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-- utilities for dealing with angles and rotation

local abs = math.abs;
local atan2 = math.atan2

local CIRCLE = 2 * math.pi

local angles = {CIRCLE = CIRCLE}

local function normalize(r)
    if r < 0 then
        r = r + CIRCLE
    elseif r > CIRCLE then
        r = math.mod(r, CIRCLE)
    end

    return r
end

function angles.rotateby(r, deltar)
    return normalize(r + deltar)
end

-- angle from fx, fy to tx, ty
function angles.to(fx, fy, tx, ty)
    return normalize(atan2(ty - fy, tx - fx))
end


-- Adjust r towards targetr by amount
-- this may increase or decreate targetr
-- returns normalized value
function angles.turnto(r, targetr, amount)
    local delta = targetr - r

    if delta > 0 and delta <= math.pi then
        r = r + amount 
    else    
        r = r - amount
    end

    return normalize(r)
end

return angles