phoi_Reposition items, treating contiguous groups of items as single items

-- CONFIG
local EPSILON = 0.001 -- maximum distance for items to be considered contiguous in seconds, i.e. 1 millisecond
local SAVE_VALS = true -- set to true for settings to be retained between invocations of this script
local VALS_PERSIST = true -- set to true for settings to be retained between sessions; if SAVE_VALS is not true, this does nothing

-- NAME
local scriptName = ({reaper. get_action_context()})[2]:match("([^/\\]+)%.lua$") -- generate default scriptName from file

--FUNCTIONS FOR DEBUG
function msg(msg)
    reaper.ShowConsoleMsg(tostring(msg) .. "\n")
end

function getSelectedItems()
    local items = {}
    local iCount = reaper.CountSelectedMediaItems(0)
    for i = 1, iCount do
        items[i] = reaper.GetSelectedMediaItem(0, i - 1)
    end
    return items
end

function getSelectedItemsOnTrack(track)
    local items = {}
    for i = 0, reaper.CountTrackMediaItems(track) - 1 do
        local it = reaper.GetTrackMediaItem(track, i)
        if reaper.IsMediaItemSelected(it) then items[#items+1] = it end
    end
    return items
end

function toCSV(tt)
-- Convert from table to CSV string
    local function escapeCSV(s) --Used to escape "'s by toCSV
        if string.find(s, '[,"]') then
                s = '"' .. string.gsub(s, '"', '""') .. '"'
        end
        return s
    end
    local s = ""
    for _,p in ipairs(tt) do
        s = s .. "," .. escapeCSV(p)
    end
    return string.sub(s, 2)         -- remove first comma
end

function fromCSV(vals_csv, outputTypes)
    local t = {}
    local i = 0
    for line in vals_csv:gmatch("[^" .. "," .. "]*") do
        i = i + 1
        if #outputTypes == 1 and outputTypes[1] == "number" then
            t[i] = tonumber(line)
        elseif outputTypes[i] == "number" then
            t[i] = tonumber(line)
        else
            t[i] = line
        end
    end
    return t
end

function multiUserInput(outputTypes, windowName, numberOfParams, paramNames, defaultVals, saveVals, valsPersist, valsKeySuffix)
--[[ returns retval, input values as a table
Examples:

retval, inputs = multiUserInput({"number"}, "Test", 3, {"Threshold", "Ratio", "Output"}, {-18, 4, 6}, true, false, "")
if retval then msg(inputs[1]) end

Note: outputTypes can take a 1-element table, which will apply that value type to all inputs.
Otherwise specify output type for each value
--]]
    paramNames_csv = toCSV(paramNames)
    if saveVals and reaper.HasExtState(scriptName, scriptName .. "_Vals" .. valsKeySuffix) then -- restore previous values on run if saveVals is true and the values exist
        defaultVals_csv = reaper.GetExtState(scriptName, scriptName .. "_Vals" .. valsKeySuffix)
    else
        defaultVals_csv = toCSV(defaultVals)
    end
    retval, retvals_csv = reaper.GetUserInputs(tostring(windowName), numberOfParams, paramNames_csv, defaultVals_csv)
    if retval and saveVals then
        reaper.SetExtState(scriptName, scriptName .. "_Vals" .. valsKeySuffix, retvals_csv, valsPersist) -- save new defaults
    end
    if retval then
        vals = fromCSV(retvals_csv, outputTypes)
    else
        vals = nil
    end
    return retval, vals
end

function itemEnd(it)
    local p = reaper.GetMediaItemInfo_Value(it, "D_POSITION")
    local e = reaper.GetMediaItemInfo_Value(it, "D_LENGTH")
    return p + e
end

function getOverlap(it1, it2)
    return reaper.GetMediaItemInfo_Value(it2, "D_POSITION") - itemEnd(it1)
end

function getIfOverlap(it1, it2)
    return getOverlap(it1, it2) <= EPSILON
end

function name(it)
    return reaper.GetTakeName(reaper.GetActiveTake(it))
end

function mv(its, pos)
    local dposs = {0}
    for i = 1, #its do
        local it = its[i]
        local len = reaper.GetMediaItemInfo_Value(it, "D_LENGTH")
        local ol
        if i < #its then ol = getOverlap(it, its[i+1]) else ol = 0 end
        dposs[#dposs+1] = dposs[#dposs] + len + ol
    end
    for i = 1, #its do
        reaper.SetMediaItemPosition(its[i], pos+dposs[i], false)
    end
end

function nextPos(it, fromStart, offset)
    local p = reaper.GetMediaItemInfo_Value(it, "D_POSITION")
    if fromStart <= 0 then p = p + reaper.GetMediaItemInfo_Value(it, "D_LENGTH") end
    if offset > 0 then p = p + reaper.GetMediaItemInfo_Value(it, "D_SNAPOFFSET") end
    return p
end

function reposition(items, dist, fromStart, offset) -- fromStart and offset 0/1
    local times = {}
    local j = 1
    while j <= #items do
        local it = items[j]
        local its = {it}
        while j < #items and getIfOverlap(it, items[j+1]) do
            j = j + 1
            it = items[j]
            its[#its+1] = it
        end
        if #times > 0 then -- if this is not first iteration
            mv(its, times[#times] + dist)
        end
        local p = nextPos(its[#its], fromStart, offset)
        times[#times+1] = p
        j = j + 1
    end
end

function main()
    reaper.Undo_BeginBlock()
    local retval, inputs = multiUserInput(
        {"number"},
        scriptName,
        5,
        {"Distance", "Seconds / Beats (0/1)", "From end / start of prev. item (0/1)", "Per track (0/1)", "Include snap offset (0/1)"},
        {"1", "0", "0", "1", "1"},
        SAVE_VALS,
        VALS_PERSIST,
        '')
    if not retval then return end
    local input_dist, input_beats, input_fromStart, input_perTrack, input_offset = inputs[1], inputs[2], inputs[3], inputs[4], inputs[5]
    if input_beats > 0 then input_dist = reaper.TimeMap2_beatsToTime(0, input_dist) end
    if input_perTrack > 0 then
        local tracks = {}
        for i = 0, reaper.CountSelectedMediaItems(0) - 1 do
            local it = reaper.GetSelectedMediaItem(0, i)
            local tr = reaper.GetMediaItemTrack(it)
            if tr ~= tracks[#tracks] then tracks[#tracks+1] = tr end
        end
        for i = 1, #tracks do
            local tr = tracks[i]
            local items = getSelectedItemsOnTrack(tr)
            reposition(items, input_dist, input_fromStart, input_offset)
        end
    else
        items = getSelectedItems()
        reposition(items, input_dist, input_fromStart, input_offset)
    end
    reaper.Undo_EndBlock(scriptName, -1)
end

reaper.PreventUIRefresh(1)
main()
reaper.PreventUIRefresh(-1)
reaper.UpdateArrange()