// Package notifications is the one writer of the per-user notifications inbox
// (M489, #726). Producers across the server call Notifier.Notify; nothing else
// inserts into user_notifications.
//
// The event bus alone was fire-and-forget: a client that was not connected
// when a request completed, or when tracks went missing, never heard of it. A
// row here is the durable record. The bus only nudges open clients to come
// and read it.
package notifications

// Kind names one sort of notification. The set is CHECK-gated in migration
// 0073, swapped since by 0075 (rule 36): a new kind adds its value in a
// migration of the same change, and TestEveryKindPassesTheSchemaChecks
// fails until it does.
type Kind string

const (
	KindRequestApproved   Kind = "request_approved"
	KindRequestRejected   Kind = "request_rejected"
	KindRequestCompleted  Kind = "request_completed"
	KindRequestPending    Kind = "request_pending"
	KindQuarantineFlagged Kind = "quarantine_flagged"
	KindScanFailed        Kind = "scan_failed"
	KindTracksMissing     Kind = "tracks_missing"
	KindDuplicatesFound   Kind = "duplicates_found"
	// KindDuplicatesResolved: the duplicate resolver (M498) merged copies or
	// changed a Lidarr release on its own. The operator asked for that to
	// happen automatically; this is how it stays visible.
	KindDuplicatesResolved Kind = "duplicates_resolved"
	KindPlaybackErrors     Kind = "playback_errors"
)

// Audience is who a kind can reach. Admin kinds are never offered to, or
// stored for, a non-admin.
type Audience int

const (
	AudienceRequester Audience = iota
	AudienceAdmin
)

// EmailGroup is how a kind's emails are grouped. Nothing is emailed per event.
type EmailGroup int

const (
	// EmailBatch: one email per batch window, holding everything that
	// accumulated since the first un-emailed item.
	EmailBatch EmailGroup = iota
	// EmailSummary: at most one summary a day, at a set local hour. For new
	// music arriving, which comes in bursts and is not urgent.
	EmailSummary
)

// Channels are where a kind reaches a user. Inbox is the master switch: with
// it off nothing is stored, so there is nothing for the phone or email to
// deliver. Effective applies that.
type Channels struct {
	Inbox bool
	Phone bool
	Email bool
}

// Effective is what will actually be delivered: phone and email ride on the
// inbox row, so they cannot be on without it.
func (c Channels) Effective() Channels {
	return Channels{Inbox: c.Inbox, Phone: c.Inbox && c.Phone, Email: c.Inbox && c.Email}
}

type spec struct {
	audience Audience
	// coalesce: while one of these is unread, a new event updates it in place
	// rather than adding a row. For the burst-prone admin kinds.
	coalesce bool
	// sumCount: a coalesced update adds the payload's `count` to the unread
	// row's, because each event is "N more". Without it the newer payload
	// replaces the older, because each event states the whole current total.
	sumCount bool
	group    EmailGroup
	defaults Channels
}

var (
	allOn       = Channels{Inbox: true, Phone: true, Email: true}
	healthAlert = Channels{Inbox: true, Phone: true, Email: false}
	// inboxOnly: news an admin may want to read but never needs to be
	// interrupted for.
	inboxOnly = Channels{Inbox: true}
)

var specs = map[Kind]spec{
	KindRequestApproved:   {audience: AudienceRequester, group: EmailBatch, defaults: allOn},
	KindRequestRejected:   {audience: AudienceRequester, group: EmailBatch, defaults: allOn},
	KindRequestCompleted:  {audience: AudienceRequester, group: EmailSummary, defaults: allOn},
	KindRequestPending:    {audience: AudienceAdmin, group: EmailBatch, defaults: allOn},
	KindQuarantineFlagged: {audience: AudienceAdmin, group: EmailBatch, defaults: allOn},
	KindScanFailed:        {audience: AudienceAdmin, coalesce: true, sumCount: true, group: EmailBatch, defaults: healthAlert},
	KindTracksMissing:     {audience: AudienceAdmin, coalesce: true, sumCount: true, group: EmailBatch, defaults: healthAlert},
	KindDuplicatesFound:   {audience: AudienceAdmin, coalesce: true, group: EmailBatch, defaults: healthAlert},
	// Each pass reports what it did itself, so the counts add up.
	KindDuplicatesResolved: {audience: AudienceAdmin, coalesce: true, sumCount: true, group: EmailBatch, defaults: inboxOnly},
	KindPlaybackErrors:     {audience: AudienceAdmin, coalesce: true, group: EmailBatch, defaults: healthAlert},
}

// order is the display order for settings screens: the requester's own kinds
// first, then the admin ones.
var order = []Kind{
	KindRequestApproved,
	KindRequestRejected,
	KindRequestCompleted,
	KindRequestPending,
	KindQuarantineFlagged,
	KindScanFailed,
	KindTracksMissing,
	KindDuplicatesFound,
	KindDuplicatesResolved,
	KindPlaybackErrors,
}

// Kinds returns every kind in display order.
func Kinds() []Kind { return append([]Kind(nil), order...) }

// Valid reports whether k is a known kind.
func (k Kind) Valid() bool { _, ok := specs[k]; return ok }

// AdminOnly reports whether k reaches only admins.
func (k Kind) AdminOnly() bool { return specs[k].audience == AudienceAdmin }

// Defaults are the channels a user has for k until they change them.
func (k Kind) Defaults() Channels { return specs[k].defaults }

// EmailGroup is how k's emails are grouped.
func (k Kind) EmailGroup() EmailGroup { return specs[k].group }

// coalesceKey is the key k's rows coalesce on, or "" when k never coalesces.
// One key per kind: two unread "tracks missing" rows would only split a count.
func (k Kind) coalesceKey() string {
	if specs[k].coalesce {
		return string(k)
	}
	return ""
}