/*
 * decaffeinate suggestions:
 * DS102: Remove unnecessary code created because of implicit returns
 * DS207: Consider shorter variations of null checks
 * Full docs: https://github.com/decaffeinate/decaffeinate/blob/master/docs/suggestions.md
 */
let OutputFileOptimiser;
const fs = require("fs");
const Path = require("path");
const { spawn } = require("child_process");
const logger = require("logger-sharelatex");
const Metrics = require("./Metrics");
const _ = require("underscore");

module.exports = (OutputFileOptimiser = {

	optimiseFile(src, dst, callback) {
		// check output file (src) and see if we can optimise it, storing
		// the result in the build directory (dst)
		if (callback == null) { callback = function(error) {}; }
		if (src.match(/\/output\.pdf$/)) {
			return OutputFileOptimiser.checkIfPDFIsOptimised(src, function(err, isOptimised) {
				if ((err != null) || isOptimised) { return callback(null); }
				return OutputFileOptimiser.optimisePDF(src, dst, callback);
			});
		} else {
			return callback((null));
		}
	},

	checkIfPDFIsOptimised(file, callback) {
		const SIZE = 16*1024; // check the header of the pdf
		const result = new Buffer(SIZE);
		result.fill(0); // prevent leakage of uninitialised buffer
		return fs.open(file, "r", function(err, fd) {
			if (err != null) { return callback(err); }
			return fs.read(fd, result, 0, SIZE, 0, (errRead, bytesRead, buffer) =>
				fs.close(fd, function(errClose) {
					if (errRead != null) { return callback(errRead); }
					if (typeof errReadClose !== 'undefined' && errReadClose !== null) { return callback(errClose); }
					const isOptimised = buffer.toString('ascii').indexOf("/Linearized 1") >= 0;
					return callback(null, isOptimised);
				})
			);
		});
	},

	optimisePDF(src, dst, callback) {
		if (callback == null) { callback = function(error) {}; }
		const tmpOutput = dst + '.opt';
		const args = ["--linearize", src, tmpOutput];
		logger.log({args}, "running qpdf command");

		const timer = new Metrics.Timer("qpdf");
		const proc = spawn("qpdf", args);
		let stdout = "";
		proc.stdout.on("data", chunk => stdout += chunk.toString());
		callback = _.once(callback); // avoid double call back for error and close event
		proc.on("error", function(err) {
			logger.warn({err, args}, "qpdf failed");
			return callback(null);
		}); // ignore the error
		return proc.on("close", function(code) {
			timer.done();
			if (code !== 0) {
				logger.warn({code, args}, "qpdf returned error");
				return callback(null); // ignore the error
			}
			return fs.rename(tmpOutput, dst, function(err) {
				if (err != null) {
					logger.warn({tmpOutput, dst}, "failed to rename output of qpdf command");
				}
				return callback(null);
			});
		});
	} // ignore the error
});