stream-transform/lib/index.js

Object transformations implementing the Node.js `stream.Transform` API

/*
Stream Transform

Please look at the [project documentation](https://csv.js.org/transform/) for
additional information.
*/

import stream from "stream";
import util from "util";

const Transformer = function (options = {}, handler) {
  this.options = options;
  if (options.consume === undefined || options.consume === null) {
    this.options.consume = false;
  }
  this.options.objectMode = true;
  if (options.parallel === undefined || options.parallel === null) {
    this.options.parallel = 100;
  }
  if (options.params === undefined || options.params === null) {
    options.params = null;
  }
  this.handler = handler;
  stream.Transform.call(this, this.options);
  this.state = {
    running: 0,
    started: 0,
    finished: 0,
    paused: false,
  };
  return this;
};

util.inherits(Transformer, stream.Transform);

Transformer.prototype._transform = function (chunk, _, cb) {
  this.state.started++;
  this.state.running++;
  // Accept additionnal chunks to be processed in parallel
  if (!this.state.paused && this.state.running < this.options.parallel) {
    cb();
    cb = null; // Cancel further callback execution
  }
  try {
    let l = this.handler.length;
    if (this.options.params !== null) {
      l--;
    }
    if (l === 1) {
      // sync
      const result = this.handler.call(this, chunk, this.options.params);
      if (result && result.then) {
        result.then((result) => {
          this.__done(null, [result], cb);
        });
        result.catch((err) => {
          this.__done(err);
        });
      } else {
        this.__done(null, [result], cb);
      }
    } else if (l === 2) {
      // async
      const callback = (err, ...chunks) => this.__done(err, chunks, cb);
      this.handler.call(this, chunk, callback, this.options.params);
    } else {
      throw Error("Invalid handler arguments");
    }
    return false;
  } catch (err) {
    this.__done(err);
  }
};
Transformer.prototype._flush = function (cb) {
  if (this.state.running === 0) {
    cb();
  } else {
    this._ending = function () {
      cb();
    };
  }
};
Transformer.prototype.__done = function (err, chunks, cb) {
  this.state.running--;
  if (err) {
    return this.destroy(err);
    // return this.emit('error', err);
  }
  this.state.finished++;
  for (let chunk of chunks) {
    if (typeof chunk === "number") {
      chunk = `${chunk}`;
    }
    // We dont push empty string
    // See https://nodejs.org/api/stream.html#stream_readable_push
    if (chunk !== undefined && chunk !== null && chunk !== "") {
      this.state.paused = !this.push(chunk);
    }
  }
  // Chunk has been processed
  if (cb) {
    cb();
  }
  if (this._ending && this.state.running === 0) {
    this._ending();
  }
};
const transform = function () {
  let options = {};
  let callback, handler, records;
  for (let i = 0; i < arguments.length; i++) {
    const argument = arguments[i];
    let type = typeof argument;
    if (argument === null) {
      type = "null";
    } else if (type === "object" && Array.isArray(argument)) {
      type = "array";
    }
    if (type === "array") {
      records = argument;
    } else if (type === "object") {
      options = { ...argument };
    } else if (type === "function") {
      if (handler && i === arguments.length - 1) {
        callback = argument;
      } else {
        handler = argument;
      }
    } else if (type !== "null") {
      throw new Error(
        `Invalid Arguments: got ${JSON.stringify(argument)} at position ${i}`,
      );
    }
  }
  const transformer = new Transformer(options, handler);
  let error = false;
  if (records) {
    const writer = function () {
      for (const record of records) {
        if (error) break;
        transformer.write(record);
      }
      transformer.end();
    };
    // Support Deno, Rollup doesnt provide a shim for setImmediate
    if (typeof setImmediate === "function") {
      setImmediate(writer);
    } else {
      setTimeout(writer, 0);
    }
  }
  if (callback || options.consume) {
    const result = [];
    transformer.on("readable", function () {
      let record;
      while ((record = transformer.read()) !== null) {
        if (callback) {
          result.push(record);
        }
      }
    });
    transformer.on("error", function (err) {
      error = true;
      if (callback) callback(err);
    });
    transformer.on("end", function () {
      if (callback && !error) callback(null, result);
    });
  }
  return transformer;
};

// export default transform
export { transform, Transformer };