# Originally designed by Ben Laurie
# Adapted from https://github.com/benlaurie/objecthash/blob/master/objecthash.py

require "objecthash/version"

require "digest/sha2"
require "set"

# A content hash algorithm which works across multiple encodings (JSON, Protobufs, etc)
class ObjectHash
  # Default algorithm to use for computing object hashes
  DEFAULT_HASH_ALGORITHM = Digest::SHA256

  # Compute a raw ObjectHash digest using the default algorithm
  def self.digest(object, normalize: true)
    new.digest(object, normalize: normalize)
  end

  # Compute an hex ObjectHash digest using the default algorithm
  def self.hexdigest(object, normalize: true)
    new.hexdigest(object, normalize: normalize)
  end

  def initialize(hash_algorithm = DEFAULT_HASH_ALGORITHM)
    @hash_algorithm = hash_algorithm
  end

  # Compute the ObjectHash of the given object
  def digest(object, normalize: true)
    case object
    when Array       then obj_hash_list(object)
    when Hash        then obj_hash_dict(object)
    when String      then obj_hash_unicode(object, normalize)
    when Symbol      then obj_hash_unicode(object.to_s, normalize)
    when Float       then obj_hash_float(object)
    when Fixnum      then obj_hash_int(object)
    when Set         then obj_hash_set(object)
    when true, false then obj_hash_bool(object)
    when nil         then hash_primitive("n", "")
    else             raise TypeError, "unsupported: #{object.class}"
    end
  end

  # Compute the ObjectHash of the given object as hexadecimal
  def hexdigest(object, normalize: true)
    digest(object, normalize: normalize).unpack("H*").first
  end

  private

  def hash_primitive(t, b)
    m = @hash_algorithm.is_a?(Proc) ? @hash_algorithm.call : @hash_algorithm.new
    m.update(t)
    m.update(b)
    m.digest
  end

  def obj_hash_bool(b)
    hash_primitive("b", b ? "1" : "0")
  end

  def obj_hash_list(l)
    h = l.map { |o| digest(o) }.join
    hash_primitive("l", h)
  end

  def obj_hash_dict(d)
    h = d.map { |k, v| digest(k) + digest(v) }.sort.join
    hash_primitive("d", h)
  end

  # Takes a unicode string and a boolean to indicate
  # whether to normalize unicode or not.
  def obj_hash_unicode(u, n)
    u_enc = u.encode("utf-8")
    u_norm = n ? u_enc.unicode_normalize(:nfc) : u_enc
    hash_primitive("u", u_norm)
  end

  # rubocop:disable Metrics/AbcSize
  # rubocop:disable Metrics/CyclomaticComplexity
  def float_normalize(f)
    # special case 0
    # Note that if we allowed f to end up > .5 or == 0, we'd get the same thing
    return "+0:" if f == 0.0

    # sign
    if f >= 0
      s = "+"
    else
      s = "-"
      f = -f
    end

    # exponent
    e = 0
    while f > 1
      f /= 2
      e += 1
    end

    while f <= 0.5
      f *= 2
      e -= 1
    end

    s += "#{e}:"

    # mantissa
    raise unless f <= 1
    raise unless f > 0.5

    while f != 0.0
      if f >= 1
        s += "1"
        f -= 1
      else
        s += "0"
      end

      raise unless f < 1
      raise unless s.length < 1000
      f *= 2
    end

    s
  end
  # rubocop:enable Metrics/AbcSize
  # rubocop:enable Metrics/CyclomaticComplexity

  def obj_hash_float(f)
    hash_primitive("f", float_normalize(f))
  end

  def obj_hash_int(i)
    hash_primitive("i", i.to_s)
  end

  def obj_hash_set(s)
    h = s.map { |e| e << digest(e) }.sort.join
    hash_primitive("s", h)
  end
end