import XCTest
@testable import LChatCore

// 🤖 The two-generation memo's contract (#1210): a fill never wipes the hot
// set (the removeAll() bug re-parsed whole feeds on thread open), cold hits
// promote, and only the stalest generation is ever dropped.
final class MemoTests: XCTestCase {
    func testHitsDoNotRebuild() {
        var memo = Memo<String, Int>(cap: 4)
        var builds = 0
        XCTAssertEqual(memo.get("a") { builds += 1; return 1 }, 1)
        XCTAssertEqual(memo.get("a") { builds += 1; return 99 }, 1)
        XCTAssertEqual(builds, 1)
    }

    func testFillKeepsRecentEntriesReachable() {
        var memo = Memo<Int, Int>(cap: 2)
        var builds = 0
        for k in 0..<4 { _ = memo.get(k) { builds += 1; return k } }
        XCTAssertEqual(builds, 4)
        // 2 and 3 straddle the last rotation (one hot, one cold) — both must
        // still be served without rebuilding. THIS is what removeAll() broke.
        _ = memo.get(3) { builds += 1; return -1 }
        _ = memo.get(2) { builds += 1; return -1 }
        XCTAssertEqual(builds, 4)
    }

    func testOnlyStalestGenerationDrops() {
        var memo = Memo<Int, Int>(cap: 2)
        var builds = 0
        for k in 0..<2 { _ = memo.get(k) { builds += 1; return k } }   // hot = {0,1}
        _ = memo.get(2) { builds += 1; return 2 }                      // rotate: cold={0,1}, hot={2}
        _ = memo.get(0) { builds += 1; return 0 }                      // cold hit → promoted, no rebuild
        XCTAssertEqual(builds, 3)
        // Fill until 1's generation is two rotations back — only THEN does it rebuild.
        for k in 10..<14 { _ = memo.get(k) { builds += 1; return k } }
        _ = memo.get(1) { builds += 1; return 1 }
        XCTAssertEqual(builds, 8)
    }
}