CoreModule.md

Core Module (com.group5.csv.core)

The core module defines the in-memory representation of CSV data and the type system used by the rest of the project. It is intentionally independent of I/O concerns so it can be reused by multiple front-ends (CLI, GUI, libraries).

Key Classes

• Headers

  • Represents the logical column layout (header row).
  • Provides name-to-index lookup and column existence checks.
  • Defines the canonical ordering of columns used by Row and RowBuilder.

• Row

  • Immutable representation of a single CSV record.
  • Holds a Headers reference and an ordered set of values/fields.
  • Accessors typically include:
    • get(int index)
    • get(String columnName)
    • size(), headers(), etc.

• Field

  • Represents a single cell within a Row.
  • Exposes:
    • Raw text: raw()
    • Typed value: value(), valueAs(Class<T>)
    • Metadata: index(), name()
    • Validation state: isMissing(), isValid(), errors()
    • Type-specific specs: decimalSpec(), dateSpec(), dateTimeSpec()
  • Designed to be immutable and safe for lazy parsing + memoization.

• FieldType

  • Enum describing the supported logical types:
    • STRING, INT, LONG, DOUBLE, DECIMAL, BOOLEAN, DATE, DATETIME
  • Responsible for parsing & formatting:
    • Object parse(String raw, Field field)
    • String format(Object value, Field field)
  • Uses the specs exposed by Field for complex types such as decimal and date/time.

• RowBuilder

  • Mutable helper class to construct Row instances safely.
  • Tied to a Headers instance, which defines the expected number and order of columns.
  • Collects raw values via:
    • add(String value)
    • addAll(List<String> values)
    • set(int index, String value)
    • set(String name, String value)
  • Enforces that the number of collected values matches headers.size() before building a Row.

Row Construction Workflow

1. Headers created
   Usually from the first line of the CSV file:

Headers headers = new Headers(List.of("id", "name", "age"));

2. RowBuilder created for these headers

RowBuilder builder = new RowBuilder(headers);

3. Values added as the CSV reader parses a line

builder.add("1")
       .add("Jim")
       .add("40");

4. Immutable Row built

Row row = builder.build();

5. Row consumed via index or column name

String name = row.get("name");   // "Alice"
int age = Integer.parseInt(row.get("age"));

This separation of concerns keeps parsing/validation logic cleanly separated from I/O, and makes it easy to unit test each part of the system (Headers, Field, FieldType, Row, RowBuilder) in isolation.