Count the number of characters typed in the Mastodon post screen.

CountChar.swift

import Foundation
import RegexBuilder

private let urlRegex = Regex {
    Capture(.url(scheme: .required))
}

private let mentionRegex = Regex {
    Capture {
        ChoiceOf {
            #/^/#
            One(.word.inverted)
        }
    }
    "@"
    Capture {
        Regex {
            Capture {
                OneOrMore {
                    CharacterClass(
                        .anyOf("_"),
                        "a" ... "z",
                        "0" ... "9"
                    )
                }
            }
            "@"
            OneOrMore {
                CharacterClass(
                    .anyOf(".-"),
                    "a" ... "z",
                    "0" ... "9"
                )
            }
            OneOrMore {
                CharacterClass(
                    "a" ... "z",
                    "0" ... "9"
                )
            }
        }
    }
}
.ignoresCase()

func count(
    status: String,
    spoilerText: String?,
    charactersReservedPerURL: Int
) -> Int {
    let urlFilling = "".padding(toLength: charactersReservedPerURL, withPad: "_", startingAt: 0)
    let replaced = status.replacing(urlRegex, with: urlFilling)
        .replacing(mentionRegex) { match in
            "\(match.output.1)@\(match.output.3)"
        }
    return replaced.count + (spoilerText?.count ?? 0)
}