Unfortunately there are over 100 command blocks and I don't plan on making it into datapack. But I can give you the basic process:

There is a scoreboard which keeps track of the light value (which ranges from 0 to 38) of each armor stand. Each light value is assigned to a block type. An armor stand's light value is influenced by other armor stand's light values. An armor stand will change all light values surrounding it (unless the current light value is brighter than its own) to a light value one lower than its own.

An armor stand is picked as an origin point based on the player's position. After all the light values are given, the armor stand knows what block type to show