'use strict';

// ─── Error ────────────────────────────────────────────────────────────────────

export class QueryBuilderError extends Error {
  operation: string | null;
  dialect: string | null;

  constructor(
    message: string,
    { operation = null, dialect = null }: { operation?: string | null; dialect?: string | null } = {}
  ) {
    super(message);
    this.name = 'QueryBuilderError';
    this.operation = operation;
    this.dialect = dialect;
  }
}

// ─── Constants ────────────────────────────────────────────────────────────────

const OPERATORS: Record<string, string> = {
  eq: '=',
  neq: '!=',
  gt: '>',
  gte: '>=',
  lt: '<',
  lte: '<=',
  like: 'LIKE',
  ilike: 'ILIKE', // PostgreSQL native; falls back to LIKE on other dialects
  in: 'IN',
  not_in: 'NOT IN',
  between: 'BETWEEN',
};

const AGGREGATE_FNS = new Set(['sum', 'count', 'avg', 'min', 'max', 'count_distinct']);

const VALID_ORDER_DIRECTIONS = new Set(['ASC', 'DESC']);

// ─── Dialects ─────────────────────────────────────────────────────────────────

abstract class BaseDialect {
  abstract quote(id: string): string;
  limitOffset(_limit: number | string | null | undefined, _offset: number | string | null | undefined): string {
    return '';
  }
  supportsIlike(): boolean {
    return false;
  }
}

class PostgreSQLDialect extends BaseDialect {
  get name() {
    return 'postgresql';
  }
  quote(id: string): string {
    return `"${String(id).replace(/"/g, '""')}"`;
  }
  supportsIlike(): boolean {
    return true;
  }
  limitOffset(limit: number | string | null | undefined, offset: number | string | null | undefined): string {
    let s = '';
    if (limit != null) s += ` LIMIT ${toPositiveInt(limit)}`;
    if (offset != null) s += ` OFFSET ${toPositiveInt(offset)}`;
    return s;
  }
}

class MySQLDialect extends BaseDialect {
  get name() {
    return 'mysql';
  }
  quote(id: string): string {
    return `\`${String(id).replace(/`/g, '``')}\``;
  }
  limitOffset(limit: number | string | null | undefined, offset: number | string | null | undefined): string {
    if (limit == null) return '';
    let s = ` LIMIT ${toPositiveInt(limit)}`;
    if (offset != null) s += ` OFFSET ${toPositiveInt(offset)}`;
    return s;
  }
}

class MSSQLDialect extends BaseDialect {
  get name() {
    return 'mssql';
  }
  quote(id: string): string {
    return `[${String(id).replace(/\]/g, ']]')}]`;
  }
  /**
   * MSSQL OFFSET/FETCH – requires ORDER BY in the surrounding query.
   * Call only when offset is set; TOP handles the limit-only case.
   */
  limitOffset(limit: number | string | null | undefined, offset: number | string | null | undefined): string {
    if (offset == null) return '';
    const offsetPart = ` OFFSET ${toPositiveInt(offset)} ROWS`;
    if (limit != null) return `${offsetPart} FETCH NEXT ${toPositiveInt(limit)} ROWS ONLY`;
    return offsetPart;
  }
}

// ─── Helpers ──────────────────────────────────────────────────────────────────

function toPositiveInt(value: number | string): number {
  const parsedNumber = parseInt(String(value), 10);
  if (isNaN(parsedNumber) || parsedNumber < 0) {
    throw new QueryBuilderError(`Expected a non-negative integer, got: "${value}"`);
  }
  return parsedNumber;
}

function getDialect(name: string): BaseDialect {
  switch (String(name).toLowerCase()) {
    case 'postgresql':
    case 'postgres':
      return new PostgreSQLDialect();
    case 'mysql':
      return new MySQLDialect();
    case 'mssql':
    case 'sqlserver':
      return new MSSQLDialect();
    default:
      throw new QueryBuilderError(`Unsupported dialect: "${name}"`);
  }
}

// ─── Types ────────────────────────────────────────────────────────────────────

interface WhereFilter {
  column: string;
  operator: string;
  value?: unknown;
}

interface OrderFilter {
  column: string;
  order?: string;
}

interface AggregateEntry {
  aggFx: string;
  column: string;
  table_id?: string;
}

interface CreateRowEntry {
  column: string;
  value?: unknown;
}

interface UpdateRowEntry {
  column: string;
  value?: unknown;
}

interface ListRowsInput {
  schema?: string;
  aggregates?: Record<string, AggregateEntry>;
  group_by?: Record<string, string[]>;
  where_filters?: Record<string, WhereFilter>;
  order_filters?: Record<string, OrderFilter>;
  limit?: string | number;
  offset?: string | number;
  fields?: Array<{ name: string; table: string }>;
}

interface DeleteRowsInput {
  schema?: string;
  limit?: string | number;
  where_filters?: Record<string, WhereFilter>;
}

interface UpdateRowsInput {
  schema?: string;
  columns: Record<string, UpdateRowEntry>;
  where_filters?: Record<string, WhereFilter>;
}

interface UpsertRowsInput {
  schema?: string;
  primary_key_columns: string | string[];
  columns: Record<string, UpdateRowEntry>;
}

interface BulkInsertInput {
  schema?: string;
  rows_insert: Record<string, unknown>[];
}

interface BulkUpdateWithPrimaryKeyInput {
  schema?: string;
  primary_key: string | string[];
  rows_update: Record<string, unknown>[];
}

interface BulkUpsertWithPrimaryKeyInput {
  schema?: string;
  primary_key: string | string[];
  row_upsert: Record<string, unknown>[];
}

interface QueryResult {
  query: string;
  params: unknown[];
}

interface BulkQueryResult {
  queries: QueryResult[];
}

// ─── QueryBuilder ─────────────────────────────────────────────────────────────

export class QueryBuilder {
  private _dialect: BaseDialect;
  private _params: unknown[];

  constructor(dialectName = 'postgresql') {
    this._dialect = getDialect(dialectName);
    this._params = [];
  }

  // ── Internal state ──────────────────────────────────────────────────────────

  private _reset(): void {
    this._params = [];
  }

  private _normalizePrimaryKey(primaryKey: string | string[] | undefined | null): string[] {
    if (Array.isArray(primaryKey)) return primaryKey.filter(Boolean);
    if (typeof primaryKey === 'string' && primaryKey.trim()) return [primaryKey.trim()];
    return [];
  }

  private _addParam(value: unknown): string {
    this._params.push(value);
    return '?';
  }

  // Builds a fully-qualified table reference: "schema"."table" or just "table"
  private _buildTableRef(tableName: string, schema?: string | null): string {
    const trimmedSchema = schema && String(schema).trim();
    if (trimmedSchema) {
      return `${this._dialect.quote(trimmedSchema)}.${this._dialect.quote(tableName)}`;
    }
    return this._dialect.quote(tableName);
  }

  // ── WHERE builder ───────────────────────────────────────────────────────────

  private _whereClause(whereFilters: Record<string, WhereFilter> | null | undefined): string {
    if (!whereFilters || Object.keys(whereFilters).length === 0) return '';
    const conditions = Object.values(whereFilters)
      .map((f) => this._condition(f))
      .filter((c): c is string => c !== null);
    if (conditions.length === 0) return '';
    return ` WHERE ${conditions.join(' AND ')}`;
  }

  private _condition({ column, operator, value }: WhereFilter): string | null {
    const hasColumn = !!(column && String(column).trim());
    const hasOperator = !!(operator && String(operator).trim());
    const isValueEmpty = value === undefined || value === null || value === '';

    // Fully empty row — silently skip
    if (!hasColumn && !hasOperator && isValueEmpty) return null;

    if (!hasColumn) throw new QueryBuilderError('A filter condition has a value or operator but no column specified');
    if (!hasOperator) throw new QueryBuilderError(`Filter on column "${column}" is missing an operator`);

    const col = this._dialect.quote(column);

    // 'is' operator: the stored value ('null' | 'not_null') determines the SQL fragment
    if (operator === 'is') {
      if (value === 'null') return `${col} IS NULL`;
      if (value === 'not_null') return `${col} IS NOT NULL`;
      throw new QueryBuilderError(`Unknown value for "is" operator: "${value}". Expected "null" or "not_null".`);
    }

    const sqlOp = OPERATORS[operator];
    if (!sqlOp) throw new QueryBuilderError(`Unknown operator: "${operator}"`);

    const effectiveOp = operator === 'ilike' && !this._dialect.supportsIlike() ? 'LIKE' : sqlOp;

    if (operator === 'in' || operator === 'not_in') {
      const values: unknown[] = Array.isArray(value)
        ? value
        : String(value)
            .split(',')
            .map((v) => v.trim());
      if ((values as unknown[]).length === 0) {
        throw new QueryBuilderError(`"${operator}" requires at least one value`);
      }
      const placeholders = (values as unknown[]).map((v) => this._addParam(v));
      return `${col} ${effectiveOp} (${placeholders.join(', ')})`;
    }

    if (operator === 'between') {
      if (!Array.isArray(value) || (value as unknown[]).length !== 2) {
        throw new QueryBuilderError('"between" requires value to be a 2-element array [from, to]');
      }
      return `${col} ${effectiveOp} ${this._addParam((value as unknown[])[0])} AND ${this._addParam(
        (value as unknown[])[1]
      )}`;
    }

    return `${col} ${effectiveOp} ${this._addParam(value)}`;
  }

  // ── SELECT clause builder ───────────────────────────────────────────────────

  private _selectClause(
    fields: Array<{ name: string; table: string }> | null | undefined,
    aggregates: Record<string, AggregateEntry> | null | undefined
  ): string {
    const parts: string[] = [];

    if (fields && fields.length > 0) {
      parts.push(
        ...fields.map((f) => {
          if (!f.name) throw new QueryBuilderError('fields entry is missing "name"');
          return this._dialect.quote(f.name);
        })
      );
    }

    if (aggregates && Object.keys(aggregates).length > 0) {
      for (const agg of Object.values(aggregates)) {
        const hasAggFx = !!(agg.aggFx && String(agg.aggFx).trim());
        const hasColumn = !!(agg.column && String(agg.column).trim());
        if (!hasAggFx && !hasColumn) continue; // skip fully empty aggregate entry
        if (!hasAggFx) throw new QueryBuilderError(`Aggregate on column "${agg.column}" is missing a function`);
        if (!hasColumn) throw new QueryBuilderError(`Aggregate function "${agg.aggFx}" is missing a column`);
        const fn = String(agg.aggFx).toLowerCase();
        if (!AGGREGATE_FNS.has(fn)) {
          throw new QueryBuilderError(`Unknown aggregate function: "${agg.aggFx}"`);
        }
        const col = this._dialect.quote(agg.column);
        parts.push(fn === 'count_distinct' ? `COUNT(DISTINCT ${col})` : `${fn.toUpperCase()}(${col})`);
      }
    }

    return parts.length > 0 ? parts.join(', ') : '*';
  }

  // ── Operations ──────────────────────────────────────────────────────────────
  createRow(
    tableName: string,
    schema: string | undefined | null,
    columns: Record<string, CreateRowEntry> | undefined | null
  ): QueryResult {
    this._reset();
    this._assertTableName(tableName, 'create_row');

    const table = this._buildTableRef(tableName, schema);

    const entries = Object.values(columns || {}).filter((entry) => {
      const hasColumn = !!(entry.column && String(entry.column).trim());
      const isValueEmpty = entry.value === undefined || entry.value === null || entry.value === '';
      if (!hasColumn && isValueEmpty) return false; // skip fully empty
      if (!hasColumn) throw new QueryBuilderError('A column entry has a value but no column name specified');
      return true;
    });

    if (entries.length === 0) {
      const query = `INSERT INTO ${table} DEFAULT VALUES`;
      return { query, params: [] };
    }

    const cols = entries.map((e) => this._dialect.quote(e.column));
    const placeholders = entries.map((e) => this._addParam(e.value));

    const query = `INSERT INTO ${table} (${cols.join(', ')}) VALUES (${placeholders.join(', ')})`;
    return { query, params: [...this._params] };
  }

  updateRows(tableName: string, updateRows: UpdateRowsInput): QueryResult {
    this._reset();
    this._assertTableName(tableName, 'update_rows');

    const { schema, columns, where_filters } = updateRows;

    const validColumnEntries = Object.values(columns || {}).filter((col) => {
      const hasColumn = !!(col.column && String(col.column).trim());
      const isValueEmpty = col.value === undefined || col.value === null || col.value === '';
      if (!hasColumn && isValueEmpty) return false; // skip fully empty
      if (!hasColumn) throw new QueryBuilderError('An update entry has a value but no column name specified');
      return true;
    });

    if (validColumnEntries.length === 0) {
      throw new QueryBuilderError('At least one column to update is required');
    }

    const setClauses = validColumnEntries.map(
      (col) => `${this._dialect.quote(col.column)} = ${this._addParam(col.value)}`
    );

    const table = this._buildTableRef(tableName, schema);
    let query = `UPDATE ${table} SET ${setClauses.join(', ')}`;
    query += this._whereClause(where_filters);

    return { query, params: [...this._params] };
  }

  upsertRows(tableName: string, upsertRowsData: UpsertRowsInput): QueryResult {
    this._reset();
    this._assertTableName(tableName, 'upsert_rows');

    const { schema, primary_key_columns: rawPrimaryKeyColumns, columns } = upsertRowsData;
    const primary_key_columns = this._normalizePrimaryKey(rawPrimaryKeyColumns);

    if (primary_key_columns.length === 0) {
      throw new QueryBuilderError('At least one primary key column is required for upsert');
    }

    const columnEntries = Object.values(columns || {}).filter((entry) => {
      const hasColumn = !!(entry.column && String(entry.column).trim());
      const isValueEmpty = entry.value === undefined || entry.value === null || entry.value === '';
      if (!hasColumn && isValueEmpty) return false; // skip fully empty
      if (!hasColumn) throw new QueryBuilderError('An upsert entry has a value but no column name specified');
      return true;
    });

    if (columnEntries.length === 0) {
      throw new QueryBuilderError('At least one column is required for upsert');
    }

    const primaryKeySet = new Set(primary_key_columns);
    const allColumnNames = columnEntries.map((entry) => entry.column);
    const updateColumnNames = allColumnNames.filter((col) => !primaryKeySet.has(col));
    const row = Object.fromEntries(columnEntries.map((entry) => [entry.column, entry.value]));
    const table = this._buildTableRef(tableName, schema);

    if (this._dialect instanceof PostgreSQLDialect) {
      return this._pgUpsert(table, primary_key_columns, allColumnNames, updateColumnNames, row);
    } else if (this._dialect instanceof MySQLDialect) {
      return this._mysqlUpsert(table, primary_key_columns, allColumnNames, updateColumnNames, row);
    } else {
      return this._mssqlUpsert(table, primary_key_columns, allColumnNames, updateColumnNames, row);
    }
  }

  deleteRows(tableName: string, deleteRows: DeleteRowsInput): QueryResult {
    this._reset();
    this._assertTableName(tableName, 'delete_rows');

    const { schema, limit: rawLimit, where_filters } = deleteRows;
    const limitStr = rawLimit == null ? '' : String(rawLimit).trim();
    const limit = limitStr === '' ? undefined : limitStr;
    const table = this._buildTableRef(tableName, schema);
    let query: string;

    if (this._dialect instanceof MySQLDialect) {
      query = `DELETE FROM ${table}`;
      query += this._whereClause(where_filters);
      if (limit != null) query += ` LIMIT ${toPositiveInt(limit)}`;
    } else if (this._dialect instanceof MSSQLDialect) {
      const top = limit != null ? `TOP(${toPositiveInt(limit)}) ` : '';
      query = `DELETE ${top}FROM ${table}`;
      query += this._whereClause(where_filters);
    } else {
      // PostgreSQL – use ctid subquery to honour a LIMIT
      if (limit != null) {
        const innerWhere = this._whereClause(where_filters);
        query = `DELETE FROM ${table} WHERE ctid IN (SELECT ctid FROM ${table}${innerWhere} LIMIT ${toPositiveInt(
          limit
        )})`;
      } else {
        query = `DELETE FROM ${table}`;
        query += this._whereClause(where_filters);
      }
    }

    return { query, params: [...this._params] };
  }

  listRows(tableName: string, listRows: ListRowsInput = {}): QueryResult {
    this._reset();
    this._assertTableName(tableName, 'list_rows');

    const {
      schema,
      aggregates,
      group_by,
      where_filters,
      order_filters,
      limit: rawLimit,
      offset: rawOffset,
      fields,
    } = listRows;
    const limitStr = rawLimit == null ? '' : String(rawLimit).trim();
    const limit = limitStr === '' ? undefined : limitStr;
    const offsetStr = rawOffset == null ? '' : String(rawOffset).trim();
    const offset = offsetStr === '' ? undefined : offsetStr;
    const table = this._buildTableRef(tableName, schema);

    const selectExpr = this._selectClause(fields, aggregates);

    let topClause = '';
    if (this._dialect instanceof MSSQLDialect && limit != null && offset == null) {
      topClause = `TOP ${toPositiveInt(limit)} `;
    }

    let query = `SELECT ${topClause}${selectExpr} FROM ${table}`;

    query += this._whereClause(where_filters);

    if (group_by && Object.keys(group_by).length > 0) {
      const cols = Object.values(group_by)
        .flat()
        .map((c) => this._dialect.quote(c));
      query += ` GROUP BY ${cols.join(', ')}`;
    }

    let hasOrderBy = false;
    if (order_filters && Object.keys(order_filters).length > 0) {
      const orders = Object.values(order_filters)
        .filter((of) => !!(of.column && String(of.column).trim())) // skip empty column entries
        .map((of) => {
          const dir = String(of.order || 'ASC').toUpperCase();
          if (!VALID_ORDER_DIRECTIONS.has(dir)) {
            throw new QueryBuilderError(`Invalid sort direction: "${of.order}". Use "asc" or "desc".`);
          }
          return `${this._dialect.quote(of.column)} ${dir}`;
        });
      if (orders.length > 0) {
        query += ` ORDER BY ${orders.join(', ')}`;
        hasOrderBy = true;
      }
    }

    if (this._dialect instanceof MSSQLDialect) {
      if (offset != null) {
        if (!hasOrderBy) query += ' ORDER BY (SELECT NULL)';
        query += this._dialect.limitOffset(limit, offset);
      }
    } else {
      query += this._dialect.limitOffset(limit, offset);
    }

    return { query, params: [...this._params] };
  }

  bulkInsert(tableName: string, bulkInsert: BulkInsertInput): QueryResult {
    this._reset();
    this._assertTableName(tableName, 'bulk_insert');

    const { schema, rows_insert } = bulkInsert;
    if (!rows_insert || rows_insert.length === 0) {
      throw new QueryBuilderError('Bulk insert requires at least one row', { operation: 'bulk_insert' });
    }

    const allCols = [...new Set(rows_insert.flatMap((row) => Object.keys(row)))];
    if (allCols.length === 0) {
      throw new QueryBuilderError('Bulk insert rows must have at least one column', { operation: 'bulk_insert' });
    }

    const quotedCols = allCols.map((c) => this._dialect.quote(c));
    const valueGroups = rows_insert.map((row) => {
      const placeholders = allCols.map((col) => this._addParam(col in row ? row[col] : null));
      return `(${placeholders.join(', ')})`;
    });

    const table = this._buildTableRef(tableName, schema);
    const query = `INSERT INTO ${table} (${quotedCols.join(', ')}) VALUES ${valueGroups.join(', ')}`;
    return { query, params: [...this._params] };
  }

  bulkUpdateWithPrimaryKey(tableName: string, bulkUpdate: BulkUpdateWithPrimaryKeyInput): BulkQueryResult {
    this._assertTableName(tableName, 'bulk_update_with_primary_key');

    const { schema, primary_key: rawPrimaryKey, rows_update } = bulkUpdate;
    const primary_key = this._normalizePrimaryKey(rawPrimaryKey);
    if (primary_key.length === 0) {
      throw new QueryBuilderError('Bulk update requires at least one primary key column', {
        operation: 'bulk_update_with_primary_key',
      });
    }
    if (!rows_update || rows_update.length === 0) {
      throw new QueryBuilderError('Bulk update requires at least one row', {
        operation: 'bulk_update_with_primary_key',
      });
    }

    const primaryKeySet = new Set(primary_key);
    const table = this._buildTableRef(tableName, schema);

    const queries = rows_update.map((row, rowIndex) => {
      this._reset();

      for (const primaryKey of primary_key) {
        if (!(primaryKey in row)) {
          throw new QueryBuilderError(`Row ${rowIndex + 1} is missing primary key column "${primaryKey}"`, {
            operation: 'bulk_update_with_primary_key',
          });
        }
      }

      const updateCols = Object.keys(row).filter((col) => !primaryKeySet.has(col));
      if (updateCols.length === 0) {
        throw new QueryBuilderError(`Row ${rowIndex + 1} has no columns to update (only primary key columns present)`, {
          operation: 'bulk_update_with_primary_key',
        });
      }

      const setClauses = updateCols.map((col) => `${this._dialect.quote(col)} = ${this._addParam(row[col])}`);
      const whereClauses = primary_key.map((pk) => `${this._dialect.quote(pk)} = ${this._addParam(row[pk])}`);

      const query = `UPDATE ${table} SET ${setClauses.join(', ')} WHERE ${whereClauses.join(' AND ')}`;
      return { query, params: [...this._params] };
    });

    return { queries };
  }

  bulkUpsertWithPrimaryKey(tableName: string, bulkUpsert: BulkUpsertWithPrimaryKeyInput): BulkQueryResult {
    this._assertTableName(tableName, 'bulk_upsert_with_primary_key');

    const { schema, primary_key: rawPrimaryKey, row_upsert } = bulkUpsert;
    const primary_key = this._normalizePrimaryKey(rawPrimaryKey);
    if (primary_key.length === 0) {
      throw new QueryBuilderError('Bulk upsert requires at least one primary key column', {
        operation: 'bulk_upsert_with_primary_key',
      });
    }
    if (!row_upsert || row_upsert.length === 0) {
      throw new QueryBuilderError('Bulk upsert requires at least one row', {
        operation: 'bulk_upsert_with_primary_key',
      });
    }

    const primaryKeySet = new Set(primary_key);
    const table = this._buildTableRef(tableName, schema);

    const queries = row_upsert.map((row, rowIndex) => {
      this._reset();

      for (const primaryKey of primary_key) {
        if (!(primaryKey in row)) {
          throw new QueryBuilderError(`Row ${rowIndex + 1} is missing primary key column "${primaryKey}"`, {
            operation: 'bulk_upsert_with_primary_key',
          });
        }
      }

      const allCols = Object.keys(row);
      const updateCols = allCols.filter((col) => !primaryKeySet.has(col));

      if (this._dialect instanceof PostgreSQLDialect) {
        return this._pgUpsert(table, primary_key, allCols, updateCols, row);
      } else if (this._dialect instanceof MySQLDialect) {
        return this._mysqlUpsert(table, primary_key, allCols, updateCols, row);
      } else {
        return this._mssqlUpsert(table, primary_key, allCols, updateCols, row);
      }
    });

    return { queries };
  }

  // ── Dialect-specific upsert helpers ─────────────────────────────────────────

  private _pgUpsert(
    table: string,
    primaryKey: string[],
    allCols: string[],
    updateCols: string[],
    row: Record<string, unknown>
  ): QueryResult {
    const quotedCols = allCols.map((c) => this._dialect.quote(c));
    const placeholders = allCols.map((col) => this._addParam(row[col]));
    const conflictTarget = primaryKey.map((pk) => this._dialect.quote(pk)).join(', ');

    let query = `INSERT INTO ${table} (${quotedCols.join(', ')}) VALUES (${placeholders.join(', ')})`;
    query += ` ON CONFLICT (${conflictTarget})`;
    query +=
      updateCols.length === 0
        ? ' DO NOTHING'
        : ` DO UPDATE SET ${updateCols
            .map((col) => `${this._dialect.quote(col)} = EXCLUDED.${this._dialect.quote(col)}`)
            .join(', ')}`;

    return { query, params: [...this._params] };
  }

  private _mysqlUpsert(
    table: string,
    primaryKey: string[],
    allCols: string[],
    updateCols: string[],
    row: Record<string, unknown>
  ): QueryResult {
    const quotedCols = allCols.map((c) => this._dialect.quote(c));
    const placeholders = allCols.map((col) => this._addParam(row[col]));

    let query = `INSERT INTO ${table} (${quotedCols.join(', ')}) VALUES (${placeholders.join(', ')})`;

    const setCols = updateCols.length > 0 ? updateCols : [primaryKey[0]];
    const setClauses = setCols.map((col) => `${this._dialect.quote(col)} = VALUES(${this._dialect.quote(col)})`);
    query += ` ON DUPLICATE KEY UPDATE ${setClauses.join(', ')}`;

    return { query, params: [...this._params] };
  }

  private _mssqlUpsert(
    table: string,
    primaryKey: string[],
    allCols: string[],
    updateCols: string[],
    row: Record<string, unknown>
  ): QueryResult {
    const quotedCols = allCols.map((c) => this._dialect.quote(c));
    const placeholders = allCols.map((col) => this._addParam(row[col]));
    const onClause = primaryKey
      .map((pk) => `[_target].${this._dialect.quote(pk)} = [_source].${this._dialect.quote(pk)}`)
      .join(' AND ');

    let query = `MERGE INTO ${table} WITH (HOLDLOCK) AS [_target]`;
    query += ` USING (VALUES (${placeholders.join(', ')})) AS [_source] (${quotedCols.join(', ')})`;
    query += ` ON ${onClause}`;

    if (updateCols.length > 0) {
      const setClauses = updateCols.map(
        (col) => `[_target].${this._dialect.quote(col)} = [_source].${this._dialect.quote(col)}`
      );
      query += ` WHEN MATCHED THEN UPDATE SET ${setClauses.join(', ')}`;
    }

    const insertValues = allCols.map((c) => `[_source].${this._dialect.quote(c)}`).join(', ');
    query += ` WHEN NOT MATCHED THEN INSERT (${quotedCols.join(', ')}) VALUES (${insertValues});`;

    return { query, params: [...this._params] };
  }

  // ── Unified entry point ─────────────────────────────────────────────────────

  build(operation: string, tableName: string, data: Record<string, unknown>): QueryResult | BulkQueryResult {
    switch (String(operation).toLowerCase()) {
      case 'create_row':
        return this.createRow(tableName, data.schema as string | undefined, data as Record<string, CreateRowEntry>);
      case 'update_rows':
        return this.updateRows(tableName, data as unknown as UpdateRowsInput);
      case 'upsert_rows':
        return this.upsertRows(tableName, data as unknown as UpsertRowsInput);
      case 'delete_rows':
        return this.deleteRows(tableName, data as DeleteRowsInput);
      case 'list_rows':
        return this.listRows(tableName, data as ListRowsInput);
      case 'bulk_insert':
        return this.bulkInsert(tableName, data as unknown as BulkInsertInput);
      case 'bulk_update_with_primary_key':
        return this.bulkUpdateWithPrimaryKey(tableName, data as unknown as BulkUpdateWithPrimaryKeyInput);
      case 'bulk_upsert_with_primary_key':
        return this.bulkUpsertWithPrimaryKey(tableName, data as unknown as BulkUpsertWithPrimaryKeyInput);
      default:
        throw new QueryBuilderError(`Unsupported operation: "${operation}"`, { operation });
    }
  }

  // ── Validation ──────────────────────────────────────────────────────────────

  private _assertTableName(tableName: string, operation: string): void {
    if (!tableName || typeof tableName !== 'string' || !tableName.trim()) {
      throw new QueryBuilderError('table_name is required and must be a non-empty string', { operation });
    }
  }
}

// ─── Factory ──────────────────────────────────────────────────────────────────

export function createQueryBuilder(dialect = 'postgresql'): QueryBuilder {
  return new QueryBuilder(dialect);
}