//! OpenCode GO adapter — multi-vendor curated gateway via opencode.ai/zen/go.
//!
//! One sk-* key reaches Claude Opus 4.7, GPT-5.5-pro, Gemini 3.1-pro,
//! Kimi K2.6, DeepSeek, GLM, Qwen, plus 4 free-tier models.
//! OpenAI-compatible Chat Completions; auth via Bearer.
//!
//! Why a separate adapter (vs reusing openrouter.rs):
//! - Different account, different key, different base_url
//! - No HTTP-Referer / X-Title headers (those are OpenRouter-specific)
//! - Future-proof for any opencode-only request shaping
//!
//! Key sourcing priority:
//!   1. Env var `OPENCODE_API_KEY` (loaded from /etc/lakehouse/opencode.env
//!      via systemd EnvironmentFile=)
//!   2. /etc/lakehouse/opencode.env directly (rescue path if env missing)
//!
//! Resolved once at gateway startup, stored on `V1State.opencode_key`.
//! Model-prefix routing: "opencode/<model>" auto-routes here, prefix
//! stripped before upstream call.

use std::time::Duration;
use serde::{Deserialize, Serialize};

use super::{ChatRequest, ChatResponse, Choice, Message, UsageBlock};

// /zen/v1 is the unified OpenCode endpoint that covers BOTH the
// Zen pay-per-token tier (Claude/GPT/Gemini frontier) AND the Go
// subscription tier (Kimi/GLM/DeepSeek/Qwen/Minimax/mimo). When the
// caller has both, opencode bills per-model: Zen models charge Zen
// balance, Go models charge against the Go subscription cap.
//
// /zen/go/v1 exists as a Go-only sub-path (rejects Zen models with
// "Model not supported"); we use the unified /zen/v1 since the same
// key works for both with correct billing routing upstream.
const OPENCODE_BASE_URL: &str = "https://opencode.ai/zen/v1";
// 600s default — opencode upstream models include reasoning-heavy
// variants (Claude Opus, Kimi K2.6, GLM-5.1) that legitimately take
// 3-5 min on big audit prompts. Override via OPENCODE_TIMEOUT_SECS.
const OPENCODE_TIMEOUT_SECS_DEFAULT: u64 = 600;

fn opencode_timeout_secs() -> u64 {
    std::env::var("OPENCODE_TIMEOUT_SECS")
        .ok()
        .and_then(|s| s.trim().parse::<u64>().ok())
        .filter(|&n| n > 0)
        .unwrap_or(OPENCODE_TIMEOUT_SECS_DEFAULT)
}

pub fn resolve_opencode_key() -> Option<String> {
    if let Ok(k) = std::env::var("OPENCODE_API_KEY") {
        if !k.trim().is_empty() { return Some(k.trim().to_string()); }
    }
    if let Ok(raw) = std::fs::read_to_string("/etc/lakehouse/opencode.env") {
        for line in raw.lines() {
            if let Some(rest) = line.strip_prefix("OPENCODE_API_KEY=") {
                let k = rest.trim().trim_matches('"').trim_matches('\'');
                if !k.is_empty() { return Some(k.to_string()); }
            }
        }
    }
    None
}

pub async fn chat(
    key: &str,
    req: &ChatRequest,
) -> Result<ChatResponse, String> {
    // Strip the "opencode/" namespace prefix so the upstream sees the
    // bare model id (e.g. "claude-opus-4-7", "kimi-k2.6").
    let model = req.model.strip_prefix("opencode/").unwrap_or(&req.model).to_string();

    // Anthropic models on opencode reject `temperature` with a 400
    // "temperature is deprecated for this model" error. Strip the
    // field for claude-* and the new gpt-5.x reasoning lineages
    // (Anthropic/OpenAI's reasoning models all moved away from temp).
    // Other models keep the caller's value or default to 0.3.
    let drop_temp = model.starts_with("claude-")
        || model.starts_with("gpt-5")
        || model.starts_with("o1")
        || model.starts_with("o3")
        || model.starts_with("o4");
    let body = OCChatBody {
        model: model.clone(),
        messages: req.messages.iter().map(|m| OCMessage {
            role: m.role.clone(),
            content: m.content.clone(),
        }).collect(),
        // filter(|&n| n > 0) catches Some(0) — same trap that bit the
        // Kimi adapter when callers passed empty-env-parsed-to-0.
        max_tokens: req.max_tokens.filter(|&n| n > 0).unwrap_or(800),
        temperature: if drop_temp { None } else { Some(req.temperature.unwrap_or(0.3)) },
        stream: false,
    };

    let client = reqwest::Client::builder()
        .timeout(Duration::from_secs(opencode_timeout_secs()))
        .build()
        .map_err(|e| format!("build client: {e}"))?;

    let t0 = std::time::Instant::now();
    let resp = client
        .post(format!("{}/chat/completions", OPENCODE_BASE_URL))
        .bearer_auth(key)
        .json(&body)
        .send()
        .await
        .map_err(|e| format!("opencode.ai unreachable: {e}"))?;

    let status = resp.status();
    if !status.is_success() {
        let body = resp.text().await.unwrap_or_else(|_| "?".into());
        return Err(format!("opencode.ai {}: {}", status, body));
    }

    let parsed: OCChatResponse = resp.json().await
        .map_err(|e| format!("invalid opencode response: {e}"))?;

    let latency_ms = t0.elapsed().as_millis();
    let choice = parsed.choices.into_iter().next()
        .ok_or_else(|| "opencode returned no choices".to_string())?;
    let text = choice.message.content;

    let prompt_tokens = parsed.usage.as_ref().map(|u| u.prompt_tokens).unwrap_or_else(|| {
        let chars: usize = req.messages.iter().map(|m| m.text().chars().count()).sum();
        ((chars + 3) / 4) as u32
    });
    let completion_tokens = parsed.usage.as_ref().map(|u| u.completion_tokens).unwrap_or_else(|| {
        ((text.chars().count() + 3) / 4) as u32
    });

    tracing::info!(
        target: "v1.chat",
        provider = "opencode",
        model = %model,
        prompt_tokens,
        completion_tokens,
        latency_ms = latency_ms as u64,
        "opencode chat completed",
    );

    Ok(ChatResponse {
        id: format!("chatcmpl-{}", chrono::Utc::now().timestamp_nanos_opt().unwrap_or(0)),
        object: "chat.completion",
        created: chrono::Utc::now().timestamp(),
        model,
        choices: vec![Choice {
            index: 0,
            message: Message { role: "assistant".into(), content: serde_json::Value::String(text) },
            finish_reason: choice.finish_reason.unwrap_or_else(|| "stop".into()),
        }],
        usage: UsageBlock {
            prompt_tokens,
            completion_tokens,
            total_tokens: prompt_tokens + completion_tokens,
        },
    })
}

// -- OpenCode wire shapes (OpenAI-compatible) --

#[derive(Serialize)]
struct OCChatBody {
    model: String,
    messages: Vec<OCMessage>,
    max_tokens: u32,
    #[serde(skip_serializing_if = "Option::is_none")]
    temperature: Option<f64>,
    stream: bool,
}

#[derive(Serialize)]
struct OCMessage { role: String, content: serde_json::Value }

#[derive(Deserialize)]
struct OCChatResponse {
    choices: Vec<OCChoice>,
    #[serde(default)]
    usage: Option<OCUsage>,
}

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

#[derive(Deserialize)]
struct OCMessageResp { content: String }

#[derive(Deserialize)]
struct OCUsage { prompt_tokens: u32, completion_tokens: u32 }

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

    #[test]
    fn resolve_opencode_key_does_not_panic() {
        let _ = resolve_opencode_key();
    }

    #[test]
    fn model_prefix_strip() {
        let cases = [
            ("opencode/claude-opus-4-7", "claude-opus-4-7"),
            ("opencode/kimi-k2.6", "kimi-k2.6"),
            ("claude-opus-4-7", "claude-opus-4-7"),
        ];
        for (input, expected) in cases {
            let out = input.strip_prefix("opencode/").unwrap_or(input);
            assert_eq!(out, expected);
        }
    }

    #[test]
    fn max_tokens_filters_zero() {
        // The trap: empty env -> Number("") -> 0 -> Some(0). Adapter
        // must not pass 0 upstream; should fall to 800.
        let some_zero: Option<u32> = Some(0);
        let result = some_zero.filter(|&n| n > 0).unwrap_or(800);
        assert_eq!(result, 800);
        let some_real: Option<u32> = Some(4096);
        assert_eq!(some_real.filter(|&n| n > 0).unwrap_or(800), 4096);
        let none_val: Option<u32> = None;
        assert_eq!(none_val.filter(|&n| n > 0).unwrap_or(800), 800);
    }
}