class Gem::Package::TarTestCase

def ASCIIZ(str, length)
  str + "\0" * (length - str.length)
end

def SP(s)
  s + " "
end

def SP_Z(s)
  s + " \0"
end

def Z(s)
  s + "\0"
end

def assert_headers_equal(expected, actual)
  expected = expected.to_s unless String === expected
  actual = actual.to_s unless String === actual
  fields = %w[
    name 100
    mode 8
    uid 8
    gid 8
    size 12
    mtime 12
    checksum 8
    typeflag 1
    linkname 100
    magic 6
    version 2
    uname 32
    gname 32
    devmajor 8
    devminor 8
    prefix 155
  ]
  offset = 0
  until fields.empty? do
    name = fields.shift
    length = fields.shift.to_i
    if name == "checksum"
      chksum_off = offset
      offset += length
      next
    end
    assert_equal expected[offset, length], actual[offset, length],
                 "Field #{name} of the tar header differs."
    offset += length
  end
  assert_equal expected[chksum_off, 8], actual[chksum_off, 8]
end

def calc_checksum(header)
  sum = header.unpack("C*").inject{|s,a| s + a }
  SP(Z(to_oct(sum, 6)))
end

def header(type, fname, dname, length, mode, mtime, checksum = nil, linkname = "")
  checksum ||= " " * 8
  arr = [                  # struct tarfile_entry_posix
    ASCIIZ(fname, 100),    # char name[100];     ASCII + (Z unless filled)
    Z(to_oct(mode, 7)),    # char mode[8];       0 padded, octal null
    Z(to_oct(0, 7)),       # char uid[8];        ditto
    Z(to_oct(0, 7)),       # char gid[8];        ditto
    Z(to_oct(length, 11)), # char size[12];      0 padded, octal, null
    Z(to_oct(mtime, 11)),  # char mtime[12];     0 padded, octal, null
    checksum,              # char checksum[8];   0 padded, octal, null, space
    type,                  # char typeflag[1];   file: "0"  dir: "5"
    ASCIIZ(linkname, 100), # char linkname[100]; ASCII + (Z unless filled)
    "ustar\0",             # char magic[6];      "ustar\0"
    "00",                  # char version[2];    "00"
    ASCIIZ("wheel", 32),   # char uname[32];     ASCIIZ
    ASCIIZ("wheel", 32),   # char gname[32];     ASCIIZ
    Z(to_oct(0, 7)),       # char devmajor[8];   0 padded, octal, null
    Z(to_oct(0, 7)),       # char devminor[8];   0 padded, octal, null
    ASCIIZ(dname, 155), # char prefix[155];   ASCII + (Z unless filled)
  ]
  h = arr.join
  ret = h + "\0" * (512 - h.size)
  assert_equal(512, ret.size)
  ret
end

def tar_dir_header(name, prefix, mode, mtime)
  h = header("5", name, prefix, 0, mode, mtime)
  checksum = calc_checksum(h)
  header("5", name, prefix, 0, mode, mtime, checksum)
end

def tar_file_header(fname, dname, mode, length, mtime)
  h = header("0", fname, dname, length, mode, mtime)
  checksum = calc_checksum(h)
  header("0", fname, dname, length, mode, mtime, checksum)
end

def tar_symlink_header(fname, prefix, mode, mtime, linkname)
  h = header("2", fname, prefix, 0, mode, mtime, nil, linkname)
  checksum = calc_checksum(h)
  header("2", fname, prefix, 0, mode, mtime, checksum, linkname)
end

def to_oct(n, pad_size)
  "%0#{pad_size}o" % n
end

def util_dir_entry
  util_entry tar_dir_header("foo", "bar", 0, Time.now)
end

def util_entry(tar)
  io = TempIO.new tar
  header = Gem::Package::TarHeader.from io
  Gem::Package::TarReader::Entry.new header, io
end

def util_symlink_entry
  util_entry tar_symlink_header("foo", "bar", 0, Time.now, "link")
end