tkach 0.3.0

//! OpenAI-compatible provider.
//!
//! Works against any endpoint that speaks `POST /chat/completions` in
//! OpenAI's non-streaming shape: OpenAI itself, Moonshot (Kimi), DeepSeek,
//! Ollama's OpenAI-compat layer, Together, Groq, and many more. Point
//! `base_url` at the endpoint root (without `/chat/completions`) and
//! authenticate with a bearer API key. OAuth is explicitly out of scope.
//!
//! ## Format bridge
//!
//! The OpenAI message model differs from ours in two ways that need care:
//!
//! 1. **`tool_calls.arguments` is a JSON string**, not an object. We
//!    serialize ours on the way out and parse on the way back.
//! 2. **Tool results are a separate message per call** with
//!    `role: "tool"` and `tool_call_id`. Our single `user` message
//!    carrying multiple `ToolResult` blocks fans out into N messages on
//!    the wire.

use std::collections::BTreeMap;

use async_trait::async_trait;
use eventsource_stream::Eventsource;
use futures::StreamExt;
use serde::{Deserialize, Serialize};
use serde_json::Value;

use crate::error::ProviderError;
use crate::message::{Content, Message, Role, StopReason, Usage};
use crate::provider::{LlmProvider, Request, Response};
use crate::stream::{ProviderEventStream, StreamEvent};

const DEFAULT_BASE_URL: &str = "https://api.openai.com/v1";

pub struct OpenAICompatible {
    api_key: String,
    base_url: String,
    client: reqwest::Client,
}

impl OpenAICompatible {
    pub fn new(api_key: impl Into<String>) -> Self {
        Self {
            api_key: api_key.into(),
            base_url: DEFAULT_BASE_URL.to_string(),
            client: reqwest::Client::new(),
        }
    }

    /// Override the endpoint root (without trailing `/chat/completions`).
    ///
    /// Examples:
    /// - Moonshot: `https://api.moonshot.cn/v1`
    /// - DeepSeek: `https://api.deepseek.com/v1`
    /// - Ollama:   `http://localhost:11434/v1`
    pub fn with_base_url(mut self, base_url: impl Into<String>) -> Self {
        self.base_url = base_url.into();
        self
    }

    /// Read `OPENAI_API_KEY` from the environment.
    pub fn from_env() -> Self {
        let api_key = std::env::var("OPENAI_API_KEY").expect("OPENAI_API_KEY env var is required");
        Self::new(api_key)
    }
}

#[async_trait]
impl LlmProvider for OpenAICompatible {
    async fn stream(&self, request: Request) -> Result<ProviderEventStream, ProviderError> {
        let mut body = build_request_body(&request);
        body.stream = true;
        body.stream_options = Some(StreamOptions {
            include_usage: true,
        });
        let url = format!("{}/chat/completions", self.base_url);

        let response = self
            .client
            .post(&url)
            .bearer_auth(&self.api_key)
            .header("content-type", "application/json")
            .header("accept", "text/event-stream")
            .json(&body)
            .send()
            .await?;

        let status = response.status().as_u16();

        if status >= 400 {
            let retry_after_ms = parse_retry_after(response.headers());
            let text = response.text().await.unwrap_or_default();
            return Err(classify_error(status, text, retry_after_ms));
        }

        let event_stream = response.bytes_stream().eventsource();
        Ok(Box::pin(openai_event_stream(event_stream)))
    }

    async fn complete(&self, request: Request) -> Result<Response, ProviderError> {
        let body = build_request_body(&request);
        let url = format!("{}/chat/completions", self.base_url);

        let response = self
            .client
            .post(&url)
            .bearer_auth(&self.api_key)
            .header("content-type", "application/json")
            .json(&body)
            .send()
            .await?;

        let status = response.status().as_u16();

        if status >= 400 {
            let retry_after_ms = parse_retry_after(response.headers());
            let text = response.text().await.unwrap_or_default();
            return Err(classify_error(status, text, retry_after_ms));
        }

        // Read body as text first, then parse explicitly. `response.json()`
        // would map serde failures to `reqwest::Error` → `ProviderError::Http`
        // which `is_retryable()` treats as retryable — wrong for malformed
        // 2xx payloads. Persistent garbage should fail fast, not loop.
        let body = response.text().await?;
        let api_response: ApiResponse = serde_json::from_str(&body)?;
        convert_response(api_response)
    }
}

fn classify_error(status: u16, message: String, retry_after_ms: Option<u64>) -> ProviderError {
    match status {
        429 => ProviderError::RateLimit { retry_after_ms },
        503 => ProviderError::Overloaded { retry_after_ms },
        500 | 502 | 504 => ProviderError::Api {
            status,
            message,
            retryable: true,
        },
        s => ProviderError::Api {
            status: s,
            message,
            retryable: (500..600).contains(&s),
        },
    }
}

fn parse_retry_after(headers: &reqwest::header::HeaderMap) -> Option<u64> {
    let raw = headers.get(reqwest::header::RETRY_AFTER)?.to_str().ok()?;
    raw.trim().parse::<u64>().ok().map(|s| s * 1_000)
}

// --- Wire types ---

#[derive(Serialize)]
struct ApiRequest {
    model: String,
    messages: Vec<ApiMessage>,
    #[serde(skip_serializing_if = "Vec::is_empty")]
    tools: Vec<ApiTool>,
    #[serde(skip_serializing_if = "Option::is_none")]
    max_tokens: Option<u32>,
    #[serde(skip_serializing_if = "Option::is_none")]
    temperature: Option<f32>,
    /// `stream: true` switches the response to SSE; default false.
    #[serde(skip_serializing_if = "std::ops::Not::not")]
    stream: bool,
    /// `stream_options.include_usage: true` requests usage in the final
    /// chunk; without this OpenAI omits usage entirely from streamed
    /// responses (only complete() carries it).
    #[serde(skip_serializing_if = "Option::is_none")]
    stream_options: Option<StreamOptions>,
}

#[derive(Serialize)]
struct StreamOptions {
    include_usage: bool,
}

#[derive(Serialize)]
#[serde(untagged)]
enum ApiMessage {
    /// system / user — simple content string.
    Simple { role: &'static str, content: String },
    /// assistant — may have text content, tool_calls, or both.
    Assistant {
        role: &'static str,
        #[serde(skip_serializing_if = "Option::is_none")]
        content: Option<String>,
        #[serde(skip_serializing_if = "Vec::is_empty")]
        tool_calls: Vec<ApiToolCallOut>,
    },
    /// tool — result paired with its originating tool_call_id.
    Tool {
        role: &'static str,
        tool_call_id: String,
        content: String,
    },
}

#[derive(Serialize)]
struct ApiToolCallOut {
    id: String,
    #[serde(rename = "type")]
    kind: &'static str,
    function: ApiFunctionOut,
}

#[derive(Serialize)]
struct ApiFunctionOut {
    name: String,
    /// JSON-encoded string, not a nested object — OpenAI's quirk.
    arguments: String,
}

#[derive(Serialize)]
struct ApiTool {
    #[serde(rename = "type")]
    kind: &'static str,
    function: ApiFunctionDef,
}

#[derive(Serialize)]
struct ApiFunctionDef {
    name: String,
    description: String,
    parameters: Value,
}

#[derive(Deserialize)]
struct ApiResponse {
    choices: Vec<ApiChoice>,
    #[serde(default)]
    usage: Option<ApiUsage>,
}

#[derive(Deserialize)]
struct ApiChoice {
    message: ApiResponseMessage,
    #[serde(default)]
    finish_reason: Option<String>,
}

#[derive(Deserialize)]
struct ApiResponseMessage {
    #[serde(default)]
    content: Option<String>,
    #[serde(default)]
    tool_calls: Vec<ApiToolCallIn>,
}

#[derive(Deserialize)]
struct ApiToolCallIn {
    id: String,
    #[serde(default)]
    function: ApiFunctionIn,
}

#[derive(Deserialize, Default)]
struct ApiFunctionIn {
    #[serde(default)]
    name: String,
    #[serde(default)]
    arguments: String,
}

#[derive(Deserialize)]
struct ApiUsage {
    #[serde(default)]
    prompt_tokens: u32,
    #[serde(default)]
    completion_tokens: u32,
}

// --- Conversion ---

fn build_request_body(request: &Request) -> ApiRequest {
    let mut messages: Vec<ApiMessage> = Vec::new();

    // OpenAI's chat-completions schema has a single string `system`
    // field. Concatenate all SystemBlocks with `\n\n` and drop
    // cache_control — non-Anthropic providers don't speak prompt
    // caching.
    if let Some(blocks) = request.system.as_ref() {
        if !blocks.is_empty() {
            let joined = blocks
                .iter()
                .map(|b| b.text.as_str())
                .collect::<Vec<_>>()
                .join("\n\n");
            messages.push(ApiMessage::Simple {
                role: "system",
                content: joined,
            });
        }
    }

    for msg in &request.messages {
        extend_with_message(&mut messages, msg);
    }

    let tools = request
        .tools
        .iter()
        .map(|t| ApiTool {
            kind: "function",
            function: ApiFunctionDef {
                name: t.name.clone(),
                description: t.description.clone(),
                parameters: t.input_schema.clone(),
            },
        })
        .collect();

    ApiRequest {
        model: request.model.clone(),
        messages,
        tools,
        max_tokens: Some(request.max_tokens),
        temperature: request.temperature,
        stream: false,
        stream_options: None,
    }
}

/// Fan our single `Message` out into one-or-more OpenAI messages.
///
/// - `user` with `Text` → simple `{role: user, content}`
/// - `user` with N `ToolResult` blocks → N separate `{role: tool, ...}`
/// - `assistant` with text and/or `ToolUse` blocks → one
///   `{role: assistant, content?, tool_calls?}`
fn extend_with_message(out: &mut Vec<ApiMessage>, msg: &Message) {
    match msg.role {
        Role::User => {
            let mut text_buf = String::new();
            for c in &msg.content {
                match c {
                    Content::Text { text, .. } => {
                        if !text_buf.is_empty() {
                            text_buf.push('\n');
                        }
                        text_buf.push_str(text);
                    }
                    Content::ToolResult {
                        tool_use_id,
                        content,
                        is_error,
                        ..
                    } => {
                        // Flush any pending user text before the tool results.
                        if !text_buf.is_empty() {
                            out.push(ApiMessage::Simple {
                                role: "user",
                                content: std::mem::take(&mut text_buf),
                            });
                        }
                        // OpenAI's `role: "tool"` schema has no is_error field;
                        // tools that returned errors would otherwise look
                        // identical to successful results to the next turn.
                        // Prefix the content with [error] so the model can
                        // disambiguate. Anthropic-via-OpenRouter strips this
                        // back out on its side; native OpenAI sees it inline.
                        let wire_content = if *is_error {
                            format!("[error] {content}")
                        } else {
                            content.clone()
                        };
                        out.push(ApiMessage::Tool {
                            role: "tool",
                            tool_call_id: tool_use_id.clone(),
                            content: wire_content,
                        });
                    }
                    Content::ToolUse { .. } => {
                        // Should not appear in a user message; skip silently.
                    }
                }
            }
            if !text_buf.is_empty() {
                out.push(ApiMessage::Simple {
                    role: "user",
                    content: text_buf,
                });
            }
        }
        Role::Assistant => {
            let mut text_parts: Vec<String> = Vec::new();
            let mut tool_calls: Vec<ApiToolCallOut> = Vec::new();
            for c in &msg.content {
                match c {
                    Content::Text { text, .. } => text_parts.push(text.clone()),
                    Content::ToolUse { id, name, input } => {
                        tool_calls.push(ApiToolCallOut {
                            id: id.clone(),
                            kind: "function",
                            function: ApiFunctionOut {
                                name: name.clone(),
                                // arguments is a JSON string on the wire.
                                arguments: serde_json::to_string(input)
                                    .unwrap_or_else(|_| "{}".to_string()),
                            },
                        });
                    }
                    Content::ToolResult { .. } => {
                        // Not expected on assistant side; skip.
                    }
                }
            }
            // An empty assistant message ({"role":"assistant"}) is rejected
            // by many compat backends ("messages must have content"). This
            // can happen if the model produced a turn with no text and no
            // tool_calls — replay through the agent's stateless flow would
            // otherwise corrupt history. Skip it; the next user message
            // follows directly.
            if text_parts.is_empty() && tool_calls.is_empty() {
                return;
            }
            out.push(ApiMessage::Assistant {
                role: "assistant",
                content: if text_parts.is_empty() {
                    None
                } else {
                    Some(text_parts.join("\n"))
                },
                tool_calls,
            });
        }
    }
}

fn convert_response(api: ApiResponse) -> Result<Response, ProviderError> {
    let choice = api
        .choices
        .into_iter()
        .next()
        .ok_or_else(|| ProviderError::Other("response had no choices".into()))?;

    let mut content: Vec<Content> = Vec::new();
    if let Some(text) = choice.message.content {
        if !text.is_empty() {
            content.push(Content::text(text));
        }
    }
    for tc in choice.message.tool_calls {
        // arguments is a JSON string per OpenAI spec. Treat unparseable
        // arguments as an empty object rather than failing the whole
        // response — tool-side schema validation will catch abuse.
        let input = if tc.function.arguments.trim().is_empty() {
            Value::Object(Default::default())
        } else {
            serde_json::from_str(&tc.function.arguments)
                .unwrap_or(Value::Object(Default::default()))
        };
        content.push(Content::ToolUse {
            id: tc.id,
            name: tc.function.name,
            input,
        });
    }

    let has_tool_use = content.iter().any(|c| matches!(c, Content::ToolUse { .. }));

    let stop_reason = match choice.finish_reason.as_deref() {
        Some("stop") => StopReason::EndTurn,
        Some("tool_calls") | Some("function_call") => StopReason::ToolUse,
        Some("length") => StopReason::MaxTokens,
        Some("content_filter") => StopReason::EndTurn,
        // `stop_sequence`-style markers aren't standard in OpenAI; map to
        // our StopSequence when we see it (some providers use this).
        Some("stop_sequence") => StopReason::StopSequence,
        // Missing or unknown finish_reason: if the response has tool_calls
        // we know the model wants to use them — defaulting to EndTurn
        // would make the agent loop terminate without invoking the tool.
        // Some compat backends omit finish_reason on tool-use turns.
        _ if has_tool_use => StopReason::ToolUse,
        _ => StopReason::EndTurn,
    };

    let usage = api
        .usage
        .map(|u| Usage {
            input_tokens: u.prompt_tokens,
            output_tokens: u.completion_tokens,
            cache_creation_input_tokens: 0,
            cache_read_input_tokens: 0,
        })
        .unwrap_or_default();

    Ok(Response {
        content,
        stop_reason,
        usage,
    })
}

// --- Streaming SSE state machine ---
//
// OpenAI's SSE format is simpler than Anthropic's: every line is just
// `data: <json>\n` (no `event:` field), terminated by a literal
// `data: [DONE]\n`. Each chunk's `choices[0].delta` carries either a
// piece of `content` (text), or one or more `tool_calls[]` entries.
//
// Tool calls accumulate across chunks. The first chunk for a given
// tool slot carries `id`, `type: "function"`, and `function.name`;
// subsequent chunks carry only `function.arguments` deltas. We index
// by the `index` field (or fall back to position) and emit one atomic
// `StreamEvent::ToolUse` per slot on `finish_reason: tool_calls`.
//
// Usage arrives in the final chunk only when the request was sent
// with `stream_options.include_usage: true`.

#[derive(Deserialize)]
struct ChatChunk {
    #[serde(default)]
    choices: Vec<ChatChoice>,
    #[serde(default)]
    usage: Option<ChunkUsage>,
}

#[derive(Deserialize)]
struct ChatChoice {
    #[serde(default)]
    delta: ChatDelta,
    #[serde(default)]
    finish_reason: Option<String>,
}

#[derive(Deserialize, Default)]
struct ChatDelta {
    #[serde(default)]
    content: Option<String>,
    #[serde(default)]
    tool_calls: Vec<ToolCallChunk>,
}

#[derive(Deserialize)]
struct ToolCallChunk {
    /// Index identifies the tool slot. May be missing in malformed
    /// streams; we fall back to insertion order in that case.
    #[serde(default)]
    index: Option<usize>,
    #[serde(default)]
    id: Option<String>,
    #[serde(default)]
    function: Option<ToolCallFunctionChunk>,
}

#[derive(Deserialize, Default)]
struct ToolCallFunctionChunk {
    #[serde(default)]
    name: Option<String>,
    #[serde(default)]
    arguments: Option<String>,
}

#[derive(Deserialize)]
struct ChunkUsage {
    #[serde(default)]
    prompt_tokens: u32,
    #[serde(default)]
    completion_tokens: u32,
}

#[derive(Default)]
struct ToolSlot {
    id: String,
    name: String,
    args_buf: String,
}

/// State carried across `unfold` polls. Factored out to satisfy
/// clippy::type_complexity and document each slot's role.
struct StreamState<S> {
    sse: S,
    /// Per-tool-slot accumulator keyed by `index` (BTreeMap to preserve
    /// LLM-issued order on flush).
    slots: BTreeMap<usize, ToolSlot>,
    /// Latest non-`null` `finish_reason` seen on a chunk.
    pending_stop: Option<StopReason>,
    /// Pre-emit buffer; one SSE chunk can produce multiple StreamEvents.
    buffer: std::collections::VecDeque<Result<StreamEvent, ProviderError>>,
    /// True after we have emitted the synthetic `Done` terminal — used
    /// to short-circuit further `next()` calls so consumers see `None`.
    emitted_done: bool,
}

fn openai_event_stream<S>(sse: S) -> impl futures::Stream<Item = Result<StreamEvent, ProviderError>>
where
    S: futures::Stream<
            Item = Result<
                eventsource_stream::Event,
                eventsource_stream::EventStreamError<reqwest::Error>,
            >,
        > + Send
        + Unpin
        + 'static,
{
    use std::collections::VecDeque;

    let initial = StreamState {
        sse,
        slots: BTreeMap::new(),
        pending_stop: None,
        buffer: VecDeque::new(),
        emitted_done: false,
    };

    futures::stream::unfold(initial, |mut state| async move {
        loop {
            if let Some(ev) = state.buffer.pop_front() {
                return Some((ev, state));
            }

            if state.emitted_done {
                return None;
            }

            let next = state.sse.next().await;
            let event = match next {
                None => {
                    // Stream ended without a `data: [DONE]`. Flush any
                    // pending tool slots + stop reason + Done.
                    flush_terminal(&mut state.slots, &mut state.pending_stop, &mut state.buffer);
                    if state.buffer.is_empty() {
                        return None;
                    }
                    state.emitted_done = true;
                    continue;
                }
                Some(Ok(ev)) => ev,
                Some(Err(e)) => {
                    let err = ProviderError::Other(format!("SSE read error: {e}"));
                    return Some((Err(err), state));
                }
            };

            let data = event.data.trim();
            if data == "[DONE]" {
                flush_terminal(&mut state.slots, &mut state.pending_stop, &mut state.buffer);
                state.emitted_done = true;
                continue;
            }
            if data.is_empty() {
                continue;
            }

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

            process_chunk(
                chunk,
                &mut state.slots,
                &mut state.pending_stop,
                &mut state.buffer,
            );
        }
    })
}

fn process_chunk(
    chunk: ChatChunk,
    slots: &mut BTreeMap<usize, ToolSlot>,
    pending_stop: &mut Option<StopReason>,
    buffer: &mut std::collections::VecDeque<Result<StreamEvent, ProviderError>>,
) {
    if let Some(choice) = chunk.choices.into_iter().next() {
        if let Some(text) = choice.delta.content {
            if !text.is_empty() {
                buffer.push_back(Ok(StreamEvent::ContentDelta(text)));
            }
        }
        for tc in choice.delta.tool_calls {
            let idx = tc.index.unwrap_or(slots.len());
            let slot = slots.entry(idx).or_default();
            if let Some(id) = tc.id {
                slot.id = id;
            }
            if let Some(f) = tc.function {
                if let Some(name) = f.name {
                    slot.name = name;
                }
                if let Some(args) = f.arguments {
                    slot.args_buf.push_str(&args);
                }
            }
        }
        if let Some(reason) = choice.finish_reason {
            *pending_stop = Some(map_finish_reason(&reason));
        }
    }

    if let Some(usage) = chunk.usage {
        buffer.push_back(Ok(StreamEvent::Usage(Usage {
            input_tokens: usage.prompt_tokens,
            output_tokens: usage.completion_tokens,
            cache_creation_input_tokens: 0,
            cache_read_input_tokens: 0,
        })));
    }
}

/// Flush accumulated tool slots into atomic ToolUse events, then emit
/// pending MessageDelta and Done. Called on `[DONE]` or stream end.
fn flush_terminal(
    slots: &mut BTreeMap<usize, ToolSlot>,
    pending_stop: &mut Option<StopReason>,
    buffer: &mut std::collections::VecDeque<Result<StreamEvent, ProviderError>>,
) {
    // BTreeMap iteration is index-sorted, preserving LLM-issued order.
    for (_, slot) in std::mem::take(slots) {
        if slot.id.is_empty() && slot.name.is_empty() {
            continue;
        }
        let input: Value = if slot.args_buf.trim().is_empty() {
            Value::Object(Default::default())
        } else {
            serde_json::from_str(&slot.args_buf).unwrap_or(Value::Object(Default::default()))
        };
        buffer.push_back(Ok(StreamEvent::ToolUse {
            id: slot.id,
            name: slot.name,
            input,
        }));
    }
    if let Some(stop) = pending_stop.take() {
        buffer.push_back(Ok(StreamEvent::MessageDelta { stop_reason: stop }));
    }
    buffer.push_back(Ok(StreamEvent::Done));
}

fn map_finish_reason(reason: &str) -> StopReason {
    match reason {
        "stop" => StopReason::EndTurn,
        "tool_calls" | "function_call" => StopReason::ToolUse,
        "length" => StopReason::MaxTokens,
        "content_filter" => StopReason::EndTurn,
        "stop_sequence" => StopReason::StopSequence,
        _ => StopReason::EndTurn,
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::message::CacheControl;
    use crate::provider::SystemBlock;

    #[test]
    fn request_maps_system_and_user_text() {
        let req = Request {
            model: "gpt-4".into(),
            system: Some(vec![SystemBlock::text("be brief")]),
            messages: vec![Message::user_text("hi")],
            tools: vec![],
            max_tokens: 100,
            temperature: Some(0.5),
        };
        let body = build_request_body(&req);
        let json = serde_json::to_value(&body).unwrap();
        assert_eq!(json["model"], "gpt-4");
        assert_eq!(json["messages"][0]["role"], "system");
        assert_eq!(json["messages"][0]["content"], "be brief");
        assert_eq!(json["messages"][1]["role"], "user");
        assert_eq!(json["messages"][1]["content"], "hi");
        assert_eq!(json["temperature"], 0.5);
        assert_eq!(json["max_tokens"], 100);
    }

    #[test]
    fn multiple_system_blocks_concatenate_with_double_newline() {
        let req = Request {
            model: "gpt-4".into(),
            system: Some(vec![
                SystemBlock::text("base instructions"),
                SystemBlock::cached("long stable context"),
                SystemBlock::text("final tail"),
            ]),
            messages: vec![Message::user_text("hi")],
            tools: vec![],
            max_tokens: 10,
            temperature: None,
        };
        let body = build_request_body(&req);
        let json = serde_json::to_value(&body).unwrap();
        assert_eq!(json["messages"][0]["role"], "system");
        assert_eq!(
            json["messages"][0]["content"],
            "base instructions\n\nlong stable context\n\nfinal tail"
        );
        // cache_control silently dropped — OpenAI-compat has no equivalent.
    }

    #[test]
    fn empty_system_vec_emits_no_system_message() {
        let req = Request {
            model: "gpt-4".into(),
            system: Some(vec![]),
            messages: vec![Message::user_text("hi")],
            tools: vec![],
            max_tokens: 10,
            temperature: None,
        };
        let body = build_request_body(&req);
        let json = serde_json::to_value(&body).unwrap();
        assert_eq!(json["messages"][0]["role"], "user");
    }

    #[test]
    fn tool_definition_cache_control_is_ignored_silently() {
        // Caller-set cache_control on a ToolDefinition should not break
        // OpenAI-compat — the field is simply not threaded into the
        // wire tool schema.
        use crate::provider::ToolDefinition;
        let req = Request {
            model: "gpt-4".into(),
            system: None,
            messages: vec![Message::user_text("hi")],
            tools: vec![ToolDefinition {
                name: "bash".into(),
                description: "run a shell command".into(),
                input_schema: serde_json::json!({"type": "object"}),
                cache_control: Some(CacheControl::ephemeral()),
            }],
            max_tokens: 10,
            temperature: None,
        };
        let body = build_request_body(&req);
        let json = serde_json::to_value(&body).unwrap();
        let tool = &json["tools"][0];
        assert!(tool.get("cache_control").is_none());
        assert_eq!(tool["function"]["name"], "bash");
    }

    #[test]
    fn request_fans_out_tool_results_to_separate_tool_messages() {
        let req = Request {
            model: "m".into(),
            system: None,
            messages: vec![Message::user(vec![
                Content::tool_result("call_1", "ok", false),
                Content::tool_result("call_2", "bad", true),
            ])],
            tools: vec![],
            max_tokens: 10,
            temperature: None,
        };
        let body = build_request_body(&req);
        let json = serde_json::to_value(&body).unwrap();
        let msgs = json["messages"].as_array().unwrap();
        assert_eq!(msgs.len(), 2);
        assert_eq!(msgs[0]["role"], "tool");
        assert_eq!(msgs[0]["tool_call_id"], "call_1");
        assert_eq!(msgs[1]["tool_call_id"], "call_2");
    }

    #[test]
    fn request_encodes_assistant_tool_use_as_tool_calls_with_string_arguments() {
        let req = Request {
            model: "m".into(),
            system: None,
            messages: vec![Message::assistant(vec![
                Content::text("let me check"),
                Content::ToolUse {
                    id: "call_x".into(),
                    name: "bash".into(),
                    input: serde_json::json!({"command": "ls"}),
                },
            ])],
            tools: vec![],
            max_tokens: 10,
            temperature: None,
        };
        let body = build_request_body(&req);
        let json = serde_json::to_value(&body).unwrap();
        let msg = &json["messages"][0];
        assert_eq!(msg["role"], "assistant");
        assert_eq!(msg["content"], "let me check");
        let tc = &msg["tool_calls"][0];
        assert_eq!(tc["id"], "call_x");
        assert_eq!(tc["type"], "function");
        assert_eq!(tc["function"]["name"], "bash");
        // Arguments on the wire are a JSON *string*, not an object.
        let args_str = tc["function"]["arguments"].as_str().unwrap();
        let parsed: Value = serde_json::from_str(args_str).unwrap();
        assert_eq!(parsed["command"], "ls");
    }

    #[test]
    fn response_decodes_text_and_tool_calls() {
        let raw = serde_json::json!({
            "choices": [{
                "message": {
                    "role": "assistant",
                    "content": "calling a tool",
                    "tool_calls": [{
                        "id": "call_1",
                        "type": "function",
                        "function": {
                            "name": "bash",
                            "arguments": "{\"command\":\"echo hi\"}"
                        }
                    }]
                },
                "finish_reason": "tool_calls"
            }],
            "usage": { "prompt_tokens": 10, "completion_tokens": 3 }
        });
        let api: ApiResponse = serde_json::from_value(raw).unwrap();
        let resp = convert_response(api).unwrap();
        assert_eq!(resp.stop_reason, StopReason::ToolUse);
        assert_eq!(resp.usage.input_tokens, 10);
        assert_eq!(resp.usage.output_tokens, 3);
        match &resp.content[0] {
            Content::Text { text, .. } => assert_eq!(text, "calling a tool"),
            _ => panic!("expected text"),
        }
        match &resp.content[1] {
            Content::ToolUse { id, name, input } => {
                assert_eq!(id, "call_1");
                assert_eq!(name, "bash");
                assert_eq!(input["command"], "echo hi");
            }
            _ => panic!("expected tool_use"),
        }
    }

    #[test]
    fn response_maps_finish_reasons() {
        fn stop_for(reason: &str) -> StopReason {
            let raw = serde_json::json!({
                "choices": [{
                    "message": {"role": "assistant", "content": ""},
                    "finish_reason": reason
                }]
            });
            let api: ApiResponse = serde_json::from_value(raw).unwrap();
            convert_response(api).unwrap().stop_reason
        }
        assert_eq!(stop_for("stop"), StopReason::EndTurn);
        assert_eq!(stop_for("length"), StopReason::MaxTokens);
        assert_eq!(stop_for("tool_calls"), StopReason::ToolUse);
        assert_eq!(stop_for("content_filter"), StopReason::EndTurn);
    }

    #[test]
    fn classify_maps_retryable_status_codes() {
        assert!(matches!(
            classify_error(429, "".into(), Some(1000)),
            ProviderError::RateLimit {
                retry_after_ms: Some(1000)
            }
        ));
        assert!(matches!(
            classify_error(503, "".into(), None),
            ProviderError::Overloaded {
                retry_after_ms: None
            }
        ));
        assert!(matches!(
            classify_error(500, "oops".into(), None),
            ProviderError::Api {
                retryable: true,
                ..
            }
        ));
        assert!(matches!(
            classify_error(400, "bad".into(), None),
            ProviderError::Api {
                retryable: false,
                ..
            }
        ));
    }

    #[test]
    fn response_infers_tool_use_when_finish_reason_missing() {
        // Some compat backends omit `finish_reason` on tool-use turns.
        // The response carries `tool_calls` so we should still recognise
        // it as a ToolUse stop, not default to EndTurn.
        let raw = serde_json::json!({
            "choices": [{
                "message": {
                    "role": "assistant",
                    "tool_calls": [{
                        "id": "call_1",
                        "type": "function",
                        "function": {"name": "bash", "arguments": "{}"}
                    }]
                }
                // finish_reason intentionally absent
            }]
        });
        let api: ApiResponse = serde_json::from_value(raw).unwrap();
        let resp = convert_response(api).unwrap();
        assert_eq!(resp.stop_reason, StopReason::ToolUse);
    }

    #[test]
    fn request_marks_error_tool_results_with_prefix() {
        // The OpenAI tool-message schema has no is_error field; we must
        // encode the error state in the content so the next assistant
        // turn can disambiguate success from failure.
        let req = Request {
            model: "m".into(),
            system: None,
            messages: vec![Message::user(vec![
                Content::tool_result("call_ok", "all good", false),
                Content::tool_result("call_bad", "something broke", true),
            ])],
            tools: vec![],
            max_tokens: 10,
            temperature: None,
        };
        let body = build_request_body(&req);
        let json = serde_json::to_value(&body).unwrap();
        let msgs = json["messages"].as_array().unwrap();
        assert_eq!(msgs[0]["content"], "all good");
        assert_eq!(msgs[1]["content"], "[error] something broke");
    }

    #[test]
    fn request_skips_empty_assistant_messages() {
        // An assistant turn with neither text nor tool_calls would emit
        // {"role":"assistant"} — many compat endpoints reject this on the
        // next call. The encoder should drop it instead.
        let req = Request {
            model: "m".into(),
            system: None,
            messages: vec![
                Message::user_text("hi"),
                Message::assistant(vec![]), // empty turn
                Message::user_text("still there?"),
            ],
            tools: vec![],
            max_tokens: 10,
            temperature: None,
        };
        let body = build_request_body(&req);
        let json = serde_json::to_value(&body).unwrap();
        let msgs = json["messages"].as_array().unwrap();
        // Expect: user "hi", user "still there?" — empty assistant skipped.
        assert_eq!(msgs.len(), 2);
        assert_eq!(msgs[0]["role"], "user");
        assert_eq!(msgs[1]["role"], "user");
    }
}