import fs from "node:fs";

interface EnvEntry {
  key: string;
  value: string;
}

function parseEnvLines(content: string): EnvEntry[] {
  const entries: EnvEntry[] = [];
  for (const line of content.split("\n")) {
    const trimmed = line.trim();
    if (!trimmed || trimmed.startsWith("#")) continue;
    const eq = trimmed.indexOf("=");
    if (eq === -1) continue;
    entries.push({ key: trimmed.slice(0, eq), value: trimmed.slice(eq + 1) });
  }
  return entries;
}

/** Loads a `.env` file into `process.env`, without overriding vars already set. */
export function loadDotenv(envPath: string): void {
  if (!fs.existsSync(envPath)) return;
  for (const { key, value } of parseEnvLines(fs.readFileSync(envPath, "utf-8"))) {
    if (process.env[key] === undefined) process.env[key] = value;
  }
}

/** Sets `key=value` in a `.env` file, replacing an existing line for that key rather than duplicating it. */
export function upsertEnvVar(envPath: string, key: string, value: string): void {
  const lines = fs.existsSync(envPath)
    ? fs.readFileSync(envPath, "utf-8").split("\n")
    : [];
  const prefix = `${key}=`;
  const index = lines.findIndex((line) => line.startsWith(prefix));
  const newLine = `${key}=${value}`;
  if (index >= 0) {
    lines[index] = newLine;
  } else {
    if (lines.length > 0 && lines[lines.length - 1] === "") lines.pop();
    lines.push(newLine);
  }
  fs.writeFileSync(envPath, lines.join("\n") + "\n");
}