See who is still on old pricing and migrate them safely

Build me a price book console for our Chargebee catalog that answers "who is still on our old pricing?" without exporting anything. Finance and product reopen this at every pricing review, so it needs to be a screen we work in, not a report we run.

The main view is the price book. Load our catalog with List Item Families, List Items and List Item Prices, and present it grouped by family, then item, then the price points under each item. Every price point row shows its external name and id, currency, amount, and billing period, and next to that two numbers that are the whole point of the console: how many active subscriptions sit on that exact price point, and how much recurring revenue that represents. Both come from List Subscriptions.

How you count matters. Do not fire a subscription lookup per catalog row. Page List Subscriptions in batches using the maximum page size and the next_offset token, filtered to active subscriptions, and in a single pass build an index of subscription items keyed by item price id, accumulating both a count and a revenue total per key. Cache that index for the session and have every price point row read from it. Chargebee live sites allow roughly 150 API calls per minute, so a large catalog must not turn into a call per price point. Show when the numbers were last refreshed and give me a refresh control to rebuild the index on demand.

Amounts are integers in the currency's smallest unit, so divide before displaying and format per currency. Group counts and revenue by currency and never sum across currencies into one total. This is Product Catalog 2.0 only. Work entirely in item families, items and item prices, and never reference legacy plans or addons.

Clicking a price point drills into the accounts sitting on it. List the subscriptions on that price point, and for each one enrich with Retrieve Subscription and Retrieve Customer so the table shows the company or customer name, email, subscription id, status, quantity, what the account currently pays, the next billing date and the current term end. This is the view where finance and product can see exactly who is grandfathered, so make it sortable by revenue and filterable, and let me search it.

From that drill-in I select a cohort and build a migration. I choose the accounts, pick the destination price point, and choose whether the change applies immediately or at the end of each account's term. Before anything is applied, the console previews each selected account with Update Subscription Estimate For Items and shows me a per account row with the current charge, the new charge, the proration and any credits, what would be charged now, the next renewal amount, and the difference. Preview before apply is a hard requirement. Never apply a cohort without a per account confirmation step, so each previewed row is individually accepted or skipped, and any account whose estimate fails shows the error inline and is excluded from the apply.

Applying runs Update Subscription For Items for the accepted rows only, honouring the immediate or end of term choice. Throttle the calls rather than firing them all at once, show progress and a per account result as it goes, and let a single failure fail just that account without stopping the rest of the run.

Every applied migration writes a run log to Google Sheets. Create the log spreadsheet with Create Spreadsheet the first time and remember its id afterwards, then use Append Values to add one row per account with the timestamp, who ran it, the subscription id, the customer, the price point moved from and to, the old and new amounts, the proration, the timing choice, and the result. Then post a summary to Slack with Send a Message to a channel I pick, covering how many accounts moved, how many were skipped or failed, the revenue impact by currency, the price points involved and a link to the log spreadsheet.

The console should also let me create a new price point in place with Create Item Price, on an existing item, taking the name, external id, currency, amount in the smallest unit, and billing period and unit. A new price point appears in the price book immediately and is selectable as a migration destination straight away, so a pricing change and the migration that follows it happen on one screen.

Remember my chosen Slack channel and the run log spreadsheet across sessions, and keep the history of past migration runs so I can open a previous run and see which accounts were moved and what the revenue impact was.