oxi_ai/providers/

openai.rs

//! OpenAI-compatible provider implementation

use async_trait::async_trait;
use bytes::Bytes;
use futures::{Stream, StreamExt};
use reqwest::Client;
use serde::Deserialize;
use serde_json::Value as JsonValue;
use std::pin::Pin;

use super::openai_responses_shared::parse_streaming_json;
use super::shared_client;
use crate::{
    error::ProviderError, Api, AssistantMessage, ContentBlock, Context, Model, Provider,
    ProviderEvent, StopReason, StreamOptions, TextContent, ThinkingContent, Usage,
};

/// Detect whether a model targets the ZAI provider.
fn is_zai(model: &Model) -> bool {
    model.provider.eq_ignore_ascii_case("zai") || model.base_url.contains("api.z.ai")
}

/// OpenAI-compatible provider
#[derive(Clone)]
pub struct OpenAiProvider {
    client: &'static Client,
    api_key: Option<String>,
    base_url: Option<String>,
}

impl OpenAiProvider {
    /// Create a new OpenAI provider without an API key.
    ///
    /// API keys are resolved at request time via auth.json or StreamOptions.
    /// Use `with_api_key()` for explicit key injection.
    pub fn new() -> Self {
        Self {
            client: shared_client(),
            api_key: None,
            base_url: None,
        }
    }

    /// Create with explicit API key (public API for external consumers)
    pub fn with_api_key(api_key: impl Into<String>) -> Self {
        Self {
            client: shared_client(),
            api_key: Some(api_key.into()),
            base_url: None,
        }
    }

    /// Create with a custom base URL (API key resolved from auth storage).
    ///
    /// Used for built-in OpenAI-compatible providers like ZAI.
    pub fn with_base_url(base_url: &str) -> Self {
        Self {
            client: shared_client(),
            api_key: None,
            base_url: Some(base_url.to_string()),
        }
    }

    /// Create with a custom base URL and optional API key.
    ///
    /// Used for registering custom OpenAI-compatible providers (Minimax, ZAI, etc.).
    pub fn with_base_url_and_key(base_url: &str, api_key: Option<String>) -> Self {
        Self {
            client: shared_client(),
            api_key,
            base_url: Some(base_url.to_string()),
        }
    }
}

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

#[async_trait]
impl Provider for OpenAiProvider {
    async fn stream(
        &self,
        model: &Model,
        context: &Context,
        options: Option<StreamOptions>,
    ) -> Result<Pin<Box<dyn Stream<Item = ProviderEvent> + Send>>, ProviderError> {
        let options = options.unwrap_or_default();

        // Build the request
        let effective_base_url = self.base_url.as_deref().unwrap_or(&model.base_url);
        let url = format!("{}/chat/completions", effective_base_url);

        // Get API key
        let api_key = options
            .api_key
            .as_ref()
            .or(self.api_key.as_ref())
            .ok_or_else(|| ProviderError::MissingApiKey)?;

        // Build messages
        let messages = build_messages(context)?;

        // Build request body
        let mut body = serde_json::json!({
            "model": model.id,
            "messages": messages,
            "stream": true,
            "stream_options": { "include_usage": true },
        });

        // Add optional parameters
        if let Some(temp) = options.temperature {
            body["temperature"] = serde_json::json!(temp);
        }

        if let Some(max) = options.max_tokens {
            body["max_tokens"] = serde_json::json!(max);
        }

        // Add tools if present
        if !context.tools.is_empty() {
            body["tools"] = build_tools(&context.tools)?;
        }

        // ── ZAI-specific parameters ──────────────────────────────────
        // Mirror pi's detectCompat: when provider is ZAI (or base_url contains
        // api.z.ai), send enable_thinking and tool_stream.
        if is_zai(model) {
            if model.reasoning {
                body["enable_thinking"] = serde_json::json!(true);
            }
            if !context.tools.is_empty() {
                body["tool_stream"] = serde_json::json!(true);
            }
        }

        tracing::info!(
            "Sending request to {} model={} body_len={} enable_thinking={} tool_stream={}",
            url,
            model.id,
            body.to_string().len(),
            body.get("enable_thinking").is_some(),
            body.get("tool_stream").is_some()
        );
        tracing::debug!("Request body: {}", body.to_string());

        // Build headers
        let mut headers = reqwest::header::HeaderMap::new();
        headers.insert(
            reqwest::header::AUTHORIZATION,
            format!("Bearer {}", api_key)
                .parse()
                .expect("valid bearer header"),
        );
        headers.insert(
            reqwest::header::CONTENT_TYPE,
            "application/json".parse().expect("valid header value"),
        );

        for (k, v) in &options.headers {
            if let (Ok(name), Ok(value)) = (
                k.parse::<reqwest::header::HeaderName>(),
                v.parse::<reqwest::header::HeaderValue>(),
            ) {
                headers.insert(name, value);
            }
        }

        // Make request
        let response = self
            .client
            .post(&url)
            .headers(headers)
            .json(&body)
            .send()
            .await
            .map_err(ProviderError::RequestFailed)?;

        if !response.status().is_success() {
            let status = response.status();
            let body: String = response.text().await.unwrap_or_default();
            return Err(ProviderError::HttpError(status.as_u16(), body));
        }

        // Create event stream
        let provider_name = model.provider.clone();
        let model_id = model.id.clone();

        // Emit Start event once at the beginning of the stream (matches pi's behavior)
        let start_event = ProviderEvent::Start {
            partial: AssistantMessage::new(Api::OpenAiCompletions, &provider_name, &model_id),
        };

        // Stateful stream parser that accumulates tool calls across chunks.
        // OpenAI sends tool calls as multiple deltas (id, name, arguments fragments)
        // that must be reassembled before emitting ToolCallEnd.
        //
        // State:
        //   pending_bytes     – incomplete UTF-8 bytes from the previous HTTP chunk
        //   pending_tc_index  – accumulated tool calls keyed by streaming index
        //   pending_tc_id     – secondary lookup by tool-call ID (ZAI et al. may
        //                       omit the index on continuation deltas)
        //   thinking_started  – whether ThinkingStart has been emitted
        let stream = response
            .bytes_stream()
            .scan(
                (
                    Vec::new(),
                    std::collections::HashMap::<usize, (String, String, String)>::new(),
                    std::collections::HashMap::<String, usize>::new(), // id → index
                    false,
                    AssistantMessage::new(Api::OpenAiCompletions, &provider_name, &model_id),
                ),
                move |(
                    pending_bytes,
                    pending_tc,
                    tc_id_to_index,
                    thinking_started,
                    accumulated_output,
                ),
                      chunk: Result<Bytes, reqwest::Error>| {
                    let events = match chunk {
                        Ok(bytes) => {
                            // Prepend any incomplete bytes from previous chunk
                            let mut combined =
                                Vec::with_capacity(pending_bytes.len() + bytes.len());
                            combined.extend_from_slice(pending_bytes);
                            combined.extend_from_slice(&bytes);

                            // Split into complete lines (ending with \n) and trailing incomplete data.
                            // This prevents JSON parse failures from partial SSE lines
                            // that were split across HTTP chunks.
                            let (text, trailing) = split_complete_lines(&combined);
                            *pending_bytes = trailing;

                            tracing::debug!(
                                "parse_sse_events input: {} bytes, {} lines",
                                text.len(),
                                text.lines().count()
                            );
                            let raw_events = parse_sse_events(
                                &text,
                                &provider_name,
                                &model_id,
                                accumulated_output,
                            );
                            tracing::debug!("parse_sse_events output: {} events", raw_events.len());

                            // Post-process: accumulate tool call deltas, inject ThinkingStart once
                            let mut processed = Vec::new();
                            for event in raw_events {
                                match &event {
                                    ProviderEvent::ThinkingDelta { content_index, .. } => {
                                        // Inject ThinkingStart before the first ThinkingDelta
                                        if !*thinking_started {
                                            *thinking_started = true;
                                            processed.push(ProviderEvent::ThinkingStart {
                                                content_index: *content_index,
                                                partial: AssistantMessage::new(
                                                    Api::OpenAiCompletions,
                                                    &provider_name,
                                                    &model_id,
                                                ),
                                            });
                                        }
                                        processed.push(event);
                                    }
                                    ProviderEvent::ToolCallStart {
                                        content_index,
                                        tool_call_id,
                                        tool_name,
                                        ..
                                    } => {
                                        let entry =
                                            pending_tc.entry(*content_index).or_insert_with(|| {
                                                (String::new(), String::new(), String::new())
                                            });
                                        if let Some(ref id) = tool_call_id {
                                            if !id.is_empty() {
                                                entry.0 = id.clone();
                                                tc_id_to_index.insert(id.clone(), *content_index);
                                            }
                                        }
                                        if let Some(ref name) = tool_name {
                                            if !name.is_empty() {
                                                entry.1 = name.clone();
                                            }
                                        }
                                        processed.push(event);
                                    }
                                    ProviderEvent::ToolCallDelta {
                                        content_index,
                                        delta,
                                        ..
                                    } => {
                                        // Dual-map lookup: prefer index, fall back to ID
                                        let idx = if pending_tc.contains_key(content_index) {
                                            *content_index
                                        } else {
                                            // Scan id→index map for a match
                                            tc_id_to_index
                                                .values()
                                                .copied()
                                                .find(|i| *i == *content_index)
                                                .unwrap_or(*content_index)
                                        };
                                        let entry = pending_tc.entry(idx).or_insert_with(|| {
                                            (String::new(), String::new(), String::new())
                                        });
                                        tracing::debug!(
                                            "[TC-DELTA] idx={}, delta_len={}, accumulated_len={}",
                                            idx,
                                            delta.len(),
                                            entry.2.len() + delta.len()
                                        );
                                        entry.2.push_str(delta);
                                        processed.push(event);
                                    }
                                    ProviderEvent::ToolCallEnd { .. } => {
                                        // Already a ToolCallEnd from parse_sse_events
                                        processed.push(event);
                                    }
                                    ProviderEvent::Done { reason, .. } => {
                                        // Before Done, emit ToolCallEnd for all accumulated tool calls
                                        if matches!(reason, StopReason::ToolUse) {
                                            let mut indices: Vec<usize> =
                                                pending_tc.keys().copied().collect();
                                            indices.sort();
                                            for idx in indices {
                                                let (id, name, arguments) = &pending_tc[&idx];
                                                tracing::debug!(
                                                    "[TC-END] idx={}, id={}, name={}, args_len={}",
                                                    idx,
                                                    id.len(),
                                                    name.len(),
                                                    arguments.len()
                                                );
                                                let args_value = parse_streaming_json(arguments);
                                                processed.push(ProviderEvent::ToolCallEnd {
                                                    content_index: idx,
                                                    tool_call: crate::ToolCall {
                                                        content_type:
                                                            crate::messages::ToolCallType::ToolCall,
                                                        id: id.clone(),
                                                        name: name.clone(),
                                                        arguments: args_value,
                                                        thought_signature: None,
                                                    },
                                                    partial: AssistantMessage::new(
                                                        Api::OpenAiCompletions,
                                                        &provider_name,
                                                        &model_id,
                                                    ),
                                                });
                                            }
                                        }
                                        // Clear pending_tc for the next stream/turn.
                                        // Without this, tool call arguments from the previous
                                        // turn leak into the next turn's accumulation.
                                        pending_tc.clear();
                                        tc_id_to_index.clear();
                                        processed.push(event);
                                    }
                                    _ => {
                                        processed.push(event);
                                    }
                                }
                            }
                            processed
                        }
                        Err(e) => {
                            vec![ProviderEvent::Error {
                                reason: StopReason::Error,
                                error: create_error_message(
                                    &e.to_string(),
                                    &provider_name,
                                    &model_id,
                                ),
                            }]
                        }
                    };
                    // Return Some to continue, wrap events in an iterator
                    async move { Some(futures::stream::iter(events)) }
                },
            )
            .flatten();

        // Prepend Start event to the stream
        let stream_with_start = futures::stream::once(async move { start_event }).chain(stream);
        Ok(Box::pin(stream_with_start))
    }

    fn name(&self) -> &str {
        "openai"
    }
}

/// Build messages array from context
fn build_messages(context: &Context) -> Result<Vec<JsonValue>, ProviderError> {
    let mut messages = Vec::new();

    // System prompt
    if let Some(ref prompt) = context.system_prompt {
        messages.push(serde_json::json!({
            "role": "system",
            "content": prompt,
        }));
    }

    // Conversation messages
    for msg in &context.messages {
        match msg {
            crate::Message::User(u) => {
                let content: String = match &u.content {
                    crate::MessageContent::Text(s) => s.clone(),
                    crate::MessageContent::Blocks(blocks) => blocks_to_content(blocks)?.to_string(),
                };
                messages.push(serde_json::json!({
                    "role": "user",
                    "content": content,
                }));
            }
            crate::Message::Assistant(a) => {
                // OpenAI format: separate content (text) and tool_calls
                let mut text_parts = Vec::new();
                let mut tool_calls = Vec::new();
                for block in &a.content {
                    match block {
                        ContentBlock::Text(t) => {
                            text_parts.push(t.text.clone());
                        }
                        ContentBlock::Thinking(_) => {
                            // Skip thinking blocks in message history
                        }
                        ContentBlock::ToolCall(tc) => {
                            tool_calls.push(serde_json::json!({
                                "id": tc.id,
                                "type": "function",
                                "function": {
                                    "name": tc.name,
                                    "arguments": tc.arguments.to_string(),
                                },
                            }));
                        }
                        ContentBlock::Image(_) | ContentBlock::Unknown(_) => {}
                    }
                }
                let mut msg = serde_json::json!({
                    "role": "assistant",
                    "content": text_parts.join(""),
                });
                if !tool_calls.is_empty() {
                    msg["tool_calls"] = serde_json::json!(tool_calls);
                }
                messages.push(msg);
            }
            crate::Message::ToolResult(t) => {
                let result_text: String = t
                    .content
                    .iter()
                    .filter_map(|b| b.as_text())
                    .collect::<Vec<_>>()
                    .join("");
                messages.push(serde_json::json!({
                    "role": "tool",
                    "tool_call_id": t.tool_call_id,
                    "content": result_text,
                }));
            }
        }
    }

    Ok(messages)
}

/// Convert content blocks to a string representation
fn blocks_to_content(blocks: &[ContentBlock]) -> Result<JsonValue, ProviderError> {
    if blocks.len() == 1 {
        if let Some(text) = blocks[0].as_text() {
            return Ok(JsonValue::String(text.to_string()));
        }
    }

    let items: Result<Vec<_>, _> = blocks
        .iter()
        .map(|block| match block {
            ContentBlock::Text(t) => Ok(serde_json::json!({
                "type": "text",
                "text": t.text,
            })),
            ContentBlock::ToolCall(tc) => Ok(serde_json::json!({
                "type": "function",
                "id": tc.id,
                "function": {
                    "name": tc.name,
                    "arguments": tc.arguments.to_string(),
                },
            })),
            ContentBlock::Thinking(th) => Ok(serde_json::json!({
                "type": "thinking",
                "thinking": th.thinking,
            })),
            ContentBlock::Image(img) => Ok(serde_json::json!({
                "type": "image_url",
                "image_url": {
                    "url": format!("data:{};base64,{}", img.mime_type, img.data),
                },
            })),
            ContentBlock::Unknown(_) => Err(ProviderError::InvalidResponse(
                "Unknown content block type".into(),
            )),
        })
        .collect();

    Ok(serde_json::json!(items?))
}

/// Build tools array
fn build_tools(tools: &[crate::Tool]) -> Result<JsonValue, ProviderError> {
    let items: Vec<_> = tools
        .iter()
        .map(|tool| {
            serde_json::json!({
                "type": "function",
                "function": {
                    "name": tool.name,
                    "description": tool.description,
                    "parameters": tool.parameters,
                },
            })
        })
        .collect();

    Ok(serde_json::json!(items))
}

/// Extract the longest valid UTF-8 prefix from a byte slice.
///
/// Returns the valid string and the trailing bytes that form an incomplete UTF-8
/// sequence. These trailing bytes should be prepended to the next chunk to
/// ensure no characters are lost at HTTP chunk boundaries.
fn find_valid_utf8_prefix(bytes: &[u8]) -> (String, Vec<u8>) {
    match std::str::from_utf8(bytes) {
        Ok(s) => (s.to_string(), Vec::new()),
        Err(e) => {
            let valid = &bytes[..e.valid_up_to()];
            let trailing = bytes[e.valid_up_to()..].to_vec();
            (String::from_utf8_lossy(valid).to_string(), trailing)
        }
    }
}

/// Split bytes into complete lines (ending with \n) and trailing incomplete data.
/// This ensures `parse_sse_events` only receives complete SSE `data:` lines,
/// preventing JSON parse failures from lines split across HTTP chunks.
pub fn split_complete_lines(bytes: &[u8]) -> (String, Vec<u8>) {
    // Find the last newline — everything up to and including it is complete.
    match bytes.iter().rposition(|&b| b == b'\n') {
        Some(last_nl) => {
            let split_at = last_nl + 1;
            let complete = match std::str::from_utf8(&bytes[..split_at]) {
                Ok(s) => s.to_string(),
                Err(_) => {
                    let (s, _) = find_valid_utf8_prefix(&bytes[..split_at]);
                    s
                }
            };
            let trailing = bytes[split_at..].to_vec();
            (complete, trailing)
        }
        None => {
            // No newline at all — the entire buffer is incomplete.
            // Check if it's valid UTF-8; if not, save as pending.
            (String::new(), bytes.to_vec())
        }
    }
}

/// Parse SSE event stream from a byte buffer.
///
/// Optimizations over a naïve implementation:
/// - **Fast-line splitting** – iterates over `\n` boundaries via `split`
///   instead of allocating an intermediate `String` per line.
/// - **Early `DONE` exit** – breaks immediately when `data: [DONE]` is
///   encountered.
/// - **Pre-allocated events** – reserves capacity based on data-line count.
/// - **Accumulated usage** – tracks usage separately, only cloning into
///   the Done message at stream end, not on every chunk.
fn parse_sse_events(
    text: &str,
    _provider: &str,
    _model_id: &str,
    output: &mut AssistantMessage,
) -> Vec<ProviderEvent> {
    let mut events = Vec::new();

    // Pre-estimate capacity: one event per data line is a reasonable upper bound.
    let estimated_events = text.split('\n').filter(|l| l.starts_with("data: ")).count();
    events.reserve(estimated_events);

    let mut accumulated_usage = Usage::default();

    for line in text.split('\n') {
        let line = line.trim_end_matches('\r');
        if line.is_empty() {
            continue;
        }

        // Fast rejection for non-data lines (comments, event tags, etc.)
        if !line.starts_with("data: ") {
            continue;
        }

        let data = &line[6..]; // skip "data: "

        // Early exit on stream end
        if data == "[DONE]" {
            break;
        }

        if data.is_empty() {
            continue;
        }

        let chunk = match serde_json::from_str::<SSEChunk>(data) {
            Ok(c) => c,
            Err(_) => continue,
        };

        for choice in &chunk.choices {
            if let Some(delta) = &choice.delta {
                if let Some(content) = &delta.content {
                    // pi-mono: append to the output's text block
                    let last_text_idx = output
                        .content
                        .iter()
                        .rposition(|b| matches!(b, ContentBlock::Text(_)));
                    if let Some(idx) = last_text_idx {
                        if let ContentBlock::Text(t) = &mut output.content[idx] {
                            t.text.push_str(content);
                        }
                    } else {
                        output
                            .content
                            .push(ContentBlock::Text(TextContent::new(content.clone())));
                    }
                    events.push(ProviderEvent::TextDelta {
                        content_index: choice.index,
                        delta: content.clone(),
                        partial: output.clone(),
                    });
                }

                // Handle GLM's reasoning_content field (thinking/thought chain)
                if let Some(ref reasoning) = delta.reasoning_content {
                    if !reasoning.is_empty() {
                        // pi-mono: append to the output's thinking block
                        let last_think_idx = output
                            .content
                            .iter()
                            .rposition(|b| matches!(b, ContentBlock::Thinking(_)));
                        if let Some(idx) = last_think_idx {
                            if let ContentBlock::Thinking(t) = &mut output.content[idx] {
                                t.thinking.push_str(reasoning);
                            }
                        } else {
                            output
                                .content
                                .push(ContentBlock::Thinking(ThinkingContent::new(
                                    reasoning.clone(),
                                )));
                        }
                        events.push(ProviderEvent::ThinkingDelta {
                            content_index: choice.index,
                            delta: reasoning.clone(),
                            partial: output.clone(),
                        });
                    }
                }

                if let Some(tool_calls) = &delta.tool_calls {
                    for tc in tool_calls {
                        let tc_index = tc.index.unwrap_or(choice.index);

                        // Emit ToolCallStart when id or name is present (first delta)
                        if tc.id.is_some()
                            || tc.function.as_ref().and_then(|f| f.name.as_ref()).is_some()
                        {
                            events.push(ProviderEvent::ToolCallStart {
                                content_index: tc_index,
                                tool_call_id: tc.id.clone(),
                                tool_name: tc.function.as_ref().and_then(|f| f.name.clone()),
                                partial: output.clone(),
                            });
                        }

                        // Emit ToolCallDelta for arguments
                        if let Some(func) = &tc.function {
                            events.push(ProviderEvent::ToolCallDelta {
                                content_index: tc_index,
                                delta: func.arguments.clone().unwrap_or_default(),
                                partial: output.clone(),
                            });
                        }
                    }
                }
            }

            if choice.finish_reason.is_some() {
                let reason = match choice.finish_reason.as_deref() {
                    Some("stop") | Some("end") => StopReason::Stop,
                    Some("length") => StopReason::Length,
                    Some("tool_calls") | Some("function_call") => StopReason::ToolUse,
                    Some("content_filter") => StopReason::Error,
                    Some(unknown) => {
                        tracing::warn!("Unknown finish_reason: '{}', treating as Error", unknown);
                        StopReason::Error
                    }
                    None => StopReason::Stop,
                };
                tracing::info!("finish_reason={:?} → {:?}", choice.finish_reason, reason);

                let mut done_msg = output.clone();
                done_msg.stop_reason = reason;
                done_msg.usage = accumulated_usage.clone();
                events.push(ProviderEvent::Done {
                    reason,
                    message: done_msg,
                });
            }
        }

        // Accumulate usage from the chunk (if present).
        if let Some(chunk_usage) = chunk.usage {
            accumulated_usage.input = chunk_usage.prompt_tokens;
            accumulated_usage.output = chunk_usage.completion_tokens;
            accumulated_usage.cache_read = chunk_usage
                .prompt_tokens_details
                .as_ref()
                .map(|d| d.cached_tokens)
                .unwrap_or(0);
            accumulated_usage.total_tokens = chunk_usage.total_tokens;
        }
    }

    events
}

/// Create error assistant message
fn create_error_message(msg: &str, provider: &str, model_id: &str) -> AssistantMessage {
    let mut message = AssistantMessage::new(Api::OpenAiCompletions, provider, model_id);
    message.stop_reason = StopReason::Error;
    message.error_message = Some(msg.to_string());
    message
}

// SSE chunk structure
#[derive(Debug, Deserialize)]
// serde deserialization structs
struct SSEChunk {
    _id: Option<String>,
    #[serde(rename = "model")]
    _model: Option<String>,
    choices: Vec<Choice>,
    usage: Option<UsageInfo>,
}

#[derive(Debug, Deserialize)]
// serde deserialization structs
struct Choice {
    index: usize,
    delta: Option<Delta>,
    finish_reason: Option<String>,
}

#[derive(Debug, Deserialize)]
struct Delta {
    content: Option<String>,
    reasoning_content: Option<String>,
    tool_calls: Option<Vec<ToolCallDelta>>,
}

#[derive(Debug, Deserialize)]
// serde deserialization structs
struct ToolCallDelta {
    index: Option<usize>,
    id: Option<String>,
    #[serde(rename = "type")]
    _type_: Option<String>,
    function: Option<FunctionDelta>,
}

#[derive(Debug, Deserialize)]
// serde deserialization structs
struct FunctionDelta {
    name: Option<String>,
    arguments: Option<String>,
}

#[derive(Debug, Deserialize, Clone)]
struct UsageInfo {
    prompt_tokens: usize,
    completion_tokens: usize,
    total_tokens: usize,
    #[serde(rename = "prompt_tokens_details")]
    prompt_tokens_details: Option<PromptTokensDetails>,
}

#[derive(Debug, Deserialize, Clone)]
struct PromptTokensDetails {
    #[serde(rename = "cached_tokens")]
    cached_tokens: usize,
}

#[cfg(test)]
mod tests {
    use super::*;

    const PROVIDER: &str = "openai";
    const MODEL: &str = "gpt-4o";

    fn parse_sse(sse: &str) -> Vec<ProviderEvent> {
        let mut output = AssistantMessage::new(Api::OpenAiCompletions, PROVIDER, MODEL);
        parse_sse_events(sse, PROVIDER, MODEL, &mut output)
    }

    // ── SSE event parsing ──────────────────────────────────────────────

    #[test]
    fn parse_single_text_event() {
        let sse = "data: {\"id\":\"chatcmpl-1\",\"choices\":[{\"index\":0,\"delta\":{\"content\":\"Hello\"}}]}\n\n";
        let events = parse_sse(sse);
        assert_eq!(events.len(), 1);
        match &events[0] {
            ProviderEvent::TextDelta {
                delta,
                content_index,
                ..
            } => {
                assert_eq!(delta, "Hello");
                assert_eq!(*content_index, 0);
            }
            other => panic!("expected TextDelta, got {other:?}"),
        }
    }

    #[test]
    fn parse_multiple_text_events() {
        let sse = concat!(
            "data: {\"id\":\"c\",\"choices\":[{\"index\":0,\"delta\":{\"content\":\"Hel\"}}]}\n",
            "\n",
            "data: {\"id\":\"c\",\"choices\":[{\"index\":0,\"delta\":{\"content\":\"lo!\"}}]}\n",
            "\n"
        );
        let events = parse_sse(sse);
        assert_eq!(events.len(), 2);
        let texts: Vec<&str> = events
            .iter()
            .filter_map(|e| match e {
                ProviderEvent::TextDelta { delta, .. } => Some(delta.as_str()),
                _ => None,
            })
            .collect();
        assert_eq!(texts, vec!["Hel", "lo!"]);
    }

    #[test]
    fn parse_done_terminator() {
        let sse = concat!(
            "data: {\"id\":\"c\",\"choices\":[{\"index\":0,\"delta\":{\"content\":\"X\"}}]}\n",
            "\n",
            "data: [DONE]\n",
            "\n",
            "data: {\"id\":\"c\",\"choices\":[{\"index\":0,\"delta\":{\"content\":\"NEVER\"}}]}\n"
        );
        let events = parse_sse(sse);
        // Should stop at [DONE]; the final data line is never parsed
        assert_eq!(events.len(), 1);
        match &events[0] {
            ProviderEvent::TextDelta { delta, .. } => assert_eq!(delta, "X"),
            other => panic!("expected TextDelta, got {other:?}"),
        }
    }

    // ── Content extraction ─────────────────────────────────────────────

    #[test]
    fn parse_finish_reason_stop() {
        let sse = "data: {\"id\":\"c\",\"choices\":[{\"index\":0,\"delta\":null,\"finish_reason\":\"stop\"}]}\n\n";
        let events = parse_sse(sse);
        assert_eq!(events.len(), 1);
        match &events[0] {
            ProviderEvent::Done { reason, .. } => assert!(matches!(reason, StopReason::Stop)),
            other => panic!("expected Done, got {other:?}"),
        }
    }

    #[test]
    fn parse_finish_reason_length() {
        let sse = "data: {\"id\":\"c\",\"choices\":[{\"index\":0,\"delta\":null,\"finish_reason\":\"length\"}]}\n\n";
        let events = parse_sse(sse);
        match &events[0] {
            ProviderEvent::Done { reason, .. } => assert!(matches!(reason, StopReason::Length)),
            other => panic!("expected Done with Length, got {other:?}"),
        }
    }

    #[test]
    fn parse_finish_reason_tool_calls() {
        let sse = "data: {\"id\":\"c\",\"choices\":[{\"index\":0,\"delta\":null,\"finish_reason\":\"tool_calls\"}]}\n\n";
        let events = parse_sse(sse);
        match &events[0] {
            ProviderEvent::Done { reason, .. } => assert!(matches!(reason, StopReason::ToolUse)),
            other => panic!("expected Done with ToolUse, got {other:?}"),
        }
    }

    // ── Tool call delta accumulation ───────────────────────────────────

    #[test]
    fn parse_tool_call_deltas() {
        let sse = concat!(
            "data: {\"id\":\"c\",\"choices\":[{\"index\":0,\"delta\":{\"tool_calls\":[{\"index\":0,\"id\":\"call_1\",\"type\":\"function\",\"function\":{\"name\":\"get_weather\",\"arguments\":\"\"}}]}}]}\n",
            "\n",
            "data: {\"id\":\"c\",\"choices\":[{\"index\":0,\"delta\":{\"tool_calls\":[{\"index\":0,\"function\":{\"arguments\":\"{\\\"city\\\":\\\"SF\\\"}\"}}]}}]}\n",
            "\n"
        );
        let events = parse_sse(sse);
        // First chunk: ToolCallStart (id+name present) + ToolCallDelta (function present)
        // Second chunk: ToolCallDelta only
        assert_eq!(events.len(), 3);
        let starts: Vec<&str> = events
            .iter()
            .filter_map(|e| match e {
                ProviderEvent::ToolCallStart { tool_name, .. } => tool_name.as_deref(),
                _ => None,
            })
            .collect();
        assert_eq!(starts, vec!["get_weather"]);
        let deltas: Vec<&str> = events
            .iter()
            .filter_map(|e| match e {
                ProviderEvent::ToolCallDelta { delta, .. } => Some(delta.as_str()),
                _ => None,
            })
            .collect();
        assert_eq!(deltas, vec!["", "{\"city\":\"SF\"}"]);
    }

    #[test]
    fn parse_tool_call_with_no_arguments_field() {
        // function field present but arguments is null → emits ToolCallStart + ToolCallDelta
        let sse = "data: {\"id\":\"c\",\"choices\":[{\"index\":0,\"delta\":{\"tool_calls\":[{\"index\":0,\"function\":{\"name\":\"run\"}}]}}]}\n\n";
        let events = parse_sse(sse);
        assert_eq!(events.len(), 2);
        match &events[0] {
            ProviderEvent::ToolCallStart { tool_name, .. } => {
                assert_eq!(tool_name.as_deref(), Some("run"));
            }
            other => panic!("expected ToolCallStart, got {other:?}"),
        }
        match &events[1] {
            ProviderEvent::ToolCallDelta { delta, .. } => assert_eq!(delta, ""),
            other => panic!("expected ToolCallDelta, got {other:?}"),
        }
    }

    // ── Usage accumulation ─────────────────────────────────────────────

    #[test]
    fn parse_usage_in_chunk() {
        // Usage is accumulated from earlier chunks; the Done event captures
        // usage that was accumulated *before* the finish_reason chunk.
        let sse = concat!(
            "data: {\"id\":\"c\",\"choices\":[{\"index\":0,\"delta\":{\"content\":\"hi\"}}],\"usage\":{\"prompt_tokens\":10,\"completion_tokens\":8,\"total_tokens\":18,\"prompt_tokens_details\":{\"cached_tokens\":3}}}\n",
            "\n",
            "data: {\"id\":\"c\",\"choices\":[{\"index\":0,\"delta\":null,\"finish_reason\":\"stop\"}]}\n"
        );
        let events = parse_sse(sse);
        // TextDelta + Done
        assert_eq!(events.len(), 2);
        match &events[1] {
            ProviderEvent::Done { message, .. } => {
                assert_eq!(message.usage.input, 10);
                assert_eq!(message.usage.output, 8);
                assert_eq!(message.usage.total_tokens, 18);
                assert_eq!(message.usage.cache_read, 3);
            }
            other => panic!("expected Done, got {other:?}"),
        }
    }

    #[test]
    fn parse_usage_without_cache_details() {
        // Usage from an earlier chunk; Done event on a separate chunk without usage.
        let sse = concat!(
            "data: {\"id\":\"c\",\"choices\":[],\"usage\":{\"prompt_tokens\":5,\"completion_tokens\":2,\"total_tokens\":7}}\n",
            "\n",
            "data: {\"id\":\"c\",\"choices\":[{\"index\":0,\"delta\":null,\"finish_reason\":\"stop\"}]}\n"
        );
        let events = parse_sse(sse);
        match &events[0] {
            ProviderEvent::Done { message, .. } => {
                assert_eq!(message.usage.input, 5);
                assert_eq!(message.usage.output, 2);
                assert_eq!(message.usage.cache_read, 0);
            }
            other => panic!("expected Done, got {other:?}"),
        }
    }

    // ── Empty / malformed handling ─────────────────────────────────────

    #[test]
    fn parse_empty_input() {
        let events = parse_sse("");
        assert!(events.is_empty());
    }

    #[test]
    fn parse_only_empty_lines() {
        let events = parse_sse("\n\n\n");
        assert!(events.is_empty());
    }

    #[test]
    fn parse_malformed_json_after_data() {
        let sse = "data: {not json at all}\ndata: also bad\ndata: {\"id\":\"c\",\"choices\":[{\"index\":0,\"delta\":{\"content\":\"ok\"}}]}\n";
        let events = parse_sse(sse);
        // Malformed lines are skipped, only the valid one emits
        assert_eq!(events.len(), 1);
        match &events[0] {
            ProviderEvent::TextDelta { delta, .. } => assert_eq!(delta, "ok"),
            other => panic!("expected TextDelta, got {other:?}"),
        }
    }

    #[test]
    fn parse_empty_data_line() {
        let sse = "data: \ndata: {\"id\":\"c\",\"choices\":[{\"index\":0,\"delta\":{\"content\":\"X\"}}]}\n";
        let events = parse_sse(sse);
        assert_eq!(events.len(), 1);
    }

    #[test]
    fn parse_non_data_lines_ignored() {
        let sse = "event: ping\nid: 42\nretry: 5000\ndata: {\"id\":\"c\",\"choices\":[{\"index\":0,\"delta\":{\"content\":\"Y\"}}]}\n";
        let events = parse_sse(sse);
        assert_eq!(events.len(), 1);
    }

    #[test]
    fn parse_carriage_return_line_endings() {
        let sse = "data: {\"id\":\"c\",\"choices\":[{\"index\":0,\"delta\":{\"content\":\"CR\"}}]}\r\n\r\n";
        let events = parse_sse(sse);
        assert_eq!(events.len(), 1);
        match &events[0] {
            ProviderEvent::TextDelta { delta, .. } => assert_eq!(delta, "CR"),
            other => panic!("expected TextDelta, got {other:?}"),
        }
    }

    // ── Mixed content + tool + done ────────────────────────────────────

    #[test]
    fn parse_full_stream_with_text_tool_and_done() {
        let sse = concat!(
            "data: {\"id\":\"c\",\"choices\":[{\"index\":0,\"delta\":{\"content\":\"Let me\"}}]}\n",
            "\n",
            "data: {\"id\":\"c\",\"choices\":[{\"index\":0,\"delta\":{\"content\":\" check\"}}]}\n",
            "\n",
            "data: {\"id\":\"c\",\"choices\":[{\"index\":0,\"delta\":{\"tool_calls\":[{\"index\":0,\"id\":\"call_1\",\"type\":\"function\",\"function\":{\"name\":\"search\",\"arguments\":\"{\\\"q\\\":\\\"rust\\\"}\"}}]}}]}\n",
            "\n",
            "data: {\"id\":\"c\",\"choices\":[{\"index\":0,\"delta\":null,\"finish_reason\":\"tool_calls\"}]}\n",
            "\n",
            "data: [DONE]\n"
        );
        let events = parse_sse(sse);
        assert_eq!(events.len(), 5); // 2 TextDelta + ToolCallStart + ToolCallDelta + Done

        let mut text_count = 0;
        let mut tc_start_count = 0;
        let mut tc_delta_count = 0;
        let mut done_count = 0;
        for e in &events {
            match e {
                ProviderEvent::TextDelta { .. } => text_count += 1,
                ProviderEvent::ToolCallStart { .. } => tc_start_count += 1,
                ProviderEvent::ToolCallDelta { .. } => tc_delta_count += 1,
                ProviderEvent::Done { reason, .. } => {
                    done_count += 1;
                    assert!(matches!(reason, StopReason::ToolUse));
                }
                other => panic!("unexpected event: {other:?}"),
            }
        }
        assert_eq!(text_count, 2);
        assert_eq!(tc_start_count, 1);
        assert_eq!(tc_delta_count, 1);
        assert_eq!(done_count, 1);
    }
}