Question API — src/pages/api/question.ts

GET /api/question. Returns one question from an in-memory cache loaded from public/dataset.csv on first call. Filters are ANDed together. Returns a random match from all qualifying rows.

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Question interface

Field	Type	Description
id	number	Zero-based CSV row index.
questionId	number	LeetCode question ID.
title	string	Question title.
slug	string	URL-safe identifier (e.g. "two-sum"). Unique.
text	string	Problem statement, whitespace-trimmed.
topics	string[]	Topic tags. May be empty.
difficulty	"Easy" | "Medium" | "Hard"	Difficulty level.
successRate	number	Accepted / total submissions (0–1).
totalSubmissions	number	Total submission count.
totalAccepted	number	Total accepted submission count.
likes	number	Upvote count.
dislikes	number	Downvote count.
likeRatio	number	likes / (likes + dislikes).
hints	string[]	Hints. May be empty.
similarQuestionIds	number[]	questionIds of related questions. May be empty.
similarQuestionTitles	string[]	Titles matching similarQuestionIds order. May be empty.

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Module-level state

Name	Type	Description
cachedQuestions	Question[] | null	null until first call to loadQuestions(). Write-once — never modified after population.

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Functions

loadQuestions(): Promise<Question[]> (private)

Parses public/dataset.csv into Question[] and caches the result. Returns the cached array on subsequent calls without re-reading the file.

Preconditions:

• public/dataset.csv exists at process.cwd()/public/dataset.csv.
• CSV has a header row as row 1 (skipped via from_line: 2).
• Columns must be in the declared order.

Postconditions:

• Returns the same array reference on every call after the first.
• Rows with parse errors are silently skipped (skipRecordsWithError: true).

Throws:

• Node.js Error (ENOENT, EACCES, etc.) if the file does not exist or cannot be read.
• Rejects if the CSV stream itself errors (malformed file).

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handler(req: NextApiRequest, res: NextApiResponse): Promise<void>

Method: GET only. Returns 405 for any other method.

Query parameters

Param	Type	Filter applied
id	string?	question.questionId === Number(id)
slug	string?	question.slug === slug (exact match)
difficulty	string?	question.difficulty case-insensitive match against "Easy", "Medium", or "Hard"
topic	string?	Any topic tag contains topic (case-insensitive substring)

Returns: { question: Question } — one randomly selected match.

Preconditions:

• At least one question must match the filter set, or no filters are provided.

Error responses:

Status	Condition	Body
405	Non-GET request	{ error: "Method not allowed" }
404	No questions match filters	{ error: "No questions match the given filters" }
500	loadQuestions() rejected	{ error: "Failed to load questions" } (also logs to console.error)

Examples:

GET /api/question
-> 200 { question: { questionId: 1, title: "Two Sum", ... } }

GET /api/question?difficulty=Hard&topic=graph
-> 200 { question: { ... } }

GET /api/question?id=9999
-> 404 { error: "No questions match the given filters" }

POST /api/question
-> 405 { error: "Method not allowed" }