package main

import (
	"bufio"
	"flag"
	"fmt"
	"io"
	"os"
	"regexp"
	"strings"
	"text/tabwriter"
)

type queue struct {
	q    []string
	maxl int
}

func (q *queue) insert(s string) {
	if len(q.q) <= q.maxl {
		q.q = append(q.q, s)
		return
	}
	q.q = append(q.q[1:len(q.q)], s)
}

type work struct {
	c    chan string
	left int
	done chan struct{}
}

// By writing to w.done we make sure that the goroutine has finished
// sending to the out channel before returning from this method.
func (w *work) finish() {
	close(w.c)
	w.done <- struct{}{}
	return
}

func (w *work) print_kwic(sl []string, out chan string) {
	for word := range w.c {
		sl = append(sl, word)
	}
	out <- strings.Join(sl, "\t")
	<-w.done
}

func feedworkers(wlist []*work, w string) []*work {
	var ret []*work
	if len(wlist) == 0 {
		return ret
	}
	ret = make([]*work, len(wlist))

	copy(ret, wlist)

	for _, wc := range wlist {
		if wc.left == 0 {
			wc.finish()
			ret = wlist[1:]
		} else {
			wc.c <- w
			wc.left -= 1
		}
	}

	return ret
}

func printqueue(q *queue, words chan string, kw string, left int, out chan string) {
	var hungryhippos []*work

	for w := range words {
		index := strings.Index(w, kw)
		if index < 0 {
			q.insert(w)
			hungryhippos = feedworkers(hungryhippos, w)
			continue
		}

		qstr := fmt.Sprintf("%q", w)
		q.insert(qstr)

		wc := &work{c: make(chan string, 10), left: 5, done: make(chan struct{})}

		hungryhippos = feedworkers(hungryhippos, qstr)

		sl := make([]string, MAX)
		copy(sl, q.q[6:])

		hungryhippos = append(hungryhippos, wc)

		go wc.print_kwic(sl, out)
	}
	for _, wc := range hungryhippos {
		wc.finish()
	}
	close(out)
}

var tw *tabwriter.Writer

const MAX int = 11

func main() {
	flag.Parse()
	kw := flag.Arg(0)
	if len(kw) == 0 {
		fmt.Printf("Need a string to search for as an argument.\n")
		os.Exit(1)
	}
	tw = tabwriter.NewWriter(os.Stdout, 1, 1, 1, ' ', 0)
	splitreg := regexp.MustCompile("[ \t\n]")

	q := queue{maxl: MAX, q: make([]string, MAX)}
	sc := make(chan string, 1000)
	out := make(chan string, 1000)

	reader := bufio.NewReader(os.Stdin)
	line, err := reader.ReadString(byte('\n'))
	go func(c chan string) {
		var w string
		for err == nil {
			splline := splitreg.Split(line, -1)
			for _, w = range splline {
				c <- w
			}
			line, err = reader.ReadString(byte('\n'))
		}
		if err != io.EOF {
			fmt.Printf("Got an error: %q.\n", err)
		}

		c <- w
		close(c)
	}(sc)

	go printqueue(&q, sc, kw, 5, out)

	for l := range out {
		fmt.Fprintf(tw, "%s\n", l)
	}
	tw.Flush()
}