use crate::domain::error::{AppError, AppResult};
use crate::infrastructure::repositories::{IdempotencyRecord, IdempotencyRepository};
use async_trait::async_trait;
use dashmap::DashMap;
use once_cell::sync::Lazy;
use sha2::{Digest, Sha256};
use std::sync::Arc;
use std::time::{Duration, Instant};

#[derive(Clone)]
struct CachedIdempotency {
    response_data: Option<String>,
    request_hash: String,
    status: String,
    expires_at: Instant,
}

static IDEMPOTENCY_CACHE: Lazy<DashMap<String, CachedIdempotency>> = Lazy::new(DashMap::new);
const MAX_IDEMPOTENCY_ENTRIES: usize = 50_000;

fn prune_idempotency_cache() {
    let now = Instant::now();
    IDEMPOTENCY_CACHE.retain(|_, cached| cached.expires_at > now);
    if IDEMPOTENCY_CACHE.len() > MAX_IDEMPOTENCY_ENTRIES {
        let mut keys_to_remove = Vec::new();
        for entry in IDEMPOTENCY_CACHE.iter() {
            keys_to_remove.push(entry.key().clone());
            if keys_to_remove.len() >= MAX_IDEMPOTENCY_ENTRIES / 2 {
                break;
            }
        }
        for k in keys_to_remove {
            IDEMPOTENCY_CACHE.remove(&k);
        }
    }
}

#[async_trait]
pub trait IdempotencyService: Send + Sync {
    async fn check_idempotency(
        &self,
        key: &str,
        merchant_id: &str,
        action_scope: &str,
        request_body: &[u8],
    ) -> AppResult<IdempotencyStatus>;

    async fn complete_idempotency(
        &self,
        key: &str,
        merchant_id: &str,
        action_scope: &str,
        response_json: &str,
    ) -> AppResult<()>;
}

pub enum IdempotencyStatus {
    New,
    InProgress,
    Completed(String),
}

pub struct RtixIdempotencyService {
    repo: Arc<dyn IdempotencyRepository>,
}

impl RtixIdempotencyService {
    pub fn new(repo: Arc<dyn IdempotencyRepository>) -> Self {
        Self { repo }
    }

    fn calculate_hash(data: &[u8]) -> String {
        let mut hasher = Sha256::new();
        hasher.update(data);
        format!("{:x}", hasher.finalize())
    }
}

#[async_trait]
impl IdempotencyService for RtixIdempotencyService {
    async fn check_idempotency(
        &self,
        key: &str,
        merchant_id: &str,
        action_scope: &str,
        request_body: &[u8],
    ) -> AppResult<IdempotencyStatus> {
        let request_hash = Self::calculate_hash(request_body);
        let cache_key = format!("{}:{}:{}", key, merchant_id, action_scope);

        // 1. Check Cache
        if let Some(cached) = IDEMPOTENCY_CACHE.get(&cache_key) {
            if cached.expires_at > Instant::now() {
                if cached.request_hash != request_hash {
                    return Err(AppError::Conflict(
                        "Idempotency key reused with different request payload".to_string(),
                    ));
                }

                return match cached.status.as_str() {
                    "COMPLETED" => Ok(IdempotencyStatus::Completed(
                        cached.response_data.clone().unwrap_or_default(),
                    )),
                    "IN_PROGRESS" => Ok(IdempotencyStatus::InProgress),
                    _ => Ok(IdempotencyStatus::New),
                };
            }
        }

        // 2. Check Repository
        if let Some(record) = self.repo.get_record(key, merchant_id, action_scope).await? {
            if record.request_hash != request_hash {
                return Err(AppError::Conflict(
                    "Idempotency key reused with different request payload".to_string(),
                ));
            }

            prune_idempotency_cache();
            IDEMPOTENCY_CACHE.insert(
                cache_key,
                CachedIdempotency {
                    response_data: record.response_data.clone(),
                    request_hash: record.request_hash.clone(),
                    status: record.status.clone(),
                    expires_at: Instant::now() + Duration::from_secs(3600),
                },
            );

            return match record.status.as_str() {
                "COMPLETED" => Ok(IdempotencyStatus::Completed(
                    record.response_data.unwrap_or_default(),
                )),
                "IN_PROGRESS" => Ok(IdempotencyStatus::InProgress),
                _ => Ok(IdempotencyStatus::New),
            };
        }

        // Create new record
        let record = IdempotencyRecord {
            key: key.to_string(),
            merchant_id: merchant_id.to_string(),
            action_scope: action_scope.to_string(),
            request_hash: request_hash.clone(),
            response_data: None,
            status: "IN_PROGRESS".to_string(),
        };

        self.repo.save_record(&record).await?;

        prune_idempotency_cache();
        IDEMPOTENCY_CACHE.insert(
            cache_key,
            CachedIdempotency {
                response_data: None,
                request_hash,
                status: "IN_PROGRESS".to_string(),
                expires_at: Instant::now() + Duration::from_secs(3600),
            },
        );

        Ok(IdempotencyStatus::New)
    }

    async fn complete_idempotency(
        &self,
        key: &str,
        merchant_id: &str,
        action_scope: &str,
        response_json: &str,
    ) -> AppResult<()> {
        self.repo
            .update_response(key, merchant_id, action_scope, response_json, "COMPLETED")
            .await?;

        let cache_key = format!("{}:{}:{}", key, merchant_id, action_scope);
        if let Some(mut cached) = IDEMPOTENCY_CACHE.get_mut(&cache_key) {
            cached.status = "COMPLETED".to_string();
            cached.response_data = Some(response_json.to_string());
            cached.expires_at = Instant::now() + Duration::from_secs(3600);
        } else {
            if let Ok(Some(record)) = self.repo.get_record(key, merchant_id, action_scope).await {
                prune_idempotency_cache();
                IDEMPOTENCY_CACHE.insert(
                    cache_key,
                    CachedIdempotency {
                        response_data: Some(response_json.to_string()),
                        request_hash: record.request_hash,
                        status: "COMPLETED".to_string(),
                        expires_at: Instant::now() + Duration::from_secs(3600),
                    },
                );
            }
        }
        Ok(())
    }
}