element-x-ios/ElementX/Sources/Services/Timeline/TimelineItems/RoomStateEventStringBuilder.swift

//
// Copyright 2025 Element Creations Ltd.
// Copyright 2023-2025 New Vector Ltd.
//
// SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial.
// Please see LICENSE files in the repository root for full details.
//

import MatrixRustSDK
import UIKit

nonisolated struct RoomStateEventStringBuilder {
    let userID: String
    
    func buildString(for change: MembershipChange?,
                     reason: String?,
                     memberUserID: String,
                     memberDisplayName: String?,
                     sender: TimelineItemSender,
                     isOutgoing: Bool) -> String? {
        guard let change else {
            MXLog.verbose("Filtering timeline item for membership change that is nil")
            return nil
        }
        
        let senderIsYou = isOutgoing
        let memberIsYou = memberUserID == userID
        let member = memberDisplayName ?? memberUserID
        let senderDisplayName = sender.disambiguatedDisplayName ?? sender.id
        
        switch change {
        case .joined:
            return memberIsYou ? L10n.stateEventRoomJoinByYou : L10n.stateEventRoomJoin(senderDisplayName)
        case .left:
            return memberIsYou ? L10n.stateEventRoomLeaveByYou : L10n.stateEventRoomLeave(member)
        case .banned, .kickedAndBanned:
            return switch (senderIsYou, reason) {
            case (true, .some(let reason)): L10n.stateEventRoomBanByYouWithReason(member, reason)
            case (true, .none): L10n.stateEventRoomBanByYou(member)
            case (false, .some(let reason)): L10n.stateEventRoomBanWithReason(senderDisplayName, member, reason)
            case (false, .none): L10n.stateEventRoomBan(senderDisplayName, member)
            }
        case .unbanned:
            return senderIsYou ? L10n.stateEventRoomUnbanByYou(member) : L10n.stateEventRoomUnban(senderDisplayName, member)
        case .kicked:
            return switch (senderIsYou, reason) {
            case (true, .some(let reason)): L10n.stateEventRoomRemoveByYouWithReason(member, reason)
            case (true, .none): L10n.stateEventRoomRemoveByYou(member)
            case (false, .some(let reason)): L10n.stateEventRoomRemoveWithReason(senderDisplayName, member, reason)
            case (false, .none): L10n.stateEventRoomRemove(senderDisplayName, member)
            }
        case .invited:
            if senderIsYou {
                return L10n.stateEventRoomInviteByYou(member)
            } else if memberIsYou {
                return buildInvitedYouString(senderDisplayName)
            } else {
                return L10n.stateEventRoomInvite(senderDisplayName, member)
            }
        case .invitationAccepted:
            return memberIsYou ? L10n.stateEventRoomInviteAcceptedByYou : L10n.stateEventRoomInviteAccepted(member)
        case .invitationRejected:
            return memberIsYou ? L10n.stateEventRoomRejectByYou : L10n.stateEventRoomReject(senderDisplayName)
        case .invitationRevoked:
            return senderIsYou ? L10n.stateEventRoomThirdPartyRevokedInviteByYou(member) : L10n.stateEventRoomThirdPartyRevokedInvite(senderDisplayName, member)
        case .knocked:
            return memberIsYou ? L10n.stateEventRoomKnockByYou : L10n.stateEventRoomKnock(member)
        case .knockAccepted:
            return senderIsYou ? L10n.stateEventRoomKnockAcceptedByYou(member) : L10n.stateEventRoomKnockAccepted(senderDisplayName, member)
        case .knockRetracted:
            return memberIsYou ? L10n.stateEventRoomKnockRetractedByYou : L10n.stateEventRoomKnockRetracted(member)
        case .knockDenied:
            if senderIsYou {
                return L10n.stateEventRoomKnockDeniedByYou(member)
            } else if memberIsYou {
                return L10n.stateEventRoomKnockDeniedYou(senderDisplayName)
            } else {
                return L10n.stateEventRoomKnockDenied(senderDisplayName, member)
            }
        case .none, .error, .notImplemented: // Not useful information for the user.
            MXLog.verbose("Filtering timeline item for membership change: \(change)")
            return nil
        }
    }
    
    func buildInvitedYouString(_ senderDisplayName: String) -> String {
        L10n.stateEventRoomInviteYou(senderDisplayName)
    }
    
    /// - Parameters:
    ///   - displayName: The new display name, only set by the SDK when the display name changed.
    ///   - previousDisplayName: The old display name, only set by the SDK when the display name changed.
    ///   - avatarURLString: The new avatar URL, only set by the SDK when the avatar changed.
    ///   - previousAvatarURLString: The old avatar URL, only set by the SDK when the avatar changed.
    ///   - memberID: The member's user ID, used in the display name change strings.
    ///   - memberDisplayName: The member's disambiguated display name, used when only the avatar changed.
    ///   - memberIsYou: Whether the member is the current user, which selects the "You" variant of the strings.
    func buildProfileChangeString(displayName: String?,
                                  previousDisplayName: String?,
                                  avatarURLString: String?,
                                  previousAvatarURLString: String?,
                                  memberID: String,
                                  memberDisplayName: String,
                                  memberIsYou: Bool) -> String? {
        let displayNameChanged = displayName != previousDisplayName
        let avatarChanged = avatarURLString != previousAvatarURLString
        
        switch (displayNameChanged, avatarChanged, memberIsYou) {
        case (true, false, false):
            if let displayName, let previousDisplayName {
                return L10n.stateEventDisplayNameChangedFrom(memberID, previousDisplayName, displayName)
            } else if let displayName {
                return L10n.stateEventDisplayNameSet(memberID, displayName)
            } else if let previousDisplayName {
                return L10n.stateEventDisplayNameRemoved(memberID, previousDisplayName)
            } else {
                MXLog.error("The display name changed from nil to nil, filtering the item.")
                return nil
            }
        case (false, true, false):
            // The SDK only sets displayName when it changed, so it's nil here and we need the member's current name.
            return L10n.stateEventAvatarUrlChanged(memberDisplayName)
        case (true, false, true):
            if let displayName, let previousDisplayName {
                return L10n.stateEventDisplayNameChangedFromByYou(previousDisplayName, displayName)
            } else if let displayName {
                return L10n.stateEventDisplayNameSetByYou(displayName)
            } else if let previousDisplayName {
                return L10n.stateEventDisplayNameRemovedByYou(previousDisplayName)
            } else {
                MXLog.error("The display name changed from nil to nil, filtering the item.")
                return nil
            }
        case (false, true, true):
            return L10n.stateEventAvatarUrlChangedByYou
        case (true, true, _):
            // When both have changed, get the string for the display name and tack on that the avatar changed too.
            guard let string = buildProfileChangeString(displayName: displayName,
                                                        previousDisplayName: previousDisplayName,
                                                        avatarURLString: nil,
                                                        previousAvatarURLString: nil,
                                                        memberID: memberID,
                                                        memberDisplayName: memberDisplayName,
                                                        memberIsYou: memberIsYou) else { return nil }
            return string + "\n" + L10n.stateEventAvatarChangedToo
        case (false, false, _):
            MXLog.error("Nothing changed, shouldn't be possible. Filtering the item.")
            return nil
        }
    }
    
    func buildString(for state: OtherState, sender: TimelineItemSender, isOutgoing: Bool) -> String? {
        let displayName = sender.disambiguatedDisplayName ?? sender.id
        
        switch state {
        case .roomAvatar(let url):
            switch (url, isOutgoing) {
            case (.some, false):
                return L10n.stateEventRoomAvatarChanged(displayName)
            case (nil, false):
                return L10n.stateEventRoomAvatarRemoved(displayName)
            case (.some, true):
                return L10n.stateEventRoomAvatarChangedByYou
            case (nil, true):
                return L10n.stateEventRoomAvatarRemovedByYou
            }
        case .roomCreate:
            return isOutgoing ? L10n.stateEventRoomCreatedByYou : L10n.stateEventRoomCreated(displayName)
        case .roomEncryption:
            return L10n.commonEncryptionEnabled
        case .roomName(let name):
            switch (name, isOutgoing) {
            case (.some(let name), false):
                return L10n.stateEventRoomNameChanged(displayName, name)
            case (nil, false):
                return L10n.stateEventRoomNameRemoved(displayName)
            case (.some(let name), true):
                return L10n.stateEventRoomNameChangedByYou(name)
            case (nil, true):
                return L10n.stateEventRoomNameRemovedByYou
            }
        case .roomThirdPartyInvite(let displayName):
            guard let displayName else {
                MXLog.error("roomThirdPartyInvite undisplayable due to missing name.")
                return nil
            }
            
            if isOutgoing {
                return L10n.stateEventRoomThirdPartyInviteByYou(displayName)
            } else {
                return L10n.stateEventRoomThirdPartyInvite(displayName, displayName)
            }
        case .roomTopic(let topic):
            switch (topic, isOutgoing) {
            case (.some(let topic), false) where !topic.isBlank:
                return L10n.stateEventRoomTopicChanged(displayName, topic)
            case (_, false):
                return L10n.stateEventRoomTopicRemoved(displayName)
            case (.some(let topic), true) where !topic.isBlank:
                return L10n.stateEventRoomTopicChangedByYou(topic)
            case (_, true):
                return L10n.stateEventRoomTopicRemovedByYou
            }
        case .roomPinnedEvents(let change):
            switch change {
            case .added:
                return isOutgoing ? L10n.stateEventRoomPinnedEventsPinnedByYou : L10n.stateEventRoomPinnedEventsPinned(displayName)
            case .changed:
                return isOutgoing ? L10n.stateEventRoomPinnedEventsChangedByYou : L10n.stateEventRoomPinnedEventsChanged(displayName)
            case .removed:
                return isOutgoing ? L10n.stateEventRoomPinnedEventsUnpinnedByYou : L10n.stateEventRoomPinnedEventsUnpinned(displayName)
            }
        case .roomPowerLevels: // Long term we might show only the user changes, but we need an SDK filter to fix read receipts in that case.
            break
        case .policyRuleRoom, .policyRuleServer, .policyRuleUser: // No strings available.
            break
        case .roomCanonicalAlias: // Doesn't provide the alias.
            break
        case .roomGuestAccess, .roomHistoryVisibility: // Doesn't provide information about the change.
            break
        case .roomJoinRules: // Doesn't provide information about the change.
            break
        case .roomServerAcl: // Doesn't provide information about the change.
            break
        case .roomTombstone: // Handle as a virtual timeline item with a link to the upgraded room.
            break
        case .spaceChild, .spaceParent: // Users shouldn't see the timeline of a Space.
            break
        case .custom: // Won't provide actionable information to the user.
            break
        }
        
        MXLog.verbose("Filtering timeline item for state: \(state)")
        return nil
    }
}