mri_to_webp.lua

local moses = require("moses")

local function parse_mri_to_webp(mri_path)
    local name = string.match(mri_path, "(%w+)%.")
    local fsi = io.open(mri_path, "rb")
    local idata = fsi:read("*all")
    fsi:close()

    local size = #idata
    local n = size + 7
    local odata = {
        82,  -- R
        73,  -- I
        70,  -- F
        70,  -- F
        (n >> 24) & 255,
        (n >> 16) & 255,
        (n >> 8) & 255,
        255 & n,
        87,  -- W
        69,  -- E
        66,  -- B
        80,  -- P
        86,  -- V
        80,  -- P
        56,  -- 8
    }

    for i=1, size do
        local char = idata:sub(i, i)
        local byte = string.byte(char)
        table.insert(odata, 101 ~ byte)
    end

    local fso = io.open(name .. "_l.webp", "wb")
    fso:write(table.concat(moses.map(odata, function (v)
        return string.char(v)
    end), ''))
    fso:close()
end

local function main(path_list)
    for _, path in pairs(path_list) do
        parse_mri_to_webp(path)
    end
end

if arg[-1] then
    main(moses.slice(arg, 1))
end