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How AChat works

AChat is built around one idea: nothing is meant to last. Every chat, message, and file is written with an expiresAt timestamp set about 10 days in the future, and Firestore's TTL feature deletes them automatically once they expire. There is no long-term archive by design.

The moving parts​

PartRole
Browser appReact app that does all encryption, rendering, and TTL stamping client-side.
FirestoreStores chats, messages, files, reactions, presence, polls — each with an expiresAt.
Firestore TTL policiesAuto-delete expired documents (within ~24h of expiry). Free on the Spark plan.
FilesHubStores uploaded file bytes; cleaned up lazily on the client.
Firebase Auth (optional)Only for users who sign in to reserve chats.

There are no server-side functions and no paid backend — the app talks to Firestore and FilesHub directly, gated by security rules.

The data model (simplified)​

chats/{chatId}                     ← 8–20 char id; createdAt, expiresAt (TTL), hasPassword, salt?, verifier?
  messages/{msgId}                 ← createdAt, expiresAt (TTL), authorId, kind, body | {ciphertext, iv}
  files/{fileId}                   ← createdAt, expiresAt (TTL), fileshubId, metadata | {ciphertext, iv}
  reactions / presence / pins / polls   ← each with its own expiresAt TTL

users/{uid}                        ← optional accounts (NOT auto-deleted)
communities/{chatId}               ← public discovery index (NOT auto-deleted; messages inside still TTL)

Grouping/metadata fields (kind, title, topic, thread threadParentId/replyCount, reservation fields) stay plaintext even on passworded chats; only message bodies and file metadata are encrypted.

The 10-day lifecycle​

What persists, and what doesn't​

  • Ephemeral (auto-deleted): chats, messages, files, reactions, presence, pins, polls.
  • Persistent (not auto-deleted): optional user accounts, community discovery records, and any chat you explicitly reserved (its expiresAt is simply pushed further out).

Why this design​

  • Privacy by expiry: the less data that lingers, the less there is to leak.
  • No account friction: the link is the room; identity is optional.
  • Free to run: Firestore TTL + FilesHub keep it on free tiers with no server compute.