using System;
using System.Collections.Generic;

namespace GB5Shared.ListQuery
{
    // ─────────────────────────────────────────────────────────────────────
    //  QueryContext  – carries the alias map and optional schema map for
    //  one specific query.
    //
    //  Problem it solves:
    //    Legacy SqlClauses methods hardcoded table aliases as magic strings
    //    ("a.", "b.", "e."), so changing an alias broke every clause method.
    //    QueryContext makes aliases declarative: each query builder registers
    //    its own alias map, and all clause methods use ctx.Col() to qualify
    //    columns — no "a." floating in the clause library.
    //
    //  Schema support:
    //    Existing tables are unqualified (dbo, default schema). New tables
    //    in module-specific schemas (e.g. "mm") are registered with a schema.
    //    ctx.Table() emits "mm.tmtrrecord" for schema-qualified tables and
    //    just "tallocation" for unqualified ones — zero impact on existing QB files.
    //
    //  Usage:
    //      var ctx = new QueryContext(dialect)
    //          .Register("allocation", "a")               // unqualified table
    //          .Register("mtrrecord",  "r", schema:"mm"); // schema-qualified
    //
    //      ctx.Col("allocation", "ALLOCATIONID")  → "a.ALLOCATIONID"
    //      ctx.Table("mtrrecord", "tmtrrecord")   → "mm.tmtrrecord"
    //      ctx.Table("allocation", "tallocation") → "tallocation"
    // ─────────────────────────────────────────────────────────────────────
    public sealed class QueryContext
    {
        private readonly Dictionary<string, string> _aliases =
            new(StringComparer.OrdinalIgnoreCase);

        private readonly Dictionary<string, string> _schemas =
            new(StringComparer.OrdinalIgnoreCase);

        /// <summary>The SQL dialect active for this query.</summary>
        public ISqlDialect Dialect { get; }

        public QueryContext(ISqlDialect dialect) => Dialect = dialect;

        // ── Registration ─────────────────────────────────────────────────

        /// <summary>
        /// Registers a logical table name with its SQL alias and optional schema.
        /// </summary>
        /// <param name="logicalName">Logical name used in builder code (e.g. "allocation").</param>
        /// <param name="alias">SQL alias used in the query (e.g. "a").</param>
        /// <param name="schema">
        ///   Optional DB schema (e.g. "mm"). When empty the table is referenced without
        ///   a schema prefix — matching the existing GB5 convention for dbo tables.
        /// </param>
        public QueryContext Register(string logicalName, string alias, string schema = "")
        {
            _aliases[logicalName] = alias;
            if (!string.IsNullOrEmpty(schema))
                _schemas[logicalName] = schema;
            return this;
        }

        // ── Column qualification ──────────────────────────────────────────

        /// <summary>
        /// Returns "alias.column" for the given logical table and column name.
        /// Example: ctx.Col("allocation", "ALLOCATIONID") → "a.ALLOCATIONID"
        /// </summary>
        public string Col(string logicalTable, string column) =>
            $"{Alias(logicalTable)}.{column}";

        /// <summary>
        /// Returns just the alias for the logical table name.
        /// Falls back to the logical name itself if not registered (safe for simple queries).
        /// </summary>
        public string Alias(string logicalName) =>
            _aliases.TryGetValue(logicalName, out var alias) ? alias : logicalName;

        // ── Table name (with optional schema) ─────────────────────────────

        /// <summary>
        /// Returns the fully qualified table reference for use in FROM/JOIN clauses.
        /// <list type="bullet">
        ///   <item>When schema is registered: returns "schema.tableName" (e.g. "mm.tmtrrecord")</item>
        ///   <item>When no schema: returns just "tableName" (e.g. "tallocation")</item>
        /// </list>
        /// The alias is NOT appended here — callers write:
        ///   <c>$"FROM {ctx.Table("mtrrecord", "tmtrrecord")} r"</c>
        /// </summary>
        /// <param name="logicalName">Logical name used when registering (e.g. "mtrrecord").</param>
        /// <param name="tableName">Physical table name (e.g. "tmtrrecord").</param>
        public string Table(string logicalName, string tableName)
        {
            if (_schemas.TryGetValue(logicalName, out var schema) && !string.IsNullOrEmpty(schema))
                return $"{schema}.{tableName}";
            return tableName;
        }
    }
}