Source MD grabber

--[[
> lua this_script.lua -i file1.c -i file2.h -o doc.md
You can easily change regex and grab md text from any language
(c) Snooze 2020.
]]

local function argparse(t)
    local conf = {}
    local i = 0
    while i < #arg do
        i = i + 1
        local v = arg[i]
        if v:find('^[\\-]') then
            i = i + 1
            local key = v:match('^[\\-]*(.*)')
            local t = conf[key] or {}
            table.insert(t, arg[i])
            conf[key] = t
        else
            table.insert(conf, v)
        end
    end
    return conf
end

local function check(v, msg)
    return v or (print(msg) and os.exit())
end

local function readfile(filename)

    local file, err = io.open(filename, 'rb')
    if not file then
        print( ("Can't read %s file: %s"):format(filename, err) )
        return nil, err
    end
    return file:read("*a"), file:close()
end

local conf = argparse(arg)

local files = check(conf.i and #conf.i > 0 and conf.i, "No input files specified")
local out   = (conf.o or {})[1] or "README.md"
print("Files to process: \n  " .. table.concat(files, ',\n  '))
print("Output file: \n  "      .. out)

local md_data = {}

print("Parsing")
for i, filename in ipairs(files) do
    print("  " .. filename)
    local data = readfile(filename)
    if data then
        for line in data:gmatch("/%*%s?![mM][dD](.-)%*/") do
            table.insert(md_data, line)
        end
    end
end

local text = table.concat(md_data, '\n')
out = check(io.open(out, 'wb'))
out:write(text)
out:close()
print("OK")