completed save rect to RLE file feature

rle/rle.go

@@ -1,8 +1,9 @@
-// source: https://github.com/nhoffmann/life by N.Hoffmann 2020.
+// original source: https://github.com/nhoffmann/life by N.Hoffmann 2020.
 package rle
 
 import (
 	"fmt"
+	"os"
 	"regexp"
 	"strconv"
 	"strings"
@@ -52,7 +53,7 @@ func (rle *RLE) partitionFile() error {
 		}
 	}
 
-	return fmt.Errorf("Invlaid input: Header is missing")
+	return fmt.Errorf("invalid input: Header is missing")
 }
 
 func (rle *RLE) parseComments() error {
@@ -98,3 +99,78 @@ func removeWhitespace(input string) string {
 	re := regexp.MustCompile(` *\t*\r*\n*`)
 	return re.ReplaceAllString(input, "")
 }
+
+// Store a grid to an RLE file
+func StoreGridToRLE(grid [][]int64, filename, rule string, width, height int) error {
+	fd, err := os.Create(filename)
+	if err != nil {
+		return err
+	}
+
+	var pattern string
+
+	for y := 0; y < height; y++ {
+		line := ""
+		for x := 0; x < width; x++ {
+			switch grid[y][x] {
+			case 0:
+				line += "b"
+			case 1:
+				line += "o"
+			}
+		}
+
+		// if first row is: 001011110, then line is now:
+		//                  bboboooob
+
+		encoded := RunLengthEncode(line)
+
+		// and now its:     2bob4ob
+		pattern += encoded
+
+		if y != height-1 {
+			pattern += "$"
+		}
+	}
+
+	pattern += "!"
+
+	wrapped := ""
+	for idx, char := range pattern {
+		if idx%70 == 0 && idx != 0 {
+			wrapped += "\n"
+		}
+		wrapped += string(char)
+	}
+
+	_, err = fmt.Fprintf(fd, "#N %s\nx = %d, y = %d, rule = %s\n%s\n",
+		filename, width, height, rule, wrapped)
+
+	if err != nil {
+		return err
+	}
+
+	return nil
+}
+
+// by peterSO on
+// https://codereview.stackexchange.com/questions/238893/run-length-encoding-in-golang
+func RunLengthEncode(s string) string {
+	e := make([]byte, 0, len(s))
+	for i := 0; i < len(s); i++ {
+		c := s[i]
+		j := i + 1
+		for ; j <= len(s); j++ {
+			if j < len(s) && s[j] == c {
+				continue
+			}
+			if j-i > 1 {
+				e = strconv.AppendInt(e, int64(j-i), 10)
+			}
+			e = append(e, c)
+			break
+		}
+		i = j - 1
+	}
+	return string(e)
+}