import Foundation
import Darwin

enum FFmpegRuntime {
    static func error(for app: URL) -> String? {
        let manifest = app.appendingPathComponent("Contents/Resources/ffmpeg-libraries.txt")
        let metadataError = "This app's FFmpeg library metadata is missing or invalid. Rebuild and reinstall terebi."
        guard let contents = try? String(contentsOf: manifest, encoding: .utf8) else {
            return metadataError
        }
        var paths = contents.components(separatedBy: "\n")
        if paths.last == "" { paths.removeLast() }
        let libraries: Set<String> = ["libavformat", "libavcodec", "libavutil", "libswresample", "libswscale"]
        guard paths.count == libraries.count else { return metadataError }
        var found = Set<String>()
        for path in paths {
            guard path.hasPrefix("/"), !path.contains("\0"), !path.contains("\r") else {
                return metadataError
            }
            let parts = URL(fileURLWithPath: path).lastPathComponent.split(separator: ".", omittingEmptySubsequences: false)
            guard parts.count >= 2, parts.last == "dylib" else { return metadataError }
            let library = String(parts[0])
            guard libraries.contains(library),
                  parts.dropFirst().dropLast().allSatisfy({ !$0.isEmpty && $0.utf8.allSatisfy { (48...57).contains($0) } }),
                  found.insert(library).inserted else {
                return metadataError
            }
        }
        for path in paths {
            _ = dlerror()
            guard dlopen(path, RTLD_NOW | RTLD_LOCAL) != nil else {
                let detail = dlerror().map { String(cString: $0) } ?? "The dynamic loader could not load this library."
                return "The FFmpeg libraries required by this build are unavailable or broken.\n\nRequired library: \(path)\n\(detail)\n\nInstall FFmpeg with `brew install ffmpeg`. If FFmpeg was upgraded or its library versions changed, rebuild and reinstall terebi."
            }
            // Deliberately never dlclose: retain successful loads until exit or bootstrap exec.
        }
        return nil
    }
}