import XCTest
import UIKit

/// PDF 翻页后白页回归。
///
/// 判定方式：每次翻页稳定后截屏，统计画面中部的深色像素占比。正常 PDF 正文页
/// 含文字与线条，占比明显高于阈值；页面图片没有装配到视图上时几乎全白。
final class PDFPageTurnBlankPageTests: XCTestCase {
    private let app = XCUIApplication()

    /// 深色像素占比低于该值即视为白页。样张实测：白页为 0.0000，
    /// 内容最少的扉页约 0.0020，正文页在 0.0100 以上。
    private let blankInkRatioThreshold = 0.0005

    override func setUpWithError() throws {
        continueAfterFailure = false
    }

    func testPageCurlForwardTurnsRenderPageContent() {
        openDictionaryPDF(displayType: "pagecurl")
        assertForwardTurnsRenderContent(turns: 8, mode: "仿真翻页")
    }

    func testHorizontalScrollForwardTurnsRenderPageContent() {
        openDictionaryPDF(displayType: "horizontalscroll")
        assertForwardTurnsRenderContent(turns: 8, mode: "横向滚动")
    }

    /// 回翻同样依赖 `viewControllerBefore` 预建的页面视图，需要单独覆盖。
    func testPageCurlBackwardTurnsRenderPageContent() {
        openDictionaryPDF(displayType: "pagecurl")
        assertForwardTurnsRenderContent(turns: 5, mode: "仿真翻页")
        assertBackwardTurnsRenderContent(from: 6, turns: 5, mode: "仿真回翻")
    }

    // MARK: - 步骤

    private func openDictionaryPDF(displayType: String) {
        app.launchAndOpenSampleBook(
            bookTitleQuery: "英汉大词典",
            displayType: displayType,
            resetsReaderState: true
        )
        app.waitForReader(timeout: 30)
        app.waitForReaderPage(1, timeout: 30)
        // 首页首次渲染需要等待异步解码完成，避免把加载中误判成白页。
        RunLoop.current.run(until: Date().addingTimeInterval(2.5))
    }

    private func assertForwardTurnsRenderContent(turns: Int, mode: String) {
        var blankPages: [Int] = []

        recordInk(page: 1, mode: mode, blankPages: &blankPages)

        for step in 1...turns {
            let expectedPage = step + 1
            turnToNextPage()
            app.waitForDemoReaderState(timeout: 15, description: "\(mode) page=\(expectedPage)") {
                $0.page == expectedPage
            }
            // 翻页动画结束后再取样，排除卷页过程中的中间帧。
            RunLoop.current.run(until: Date().addingTimeInterval(1.2))
            recordInk(page: expectedPage, mode: mode, blankPages: &blankPages)
        }

        XCTAssertTrue(
            blankPages.isEmpty,
            "\(mode)：翻页后出现白页，页码 \(blankPages.map(String.init).joined(separator: ", "))"
        )
    }

    private func assertBackwardTurnsRenderContent(from startPage: Int, turns: Int, mode: String) {
        var blankPages: [Int] = []

        for step in 1...turns {
            let expectedPage = startPage - step
            guard expectedPage >= 1 else { break }
            turnPage(forward: false)
            app.waitForDemoReaderState(timeout: 15, description: "\(mode) page=\(expectedPage)") {
                $0.page == expectedPage
            }
            RunLoop.current.run(until: Date().addingTimeInterval(1.2))
            recordInk(page: expectedPage, mode: mode, blankPages: &blankPages)
        }

        XCTAssertTrue(
            blankPages.isEmpty,
            "\(mode)：翻页后出现白页，页码 \(blankPages.map(String.init).joined(separator: ", "))"
        )
    }

    private func turnToNextPage() { turnPage(forward: true) }

    private func turnPage(forward: Bool) {
        let content = app.otherElements[IDs.readerContent].firstMatch
        let target: XCUIElement = content.exists ? content : app.windows.firstMatch
        let leading = CGVector(dx: 0.08, dy: 0.5)
        let trailing = CGVector(dx: 0.88, dy: 0.5)
        let start = target.coordinate(withNormalizedOffset: forward ? trailing : leading)
        let end = target.coordinate(withNormalizedOffset: forward ? leading : trailing)
        start.press(forDuration: 0.05, thenDragTo: end)
    }

    private func recordInk(page: Int, mode: String, blankPages: inout [Int]) {
        let screenshot = XCUIScreen.main.screenshot()
        let ratio = inkRatio(of: screenshot.image)

        let attachment = XCTAttachment(screenshot: screenshot)
        attachment.name = "\(mode)-page-\(page)-ink-\(String(format: "%.4f", ratio))"
        attachment.lifetime = .keepAlways
        add(attachment)

        if ratio < blankInkRatioThreshold {
            blankPages.append(page)
        }
    }

    /// 画面中部深色像素占比。裁掉上下边缘以排除状态栏、工具栏和页面外底色。
    private func inkRatio(of image: UIImage) -> Double {
        guard let cgImage = image.cgImage else { return 0 }
        let cropRect = CGRect(
            x: CGFloat(cgImage.width) * 0.12,
            y: CGFloat(cgImage.height) * 0.16,
            width: CGFloat(cgImage.width) * 0.76,
            height: CGFloat(cgImage.height) * 0.68
        ).integral
        guard let cropped = cgImage.cropping(to: cropRect) else { return 0 }

        let side = 400
        var pixels = [UInt8](repeating: 255, count: side * side)
        guard let context = CGContext(
            data: &pixels,
            width: side,
            height: side,
            bitsPerComponent: 8,
            bytesPerRow: side,
            space: CGColorSpaceCreateDeviceGray(),
            bitmapInfo: CGImageAlphaInfo.none.rawValue
        ) else { return 0 }
        context.draw(cropped, in: CGRect(x: 0, y: 0, width: side, height: side))

        let darkCount = pixels.reduce(into: 0) { partial, value in
            if value < 150 { partial += 1 }
        }
        return Double(darkCount) / Double(side * side)
    }
}