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using System;
using System.IO;
using System.Xml;
using System.Collections;
using System.Text;
using System.Security.Cryptography;
using YYProject.XXHash;

namespace CommandLib
{
    /// <summary>
    /// Thrown if we fail to verify a block (ie sha1) checksum
    /// </summary>
    public class BlockChecksumFailed : ApplicationException
    {
        private string block;
        private string recomputed;
        private string original;

        public BlockChecksumFailed(string block, string recomputed, string original)
        {
            this.block = block;
            this.recomputed = recomputed;
            this.original = original;
        }

        public override string ToString()
        {
            return "Failed to verify the block checksum: block = " + block + "; recomputed = " + recomputed + "; original = " + original;
        }
    }

    public class Export
    {
        [System.Diagnostics.CodeAnalysis.SuppressMessage("csharpsquid",
            "S4790:Using weak hashing algorithms is security-sensitive",
            Justification = "Used only for checksum verification for backwards compatibility.")]
        [System.Diagnostics.CodeAnalysis.SuppressMessage("csharpsquid",
            "S2070:SHA-1 and Message-Digest hash algorithms should not be used in secure contexts",
            Justification = "Used only for checksum verification for backwards compatibility.")]
        private readonly SHA1 _sha1 = new SHA1CryptoServiceProvider();

        private readonly XXHash64 _xxHash = new XXHash64();

        public static bool verbose_debugging = false;

        private static void debug(string x)
        {
            if (verbose_debugging)
                Console.WriteLine(x);
        }

        private string checksum_sha1(byte[] data)
        {
            byte[] result = _sha1.ComputeHash(data);
            return hex(result).ToLower();
        }

        private string hex(byte[] bytes)
        {
            char[] chars = {'0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F'};
            char[] output = new char[bytes.Length * 2];

            for (uint i = 0; i < bytes.Length; i++)
            {
                uint b = (uint)bytes[i];
                output[i * 2] = chars[b >> 4];
                output[i * 2 + 1] = chars[b & 0x0F];
            }

            return new string(output);
        }

        private string checksum_xxhash(byte[] data)
        {
            _xxHash.Initialize();
            return hex(_xxHash.ComputeHash(data));
        }

        private static Hashtable parse_checksum_table(string checksum_xml)
        {
            Hashtable table = new Hashtable();

            XmlDocument xmlDoc = new System.Xml.XmlDocument();
            xmlDoc.LoadXml(checksum_xml);
            XmlNodeList members = xmlDoc.GetElementsByTagName("member");
            string name;
            string value;
            foreach (XmlNode member in members)
            {
                name = "";
                value = "";
                foreach (XmlNode child in member.ChildNodes)
                {
                    XmlNode v = child.FirstChild;
                    if (child.Name.Equals("name"))
                        name = v.Value;
                    if (child.Name.Equals("value"))
                        value = v.Value;
                }

                debug(String.Format("adding {0} = {1}", name, value));
                table.Add(name, value);
            }

            return table;
        }

        private static void compare_tables(Hashtable recomputed, Hashtable original)
        {
            foreach (DictionaryEntry x in recomputed)
            {
                string ours = (string)x.Value;
                string theirs = (string)original[x.Key];
                if (!ours.Equals(theirs))
                {
                    throw new BlockChecksumFailed((string)x.Key, ours, theirs);
                }
                else
                {
                    debug(String.Format("{0} hash OK", (string)x.Key));
                }
            }
        }

        private static string string_of_byte_array(byte[] payload)
        {
            Decoder decoder = Encoding.UTF8.GetDecoder();
            char[] chars = new char[decoder.GetCharCount(payload, 0, (int)payload.Length)];
            decoder.GetChars(payload, 0, (int)payload.Length, chars, 0);
            return new string(chars);
        }

        public delegate void verifyCallback(uint read);

        public delegate bool cancellingCallback();

        /// <summary>
        /// 'input' is the source of the export data, if 'output' is not null then
        /// a perfect copy should be echoed there. 
        /// </summary>
        public void verify(Stream input, Stream output, cancellingCallback cancelling)
        {
            verify(input, output, cancelling, null);
        }

        private Header nextHeader(Stream input, Stream output, verifyCallback callback)
        {
            // Interperate the next bytes from the stream as a Tar header
            byte[] bytes = nextData(input, output, callback, Header.length);

            if (Header.all_zeroes(bytes)) // Tar headers are 512-byte blocks in size
            {
                bytes = nextData(input, output, callback, Header.length);

                if (Header.all_zeroes(bytes))
                {
                    // Tars end with an End-Of-Archive marker, which is two consecutive 512-byte blocks of zero bytes
                    throw new EndOfArchive();
                }
            }

            return new Header(bytes);
        }

        private byte[] nextData(Stream input, Stream output, verifyCallback callback, uint size)
        {
            // Returns the next given number of bytes from the input
            byte[] bytes = IO.unmarshal_n(input, size);
            callback?.Invoke(size);
            if (output != null) output.Write(bytes, 0, bytes.Length);
            return bytes;
        }

        public void verify(Stream input, Stream output, cancellingCallback cancelling, verifyCallback callback)
        {
            Hashtable recomputed_checksums = new Hashtable();
            Hashtable original_checksums = null;

            try
            {
                while (!cancelling())
                {
                    Header header_data = nextHeader(input, output, callback);
                    debug(header_data.ToString());

                    byte[] bytes_data = nextData(input, output, callback, header_data.file_size);

                    if (header_data.file_name.Equals("ova.xml"))
                    {
                        debug("Skipping ova.xml");
                    }
                    else if (header_data.file_name.EndsWith("checksum.xml"))
                    {
                        string xml = string_of_byte_array(bytes_data);
                        original_checksums = parse_checksum_table(xml);
                    }
                    else
                    {
                        // The file has no extension (must be a data file) so will have a .checksum or .xxhash file right after it
                        Header header_checksum = nextHeader(input, output, callback);
                        byte[] bytes_checksum = nextData(input, output, callback, header_checksum.file_size);
                        string csum_compare = string_of_byte_array(bytes_checksum);

                        string csum = header_checksum.file_name.EndsWith(".xxhash") ? checksum_xxhash(bytes_data) : checksum_sha1(bytes_data);

                        if (!csum.Equals(csum_compare))
                            throw new BlockChecksumFailed(header_data.file_name, csum, csum_compare);

                        debug(String.Format(" has checksum: {0}", csum));
                        recomputed_checksums.Add(header_data.file_name, csum);

                        nextData(input, output, callback, header_checksum.paddingLength()); // Eat the padding for the checksum file
                    }

                    nextData(input, output, callback, header_data.paddingLength()); // Eat the padding for the data file
                }
            }
            catch (EndOfArchive)
            {
                debug("EOF");
                if (original_checksums != null)
                    compare_tables(recomputed_checksums, original_checksums);
            }
        }
    }
}