// Package grep is a simple grep program.
package grep
import (
	"bufio"
	"log"
	"os"
	"strconv"
	"strings"
)
type config struct {
	lineNum    bool // print line numbers for matches
	onlyFile   bool // only print filenames with match
	caseInsens bool // case-insensitive search
	invert     bool // collect non-matching lines
	exact      bool // match full lines, no partials
}
func newConfig(flags []string) *config {
	c := config{}
	for _, f := range flags {
		switch f {
		case "-n":
			c.lineNum = true
		case "-l":
			c.onlyFile = true
		case "-i":
			c.caseInsens = true
		case "-v":
			c.invert = true
		case "-x":
			c.exact = true
		}
	}
	return &c
}
// Search finds pattern in files. Behavior adjusted with flags.
func Search(pattern string, flags []string, files []string) []string {
	c := newConfig(flags)
	ret := []string{}
	for _, fname := range files {
		f, err := os.Open(fname)
		if err != nil {
			log.Panicln(err)
		}
		defer f.Close()
		buff := bufio.NewScanner(f)
		for i := 1; buff.Scan(); i++ {
			line, matchLine := buff.Text(), buff.Text()
			if c.caseInsens {
				pattern = strings.ToLower(pattern)
				matchLine = strings.ToLower(line)
			}
			if c.match(matchLine, pattern) {
				if c.onlyFile {
					ret = append(ret, fname)
					break
				} else {
					var out strings.Builder
					if len(files) > 1 {
						out.WriteString(fname + ":")
					}
					if c.lineNum {
						out.WriteString(strconv.Itoa(i) + ":")
					}
					out.WriteString(line)
					ret = append(ret, out.String())
				}
			}
		}
	}
	return ret
}
func (c *config) match(line, pattern string) bool {
	if c.exact {
		if c.invert {
			return !(pattern == line)
		}
		return pattern == line
	}
	if c.invert {
		return !strings.Contains(line, pattern)
	}
	return strings.Contains(line, pattern)
}