add: push changes to gitea server after merging local changes

This implementation has no configuration yet to authorize accordingly.
WIP for #3 and #4.

internal/diff/diff.go

@@ -1,11 +1,72 @@
 package diff
 
-import "fmt"
+import (
+	"errors"
+	"fmt"
+	"os"
+	"os/exec"
+	"regexp"
+	"strings"
+)
 
 func Prompt(value, theirs, mine string) string {
 	// TODO: create tmp file with the corresponding contents
 	// open tmp file using the $EDITOR environment variable
 	// parse and return output of tmp file after $EDITOR execution has been completed
-	fmt.Printf("\tPrompting for value: '%s'\n", value)
-	return value
+	value = strings.ReplaceAll(value, "\r\n", "\n")
+	theirs = strings.ReplaceAll(theirs, "\r\n", "\n")
+	mine = strings.ReplaceAll(mine, "\r\n", "\n")
+	file, err := os.CreateTemp("", "gitw-*")
+	if err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		return value
+	}
+	defer os.Remove(file.Name())
+
+	// prepare file contents
+	if _, err := file.WriteString(value); err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		os.Exit(-1)
+	}
+	if _, err := file.WriteString("\n\n--- theirs ---\n\n"); err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		os.Exit(-1)
+	}
+	if _, err := file.WriteString(theirs); err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		os.Exit(-1)
+	}
+	if _, err := file.WriteString("\n\n--- mine ---\n\n"); err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		os.Exit(-1)
+	}
+	if _, err := file.WriteString(mine); err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		os.Exit(-1)
+	}
+	file.Close()
+
+	cmd := exec.Command(os.Getenv("EDITOR"), file.Name())
+	cmd.Stdin = os.Stdin
+	cmd.Stdout = os.Stdout
+	cmd.Stderr = os.Stderr
+	if err := cmd.Run(); err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		return value
+	}
+	contents, err := os.ReadFile(file.Name())
+	if err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		os.Exit(-1)
+	}
+	// TODO: what should I do with the '\r' characters? Who and when should they be handled?
+	re := regexp.MustCompile("(?s)^(.*)--- theirs ---")
+	matches := re.FindAllStringSubmatch(string(contents), -1)
+	if len(matches) > 0 && len(matches[0]) == 2 {
+		return matches[0][1]
+	} else {
+		fmt.Fprintln(os.Stderr, errors.New("No matches found, could not read merged value. Aborting."))
+		os.Exit(-1)
+		return "" // just to make compiler happy
+	}
 }