const fs = require("fs");
const fsp = require("fs/promises");

function createJsonStorage(options) {
  const dataDir = options.dataDir;

  return {
    id: "json",
    async init() {
      await fsp.mkdir(dataDir, { recursive: true });
    },
    async exists(key) {
      return fs.existsSync(key);
    },
    async readJson(key, fallback = null) {
      try {
        const raw = await fsp.readFile(key, "utf8");
        const parsed = parseJsonWithTrailingRecovery(raw);
        if (parsed.ok) {
          if (parsed.repaired) {
            await backupCorruptJsonFile(key, raw, "trailing-garbage");
            await fsp.writeFile(key, `${JSON.stringify(parsed.value, null, 2)}\n`, "utf8");
            console.warn(`[json-storage] repaired trailing JSON data in ${key}`);
          }
          return parsed.value;
        }

        if (fallback !== undefined) {
          await backupCorruptJsonFile(key, raw, "invalid-json");
          await fsp.writeFile(key, `${JSON.stringify(fallback, null, 2)}\n`, "utf8");
          console.warn(`[json-storage] invalid JSON in ${key}, restored fallback`);
          return fallback;
        }
        throw parsed.error;
      } catch (error) {
        if (error.code === "ENOENT") {
          return fallback;
        }
        throw error;
      }
    },
    async writeJson(key, value) {
      await fsp.writeFile(key, `${JSON.stringify(value, null, 2)}\n`, "utf8");
    },
    async appendText(key, text) {
      await fsp.appendFile(key, text, "utf8");
    },
    async readText(key, fallback = "") {
      try {
        return await fsp.readFile(key, "utf8");
      } catch (error) {
        if (error.code === "ENOENT") {
          return fallback;
        }
        throw error;
      }
    },
    async writeText(key, text) {
      await fsp.writeFile(key, text, "utf8");
    }
  };
}

function parseJsonWithTrailingRecovery(raw) {
  try {
    return { ok: true, repaired: false, value: JSON.parse(raw) };
  } catch (error) {
    const message = String(error && error.message ? error.message : "");
    const match = message.match(/position\s+(\d+)/i);
    if (!match) {
      return { ok: false, error };
    }
    const position = Number(match[1]);
    if (!Number.isFinite(position) || position <= 0 || position >= raw.length) {
      return { ok: false, error };
    }
    const prefix = raw.slice(0, position).trimEnd();
    if (!prefix) {
      return { ok: false, error };
    }
    try {
      return { ok: true, repaired: true, value: JSON.parse(prefix) };
    } catch {
      return { ok: false, error };
    }
  }
}

async function backupCorruptJsonFile(key, raw, reason) {
  try {
    const stamp = new Date().toISOString().replace(/[:.]/g, "-");
    const suffix = String(reason || "corrupt").replace(/[^a-z0-9-]/gi, "-").toLowerCase();
    const backupPath = `${key}.${suffix}.${stamp}.bak`;
    await fsp.writeFile(backupPath, raw, "utf8");
  } catch {
    // best effort backup only
  }
}

module.exports = {
  createJsonStorage
};