// api/openai.rs — OpenAI-compatible backend
//
// Works with any provider that implements the OpenAI chat completions
// API: OpenRouter, vLLM, llama.cpp, Fireworks, Together, etc.
// Also used for local models (Qwen, llama) via compatible servers.

use anyhow::Result;
use reqwest::Client;
use tokio::sync::mpsc;

use super::types::*;
use crate::user::ui_channel::{UiMessage, UiSender};
use super::StreamEvent;

/// Stream SSE events from an OpenAI-compatible endpoint, sending
/// parsed StreamEvents through the channel. The caller (runner)
/// handles routing to the UI.
pub(super) async fn stream_events(
    client: &Client,
    base_url: &str,
    api_key: &str,
    model: &str,
    messages: &[Message],
    tools_json: &serde_json::Value,
    tx: &mpsc::UnboundedSender<StreamEvent>,
    ui_tx: &UiSender,
    reasoning_effort: &str,
    sampling: super::SamplingParams,
    priority: Option<i32>,
) -> Result<()> {
    let has_tools = tools_json.as_array().map_or(false, |a| !a.is_empty());
    let request = ChatRequest {
        model: model.to_string(),
        messages: messages.to_vec(),
        tool_choice: if has_tools { Some("auto".to_string()) } else { None },
        tools: if has_tools { Some(tools_json.clone()) } else { None },
        max_tokens: Some(16384),
        temperature: Some(sampling.temperature),
        top_p: Some(sampling.top_p),
        top_k: Some(sampling.top_k),
        stream: Some(true),
        reasoning: if reasoning_effort != "none" && reasoning_effort != "default" {
            Some(ReasoningConfig {
                enabled: true,
                effort: Some(reasoning_effort.to_string()),
            })
        } else {
            None
        },
        chat_template_kwargs: None,
        priority,
    };

    let url = format!("{}/chat/completions", base_url);
    let msg_count = request.messages.len();
    let pri_label = match priority {
        Some(p) => format!(", priority={}", p),
        None => String::new(),
    };
    let debug_label = format!("{} messages, model={}{}", msg_count, model, pri_label);
    let request_json = serde_json::to_string_pretty(&request).ok();

    let mut response = super::send_and_check(
        client,
        &url,
        &request,
        ("Authorization", &format!("Bearer {}", api_key)),
        &[],
        ui_tx,
        &debug_label,
        request_json.as_deref(),
    )
    .await?;

    let mut reader = super::SseReader::new(ui_tx);
    reader.request_json = request_json;

    let mut content_len: usize = 0;
    let mut reasoning_chars: usize = 0;
    let mut tool_call_count: usize = 0;
    let mut empty_deltas: u64 = 0;
    let mut first_content_at = None;
    let mut finish_reason = None;
    let mut usage = None;

    while let Some(event) = reader.next_event(&mut response).await? {
        if let Some(err_msg) = event["error"]["message"].as_str() {
            let raw = event["error"]["metadata"]["raw"].as_str().unwrap_or("");
            let _ = ui_tx.send(UiMessage::Debug(format!(
                "API error in stream: {}", err_msg
            )));
            anyhow::bail!("API error in stream: {} {}", err_msg, raw);
        }

        let chunk: ChatCompletionChunk = match serde_json::from_value(event.clone()) {
            Ok(c) => c,
            Err(e) => {
                let preview = event.to_string();
                let _ = ui_tx.send(UiMessage::Debug(format!(
                    "unparseable SSE event ({}): {}",
                    e, &preview[..preview.len().min(300)]
                )));
                continue;
            }
        };

        if let Some(ref u) = chunk.usage {
            let _ = tx.send(StreamEvent::Usage(u.clone()));
            usage = chunk.usage;
        }

        for choice in &chunk.choices {
            if choice.finish_reason.is_some() {
                finish_reason = choice.finish_reason.clone();
            }

            let has_content = choice.delta.content.is_some();
            let has_tools = choice.delta.tool_calls.is_some();

            // Reasoning tokens — multiple field names across providers
            let mut has_reasoning = false;
            for r in [
                choice.delta.reasoning_content.as_ref(),
                choice.delta.reasoning.as_ref(),
            ].into_iter().flatten() {
                reasoning_chars += r.len();
                has_reasoning = true;
                if !r.is_empty() {
                    let _ = tx.send(StreamEvent::Reasoning(r.clone()));
                }
            }
            if let Some(ref r) = choice.delta.reasoning_details {
                let s = r.to_string();
                reasoning_chars += s.len();
                has_reasoning = true;
                if !s.is_empty() && s != "null" {
                    let _ = tx.send(StreamEvent::Reasoning(s));
                }
            }

            if let Some(ref text_delta) = choice.delta.content {
                if first_content_at.is_none() && !text_delta.is_empty() {
                    first_content_at = Some(reader.stream_start.elapsed());
                }
                content_len += text_delta.len();
                let _ = tx.send(StreamEvent::Content(text_delta.clone()));
            }

            if let Some(ref tc_deltas) = choice.delta.tool_calls {
                for tc_delta in tc_deltas {
                    tool_call_count = tool_call_count.max(tc_delta.index + 1);
                    let _ = tx.send(StreamEvent::ToolCallDelta {
                        index: tc_delta.index,
                        id: tc_delta.id.clone(),
                        call_type: tc_delta.call_type.clone(),
                        name: tc_delta.function.as_ref().and_then(|f| f.name.clone()),
                        arguments: tc_delta.function.as_ref().and_then(|f| f.arguments.clone()),
                    });
                }
            }

            if !has_reasoning && !has_content && !has_tools && choice.finish_reason.is_none() {
                empty_deltas += 1;
            }
        }
    }

    let total_elapsed = reader.stream_start.elapsed();

    super::log_diagnostics(
        ui_tx,
        content_len,
        tool_call_count,
        reasoning_chars,
        reasoning_effort,
        &finish_reason,
        reader.chunks_received,
        reader.sse_lines_parsed,
        reader.sse_parse_errors,
        empty_deltas,
        total_elapsed,
        first_content_at,
        &usage,
        &[], // tool_calls not accumulated here anymore
    );

    let reason = finish_reason.unwrap_or_default();
    let (pt, ct) = usage.as_ref()
        .map(|u| (u.prompt_tokens, u.completion_tokens))
        .unwrap_or((0, 0));
    let _ = tx.send(StreamEvent::Finished {
        reason,
        prompt_tokens: pt,
        completion_tokens: ct,
    });

    Ok(())
}