local M = {}

-- Base64 字符集
local b64chars = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/'
-- 创建 Base64 反向查找表
local b64lookup = {}
for i = 1, #b64chars do
    b64lookup[string.sub(b64chars, i, i)] = i - 1
end

M.encode = function(input)
    local output = {}
    local len = #input
    for i = 1, len, 3 do
        local a, b, c = string.byte(input, i, i + 2)
        local chunk = (a or 0) << 16 | (b or 0) << 8 | (c or 0)

        output[#output + 1] = b64chars:sub(((chunk >> 18) & 0x3F) + 1, ((chunk >> 18) & 0x3F) + 1)
        output[#output + 1] = b64chars:sub(((chunk >> 12) & 0x3F) + 1, ((chunk >> 12) & 0x3F) + 1)
        output[#output + 1] = b and b64chars:sub(((chunk >> 6) & 0x3F) + 1, ((chunk >> 6) & 0x3F) + 1) or "="
        output[#output + 1] = c and b64chars:sub((chunk & 0x3F) + 1, (chunk & 0x3F) + 1) or "="
    end
    return table.concat(output)
end

-- Base64 解码函数
M.decode = function(input)
    input = input:gsub("%s", ""):gsub("=", "")  -- 去除空白和填充符
    local output = {}
    for i = 1, #input, 4 do
        local a, b, c, d = b64lookup[input:sub(i, i)], b64lookup[input:sub(i + 1, i + 1)],
                            b64lookup[input:sub(i + 2, i + 2)] or 0, b64lookup[input:sub(i + 3, i + 3)] or 0
        local chunk = (a << 18) | (b << 12) | (c << 6) | d

        output[#output + 1] = string.char((chunk >> 16) & 0xFF)
        if input:sub(i + 2, i + 2) ~= "" then
            output[#output + 1] = string.char((chunk >> 8) & 0xFF)
        end
        if input:sub(i + 3, i + 3) ~= "" then
            output[#output + 1] = string.char(chunk & 0xFF)
        end
    end
    return table.concat(output)
end





return M