/// PythonBridge — nosūta HTTP pieprasījumus uz core-python FastAPI servisu.
use anyhow::{anyhow, Result};
use reqwest::{Client, Response};
use serde::de::DeserializeOwned;
use serde_json::Value;
use std::time::Duration;
use tracing::warn;

use crate::inference::response_validator::ValidateCoreResponse;

pub struct PythonBridge {
    client: Client,
    base_urls: Vec<String>,
    request_timeout: Duration,
    router_timeout: Duration,
}

const DEFAULT_CONNECT_TIMEOUT_SECS: u64 = 5;
const DEFAULT_REQUEST_TIMEOUT_SECS: u64 = 45;
const DEFAULT_ROUTER_TIMEOUT_SECS: u64 = 8;
const DEFAULT_CORE_PYTHON_URL: &str = "http://localhost:8000";
const RAILWAY_PUBLIC_SUFFIX: &str = ".up.railway.app";
const RAILWAY_PRIVATE_SUFFIX: &str = ".railway.internal";
const BACKEND_SERVICE_NAME: &str = "backend";
const CORE_PYTHON_SERVICE_NAME: &str = "core-python";

fn env_u64_or_default(key: &str, default: u64) -> u64 {
    std::env::var(key)
        .ok()
        .and_then(|value| value.trim().parse::<u64>().ok())
        .filter(|value| *value > 0)
        .unwrap_or(default)
}

/// Parse an optional timeout from the environment.
///
/// Returns `Some(Duration)` when the variable contains a positive integer value
/// in seconds, otherwise returns `None` for missing, invalid, or zero values.
fn env_optional_duration(key: &str) -> Option<Duration> {
    std::env::var(key)
        .ok()
        .and_then(|value| value.trim().parse::<u64>().ok())
        .filter(|value| *value > 0)
        .map(Duration::from_secs)
}

fn resolve_request_timeout() -> Duration {
    env_optional_duration("CORE_PYTHON_TIMEOUT_SECS")
        .unwrap_or_else(|| Duration::from_secs(DEFAULT_REQUEST_TIMEOUT_SECS))
}

fn resolve_router_timeout(request_timeout: Duration) -> Duration {
    env_optional_duration("CORE_PYTHON_ROUTER_TIMEOUT_SECS")
        .unwrap_or_else(|| Duration::from_secs(DEFAULT_ROUTER_TIMEOUT_SECS))
        .min(request_timeout)
}

fn first_non_empty_env_value(keys: &[&str]) -> Option<String> {
    keys.iter()
        .find_map(|key| std::env::var(key).ok())
        .map(|value| value.trim().to_string())
        .filter(|value| !value.is_empty())
}

fn strip_url_scheme(value: &str) -> &str {
    value
        .strip_prefix("https://")
        .or_else(|| value.strip_prefix("http://"))
        .or_else(|| value.strip_prefix("wss://"))
        .or_else(|| value.strip_prefix("ws://"))
        .unwrap_or(value)
}

fn replace_service_token(label: &str, source: &str, target: &str) -> Option<String> {
    let mut replaced = false;
    let tokens = label
        .split('-')
        .map(|token| {
            if !replaced && token == source {
                replaced = true;
                target
            } else {
                token
            }
        })
        .collect::<Vec<_>>();

    replaced.then(|| tokens.join("-"))
}

fn label_contains_service(label: &str, service: &str) -> bool {
    label == service
        || label.starts_with(&format!("{service}-"))
        || label.ends_with(&format!("-{service}"))
        || label.contains(&format!("-{service}-"))
}

fn infer_railway_sibling_hostname(domain: &str, source: &str, target: &str) -> Option<String> {
    let hostname = strip_url_scheme(domain.trim())
        .trim_end_matches('/')
        .trim()
        .to_string();
    let (label, rest) = hostname.split_once('.')?;
    let replaced = replace_service_token(label, source, target)?;
    Some(format!("{replaced}.{rest}"))
}

fn infer_private_core_python_url() -> Option<String> {
    first_non_empty_env_value(&["RAILWAY_PRIVATE_DOMAIN"])
        .and_then(|domain| {
            infer_railway_sibling_hostname(&domain, BACKEND_SERVICE_NAME, CORE_PYTHON_SERVICE_NAME)
        })
        .map(|hostname| format!("http://{hostname}"))
}

fn is_public_railway_core_python_url(base_url: &str) -> bool {
    let hostname = strip_url_scheme(base_url).trim_end_matches('/');

    hostname.ends_with(RAILWAY_PUBLIC_SUFFIX)
        && hostname
            .split('.')
            .next()
            .is_some_and(|label| label_contains_service(label, CORE_PYTHON_SERVICE_NAME))
}

fn resolve_core_python_base_url() -> String {
    let configured_value = first_non_empty_env_value(&["CORE_PYTHON_URL"]);
    let normalized = normalize_http_base_url(
        configured_value
            .as_deref()
            .unwrap_or(DEFAULT_CORE_PYTHON_URL),
    );

    if let Some(private_url) = infer_private_core_python_url() {
        if configured_value.is_none()
            || normalized == DEFAULT_CORE_PYTHON_URL
            || is_public_railway_core_python_url(&normalized)
        {
            return private_url;
        }
    }

    normalized
}

fn add_url_candidate(candidates: &mut Vec<String>, candidate: String) {
    if !candidates.iter().any(|existing| existing == &candidate) {
        candidates.push(candidate);
    }
}

fn railway_private_url_with_default_port(base_url: &str, default_port: u16) -> Option<String> {
    let (scheme, rest) = base_url
        .strip_prefix("http://")
        .map(|rest| ("http://", rest))
        .or_else(|| {
            base_url
                .strip_prefix("https://")
                .map(|rest| ("https://", rest))
        })?;
    let (authority, suffix) = match rest.find('/') {
        Some(index) => (&rest[..index], &rest[index..]),
        None => (rest, ""),
    };

    if authority.contains(':') || !authority.ends_with(RAILWAY_PRIVATE_SUFFIX) {
        return None;
    }

    Some(format!("{scheme}{authority}:{default_port}{suffix}"))
}

fn resolve_core_python_base_urls() -> Vec<String> {
    let configured_value = first_non_empty_env_value(&["CORE_PYTHON_URL"]);
    let primary = resolve_core_python_base_url();
    let mut candidates = vec![primary.clone()];

    if let Some(port_variant) = railway_private_url_with_default_port(&primary, 8000) {
        add_url_candidate(&mut candidates, port_variant);
    }

    if let Some(configured) = configured_value {
        let normalized = normalize_http_base_url(&configured);
        add_url_candidate(&mut candidates, normalized.clone());

        if let Some(port_variant) = railway_private_url_with_default_port(&normalized, 8000) {
            add_url_candidate(&mut candidates, port_variant);
        }
    }

    candidates
}

pub(crate) fn normalize_http_base_url(base_url: &str) -> String {
    let trimmed = base_url.trim().trim_end_matches('/');

    if trimmed.is_empty() {
        return DEFAULT_CORE_PYTHON_URL.to_string();
    }

    let normalized = if trimmed.starts_with("http://") || trimmed.starts_with("https://") {
        trimmed.to_string()
    } else if trimmed.starts_with("localhost")
        || trimmed.starts_with("127.")
        || trimmed.starts_with("0.0.0.0")
        || trimmed.contains(':')
        || trimmed.ends_with(".local")
        || trimmed.ends_with(RAILWAY_PRIVATE_SUFFIX)
    {
        format!("http://{trimmed}")
    } else {
        format!("https://{trimmed}")
    };

    normalized
}

impl PythonBridge {
    fn timeout_for_endpoint(&self, endpoint: &str) -> Duration {
        if endpoint == "orchestrator/route" {
            self.router_timeout
        } else {
            self.request_timeout
        }
    }

    pub fn new() -> Self {
        let base_urls = resolve_core_python_base_urls();

        let request_timeout = resolve_request_timeout();
        let router_timeout = resolve_router_timeout(request_timeout);
        let connect_timeout = Duration::from_secs(env_u64_or_default(
            "CORE_PYTHON_CONNECT_TIMEOUT_SECS",
            DEFAULT_CONNECT_TIMEOUT_SECS,
        ));

        let client_builder = Client::builder()
            .connect_timeout(connect_timeout)
            // Use a per-read timeout so SSE/text streams can stay open while bytes
            // continue flowing, but stalled model generations still fail cleanly.
            .read_timeout(request_timeout);
        let client = client_builder.build().expect("Failed to build HTTP client");

        Self {
            client,
            base_urls,
            request_timeout,
            router_timeout,
        }
    }

    /// Izsauc core-python API endpoint.
    /// `endpoint` — ceļš bez slīpsvītras sākumā, piem. "text/generate"
    pub async fn call<T>(&self, endpoint: &str, payload: &Value) -> Result<T>
    where
        T: DeserializeOwned + ValidateCoreResponse,
    {
        let mut last_error = None;

        for (index, base_url) in self.base_urls.iter().enumerate() {
            let url = format!("{base_url}/v1/{endpoint}");
            let request_timeout = self.timeout_for_endpoint(endpoint);
            let response = match self
                .client
                .post(&url)
                .timeout(request_timeout)
                .json(payload)
                .send()
                .await
            {
                Ok(response) => response,
                Err(error) => {
                    let error = if error.is_timeout() {
                        anyhow!(
                            "Python bridge timeout pēc {}s ({url})",
                            request_timeout.as_secs()
                        )
                    } else {
                        anyhow!("Python bridge HTTP kļūda: {}", error)
                    };

                    if let Some(next_base_url) = self.base_urls.get(index + 1) {
                        warn!(
                            "Python bridge request to {url} failed, retrying {}: {error}",
                            format!("{next_base_url}/v1/{endpoint}")
                        );
                    }

                    last_error = Some(error);
                    continue;
                }
            };

            if !response.status().is_success() {
                let status = response.status();
                let body = response.text().await.unwrap_or_default();
                return Err(anyhow!("Python bridge atbildēja ar {}: {}", status, body));
            }

            let json: T = response
                .json()
                .await
                .map_err(|e| anyhow!("Python bridge JSON kļūda: {}", e))?;

            return json
                .validate()
                .map_err(|e| anyhow!("Python bridge atgrieza nederīgu payload: {}", e));
        }

        Err(last_error.unwrap_or_else(|| anyhow!("Python bridge URL nav konfigurēts")))
    }

    pub async fn get<T>(&self, endpoint: &str) -> Result<T>
    where
        T: DeserializeOwned + ValidateCoreResponse,
    {
        let mut last_error = None;

        for (index, base_url) in self.base_urls.iter().enumerate() {
            let url = format!("{base_url}/v1/{endpoint}");
            let request_timeout = self.timeout_for_endpoint(endpoint);
            let response = match self.client.get(&url).timeout(request_timeout).send().await {
                Ok(response) => response,
                Err(error) => {
                    let error = if error.is_timeout() {
                        anyhow!(
                            "Python bridge timeout pēc {}s ({url})",
                            request_timeout.as_secs()
                        )
                    } else {
                        anyhow!("Python bridge HTTP kļūda: {}", error)
                    };

                    if let Some(next_base_url) = self.base_urls.get(index + 1) {
                        warn!(
                            "Python bridge GET request to {url} failed, retrying {}: {error}",
                            format!("{next_base_url}/v1/{endpoint}")
                        );
                    }

                    last_error = Some(error);
                    continue;
                }
            };

            if !response.status().is_success() {
                let status = response.status();
                let body = response.text().await.unwrap_or_default();
                return Err(anyhow!("Python bridge atbildēja ar {}: {}", status, body));
            }

            let json: T = response
                .json()
                .await
                .map_err(|e| anyhow!("Python bridge JSON kļūda: {}", e))?;

            return json
                .validate()
                .map_err(|e| anyhow!("Python bridge atgrieza nederīgu payload: {}", e));
        }

        Err(last_error.unwrap_or_else(|| anyhow!("Python bridge URL nav konfigurēts")))
    }

    pub async fn stream(&self, endpoint: &str, payload: &Value) -> Result<Response> {
        let mut last_error = None;

        for (index, base_url) in self.base_urls.iter().enumerate() {
            let url = format!("{base_url}/v1/{endpoint}");
            let request_timeout = self.timeout_for_endpoint(endpoint);
            let response = match self
                .client
                .post(&url)
                .timeout(request_timeout)
                .header("Accept", "text/event-stream")
                .json(payload)
                .send()
                .await
            {
                Ok(response) => response,
                Err(error) => {
                    let error = if error.is_timeout() {
                        anyhow!(
                            "Python bridge timeout pēc {}s ({url})",
                            request_timeout.as_secs()
                        )
                    } else {
                        anyhow!("Python bridge HTTP kļūda: {}", error)
                    };

                    if let Some(next_base_url) = self.base_urls.get(index + 1) {
                        warn!(
                            "Python bridge stream request to {url} failed, retrying {}: {error}",
                            format!("{next_base_url}/v1/{endpoint}")
                        );
                    }

                    last_error = Some(error);
                    continue;
                }
            };

            if !response.status().is_success() {
                let status = response.status();
                let body = response.text().await.unwrap_or_default();
                return Err(anyhow!("Python bridge atbildēja ar {}: {}", status, body));
            }

            return Ok(response);
        }

        Err(last_error.unwrap_or_else(|| anyhow!("Python bridge URL nav konfigurēts")))
    }
}

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

#[cfg(test)]
mod tests {
    use super::{
        env_optional_duration, env_u64_or_default, normalize_http_base_url,
        resolve_core_python_base_url, resolve_core_python_base_urls, resolve_request_timeout,
        resolve_router_timeout, DEFAULT_CORE_PYTHON_URL, DEFAULT_REQUEST_TIMEOUT_SECS,
        DEFAULT_ROUTER_TIMEOUT_SECS,
    };
    use std::env;
    use std::sync::{LazyLock, Mutex};
    use std::time::Duration;

    static ENV_LOCK: LazyLock<Mutex<()>> = LazyLock::new(|| Mutex::new(()));

    struct EnvGuard {
        previous: Vec<(&'static str, Option<String>)>,
    }

    impl EnvGuard {
        fn set(entries: &[(&'static str, Option<&str>)]) -> Self {
            let previous = entries
                .iter()
                .map(|(key, value)| {
                    let original = env::var(key).ok();
                    match value {
                        Some(value) => env::set_var(key, value),
                        None => env::remove_var(key),
                    }
                    (*key, original)
                })
                .collect();

            Self { previous }
        }
    }

    impl Drop for EnvGuard {
        fn drop(&mut self) {
            for (key, value) in self.previous.drain(..) {
                match value {
                    Some(value) => env::set_var(key, value),
                    None => env::remove_var(key),
                }
            }
        }
    }

    #[test]
    fn adds_https_for_public_host_values() {
        assert_eq!(
            normalize_http_base_url("maris-core-python.up.railway.app"),
            "https://maris-core-python.up.railway.app"
        );
    }

    #[test]
    fn adds_http_for_localhost_values() {
        assert_eq!(
            normalize_http_base_url("localhost:8000"),
            "http://localhost:8000"
        );
    }

    #[test]
    fn adds_http_for_bare_hostport_values() {
        assert_eq!(
            normalize_http_base_url("maris-core-python:8000"),
            "http://maris-core-python:8000"
        );
    }

    #[test]
    fn keeps_explicit_port_on_railway_private_url() {
        assert_eq!(
            normalize_http_base_url("http://maris-core-python.railway.internal:8000/"),
            "http://maris-core-python.railway.internal:8000"
        );
    }

    #[test]
    fn reads_timeout_value_from_env() {
        let _env_lock = ENV_LOCK.lock().unwrap();
        let _env_guard = EnvGuard::set(&[("MARIS_TEST_TIMEOUT_SECS_VALID", Some("42"))]);
        assert_eq!(env_u64_or_default("MARIS_TEST_TIMEOUT_SECS_VALID", 30), 42);
    }

    #[test]
    fn env_optional_duration_returns_none_when_missing() {
        let _env_lock = ENV_LOCK.lock().unwrap();
        let _env_guard = EnvGuard::set(&[("MARIS_TEST_TIMEOUT_SECS_OPTIONAL", None)]);
        assert_eq!(
            env_optional_duration("MARIS_TEST_TIMEOUT_SECS_OPTIONAL"),
            None
        );
    }

    #[test]
    fn core_python_timeout_uses_default_when_env_is_missing() {
        let _env_lock = ENV_LOCK.lock().unwrap();
        let _env_guard = EnvGuard::set(&[("CORE_PYTHON_TIMEOUT_SECS", None)]);
        assert_eq!(
            resolve_request_timeout(),
            Duration::from_secs(DEFAULT_REQUEST_TIMEOUT_SECS)
        );
    }

    #[test]
    fn router_timeout_uses_default_when_env_is_missing() {
        let _env_lock = ENV_LOCK.lock().unwrap();
        let _env_guard = EnvGuard::set(&[("CORE_PYTHON_ROUTER_TIMEOUT_SECS", None)]);
        assert_eq!(
            resolve_router_timeout(Duration::from_secs(DEFAULT_REQUEST_TIMEOUT_SECS)),
            Duration::from_secs(DEFAULT_ROUTER_TIMEOUT_SECS)
        );
    }

    #[test]
    fn router_timeout_is_capped_by_global_request_timeout() {
        let _env_lock = ENV_LOCK.lock().unwrap();
        let _env_guard = EnvGuard::set(&[("CORE_PYTHON_ROUTER_TIMEOUT_SECS", Some("20"))]);
        assert_eq!(
            resolve_router_timeout(Duration::from_secs(6)),
            Duration::from_secs(6)
        );
    }

    #[test]
    fn reads_optional_timeout_value_from_env() {
        let _env_lock = ENV_LOCK.lock().unwrap();
        let _env_guard = EnvGuard::set(&[("MARIS_TEST_TIMEOUT_SECS_OPTIONAL", Some("42"))]);
        assert_eq!(
            env_optional_duration("MARIS_TEST_TIMEOUT_SECS_OPTIONAL"),
            Some(Duration::from_secs(42))
        );
    }

    #[test]
    fn falls_back_when_env_timeout_invalid() {
        let _env_lock = ENV_LOCK.lock().unwrap();
        let _env_guard = EnvGuard::set(&[("MARIS_TEST_TIMEOUT_SECS_INVALID", Some("abc"))]);
        assert_eq!(
            env_u64_or_default("MARIS_TEST_TIMEOUT_SECS_INVALID", 30),
            30
        );
    }

    #[test]
    fn infers_private_core_python_url_when_env_is_missing_on_railway() {
        let _env_lock = ENV_LOCK.lock().unwrap();
        let _env_guard = EnvGuard::set(&[
            ("CORE_PYTHON_URL", None),
            (
                "RAILWAY_PRIVATE_DOMAIN",
                Some("maris-backend.railway.internal"),
            ),
        ]);

        assert_eq!(
            resolve_core_python_base_url(),
            "http://maris-core-python.railway.internal"
        );
    }

    #[test]
    fn rewrites_public_railway_core_python_url_to_private_sibling_when_available() {
        let _env_lock = ENV_LOCK.lock().unwrap();
        let _env_guard = EnvGuard::set(&[
            (
                "CORE_PYTHON_URL",
                Some("https://maris-core-python.up.railway.app"),
            ),
            (
                "RAILWAY_PRIVATE_DOMAIN",
                Some("maris-backend.railway.internal"),
            ),
        ]);

        assert_eq!(
            resolve_core_python_base_url(),
            "http://maris-core-python.railway.internal"
        );
    }

    #[test]
    fn keeps_explicit_non_railway_core_python_url() {
        let _env_lock = ENV_LOCK.lock().unwrap();
        let _env_guard = EnvGuard::set(&[
            ("CORE_PYTHON_URL", Some("https://example.com/core")),
            (
                "RAILWAY_PRIVATE_DOMAIN",
                Some("maris-backend.railway.internal"),
            ),
        ]);

        assert_eq!(resolve_core_python_base_url(), "https://example.com/core");
    }

    #[test]
    fn adds_default_private_port_fallback_for_railway_internal_targets() {
        let _env_lock = ENV_LOCK.lock().unwrap();
        let _env_guard = EnvGuard::set(&[
            ("CORE_PYTHON_URL", None),
            (
                "RAILWAY_PRIVATE_DOMAIN",
                Some("maris-backend.railway.internal"),
            ),
        ]);

        assert_eq!(
            resolve_core_python_base_urls(),
            vec![
                "http://maris-core-python.railway.internal".to_string(),
                "http://maris-core-python.railway.internal:8000".to_string()
            ]
        );
    }

    #[test]
    fn keeps_explicit_ported_private_url_as_primary_candidate() {
        let _env_lock = ENV_LOCK.lock().unwrap();
        let _env_guard = EnvGuard::set(&[
            (
                "CORE_PYTHON_URL",
                Some("http://maris-core-python.railway.internal:8000/"),
            ),
            ("RAILWAY_PRIVATE_DOMAIN", None),
        ]);

        assert_eq!(
            resolve_core_python_base_urls(),
            vec!["http://maris-core-python.railway.internal:8000".to_string()]
        );
    }

    #[test]
    fn keeps_local_default_when_not_running_on_railway() {
        let _env_lock = ENV_LOCK.lock().unwrap();
        let _env_guard =
            EnvGuard::set(&[("CORE_PYTHON_URL", None), ("RAILWAY_PRIVATE_DOMAIN", None)]);

        assert_eq!(resolve_core_python_base_url(), DEFAULT_CORE_PYTHON_URL);
    }
}