import Foundation
import EmbraceIO
import CryptoKit

extension UserDefaults {
    static var embrace: UserDefaults {
        UserDefaults(suiteName: "EmbraceReactNative") ?? .standard
    }
}

private struct LastBundleComputation: Codable {
    private static let STORAGE_KEY = "EMBRACE_LAST_BUNDLE_COMPUTATION"
    var path: String
    var computedAt: Date?
    var id: String

    func store () {
        if let encoded = try? JSONEncoder().encode(self) {
            UserDefaults.embrace.set(encoded, forKey: LastBundleComputation.STORAGE_KEY)
        }
    }

    static func fromStorage() -> LastBundleComputation {
        if let storedData = UserDefaults.embrace.object(forKey: LastBundleComputation.STORAGE_KEY) as? Data,
           let loaded = try? JSONDecoder().decode(LastBundleComputation.self, from: storedData) {
            return loaded
        }

        return LastBundleComputation(path: "", computedAt: nil, id: "")
    }
}

enum ComputeBundleIDErrors: Error, LocalizedError {
    case emptyPath
    case fileReadError(path: String, underlying: Error)

    var errorDescription: String? {
        switch self {
        case .emptyPath:
            return "Bundle path is empty"
        case .fileReadError(let path, let underlying):
            return "Failed to read bundle at path '\(path)': \(underlying.localizedDescription)"
        default:
            return "An unexpected ComputeBundleIDErrors occurred: \(self)"
        }
    }
}

struct BundleID {
    var id: String
    var cached: Bool
}

func computeBundleID(path: String) throws -> BundleID {
    if path.isEmpty {
        throw ComputeBundleIDErrors.emptyPath
    }

    var last = LastBundleComputation.fromStorage()

    // Check if we can re-use our last computed bundle ID, this is true only if the path hasn't changed and
    // the file contents at that path haven't been modified since the last time we computed the ID
    if path == last.path {
        let attributes = try? FileManager.default.attributesOfItem(atPath: path)
        if let lastComputed = last.computedAt, let modifiedAt = attributes?[FileAttributeKey.modificationDate] as? Date,
           modifiedAt <= lastComputed {
            return BundleID(id: last.id, cached: true)
        }
    }

    do {
        let fileData = try Data(contentsOf: URL(fileURLWithPath: path))

        // https://stackoverflow.com/a/56578995
        let bundleID = Insecure.MD5.hash(data: fileData).map {
            String(format: "%02hhx", $0)
        }.joined()

        last.computedAt = Date()
        last.path = path
        last.id = bundleID
        last.store()

    } catch {
        throw ComputeBundleIDErrors.fileReadError(path: path, underlying: error)
    }

    return BundleID(id: last.id, cached: false)
}