package main

import (
	"bufio"
	"compress/gzip"
	"fmt"
	"os"
	"time"

	xmlparser "github.com/tamerh/xml-stream-parser"
	// Dá se získat pomocí "go get -u github.com/tamerh/xml-stream-parser"
)

// Funkce na kontrolu jestli má tag elementu danou hodnotu
func hasTagValue(el *xmlparser.XMLElement, name string, value string) bool {
	for _, tag := range el.Childs["tag"] {
		if tag.Attrs["k"] == name {
			return tag.Attrs["v"] == value
		}
	}
	return false
}

func die(exitcode int, format string, a ...interface{}) {
	fmt.Fprintf(os.Stderr, format, a...)
	os.Exit(1)
}

func main() {
	if len(os.Args) != 2 {
		die(1, "Usage: %s <file.xml.gz>\n", os.Args[0])
	}
	// 1. Otevřeme soubor
	file, err := os.Open(os.Args[1])
	if err != nil {
		die(1, "Cannot open file: %v\n", err)
	}
	// 2. Gzip streamový reader
	gzipReader, err := gzip.NewReader(file)
	if err != nil {
		die(1, "Cannot construct gzip stream reader: %v\n", err)
	}
	// 3. XML streamový parser
	buffer := bufio.NewReaderSize(gzipReader, 1024*1024*256)
	parser := xmlparser.NewXMLParser(buffer, "node", "way")
	parser.SkipElements([]string{"relation"}).SkipOuterElements()

	nodes, ways, libNodes, libWays := 0, 0, 0, 0
	start := time.Now()
	// funkce na vypisování statistiky
	printStat := func() {
		megabytes := float64(parser.TotalReadSize) / 1024 / 1024
		elapsed := time.Now().Sub(start)
		fmt.Fprintf(os.Stderr,
			"Elapsed: %-20s Read: %10.2fMB (%.2fMB/s)\tLibraries in nodes: %6d/%-10d\tLibraries in ways: %6d/%-10d\r",
			elapsed, megabytes, megabytes/elapsed.Seconds(), libNodes, nodes, libWays, ways,
		)
	}

	// 4. Čteme element po elementu
	for xml := range parser.Stream() {
		switch xml.Name {
		case "node":
			nodes++
			if hasTagValue(xml, "amenity", "library") {
				libNodes++
				fmt.Printf("Library: %v\n", xml)
			}
		case "way":
			ways++
			if hasTagValue(xml, "amenity", "library") {
				libWays++
				fmt.Printf("Library area: %v\n", xml)
			}
		}

		// Vypíšeme statistiku každých 10000 načtených elementů
		if (nodes+ways)%10000 == 0 {
			printStat()
		}
	}

	printStat()
	fmt.Fprintf(os.Stderr, "\n\nTotal time: %v\n", time.Now().Sub(start))
}