import type { OpenAI } from 'openai';

export type HumanReadableToLookbackMinutesReturnType = {
  minutes: number;
  _raw?: string;
};

const MINUTE = 1;
const HOUR = 60;
const DAY = 24 * HOUR;

const COMMON_MAP: Record<string, number> = {
  '1h': HOUR,
  '1 hour': HOUR,
  'one hour': HOUR,
  '2h': 2 * HOUR,
  '2 hours': 2 * HOUR,
  '6h': 6 * HOUR,
  '6 hours': 6 * HOUR,
  '12h': 12 * HOUR,
  '12 hours': 12 * HOUR,
  '24h': 24 * HOUR,
  '24 hours': 24 * HOUR,
  '1d': DAY,
  '1 day': DAY,
  day: DAY,
  '30m': 30,
  '30 minutes': 30,
  '15m': 15,
  '15 minutes': 15,
};

/**
 * Lightweight local parser for common patterns: "X minutes/hours/days"
 */
export function parseLookbackToMinutesLocal(text: string): number | null {
  const t = text.toLowerCase().trim();
  if (t in COMMON_MAP) return COMMON_MAP[t];

  // e.g. "last 6 hours", "6h", "6 hours", "90 minutes", "1 day"
  const re = /(last\s+)?(\d+(?:\.\d+)?)\s*(minutes?|mins?|m|hours?|hrs?|h|days?|d)\b/;
  const m = t.match(re);
  if (!m) return null;
  const value = parseFloat(m[2]);
  const unit = m[3];
  if (Number.isNaN(value)) return null;

  if (/^m(in(ute)?s?)?$/.test(unit)) return Math.round(value * MINUTE);
  if (/^h((ou)?rs?)?$/.test(unit)) return Math.round(value * HOUR);
  if (/^d(ays?)?$/.test(unit)) return Math.round(value * DAY);
  return null;
}

/**
 * Uses OpenAI to convert a human prompt like "last 6 hours" into minutes
 */
export async function humanReadableToLookbackMinutes(
  openai: OpenAI,
  prompt: string,
): Promise<HumanReadableToLookbackMinutesReturnType> {
  const local = parseLookbackToMinutesLocal(prompt);
  if (local !== null) {
    return { minutes: local, _raw: 'local' };
  }

  const resp = await openai.chat.completions.create({
    model: 'gpt-4o-mini',
    temperature: 0,
    messages: [
      {
        role: 'system',
        content:
          'Convert the user text describing a time window into a single integer number of minutes. Return ONLY the integer. Examples: "6 hours" => 360; "90 minutes" => 90; "1 day" => 1440.',
      },
      { role: 'user', content: prompt },
    ],
  });
  const content = resp.choices?.[0]?.message?.content?.trim();
  if (!content) throw new Error('OpenAI returned empty content');
  const minutes = parseInt(content.replace(/[^0-9]/g, ''), 10);
  if (!Number.isFinite(minutes) || minutes <= 0) {
    throw new Error('Failed to parse minutes');
  }
  return { minutes, _raw: content };
}