import Foundation
import zlib

public enum HTTPBodyDecoder {
    private static let inflateChunkSize = 64 * 1024
    private static let maxDecodedBodyBytes = 8 * 1024 * 1024

    public static func headerValue(named name: String, in headers: [String: String]) -> String? {
        headers.first { $0.key.caseInsensitiveCompare(name) == .orderedSame }?.value
    }

    public static func decodingHint(for body: Data?, headers: [String: String]) -> String {
        guard let body, !body.isEmpty else { return "empty" }

        let encodings = contentEncodings(in: headers)
        if encodings.isEmpty {
            return hasGzipMagic(body) ? "gzip-magic-no-header" : "identity"
        }

        var current = body
        var applied: [String] = []

        for encoding in encodings.reversed() {
            switch encoding {
            case "identity":
                continue
            case "gzip", "x-gzip":
                guard let decoded = inflatePayload(current, windowBits: 47) else {
                    return "failed(\(encoding))"
                }
                current = decoded
                applied.append(encoding)
            case "deflate":
                guard let decoded = inflateDeflatePayload(current) else {
                    return "failed(\(encoding))"
                }
                current = decoded
                applied.append(encoding)
            default:
                return "unsupported(\(encoding))"
            }
        }

        if applied.isEmpty {
            return "identity"
        }

        return "decoded(\(applied.joined(separator: ",")))"
    }

    public static func decodedBodyData(from body: Data?, headers: [String: String]) -> Data? {
        guard let body, !body.isEmpty else { return nil }

        let encodings = contentEncodings(in: headers)
        if encodings.isEmpty {
            return hasGzipMagic(body) ? inflatePayload(body, windowBits: 47) : body
        }

        var current = body

        for encoding in encodings.reversed() {
            switch encoding {
            case "identity":
                continue
            case "gzip", "x-gzip":
                guard let decoded = inflatePayload(current, windowBits: 47) else { return nil }
                current = decoded
            case "deflate":
                guard let decoded = inflateDeflatePayload(current) else { return nil }
                current = decoded
            default:
                return nil
            }
        }

        return current
    }

    public static func searchableText(from body: Data?, headers: [String: String]) -> String? {
        guard let body, !body.isEmpty else { return nil }

        let candidate = decodedBodyData(from: body, headers: headers) ?? body

        if let jsonText = searchableJSONText(from: candidate) {
            return jsonText
        }

        guard let string = String(data: candidate, encoding: .utf8)?
            .trimmingCharacters(in: .whitespacesAndNewlines),
            !string.isEmpty else {
            return nil
        }

        return string
    }

    private static func contentEncodings(in headers: [String: String]) -> [String] {
        guard let value = headerValue(named: "Content-Encoding", in: headers)?
            .lowercased()
            .trimmingCharacters(in: .whitespacesAndNewlines),
              !value.isEmpty else {
            return []
        }

        return value
            .split(separator: ",")
            .map { $0.trimmingCharacters(in: .whitespacesAndNewlines) }
            .filter { !$0.isEmpty }
    }

    private static func searchableJSONText(from data: Data) -> String? {
        guard let jsonObject = try? JSONSerialization.jsonObject(with: data) else {
            return nil
        }

        let fragments = flattenedSearchFragments(from: jsonObject)
            .map { $0.trimmingCharacters(in: .whitespacesAndNewlines) }
            .filter { !$0.isEmpty }

        guard !fragments.isEmpty else { return nil }
        return fragments.joined(separator: "\n")
    }

    private static func flattenedSearchFragments(from value: Any) -> [String] {
        switch value {
        case let dict as [String: Any]:
            return dict.sorted(by: { $0.key < $1.key }).flatMap { key, nestedValue in
                [key] + flattenedSearchFragments(from: nestedValue)
            }
        case let array as [Any]:
            return array.flatMap(flattenedSearchFragments(from:))
        case let string as String:
            return [string]
        case let number as NSNumber:
            return ["\(number)"]
        case _ as NSNull:
            return []
        default:
            return ["\(value)"]
        }
    }

    private static func inflateDeflatePayload(_ data: Data) -> Data? {
        inflatePayload(data, windowBits: 47) ??
        inflatePayload(data, windowBits: 15) ??
        inflatePayload(data, windowBits: -15)
    }

    private static func inflatePayload(_ data: Data, windowBits: Int32) -> Data? {
        guard !data.isEmpty else { return Data() }

        return data.withUnsafeBytes { rawBuffer in
            guard let sourceBytes = rawBuffer.bindMemory(to: Bytef.self).baseAddress else {
                return Data()
            }

            var stream = z_stream()
            stream.next_in = UnsafeMutablePointer(mutating: sourceBytes)
            stream.avail_in = uInt(data.count)

            let status = inflateInit2_(&stream, windowBits, ZLIB_VERSION, Int32(MemoryLayout<z_stream>.size))
            guard status == Z_OK else { return nil }
            defer { inflateEnd(&stream) }

            var output = Data()
            var buffer = [UInt8](repeating: 0, count: inflateChunkSize)

            while true {
                let result = buffer.withUnsafeMutableBufferPointer { outputBuffer -> Int32 in
                    stream.next_out = outputBuffer.baseAddress
                    stream.avail_out = uInt(outputBuffer.count)
                    return zlib.inflate(&stream, Z_SYNC_FLUSH)
                }

                let produced = inflateChunkSize - Int(stream.avail_out)
                if produced > 0 {
                    buffer.withUnsafeBufferPointer { outputBuffer in
                        guard let baseAddress = outputBuffer.baseAddress else { return }
                        output.append(baseAddress, count: produced)
                    }

                    if output.count >= maxDecodedBodyBytes {
                        return Data(output.prefix(maxDecodedBodyBytes))
                    }
                }

                switch result {
                case Z_STREAM_END:
                    return output
                case Z_OK:
                    continue
                default:
                    return nil
                }
            }
        }
    }

    private static func hasGzipMagic(_ data: Data) -> Bool {
        guard data.count >= 2 else { return false }
        return data[data.startIndex] == 0x1f && data[data.index(after: data.startIndex)] == 0x8b
    }
}