Structure for lesson:

• Intro / What do we want to build?
• What do we need to build it? (data for tiers, mappings, etc)
• Basic contract, inheriting ERC721 from OpenZeppelin
• override constructor (only set the number of tiers we want) and maxTiers state var
• struct Tier: data in a struct - introduce complex data structures in solidity
• state vars to map NFTs to tiers (tokenTier and tiers)
• a function to setTierData so we can define/update our Tiers once we created our contract
  • a lot of require here so, the values of the tiers are correct
• event TierValuesUpdated so we have a history of the changes to the Tiers, in case the subscription prices change
• mint function: how to select Tiers with the msg.value the user sent to the contract (first and hopefully last use of a cycle in the lessons)
• tokenURI overriding function to create the json on-the-fly (and also maybe an SVG ?? so it's all on-chain) - imports Strings and Base64 from OpenZeppelin
• Now that the contract can receive value/eth in it, we need a way to extract it: withdraw function
  • Important to mention different ways of transferring value: transfer vs. send vs. call
• Ooops moment, we cannot let anyone withdraw money. Introduce Ownable pattern importing Ownable from OpenZeppelin
• Finished contract → deploy to a testnet (maybe polygon-mumbai this time?)
• Showing our example on etherscan/polygonscan and OpenSea

Example SVG:

Version 01

Version 02