import Foundation
import OpenClawChatUI

struct CommandSessionSection: Identifiable {
    enum ID: Hashable {
        case pinned
        case category(String)
        case ungrouped
    }

    let id: ID
    let title: String
    let entries: [OpenClawChatSessionEntry]
    let showsHeader: Bool
}

enum CommandSessionGrouping {
    static func sections(
        from entries: [OpenClawChatSessionEntry],
        knownGroups: [String] = []) -> [CommandSessionSection]
    {
        let pinned = self.sortedByActivity(entries.filter { $0.pinned == true })
        let unpinned = entries.filter { $0.pinned != true }
        // Stored-but-empty groups still render as sections so they remain
        // visible move targets after their last member leaves.
        let categoryNames = Set(unpinned.compactMap { self.normalizedCategory($0.category) })
            .union(knownGroups.compactMap(self.normalizedCategory))
            .sorted(by: self.categoryComesBefore)
        var sections: [CommandSessionSection] = []

        if !pinned.isEmpty {
            sections.append(CommandSessionSection(
                id: .pinned,
                title: "Pinned",
                entries: pinned,
                showsHeader: true))
        }

        for category in categoryNames {
            let categoryEntries = unpinned.filter { self.normalizedCategory($0.category) == category }
            sections.append(CommandSessionSection(
                id: .category(category),
                title: category,
                entries: self.sortedByActivity(categoryEntries),
                showsHeader: true))
        }

        let ungrouped = self.sortedByActivity(unpinned.filter { self.normalizedCategory($0.category) == nil })
        if !ungrouped.isEmpty {
            sections.append(CommandSessionSection(
                id: .ungrouped,
                title: "Ungrouped",
                entries: ungrouped,
                showsHeader: !categoryNames.isEmpty))
        }

        return sections
    }

    static func previewOrder(_ entries: [OpenClawChatSessionEntry]) -> [OpenClawChatSessionEntry] {
        entries.sorted { lhs, rhs in
            if (lhs.pinned == true) != (rhs.pinned == true) {
                return lhs.pinned == true
            }
            let left = self.activityTimestamp(lhs)
            let right = self.activityTimestamp(rhs)
            return left == right ? lhs.key < rhs.key : left > right
        }
    }

    /// Capped preview that always keeps the open chat visible: when the current
    /// session falls outside the cap it leads the list (pre-existing Command
    /// Center contract), otherwise natural pinned/activity order wins.
    static func previewSelection(
        _ entries: [OpenClawChatSessionEntry],
        currentKey: String,
        limit: Int = 3) -> [OpenClawChatSessionEntry]
    {
        let ordered = self.previewOrder(entries)
        let capped = Array(ordered.prefix(limit))
        guard !currentKey.isEmpty,
              !capped.contains(where: { $0.key == currentKey }),
              let current = ordered.first(where: { $0.key == currentKey })
        else { return capped }
        return [current] + capped.prefix(max(0, limit - 1))
    }

    static func categories(
        from entries: [OpenClawChatSessionEntry],
        knownGroups: [String] = []) -> [String]
    {
        Set(entries.compactMap { self.normalizedCategory($0.category) })
            .union(knownGroups.compactMap(self.normalizedCategory))
            .sorted(by: self.categoryComesBefore)
    }

    /// Union of the active and archived enumerations, deduped by key. Group
    /// mutations must patch archived members too so restores land back in the
    /// renamed group instead of the stale one.
    static func members(
        of group: String,
        in lists: [[OpenClawChatSessionEntry]]) -> [OpenClawChatSessionEntry]
    {
        guard let target = self.normalizedCategory(group) else { return [] }
        var seen = Set<String>()
        return lists.flatMap(\.self).filter { entry in
            self.normalizedCategory(entry.category) == target && seen.insert(entry.key).inserted
        }
    }

    static func activityTimestamp(_ entry: OpenClawChatSessionEntry) -> Double {
        entry.lastActivityAt ?? entry.updatedAt ?? 0
    }

    private static func sortedByActivity(
        _ entries: [OpenClawChatSessionEntry]) -> [OpenClawChatSessionEntry]
    {
        entries.sorted { lhs, rhs in
            let left = self.activityTimestamp(lhs)
            let right = self.activityTimestamp(rhs)
            return left == right ? lhs.key < rhs.key : left > right
        }
    }

    private static func normalizedCategory(_ category: String?) -> String? {
        guard let category else { return nil }
        let trimmed = category.trimmingCharacters(in: .whitespacesAndNewlines)
        return trimmed.isEmpty ? nil : trimmed
    }

    private static func categoryComesBefore(_ lhs: String, _ rhs: String) -> Bool {
        let order = lhs.localizedCaseInsensitiveCompare(rhs)
        return order == .orderedSame ? lhs < rhs : order == .orderedAscending
    }
}