{Duration, SystemTime, UNIX_EPOCH};

use async_std::io::WriteExt;
use async_std::path::Path;
use async_std::stream::{IntoStream, StreamExt};
use async_std::task;
use base64;
use sdk_common::log;
use serde_json::json;
use tide::{Request, Response, StatusCode};

const STORAGE_DIR: &str = "./storage";
const MIN_TTL: u64 = 60; // 1 minute
const DEFAULT_TTL: u64 = 86400; // 1 day
const MAX_TTL: u64 = 31_536_000; // 1 year, to be discussed

/// Scans storage and removes expired files
async fn cleanup_expired_files() {
    loop {
        log::debug!("Running cleanup routine...");
        // Traverse storage directory
        let mut entries = match read_dir(STORAGE_DIR).await {
            Ok(entry) => entry,
            Err(e) => {
                log::error!("Failed to read storage dir: {}", e);
                task::sleep(Duration::from_secs(60)).await;
                continue;
            }
        };

        let now = system_time_to_unix(SystemTime::now());
        while let Some(entry) = entries.next().await {
            let e = match entry {
                Ok(e) => e,
                Err(e) => {
                    log::error!("entry returned error: {}", e);
                    continue;
                }
            };
            let path = e.path();
            if path.is_dir().await {
                if let Ok(mut sub_entries) = read_dir(&path).await {
                    while let Some(sub_entry) = sub_entries.next().await {
                        if let Ok(sub_entry) = sub_entry {
                            let file_path = sub_entry.path();
                            if file_path.extension() == Some("meta".as_ref()) {
                                if let Err(err) = handle_file_cleanup(now, &file_path).await {
                                    log::error!("Error cleaning file {:?}: {}", file_path, err);
                                }
                            }
                        }
                    }
                }
            }
        }
        // Sleep for 1 minute before next cleanup
        // task::sleep(Duration::from_secs(60)).await;
        task::sleep(Duration::from_secs(10)).await;
    }
}

#[derive(Debug, Deserialize, Serialize)]
struct Metadata {
    expires_at: u64,
}

/// Converts a `SystemTime` to a UNIX timestamp (seconds since UNIX epoch).
fn system_time_to_unix(system_time: SystemTime) -> u64 {
    system_time
        .duration_since(UNIX_EPOCH)
        .expect("SystemTime before UNIX_EPOCH!")
        .as_secs()
}

/// Converts a UNIX timestamp (seconds since UNIX epoch) back to `SystemTime`.
fn unix_to_system_time(unix_timestamp: u64) -> SystemTime {
    UNIX_EPOCH + Duration::from_secs(unix_timestamp)
}

#[derive(Deserialize)]
struct StoreRequest {
    key: String,
    value: String,
    ttl: Option<u64>,
}

#[derive(Serialize)]
struct ApiResponse {
    message: String,
}

#[derive(Serialize)]
struct RetrieveResponse {
    key: String,
    value: String,
}

async fn get_file_path(key: &str) -> String {
    let dir_name = format!("{}/{}", STORAGE_DIR, &key[..2]);
    let file_path = format!("{}/{}", dir_name, &key[2..]);

    file_path
}

/// Store data on the filesystem
async fn store_data(key: &str, value: &[u8], expires_at: SystemTime) -> Result<(), tide::Error> {
    let file_name = get_file_path(key).await;
    let file_path = Path::new(&file_name);

    // Check if key exists
    if file_path.exists().await {
        return Err(tide::Error::from_str(
            StatusCode::Conflict,
            "Key already exists",
        ));
    }

    create_dir_all(file_path.parent().ok_or(tide::Error::from_str(
        StatusCode::InternalServerError,
        "File path doesn't have parent",
    ))?)
    .await
    .map_err(|e| tide::Error::new(StatusCode::InternalServerError, e))?;

    let metadata_path = format!("{}.meta", file_name);

    let mut file = File::create(&file_path)
        .await
        .map_err(|e| tide::Error::new(StatusCode::InternalServerError, e))?;
    file.write_all(value)
        .await
        .map_err(|e| tide::Error::new(StatusCode::InternalServerError, e))?;

    let metadata = Metadata {
        expires_at: system_time_to_unix(expires_at),
    };

    let metadata_json = serde_json::to_string(&metadata)
        .map_err(|e| tide::Error::new(StatusCode::InternalServerError, e))?;
    let mut meta_file = File::create(&metadata_path)
        .await
        .map_err(|e| tide::Error::new(StatusCode::InternalServerError, e))?;
    meta_file
        .write_all(metadata_json.as_bytes())
        .await
        .map_err(|e| tide::Error::new(StatusCode::InternalServerError, e))?;

    Ok(())
}

async fn retrieve_data(key: &str) -> Result<Vec<u8>, String> {
    let file_path = format!("{}/{}/{}", STORAGE_DIR, &key[..2], &key[2..]);

    let mut file = File::open(&file_path)
        .await
        .map_err(|_| "Key not found.".to_string())?;
    let mut buffer = Vec::new();
    async_std::io::ReadExt::read_to_end(&mut file, &mut buffer)
        .await
        .map_err(|e| e.to_string())?;
    Ok(buffer)
}

/// Handler for the /store endpoint
async fn handle_store(mut req: Request<()>) -> tide::Result<Response> {
    // Parse the JSON body
    let data: StoreRequest = match req.body_json().await {
        Ok(data) => data,
        Err(e) => {
            return Ok(Response::builder(StatusCode::BadRequest)
                .body(format!("Invalid request: {}", e))
                .build());
        }
    };

    // Validate the key
    if data.key.len() != 64 || !data.key.chars().all(|c| c.is_ascii_hexdigit()) {
        return Ok(Response::builder(StatusCode::BadRequest)
            .body("Invalid key: must be a 32 bytes hex string.".to_string())
            .build());
    }

    // Validate the ttl
    let live_for = if let Some(ttl) = data.ttl {
        if ttl < MIN_TTL {
            return Ok(Response::builder(StatusCode::BadRequest)
                .body(format!(
                    "Invalid ttl: must be at least {} seconds.",
                    MIN_TTL
                ))
                .build());
        } else if ttl > MAX_TTL {
            return Ok(Response::builder(StatusCode::BadRequest)
                .body(format!("Invalid ttl: must be at most {} seconds.", MAX_TTL))
                .build());
        }
        Duration::from_secs(ttl)
    } else {
        Duration::from_secs(DEFAULT_TTL)
    };

    let now = SystemTime::now();
    let expires_at = now
        .checked_add(live_for)
        .ok_or(tide::Error::from_str(StatusCode::BadRequest, "Invalid ttl"))?;

    // Decode the value from Base64
    let value_bytes = match Vec::from_hex(&data.value) {
        Ok(value) => value,
        Err(e) => {
            return Ok(Response::builder(StatusCode::BadRequest)
                .body(format!("Invalid request: {}", e))
                .build());
        }
    };

    // Store the data
    match store_data(&data.key, &value_bytes, expires_at).await {
        Ok(()) => Ok(Response::builder(StatusCode::Ok)
            .body(serde_json::to_value(&ApiResponse {
                message: "Data stored successfully.".to_string(),
            })?)
            .build()),
        Err(e) => Ok(Response::builder(e.status())
            .body(serde_json::to_value(&ApiResponse {
                message: e.to_string(),
            })?)
            .build()),
    }
}

async fn handle_retrieve(req: Request<()>) -> tide::Result<Response> {
    let key: String = req.param("key")?.to_string();

    if key.len() != 64 || !key.chars().all(|c| c.is_ascii_hexdigit()) {
        return Ok(Response::builder(StatusCode::BadRequest)
            .body("Invalid key: must be a 32 bytes hex string.".to_string())
            .build());
    }

    match retrieve_data(&key).await {
        Ok(value) => {
            let encoded_value = value.to_lower_hex_string();
            Ok(Response::builder(StatusCode::Ok)
                .body(serde_json::to_value(&RetrieveResponse {
                    key,
                    value: encoded_value,
                })?)
                .build())
        }
        Err(e) => Ok(Response::builder(StatusCode::NotFound).body(e).build()),
    }
}

/// Checks a metadata file and deletes the associated data file if expired
async fn handle_file_cleanup(now: u64, meta_path: &Path) -> Result<(), String> {
    let meta_content = read_to_string(meta_path)
        .await
        .map_err(|e| format!("Failed to read metadata: {}", e.to_string()))?;
    let metadata: Metadata = serde_json::from_str(&meta_content)
        .map_err(|e| format!("Failed to parse metadata: {}", e.to_string()))?;

    if metadata.expires_at < now {
        let data_file_path = meta_path.with_extension("");
        remove_file(&data_file_path)
            .await
            .map_err(|e| format!("Failed to remove data file: {}", e.to_string()))?;
        remove_file(meta_path)
            .await
            .map_err(|e| format!("Failed to remove metadata file: {}", e.to_string()))?;
        log::debug!("Removed expired file: {:?}", data_file_path);
    }
    Ok(())
}

#[async_std::main]
async fn main() -> tide::Result<()> {
    sdk_common::env_logger::init();
    create_dir_all(STORAGE_DIR)
        .await
        .expect("Failed to create storage directory.");

    task::spawn(cleanup_expired_files());

    let mut app = tide::new();
    app.at("/store").post(handle_store);
    app.at("/retrieve/:key").get(handle_retrieve);
    app.listen("0.0.0.0:8080").await?;

    log::info!("Server running at http://0.0.0.0:8080");

    Ok(())
}