local camera = require('openmw.camera')
local self = require('openmw.self')
local settings = require('openmw.settings')
local util = require('openmw.util')

local doubleStepLength = settings._getFloatFromSettingsCfg('Camera', 'head bobbing step') * 2
local stepHeight = settings._getFloatFromSettingsCfg('Camera', 'head bobbing height')
local maxRoll = math.rad(settings._getFloatFromSettingsCfg('Camera', 'head bobbing roll'))

local effectWeight = 0
local totalMovement = 0

local M = {
    enabled = settings._getBoolFromSettingsCfg('Camera', 'head bobbing')
}

-- Trajectory of each step is a scaled arc of 60 degrees.
local halfArc = math.rad(30)
local sampleArc = function(x) return 1 - math.cos(x * halfArc) end
local arcHeight = sampleArc(1)

function M.update(dt, smoothedSpeed)
    local speed = self:getCurrentSpeed()
    speed = speed / (1 + speed / 500)  -- limit bobbing frequency if the speed is very high
    totalMovement = totalMovement + speed * dt
    if not M.enabled or camera.getMode() ~= camera.MODE.FirstPerson then
        effectWeight = 0
        return
    end
    if self:isOnGround() then
        effectWeight = math.min(1, effectWeight + dt * 5)
    else
        effectWeight = math.max(0, effectWeight - dt * 5)
    end

    local doubleStepState = totalMovement / doubleStepLength
    doubleStepState = doubleStepState - math.floor(doubleStepState)  -- from 0 to 1 during 2 steps
    local stepState = math.abs(doubleStepState * 4 - 2) - 1  -- from -1 to 1 on even steps and from 1 to -1 on odd steps
    local effect = sampleArc(stepState) / arcHeight  -- range from 0 to 1

    -- Smoothly reduce the effect to zero when the player stops
    local coef = math.min(smoothedSpeed / 300, 1) * effectWeight

    local zOffset = (0.5 - effect) * coef * stepHeight  -- range from -stepHeight/2 to stepHeight/2
    local roll = ((stepState > 0 and 1) or -1) * effect * coef * maxRoll  -- range from -maxRoll to maxRoll
    camera.setFirstPersonOffset(camera.getFirstPersonOffset() + util.vector3(0, 0, zOffset))
    camera.setRoll(camera.getRoll() + roll)
end

return M