--[[

SCRIPT: SNAPFLAP
AUTHOR: Mike Shellim
URL: http://www.rc-soar.com/opentx
DATE: 22 August 2014
VERSION: 2.02A
DESCRIPTION:

Adjustable snapflap mix.

INPUTS:
	ctrl_p1		control for adjusting elevator value at which snapflap starts
					1=S1 (default)
					2=S2
					3=LS
					4=RS
					5=TrmT (throttle trim)
    p2			elev value at which max snapflap is reached
					min=20
					max=100
					default=100

OUTPUTS:
	Snap -  snapflap value -100 to +100


           Snap
             ^
             |
             |
        100  |  -----        xxxxxxxx
             |             x
             |           x
             |         x
             |       x
             |     x
             |xxxx------------------ |elev| -->
             |   |           |
             |   p1          p2
             |


INSTALLATION
1. Save script with .LUA extension, store in /SCRIPTS/MIXES folder on SD Card
2. Open Custom Scripts menu in the transmitter
3. Assign this LUA script to an empty slot
4. Test by moving elevator stick and observing 'snap' value
5. Close Custom Scripts menu
6. Check that [i]Snap appears in the mixer Src list

MIXER SETUP
- Create new mixer line in wing servo channel, call it 'snap'
	Src = [i]Snap
	[optional] to restrict snapflap to one direction, specify curve="x<0" or "x>0"

ADJUSTMENTS
- To alter p1, rotate designated control (s1, s2, ls, lr or trmT)
- To alter p2, enter a value for p2 in the script menu
- To alter snapflap volume, adjust wt in 'snap' mixer line
-    Alternatively adjust via another control in a subsequent MULTiply mixer line
--]]


local MIN_INTERVAL = 20	-- minimum interval between p1 and p2
local control_id = {}  	-- array of control ids
local out = {"Snap"} 	-- outputs definition

-- inputs definition
local inp =
    {
        { "ctrl_p1", VALUE, 1, 5, 1},			-- index into controls table, defines adjuster for p1. Default = 1, i.e S1
        { "p2", VALUE, MIN_INTERVAL, 100, 100 } -- Value of p2. Default = 100.
    }


-- initialisation function (called once)
local function init_func()

	-- Store ids of permissable adjuster controls in array
	-- (saves expensive lookups in run_func)

	control_id [1] = getFieldInfo ("s1").id
	control_id [2] = getFieldInfo ("s2").id
	control_id [3] = getFieldInfo ("ls").id
	control_id [4] = getFieldInfo ("rs").id
	control_id [5] = getFieldInfo ("trim-thr").id

end

-- periodically called function
local function run_func(ctrl_p1, p2)

    local p1
	local elev_in
    local elev
    local snap

    -- initialise variables

    snap = 0

    ---------------------------------
    -- convert inputs to script units
    ---------------------------------

    -- Map el_p1_control (-100 to +100) to snap_sta (0 to 1024)

	p1 = getValue (control_id[ctrl_p1])
	p1 = ((p1 * 0.5) + 512)


    -- convert p2 to script units

    p2 = p2 * 10.24

    -----------------------------------
    -- check interval between p1 and p2
    -----------------------------------

    if p2 - p1 < MIN_INTERVAL then
        p1 = p2 - MIN_INTERVAL
    end


    ----------------------------
    -- get abs value of elevator
    ----------------------------

    elev_in = getValue (MIXSRC_Ele)

    if elev_in < 0 then
        elev = -elev_in
    else
        elev = elev_in
    end

    ---------------------
    -- determine snapflap
    ---------------------

    if elev >= p2 then
        snap = 1024
    elseif elev <= p1 then
        snap = 0
    else
        snap = (1024 *(elev-p1))/(p2-p1)
    end

    -- negate result if elev was negative

    if elev_in < 0 then
        snap = -snap
    end

    return snap
end

return { init=init_func, run=run_func, input=inp, output=out}