Implement a simplified grep with extensible flags

Problem

Implement a simplified version of grep that searches a text file and returns the lines that match a given query string.

You should focus on clean, readable, extensible design (e.g., parsing flags/options in a way that makes it easy to add new flags later), not on advanced algorithms.

Requirements

• Input:
  • pattern: a non-empty string to search for.
  • lines: an array/list of strings representing the file content, one element per line.
  • flags/options: a set of optional flags (you may choose the interface, e.g., CLI args, a struct/object, or a map).
• Output:
  • The matching lines, in original order.

Supported flags (minimum)

Define at least a few flags and implement them, such as:

• Case-insensitive match (e.g., -i)
• Print line numbers along with matched lines (e.g., -n)
• Invert match (return non-matching lines) (e.g., -v)

Notes

• Assume a simple substring match (not full regex).
• Be explicit about edge cases (empty file, empty lines, pattern casing, etc.).
• The interviewer will evaluate:
  • Code organization (separation of concerns: parsing, matching, formatting)
  • Extensibility (how easy it is to add a new flag)
  • Correctness and testability

Example

Given:

• pattern = "error"
• lines = ["ok", "Error: disk full", "no issue", "error again"]
• flags: case-insensitive

Output:

• "Error: disk full"
• "error again"