const fs = require("fs");
const crypto = require("crypto");
const { resolveData } = require("./paths");

class SafeAnswerCache {
  constructor(getConfig) {
    this.getConfig = getConfig;
    this.file = resolveData("cache", "gate-answers.json");
  }

  key({ message, role, platform }) {
    const normalized = String(message || "").toLowerCase().replace(/\s+/g, " ").trim();
    return crypto.createHash("sha256")
      .update(`gate-cache-v2\n${role || "user"}\n${platform || "webui"}\n${normalized}`)
      .digest("hex");
  }

  get(input) {
    const entry = this.read().entries[this.key(input)];
    if (!entry) return null;
    if (new Date(entry.expires_at).getTime() <= Date.now()) {
      this.delete(input);
      return null;
    }
    return entry;
  }

  set(input, answer) {
    if (!answer?.text || answer.safe !== true) return null;
    const ttlSeconds = Math.max(30, Number(this.getConfig()?.gate?.cache_ttl_seconds) || 3600);
    const store = this.read();
    const key = this.key(input);
    store.entries[key] = {
      text: String(answer.text),
      links: Array.isArray(answer.links) ? answer.links.slice(0, 8) : [],
      source: answer.source || null,
      created_at: new Date().toISOString(),
      expires_at: new Date(Date.now() + ttlSeconds * 1000).toISOString()
    };
    this.write(store);
    return store.entries[key];
  }

  delete(input) {
    const store = this.read();
    delete store.entries[this.key(input)];
    this.write(store);
  }

  read() {
    try {
      const parsed = JSON.parse(fs.readFileSync(this.file, "utf8"));
      return { entries: parsed.entries || {} };
    } catch {
      return { entries: {} };
    }
  }

  write(store) {
    const tmp = `${this.file}.${process.pid}.${crypto.randomBytes(4).toString("hex")}.tmp`;
    try {
      fs.writeFileSync(tmp, `${JSON.stringify(store, null, 2)}\n`);
      fs.renameSync(tmp, this.file);
    } finally {
      fs.rmSync(tmp, { force: true });
    }
  }
}

module.exports = { SafeAnswerCache };