--[[

	tail physics
	version 3.2
	
	developed by @zephyrr skidded off @r3dtuxedo
	
]]--

local config={
    stiffness=96,
    damping=9,
    linearamp=Vector3.new(6.4,2.5333333,6.4),
    angularamp=Vector3.new(0,18,0),
    wagenabled=true,
    wagdrop=0.2,
    wagsway=0.4,
    wagroll=0.5,
    wagblendin=0.008,
    wagblendout=0.02,
    wagspeed=1,
    timescale=1,
    windenabled=false,
    gravityenabled=false,
    customwind=Vector3.new(0,0,0),
    customforce=Vector3.new(0,0,0),
    maxdistance=900,
    maxtails=5,
    movethreshold=15,
    includednames={}
}

local run=game:GetService("RunService")
local players=game:GetService("Players")
local player=players.LocalPlayer
local char=player.Character or player.CharacterAdded:Wait()
local cam=workspace.CurrentCamera

local sin=math.sin
local cos=math.cos
local min=math.min
local max=math.max
local insert=table.insert
local find=table.find
local remove=table.remove
local sort=table.sort

local timestep=1/120
local inversetimestep=120

local tails={}
local tracked={}
local wagtime=0
local windtime=0
local accum=0

local winddir=Vector3.new(0,0,0)
local windalpha=0
local windalpha04=0
local windalpha006=0
local haswind=false

local gravforce=Vector3.new(0,0,0)
local linearforce=Vector3.new(0,0,0)
local haslinear=false

local function springcalc(pos,vel,stiff,damp)
    local accel=stiff*pos+damp*vel
    local newvel=vel-accel*timestep
    return pos+newvel*timestep,newvel
end

local function vectoangles(v)
    return CFrame.fromEulerAngles(v.X,v.Y,v.Z)
end

local function lerp(a,b,t)
    return a+(b-a)*t
end

local function updatewind()
    local windforce=config.windenabled and (workspace.GlobalWind+config.customwind) or config.customwind
    winddir=windforce.Unit
    windalpha=windforce.Magnitude*0.5
    windalpha04=windalpha*0.4
    windalpha006=windalpha*windalpha*0.06
    haswind=windalpha>0
end

local function updatelinear()
    linearforce=config.gravityenabled and (gravforce+config.customforce) or config.customforce
    haslinear=linearforce.Magnitude>0
end

local function updategravity()
    gravforce=Vector3.new(0,max((196.2-workspace.Gravity)*0.004,-1))
    updatelinear()
end

updatewind()
updategravity()
workspace:GetPropertyChangedSignal("GlobalWind"):Connect(updatewind)
workspace:GetPropertyChangedSignal("Gravity"):Connect(updategravity)

local function getwagoffset(tail)
    local blend=tail.wagblend
    if tail.angvel.Magnitude>0.3 then blend=blend<0.01 and 0 or blend*(1-config.wagblendout) else blend=blend>0.99 and 1 or lerp(blend,1,config.wagblendin) end
    tail.wagblend=blend
    if blend>0 then local wt=wagtime+tail.seed local ft=wt+sin(wt)*sin(wt*0.22727272727272727)*0.9 return Vector3.new((sin(ft*2)+0.8)*config.wagdrop*blend,cos(ft)*config.wagsway*blend,sin(ft)*-config.wagroll*blend) end
    return Vector3.new(0,0,0)
end

local function updateinterp(tail,alpha)
    local scale=tail.invscale*tail.char:GetScale()
    local cf=tail.prevweld:Lerp(tail.curweld,alpha)
    if config.wagenabled then cf=cf*(cf:ToObjectSpace(tail.pivot*vectoangles(getwagoffset(tail))*tail.invpivot)):Inverse() end
    tail.weld.C0=cf.Rotation+cf.Position*scale
end

local function updatetail(tail,doweld,alpha)
    local rootcf=tail.root.CFrame
    local delta=tail.prevroot:ToObjectSpace(rootcf)
    if delta.Position.Magnitude>config.movethreshold then delta=delta.Rotation end
    local accel=tail.prevdelta:ToObjectSpace(delta)
    local force=accel.Position*config.linearamp
    if haswind then local s4=sin(windtime*4) local unstable=sin(windtime*2*s4)*windalpha04 local stable=sin(windtime*2)*s4 force=force-rootcf:VectorToObjectSpace(winddir*windalpha006*(1+(stable+unstable)*0.4)) end
    if haslinear then force=force-rootcf:VectorToObjectSpace(linearforce) end
    local pivot=tail.pivot
    local disp=pivot.Position-tail.prevweld.Position
    local torque=disp:Cross(force)
    local x,y,z=accel:ToEulerAnglesXYZ()
    local angaccel=Vector3.new(x,y,z)*config.angularamp
    local newangle,newangvel=springcalc(tail.angle,tail.angvel,config.stiffness,config.damping)
    tail.angle=newangle
    local scale=tail.invscale*tail.char:GetScale()
    tail.angvel=newangvel+torque/scale-angaccel
    local anglecf=vectoangles(newangle)
    local newcur=pivot*anglecf*tail.invpivot
    local newprev=tail.curweld
    if doweld then
        local cf=newprev:Lerp(newcur,alpha)
        if config.wagenabled then cf=cf*(cf:ToObjectSpace(pivot*vectoangles(getwagoffset(tail))*tail.invpivot)):Inverse() end
        tail.weld.C0=cf.Rotation+cf.Position*scale
    end
    tail.prevroot=rootcf
    tail.prevdelta=delta
    tail.prevweld=newprev
    tail.curweld=newcur
end

local function getpivot(root)
    local waistrig=root:FindFirstChild("WaistRigAttachment")
    if waistrig then return waistrig.CFrame*CFrame.new(0,0,root.Size.Z*0.5) end
    local waistback=root:FindFirstChild("WaistBackAttachment")
    if waistback then return waistback.CFrame*CFrame.new(0,0.3,0) end
    return nil
end

local function nametoseed(name)
    local seed=0
    for i=1,#name do seed=seed+string.byte(name,i)^2 end
    return seed
end

local function setupweld(character,weld,tailpart,custompivot)
    local flipped=false
    local root=weld.Part0
    if not root then warn("weld missing part0") return end
    if root==tailpart then root=weld.Part1 if not root then warn("weld missing part1") return end flipped=true end
    local pivot
    if custompivot then pivot=typeof(custompivot)=="CFrame" and custompivot or custompivot.CFrame else pivot=getpivot(root) end
    if not pivot then warn("couldnt find attachment") return end
    local origcf
    if flipped then origcf=weld.C1*weld.C0:Inverse() weld.Part0,weld.Part1=root,tailpart else origcf=weld.C0*weld.C1:Inverse() end
    weld.C0=origcf
    weld.C1=CFrame.identity
    pivot=origcf:ToObjectSpace(CFrame.new(pivot.Position))
    local seed=nametoseed(character.Name)
    local plr=players:GetPlayerFromCharacter(character)
    if plr then seed=seed+plr.UserId end
    local tail={root=root,prevroot=root.CFrame,prevdelta=CFrame.identity,weld=weld,origcf=origcf,prevweld=origcf,curweld=origcf,angle=Vector3.new(0,0,0),angvel=Vector3.new(0,0,0),wagblend=0,seed=seed,pivot=origcf*pivot,invpivot=pivot:Inverse(),char=character,invscale=1/character:GetScale(),dist=0,rendering=false}
    insert(tails,tail)
    weld.AncestryChanged:Connect(function() if not weld.Parent then local idx=find(tails,tail) if idx then remove(tails,idx) end end end)
end

local function setupaccessory(character,accessory)
    local handle=accessory:FindFirstChild("Handle")
    if not handle then accessory.ChildAdded:Once(function() setupaccessory(character,accessory) end) return end
    local weld=handle:FindFirstChild("AccessoryWeld")
    if weld then setupweld(character,weld,handle) end
end

local function istail(accessory)
    local acctype=accessory.AccessoryType
    local accname=accessory.Name:lower()
    if acctype==Enum.AccessoryType.Back or acctype==Enum.AccessoryType.Waist then
        if accname:find("tail",1,true) then return true end
        if #config.includednames>0 then for _,name in ipairs(config.includednames) do if accessory.Name==name then return true end end end
    end
    return false
end

local function setupchar(character)
    if tracked[character] then return end
    tracked[character]=true
    print("setting up "..character.Name)
    character.ChildAdded:Connect(function(child) if child:IsA("Accessory") and istail(child) then print("found new tail "..child.Name) setupaccessory(character,child) end end)
    local count=0
    for _,child in ipairs(character:GetChildren()) do if child:IsA("Accessory") and istail(child) then print("found tail "..child.Name) setupaccessory(character,child) count=count+1 end end
    if count>0 then print("setup "..count.." tails") else print("no tails found") end
    character:GetPropertyChangedSignal("Parent"):Connect(function() if not character.Parent then tracked[character]=nil end end)
end

setupchar(char)
player.CharacterAdded:Connect(function(c) 
    char=c 
    tails={}
    tracked={}
    wagtime=0
    windtime=0
    accum=0
    print("resetting physics")
    task.wait(0.5)
    setupchar(c) 
end)

local function sortbydist(a,b) return a.dist<b.dist end

run.PreRender:Connect(function(dt)
    dt=min(dt,0.1)*config.timescale
    wagtime=wagtime+dt*config.wagspeed
    windtime=windtime+dt
    accum=accum+dt
    local steps=0
    while accum>=timestep do accum=accum-timestep steps=steps+1 end
    local campos=cam.CFrame.Position
    local rendering={}
    for _,tail in ipairs(tails) do
        local dist=(tail.root.CFrame.Position-campos).Magnitude
        if dist<=config.maxdistance then tail.dist=dist insert(rendering,tail)
        elseif tail.rendering then tail.rendering=false local scale=tail.invscale*tail.char:GetScale() tail.weld.C0=tail.origcf.Rotation+tail.origcf.Position*scale end
    end
    sort(rendering,sortbydist)
    local interp=steps==0
    local alpha=accum*inversetimestep
    local updated=0
    for _,tail in ipairs(rendering) do
        if updated>=config.maxtails then if tail.rendering then tail.rendering=false local scale=tail.invscale*tail.char:GetScale() tail.weld.C0=tail.origcf.Rotation+tail.origcf.Position*scale end
        else
            if interp then if not tail.rendering then continue end updateinterp(tail,alpha)
            else
                if not tail.rendering then tail.prevroot=tail.root.CFrame tail.prevdelta=CFrame.identity tail.prevweld=tail.origcf tail.curweld=tail.origcf tail.angle=Vector3.new(0,0,0) tail.angvel=Vector3.new(0,0,0) tail.wagblend=0 tail.rendering=true end
                for i=1,steps do updatetail(tail,steps==i,alpha) end
            end
            updated=updated+1
        end
    end
end)

print("tracking "..#tails.." tails")