//! OpenAI Chat Completions API (/v1/chat/completions) handler.

use axum::{
    extract::State,
    http::StatusCode,
    response::{sse::Event, IntoResponse, Json, Sse},
};
use rand::Rng;
use std::sync::Arc;
use tracing::{debug, info, warn};

use super::models::{lookup_model, DEFAULT_MODEL, MODELS};
use super::polling::{extract_response_text, is_response_done, poll_for_response};
use super::types::*;
use super::util::{err_response, now_unix};
use super::AppState;

// ─── Input extraction ────────────────────────────────────────────────────────

/// Extract user text from Chat Completions messages array.
fn extract_chat_input(messages: &[CompletionMessage]) -> String {
    let mut system_parts = Vec::new();
    let mut user_parts = Vec::new();

    for msg in messages {
        let text = match &msg.content {
            serde_json::Value::String(s) => s.clone(),
            serde_json::Value::Array(arr) => arr
                .iter()
                .filter_map(|item| item["text"].as_str())
                .collect::<Vec<_>>()
                .join("\n"),
            _ => continue,
        };
        match msg.role.as_str() {
            "system" | "developer" => system_parts.push(text),
            "user" => user_parts.push(text),
            _ => {}
        }
    }

    let mut result = String::new();
    if !system_parts.is_empty() {
        result.push_str(&system_parts.join("\n"));
        result.push_str("\n\n");
    }
    // Use the last user message
    if let Some(last) = user_parts.last() {
        result.push_str(last);
    }
    result.trim().to_string()
}

// ─── Handler ─────────────────────────────────────────────────────────────────

/// POST /v1/chat/completions — OpenAI Chat Completions API compatibility shim.
/// Accepts standard messages format, reuses the same backend cascade, and
/// outputs in the Chat Completions streaming/sync format.
pub(crate) async fn handle_completions(
    State(state): State<Arc<AppState>>,
    Json(body): Json<CompletionRequest>,
) -> axum::response::Response {
    let model_name = body.model.as_deref().unwrap_or(DEFAULT_MODEL);
    info!(
        "POST /v1/chat/completions model={} stream={}",
        model_name, body.stream
    );

    let model = match lookup_model(model_name) {
        Some(m) => m,
        None => {
            let names: Vec<&str> = MODELS.iter().map(|m| m.name).collect();
            return err_response(
                StatusCode::BAD_REQUEST,
                format!("Unknown model: {model_name}. Available: {names:?}"),
                "invalid_request_error",
            );
        }
    };

    // Store client tools from this request (or clear stale ones from other endpoints)
    if let Some(ref tools) = body.tools {
        let gemini_tools = crate::mitm::modify::openai_tools_to_gemini(tools);
        if !gemini_tools.is_empty() {
            state.mitm_store.set_tools(gemini_tools).await;
            if let Some(ref choice) = body.tool_choice {
                let gemini_config = crate::mitm::modify::openai_tool_choice_to_gemini(choice);
                state.mitm_store.set_tool_config(gemini_config).await;
            }
            info!(count = tools.len(), "Completions: stored client tools for MITM injection");
        } else {
            state.mitm_store.clear_tools().await;
        }
    } else {
        state.mitm_store.clear_tools().await;
    }
    state.mitm_store.clear_active_function_call();

    let token = state.backend.oauth_token().await;
    if token.is_empty() {
        return err_response(
            StatusCode::UNAUTHORIZED,
            "No OAuth token. POST to /v1/token or set ANTIGRAVITY_OAUTH_TOKEN env var.".into(),
            "authentication_error",
        );
    }

    let user_text = extract_chat_input(&body.messages);
    if user_text.is_empty() {
        return err_response(
            StatusCode::BAD_REQUEST,
            "No user message found".to_string(),
            "invalid_request_error",
        );
    }

    // Fresh cascade per request
    let cascade_id = match state.backend.create_cascade().await {
        Ok(cid) => cid,
        Err(e) => {
            return err_response(
                StatusCode::BAD_GATEWAY,
                format!("StartCascade failed: {e}"),
                "server_error",
            );
        }
    };

    // Send message
    match state
        .backend
        .send_message(&cascade_id, &user_text, model.model_enum)
        .await
    {
        Ok((200, _)) => {
            let bg = Arc::clone(&state.backend);
            let cid = cascade_id.clone();
            tokio::spawn(async move {
                let _ = bg.update_annotations(&cid).await;
            });
        }
        Ok((status, _)) => {
            return err_response(
                StatusCode::BAD_GATEWAY,
                format!("Backend returned {status}"),
                "server_error",
            );
        }
        Err(e) => {
            return err_response(
                StatusCode::BAD_GATEWAY,
                format!("Send failed: {e}"),
                "server_error",
            );
        }
    }

    let completion_id = format!(
        "chatcmpl-{}",
        uuid::Uuid::new_v4().to_string().replace('-', "")
    );

    if body.stream {
        chat_completions_stream(
            state,
            completion_id,
            model_name.to_string(),
            cascade_id,
            body.timeout,
        )
        .await
    } else {
        chat_completions_sync(
            state,
            completion_id,
            model_name.to_string(),
            cascade_id,
            body.timeout,
        )
        .await
    }
}

// ─── Streaming ───────────────────────────────────────────────────────────────

/// Streaming output in Chat Completions format.
async fn chat_completions_stream(
    state: Arc<AppState>,
    completion_id: String,
    model_name: String,
    cascade_id: String,
    timeout: u64,
) -> axum::response::Response {
    let stream = async_stream::stream! {
        let start = std::time::Instant::now();
        let mut last_text = String::new();

        // Initial role chunk
        yield Ok::<_, std::convert::Infallible>(Event::default().data(serde_json::to_string(&serde_json::json!({
            "id": completion_id,
            "object": "chat.completion.chunk",
            "created": now_unix(),
            "model": model_name,
            "choices": [{
                "index": 0,
                "delta": {"role": "assistant", "content": ""},
                "finish_reason": serde_json::Value::Null,
            }],
        })).unwrap_or_default()));

        while start.elapsed().as_secs() < timeout {
            if let Ok((status, data)) = state.backend.get_steps(&cascade_id).await {
                if status == 200 {
                    if let Some(steps) = data["steps"].as_array() {
                        // Check for MITM-captured function calls FIRST (before text)
                        // This prevents dummy placeholder text from leaking to client
                        let captured = state.mitm_store.take_any_function_calls().await;
                        if let Some(ref calls) = captured {
                            if !calls.is_empty() {
                                // Emit tool_calls in OpenAI streaming format — NO text
                                let mut tool_calls = Vec::new();
                                for (i, fc) in calls.iter().enumerate() {
                                    let call_id = format!(
                                        "call_{}",
                                        uuid::Uuid::new_v4().to_string().replace('-', "")[..24].to_string()
                                    );
                                    let arguments = serde_json::to_string(&fc.args).unwrap_or_default();
                                    tool_calls.push(serde_json::json!({
                                        "index": i,
                                        "id": call_id,
                                        "type": "function",
                                        "function": {
                                            "name": fc.name,
                                            "arguments": arguments,
                                        },
                                    }));
                                }
                                yield Ok(Event::default().data(serde_json::to_string(&serde_json::json!({
                                    "id": completion_id,
                                    "object": "chat.completion.chunk",
                                    "created": now_unix(),
                                    "model": model_name,
                                    "choices": [{
                                        "index": 0,
                                        "delta": {"tool_calls": tool_calls},
                                        "finish_reason": serde_json::Value::Null,
                                    }],
                                })).unwrap_or_default()));

                                // Finish with tool_calls reason
                                yield Ok(Event::default().data(serde_json::to_string(&serde_json::json!({
                                    "id": completion_id,
                                    "object": "chat.completion.chunk",
                                    "created": now_unix(),
                                    "model": model_name,
                                    "choices": [{
                                        "index": 0,
                                        "delta": {},
                                        "finish_reason": "tool_calls",
                                    }],
                                })).unwrap_or_default()));
                                yield Ok(Event::default().data("[DONE]"));
                                return;
                            }
                        }

                        // Normal text streaming (only when no function calls)
                        let text = extract_response_text(steps);

                        if !text.is_empty() && text != last_text {
                            let delta = if text.len() > last_text.len() && text.starts_with(&*last_text) {
                                &text[last_text.len()..]
                            } else {
                                &text
                            };

                            if !delta.is_empty() {
                                yield Ok(Event::default().data(serde_json::to_string(&serde_json::json!({
                                    "id": completion_id,
                                    "object": "chat.completion.chunk",
                                    "created": now_unix(),
                                    "model": model_name,
                                    "choices": [{
                                        "index": 0,
                                        "delta": {"content": delta},
                                        "finish_reason": serde_json::Value::Null,
                                    }],
                                })).unwrap_or_default()));
                                last_text = text.to_string();
                            }
                        }

                        // Done check: need DONE status AND non-empty text
                        if is_response_done(steps) && !last_text.is_empty() {
                            debug!("Completions stream done, text length={}", last_text.len());
                            yield Ok(Event::default().data(serde_json::to_string(&serde_json::json!({
                                "id": completion_id,
                                "object": "chat.completion.chunk",
                                "created": now_unix(),
                                "model": model_name,
                                "choices": [{
                                    "index": 0,
                                    "delta": {},
                                    "finish_reason": "stop",
                                }],
                            })).unwrap_or_default()));
                            yield Ok(Event::default().data("[DONE]"));
                            return;
                        }

                        // IDLE fallback: check trajectory status periodically
                        // Only check every 5th step count to reduce backend traffic
                        let step_count = steps.len();
                        if step_count > 4 && step_count % 5 == 0 {
                            if let Ok((ts, td)) = state.backend.get_trajectory(&cascade_id).await {
                                if ts == 200 {
                                    let run_status = td["status"].as_str().unwrap_or("");
                                    if run_status.contains("IDLE") && !last_text.is_empty() {
                                        debug!("Completions IDLE, text length={}", last_text.len());
                                        yield Ok(Event::default().data(serde_json::to_string(&serde_json::json!({
                                            "id": completion_id,
                                            "object": "chat.completion.chunk",
                                            "created": now_unix(),
                                            "model": model_name,
                                            "choices": [{
                                                "index": 0,
                                                "delta": {},
                                                "finish_reason": "stop",
                                            }],
                                        })).unwrap_or_default()));
                                        yield Ok(Event::default().data("[DONE]"));
                                        return;
                                    }
                                }
                            }
                        }
                    }
                }
            }

            let poll_ms: u64 = rand::thread_rng().gen_range(800..1200);
            tokio::time::sleep(tokio::time::Duration::from_millis(poll_ms)).await;
        }

        // Timeout
        warn!("Completions stream timeout after {}s", timeout);
        yield Ok(Event::default().data(serde_json::to_string(&serde_json::json!({
            "id": completion_id,
            "object": "chat.completion.chunk",
            "created": now_unix(),
            "model": model_name,
            "choices": [{
                "index": 0,
                "delta": {"content": if last_text.is_empty() { "[Timeout waiting for response]" } else { "" }},
                "finish_reason": "stop",
            }],
        })).unwrap_or_default()));
        yield Ok(Event::default().data("[DONE]"));
    };

    Sse::new(stream)
        .keep_alive(
            axum::response::sse::KeepAlive::new()
                .interval(std::time::Duration::from_secs(15))
                .text(""),
        )
        .into_response()
}

// ─── Sync ────────────────────────────────────────────────────────────────────

/// Sync output in Chat Completions format.
async fn chat_completions_sync(
    state: Arc<AppState>,
    completion_id: String,
    model_name: String,
    cascade_id: String,
    timeout: u64,
) -> axum::response::Response {
    let result = poll_for_response(&state, &cascade_id, timeout).await;

    // Check MITM store first for real intercepted usage (fallback to _latest)
    let mitm = match state.mitm_store.take_usage(&cascade_id).await {
        Some(u) => Some(u),
        None => state.mitm_store.take_usage("_latest").await,
    };
    let (prompt_tokens, completion_tokens, cached_tokens) = if let Some(mitm_usage) = mitm {
        (mitm_usage.input_tokens, mitm_usage.output_tokens, mitm_usage.cache_read_input_tokens)
    } else if let Some(u) = &result.usage {
        (u.input_tokens, u.output_tokens, 0)
    } else {
        (0, 0, 0)
    };

    Json(serde_json::json!({
        "id": completion_id,
        "object": "chat.completion",
        "created": now_unix(),
        "model": model_name,
        "choices": [{
            "index": 0,
            "message": {
                "role": "assistant",
                "content": result.text,
            },
            "finish_reason": "stop",
        }],
        "usage": {
            "prompt_tokens": prompt_tokens,
            "completion_tokens": completion_tokens,
            "total_tokens": prompt_tokens + completion_tokens,
            "prompt_tokens_details": {
                "cached_tokens": cached_tokens,
            },
        },
    }))
    .into_response()
}