import Foundation
import Testing

@testable import Photochk

@Suite("dHash")
struct DHashTests {
    @Test("同じ値のハミング距離は 0")
    func identical() {
        #expect(DHash.hammingDistance(0xDEAD_BEEF_1234_5678, 0xDEAD_BEEF_1234_5678) == 0)
    }

    @Test("違うビットの数がそのまま距離になる")
    func differingBits() {
        #expect(DHash.hammingDistance(0, 0b1011) == 3)
        #expect(DHash.hammingDistance(.max, 0) == 64)
        #expect(DHash.hammingDistance(0b1100, 0b0110) == 2)
    }

    @Test("生成した画像から 64bit のハッシュが取れる")
    func computesFromImage() throws {
        let directory = try TestImages.makeTemporaryDirectory()
        defer { try? FileManager.default.removeItem(at: directory) }

        let url = directory.appendingPathComponent("base.jpg")
        try TestImages.writeJPEG(TestImages.pattern(seed: 1), to: url, quality: 0.9)

        let basics = try #require(DHash.compute(for: url))
        #expect(basics.pixelWidth == TestImages.width)
        #expect(basics.pixelHeight == TestImages.height)

        // 同じファイルからは必ず同じ値が出る
        let again = try #require(DHash.compute(for: url))
        #expect(basics.dHash == again.dHash)
    }

    @Test("リサイズしてもハッシュはほとんど変わらず、別の絵柄とは大きく離れる")
    func robustToResize() throws {
        let directory = try TestImages.makeTemporaryDirectory()
        defer { try? FileManager.default.removeItem(at: directory) }

        let base = directory.appendingPathComponent("base.jpg")
        let small = directory.appendingPathComponent("small.jpg")
        let other = directory.appendingPathComponent("other.jpg")

        let pattern = TestImages.pattern(seed: 7)
        try TestImages.writeJPEG(pattern, to: base, quality: 0.9)
        try TestImages.writeJPEG(TestImages.scaled(pattern, factor: 0.5), to: small, quality: 0.8)
        try TestImages.writeJPEG(TestImages.pattern(seed: 99), to: other, quality: 0.9)

        let baseHash = try #require(DHash.compute(for: base)).dHash
        let smallHash = try #require(DHash.compute(for: small)).dHash
        let otherHash = try #require(DHash.compute(for: other)).dHash

        #expect(DHash.hammingDistance(baseHash, smallHash) <= 12)
        #expect(DHash.hammingDistance(baseHash, otherHash) > 12)
    }
}