using System.Data.Common;
using System.Globalization;
using Microsoft.Data.SqlClient;
using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
using ZB.MOM.WW.OtOpcUa.Driver.Sql.Contracts;

namespace ZB.MOM.WW.OtOpcUa.Driver.Sql;

/// <summary>
///     Microsoft SQL Server dialect (design §2.2) — the only provider v1 constructs. Bracket quoting,
///     <c>INFORMATION_SCHEMA</c> catalog SQL, and the design §3.7 type-family map.
///     <para>Stateless and immutable, so a single instance is safely shared by the driver's poll reader and
///     the AdminUI browse session.</para>
/// </summary>
public sealed class SqlServerDialect : ISqlDialect
{
    /// <summary>
    ///     T-SQL's regular-identifier ceiling (<c>sysname</c> = <c>nvarchar(128)</c>). Enforced because a
    ///     longer string cannot name a real catalog object — it is either a config mistake or padding, and
    ///     rejecting it keeps the quoted output bounded.
    /// </summary>
    internal const int MaxIdentifierLength = 128;

    /// <inheritdoc/>
    public SqlProvider Provider => SqlProvider.SqlServer;

    /// <inheritdoc/>
    public DbProviderFactory Factory => SqlClientFactory.Instance;

    /// <inheritdoc/>
    public string LivenessSql => "SELECT 1";

    /// <summary>
    ///     T-SQL limits after the <c>SELECT</c> keyword, so the whole limit lives in the prefix —
    ///     <c>"TOP 1 "</c>, trailing space included so <c>SELECT TOP 1 [col]</c> composes with no extra
    ///     separator at the call site.
    /// </summary>
    public string SingleRowLimitPrefix => "TOP 1 ";

    /// <summary>Empty — T-SQL has no trailing row-limit clause (<c>OFFSET/FETCH</c> is a paging construct, not this).</summary>
    public string SingleRowLimitSuffix => string.Empty;

    /// <inheritdoc/>
    public string ListSchemasSql =>
        "SELECT DISTINCT TABLE_SCHEMA FROM INFORMATION_SCHEMA.TABLES ORDER BY TABLE_SCHEMA";

    /// <summary>
    ///     <c>SCHEMA_NAME()</c> with no argument returns the calling principal's default schema — the one an
    ///     unqualified object name resolves in, which is precisely the question the catalog gate asks.
    /// </summary>
    public string DefaultSchemaSql => "SELECT SCHEMA_NAME()";

    /// <inheritdoc/>
    public string ListTablesSql =>
        "SELECT TABLE_NAME, TABLE_TYPE FROM INFORMATION_SCHEMA.TABLES " +
        "WHERE TABLE_SCHEMA = @schema ORDER BY TABLE_NAME";

    /// <inheritdoc/>
    public string ListColumnsSql =>
        "SELECT COLUMN_NAME, DATA_TYPE, IS_NULLABLE FROM INFORMATION_SCHEMA.COLUMNS " +
        "WHERE TABLE_SCHEMA = @schema AND TABLE_NAME = @table ORDER BY ORDINAL_POSITION";

    /// <summary>
    ///     Brackets one identifier part, doubling any embedded <c>]</c> — the T-SQL escape rule, and the only
    ///     metacharacter that could terminate a bracketed identifier early. <c>[</c>, quotes, semicolons and
    ///     comment markers are inert inside brackets and are therefore passed through unchanged.
    /// </summary>
    /// <remarks>
    ///     <para><b>Rejects</b> (all as <see cref="ArgumentException"/>): null / empty / all-whitespace; longer
    ///     than <see cref="MaxIdentifierLength"/>; any control character (which covers embedded NUL, and the
    ///     C0/C1 ranges that can truncate or corrupt a logged/audited statement); and any Unicode
    ///     <see cref="System.Globalization.UnicodeCategory.Format"/> character — bidi overrides, zero-width
    ///     spaces, soft hyphen, BOM. Those last cannot escape the brackets, but they spoof the <em>rendered</em>
    ///     text of a log line or an AdminUI label while comparing byte-different from the real catalog name
    ///     (the Trojan-Source class, CVE-2021-42574) — the same log/audit-integrity concern that motivates the
    ///     control-character rule.</para>
    ///     <para>The rejection messages deliberately do <b>not</b> echo the offending value — it is untrusted
    ///     input and this exception's text reaches the driver log.</para>
    ///     <para><b>This is a backstop, not the only defence.</b> Design §8.1's catalog gate
    ///     (<see cref="SqlCatalogGate"/>) resolves an authored table/column against the live catalog at
    ///     Initialize and substitutes the catalog's own spelling, so on the poll path the value arriving here
    ///     is a string read back out of the catalog. The rules below still run — the gate uses them as its own
    ///     charset filter, and they must hold for any future caller that has no catalog to check against.</para>
    /// </remarks>
    /// <param name="ident">The bare, unquoted identifier part.</param>
    /// <returns>The bracket-quoted identifier.</returns>
    /// <exception cref="ArgumentException">The value cannot be a valid SQL Server identifier.</exception>
    public string QuoteIdentifier(string ident)
    {
        if (string.IsNullOrWhiteSpace(ident))
            throw new ArgumentException(
                "A SQL identifier must be a non-empty, non-whitespace name.", nameof(ident));

        if (ident.Length > MaxIdentifierLength)
            throw new ArgumentException(
                $"A SQL Server identifier may not exceed {MaxIdentifierLength} characters (got {ident.Length}).",
                nameof(ident));

        foreach (var ch in ident)
        {
            if (char.IsControl(ch))
                throw new ArgumentException(
                    "A SQL identifier may not contain control characters (including NUL).", nameof(ident));

            // Cf is a *separate* category from Cc, so char.IsControl misses every bidi override and
            // zero-width character. They are inert inside brackets but spoof rendered log/UI text.
            if (CharUnicodeInfo.GetUnicodeCategory(ch) == UnicodeCategory.Format)
                throw new ArgumentException(
                    "A SQL identifier may not contain Unicode format characters "
                    + "(bidi overrides, zero-width spaces, soft hyphen, BOM).", nameof(ident));
        }

        return string.Concat("[", ident.Replace("]", "]]", StringComparison.Ordinal), "]");
    }

    /// <summary>
    ///     Folds an <c>INFORMATION_SCHEMA.COLUMNS.DATA_TYPE</c> family name onto a
    ///     <see cref="DriverDataType"/> per design §3.7.
    /// </summary>
    /// <remarks>
    ///     <para><b>Precision caveat:</b> <c>decimal</c> / <c>numeric</c> / <c>money</c> / <c>smallmoney</c>
    ///     collapse to <see cref="DriverDataType.Float64"/> in v1. A .NET <c>decimal</c> carries more
    ///     significant digits than a <c>double</c>, so a high-precision column (e.g. <c>decimal(38,10)</c>)
    ///     loses low-order digits. Authoring an explicit <c>"type": "String"</c> on the tag preserves the exact
    ///     textual value when that matters.</para>
    ///     <para><b>Fallback:</b> an unrecognised family maps to <see cref="DriverDataType.String"/> and never
    ///     throws — a schema browse must render a table containing an exotic column (<c>xml</c>,
    ///     <c>geography</c>, <c>hierarchyid</c>, <c>sql_variant</c>, a CLR UDT, <c>varbinary</c>) rather than
    ///     crash on it. Null/blank input takes the same fallback.</para>
    ///     <para><b>Deliberate non-mappings:</b> SQL Server's <c>timestamp</c>/<c>rowversion</c> is an opaque
    ///     8-byte row version, <em>not</em> a date — it falls back to <see cref="DriverDataType.String"/>
    ///     rather than being mistaken for a <see cref="DriverDataType.DateTime"/>. <c>time</c> is a
    ///     time-of-day span, likewise not a point in time, and takes the same fallback.</para>
    ///     <para><c>tinyint</c> widens to <see cref="DriverDataType.Int16"/> (it is unsigned 0–255 in T-SQL, so
    ///     a signed 8-bit type would not hold it, and the driver type set has no <c>Byte</c>).</para>
    /// </remarks>
    /// <param name="sqlDataType">The bare SQL type family name; matched case-insensitively.</param>
    /// <returns>The mapped driver data type, or <see cref="DriverDataType.String"/> when unrecognised.</returns>
    public DriverDataType MapColumnType(string sqlDataType)
    {
        if (string.IsNullOrWhiteSpace(sqlDataType)) return DriverDataType.String;

        return sqlDataType.Trim().ToLowerInvariant() switch
        {
            "bit" or "boolean" => DriverDataType.Boolean,
            "tinyint" or "smallint" => DriverDataType.Int16,
            "int" or "integer" => DriverDataType.Int32,
            "bigint" => DriverDataType.Int64,
            "real" => DriverDataType.Float32,
            "float" or "double" or "double precision"
                or "decimal" or "numeric" or "money" or "smallmoney" => DriverDataType.Float64,
            "char" or "nchar" or "varchar" or "nvarchar" or "text" or "ntext"
                or "uniqueidentifier" => DriverDataType.String,
            "date" or "datetime" or "datetime2" or "smalldatetime"
                or "datetimeoffset" => DriverDataType.DateTime,
            _ => DriverDataType.String,
        };
    }
}
