import XCTest
@testable import SharedCore

final class WatchPayloadValidationTests: XCTestCase {
    private struct MockPayload: Codable, Equatable {
        let name: String
        let count: Int
    }

    func testValidateRejectsEmptyPayload() {
        let error = WatchPayloadValidation.validate(Data())
        XCTAssertEqual(error, .emptyPayload)
    }

    func testValidateRejectsOversizedPayload() {
        let payload = Data(repeating: 0, count: 9)
        let error = WatchPayloadValidation.validate(payload, maxBytes: 8)
        XCTAssertEqual(error, .payloadTooLarge(actualBytes: 9, maxBytes: 8))
    }

    func testDecodeAcceptsValidPayload() throws {
        let payload = try JSONEncoder().encode(MockPayload(name: "set", count: 12))
        let decoded = try WatchPayloadValidation.decode(MockPayload.self, from: payload)
        XCTAssertEqual(decoded, MockPayload(name: "set", count: 12))
    }

    func testDecodeRejectsInvalidJSON() throws {
        let invalid = Data("not-json".utf8)

        XCTAssertThrowsError(try WatchPayloadValidation.decode(MockPayload.self, from: invalid)) { error in
            XCTAssertEqual(error as? WatchPayloadValidationError, .decodeFailure)
        }
    }

    func testDecodeRejectsOversizedPayloadBeforeDecoding() {
        let payload = Data(repeating: 1, count: 32)

        XCTAssertThrowsError(
            try WatchPayloadValidation.decode(MockPayload.self, from: payload, maxBytes: 16)
        ) { error in
            XCTAssertEqual(
                error as? WatchPayloadValidationError,
                .payloadTooLarge(actualBytes: 32, maxBytes: 16)
            )
        }
    }
}