/**
 * Minimal CSV parser for test-plan.csv. Supports quoted fields containing
 * commas, escaped double-quotes (""), and arbitrary trailing columns. Returns
 * one Scenario per non-header row.
 *
 * Schema (header row must include at least id, description, inputs, expected;
 * any extra columns are surfaced verbatim in `extra` for future use):
 *
 *   id,description,inputs,expected
 *   T1,Quote 35yo male non-smoker,age=35;gender=male;smoker=no;cover=100000,premium between 140 and 160
 *
 * Deliberately hand-rolled — pulling in csv-parse adds 100KB+ for a parser
 * that lives behind a single user-facing input and never sees adversarial CSV.
 */

export interface Scenario {
  id: string;
  description: string;
  inputs: string;
  expected: string;
  extra: Record<string, string>;
}

/** Tokenise one CSV row honouring "double quotes" and escaped "" pairs. */
export const parseCsvRow = (row: string): string[] => {
  const fields: string[] = [];
  let cur = '';
  let inQuotes = false;
  for (let i = 0; i < row.length; i++) {
    const ch = row[i];
    if (inQuotes) {
      if (ch === '"' && row[i + 1] === '"') {
        cur += '"';
        i++;
      } else if (ch === '"') {
        inQuotes = false;
      } else {
        cur += ch;
      }
    } else if (ch === ',') {
      fields.push(cur);
      cur = '';
    } else if (ch === '"' && cur.length === 0) {
      inQuotes = true;
    } else {
      cur += ch;
    }
  }
  fields.push(cur);
  return fields.map((f) => f.trim());
};

const REQUIRED_COLUMNS = ['id', 'description', 'inputs', 'expected'] as const;

export const parseTestPlanCsv = (raw: string): Scenario[] => {
  const lines = raw
    .split(/\r?\n/)
    .map((l) => l.trim())
    .filter((l) => l.length > 0 && !l.startsWith('#'));

  if (lines.length < 2) {
    throw new Error('test-plan.csv must have a header row and at least one scenario row');
  }

  const header = parseCsvRow(lines[0]).map((h) => h.toLowerCase());
  for (const required of REQUIRED_COLUMNS) {
    if (!header.includes(required)) {
      throw new Error(`test-plan.csv header missing required column "${required}". Got: ${header.join(', ')}`);
    }
  }

  const scenarios: Scenario[] = [];
  for (let i = 1; i < lines.length; i++) {
    const values = parseCsvRow(lines[i]);
    if (values.length < REQUIRED_COLUMNS.length) {
      throw new Error(
        `test-plan.csv row ${i + 1}: expected at least ${REQUIRED_COLUMNS.length} columns, got ${values.length}`,
      );
    }
    const row: Record<string, string> = {};
    header.forEach((col, idx) => {
      row[col] = values[idx] ?? '';
    });

    const id = row.id;
    if (!id) {
      throw new Error(`test-plan.csv row ${i + 1}: id column is empty`);
    }

    const extra: Record<string, string> = {};
    Object.keys(row).forEach((key) => {
      if (!REQUIRED_COLUMNS.includes(key as (typeof REQUIRED_COLUMNS)[number])) {
        extra[key] = row[key];
      }
    });

    scenarios.push({
      id,
      description: row.description,
      inputs: row.inputs,
      expected: row.expected,
      extra,
    });
  }

  // Reject duplicate ids — they'd silently overwrite each other in any report.
  const seen = new Set<string>();
  for (const s of scenarios) {
    if (seen.has(s.id)) {
      throw new Error(`test-plan.csv: duplicate scenario id "${s.id}"`);
    }
    seen.add(s.id);
  }

  return scenarios;
};