using System.Data;
using System.Security.Cryptography;
using System.Text;
using ProtoBuf.Data;
using ZstdSharp;

namespace DbExporter;

public sealed class Verifier
{
    public record VerifyResult(int RowCount, List<ColumnInfo> Schema, string? ComputedHash, string? ExpectedHash, bool? HashMatch);
    public record ColumnInfo(string Name, Type Type);

    public VerifyResult Verify(string filePath, bool computeHash = false)
    {
        using var inputFile = new FileStream(filePath, FileMode.Open, FileAccess.Read, FileShare.Read, 256 * 1024);
        using var decompressStream = new DecompressionStream(inputFile);

        Stream readStream = decompressStream;
        SHA256? sha256 = null;
        CryptoStream? hashStream = null;

        if (computeHash)
        {
            sha256 = SHA256.Create();
            hashStream = new CryptoStream(decompressStream, sha256, CryptoStreamMode.Read);
            readStream = hashStream;
        }

        using var reader = DataSerializer.Deserialize(readStream);

        // Extract schema
        var schema = new List<ColumnInfo>();
        for (int i = 0; i < reader.FieldCount; i++)
        {
            schema.Add(new ColumnInfo(reader.GetName(i), reader.GetFieldType(i)));
        }

        // Count rows
        int rowCount = 0;
        while (reader.Read())
        {
            rowCount++;
        }

        string? computedHashStr = null;
        string? expectedHash = null;
        bool? hashMatch = null;

        if (computeHash && sha256 != null)
        {
            hashStream?.Dispose();
            computedHashStr = Convert.ToHexString(sha256.Hash!).ToLowerInvariant();

            // Read expected hash from sidecar
            var hashFilePath = filePath + ".sha256";
            if (File.Exists(hashFilePath))
            {
                expectedHash = File.ReadAllText(hashFilePath).Trim().ToLowerInvariant();
                hashMatch = computedHashStr == expectedHash;
            }

            sha256.Dispose();
        }

        return new VerifyResult(rowCount, schema, computedHashStr, expectedHash, hashMatch);
    }

    public string FormatSchema(List<ColumnInfo> schema)
    {
        var sb = new StringBuilder();
        foreach (var col in schema)
        {
            if (sb.Length > 0) sb.Append(", ");
            sb.Append($"{col.Name} ({col.Type.Name})");
        }
        return sb.ToString();
    }
}