// redis's admin client — redis's own code, living in the module (novox/hq ADR 0044). It speaks
// RESP directly over a raw TCP socket (node:net) so the module carries no npm dependency beyond
// @novox/mesh-sdk: no redis driver, no redis-cli in the image. Both this module's tools and its
// provisioner import it, and nothing outside redis does.
//
// The client keeps a single connection and runs one command at a time in FIFO order — enough for
// an admin surface (PING, INFO, ACL SETUSER/DELUSER, arbitrary commands). Replies come back in the
// order requests were sent, which is what the queue below relies on.

import { createConnection, type Socket } from "node:net";
import { randomBytes } from "node:crypto";
import { readFileSync } from "node:fs";

/** A parsed RESP value. Errors are surfaced as rejected commands, not as this type. */
export type RespValue = string | number | null | RespValue[];

interface Waiter {
  resolve: (v: RespValue) => void;
  reject: (e: Error) => void;
}

export class RedisClient {
  private socket: Socket | null = null;
  private buffer = Buffer.alloc(0);
  private queue: Waiter[] = [];

  constructor(
    readonly host: string,
    readonly port: number,
    private readonly password: string,
    private readonly username = "default",
  ) {}

  /**
   * Build from the module's resolved environment. Reads MESH_REDIS_* first (the documented
   * names), falling back to the MESH_PROVISION_* keys the manifest already sets on the
   * provisioner container so the module runs unchanged there. Throws if it cannot find a host and
   * an admin password — the right failure, because without them nothing it does can work.
   */
  static fromEnv(env: NodeJS.ProcessEnv = process.env): RedisClient {
    const endpoint = env.MESH_PROVISION_REDIS ?? ""; // "host:port"
    const host = env.MESH_REDIS_HOST ?? (endpoint ? endpoint.split(":")[0] : undefined);
    const port = Number(env.MESH_REDIS_PORT ?? (endpoint.includes(":") ? endpoint.split(":")[1] : "") ?? "6379") || 6379;
    const username = env.MESH_REDIS_USERNAME ?? "default";
    const password = env.MESH_REDIS_PASSWORD ?? readSecretFile(env.MESH_PROVISION_PASSWORD_FILE);
    if (!host || !password) {
      throw new Error("redis host or admin password is not set — redis's own code cannot reach the server");
    }
    return new RedisClient(host, port, password, username);
  }

  /** Open the connection (idempotent) and authenticate. Reconnects if the socket has gone away. */
  async connect(): Promise<void> {
    if (this.socket && !this.socket.destroyed) return;
    await new Promise<void>((resolve, reject) => {
      const sock = createConnection({ host: this.host, port: this.port });
      this.socket = sock;
      sock.on("data", (chunk: Buffer | string) => this.onData(typeof chunk === "string" ? Buffer.from(chunk) : chunk));
      sock.on("error", (err) => {
        this.failAll(err);
        reject(err);
      });
      sock.on("close", () => this.failAll(new Error("redis connection closed")));
      sock.once("connect", () => resolve());
    });
    if (this.password) {
      const args = this.username && this.username !== "default"
        ? ["AUTH", this.username, this.password]
        : ["AUTH", this.password];
      await this.send(args);
    }
  }

  /** Run one command and return its parsed reply. A RESP error reply rejects the promise. */
  async command(...args: (string | number)[]): Promise<RespValue> {
    await this.connect();
    return this.send(args.map(String));
  }

  async ping(): Promise<boolean> {
    return (await this.command("PING")) === "PONG";
  }

  /** Server INFO, returned both raw and parsed into the flat key/value map redis emits. */
  async info(section?: string): Promise<{ raw: string; fields: Record<string, string> }> {
    const raw = String((await this.command("INFO", ...(section ? [section] : []))) ?? "");
    const fields: Record<string, string> = {};
    for (const line of raw.split(/\r?\n/)) {
      if (!line || line.startsWith("#")) continue;
      const idx = line.indexOf(":");
      if (idx > 0) fields[line.slice(0, idx)] = line.slice(idx + 1);
    }
    return { raw, fields };
  }

  /**
   * Create (or reset to a known state) an ACL user scoped to one keyspace prefix. `reset` first
   * clears any prior rules so the call is idempotent, then the user is enabled with the given
   * password, confined to keys matching `<prefix>:*`, and allowed the ordinary command set. The
   * consumer connects as this user and can touch nothing outside its prefix.
   */
  async createAclUser(username: string, password: string, keyspacePrefix: string): Promise<void> {
    await this.command("ACL", "SETUSER", username, "reset", "on", `>${password}`, `~${keyspacePrefix}:*`, "+@all");
  }

  async deleteAclUser(username: string): Promise<void> {
    await this.command("ACL", "DELUSER", username);
  }

  close(): void {
    if (this.socket) {
      this.socket.destroy();
      this.socket = null;
    }
  }

  // --- connection plumbing ---

  /** Send an already-connected command, queuing its reply against the FIFO of in-flight requests. */
  private send(args: string[]): Promise<RespValue> {
    const sock = this.socket;
    if (!sock) return Promise.reject(new Error("redis socket is not connected"));
    return new Promise<RespValue>((resolve, reject) => {
      this.queue.push({ resolve, reject });
      sock.write(encodeCommand(args));
    });
  }

  /** Feed incoming bytes to the parser, resolving as many queued replies as the buffer completes. */
  private onData(chunk: Buffer): void {
    this.buffer = Buffer.concat([this.buffer, chunk]);
    while (this.queue.length > 0) {
      let parsed: { value: RespValue | Error; next: number } | null;
      try {
        parsed = parseReply(this.buffer, 0);
      } catch (err) {
        const waiter = this.queue.shift();
        waiter?.reject(err instanceof Error ? err : new Error(String(err)));
        this.buffer = Buffer.alloc(0);
        continue;
      }
      if (!parsed) break; // one full reply not yet in the buffer
      this.buffer = this.buffer.subarray(parsed.next);
      const waiter = this.queue.shift();
      if (!waiter) break;
      if (parsed.value instanceof Error) waiter.reject(parsed.value);
      else waiter.resolve(parsed.value);
    }
  }

  /** A socket error or close fails every pending command and forces a fresh connect next time. */
  private failAll(err: Error): void {
    const pending = this.queue;
    this.queue = [];
    for (const waiter of pending) waiter.reject(err);
    this.buffer = Buffer.alloc(0);
    if (this.socket) {
      this.socket.destroy();
      this.socket = null;
    }
  }
}

/** Generate a URL-safe password with no RESP-hostile characters. */
export function generatePassword(): string {
  return randomBytes(24).toString("base64url");
}

function readSecretFile(path: string | undefined): string | undefined {
  if (!path) return undefined;
  try {
    return readFileSync(path, "utf8").trim();
  } catch {
    return undefined;
  }
}

// --- RESP wire format ---

/** Encode a command as a RESP array of bulk strings. */
function encodeCommand(args: string[]): Buffer {
  let head = `*${args.length}\r\n`;
  for (const a of args) head += `$${Buffer.byteLength(a)}\r\n${a}\r\n`;
  return Buffer.from(head, "utf8");
}

/**
 * Parse one RESP reply starting at `i`. Returns the value and the offset just past it, or null if
 * the buffer does not yet hold a complete reply (the caller waits for more bytes). A `-` error
 * reply is returned as an Error value; the client turns that into a rejection.
 */
function parseReply(buf: Buffer, i: number): { value: RespValue | Error; next: number } | null {
  if (i >= buf.length) return null;
  const type = buf[i];
  const eol = buf.indexOf("\r\n", i + 1);
  if (eol === -1) return null; // header line not yet complete
  const line = buf.toString("utf8", i + 1, eol);
  const after = eol + 2;
  switch (type) {
    case 0x2b: // '+' simple string
      return { value: line, next: after };
    case 0x2d: // '-' error
      return { value: new Error(line), next: after };
    case 0x3a: // ':' integer
      return { value: Number(line), next: after };
    case 0x24: {
      // '$' bulk string
      const len = Number(line);
      if (len === -1) return { value: null, next: after };
      const end = after + len;
      if (buf.length < end + 2) return null; // body not fully arrived
      return { value: buf.toString("utf8", after, end), next: end + 2 };
    }
    case 0x2a: {
      // '*' array
      const count = Number(line);
      if (count === -1) return { value: null, next: after };
      const arr: RespValue[] = [];
      let cursor = after;
      for (let k = 0; k < count; k++) {
        const el = parseReply(buf, cursor);
        if (!el) return null; // array not fully arrived
        if (el.value instanceof Error) throw el.value;
        arr.push(el.value);
        cursor = el.next;
      }
      return { value: arr, next: cursor };
    }
    default:
      return { value: new Error(`unexpected RESP type byte 0x${type.toString(16)}`), next: after };
  }
}