Refactor slack bridge prelude (#517)

Distributing the source of the Slack bridge across multiple files to
increase readability and as a prelude to various refactors and
clean-ups.

bridge/slack/helpers.go

@@ -0,0 +1,116 @@
+package bslack
+
+import (
+	"fmt"
+	"regexp"
+	"strings"
+
+	"github.com/nlopes/slack"
+)
+
+func (b *Bslack) userName(id string) string {
+	for _, u := range b.Users {
+		if u.ID == id {
+			if u.Profile.DisplayName != "" {
+				return u.Profile.DisplayName
+			}
+			return u.Name
+		}
+	}
+	return ""
+}
+
+func (b *Bslack) getAvatar(userid string) string {
+	var avatar string
+	if b.Users != nil {
+		for _, u := range b.Users {
+			if userid == u.ID {
+				return u.Profile.Image48
+			}
+		}
+	}
+	return avatar
+}
+
+/*
+func (b *Bslack) getChannelByName(name string) (*slack.Channel, error) {
+	if b.channels == nil {
+		return nil, fmt.Errorf("%s: channel %s not found (no channels found)", b.Account, name)
+	}
+	for _, channel := range b.channels {
+		if channel.Name == name {
+			return &channel, nil
+		}
+	}
+	return nil, fmt.Errorf("%s: channel %s not found", b.Account, name)
+}
+*/
+
+func (b *Bslack) getChannelByID(ID string) (*slack.Channel, error) {
+	if b.channels == nil {
+		return nil, fmt.Errorf("%s: channel %s not found (no channels found)", b.Account, ID)
+	}
+	for _, channel := range b.channels {
+		if channel.ID == ID {
+			return &channel, nil
+		}
+	}
+	return nil, fmt.Errorf("%s: channel %s not found", b.Account, ID)
+}
+
+func (b *Bslack) getChannelID(name string) string {
+	idcheck := strings.Split(name, "ID:")
+	if len(idcheck) > 1 {
+		return idcheck[1]
+	}
+	for _, channel := range b.channels {
+		if channel.Name == name {
+			return channel.ID
+		}
+	}
+	return ""
+}
+
+// @see https://api.slack.com/docs/message-formatting#linking_to_channels_and_users
+func (b *Bslack) replaceMention(text string) string {
+	results := regexp.MustCompile(`<@([a-zA-Z0-9]+)>`).FindAllStringSubmatch(text, -1)
+	for _, r := range results {
+		text = strings.Replace(text, "<@"+r[1]+">", "@"+b.userName(r[1]), -1)
+	}
+	return text
+}
+
+// @see https://api.slack.com/docs/message-formatting#linking_to_channels_and_users
+func (b *Bslack) replaceChannel(text string) string {
+	results := regexp.MustCompile(`<#[a-zA-Z0-9]+\|(.+?)>`).FindAllStringSubmatch(text, -1)
+	for _, r := range results {
+		text = strings.Replace(text, r[0], "#"+r[1], -1)
+	}
+	return text
+}
+
+// @see https://api.slack.com/docs/message-formatting#variables
+func (b *Bslack) replaceVariable(text string) string {
+	results := regexp.MustCompile(`<!((?:subteam\^)?[a-zA-Z0-9]+)(?:\|@?(.+?))?>`).FindAllStringSubmatch(text, -1)
+	for _, r := range results {
+		if r[2] != "" {
+			text = strings.Replace(text, r[0], "@"+r[2], -1)
+		} else {
+			text = strings.Replace(text, r[0], "@"+r[1], -1)
+		}
+	}
+	return text
+}
+
+// @see https://api.slack.com/docs/message-formatting#linking_to_urls
+func (b *Bslack) replaceURL(text string) string {
+	results := regexp.MustCompile(`<(.*?)(\|.*?)?>`).FindAllStringSubmatch(text, -1)
+	for _, r := range results {
+		if len(strings.TrimSpace(r[2])) == 1 { // A display text separator was found, but the text was blank
+			text = strings.Replace(text, r[0], "", -1)
+		} else {
+			text = strings.Replace(text, r[0], r[1], -1)
+		}
+	}
+	return text
+}