use axum::{
    extract::State,
    http::StatusCode,
    Json,
};
use serde::{Deserialize, Serialize};
use std::sync::Arc;
use tokio::sync::OnceCell;
use std::time::{Duration, Instant};
use tokio::sync::Mutex;

use crate::AppState;

/// Cached model list with expiry.
static MODEL_CACHE: OnceCell<Mutex<CachedModels>> = OnceCell::const_new();

struct CachedModels {
    models: Vec<ModelInfo>,
    fetched_at: Instant,
}

const CACHE_TTL: Duration = Duration::from_secs(60 * 30); // 30 minutes

#[derive(Debug, Clone, Serialize)]
pub struct ModelInfo {
    pub id: String,
    pub name: String,
    pub context_length: Option<u64>,
    pub pricing_prompt: Option<String>,
    pub pricing_completion: Option<String>,
    pub supports_vision: bool,
}

#[derive(Debug, Deserialize)]
struct OpenRouterModelsResponse {
    data: Vec<OpenRouterModel>,
}

#[derive(Debug, Deserialize)]
struct OpenRouterModel {
    id: String,
    name: String,
    context_length: Option<u64>,
    pricing: Option<OpenRouterPricing>,
    architecture: Option<OpenRouterArchitecture>,
}

#[derive(Debug, Deserialize)]
struct OpenRouterPricing {
    prompt: Option<String>,
    completion: Option<String>,
}

#[derive(Debug, Deserialize)]
struct OpenRouterArchitecture {
    input_modalities: Option<Vec<String>>,
}

async fn fetch_models(api_key: &str) -> Result<Vec<ModelInfo>, String> {
    let client = reqwest::Client::new();

    let response = client
        .get("https://openrouter.ai/api/v1/models")
        .header("Authorization", format!("Bearer {}", api_key))
        .send()
        .await
        .map_err(|e| format!("Failed to fetch models: {}", e))?;

    if !response.status().is_success() {
        let status = response.status();
        let body = response.text().await.unwrap_or_default();
        return Err(format!("OpenRouter models API error {}: {}", status, body));
    }

    let data: OpenRouterModelsResponse = response
        .json()
        .await
        .map_err(|e| format!("Failed to parse models response: {}", e))?;

    let models: Vec<ModelInfo> = data
        .data
        .into_iter()
        .map(|m| {
            let pricing = m.pricing.as_ref();
            let supports_vision = m.architecture
                .as_ref()
                .and_then(|a| a.input_modalities.as_ref())
                .map(|mods| mods.iter().any(|m| m == "image"))
                .unwrap_or(false);
            ModelInfo {
                id: m.id,
                name: m.name,
                context_length: m.context_length,
                pricing_prompt: pricing.and_then(|p| p.prompt.clone()),
                pricing_completion: pricing.and_then(|p| p.completion.clone()),
                supports_vision,
            }
        })
        .collect();

    tracing::info!("Fetched {} models from OpenRouter", models.len());
    Ok(models)
}

pub async fn list_models(
    State(state): State<Arc<AppState>>,
) -> Result<Json<Vec<ModelInfo>>, (StatusCode, String)> {
    let cache = MODEL_CACHE
        .get_or_init(|| async {
            Mutex::new(CachedModels {
                models: Vec::new(),
                fetched_at: Instant::now() - CACHE_TTL - Duration::from_secs(1), // expired
            })
        })
        .await;

    let mut cached = cache.lock().await;

    if cached.models.is_empty() || cached.fetched_at.elapsed() > CACHE_TTL {
        match fetch_models(&state.openrouter_key).await {
            Ok(models) => {
                cached.models = models;
                cached.fetched_at = Instant::now();
            }
            Err(e) => {
                // If we have stale data, return it rather than erroring
                if !cached.models.is_empty() {
                    tracing::warn!("Failed to refresh models, returning stale cache: {}", e);
                    return Ok(Json(cached.models.clone()));
                }
                return Err((StatusCode::BAD_GATEWAY, e));
            }
        }
    }

    Ok(Json(cached.models.clone()))
}