//
//  Folder.swift
//  Confab
//
//  Model for grouping saved conversations
//
// SPDX-License-Identifier: PolyForm-Noncommercial-1.0.0
// Copyright (C) 2026 Rune Olsen
//
// This file is part of Confab.
//
// Confab is licensed under the PolyForm Noncommercial License 1.0.0.
// You may use, study, modify, and share it for any noncommercial
// purpose. Commercial use — including selling Confab or any part of
// it, standalone or bundled into another product or service —
// requires a separate commercial license from the copyright holder.
//
// See the LICENSE file or
// <https://polyformproject.org/licenses/noncommercial/1.0.0> for
// the full license text. For commercial licensing, contact Rune
// Olsen via <https://confab.no>.


import Foundation

struct Folder: Identifiable, Codable, Sendable {
    let id: UUID
    var name: String
    var sortOrder: Int
    let createdAt: Date
    var parentId: UUID?
    var updatedAt: Date

    nonisolated init(
        id: UUID = UUID(),
        name: String,
        sortOrder: Int = 0,
        createdAt: Date = Date(),
        parentId: UUID? = nil,
        updatedAt: Date? = nil
    ) {
        self.id = id
        self.name = name
        self.sortOrder = sortOrder
        self.createdAt = createdAt
        self.parentId = parentId
        self.updatedAt = updatedAt ?? createdAt
    }
}

extension Folder {
    /// Depth-first, indented ordering for flat-list display. Assumes `folders` already has the
    /// desired sibling order (e.g. listFolders()'s alphabetical order) — only re-groups by
    /// parent/child, preserving each existing sibling ordering.
    nonisolated static func orderedTree(from folders: [Folder]) -> [(folder: Folder, depth: Int)] {
        var childrenByParent: [UUID?: [Folder]] = [:]
        for folder in folders {
            childrenByParent[folder.parentId, default: []].append(folder)
        }
        var result: [(folder: Folder, depth: Int)] = []
        func walk(parentId: UUID?, depth: Int, visiting: Set<UUID>) {
            for folder in childrenByParent[parentId] ?? [] {
                guard !visiting.contains(folder.id) else { continue }  // defensive cycle guard
                result.append((folder, depth))
                walk(parentId: folder.id, depth: depth + 1, visiting: visiting.union([folder.id]))
            }
        }
        walk(parentId: nil, depth: 0, visiting: [])
        return result
    }

    /// True if `candidateId` is `ancestorId` itself, or nested anywhere below it. A single call
    /// `isDescendant(target.id, of: source.id, in: folders)` rejects both a self-drop (target ==
    /// source) and any deeper cycle (target currently lives under source).
    nonisolated static func isDescendant(_ candidateId: UUID, of ancestorId: UUID, in folders: [Folder]) -> Bool {
        var current: UUID? = candidateId
        var visited: Set<UUID> = []
        while let id = current, !visited.contains(id) {
            if id == ancestorId { return true }
            visited.insert(id)
            current = folders.first(where: { $0.id == id })?.parentId
        }
        return false
    }

    /// Given an ordered tree and the set of explicitly-collapsed folder ids, returns ids whose
    /// header should still render — collapsing a folder hides its whole subtree, but its own
    /// header stays visible so it can be expanded again.
    nonisolated static func visibleFolderIds(tree: [(folder: Folder, depth: Int)], collapsed: Set<UUID>) -> Set<UUID> {
        var visible: Set<UUID> = []
        var hiddenAtOrBelowDepth: Int? = nil
        for (folder, depth) in tree {
            if let hiddenDepth = hiddenAtOrBelowDepth, depth > hiddenDepth { continue }
            hiddenAtOrBelowDepth = nil
            visible.insert(folder.id)
            if collapsed.contains(folder.id) { hiddenAtOrBelowDepth = depth }
        }
        return visible
    }
}
