use reqwest::Url;
use reqwest_middleware::ClientWithMiddleware;
use serde::{Deserialize, Serialize};
use thiserror::Error;
use tracing::{debug, instrument};
use crate::models::{TokenResponse, PaginatedResponse, Requisition, Account, TransactionsResponse};

#[derive(Error, Debug)]
pub enum GoCardlessError {
    #[error("Request failed: {0}")]
    RequestFailed(#[from] reqwest::Error),
    #[error("Middleware error: {0}")]
    MiddlewareError(#[from] reqwest_middleware::Error),
    #[error("API Error: {0}")]
    ApiError(String),
    #[error("Serialization error: {0}")]
    SerializationError(#[from] serde_json::Error),
    #[error("URL Parse Error: {0}")]
    UrlParseError(#[from] url::ParseError),
}

pub struct GoCardlessClient {
    base_url: Url,
    client: ClientWithMiddleware,
    secret_id: String,
    secret_key: String,
    access_token: Option<String>,
    access_expires_at: Option<chrono::DateTime<chrono::Utc>>,
}

#[derive(Serialize)]
struct TokenRequest<'a> {
    secret_id: &'a str,
    secret_key: &'a str,
}

impl GoCardlessClient {
    pub fn new(base_url: &str, secret_id: &str, secret_key: &str) -> Result<Self, GoCardlessError> {
        Self::with_client(base_url, secret_id, secret_key, None)
    }

    pub fn with_client(base_url: &str, secret_id: &str, secret_key: &str, client: Option<ClientWithMiddleware>) -> Result<Self, GoCardlessError> {
        Ok(Self {
            base_url: Url::parse(base_url)?,
            client: client.unwrap_or_else(|| reqwest_middleware::ClientBuilder::new(reqwest::Client::new()).build()),
            secret_id: secret_id.to_string(),
            secret_key: secret_key.to_string(),
            access_token: None,
            access_expires_at: None,
        })
    }

    #[instrument(skip(self))]
    pub async fn obtain_access_token(&mut self) -> Result<(), GoCardlessError> {
        // Check if current token is still valid (with 60s buffer)
        if let Some(expires) = self.access_expires_at {
            if chrono::Utc::now() < expires - chrono::Duration::seconds(60) {
                debug!("Access token is still valid");
                return Ok(());
            }
        }

        let url = self.base_url.join("/api/v2/token/new/")?;
        let body = TokenRequest {
            secret_id: &self.secret_id,
            secret_key: &self.secret_key,
        };

        debug!("Requesting new access token");
        let response = self.client.post(url)
            .json(&body)
            .send()
            .await?;

        if !response.status().is_success() {
            let status = response.status();
            let text = response.text().await?;
            return Err(GoCardlessError::ApiError(format!("Token request failed {}: {}", status, text)));
        }

        let token_resp: TokenResponse = response.json().await?;
        self.access_token = Some(token_resp.access);
        self.access_expires_at = Some(chrono::Utc::now() + chrono::Duration::seconds(token_resp.access_expires as i64));
        debug!("Access token obtained");
        
        Ok(())
    }

    #[instrument(skip(self))]
    pub async fn get_requisitions(&self) -> Result<PaginatedResponse<Requisition>, GoCardlessError> {
        let url = self.base_url.join("/api/v2/requisitions/")?;
        self.get_authenticated(url).await
    }

    #[instrument(skip(self))]
    pub async fn get_account(&self, id: &str) -> Result<Account, GoCardlessError> {
        let url = self.base_url.join(&format!("/api/v2/accounts/{}/", id))?;
        self.get_authenticated(url).await
    }

    #[instrument(skip(self))]
    pub async fn get_transactions(&self, account_id: &str, date_from: Option<&str>, date_to: Option<&str>) -> Result<TransactionsResponse, GoCardlessError> {
        let mut url = self.base_url.join(&format!("/api/v2/accounts/{}/transactions/", account_id))?;
        
        {
            let mut pairs = url.query_pairs_mut();
            if let Some(from) = date_from {
                pairs.append_pair("date_from", from);
            }
            if let Some(to) = date_to {
                pairs.append_pair("date_to", to);
            }
        }

        self.get_authenticated(url).await
    }

    async fn get_authenticated<T: for<'de> Deserialize<'de>>(&self, url: Url) -> Result<T, GoCardlessError> {
        let token = self.access_token.as_ref().ok_or(GoCardlessError::ApiError("No access token available. Call obtain_access_token() first.".into()))?;

        let response = self.client.get(url)
            .bearer_auth(token)
            .header("accept", "application/json")
            .send()
            .await?;

        if !response.status().is_success() {
             let status = response.status();
             let text = response.text().await?;
             return Err(GoCardlessError::ApiError(format!("API request failed {}: {}", status, text)));
        }

        let data = response.json().await?;
        Ok(data)
    }
}