// api/ — LLM API client with pluggable backends
//
// Supports two wire formats:
//   - OpenAI-compatible (OpenRouter, vLLM, llama.cpp, Qwen)
//   - Anthropic Messages API (direct API access, prompt caching)
//
// The backend is auto-detected from the API base URL. Both backends
// return the same internal types (Message, Usage) so the rest of
// the codebase doesn't need to know which is in use.
//
// Diagnostics: anomalies always logged to debug panel.
// Set POC_DEBUG=1 for verbose per-turn logging.

mod anthropic;
mod openai;

use anyhow::Result;
use reqwest::Client;
use std::time::{Duration, Instant};

use crate::agent::types::*;
use crate::agent::ui_channel::{StreamTarget, UiMessage, UiSender};

enum Backend {
    OpenAi {
        base_url: String,
    },
    Anthropic,
}

pub struct ApiClient {
    client: Client,
    api_key: String,
    pub model: String,
    backend: Backend,
}

impl ApiClient {
    pub fn new(base_url: &str, api_key: &str, model: &str) -> Self {
        let client = Client::builder()
            .connect_timeout(Duration::from_secs(30))
            .timeout(Duration::from_secs(600))
            .build()
            .expect("failed to build HTTP client");

        let base = base_url.trim_end_matches('/').to_string();
        let backend = if base.contains("anthropic.com") {
            Backend::Anthropic
        } else {
            Backend::OpenAi { base_url: base }
        };

        Self {
            client,
            api_key: api_key.to_string(),
            model: model.to_string(),
            backend,
        }
    }

    /// Streaming chat completion. Returns the assembled response message
    /// plus optional usage stats. Text tokens stream through the UI channel.
    ///
    /// Empty response handling is done at the agent level (agent.rs)
    /// where the conversation can be modified between retries.
    pub async fn chat_completion_stream(
        &self,
        messages: &[Message],
        tools: Option<&[ToolDef]>,
        ui_tx: &UiSender,
        target: StreamTarget,
        reasoning_effort: &str,
    ) -> Result<(Message, Option<Usage>)> {
        self.chat_completion_stream_temp(messages, tools, ui_tx, target, reasoning_effort, None).await
    }

    pub async fn chat_completion_stream_temp(
        &self,
        messages: &[Message],
        tools: Option<&[ToolDef]>,
        ui_tx: &UiSender,
        target: StreamTarget,
        reasoning_effort: &str,
        temperature: Option<f32>,
    ) -> Result<(Message, Option<Usage>)> {
        match &self.backend {
            Backend::OpenAi { base_url } => {
                openai::stream(
                    &self.client, base_url, &self.api_key, &self.model,
                    messages, tools, ui_tx, target, reasoning_effort, temperature,
                ).await
            }
            Backend::Anthropic => {
                anthropic::stream(
                    &self.client, &self.api_key, &self.model,
                    messages, tools, ui_tx, target, reasoning_effort,
                ).await
            }
        }
    }

    /// Return a label for the active backend, used in startup info.
    pub fn backend_label(&self) -> &str {
        match &self.backend {
            Backend::OpenAi { base_url } => {
                if base_url.contains("openrouter") {
                    "openrouter"
                } else {
                    "openai-compat"
                }
            }
            Backend::Anthropic => "anthropic",
        }
    }
}

/// Send an HTTP request and check for errors. Shared by both backends.
pub(crate) async fn send_and_check(
    client: &Client,
    url: &str,
    body: &impl serde::Serialize,
    auth_header: (&str, &str),
    extra_headers: &[(&str, &str)],
    ui_tx: &UiSender,
    debug_label: &str,
) -> Result<reqwest::Response> {
    let debug = std::env::var("POC_DEBUG").is_ok();
    let start = Instant::now();

    if debug {
        let payload_size = serde_json::to_string(body)
            .map(|s| s.len())
            .unwrap_or(0);
        let _ = ui_tx.send(UiMessage::Debug(format!(
            "request: {}K payload, {}",
            payload_size / 1024, debug_label,
        )));
    }

    let mut req = client
        .post(url)
        .header(auth_header.0, auth_header.1)
        .header("Content-Type", "application/json");

    for (name, value) in extra_headers {
        req = req.header(*name, *value);
    }

    let response = req
        .json(body)
        .send()
        .await
        .map_err(|e| {
            let cause = if e.is_connect() {
                "connection refused"
            } else if e.is_timeout() {
                "request timed out"
            } else if e.is_request() {
                "request error"
            } else {
                "unknown"
            };
            anyhow::anyhow!("{} ({}): {:?}", cause, url, e.without_url())
        })?;

    let status = response.status();
    let elapsed = start.elapsed();

    if debug {
        // Log interesting response headers
        let headers = response.headers();
        for name in [
            "x-ratelimit-remaining",
            "x-ratelimit-limit",
            "x-request-id",
        ] {
            if let Some(val) = headers.get(name) {
                let _ = ui_tx.send(UiMessage::Debug(format!(
                    "header {}: {}",
                    name,
                    val.to_str().unwrap_or("?")
                )));
            }
        }
    }

    if !status.is_success() {
        let body = response.text().await.unwrap_or_default();
        let _ = ui_tx.send(UiMessage::Debug(format!(
            "HTTP {} after {:.1}s ({}): {}",
            status,
            elapsed.as_secs_f64(),
            url,
            &body[..body.len().min(500)]
        )));
        anyhow::bail!("HTTP {} ({}): {}", status, url, &body[..body.len().min(1000)]);
    }

    if debug {
        let _ = ui_tx.send(UiMessage::Debug(format!(
            "connected in {:.1}s (HTTP {})",
            elapsed.as_secs_f64(),
            status.as_u16()
        )));
    }

    Ok(response)
}

/// SSE stream reader. Handles the generic SSE plumbing shared by both
/// backends: chunk reading with timeout, line buffering, `data:` prefix
/// stripping, `[DONE]` detection, JSON parsing, and parse error diagnostics.
/// Yields parsed events as serde_json::Value — each backend handles its
/// own event types.
pub(crate) struct SseReader {
    line_buf: String,
    chunk_timeout: Duration,
    pub stream_start: Instant,
    pub chunks_received: u64,
    pub sse_lines_parsed: u64,
    pub sse_parse_errors: u64,
    debug: bool,
    ui_tx: UiSender,
    done: bool,
}

impl SseReader {
    pub fn new(ui_tx: &UiSender) -> Self {
        Self {
            line_buf: String::new(),
            chunk_timeout: Duration::from_secs(120),
            stream_start: Instant::now(),
            chunks_received: 0,
            sse_lines_parsed: 0,
            sse_parse_errors: 0,
            debug: std::env::var("POC_DEBUG").is_ok(),
            ui_tx: ui_tx.clone(),
            done: false,
        }
    }

    /// Read the next SSE event from the response stream.
    /// Returns Ok(Some(value)) for each parsed data line,
    /// Ok(None) when the stream ends or [DONE] is received.
    pub async fn next_event(
        &mut self,
        response: &mut reqwest::Response,
    ) -> Result<Option<serde_json::Value>> {
        loop {
            // Drain complete lines from the buffer before reading more chunks
            while let Some(newline_pos) = self.line_buf.find('\n') {
                let line = self.line_buf[..newline_pos].trim().to_string();
                self.line_buf = self.line_buf[newline_pos + 1..].to_string();

                if line == "data: [DONE]" {
                    self.done = true;
                    return Ok(None);
                }
                if line.is_empty()
                    || line.starts_with("event: ")
                    || !line.starts_with("data: ")
                {
                    continue;
                }

                let json_str = &line[6..];
                self.sse_lines_parsed += 1;

                match serde_json::from_str(json_str) {
                    Ok(v) => return Ok(Some(v)),
                    Err(e) => {
                        self.sse_parse_errors += 1;
                        if self.sse_parse_errors == 1 || self.debug {
                            let preview = if json_str.len() > 200 {
                                format!("{}...", &json_str[..200])
                            } else {
                                json_str.to_string()
                            };
                            let _ = self.ui_tx.send(UiMessage::Debug(format!(
                                "SSE parse error (#{}) {}: {}",
                                self.sse_parse_errors, e, preview
                            )));
                        }
                        continue;
                    }
                }
            }

            if self.done {
                return Ok(None);
            }

            // Read more data from the response stream
            match tokio::time::timeout(self.chunk_timeout, response.chunk()).await {
                Ok(Ok(Some(chunk))) => {
                    self.chunks_received += 1;
                    self.line_buf.push_str(&String::from_utf8_lossy(&chunk));
                }
                Ok(Ok(None)) => return Ok(None),
                Ok(Err(e)) => return Err(e.into()),
                Err(_) => {
                    let _ = self.ui_tx.send(UiMessage::Debug(format!(
                        "TIMEOUT: no data for {}s ({} chunks, {:.1}s elapsed)",
                        self.chunk_timeout.as_secs(),
                        self.chunks_received,
                        self.stream_start.elapsed().as_secs_f64()
                    )));
                    anyhow::bail!(
                        "stream timeout: no data for {}s ({} chunks received)",
                        self.chunk_timeout.as_secs(),
                        self.chunks_received
                    );
                }
            }
        }
    }
}

/// Build a response Message from accumulated content and tool calls.
/// Shared by both backends — the wire format differs but the internal
/// representation is the same.
///
/// If no structured tool calls came from the API but the content
/// contains leaked tool call XML (e.g. `<tool_call>...</tool_call>`
/// from models that emit tool calls as text), parse them out and
/// promote them to structured tool_calls. This way all consumers
/// see tool calls uniformly regardless of backend.
pub(crate) fn build_response_message(
    content: String,
    tool_calls: Vec<ToolCall>,
) -> Message {
    // If the API returned structured tool calls, use them as-is.
    if !tool_calls.is_empty() {
        return Message {
            role: Role::Assistant,
            content: if content.is_empty() { None }
                     else { Some(MessageContent::Text(content)) },
            tool_calls: Some(tool_calls),
            tool_call_id: None,
            name: None,
            timestamp: None,
        };
    }

    // Check for leaked tool calls in content text.
    let leaked = crate::agent::parsing::parse_leaked_tool_calls(&content);
    if !leaked.is_empty() {
        let cleaned = crate::agent::parsing::strip_leaked_artifacts(&content);
        return Message {
            role: Role::Assistant,
            content: if cleaned.trim().is_empty() { None }
                     else { Some(MessageContent::Text(cleaned)) },
            tool_calls: Some(leaked),
            tool_call_id: None,
            name: None,
            timestamp: None,
        };
    }

    Message {
        role: Role::Assistant,
        content: if content.is_empty() { None }
                 else { Some(MessageContent::Text(content)) },
        tool_calls: None,
        tool_call_id: None,
        name: None,
        timestamp: None,
    }
}

/// Log stream diagnostics. Shared by both backends.
pub(crate) fn log_diagnostics(
    ui_tx: &UiSender,
    content_len: usize,
    tool_count: usize,
    reasoning_chars: usize,
    reasoning_effort: &str,
    finish_reason: &Option<String>,
    chunks_received: u64,
    sse_lines_parsed: u64,
    sse_parse_errors: u64,
    empty_deltas: u64,
    total_elapsed: Duration,
    first_content_at: Option<Duration>,
    usage: &Option<Usage>,
    tools: &[ToolCall],
) {
    let debug = std::env::var("POC_DEBUG").is_ok();

    if reasoning_chars > 0 && reasoning_effort == "none" {
        let _ = ui_tx.send(UiMessage::Debug(format!(
            "note: {} chars leaked reasoning (suppressed from display)",
            reasoning_chars
        )));
    }
    if content_len == 0 && tool_count == 0 {
        let _ = ui_tx.send(UiMessage::Debug(format!(
            "WARNING: empty response (finish: {:?}, chunks: {}, reasoning: {}, \
             parse_errors: {}, empty_deltas: {}, {:.1}s)",
            finish_reason, chunks_received, reasoning_chars,
            sse_parse_errors, empty_deltas, total_elapsed.as_secs_f64()
        )));
    }
    if finish_reason.is_none() && chunks_received > 0 {
        let _ = ui_tx.send(UiMessage::Debug(format!(
            "WARNING: stream ended without finish_reason ({} chunks, {} content chars)",
            chunks_received, content_len
        )));
    }
    if sse_parse_errors > 0 {
        let _ = ui_tx.send(UiMessage::Debug(format!(
            "WARNING: {} SSE parse errors out of {} lines",
            sse_parse_errors, sse_lines_parsed
        )));
    }

    if debug {
        if let Some(u) = usage {
            let _ = ui_tx.send(UiMessage::Debug(format!(
                "tokens: {} prompt + {} completion = {} total",
                u.prompt_tokens, u.completion_tokens, u.total_tokens
            )));
        }
        let ttft = first_content_at
            .map(|d| format!("{:.1}s", d.as_secs_f64()))
            .unwrap_or_else(|| "none".to_string());
        let _ = ui_tx.send(UiMessage::Debug(format!(
            "stream: {:.1}s total, TTFT={}, {} chunks, {} SSE lines, \
             {} content chars, {} reasoning chars, {} tools, \
             finish={:?}",
            total_elapsed.as_secs_f64(),
            ttft,
            chunks_received,
            sse_lines_parsed,
            content_len,
            reasoning_chars,
            tool_count,
            finish_reason,
        )));
        if !tools.is_empty() {
            for (i, tc) in tools.iter().enumerate() {
                let _ = ui_tx.send(UiMessage::Debug(format!(
                    "  tool[{}]: {} (id: {}, {} arg chars)",
                    i, tc.function.name, tc.id, tc.function.arguments.len()
                )));
            }
        }
    }
}