// Package bench is a package which contains
// programs of Go Benchmark Competition.
package bench

import (
	"bytes"
	"errors"
	"fmt"
	"os"
)

var ErrNoWord = errors.New("Must pass word in")

type Match struct {
	line int
	col  int
	len  int
}

func printMatches(matches []Match) string {
	var buf bytes.Buffer
	for _, m := range matches {
		buf.WriteString(fmt.Sprintf("%d:%d,", m.line, m.col))
	}
	s := buf.String()
	return s[:len(s)-1]
}

// Find reads the text file on the `path`,
// finds the `s` words on the file and
// returns the row numbers and indices
// in the form of `r:c,r:c,...r:c`,
// at which the `s` word exists.
func Find(path, s string) (string, error) {
	if s == "" {
		return "", ErrNoWord
	}
	f, err := os.Open(path)
	if err != nil {
		return "", err
	}
	defer f.Close()
	bs := []byte(s)
	var buf [4096]byte
	matches := make([]Match, 0, 16)
	maybe := make([]Match, 0, 8)
	newmaybe := make([]Match, 0, 8)
	col := 0
	line := 1
	for n, err := f.Read(buf[:]); n > 0; {
		for i := 0; i < n; i++ {
			if buf[i] == '\n' {
				col = 0
				line++
				maybe = maybe[:0]
				continue
			}
			newmaybe := newmaybe[:0]
			for _, m := range maybe {
				if m.len == len(bs) {
					matches = append(matches, m)
					continue
				}
				if bs[m.len] == buf[i] {
					m.len++
					newmaybe = append(newmaybe, m)
				}
			}
			if bs[0] == buf[i] {
				newmaybe = append(newmaybe, Match{line, col, 1})
			}
			maybe = newmaybe
			col++
		}
		if n < len(buf) || err != nil {
			break
		}
	}
	for _, m := range maybe {
		if m.len == len(bs) {
			matches = append(matches, m)
		}
	}
	if len(matches) == 0 {
		return "", nil
	}
	return printMatches(matches), nil
}