use std::{collections::BTreeMap, time::Duration};

use crank_core::{HttpMethod, RestTarget};
use reqwest::{
    Client,
    header::{HeaderMap, HeaderName, HeaderValue},
};
use serde_json::Value;

use crate::{RestAdapterError, RestRequest, RestResponse};

#[derive(Clone, Debug)]
pub struct RestAdapter {
    client: Client,
}

impl Default for RestAdapter {
    fn default() -> Self {
        Self::new()
    }
}

impl RestAdapter {
    pub fn new() -> Self {
        Self {
            client: Client::new(),
        }
    }

    pub async fn execute(
        &self,
        target: &RestTarget,
        request: &RestRequest,
    ) -> Result<RestResponse, RestAdapterError> {
        let url = build_url(target, request)?;
        let headers = build_headers(target, request)?;
        let mut builder = self
            .client
            .request(to_reqwest_method(target.method), url)
            .headers(headers)
            .timeout(Duration::from_millis(request.timeout_ms));

        if let Some(body) = &request.body {
            builder = builder.json(body);
        }

        let response = builder.send().await?;
        let status = response.status();
        let headers = normalize_headers(response.headers());
        let body = decode_body(response).await?;

        if !status.is_success() {
            return Err(RestAdapterError::UnexpectedStatus {
                status: status.as_u16(),
                body,
            });
        }

        Ok(RestResponse {
            status_code: status.as_u16(),
            headers,
            body,
        })
    }
}

fn build_url(target: &RestTarget, request: &RestRequest) -> Result<reqwest::Url, RestAdapterError> {
    let base_url =
        reqwest::Url::parse(&target.base_url).map_err(|_| RestAdapterError::InvalidBaseUrl {
            url: target.base_url.clone(),
        })?;
    let path = substitute_path_params(&target.path_template, &request.path_params);
    let mut url = base_url.join(path.trim_start_matches('/')).map_err(|_| {
        RestAdapterError::InvalidBaseUrl {
            url: target.base_url.clone(),
        }
    })?;

    {
        let mut query = url.query_pairs_mut();
        for (key, value) in &request.query_params {
            query.append_pair(key, value);
        }
    }

    Ok(url)
}

fn substitute_path_params(path_template: &str, path_params: &BTreeMap<String, String>) -> String {
    let mut rendered = path_template.to_owned();

    for (key, value) in path_params {
        rendered = rendered.replace(&format!("{{{key}}}"), value);
    }

    rendered
}

fn build_headers(
    target: &RestTarget,
    request: &RestRequest,
) -> Result<HeaderMap, RestAdapterError> {
    let mut headers = HeaderMap::new();

    for (name, value) in &target.static_headers {
        insert_header(&mut headers, name, value)?;
    }

    for (name, value) in &request.headers {
        insert_header(&mut headers, name, value)?;
    }

    Ok(headers)
}

fn insert_header(headers: &mut HeaderMap, name: &str, value: &str) -> Result<(), RestAdapterError> {
    let header_name =
        HeaderName::try_from(name).map_err(|_| RestAdapterError::InvalidHeaderName {
            header: name.to_owned(),
        })?;
    let header_value =
        HeaderValue::try_from(value).map_err(|_| RestAdapterError::InvalidHeaderValue {
            header: name.to_owned(),
        })?;

    headers.insert(header_name, header_value);
    Ok(())
}

async fn decode_body(response: reqwest::Response) -> Result<Value, RestAdapterError> {
    let bytes = response.bytes().await?;

    if bytes.is_empty() {
        return Ok(Value::Null);
    }

    match serde_json::from_slice::<Value>(&bytes) {
        Ok(value) => Ok(value),
        Err(_) => Ok(Value::String(
            String::from_utf8_lossy(&bytes).trim().to_owned(),
        )),
    }
}

fn normalize_headers(headers: &HeaderMap) -> BTreeMap<String, String> {
    headers
        .iter()
        .filter_map(|(name, value)| {
            value
                .to_str()
                .ok()
                .map(|value| (name.as_str().to_owned(), value.to_owned()))
        })
        .collect()
}

fn to_reqwest_method(method: HttpMethod) -> reqwest::Method {
    match method {
        HttpMethod::Get => reqwest::Method::GET,
        HttpMethod::Post => reqwest::Method::POST,
        HttpMethod::Put => reqwest::Method::PUT,
        HttpMethod::Patch => reqwest::Method::PATCH,
        HttpMethod::Delete => reqwest::Method::DELETE,
    }
}

#[cfg(test)]
mod tests {
    use std::collections::BTreeMap;

    use axum::{
        Json, Router,
        extract::{Path, Query},
        http::HeaderMap,
        routing::{get, post},
    };
    use crank_core::{HttpMethod, RestTarget};
    use serde_json::{Value, json};
    use tokio::net::TcpListener;

    use crate::{RestAdapter, RestAdapterError, RestRequest};

    #[tokio::test]
    async fn executes_rest_request_and_normalizes_json_response() {
        let base_url = spawn_test_server().await;
        let adapter = RestAdapter::new();
        let target = RestTarget {
            base_url,
            method: HttpMethod::Post,
            path_template: "/users/{user_id}".to_owned(),
            static_headers: BTreeMap::from([("x-static".to_owned(), "static".to_owned())]),
        };
        let request = RestRequest {
            path_params: BTreeMap::from([("user_id".to_owned(), "42".to_owned())]),
            query_params: BTreeMap::from([("expand".to_owned(), "true".to_owned())]),
            headers: BTreeMap::from([("x-trace-id".to_owned(), "trace-123".to_owned())]),
            body: Some(json!({ "name": "Ada" })),
            timeout_ms: 1_000,
        };

        let response = adapter.execute(&target, &request).await.unwrap();

        assert_eq!(response.status_code, 200);
        assert_eq!(
            response.body,
            json!({
                "id": "42",
                "query": "true",
                "trace": "trace-123",
                "static": "static",
                "payload": { "name": "Ada" }
            })
        );
    }

    #[tokio::test]
    async fn returns_unexpected_status_with_normalized_body() {
        let base_url = spawn_test_server().await;
        let adapter = RestAdapter::new();
        let target = RestTarget {
            base_url,
            method: HttpMethod::Get,
            path_template: "/fail".to_owned(),
            static_headers: BTreeMap::new(),
        };
        let request = RestRequest {
            path_params: BTreeMap::new(),
            query_params: BTreeMap::new(),
            headers: BTreeMap::new(),
            body: None,
            timeout_ms: 1_000,
        };

        let error = adapter.execute(&target, &request).await.unwrap_err();

        assert!(matches!(
            error,
            RestAdapterError::UnexpectedStatus {
                status: 502,
                body: Value::Object(_)
            }
        ));
    }

    async fn spawn_test_server() -> String {
        let app = Router::new()
            .route("/users/{user_id}", post(create_user))
            .route("/fail", get(fail));
        let listener = TcpListener::bind("127.0.0.1:0").await.unwrap();
        let address = listener.local_addr().unwrap();

        tokio::spawn(async move {
            axum::serve(listener, app).await.unwrap();
        });

        format!("http://{}", address)
    }

    async fn create_user(
        Path(user_id): Path<String>,
        Query(query): Query<BTreeMap<String, String>>,
        headers: HeaderMap,
        Json(payload): Json<Value>,
    ) -> Json<Value> {
        let trace = headers
            .get("x-trace-id")
            .and_then(|value| value.to_str().ok())
            .unwrap_or_default();
        let static_header = headers
            .get("x-static")
            .and_then(|value| value.to_str().ok())
            .unwrap_or_default();

        Json(json!({
            "id": user_id,
            "query": query.get("expand").cloned().unwrap_or_default(),
            "trace": trace,
            "static": static_header,
            "payload": payload
        }))
    }

    async fn fail() -> (axum::http::StatusCode, Json<Value>) {
        (
            axum::http::StatusCode::BAD_GATEWAY,
            Json(json!({ "error": "upstream failed" })),
        )
    }
}