import * as gunzip from "gunzip-maybe";
import { resolve as resolvePath } from "path";
import { Readable } from "stream";
import { extract, Extract } from "tar-stream";
import { applyCallbacks } from "./callbacks";
import { ExtractAction, ExtractedLayers, FileNameAndContent } from "./types";

/**
 * Extract key files from the specified TAR stream.
 * @param layerTarStream image layer as a Readable TAR stream. Note: consumes the stream.
 * @param extractActions array of pattern, callbacks pairs
 * @returns extracted file products
 */
export async function extractImageLayer(
  layerTarStream: Readable,
  extractActions: ExtractAction[],
): Promise<ExtractedLayers> {
  return new Promise((resolve, reject) => {
    const result: ExtractedLayers = {};
    const tarExtractor: Extract = extract();

    tarExtractor.on("entry", async (headers, stream, next) => {
      if (headers.type === "file") {
        const absoluteFileName = resolvePath("/", headers.name);
        // TODO wouldn't it be simpler to first check
        // if the filename matches any patterns?
        const processedResult = await extractFileAndProcess(
          absoluteFileName,
          stream,
          extractActions,
        );
        if (processedResult !== undefined) {
          result[absoluteFileName] = processedResult;
        }
      }

      stream.resume(); // auto drain the stream
      next(); // ready for next entry
    });

    tarExtractor.on("finish", () => {
      // all layer level entries read
      resolve(result);
    });

    tarExtractor.on("error", (error) => reject(error));

    layerTarStream.pipe(gunzip()).pipe(tarExtractor);
  });
}

/**
 * Note: consumes the stream.
 */
async function extractFileAndProcess(
  fileName: string,
  fileStream: Readable,
  extractActions: ExtractAction[],
): Promise<FileNameAndContent | undefined> {
  const matchedActions = extractActions.filter((action) =>
    action.filePathMatches(fileName),
  );

  if (matchedActions.length > 0) {
    return await applyCallbacks(matchedActions, fileStream);
  }

  return undefined;
}