// ============================================================================ simple golang builder (mwx'2026)
package main

import (
	"crypto/sha256"
	"encoding/hex"
	"encoding/json"
	"flag"
	"io"
	"io/fs"
	"os"
	"os/exec"
	"os/signal"
	"path/filepath"
	"regexp"
	"runtime"
	"slices"
	"strings"
	"sync"
	"syscall"
	"time"

	"github.com/AlecAivazis/survey/v2"
	"github.com/fsnotify/fsnotify"
)

var version = "1.21.0"

var UPDATEURL = "https://gozilla.fhi.mpg.de/gbld"
var UPLOADHOST = "root@gozilla"
var UPLOADPATH = "/db/www"

var oses = []string{"darwin", "linux", "windows"}
var arches = []string{"arm64", "amd64"}

var skipdirs = []string{"bin", "tmp", "vendor", "node_modules", "testdata"}

const KEEPBACKUPS = 20 // backups per file kept in tmp/

var GO string
var GOIMPORTS string

var mu sync.Mutex // guards 'running'
var running *proc

var r1 = regexp.MustCompile(`^\.`)                                    // hidden file
var r2 = regexp.MustCompile(`^build\.go$`)                            // own build counter
var r3 = regexp.MustCompile(`\.go$`)                                  // go source
var r4 = regexp.MustCompile(`(?m)^(\s*var\s+build\s*=\s*")([^"]*)(")`) // build counter
var r5 = regexp.MustCompile(`(?im)^\s*var\s+version\s*=\s*"([^"]*)"`)  // target version
var r6 = regexp.MustCompile(`(?s)import\s*\((.*?)\)`)                 // import block
var r7 = regexp.MustCompile(`^[A-Za-z0-9._-]+$`)                      // safe build name

type opts struct { // ------------------------------------------------------------------------- command line options
  buildonly bool
  once      bool
  imports   bool
  exitafter bool
  postcmd   string
  runargs   string
}

type proc struct { // ------------------------------------------------------ started build, reaped by its own goroutine
  cmd  *exec.Cmd
  done chan struct{}
}

func main() { // ========================================================================================== main

  if len(os.Args) == 1 { // ······································· no arguments: read predefined builds or default
    os.Args = defaultargs()
  }

  opt_b := flag.Bool("b", false, "")
  opt_1 := flag.Bool("1", false, "")
  opt_i := flag.Bool("i", false, "")
  opt_x := flag.Bool("x", false, "")
  opt_c := flag.String("c", "", "")
  opt_o := flag.String("o", "", "")
  opt_a := flag.Bool("a", false, "")
  opt_v := flag.Bool("v", false, "")
  opt_h := flag.Bool("h", false, "")
  opt_u := flag.Bool("u", false, "")

  flag.Usage = func() {
    P()
    info()
    P()
    P(Cw("Usage:"))
    P(Cy("  gbld [-b] [-1] [-i] [-x] [-c <CMD>] [-o <OPTIONS>] [build name]"))
    P(Cy("  gbld [-a] [-u]"))
    P(Cw("    -b             build only"))
    P(Cw("    -1             run only once, no watching (exit code: build error or exit code of the build)"))
    P(Cw("    -i             run goimports before build"))
    P(Cw("    -x             exit after the first successful build, leave the started build running"))
    P(Cw("    -o  <OPTIONS>  exec options"))
    P(Cw("    -c  <CMD>      run command after build"))
    P(Cw("    -v             show version"))
    P(Cw("    -h             show help"))
    P(Cw("    -a             build for all platforms"))
    P(Cw("    -u             upload builds to " + UPLOADHOST))
    P()
    P(Cw("  · if no build name is supplied the current directory name will be used"))
    P()
    P(Cw("  · if no option supplied try to read '") + Cy("gbld.menu.json") + Cw("'"))
    P(Cm(`      {`))
    P(Cm(`        "build": ["-b","gbld"],`))
    P(Cm(`        "help":  ["-h"]`))
    P(Cm(`      }`))
    P()
    P(Cw("  · if no option is supplied and no '") + Cy("gbld.menu.json") + Cw("' is available"))
    P(Cw("    the current directory name with ") + Cy("-b -i -1") + Cw(" as options will be used"))
    P()
    P(Cw("  · set ") + Cy("GBLD_NO_UPDATE=1") + Cw(" to skip the update check"))
    P()
  }

  flag.Parse()

  o := opts{buildonly: *opt_b, once: *opt_1, imports: *opt_i, exitafter: *opt_x,
    postcmd: *opt_c, runargs: *opt_o}

  if *opt_v { // ·············································································· show version
    info()
    os.Exit(0)
  }

  if *opt_h { // ····················································································· show help
    flag.Usage()
    os.Exit(0)
  }

  if os.Getenv("GBLD_NO_UPDATE") == "" { // ······································· check for a newer gbld version
    checkforupdate(UPDATEURL)
  }

  GO = lookup("go") // ······················································· check for the required toolchain
  if o.imports {
    GOIMPORTS = lookup("goimports")
  }

  name := flag.Arg(0) // ································································ command line arguments
  if len(name) == 0 {
    name = dirName()
    if len(name) == 0 {
      flag.Usage()
      os.Exit(1)
    }
  }

  file := name + ".go"
  if !fileExists(file) {
    PE("file not found", file)
    os.Exit(1)
  }

  if *opt_a { // ······························································· build for other platforms
    info()
    buildall(name)
  }

  if *opt_u { // ······································································ upload builds to gozilla
    info()
    uploadall(name)
  }

  if *opt_a || *opt_u {
    os.Exit(0)
  }

  catchsignals() // ································· stop the started build when gbld itself is asked to quit

  ok := buildAndRun(name, file, o) // ································································ first build

  if o.once { // ······················· no watching: report the build result and wait for the started process
    if !ok {
      os.Exit(1)
    }
    os.Exit(waitRunning())
  }

  watcher, err := fsnotify.NewWatcher() // ····································· watch the tree for .go changes
  if err != nil {
    PE("cannot create watcher", err.Error())
    os.Exit(1)
  }
  defer watcher.Close()

  if err := watchtree(watcher, "."); err != nil {
    PE("cannot watch directory", err.Error())
    os.Exit(1)
  }

  trigger := make(chan struct{}, 1)
  go func() {
    for {
      select {
      case event, ok := <-watcher.Events:
        if !ok {
          return
        }
        if event.Op&fsnotify.Create == fsnotify.Create { // new directory: watch it as well
          if fi, err := os.Stat(event.Name); err == nil && fi.IsDir() {
            watchtree(watcher, event.Name)
            continue
          }
        }
        if event.Op&(fsnotify.Write|fsnotify.Create|fsnotify.Rename|fsnotify.Remove) == 0 {
          continue
        }
        base := filepath.Base(event.Name)
        if !r3.MatchString(base) || r1.MatchString(base) || r2.MatchString(base) {
          continue
        }
        select { // never block the watcher, one pending rebuild is enough
        case trigger <- struct{}{}:
        default:
        }
      case err, ok := <-watcher.Errors:
        if !ok {
          return
        }
        PE("watcher", err.Error())
      }
    }
  }()

  for range trigger { // ································· debounce, then build serially - never in parallel
    for settled := false; !settled; {
      select {
      case <-trigger:
      case <-time.After(100 * time.Millisecond):
        settled = true
      }
    }
    buildAndRun(name, file, o)
  }
}

func defaultargs() []string { // ------------------------------------------------- arguments if none were supplied
  c, err := os.ReadFile("gbld.menu.json")
  if err != nil {
    return []string{"gbld", "-b", "-i", "-1", dirName()}
  }

  var buildjson map[string][]string
  if err := json.Unmarshal(c, &buildjson); err != nil {
    PE("cannot parse gbld.menu.json", err.Error())
    os.Exit(1)
  }

  sel := []string{}
  for k := range buildjson {
    sel = append(sel, k)
  }
  slices.Sort(sel) // map order is random - keep the menu stable

  tmp := ""
  if err := survey.AskOne(&survey.Select{Message: "Select build", Options: sel}, &tmp); err != nil {
    P(Crb("Interrupted."))
    os.Exit(0)
  }

  args, ok := buildjson[tmp]
  if !ok {
    PE("unknown build", tmp)
    os.Exit(1)
  }
  return append([]string{"gbld"}, args...)
}

func buildAndRun(name, file string, o opts) bool { // ------------------------- build and (re)start it, ok on success
  if !o.once {
    PN("\033[2J\033[1;1H")
  }
  info()
  P(Cc("--- start compiling " + file + " ---"))

  stopRunning()
  bumpbuild()

  if o.imports {
    runimports()
  }

  target := filepath.Join("bin", name+exesuffix(runtime.GOOS))
  PF("%s %s\n", Cw("running:"), Cyb("go build "+name))

  cmd := exec.Command(GO, "build", "-o", target, ".")
  out, err := cmd.CombinedOutput()

  if err != nil { // ·········································································· build failed
    PN(Cy(string(out)))
    P(Cr("--- build failed: " + name + " ---"))
    return false
  }

  P(Cb("--- compiling done: " + name + " ---")) // ·········································· build succeeded

  if len(o.postcmd) > 0 { // ······················································· execute post command
    params := strings.Fields(o.postcmd)
    P(Cw(o.postcmd))
    post := exec.Command(params[0], params[1:]...)
    post.Stdout = os.Stdout
    post.Stdin = os.Stdin
    post.Stderr = os.Stderr
    if err := post.Run(); err != nil {
      PE("post command failed", err.Error())
    }
  }

  if !o.buildonly { // ······················································· start the new build
    args := []string{}
    if len(o.runargs) > 0 {
      args = strings.Fields(o.runargs)
    }

    cmd := exec.Command(target, args...)
    cmd.Stdout = os.Stdout
    cmd.Stdin = os.Stdin
    cmd.Stderr = os.Stderr

    if err := cmd.Start(); err != nil {
      PE("cannot start "+target, err.Error())
    } else {
      p := &proc{cmd: cmd, done: make(chan struct{})}
      go func() { cmd.Wait(); close(p.done) }() // reap it as soon as it ends on its own
      mu.Lock()
      running = p
      mu.Unlock()
      PF("%s %d\n", Cw("process started:"), cmd.Process.Pid)
    }
  }

  P(Cg("--- end building: " + name + " ---"))
  if o.exitafter { // leaves the started process running on purpose
    os.Exit(0)
  }
  return true
}

func waitRunning() int { // ------------------------------------- wait for the started build, return its exit code
  mu.Lock()
  p := running
  running = nil
  mu.Unlock()

  if p == nil {
    return 0
  }
  <-p.done
  if p.cmd.ProcessState == nil {
    return 0
  }
  return p.cmd.ProcessState.ExitCode()
}

func bumpbuild() { // ------------------------------------------------------------------ increase build number
  c, err := os.ReadFile("build.go")
  if err != nil {
    return // no build.go, nothing to count
  }

  m := r4.FindSubmatch(c)
  if m == nil {
    return
  }

  old := string(m[2])
  b := Atoi(old) + 1

  if err := backup("build.go"); err != nil { // never touch a file we could not save first
    PE("backup of build.go failed", err.Error())
    return
  }

  if err := os.WriteFile("build.go", r4.ReplaceAll(c, []byte("${1}"+Itoa(b)+"${3}")), 0644); err != nil {
    PE("cannot write build.go", err.Error())
    return
  }
  P("build:", old, "->", b)
}

func runimports() { // ------------------------------------------------- update import blocks with goimports
  files, err := os.ReadDir(".")
  if err != nil {
    PE("cannot read directory", err.Error())
    return
  }

  for _, f := range files {
    if f.IsDir() || !strings.HasSuffix(f.Name(), ".go") {
      continue
    }
    fileName := f.Name()

    output, err := exec.Command(GOIMPORTS, fileName).Output()
    if err != nil {
      continue // does not compile yet - the build will report it
    }
    m := r6.FindStringSubmatch(string(output))
    if len(m) < 2 {
      continue
    }

    origContent, err := os.ReadFile(fileName)
    if err != nil {
      continue
    }
    updatedContent := ReplaceFirst(r6, string(origContent), SF("import (%s)", m[1]))
    if string(origContent) == updatedContent {
      continue
    }

    if err := backup(fileName); err != nil {
      PE("backup of "+fileName+" failed", err.Error())
      continue
    }
    if err := os.WriteFile(fileName, []byte(updatedContent), 0644); err != nil {
      PE("cannot write "+fileName, err.Error())
      continue
    }
    PF("%s %s\n", Cw("imports updated:"), Cmb(fileName))
  }
}

func buildall(name string) { // ------------------------------------------------------ build for all platforms
  targetversion, err := gettargetversion()
  if err != nil {
    PE(err.Error())
    os.Exit(1)
  }

  P(Ccb("build for all platforms"), Cwb(targetversion))
  if err := os.MkdirAll("bin", 0755); err != nil {
    PE("cannot create bin/", err.Error())
    os.Exit(1)
  }

  sums := []string{}
  failed := 0
  for _, osys := range oses {
    for _, arch := range arches {
      ofile := filepath.Join("bin", artifact(name, targetversion, osys, arch))

      cmd := exec.Command(GO, "build", "-o", ofile, ".")
      cmd.Env = append(os.Environ(), "GOOS="+osys, "GOARCH="+arch)
      if out, err := cmd.CombinedOutput(); err != nil {
        PE("build failed: "+ofile, strings.TrimSpace(string(out)))
        failed++
        continue
      }

      sum, err := sha256file(ofile)
      if err != nil {
        PE("cannot checksum "+ofile, err.Error())
        failed++
        continue
      }
      sums = append(sums, SF("%s  %s", sum, filepath.Base(ofile)))
      P(Cy(ofile), Cw(sum[:16]))
    }
  }

  if failed > 0 { // do not publish a version whose binaries are incomplete
    PE(SF("%d of %d builds failed", failed, len(oses)*len(arches)), "version.txt not written")
    os.Exit(1)
  }

  if err := os.WriteFile(filepath.Join("bin", "checksums.txt"), []byte(strings.Join(sums, "\n")+"\n"), 0644); err != nil {
    PE("cannot write bin/checksums.txt", err.Error())
    os.Exit(1)
  }
  if err := os.WriteFile(filepath.Join("bin", "version.txt"), []byte(targetversion+"\n"), 0644); err != nil {
    PE("cannot write bin/version.txt", err.Error())
    os.Exit(1)
  }
  PO("all builds done", targetversion)
}

func uploadall(name string) { // ------------------------------------------------------- upload builds to gozilla
  if !r7.MatchString(name) { // the name ends up in a remote shell command
    PE("invalid build name", name)
    os.Exit(1)
  }

  targetversion, err := gettargetversion()
  if err != nil {
    PE(err.Error())
    os.Exit(1)
  }

  files := []string{}
  for _, osys := range oses {
    for _, arch := range arches {
      ofile := filepath.Join("bin", artifact(name, targetversion, osys, arch))
      if fileExists(ofile) {
        files = append(files, ofile)
      }
    }
  }
  if len(files) == 0 {
    PE("no builds found for version "+targetversion, "run 'gbld -a' first")
    os.Exit(1)
  }
  for _, f := range []string{"bin/checksums.txt", "bin/version.txt"} {
    if !fileExists(f) {
      PE("missing "+f, "run 'gbld -a' first")
      os.Exit(1)
    }
    files = append(files, f)
  }

  P(Ccb("upload builds to "+UPLOADHOST), Cwb(targetversion))
  dst := UPLOADPATH + "/" + name

  if err := run("ssh", UPLOADHOST, SF("mkdir -p '%s' && rm -f '%s'/*_*_*", dst, dst)); err != nil {
    os.Exit(1)
  }
  if err := run(append([]string{"scp"}, append(files, UPLOADHOST+":"+dst)...)...); err != nil {
    os.Exit(1)
  }
  PO("upload done", targetversion)
}

func run(args ...string) error { // ------------------------------------------------- run a command, report failure
  P(Cy(strings.Join(args, " ")))
  out, err := exec.Command(args[0], args[1:]...).CombinedOutput()
  if err != nil {
    PE(args[0]+" failed", strings.TrimSpace(string(out)))
  }
  return err
}

func artifact(name, version, osys, arch string) string { // ------------------------------ name of a build artifact
  return SF("%s_%s_%s_%s%s", name, version, osys, arch, exesuffix(osys))
}

func exesuffix(osys string) string { // ------------------------------------------------ windows wants '.exe'
  if osys == "windows" {
    return ".exe"
  }
  return ""
}

func sha256file(path string) (string, error) { // --------------------------------------------- checksum of a file
  f, err := os.Open(path)
  if err != nil {
    return "", err
  }
  defer f.Close()

  h := sha256.New()
  if _, err := io.Copy(h, f); err != nil {
    return "", err
  }
  return hex.EncodeToString(h.Sum(nil)), nil
}

func watchtree(w *fsnotify.Watcher, root string) error { // ------------------------- watch a directory recursively
  return filepath.WalkDir(root, func(path string, d fs.DirEntry, err error) error {
    if err != nil || !d.IsDir() {
      return nil //nolint - unreadable entries are simply not watched
    }
    base := filepath.Base(path)
    if path != root && (r1.MatchString(base) || slices.Contains(skipdirs, base)) {
      return filepath.SkipDir
    }
    return w.Add(path)
  })
}

func backup(src string) error { // ---------------------------------------------------------------- backup files
  if err := os.MkdirAll("tmp", 0755); err != nil {
    return err
  }

  sourceFile, err := os.Open(src)
  if err != nil {
    return err
  }
  defer sourceFile.Close()

  destFile, err := os.Create(SF("tmp/%s.%s", src, time.Now().Format("20060102150405")))
  if err != nil {
    return err
  }
  defer destFile.Close()

  if _, err := io.Copy(destFile, sourceFile); err != nil {
    return err
  }
  if err := destFile.Sync(); err != nil {
    return err
  }

  prunebackups(src, KEEPBACKUPS)
  return nil
}

func prunebackups(src string, keep int) { // ------------------------- keep tmp/ from growing with every rebuild
  old, err := filepath.Glob(SF("tmp/%s.*", src))
  if err != nil || len(old) <= keep {
    return
  }
  slices.Sort(old) // the timestamp suffix sorts chronologically
  for _, f := range old[:len(old)-keep] {
    os.Remove(f)
  }
}

func gettargetversion() (string, error) { // --------------------------------------------- detect target version
  files, err := filepath.Glob("*.go")
  if err != nil {
    return "", err
  }

  for _, file := range files {
    c, err := os.ReadFile(file)
    if err != nil {
      continue
    }
    if m := r5.FindSubmatch(c); m != nil {
      return string(m[1]), nil
    }
  }
  return "", SE(`target version not found, add 'var version = "x.y.z"' to your sources`)
}

func catchsignals() { // ---------------------------------------------- stop the running build before we exit
  sig := make(chan os.Signal, 1)
  signal.Notify(sig, os.Interrupt, syscall.SIGTERM)
  go func() {
    <-sig
    P()
    stopRunning()
    os.Exit(0)
  }()
}

func stopRunning() { // ------------------------------------------------------------- stop running old process
  mu.Lock()
  p := running
  running = nil
  mu.Unlock()

  if p == nil || p.cmd.Process == nil {
    return
  }
  pid := p.cmd.Process.Pid

  select {
  case <-p.done: // already gone
    return
  default:
  }

  p.cmd.Process.Signal(os.Interrupt)
  select {
  case <-p.done:
    P("process stopped:", pid)
  case <-time.After(1 * time.Second):
    p.cmd.Process.Kill()
    <-p.done
    P("process stopped forcefully:", pid)
  }
}

func lookup(what string) string { // ------------------------------------------------- find a required program
  path, err := exec.LookPath(what)
  if err != nil {
    PE(what+" not found", "please install it and make sure it is in your PATH")
    os.Exit(1)
  }
  return path
}

func fileExists(filename string) bool { // ------------------------------------------------ check if file exists
  info, err := os.Stat(filename)
  if err != nil {
    return false
  }
  return !info.IsDir()
}

func dirName() string { // ------------------------------------------------------- get name of current directory
  pwd, err := os.Getwd()
  if err == nil {
    return filepath.Base(pwd)
  }
  return ""
}

func info() { // ------------------------------------------------------------------------------------- show info
  PF("%s (%s (%s), toolbox %s, %s)\n", Cwb("gbld - simple golang builder"),
    Cgb("v"+version), Cgb(build), Cgb("v"+tbversion), Ccb("mwx'2026"))
}

// ========================================================================================================= END