import XCTest
@testable import Receiver

final class JitterBufferTests: XCTestCase {
    private func packet(seq: Int, ts: Int = 100) -> RtpPacket {
        RtpPacket(header: RtpHeader(sequenceNumber: seq, timestamp: ts), payload: [UInt8(seq)])
    }

    func testInOrderReleasesImmediately() {
        let jitter = JitterBuffer()
        XCTAssertEqual(jitter.push(packet(seq: 1)).map { $0.header.sequenceNumber }, [1])
        XCTAssertEqual(jitter.push(packet(seq: 2)).map { $0.header.sequenceNumber }, [2])
        XCTAssertEqual(jitter.push(packet(seq: 3)).map { $0.header.sequenceNumber }, [3])
    }

    func testReordersOutOfOrderPackets() {
        let jitter = JitterBuffer()
        XCTAssertEqual(jitter.push(packet(seq: 1)).map { $0.header.sequenceNumber }, [1])
        XCTAssertTrue(jitter.push(packet(seq: 3)).isEmpty)
        XCTAssertEqual(jitter.push(packet(seq: 2)).map { $0.header.sequenceNumber }, [2, 3])
    }

    func testOverflowReleasesInOrderAndAdvances() {
        let jitter = JitterBuffer(maxDepth: 4)
        XCTAssertEqual(jitter.push(packet(seq: 1)).map { $0.header.sequenceNumber }, [1])
        // seq 2 is lost; 3..6 stay buffered (within the depth bound).
        for seq in 3...6 {
            XCTAssertTrue(jitter.push(packet(seq: seq)).isEmpty)
        }
        // seq 7 overflows the buffer: 3..7 flush in order.
        XCTAssertEqual(jitter.push(packet(seq: 7)).map { $0.header.sequenceNumber }, [3, 4, 5, 6, 7])
        // Delivery continues in order afterwards.
        XCTAssertEqual(jitter.push(packet(seq: 8)).map { $0.header.sequenceNumber }, [8])
        XCTAssertEqual(jitter.push(packet(seq: 9)).map { $0.header.sequenceNumber }, [9])
    }

    func testDiscardsStragglers() {
        let jitter = JitterBuffer(maxDepth: 4)
        _ = jitter.push(packet(seq: 1))
        for seq in 3...8 {
            _ = jitter.push(packet(seq: seq))
        }
        XCTAssertTrue(jitter.push(packet(seq: 9)).isNotEmpty)
        // seq 4 is now far behind the expected sequence: discarded, not delivered.
        XCTAssertTrue(jitter.push(packet(seq: 4)).isEmpty)
        // In-order delivery continues from 10.
        XCTAssertEqual(jitter.push(packet(seq: 10)).map { $0.header.sequenceNumber }, [10])
    }

    func testClearResetsState() {
        let jitter = JitterBuffer()
        _ = jitter.push(packet(seq: 5))
        jitter.clear()
        // A completely different sequence now starts fresh.
        XCTAssertEqual(jitter.push(packet(seq: 100)).map { $0.header.sequenceNumber }, [100])
    }
}