package storage

import (
	"context"
	"errors"
)

// Errors of the admin store.
var (
	// ErrNoSuchRegistrationToken is an unknown registration token — or,
	// from UseRegistrationToken, one that is known but expired or used
	// up. A client is told the same thing either way.
	ErrNoSuchRegistrationToken = errors.New("no such registration token")

	// ErrRegistrationTokenExists is CreateRegistrationToken's answer for a
	// token that is already there.
	ErrRegistrationTokenExists = errors.New("registration token already exists")

	// ErrNoServerNoticeRoom is a user who has never been sent a server
	// notice.
	ErrNoServerNoticeRoom = errors.New("no server notice room")
)

// RegistrationToken is a token made through the admin API.
type RegistrationToken struct {
	Token string

	// UsesAllowed is how many registrations may spend the token; nil is
	// no limit.
	UsesAllowed *int

	// Completed is how many registrations have spent it.
	Completed int

	// ExpiresAtMS is when the token stops working, or 0 for never.
	ExpiresAtMS int64

	CreatedAtMS int64
}

// Usable reports whether the token can still be spent at nowMS.
func (t RegistrationToken) Usable(nowMS int64) bool {
	if t.ExpiresAtMS != 0 && t.ExpiresAtMS <= nowMS {
		return false
	}
	return t.UsesAllowed == nil || t.Completed < *t.UsesAllowed
}

// AuditEntry is one change made through the admin API.
type AuditEntry struct {
	// ID orders the log; it is assigned by AppendAudit.
	ID int64

	TSMS int64

	// Actor is the full user ID of the admin.
	Actor string

	// Action names what was done, e.g. "user.deactivate".
	Action string

	// Target is what it was done to, or empty for a server-wide change.
	Target string

	// Details is a JSON object with whatever else is worth keeping: the
	// new value of a switch, whether a deactivation erased the profile.
	Details []byte
}

// AuditFilter narrows and pages the audit log, newest first.
type AuditFilter struct {
	// Before returns entries with an ID below it; 0 starts at the newest.
	Before int64

	// Limit caps the returned entries; 0 means the store's own default.
	Limit int

	// Actor and Action, when set, must match exactly.
	Actor  string
	Action string
}

// AdminStore keeps the state of the admin API's own: registration tokens,
// the room each user's server notices go to, and the audit log.
type AdminStore interface {
	// CreateRegistrationToken stores a new token, returning
	// ErrRegistrationTokenExists when it is taken.
	CreateRegistrationToken(ctx context.Context, t RegistrationToken) error

	// RegistrationToken reads one token.
	RegistrationToken(ctx context.Context, token string) (RegistrationToken, error)

	// RegistrationTokens lists every token, ordered by token.
	RegistrationTokens(ctx context.Context) ([]RegistrationToken, error)

	// UpdateRegistrationToken replaces a token's use limit and expiry; the
	// count of uses it has had stays.
	UpdateRegistrationToken(ctx context.Context, token string, usesAllowed *int, expiresAtMS int64) error

	// DeleteRegistrationToken removes a token.
	DeleteRegistrationToken(ctx context.Context, token string) error

	// UseRegistrationToken spends one use of a token, if it is usable at
	// nowMS, in a single statement: two registrations racing for the last
	// use cannot both have it. A token that is not usable is
	// ErrNoSuchRegistrationToken.
	UseRegistrationToken(ctx context.Context, token string, nowMS int64) error

	// ReleaseRegistrationToken gives back a use taken by a registration
	// that then failed.
	ReleaseRegistrationToken(ctx context.Context, token string) error

	// AppendAudit records an entry and returns its ID.
	AppendAudit(ctx context.Context, e AuditEntry) (int64, error)

	// AuditLog reads a page of the log, newest first.
	AuditLog(ctx context.Context, f AuditFilter) ([]AuditEntry, error)

	// ServerNoticeRoom returns the room a user's server notices go to,
	// or ErrNoServerNoticeRoom.
	ServerNoticeRoom(ctx context.Context, localpart string) (string, error)

	// SetServerNoticeRoom records it, replacing any earlier one.
	SetServerNoticeRoom(ctx context.Context, localpart, roomID string) error
}

// AppServiceState is where an application service is in the event stream.
type AppServiceState struct {
	ID string

	// StreamPos is the last position whose events have been delivered or
	// skipped.
	StreamPos int64

	// TxnID is the ID of the last transaction begun. While TxnTo is
	// non-zero that transaction is in flight and holds the events in
	// (StreamPos, TxnTo].
	TxnID int64
	TxnTo int64
}

// AppServiceStore keeps the application services' delivery cursors.
type AppServiceStore interface {
	// AppServiceState reads an application service's cursor, creating it
	// at startPos the first time the service is seen: a newly registered
	// service is sent what happens from now on, not the server's history.
	AppServiceState(ctx context.Context, id string, startPos int64) (AppServiceState, error)

	// BeginTransaction records a transaction as in flight.
	BeginTransaction(ctx context.Context, id string, txnID, to int64) error

	// CompleteTransaction moves the cursor to `to` and clears the
	// transaction in flight. It is also how a stretch of the stream with
	// nothing of interest in it is skipped.
	CompleteTransaction(ctx context.Context, id string, to int64) error
}