@startuml database-schema
!theme plain
skinparam backgroundColor #FFFFFF
skinparam defaultFontName Arial
skinparam linetype ortho

title Key Database Schema - User & Authentication

entity "UserAccount" as User {
  * UserAccountId: INT <<PK>>
  --
  * Username: NVARCHAR(30) <<UNIQUE>>
  * Email: NVARCHAR(255) <<UNIQUE>>
  * FirstName: NVARCHAR(50)
  * LastName: NVARCHAR(50)
  Bio: NVARCHAR(500)
  CreatedAt: DATETIME2
  UpdatedAt: DATETIME2
  LastLoginAt: DATETIME2
}

entity "UserCredential" as Cred {
  * UserCredentialId: INT <<PK>>
  --
  * UserAccountId: INT <<FK>>
  * PasswordHash: VARBINARY(32)
  * PasswordSalt: VARBINARY(16)
  CredentialRotatedAt: DATETIME2
  CredentialExpiresAt: DATETIME2
  CredentialRevokedAt: DATETIME2
  * IsActive: BIT
  CreatedAt: DATETIME2
}

entity "UserVerification" as Verify {
  * UserVerificationId: INT <<PK>>
  --
  * UserAccountId: INT <<FK>>
  * IsVerified: BIT
  VerifiedAt: DATETIME2
  VerificationToken: NVARCHAR(255)
  TokenExpiresAt: DATETIME2
}

entity "UserAvatar" as Avatar {
  * UserAvatarId: INT <<PK>>
  --
  * UserAccountId: INT <<FK>>
  PhotoId: INT <<FK>>
  * IsActive: BIT
  CreatedAt: DATETIME2
}

entity "UserFollow" as Follow {
  * UserFollowId: INT <<PK>>
  --
  * FollowerUserId: INT <<FK>>
  * FollowedUserId: INT <<FK>>
  CreatedAt: DATETIME2
}

entity "Photo" as Photo {
  * PhotoId: INT <<PK>>
  --
  * Url: NVARCHAR(500)
  * CloudinaryPublicId: NVARCHAR(255)
  Width: INT
  Height: INT
  Format: NVARCHAR(10)
  CreatedAt: DATETIME2
}

' Relationships
User ||--o{ Cred : "has"
User ||--o| Verify : "has"
User ||--o{ Avatar : "has"
User ||--o{ Follow : "follows"
User ||--o{ Follow : "followed by"
Avatar }o--|| Photo : "refers to"

note right of Cred
  Password hashing:
  - Algorithm: Argon2id
  - Memory: 64MB
  - Iterations: 4
  - Salt: 128-bit
  - Hash: 256-bit
end note

note right of Verify
  Account verification
  via email token
  with expiry
end note

note bottom of User
  Core stored procedures:
  - USP_RegisterUser
  - USP_GetUserAccountByUsername
  - USP_RotateUserCredential
  - USP_UpdateUserAccount
end note

@enduml