package com.cloudhandson.vpdbackoffice.service;

import com.cloudhandson.vpdbackoffice.domain.structured.StructuredDataPreview;
import com.cloudhandson.vpdbackoffice.domain.structured.StructuredDataTable;
import java.util.List;
import java.util.Map;
import org.springframework.dao.DataAccessException;
import org.springframework.jdbc.core.JdbcTemplate;
import org.springframework.stereotype.Service;

@Service
public class StructuredDataService {

  private static final int ROW_LIMIT = 50;

  private final JdbcTemplate jdbcTemplate;
  private final DataCatalog catalog;

  public StructuredDataService(
      JdbcTemplate jdbcTemplate,
      DataCatalog catalog
  ) {
    this.jdbcTemplate = jdbcTemplate;
    this.catalog = catalog;
  }

  public DataCatalog catalog() {
    return catalog;
  }

  public String owner() {
    return catalog.owner();
  }

  public List<StructuredDataTable> tables() {
    return catalog.objects();
  }

  public String defaultKey() {
    return catalog.objects().getFirst().key();
  }

  public StructuredDataTable requireTable(String key) {
    return catalog.require(key);
  }

  public StructuredDataPreview preview(String key) {
    StructuredDataTable table = requireTable(key);
    try {
      List<String> columns = jdbcTemplate.query(
          """
              SELECT column_name
              FROM all_tab_columns
              WHERE owner = ?
                AND table_name = ?
              ORDER BY column_id
          """,
          (resultSet, rowNum) -> resultSet.getString(1), catalog.owner(), table.tableName());
      if (columns.isEmpty()) {
        throw new AppException("정형 데이터 테이블의 컬럼 정보를 찾을 수 없습니다.");
      }
      List<String> previewColumns =
          table.previewColumns().isEmpty() ? columns : table.previewColumns();
      if (!columns.containsAll(previewColumns)) {
        throw new AppException("환경 카탈로그의 미리보기 컬럼이 실제 객체와 일치하지 않습니다.");
      }
      List<Map<String, Object>> rows = jdbcTemplate.queryForList(
          previewSql(table, previewColumns), ROW_LIMIT);
      return new StructuredDataPreview(table, previewColumns, rows, ROW_LIMIT);
    } catch (DataAccessException exception) {
      throw new AppException("정형 데이터를 조회할 수 없습니다. " + catalog.owner()
          + " 조회 권한과 대상 객체 상태를 확인하세요.");
    }
  }

  /**
   * The table is selected from a closed application whitelist, so the query
   * text remains fixed and no request value can become a SQL identifier.
   */
  String previewSql(StructuredDataTable table) {
    return previewSql(table, table.previewColumns());
  }

  private String previewSql(
      StructuredDataTable table,
      List<String> previewColumns
  ) {
    StructuredDataTable approved = requireTable(table.key());
    if (!approved.tableName().equals(table.tableName())) {
      throw new AppException("선택할 수 없는 카탈로그 객체입니다.");
    }
    String projection = previewColumns == null || previewColumns.isEmpty()
        ? "*"
        : previewColumns.stream()
            .map(column -> "\"" + column + "\"")
            .reduce((left, right) -> left + ", " + right)
            .orElseThrow();
    return "SELECT " + projection + " FROM \"" + catalog.owner() + "\".\"" + approved.tableName()
        + "\" WHERE ROWNUM <= ?";
  }
}