Trim left edge of item to edit cursor (changing fade length)

-- if difference between item current and new edge coordinates is greater than the fade length
-- the original fade length is preserved

local r = reaper

function no_undo()
do return end
end


function Error_Tooltip(text, caps, spaced, x2, y2, want_color, want_blink)
local x, y = r.GetMousePosition()
local text = caps and text:upper() or text
local utf8 = '[\0-\127\194-\244][\128-\191]*'
local text = spaced and text:gsub(utf8,'%0 ') or text
local x2, y2 = x2 and math.floor(x2) or 0, y2 and math.floor(y2) or 0
r.TrackCtl_SetToolTip(text, x+x2, y+y2, true)
    if want_color then
    local color_init = r.GetThemeColor('col_tl_bg', 0)
    local color = color_init ~= 255 and 255 or 65535
        if want_blink then
            for i = 1, 100 do
                if i == 1 or i == 40 or i == 80 then
                r.SetThemeColor('col_tl_bg', color, 0)
                elseif i == 20 or i == 60 or i == 100 then
                r.SetThemeColor('col_tl_bg', color_init, 0)
                end
            r.UpdateTimeline()
            end
        else
        r.SetThemeColor('col_tl_bg', color, 0)
            for i = 1, 200 do
            r.UpdateTimeline()
            end
        r.SetThemeColor('col_tl_bg', color_init, 0)
        r.UpdateTimeline()
        end
    end
r.UpdateTimeline()
end


local is_new_value, scr_name, sect_ID, cmd_ID, mode, resol, val, contextstr = r.get_action_context()
scr_name = scr_name:match('([^\\/]+)%.%w+$')
local cmd_ID = scr_name:match('left edge') and 41305 or scr_name:match('right edge') and 41311
local sel_itms_cnt = r.CountSelectedMediaItems(0)

local err = not cmd_ID and 'wrong script name' or sel_itms_cnt == 0 and 'no selected items'

    if err then
    Error_Tooltip('\n\n '..err..' \n\n', 1,1)
    return r.defer(no_undo) end

local sel_items = {}

    for i=0, r.CountMediaItems(0)-1 do
    local item = r.GetMediaItem(0,i)
        if r.IsMediaItemSelected(item) then
        sel_items[#sel_items+1] = item
        end
    end


r.Undo_BeginBlock()

r.SelectAllMediaItems(0, false) -- selected false


local FADE_PARM = cmd_ID == 41305 and 'D_FADEINLEN' or 'D_FADEOUTLEN'
local fade_in = cmd_ID == 41305

    for k, item in ipairs(sel_items) do
    r.SetMediaItemSelected(item, true) -- selected true
    local pos = r.GetMediaItemInfo_Value(item, 'D_POSITION')
    local edge = fade_in and pos or pos+r.GetMediaItemInfo_Value(item, 'D_LENGTH')
    local fade_len = r.GetMediaItemInfo_Value(item, FADE_PARM)
    r.Main_OnCommand(cmd_ID,0) -- Item edit: Trim left/right edge of item to edit cursor
        if fade_len > 0 then
        local pos_new = r.GetMediaItemInfo_Value(item, 'D_POSITION')
        local edge_new = fade_in and pos_new or pos_new+r.GetMediaItemInfo_Value(item, 'D_LENGTH')
        local diff = edge_new-edge
        diff = math.abs(diff) > fade_len and 0 or diff*(fade_in and 1 or -1)
        r.SetMediaItemInfo_Value(item, FADE_PARM, math.abs(fade_len-diff))
        end
    end

    for k, item in ipairs(sel_items) do
    r.SetMediaItemSelected(item, true) -- selected true
    end

r.Undo_EndBlock(scr_name,-1)