//! SSE stream parser: converts SSE- or JSON-chunked LLM responses into
//! typed `StreamEvent` variants (tokens, reasoning, tool calls, usage, done).
pub mod turn;

use serde::{Deserialize, Serialize};
use serde_json::Value;

/// One atomic event extracted from an LLM streaming response stream.
#[derive(Debug, Clone, Serialize, Deserialize)]
pub enum StreamEvent {
    Token(String),
    Reasoning(String),
    ToolCallDelta {
        index: usize,
        id: Option<String>,
        name: Option<String>,
        arguments_delta: String,
    },
    Usage {
        prompt_tokens: u64,
        completion_tokens: u64,
        total_tokens: u64,
    },
    Done,
    Error(String),
}

/// Buffered SSE frame parser that accumulates raw `data:` lines and
/// flushes a `StreamEvent` on each blank-line boundary.
pub struct SseParser {
    buffer: String,
    event_type: Option<String>,
    data_lines: Vec<String>,
}

impl SseParser {
    /// Create a new parser with an empty buffer.
    pub fn new() -> Self {
        SseParser {
            buffer: String::new(),
            event_type: None,
            data_lines: Vec::new(),
        }
    }

    /// Feed a raw SSE chunk and produce any completed events.
    ///
    /// Flow: append chunk to buffer → scan for '\n' → strip '\r' → on
    /// blank line, call `flush_event` to parse the accumulated data →
    /// on `event:` line, store the event type → on `data:` line, append
    /// to data accumulator → continue until buffer exhausted.
    ///
    /// Edge case: a chunk may split mid-line; the remainder stays in the
    /// buffer for the next `feed()` call.
    ///
    /// Return: all `StreamEvent`s completed by this chunk.
    pub fn feed(&mut self, chunk: &str) -> Vec<StreamEvent> {
        self.buffer.push_str(chunk);
        let mut events = Vec::new();
        while let Some(line_end) = self.buffer.find('\n') {
            let line = self.buffer[..line_end].trim_end_matches('\r').to_string();
            self.buffer = self.buffer[line_end + 1..].to_string();
            if line.is_empty() {
                events.extend(self.flush_event());
            } else if let Some(ty) = line.strip_prefix("event: ") {
                self.event_type = Some(ty.trim().to_string());
            } else if let Some(data) = line.strip_prefix("data:") {
                // Handle both "data: {...}" (with space) and "data:{...}"
                // (without space). Some providers omit the trailing space.
                let data = data.trim_start().to_string();
                self.data_lines.push(data);
            }
        }
        events
    }

    /// Flush the current buffered `data:` lines as one or more `StreamEvent`s.
    ///
    /// Flow: join data lines → handle `[DONE]` sentinel → JSON-parse →
    /// emit `Usage` if a usage object is present → else match `event_type`
    /// ("message.stop", "message.delta", etc.) → extract content,
    /// reasoning, tool-call deltas, or finish-reason from the delta
    /// structure (supporting both Anthropic-style top-level delta and
    /// OpenAI-style `choices` array).
    ///
    /// Why: dual-format support in one method avoids a separate
    /// provider-specific parsing layer.
    ///
    /// Return: 0, 1, or more `StreamEvent`s from the flushed frame.

    fn flush_event(&mut self) -> Vec<StreamEvent> {
        let data = self.data_lines.join("\n");
        self.data_lines.clear();
        let event_type = self.event_type.take().unwrap_or_default();
        if data.is_empty() || data == "[DONE]" {
            if data == "[DONE]" {
                return vec![StreamEvent::Done];
            }
            return vec![];
        }
        let value: Value = match serde_json::from_str(&data) {
            Ok(v) => v,
            Err(e) => {
                tracing::warn!("[stream] failed to parse chunk: {}", e);
                return vec![];
            }
        };

        let mut events = Vec::new();

        if let Some(usage) = value.get("usage") {
            if !usage.is_null() {
                let prompt_tokens = usage
                    .get("prompt_tokens")
                    .and_then(serde_json::Value::as_u64)
                    .unwrap_or_else(|| {
                        tracing::warn!("[stream] prompt_tokens missing in usage chunk");
                        0
                    });
                let completion_tokens = usage
                    .get("completion_tokens")
                    .and_then(serde_json::Value::as_u64)
                    .unwrap_or_else(|| {
                        tracing::warn!("[stream] completion_tokens missing in usage chunk");
                        0
                    });
                let total_tokens = usage
                    .get("total_tokens")
                    .and_then(serde_json::Value::as_u64)
                    .unwrap_or_else(|| {
                        tracing::warn!("[stream] total_tokens missing in usage chunk");
                        prompt_tokens + completion_tokens
                    });
                events.push(StreamEvent::Usage {
                    prompt_tokens,
                    completion_tokens,
                    total_tokens,
                });
            }
        }

        let mut other_events = match event_type.as_str() {
            "message.stop" => vec![StreamEvent::Done],
            "message.delta" | "" => {
                let mut d_events = Vec::new();
                if let Some(delta) = value.get("delta").or_else(|| value.get("choices")) {
                    if let Some(choices) = delta.as_array() {
                        if let Some(choice) = choices.first() {
                            if let Some(d) = choice.get("delta") {
                                // Content token
                                if let Some(content) = d.get("content").and_then(|c| c.as_str()) {
                                    d_events.push(StreamEvent::Token(content.to_string()));
                                }

                                // Reasoning token
                                if let Some(reasoning) =
                                    d.get("reasoning_content").and_then(|r| r.as_str())
                                {
                                    d_events.push(StreamEvent::Reasoning(reasoning.to_string()));
                                }

                                // Tool calls — iterate ALL entries, not just first()
                                if let Some(tool_calls) =
                                    d.get("tool_calls").and_then(|tc| tc.as_array())
                                {
                                    for tc in tool_calls {
                                        let index = tc.get("index").and_then(serde_json::Value::as_u64).unwrap_or_else(|| {
                                            tracing::warn!("[stream] tool call delta missing index, defaulting to 0");
                                            0
                                        }) as usize;
                                        let id = tc
                                            .get("id")
                                            .and_then(|i| i.as_str())
                                            .map(std::string::ToString::to_string);
                                        let name = tc
                                            .get("function")
                                            .and_then(|f| f.get("name"))
                                            .and_then(|n| n.as_str())
                                            .map(std::string::ToString::to_string);
                                        let args_delta = tc
                                            .get("function")
                                            .and_then(|f| f.get("arguments"))
                                            .and_then(|a| a.as_str())
                                            .unwrap_or("")
                                            .to_string();
                                        d_events.push(StreamEvent::ToolCallDelta {
                                            index,
                                            id,
                                            name,
                                            arguments_delta: args_delta,
                                        });
                                    }
                                }

                                // Finish reason
                                if let Some(reason) =
                                    choice.get("finish_reason").and_then(|r| r.as_str())
                                {
                                    if reason == "stop" || reason == "tool_calls" {
                                        d_events.push(StreamEvent::Done);
                                    }
                                }
                            }
                        }
                    } else if let Some(content) = delta.get("content").and_then(|c| c.as_str()) {
                        d_events.push(StreamEvent::Token(content.to_string()));
                    }
                }
                d_events
            }
            _ => vec![],
        };

        events.append(&mut other_events);
        events
    }
}

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

    #[test]
    fn feed_parses_single_token_chunk() {
        let mut p = SseParser::new();
        let events = p.feed("data: {\"choices\":[{\"delta\":{\"content\":\"hello\"}}]}\n\n");
        assert_eq!(events.len(), 1);
        match &events[0] {
            StreamEvent::Token(t) => assert_eq!(t, "hello"),
            other => panic!("expected Token, got {other:?}"),
        }
    }

    #[test]
    fn feed_handles_chunk_split_mid_line() {
        let mut p = SseParser::new();
        let e1 = p.feed("data: {\"choices\":[{\"delta\":{\"content\":\"partial");
        assert!(
            e1.is_empty(),
            "no event until the line and blank separator complete"
        );
        let e2 = p.feed("\"}}]}\n\n");
        assert_eq!(e2.len(), 1);
        match &e2[0] {
            StreamEvent::Token(t) => assert_eq!(t, "partial"),
            other => panic!("expected Token, got {other:?}"),
        }
    }

    #[test]
    fn feed_emits_done_on_done_sentinel() {
        let mut p = SseParser::new();
        let events = p.feed("data: [DONE]\n\n");
        assert_eq!(events.len(), 1);
        assert!(matches!(events[0], StreamEvent::Done));
    }

    #[test]
    fn feed_emits_done_on_finish_reason_stop() {
        let mut p = SseParser::new();
        let events = p.feed("data: {\"choices\":[{\"delta\":{},\"finish_reason\":\"stop\"}]}\n\n");
        assert_eq!(events.len(), 1);
        assert!(matches!(events[0], StreamEvent::Done));
    }

    #[test]
    fn feed_parses_tool_call_delta() {
        let mut p = SseParser::new();
        let events = p.feed(
            "data: {\"choices\":[{\"delta\":{\"tool_calls\":[{\"index\":0,\"id\":\"call_1\",\"function\":{\"name\":\"bash\",\"arguments\":\"{\\\"cmd\\\"\"}}]}}]}\n\n",
        );
        assert_eq!(events.len(), 1);
        match &events[0] {
            StreamEvent::ToolCallDelta {
                index,
                id,
                name,
                arguments_delta,
            } => {
                assert_eq!(*index, 0);
                assert_eq!(id.as_deref(), Some("call_1"));
                assert_eq!(name.as_deref(), Some("bash"));
                assert_eq!(arguments_delta, "{\"cmd\"");
            }
            other => panic!("expected ToolCallDelta, got {other:?}"),
        }
    }

    #[test]
    fn feed_parses_usage_chunk() {
        let mut p = SseParser::new();
        let events = p.feed(
            "data: {\"choices\":[],\"usage\":{\"prompt_tokens\":10,\"completion_tokens\":5,\"total_tokens\":15}}\n\n",
        );
        assert_eq!(events.len(), 1);
        match &events[0] {
            StreamEvent::Usage {
                prompt_tokens,
                completion_tokens,
                total_tokens,
            } => {
                assert_eq!(*prompt_tokens, 10);
                assert_eq!(*completion_tokens, 5);
                assert_eq!(*total_tokens, 15);
            }
            other => panic!("expected Usage, got {other:?}"),
        }
    }

    #[test]
    fn feed_parses_usage_and_content_bundled_chunk() {
        let mut p = SseParser::new();
        let events = p.feed(
            "data: {\"choices\":[{\"delta\":{\"content\":\"hello\"}}],\"usage\":{\"prompt_tokens\":10,\"completion_tokens\":5,\"total_tokens\":15}}\n\n",
        );
        assert_eq!(events.len(), 2);
        match (&events[0], &events[1]) {
            (
                StreamEvent::Usage {
                    prompt_tokens,
                    completion_tokens,
                    total_tokens,
                },
                StreamEvent::Token(t),
            ) => {
                assert_eq!(*prompt_tokens, 10);
                assert_eq!(*completion_tokens, 5);
                assert_eq!(*total_tokens, 15);
                assert_eq!(t, "hello");
            }
            other => panic!("expected [Usage, Token], got {other:?}"),
        }
    }

    #[test]
    fn feed_ignores_empty_data_lines() {
        let mut p = SseParser::new();
        let events = p.feed(": comment\n\n");
        assert!(events.is_empty());
    }

    #[test]
    fn feed_multiple_events_across_one_chunk() {
        let mut p = SseParser::new();
        let chunk = "data: {\"choices\":[{\"delta\":{\"content\":\"a\"}}]}\n\ndata: {\"choices\":[{\"delta\":{\"content\":\"b\"}}]}\n\n";
        let events = p.feed(chunk);
        assert_eq!(events.len(), 2);
        match (&events[0], &events[1]) {
            (StreamEvent::Token(a), StreamEvent::Token(b)) => {
                assert_eq!(a, "a");
                assert_eq!(b, "b");
            }
            other => panic!("expected two Tokens, got {other:?}"),
        }
    }
}