import CryptoKit
import XCTest
@testable import LChatCore

// 🤖 The hashcash solver mirrors home's pow.go: SHA-256(challenge ":" nonce)
// must clear the difficulty's leading zero bits. These pin the two pure
// pieces (bit counting, solve/verify) against the same cases as the Go tests,
// so the native solver and the server can't drift.
final class PowSolverTests: XCTestCase {
    func testLeadingZeroBits() {
        XCTAssertEqual(HomeClient.leadingZeroBits([0x80]), 0)
        XCTAssertEqual(HomeClient.leadingZeroBits([0x01]), 7)
        XCTAssertEqual(HomeClient.leadingZeroBits([0x00, 0xFF]), 8)
        XCTAssertEqual(HomeClient.leadingZeroBits([0x00, 0x0F]), 12)
        XCTAssertEqual(HomeClient.leadingZeroBits([0x00, 0x00]), 16)
    }

    func testSolveAndVerify() {
        // 8 bits ≈ 256 hashes — instant. Grind exactly like the client does,
        // then check the found nonce verifies against an independent digest.
        let challenge = "test-challenge"
        var nonce = 0
        while !HomeClient.powSolves(challenge: challenge, nonce: String(nonce), bits: 8) {
            nonce += 1
            XCTAssertLessThan(nonce, 1_000_000, "8-bit solution should be found quickly")
        }
        let digest = Array(SHA256.hash(data: Data((challenge + ":" + String(nonce)).utf8)))
        XCTAssertGreaterThanOrEqual(HomeClient.leadingZeroBits(digest), 8)
        // Bits are a floor: a 8-bit solution rarely clears 32.
        XCTAssertFalse(HomeClient.powSolves(challenge: challenge, nonce: "definitely-not-it", bits: 32))
        // A solution is bound to its challenge text, not portable.
        XCTAssertTrue(HomeClient.powSolves(challenge: "anything", nonce: "0", bits: 0))
    }
}