[FeatReq] Skill Rating Approximator

[ReiFan49]

as the title said, a system that used to calculate skill rating of each producers. (well, PRP or fan count might be able to sort out for another thing, but PRP is not only about skill; it's about team combination and composition too)
it still underwent on testing here. for now (on the website), PRP is weighted per 1000 to add 1.00 bonus to rating

Note: Master+ is still under assumption

The skill rating itself only involves FC and clear count. Each difficulty represents a single weighted rating (ofc it's tentative).

• Debut: 10
• Regular: 20
• Pro: 60
• Master: 100
• Master+: x (x is total song count that have Master+)

# Difficulty Skill Contribution formula:
# [Difficulty Weight] * (
#   [Clear Count] * 40% + [Full Combo] * 60%
# ) / [Song Count on Respective Difficulties]

After obtaining the skill rating for each difficulties, find the highest one along each difficulties except Master+ and add up to 5.00 rating from the harder difficulty (Exclude Master+).

# the flow is written in Ruby

# player_skill_contrib is an OrderedDict that have:
# - kdif as the difficulty key
# - vclr as contributed value for the respective difficulty
player_skill = player_skill_contrib.inject(0.0) { |accx,(kdif,vclr)|
  idx = diff_keys.index(kdif)

  # bonus is obtained via:
  #   finding a harder difficulty from the current one on enumeration
  #   and compare which one have higher contribution along the
  #   eligible difficulties (that harder than enumerated one)
  bonus = diff_keys.select { |kdf|
    diff_keys.index(kdf) > idx
  }.inject(0.0) { |kbon,kdf|
    [player_skill_contrib.fetch(kdf,0.0),kbon].max
  }
  # acc_skill is the post-bonus given skill calculation after the
  # rating bonus from higher rating is given
  # Formula:
  # [Current Rating] + 5 * (
  #   Minimum([Current Rating],bonus)/Maximum(1,[Current Rating])
  # )
  acc_skill = vclr + 5 * Rational([vclr,bonus].min,[vclr,1].max)

  # accx is the final accumulated skill, which is counted after
  # comparing with the current difficulty skills.
  [accx,acc_skill].max
}

# Master+ bonus is added after 5.00 bonus

i hope this kind of rating might helps.