src/modules/data.js

// @flow
import {deepEqual} from 'fast-equals';
import {produce} from 'immer';
 
import department from '../resources/Department.json';
import doctor from '../resources/Doctor.json';
import patient from '../resources/Patient.json';
 
export const CHANGE_EXPR = 'CHANGE_EXPR';
export const RESET_EXPR = 'RESET_EXPR';
 
type ChangeAction = {
  type: 'CHANGE_EXPR',
  expr: {[string]: any},
  element: ?HTMLElement,
};
 
type ResetAction = {
  type: 'RESET_EXPR',
};
 
type Action = ChangeAction | ResetAction;
 
type Output = {
  name: string,
  columns: Array<string>,
  data: Array<{[string]: any}>,
};
 
/**
 * @param expr - a relational algebra expression object
 * @param element
 * @return a new CHANGE_EXPR action
 */
export function changeExpr(
  expr: {[string]: any},
  element: ?HTMLElement
): ChangeAction {
  return {type: CHANGE_EXPR, expr, element};
}
 
export function resetAction(): ResetAction {
  return {type: RESET_EXPR};
}
 
export type Data = {
  name: string,
  columns: Array<string>,
  data: Array<{[string]: any}>,
};
 
export type State = {
  current?: Data,
  sourceData: {[string]: Data},
  element: ?HTMLElement,
  expr: {[string]: any},
};
 
// Source data which can be used in SQL queries
export const initialState = {
  sourceData: {
    Department: department,
    Doctor: doctor,
    Patient: patient,
  },
  element: undefined,
  expr: {},
};
 
function getCombinedColumns(left: {[string]: any}, right: {[string]: any}) {
  // Combine columns adding relation name where needed
  const combinedColumns: Array<string> = [];
  for (const leftColumn of left.columns) {
    if (right.columns.includes(leftColumn)) {
      combinedColumns.push(left.name + '.' + leftColumn);
    } else {
      combinedColumns.push(leftColumn);
    }
  }
  for (const rightColumn of right.columns) {
    if (left.columns.includes(rightColumn)) {
      combinedColumns.push(right.name + '.' + rightColumn);
    } else {
      combinedColumns.push(rightColumn);
    }
  }
 
  return combinedColumns;
}
 
function getCombinedData(
  leftName: string,
  leftRow: {[string]: any},
  rightName: string,
  rightRow: {[string]: any},
  combinedColumns: Array<string>,
  outerJoin: ?boolean
): {[string]: any} {
  // Combine data from the two objects including the relation name
  const combinedData: {[string]: any} = {};
  for (const leftKey in leftRow) {
    combinedData[leftName + '.' + leftKey] = leftRow[leftKey];
  }
  for (const rightKey in rightRow) {
    if (outerJoin) {
      combinedData[rightName + '.' + rightKey] = null;
    } else {
      combinedData[rightName + '.' + rightKey] = rightRow[rightKey];
    }
  }
 
  // Resolve the output data according to the combined data
  // This may remove relation names where they are not needed
  const outputData: {[string]: any} = {};
  for (const column of combinedColumns) {
    outputData[column] = combinedData[resolveColumn(column, combinedData)];
  }
 
  return outputData;
}
 
function resolveColumn(path: string, row: {[string]: any}): string {
  // Avoid an error if we're projecting nothing
  if (!row) {
    return path;
  }
 
  const pathParts = path.split('.');
  let [table, maybeColumn]: [?string, ?string] = [pathParts[0], pathParts[1]];
  const column: string = maybeColumn || pathParts[0];
  if (!maybeColumn) {
    table = undefined;
  }
 
  if (table) {
    if (row.hasOwnProperty(path)) {
      // Use the dotted path
      return path;
    } else if (row.hasOwnProperty(column)) {
      // Use the column name without the table qualifier
      return column;
    }
  }
 
  // Check for bare columns first
  const columns = [];
  for (const rowCol in row) {
    if (rowCol === column) {
      columns.push(rowCol);
    }
  }
 
  // Check if we found the correct column
  if (columns.length === 1) {
    return columns[0];
  } else if (columns.length > 1) {
    throw new Error('Invalid column ' + path);
  }
 
  // Then check for the column with a prefix
  columns.splice(0);
  for (const rowCol in row) {
    const rowColParts = rowCol.split('.').length;
    if (!table && rowColParts < 3 && rowCol.endsWith('.' + column)) {
      columns.push(rowCol);
    }
  }
 
  // Check if we found the correct column
  if (columns.length === 1) {
    return columns[0];
  } else if (columns.length > 1) {
    throw new Error('Invalid column ' + path);
  }
 
  // Finally check with a table and column prefix
  columns.splice(0);
  for (const rowCol in row) {
    if (table && rowCol.endsWith('.' + table + '.' + column)) {
      columns.push(rowCol);
    }
  }
 
  // Check if we found the correct column
  if (columns.length === 1) {
    return columns[0];
  } else {
    throw new Error('Invalid column ' + path);
  }
}
 
// Try to resolve a column, otherwise treat it as a literal
function resolveValue(path: string, row: {[string]: any}): string {
  let value = path;
  try {
    value = row[resolveColumn(path, row)];
  } catch {}
  return value;
}
 
/**
 * Normalizes column names for comparison by extracting the base column name
 * @param columnName - column name (could be qualified like "Doctor.departmentId" or unqualified like "departmentId")
 * @return the base column name without table qualification
 */
function normalizeColumnName(columnName: string): string {
  if (typeof columnName !== 'string') {
    return columnName;
  }
  const parts = columnName.split('.');
  return parts[parts.length - 1]; // Return the last part (column name)
}
 
/**
 * @param expr - a relational algebra expression to evaluate
 * @param item - an item to evaluate against
 * @return result of evaluating the expression
 */
function applyItem(expr: {[string]: any}, item: {[string]: any}): any {
  const type = Object.keys(expr)[0];
  switch (type) {
    case 'cmp':
      // Get the values to compare and the comparison operator
      const lhs = resolveValue(expr.cmp.lhs, item);
      const op = expr.cmp.op;
      let rhs = resolveValue(expr.cmp.rhs, item);
 
      switch (op) {
        case '$gte':
          return lhs >= rhs;
        case '$gt':
          return lhs > rhs;
        case '$lt':
          return lhs < rhs;
        case '$lte':
          return lhs <= rhs;
        case '$ne':
          // eslint-disable-next-line eqeqeq
          return lhs != rhs;
        case '$eq':
          // eslint-disable-next-line eqeqeq
          return lhs == rhs;
        default:
          throw new Error('Invaid comparison operator');
      }
 
    case 'and':
      let andResult = true;
 
      // Loop over all expressions to be evaluated
      for (var i = 0; andResult && i < expr.and.clauses.length; i++) {
        andResult = andResult && applyItem(expr.and.clauses[i], item);
      }
      return andResult;
 
    case 'or':
      let orResult = false;
 
      // Loop over all expressions to be evaluated
      for (var i2 = 0; !orResult && i2 < expr.or.clauses.length; i2++) {
        orResult = orResult || applyItem(expr.or.clauses[i2], item);
      }
      return orResult;
 
    case 'not':
      return !applyItem(expr.not.clause, item);
 
    default:
      throw new Error('Invalid expression');
  }
}
 
/**
 * @param expr - a relational algebra expression to evaluate
 * @param sourceData - source data from relations
 * @return result of evaluating the expression
 */
export function applyExpr(
  expr: {[string]: any},
  sourceData: {[string]: any}
): {[string]: any} {
  const type = Object.keys(expr)[0];
  switch (type) {
    case 'projection':
      // Evaluate the single child of this expression
      let projData = applyExpr(expr.projection.children[0], sourceData);
 
      // Get the columns which should be deleted
      const columns = projData.columns.map((col) =>
        resolveColumn(col, projData.data[0])
      );
      const keep = expr.projection.arguments.project.map((col) =>
        resolveColumn(col, projData.data[0])
      );
      const deleted = columns.filter((column) => keep.indexOf(column) === -1);
 
      // Make a copy of the list of columns to project
      projData.columns = keep;
 
      // Delete data values which should not be included
      for (let i = 0; i < deleted.length; i++) {
        for (let j = 0; j < projData.data.length; j++) {
          delete projData.data[j][deleted[i]];
        }
      }
      return projData;
 
    case 'selection':
      // Evaluate the single child of this expression
      let selData = applyExpr(expr.selection.children[0], sourceData);
 
      let select = expr.selection.arguments.select;
      selData.data = selData.data.filter((item) => applyItem(select, item));
 
      return selData;
 
    case 'rename':
      // Evaluate the single child of this expression
      let renData = applyExpr(expr.rename.children[0], sourceData);
 
      // Loop over all pairs of things to rename
      Object.entries(expr.rename.arguments.rename.columns).forEach(
        ([from, to]) => {
          // Ensure target name is a string
          if (typeof to !== 'string') {
            throw new Error('Invalid target for rename');
          }
 
          // Add a new column with the new name
          const fromColumn = resolveColumn(from, renData.data[0]);
          renData.columns[renData.columns.indexOf(fromColumn)] = to;
 
          // Copy all column data and delete the original column
          for (let j = 0; j < renData.data.length; j++) {
            renData.data[j][to] = renData.data[j][fromColumn];
            delete renData.data[j][fromColumn];
          }
        }
      );
      return renData;
 
    case 'relation':
      // Make a copy of the data from a source table and return it
      return {...sourceData[expr.relation]};
 
    case 'order_by':
      let ordData = applyExpr(expr.order_by.children[0], sourceData);
 
      ordData.data.sort((a, b) => {
        let sortOrder = 0;
        expr.order_by.arguments.order_by.every((c) => {
          // Continue as long as column values are equal
          if (sortOrder !== 0) {
            return false;
          }
 
          if (a[c.column_name] < b[c.column_name]) {
            sortOrder = c.ascending ? -1 : 1;
          } else if (a[c.column_name] > b[c.column_name]) {
            sortOrder = c.ascending ? 1 : -1;
          }
 
          return true;
        });
 
        return sortOrder;
      });
 
      return ordData;
 
    case 'group_by':
      let groupData = applyExpr(expr.group_by.children[0], sourceData);
      const groupByColumns = expr.group_by.arguments.groupBy;
      const aggregates = expr.group_by.arguments.aggregates;
      const selectColumns = expr.group_by.arguments.selectColumns || [];
 
      // Group the data by the specified columns
      const groups: {[string]: Array<{[string]: any}>} = {};
      for (const row of groupData.data) {
        // Create a group key from the group by columns
        // If no grouping columns, use a single group for all data
        const groupKey =
          groupByColumns.length > 0
            ? groupByColumns
                .map((col) => {
                  const resolvedCol = resolveColumn(col, row);
                  return row[resolvedCol];
                })
                .join('|')
            : 'all'; // Single group key when no GROUP BY columns
 
        if (!groups[groupKey]) {
          groups[groupKey] = [];
        }
        groups[groupKey].push(row);
      }
 
      // Calculate aggregates for each group
      const resultData = [];
      // Only include explicitly selected columns, not all GROUP BY columns
      const resultColumns = [...selectColumns];
 
      // Add aggregate columns to result columns
      for (const agg of aggregates) {
        resultColumns.push(
          `${agg.aggregate.function}(${agg.aggregate.column})`
        );
      }
 
      for (const [groupKey, groupRows] of Object.entries(groups)) {
        const resultRow: {[string]: any} = {};
 
        // Add explicitly selected column values (from SELECT clause)
        if (selectColumns.length > 0) {
          const groupKeyValues = groupKey.split('|');
          for (const selectCol of selectColumns) {
            // Find the index of this select column in the groupBy columns
            const groupByIndex = groupByColumns.findIndex(
              (groupCol) =>
                normalizeColumnName(groupCol) === normalizeColumnName(selectCol)
            );
            if (groupByIndex >= 0) {
              resultRow[selectCol] = groupKeyValues[groupByIndex];
            }
          }
        }
 
        // Calculate aggregates
        for (const agg of aggregates) {
          const column = agg.aggregate.column;
          const func = agg.aggregate.function;
 
          let result;
          if (func === 'COUNT') {
            // COUNT doesn't need to resolve column, just count rows
            result = groupRows.length;
          } else {
            // Other aggregates need to resolve the column and get values
            const values = groupRows.map((row: {[string]: any}) => {
              const resolvedCol = resolveColumn(column, row);
              return parseFloat(row[resolvedCol]) || 0;
            });
 
            switch (func) {
              case 'MAX':
                result = Math.max(...values);
                break;
              case 'MIN':
                result = Math.min(...values);
                break;
              case 'AVG':
                result =
                  values.reduce((sum, val) => sum + val, 0) / values.length;
                break;
              case 'SUM':
                result = values.reduce((sum, val) => sum + val, 0);
                break;
              case 'STDEV':
                if (values.length <= 1) {
                  result = 0;
                } else {
                  const mean =
                    values.reduce((sum, val) => sum + val, 0) / values.length;
                  const variance =
                    values.reduce(
                      (sum, val) => sum + Math.pow(val - mean, 2),
                      0
                    ) /
                    (values.length - 1);
                  result = Math.sqrt(variance);
                }
                break;
              default:
                throw new Error('Unsupported aggregate function: ' + func);
            }
          }
 
          resultRow[`${func}(${column})`] = result;
        }
 
        resultData.push(resultRow);
      }
 
      return {
        name: groupData.name + ' (grouped)',
        columns: resultColumns,
        data: resultData,
      };
 
    case 'except':
    case 'intersect':
    case 'union':
      // Process each side of the operation
      const setLeft = applyExpr(expr[type].left, sourceData);
      const setRight = applyExpr(expr[type].right, sourceData);
 
      // Check for valid columns
      if (setLeft.columns.length !== setRight.columns.length) {
        throw new Error(
          'Each side of ' + type + ' must have the same number of columns'
        );
      }
 
      const outColumns: Array<string> = setLeft.columns.slice();
      const setOutput: Output = {
        name: setLeft.name + ' ∪ ' + setRight.name,
        columns: outColumns,
        data: [],
      };
 
      for (const leftRow of setLeft.data) {
        // Add the row if it doesn't exist or we don't want distinct
        if (
          !expr[type].distinct ||
          setOutput.data.find((row) => deepEqual(row, leftRow)) === undefined
        ) {
          setOutput.data.push(leftRow);
        }
      }
 
      // Generate new rows for the right side with the salem
      // column names as those on the left
      const newRight = setRight.data.map((rightRow) => {
        const newRow: {[string]: any} = {};
        for (const rightKey of Object.keys(rightRow)) {
          newRow[setLeft.columns[setRight.columns.indexOf(rightKey)]] =
            rightRow[rightKey];
        }
 
        return newRow;
      });
 
      if (type === 'intersect') {
        // Keep only rows from th left which have a match on the right
        setOutput.data = setOutput.data.filter((leftRow) => {
          for (const rightRow of newRight) {
            if (deepEqual(leftRow, rightRow)) {
              return true;
            }
          }
          return false;
        });
      } else {
        for (const rightRow of newRight) {
          if (type === 'except') {
            // Remove any matching rows
            setOutput.data = setOutput.data.filter(
              (row) => !deepEqual(row, rightRow)
            );
          } else if (type === 'union') {
            // Add the row if it doesn't exist or we don't want distinct
            if (
              !expr[type].distinct ||
              setOutput.data.find((row) => deepEqual(row, rightRow)) ===
                undefined
            ) {
              setOutput.data.push(rightRow);
            }
          }
        }
      }
 
      return setOutput;
 
    case 'join':
      // Process each side of the join
      let joinLeft = applyExpr(expr.join.left, sourceData);
      let joinRight = applyExpr(expr.join.right, sourceData);
      const combinedJoinColumns = getCombinedColumns(joinLeft, joinRight);
      let joinType = expr.join.type;
 
      let joinSymbol = ' ⋈ ';
      if (joinType === 'left') {
        joinSymbol = ' ⟕ ';
      } else if (joinType === 'right') {
        joinSymbol = ' ⟖ ';
      }
 
      const joinOutput: Output = {
        name: joinLeft.name + joinSymbol + joinRight.name,
        columns: combinedJoinColumns,
        data: [],
      };
 
      if (joinType === 'right') {
        let temp = joinLeft;
        joinLeft = joinRight;
        joinRight = temp;
      }
 
      // Perform the join
      for (const leftRow of joinLeft.data) {
        let matchFound = false;
        for (const rightRow of joinRight.data) {
          const combinedJoinData = getCombinedData(
            joinLeft.name,
            leftRow,
            joinRight.name,
            rightRow,
            combinedJoinColumns
          );
          if (applyItem(expr.join.condition, combinedJoinData)) {
            joinOutput.data.push(combinedJoinData);
            matchFound = true;
          }
        }
        if (!matchFound && joinType !== 'inner') {
          const combinedJoinData = getCombinedData(
            joinLeft.name,
            leftRow,
            joinRight.name,
            joinRight.data[0],
            combinedJoinColumns,
            true
          );
          joinOutput.data.push(combinedJoinData);
        }
      }
 
      return joinOutput;
 
    case 'product':
      // Process each side of the product
      const left = applyExpr(expr.product.left, sourceData);
      const right = applyExpr(expr.product.right, sourceData);
      const combinedColumns = getCombinedColumns(left, right);
 
      const output: Output = {
        name: left.name + ' × ' + right.name,
        columns: combinedColumns,
        data: [],
      };
 
      // Perform the cross product
      for (const leftRow of left.data) {
        for (const rightRow of right.data) {
          output.data.push(
            getCombinedData(
              left.name,
              leftRow,
              right.name,
              rightRow,
              combinedColumns
            )
          );
        }
      }
 
      return output;
 
    default:
      // Fallback in case we get something invalid to show a nice error
      throw new Error('Invalid expression');
  }
}
 
const reducer = (state: State = initialState, action: Action): State => {
  return produce(state, (draft: State) => {
    // eslint-disable-next-line default-case
    switch (action.type) {
      case RESET_EXPR:
        draft.expr = {};
        draft.current = undefined;
        draft.element = undefined;
        break;
      case CHANGE_EXPR:
        draft.expr = action.expr;
        draft.element = action.element;
        draft.current =
          JSON.stringify(action.expr) === JSON.stringify({})
            ? undefined
            : applyExpr(action.expr, draft.sourceData);
        break;
    }
  });
};
 
export default reducer;