/**
 * codex-cli adapter — bridge to a user-installed local code helper
 * binary (e.g. OpenAI's `codex` CLI or any other shell-invoked code
 * assistant) so the "DoAtlas Code" model can stream through the same
 * gateway / SSE pipeline as the cloud providers.
 *
 * Wire protocol (newline-delimited JSON, both directions):
 *
 *   stdin  (single JSON object, then EOF):
 *     {
 *       "model": "<upstreamModel>",
 *       "messages": [{ role, content, tool_call_id?, tool_calls? }, ...],
 *       "tools":    [{ name, description, parameters }, ...],
 *       "temperature"?: number,
 *       "max_tokens"?: number
 *     }
 *
 *   stdout (one JSON event per line):
 *     { "type": "text_delta",      "text": "..." }
 *     { "type": "reasoning_delta", "text": "..." }
 *     { "type": "tool_call",       "id": "...", "name": "...", "arguments": {...} }
 *     { "type": "usage",           "input_tokens": N, "output_tokens": N }
 *     { "type": "done",            "stop_reason": "end_turn" | "tool_use" | ... }
 *     { "type": "error",           "message": "...", "code"?: "..." }
 *
 * The binary is configured via env:
 *   CODEX_CLI_BIN   — absolute path or PATH-resolvable command (required)
 *   CODEX_CLI_ARGS  — optional space-separated extra args
 *   CODEX_CLI_CWD   — optional working directory (default: process.cwd())
 *
 * Anything the binary writes to stderr is forwarded to the server log
 * but never bleeds into the user-visible answer.
 */
import { spawn } from "node:child_process";
import { logger } from "../lib/logger";
import { withGateway } from "./gateway";
import type { LlmAdapter, LlmStreamOptions, StreamChunk } from "./types";

interface CodexCliConfig {
  bin: string;
  args: string[];
  cwd: string;
}

/**
 * Carries a normalised provider error code alongside the human-readable
 * message so the gateway can forward both to the SSE stream instead of
 * collapsing every codex-cli failure into a generic `unknown_error`.
 */
class CodexCliError extends Error {
  readonly providerErrorCode: string;
  constructor(message: string, providerErrorCode: string) {
    super(message);
    this.name = "CodexCliError";
    this.providerErrorCode = providerErrorCode;
  }
}

interface NodeSpawnError extends Error {
  code?: string;
  syscall?: string;
  path?: string;
}

function mapSpawnError(err: NodeSpawnError, bin: string): CodexCliError {
  const code = err.code;
  if (code === "ENOENT") {
    return new CodexCliError(
      `DoAtlas Code helper binary not found at "${bin}". ` +
        `Set CODEX_CLI_BIN to the path of an installed local code helper.`,
      "codex_cli_not_found",
    );
  }
  if (code === "EACCES" || code === "EPERM") {
    return new CodexCliError(
      `Permission denied executing DoAtlas Code helper at "${bin}". ` +
        `Make sure the file is executable (chmod +x).`,
      "codex_cli_permission_denied",
    );
  }
  return new CodexCliError(
    `Failed to launch DoAtlas Code helper at "${bin}": ${err.message}`,
    "codex_cli_spawn_failed",
  );
}

function readConfig(): CodexCliConfig {
  const bin = process.env["CODEX_CLI_BIN"];
  if (!bin) {
    throw new Error(
      "DoAtlas Code not configured: set CODEX_CLI_BIN to the local code helper binary",
    );
  }
  const rawArgs = (process.env["CODEX_CLI_ARGS"] || "").trim();
  const args = rawArgs ? rawArgs.split(/\s+/) : [];
  const cwd = process.env["CODEX_CLI_CWD"] || process.cwd();
  return { bin, args, cwd };
}

interface RawEvent {
  type?: string;
  text?: string;
  id?: string;
  name?: string;
  arguments?: Record<string, unknown>;
  input_tokens?: number;
  output_tokens?: number;
  stop_reason?: string;
  message?: string;
  code?: string;
}

function toChunk(ev: RawEvent): StreamChunk | null {
  switch (ev.type) {
    case "text_delta":
      return { type: "text_delta", text: ev.text || "" };
    case "reasoning_delta":
      return { type: "reasoning_delta", text: ev.text || "" };
    case "tool_call":
      if (!ev.id || !ev.name) return null;
      return {
        type: "tool_call",
        toolCallId: ev.id,
        toolName: ev.name,
        toolArguments: ev.arguments ?? {},
      };
    case "usage":
      return {
        type: "usage",
        inputTokens: ev.input_tokens ?? 0,
        outputTokens: ev.output_tokens ?? 0,
      };
    case "done":
      return { type: "done", stopReason: ev.stop_reason };
    case "error":
      return {
        type: "error",
        message: ev.message || "codex-cli error",
        providerErrorCode: ev.code,
      };
    default:
      return null;
  }
}

async function* runCodexCli(
  cfg: CodexCliConfig,
  opts: LlmStreamOptions,
  signal: AbortSignal,
): AsyncIterable<StreamChunk> {
  const child = spawn(cfg.bin, cfg.args, {
    cwd: cfg.cwd,
    stdio: ["pipe", "pipe", "pipe"],
    env: process.env,
  });

  let spawned = false;
  child.once("spawn", () => {
    spawned = true;
  });

  // Forward upstream aborts as SIGTERM.
  const onAbort = () => {
    if (!child.killed) child.kill("SIGTERM");
  };
  if (signal.aborted) onAbort();
  else signal.addEventListener("abort", onAbort, { once: true });

  // Stderr is captured for the server log AND mirrored into the
  // user-facing failure message when the helper exits non-zero — that
  // tail is usually the only clue the operator has about what went
  // wrong (missing model, bad config, etc.).
  let stderrBuf = "";
  child.stderr.setEncoding("utf8");
  child.stderr.on("data", (d: string) => {
    stderrBuf += d;
    if (stderrBuf.length > 8192) {
      stderrBuf = stderrBuf.slice(-8192);
    }
  });

  // Backpressure-friendly stdout queue.
  type Item = { line?: string; end?: true; err?: CodexCliError };
  const queue: Item[] = [];
  let waiter: ((it: Item) => void) | null = null;
  const push = (it: Item) => {
    if (waiter) {
      const w = waiter;
      waiter = null;
      w(it);
    } else {
      queue.push(it);
    }
  };
  const next = (): Promise<Item> =>
    queue.length > 0
      ? Promise.resolve(queue.shift()!)
      : new Promise<Item>((r) => {
          waiter = r;
        });

  // The child's stdout `end` and process `close` events fire in
  // unspecified order; we must wait for *both* before declaring the
  // request truly finished, otherwise an early `end` would race past a
  // non-zero exit code and the consumer would never see the error.
  let stdoutEnded = false;
  let childClosed = false;
  let pendingErr: CodexCliError | null = null;

  const maybeFinish = () => {
    if (!stdoutEnded || !childClosed) return;
    if (pendingErr) push({ err: pendingErr });
    push({ end: true });
  };

  let buf = "";
  child.stdout.setEncoding("utf8");
  child.stdout.on("data", (d: string) => {
    buf += d;
    let idx: number;
    while ((idx = buf.indexOf("\n")) >= 0) {
      const line = buf.slice(0, idx).trim();
      buf = buf.slice(idx + 1);
      if (line) push({ line });
    }
  });
  child.stdout.on("end", () => {
    const tail = buf.trim();
    buf = "";
    if (tail) push({ line: tail });
    stdoutEnded = true;
    maybeFinish();
  });
  child.on("error", (err) => {
    pendingErr = mapSpawnError(err as NodeSpawnError, cfg.bin);
    stdoutEnded = true;
    childClosed = true;
    maybeFinish();
  });
  child.on("close", (code, sigSignal) => {
    if (!pendingErr && code != null && code !== 0) {
      const tail = stderrBuf.trim().slice(-500);
      const detail = tail ? `: ${tail}` : "";
      pendingErr = new CodexCliError(
        `DoAtlas Code helper exited with code ${code}${detail}`,
        spawned ? "codex_cli_exited" : "codex_cli_spawn_failed",
      );
    } else if (!pendingErr && code == null && sigSignal && sigSignal !== "SIGTERM") {
      const tail = stderrBuf.trim().slice(-500);
      const detail = tail ? `: ${tail}` : "";
      pendingErr = new CodexCliError(
        `DoAtlas Code helper terminated by signal ${sigSignal}${detail}`,
        "codex_cli_exited",
      );
    }
    childClosed = true;
    maybeFinish();
  });

  // Send the request payload, then close stdin.
  const payload = JSON.stringify({
    model: opts.model,
    messages: opts.messages,
    tools: opts.tools ?? [],
    temperature: opts.temperature,
    max_tokens: opts.maxTokens,
  });
  // Swallow stdin errors here — when spawn fails (ENOENT / EACCES) the
  // stdin pipe also tears down, but the structured `child.on("error")`
  // handler above is the source of truth for the user-facing message.
  child.stdin.on("error", () => {
    /* surfaced via child.on("error") */
  });
  try {
    child.stdin.write(payload + "\n");
    child.stdin.end();
  } catch {
    /* swallowed; child.on("error") will surface the real cause */
  }

  let sawDone = false;
  let sawUsage = false;
  try {
    while (true) {
      const it = await next();
      if (it.err) throw it.err;
      if (it.end) break;
      if (!it.line) continue;
      let ev: RawEvent;
      try {
        ev = JSON.parse(it.line) as RawEvent;
      } catch {
        // Treat non-JSON lines as plain text deltas so a misbehaving
        // helper still produces *something* the user can read instead
        // of a silent hang.
        yield { type: "text_delta", text: it.line };
        continue;
      }
      const chunk = toChunk(ev);
      if (!chunk) continue;
      if (chunk.type === "usage") sawUsage = true;
      if (chunk.type === "done") sawDone = true;
      yield chunk;
    }
  } finally {
    if (!child.killed) child.kill("SIGTERM");
  }

  if (stderrBuf.trim()) {
    logger.warn(
      { adapter: "codex-cli", stderr: stderrBuf.trim().slice(0, 1000) },
      "codex-cli stderr",
    );
  }
  if (!sawUsage) {
    yield { type: "usage", inputTokens: 0, outputTokens: 0 };
  }
  if (!sawDone) {
    yield { type: "done", stopReason: "end_turn" };
  }
}

export const codexCliAdapter: LlmAdapter = {
  name: "codex-cli",
  stream(opts: LlmStreamOptions): AsyncIterable<StreamChunk> {
    const cfg = readConfig();
    return withGateway(
      { name: "codex-cli", source: "byok-direct", upstream: cfg.bin, retries: 0 },
      (signal) => runCodexCli(cfg, opts, signal),
    );
  },
};