import AppKit
import Vision

final class OCRService {
    static let shared = OCRService()

    private let queue = DispatchQueue(label: "dev.tzgyn.kapture.ocr", qos: .userInitiated)

    func recognize(_ cgImage: CGImage, completion: @escaping (String) -> Void) {
        queue.async {
            let text = Self.perform(cgImage)
            // Tiny text (small UI labels) often reads as nothing at native
            // size; retry upscaled and keep whichever pass read more.
            guard text.count < 3 else {
                completion(text)
                return
            }
            var best = text
            for factor in [CGFloat(2), CGFloat(3)] {
                guard let upscaled = Self.upscaled(cgImage, factor: factor) else { continue }
                let candidate = Self.perform(upscaled)
                if candidate.count > best.count { best = candidate }
                if best.count >= 3 { break }
            }
            completion(best)
        }
    }

    private static func perform(_ cgImage: CGImage) -> String {
        let request = VNRecognizeTextRequest()
        request.recognitionLevel = .accurate
        request.usesLanguageCorrection = true
        request.recognitionLanguages = ["en-US", "zh-Hans", "zh-Hant", "ja-JP", "ko-KR"]
        // Without this, Vision defaults to the first listed language and
        // renders CJK as Latin garbage (verified: 你好世界 -> "177WR").
        if #available(macOS 13.0, *) {
            request.automaticallyDetectsLanguage = true
        }

        let handler = VNImageRequestHandler(cgImage: cgImage, options: [:])
        do {
            try handler.perform([request])
        } catch {
            return ""
        }

        let observations = request.results ?? []
        let lines = observations
            .sorted { a, b in
                let ay = a.boundingBox.midY
                let by = b.boundingBox.midY
                if abs(ay - by) > 0.02 { return ay > by }
                return a.boundingBox.minX < b.boundingBox.minX
            }
            .compactMap { $0.topCandidates(1).first?.string }
        return lines.joined(separator: "\n")
    }

    private static func upscaled(_ cgImage: CGImage, factor: CGFloat) -> CGImage? {
        let width = Int(CGFloat(cgImage.width) * factor)
        let height = Int(CGFloat(cgImage.height) * factor)
        guard width > 0, height > 0, width <= 20000, height <= 20000 else { return nil }
        guard let ctx = CGContext(
            data: nil, width: width, height: height,
            bitsPerComponent: 8, bytesPerRow: 0,
            space: CGColorSpaceCreateDeviceRGB(),
            bitmapInfo: CGImageAlphaInfo.premultipliedLast.rawValue
        ) else { return nil }
        ctx.interpolationQuality = .high
        ctx.draw(cgImage, in: CGRect(x: 0, y: 0, width: CGFloat(width), height: CGFloat(height)))
        return ctx.makeImage()
    }
}