import XCTest
@testable import LChatCore

// 🤖 Regression guard for issue #580 (iOS threading). A stalled main thread let
// a member's repeated taps on a chat row queue; each ran the list's
// `path.append(.thread(id))`, so the NavigationStack ended up holding duplicate
// copies of one chat and "back" surfaced a phantom second copy. The push must
// be idempotent while that chat is already on top.
//
// This can't reproduce the underlying STALL (that lives in the SwiftUI layout
// engine / gesture system), but it pins the state-machine invariant the stall
// exposed: N taps on the same chat → exactly one push.
final class ChatNavGuardTests: XCTestCase {

    // Model the list's onSelect reducer over a stack of pushed thread ids
    // (empty = the chat list on top). Mirrors ThreadListView's push.
    private func applyTaps(_ taps: [String], guarded: Bool) -> [String] {
        var stack: [String] = []
        for id in taps {
            if !guarded || ChatNavGuard.shouldPush(threadID: id, topThreadID: stack.last) {
                stack.append(id)
            }
        }
        return stack
    }

    // The bug, reproduced: four queued taps on ONE chat push four copies when
    // unguarded — exactly the "back went to a second copy" report.
    func testQueuedTapsDuplicateWithoutGuard() {
        XCTAssertEqual(applyTaps(["T1", "T1", "T1", "T1"], guarded: false),
                       ["T1", "T1", "T1", "T1"])
    }

    // The fix: the same queued taps collapse to a single push.
    func testQueuedTapsCollapseWithGuard() {
        XCTAssertEqual(applyTaps(["T1", "T1", "T1", "T1"], guarded: true), ["T1"])
    }

    // Guarding must not block legitimate navigation between DIFFERENT chats.
    func testDistinctChatsStillPush() {
        XCTAssertEqual(applyTaps(["T1", "T2", "T3"], guarded: true), ["T1", "T2", "T3"])
    }

    // Re-opening a chat you just left is legitimate — it isn't on top anymore.
    func testReopenAfterLeavingPushes() {
        var stack = ["T1"]
        stack.removeLast() // back to the list
        if ChatNavGuard.shouldPush(threadID: "T1", topThreadID: stack.last) {
            stack.append("T1")
        }
        XCTAssertEqual(stack, ["T1"])
    }

    func testShouldPushPredicate() {
        XCTAssertTrue(ChatNavGuard.shouldPush(threadID: "T1", topThreadID: nil))   // from the list
        XCTAssertTrue(ChatNavGuard.shouldPush(threadID: "T2", topThreadID: "T1"))  // switching chats
        XCTAssertFalse(ChatNavGuard.shouldPush(threadID: "T1", topThreadID: "T1")) // already on top
    }
}