-- TIME_STAMP   2022-03-16 12:37:55   v 0.1



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--[[
in...:  _line       A line of text whose TAB are to be replaced by spaces.
.....:  _tabsize    TAB size in number of characters. If it is omitted, 4 is used.
out..:  The line, with TAB replaced if necessary, and the number of replacements.
]]
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TabReplace_Line = function(_line, _tabsize)
    if _line:find('^[\r\n]+$') then return _line, 0 end -- only a line break
    if _line == '' then return _line, 0 end             -- only a empty string
    local posTab = _line:find('\t')
    if posTab == nil then return _line, 0 end           -- no TAB included
    _tabsize = _tabsize or 4                            -- default TAB width
    local tTab, s, sRep, iLen, sumLen = {}, ' ', '', 0, 0
    while posTab ~= nil do
        -- calculation replacement string, taking into account characters to be inserted
        iLen = (_tabsize - ((posTab + sumLen -1) % _tabsize))
        sumLen = sumLen + iLen -1                       -- total length of the replacements
        sRep = s:rep(iLen)                              -- create replacement string
        table.insert(tTab, sRep)                        -- save to table
        posTab = _line:find('\t', posTab +1)            -- find next TAB
    end
    local idx = 0
    _line = _line:gsub('\t', function() idx = idx +1 return tTab[idx] end)
    return _line, idx
end
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--[[
in...:  _file       Path of the file whose TAB are to be replaced by spaces.
.....:  _tabsize    TAB size in number of characters. If it is omitted, 4 is used.
out..:  Success     true, count-of-replacements
.....:  Failure     false, 0
]]
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TabReplace_File = function(_file, _tabsize)
    local fh = io.open(_file, "rb")  -- check if file exists
    if fh == nil then return false, 0 end
    local read = fh:read('*a')
    local lineBreak = read:find('\r')
    if lineBreak ~= nil then lineBreak = string.char(13,10) else lineBreak = string.char(10) end
    local nRepl, sumRepl, newLine, sWrite = 0, 0, '', ''
    fh:seek("set")
    for line in fh:lines() do
        newLine, nRepl = TabReplace_Line(line, _tabsize)
        sWrite = string.format('%s%s%s', sWrite, newLine, lineBreak)
        sumRepl = sumRepl + nRepl
    end
    fh:close()

    -- • file:lines() zerstört das Zeilenende?
    -- • Füge ich kein CRLF an, wird LF verwendet, was dazu führt, dass die berechneten Ersatzstrings für TAB falsch sind.
    -- • Füge ich CRLF an, ist das Ergebnis: "Zeileninhalt" & CR & CR & CRLF.
    -- • Deshalb wird das doppelte CR hier entfernt.
    sWrite = sWrite:gsub('\r\r', '')

    if sumRepl == 0 then return true, 0 end
    fh = io.open(_file, "w+")
    fh:write(sWrite)
    fh:close()
    return true, sumRepl
end
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