//
//  DataContextSwitcherMenu.swift
//  Yattee
//
//  The one place the selected data context is switched from.
//

import SwiftUI

// MARK: - Rows

/// The switchable contexts, as rows.
///
/// Shared by every presentation of the switcher so a context that is offered in
/// one place is offered — and named — identically in all of them.
struct DataContextSwitcherRows: View {
    @Environment(\.appEnvironment) private var appEnvironment

    /// Called after a switch, for presentations that have to close themselves.
    var onSwitch: (() -> Void)?

    private var validator: DataContextValidator? { appEnvironment?.dataContextValidator }

    var body: some View {
        ForEach(validator?.availableContexts ?? [.local], id: \.self) { context in
            row(for: context)
        }
    }

    @ViewBuilder
    private func row(for context: DataContext) -> some View {
        // A menu row is a single label — a `VStack` inside one renders as
        // nothing on macOS — so the status travels in the title rather than as
        // a second line.
        let title = DataContextSwitcherLabels.title(for: context, in: appEnvironment)

        #if os(macOS)
        // The mark has to be the menu item's own. A `Label`'s `systemImage` is
        // dropped by a macOS menu row, leaving the selected context
        // indistinguishable from the rest; a `Toggle` is what SwiftUI renders
        // as a checked item, mark character included.
        Toggle(isOn: Binding(
            get: { isCurrent(context) },
            set: { isOn in
                guard isOn else { return }
                switchTo(context)
            }
        )) {
            Text(title)
        }
        #else
        Button {
            switchTo(context)
        } label: {
            if isCurrent(context) {
                Label(title, systemImage: "checkmark")
            } else {
                Text(title)
            }
        }
        #if os(tvOS)
        .buttonStyle(TVSettingsButtonStyle())
        #endif
        #endif
    }

    private func switchTo(_ context: DataContext) {
        appEnvironment?.switchDataContext(to: context)
        onSwitch?()
    }

    private func isCurrent(_ context: DataContext) -> Bool {
        appEnvironment?.accountsManager.currentContext == context
    }
}

// MARK: - Labels

/// Names the switchable contexts.
enum DataContextSwitcherLabels {
    /// The context's name, plus whatever the user needs to tell it apart.
    @MainActor
    static func title(for context: DataContext, in appEnvironment: AppEnvironment?) -> String {
        guard let appEnvironment else { return String(localized: "subscriptions.account.local") }

        return title(
            for: context,
            accountsManager: appEnvironment.accountsManager,
            validator: appEnvironment.dataContextValidator,
            username: { appEnvironment.accountCredentialsManager(for: $0)?.username(for: $0) }
        )
    }

    /// The same label, built from only what it needs.
    ///
    /// Taking the pieces rather than the environment is what lets the naming
    /// rules be exercised on their own: which suffix a name gets depends on the
    /// other accounts, the stored identifier and the host, and on nothing else.
    @MainActor
    static func title(
        for context: DataContext,
        accountsManager: AccountsManager,
        validator: DataContextValidator,
        username: (Account) -> String?
    ) -> String {
        let name = validator.displayName(for: context)

        guard case let .account(id) = context, let account = accountsManager.account(id: id) else {
            return name
        }

        var title = name

        let peers = peers(sharing: name, accountsManager: accountsManager, validator: validator)
        if peers.count > 1 {
            title = disambiguated(
                name,
                for: account,
                among: peers,
                accountsManager: accountsManager,
                username: username
            )
        }

        let status = accountsManager.displayStatus(for: account)
        guard status != .signedIn else { return title }

        return "\(title) — \(AccountStatusBadge.text(for: status))"
    }

    /// What a shared name needs added to it before it names one account.
    ///
    /// The identifier comes first: two logins on the *same* instance share a
    /// host, so a host suffix would repeat the server and still leave the user
    /// choosing between two identical rows. The host alone is what is left when
    /// the identifier is not on this device — tvOS never receives one. Neither
    /// is repeated when the name already carries it: the default name for an
    /// account *is* `identifier@host`, so appending it unguarded produced two
    /// rows reading `X · X`.
    ///
    /// The source is the last resort and the only one that can name what two
    /// logins of the same server user on two copies of the same server differ
    /// by — the thing the user chose when adding the second source.
    static func disambiguated(_ name: String, username: String?, host: String?, source: String? = nil) -> String {
        var parts: [String] = []

        if let username, !username.isEmpty, !name.localizedCaseInsensitiveContains(username) {
            if let host, !host.isEmpty, !name.localizedCaseInsensitiveContains(host) {
                parts.append("\(username)@\(host)")
            } else {
                parts.append(username)
            }
        } else if let host, !host.isEmpty, !name.localizedCaseInsensitiveContains(host) {
            parts.append(host)
        }

        if let source, !source.isEmpty, name.localizedCaseInsensitiveCompare(source) != .orderedSame {
            parts.append(source)
        }

        guard !parts.isEmpty else { return name }
        return "\(name) · \(parts.joined(separator: " · "))"
    }

    /// The identifier and the host first, and the source only once they have
    /// failed: two logins on one server are told apart by who they are, and
    /// naming the server as well would add a word that is the same on both
    /// rows. It is when that suffix still collides — the same server user
    /// signed in on two sources pointing at the same host — that the source is
    /// the only thing left that differs.
    @MainActor
    private static func disambiguated(
        _ name: String,
        for account: Account,
        among peers: [Account],
        accountsManager: AccountsManager,
        username: (Account) -> String?
    ) -> String {
        func withoutSource(_ peer: Account) -> String {
            disambiguated(
                name,
                username: username(peer),
                host: accountsManager.instance(for: peer)?.url.host
            )
        }

        let own = withoutSource(account)
        let collides = peers.contains { $0.id != account.id && withoutSource($0) == own }
        guard collides else { return own }

        return disambiguated(
            name,
            username: username(account),
            host: accountsManager.instance(for: account)?.url.host,
            source: accountsManager.instance(for: account)?.displayName
        )
    }

    @MainActor
    private static func peers(
        sharing name: String,
        accountsManager: AccountsManager,
        validator: DataContextValidator
    ) -> [Account] {
        accountsManager.selectableAccounts.filter { validator.displayName(for: $0) == name }
    }
}

// MARK: - Glyph

/// How the switcher's icon reads.
///
/// Shared by every presentation of the switcher — the toolbar menu, the
/// settings row, the tvOS button — so the same account health cannot look
/// healthy in one of them and not in another.
enum DataContextSwitcherGlyph {
    /// Whether the icon should ask to be noticed.
    ///
    /// Only the states the user can actually clear: signing in again, turning
    /// the instance back on, or switching away. A context that is merely still
    /// resolving is not one of them — badging `checking` would put an
    /// exclamation mark on every cold launch, before the Keychain has answered.
    static func needsAttention(_ validity: DataContextValidity) -> Bool {
        switch validity {
        case .valid:
            return false
        case .removed:
            return true
        case let .temporarilyUnavailable(reason):
            switch reason {
            case .instanceDisabled, .credentialRejected, .unreachable: return true
            case .checking, .instancePending, .credentialMissing: return false
            }
        }
    }

    /// The filled glyph says an account is selected; the badge says that
    /// account cannot be used right now, which is the whole reason the user
    /// would reach for this control.
    static func systemImage(for context: DataContext, validity: DataContextValidity) -> String {
        guard !context.isLocal else { return "person.crop.circle" }

        if needsAttention(validity) { return "person.crop.circle.badge.exclamationmark" }
        return "person.crop.circle.fill"
    }

    /// Orange — the colour the settings entry already badges attention with —
    /// and no tint at all otherwise, so a healthy switcher keeps whatever
    /// styling the toolbar or the list gives it.
    static func tint(for context: DataContext, validity: DataContextValidity) -> Color? {
        guard !context.isLocal, needsAttention(validity) else { return nil }
        return .orange
    }

    @MainActor
    static func systemImage(in appEnvironment: AppEnvironment?) -> String {
        guard let appEnvironment else { return "person.crop.circle" }

        return systemImage(
            for: appEnvironment.accountsManager.currentContext,
            validity: appEnvironment.dataContextValidator.validity
        )
    }

    @MainActor
    static func tint(in appEnvironment: AppEnvironment?) -> Color? {
        guard let appEnvironment else { return nil }

        return tint(
            for: appEnvironment.accountsManager.currentContext,
            validity: appEnvironment.dataContextValidator.validity
        )
    }
}

/// The switcher's icon, health included.
///
/// Hidden from assistive technology on purpose: every presentation names the
/// switcher in words beside it, and an unlabelled `Image` announces its symbol
/// — a control that read "Account" while healthy started reading
/// "person.crop.circle.badge.exclamationmark" the moment it badged.
struct DataContextSwitcherIcon: View {
    @Environment(\.appEnvironment) private var appEnvironment

    var body: some View {
        let image = Image(systemName: DataContextSwitcherGlyph.systemImage(in: appEnvironment))

        Group {
            if let tint = DataContextSwitcherGlyph.tint(in: appEnvironment) {
                image.foregroundStyle(tint)
            } else {
                image
            }
        }
        .accessibilityHidden(true)
    }
}

// MARK: - Menu

#if !os(tvOS)
/// The toolbar switcher: one tap, no confirmation — switching is reversible.
struct DataContextSwitcherMenu: View {
    @Environment(\.appEnvironment) private var appEnvironment

    var body: some View {
        Menu {
            DataContextSwitcherRows()
        } label: {
            Label {
                Text(String(localized: "accounts.switcher.title"))
            } icon: {
                DataContextSwitcherIcon()
            }
        }
        .help(contextTitle)
        .accessibilityLabel(Text(String(localized: "accounts.switcher.title")))
        .accessibilityValue(Text(contextTitle))
    }

    private var contextTitle: String {
        DataContextSwitcherLabels.title(for: currentContext, in: appEnvironment)
    }

    private var currentContext: DataContext {
        appEnvironment?.accountsManager.currentContext ?? .local
    }
}

#endif

/// A settings row naming the current context, with the switcher attached.
struct DataContextSwitcherSettingsRow: View {
    @Environment(\.appEnvironment) private var appEnvironment
    #if os(tvOS)
    @State private var showingPicker = false
    #endif

    var body: some View {
        #if os(tvOS)
        Button {
            showingPicker = true
        } label: {
            rowLabel
        }
        .buttonStyle(TVSettingsButtonStyle())
        .fullScreenCover(isPresented: $showingPicker) {
            DataContextSwitcherPicker()
        }
        #elseif os(macOS)
        // A macOS menu label renders its first text and nothing else — the
        // trailing name was dropped at every width, leaving the row silent
        // about which account is selected. So the name is the menu's *own*
        // label, and the row carries only what names the control.
        LabeledContent {
            Menu {
                DataContextSwitcherRows()
            } label: {
                Text(contextTitle)
                    .lineLimit(1)
            }
            .menuStyle(.borderlessButton)
            .help(contextTitle)
            .accessibilityLabel(Text(String(localized: "accounts.switcher.title")))
            .accessibilityValue(Text(contextTitle))
        } label: {
            Label {
                Text(String(localized: "accounts.switcher.title"))
            } icon: {
                DataContextSwitcherIcon()
            }
        }
        #else
        Menu {
            DataContextSwitcherRows()
        } label: {
            rowLabel
        }
        #endif
    }

    #if !os(macOS)
    private var rowLabel: some View {
        HStack {
            Label {
                Text(String(localized: "accounts.switcher.title"))
            } icon: {
                DataContextSwitcherIcon()
            }
            Spacer(minLength: 8)
            Text(contextTitle)
                .foregroundStyle(.secondary)
                .lineLimit(1)
        }
    }
    #endif

    private var contextTitle: String {
        DataContextSwitcherLabels.title(for: currentContext, in: appEnvironment)
    }

    private var currentContext: DataContext {
        appEnvironment?.accountsManager.currentContext ?? .local
    }
}

// MARK: - tvOS picker

#if os(tvOS)
/// The tvOS switcher, presented in a `fullScreenCover`: menus are unusable
/// there, and a sheet is a card too small to read.
struct DataContextSwitcherPicker: View {
    @Environment(\.appEnvironment) private var appEnvironment
    @Environment(\.dismiss) private var dismiss

    var body: some View {
        ZStack {
            Color.black.ignoresSafeArea()

            VStack(alignment: .leading, spacing: 24) {
                Text(String(localized: "accounts.switcher.title"))
                    .font(.title2.bold())

                ScrollView {
                    VStack(alignment: .leading, spacing: 12) {
                        DataContextSwitcherRows {
                            dismiss()
                        }
                    }
                }

                Button(String(localized: "common.close")) {
                    dismiss()
                }
                .buttonStyle(TVSettingsButtonStyle())
            }
            .frame(maxWidth: 900)
            .padding(.horizontal, 80)
            .padding(.vertical, 60)
        }
    }
}

/// The button that presents the picker, for placing beside other tvOS controls.
struct DataContextSwitcherButton: View {
    @Environment(\.appEnvironment) private var appEnvironment
    @State private var showingPicker = false

    var body: some View {
        Button {
            showingPicker = true
        } label: {
            Label {
                Text(DataContextSwitcherLabels.title(for: currentContext, in: appEnvironment))
            } icon: {
                DataContextSwitcherIcon()
            }
        }
        .buttonStyle(.bordered)
        .fullScreenCover(isPresented: $showingPicker) {
            DataContextSwitcherPicker()
        }
    }

    private var currentContext: DataContext {
        appEnvironment?.accountsManager.currentContext ?? .local
    }
}
#endif