prepare-commit-msg.swift

#!/usr/bin/swift

/* Git commit hook. Place it into your .git/hooks folder with 'prepare-commit-msg' name
 #!/bin/sh
 
 echo "Start prepare-commit-msg hook"
 
 COMMIT_MSG_FILE=$1
 COMMIT_SOURCE=$2
 #SHA1=$3
 
 PATH=path-to-file
 PREFIX=prefix
 
 swift $PATH $PREFIX $COMMIT_MSG_FILE $COMMIT_SOURCE
 
 echo "End prepare-commit-msg hook"
 */

import Foundation

// MARK: Bash

func shell(launchPath: String, arguments: [String]) -> String
{
    let task = Process()
    task.launchPath = launchPath
    task.arguments = arguments
    
    let pipe = Pipe()
    task.standardOutput = pipe
    task.launch()
    
    let data = pipe.fileHandleForReading.readDataToEndOfFile()
    let output = String(data: data, encoding: String.Encoding.utf8)!
    if output.count > 0 {
        //remove newline character.
        let count = output.count-1
        return String(output.prefix(count))
    }
    return output
}

func bash(_ command: String, _ arguments: String...) -> String {
    let whichPathForCommand = shell(launchPath: "/bin/bash", arguments: [ "-l", "-c", "which \(command)" ])
    return shell(launchPath: whichPathForCommand, arguments: arguments)
}

// MARK: Helpers

func extractTicket(branch: String) -> String? {
    guard let data = branch.split(separator: "/").last?.split(separator: "-").map({ String($0) }) else { return nil }
    guard data.count >= 2 else { return nil }
    guard data[0] == ticketPrefix else { return nil }
    guard let number = Int(data[1]) else { return nil }
    
    return "\(ticketPrefix)-\(number)"
}

// MARK: Script

let ticketPrefix = CommandLine.arguments[1]
let commitMessageFile = "\(bash("pwd"))/\(CommandLine.arguments[2])"
let commitSource = CommandLine.arguments[3]

let branch = bash("git", "symbolic-ref", "--short", "HEAD")

let ignoredCommitSources = ["merge"]

func main() throws {
    print("Commit source: \(commitSource)")
    print("Ticket prefix: \(ticketPrefix)")
    print("Branch name: \(branch)")
    
    guard !ignoredCommitSources.contains(commitSource) else {
        print("Ignored commit source: \(commitSource)")
        return
    }
    
    guard let ticket = extractTicket(branch: branch) else {
        print("Ticket can not be extracted")
        return
    }
    
    let commitText = try String(contentsOfFile: commitMessageFile, encoding: .utf8)
    let editedCommit = "\(commitText)\n\n\(ticket)"
    try editedCommit.write(toFile: commitMessageFile, atomically: false, encoding: .utf8)
    
    print("Attached ticket: \(ticket)")
}

do {
    try main()
} catch let error {
    print(error.localizedDescription)
    fatalError()
}