@startuml delete-account
!include ../../../pipeline/diagrams/biergarten-weizen-theme.puml
skinparam sequenceMessageAlign center
skinparam maxMessageSize 200

title User Authentication Flow - Delete Account

actor User
participant "API\nController" as API
participant "MediatR pipeline\n(ValidationBehavior)" as Mediator
box "Handler Layer" #F1F3EA
participant "DeleteAccountHandler" as DeleteAccountHandler
participant "UserManager<ApplicationUser>" as UserMgr
end box
box "Repository / Cross-slice" #DBEEDD
participant "DapperUserStore\n(IUserStore/IUserPasswordStore/\nIUserEmailStore)" as UserStore
end box
database "SQL Server" as DB

note over UserMgr
  ASP.NET Core Identity's UserManager<TUser>
  replaces the deleted AuthRepository: handlers
  no longer issue SQL or call Argon2 directly,
  they delegate to UserManager, which in turn
  calls DapperUserStore (persistence) and
  Argon2PasswordHasher (IPasswordHasher<TUser>).
end note

User -> API: DELETE /api/auth/account\n(requires Bearer access token)
activate API

API -> Mediator: Send(DeleteAccountCommand(\n  GetAuthenticatedUserId()))
activate Mediator

Mediator -> DeleteAccountHandler: Handle(command)
activate DeleteAccountHandler

DeleteAccountHandler -> UserMgr: FindByIdAsync(userAccountId)
activate UserMgr
UserMgr -> UserStore: FindByIdAsync(userAccountId)
UserStore --> UserMgr: ApplicationUser or null
UserMgr --> DeleteAccountHandler: ApplicationUser or null
deactivate UserMgr

alt Account not found
  DeleteAccountHandler -> Mediator: throw NotFoundException
  Mediator -> API: propagate
  API -> User: 404 Not Found
else Account found

  DeleteAccountHandler -> UserMgr: DeleteAsync(user)
  activate UserMgr
  UserMgr -> UserStore: DeleteAsync(user)
  activate UserStore
  UserStore -> DB: DELETE FROM dbo.UserAccount\nWHERE UserAccountID = @Id
  note right of UserStore
    UserCredential/UserVerification/UserAvatar
    cascade on delete. Posts, comments, photos,
    and follows use ON DELETE NO ACTION - if any
    reference this account, the DELETE throws a
    foreign key violation (SQL error 547).
  end note

  alt Foreign key violation (dependent records exist)
    UserStore --> UserMgr: IdentityResult.Failed\n(AccountHasDependentRecords)
  else Delete succeeds
    UserStore --> UserMgr: IdentityResult.Success
  end
  deactivate UserStore
  UserMgr --> DeleteAccountHandler: IdentityResult
  deactivate UserMgr

  alt Account has dependent records
    DeleteAccountHandler -> Mediator: throw ConflictException\n"Account cannot be deleted while it still\nhas associated posts, comments, photos,\nor follows."
    Mediator -> API: propagate
    API -> User: 409 Conflict
  else !result.Succeeded (other failure)
    DeleteAccountHandler -> Mediator: throw ConflictException
    Mediator -> API: propagate
    API -> User: 409 Conflict
  else result.Succeeded
    DeleteAccountHandler --> Mediator: (void)
    deactivate DeleteAccountHandler
    Mediator --> API: (void)
    deactivate Mediator
    API -> User: 200 OK\n{message: "Account deleted successfully."}
  end
end
deactivate API

@enduml