slack.go

package githubmarkdownconvertergo

import (
	"fmt"
	"regexp"
	"strings"
)

// SlackConvertOptions contains options to fine-toon GitHub to Slack markdown convert
type SlackConvertOptions struct {
	// Headlines will define if GitHub headlines will be updated to be bold text in slack
	// there is no headlines as sucks in Slack
	Headlines bool
	// Name of the git repo, used to link pull-requests/issues
	// repo name to be given in format "<owner>/<name>" (example: eritikass/githubmarkdownconvertergo)
	RepoName string
	// GitHub root url, if not given "https://github.com" is used as default
	GitHubURL string
	// CustomRefPatterns is list of patterns used to replace
	CustomRefPatterns map[string]string
}

// Slack returns github markdown converted to Slack
func Slack(markdown string, options ...SlackConvertOptions) string {
	var re *regexp.Regexp

	opt := SlackConvertOptions{}
	if len(options) > 0 {
		opt = options[0]
	}

	gitHubURL := opt.GitHubURL
	if gitHubURL == "" {
		gitHubURL = "https://github.com"
	}

	// using start and end patterns make sure we will not find match middle of the word etc.
	startOfPattern := `(?P<THE_START_OF_MATCH>^|[\s\[\(])`
	endOfPattern := `(?P<THE_END_OF_MATCH>$|[\s:\]\),.!])`

	if len(opt.CustomRefPatterns) > 0 {
		for pattern, replace := range opt.CustomRefPatterns {
			re, err := regexp.Compile(fmt.Sprintf(`%s%s%s`, startOfPattern, pattern, endOfPattern))
			if err != nil {
				println("ERROR_USING_CustomRefPatterns: " + err.Error())
				continue
			}
			markdown = re.ReplaceAllString(markdown, fmt.Sprintf(`${THE_START_OF_MATCH}%s${THE_END_OF_MATCH}`, replace))
		}
	}

	// TODO: write proper regex
	linkRegex := ".*"

	// usernames @xxx
	re = regexp.MustCompile(startOfPattern + "@(?P<USERNAME>[a-z-A-Z0-9]{3,20})" + endOfPattern)
	markdown = re.ReplaceAllString(markdown, fmt.Sprintf("${THE_START_OF_MATCH}<%s/${USERNAME}|@${USERNAME}>${THE_END_OF_MATCH}", gitHubURL))

	// This makes sure all newlines are in the correct format, since this will otherwise cause issues with further replacements
	markdown = strings.ReplaceAll(markdown, "\r\n", "\n")

	// bold **TEXT**  -> *TEXT*
	re = regexp.MustCompile(`(?miU)((\*\*).+(\*\*))`)
	markdown = re.ReplaceAllStringFunc(markdown, func(s string) string {
		return strings.ReplaceAll(s, "**", "*")
	})

	// italic same for both _TEXT_

	// strikethrough ~~TEXT~~  -> ~TEXT~
	re = regexp.MustCompile(`(?miU)((~~).+(~~))`)
	markdown = re.ReplaceAllStringFunc(markdown, func(s string) string {
		return strings.ReplaceAll(s, "~~", "~")
	})

	// links [TEXT](link) -> <link|TEXT>
	re = regexp.MustCompile(`(?miU)(\[(?P<name>[^\]]+)\]\((?P<link>` + linkRegex + `)\))`)
	markdown = re.ReplaceAllStringFunc(markdown, func(s string) string {
		match := re.FindStringSubmatch(s)
		name := ""
		link := ""
		for i, n := range re.SubexpNames() {
			if i != 0 && n == "name" {
				name = match[i]
			}
			if i != 0 && n == "link" {
				link = match[i]
			}
		}
		if name != "" && link != "" {
			return fmt.Sprintf("<%s|%s>", link, name)
		}
		return s
	})

	// * -> •
	re = regexp.MustCompile(`(?m)(^\s*)\*`)
	markdown = re.ReplaceAllString(markdown, "$1•")

	if opt.Headlines {
		re = regexp.MustCompile(`(?m)((^\t?[ ]{0,15}#{1,4}[ ]{1,})(.+))`)
		markdown = re.ReplaceAllString(markdown, "*$3*")
	}

	if opt.RepoName != "" {
		// issues, pull-requests  #<number>  => to link of given issue/pr
		re = regexp.MustCompile(`(?m)([\s(,;])([#])(\d{1,10})([):\s]|,|;|$)`)
		markdown = re.ReplaceAllStringFunc(markdown, func(s string) string {
			match := re.FindStringSubmatch(s)
			return fmt.Sprintf("%s<%s/%s/pull/%s|%s%s>%s", match[1], gitHubURL, opt.RepoName, match[3], match[2], match[3], match[4])
		})
	}

	return markdown
}