import { readFileSync } from 'node:fs';
import type { WeatherSample } from '../../src/weather/weather.ts';
import { kstClock, kstFields } from '../../src/ui/time.ts';
import { THREADS } from '../../src/constants/threads.ts';

type Condition = typeof THREADS.captionConditions[number];
export interface Captions {
  template: string[];
  testPrefix: string;
  thresholds: { fogVisibilityMeters: number; cloudyPercent: number; partlyCloudyPercent: number };
  messages: Record<Condition, string[]>;
}

export function loadCaptions(path: string | URL = new URL('../../.threads-captions.json', import.meta.url)): Captions {
  let text: string;
  try { text = readFileSync(path, 'utf8'); }
  catch (error) {
    if ((error as NodeJS.ErrnoException).code !== 'ENOENT') throw error;
    text = readFileSync(new URL('../../.threads-captions.sample.json', import.meta.url), 'utf8');
  }
  let config: Captions;
  try { config = JSON.parse(text); } catch { throw new Error('Invalid JSON in .threads-captions.json'); }
  const lines = (value: unknown): value is string[] => Array.isArray(value) && value.length > 0 && value.every(line => typeof line === 'string');
  if (!config || !lines(config.template) || typeof config.testPrefix !== 'string'
    || !THREADS.captionConditions.every(key => lines(config.messages?.[key]))) throw new Error('Invalid caption template or weather messages');
  const t = config.thresholds;
  if (!t || !Number.isFinite(t.fogVisibilityMeters) || t.fogVisibilityMeters < 0
    || !Number.isFinite(t.partlyCloudyPercent) || !Number.isFinite(t.cloudyPercent)
    || t.partlyCloudyPercent < 0 || t.cloudyPercent > 100 || t.partlyCloudyPercent >= t.cloudyPercent) {
    throw new Error('Invalid caption weather thresholds');
  }
  return config;
}

export function weatherKey(weather: WeatherSample | null, config: Captions): Condition {
  if (!weather) return 'unknown';
  if ((weather.snowfall ?? 0) > 0) return 'snow';
  if ((weather.rain ?? 0) > 0) return 'rain';
  if (weather.visibility !== null && weather.visibility < config.thresholds.fogVisibilityMeters) return 'fog';
  if (weather.rain === null || weather.snowfall === null || !Number.isFinite(weather.cloudCover)) return 'unknown';
  if (weather.cloudCover >= config.thresholds.cloudyPercent) return 'cloudy';
  if (weather.cloudCover >= config.thresholds.partlyCloudyPercent) return 'partlyCloudy';
  return 'clear';
}

export function renderCaption(config: Captions, capture: {
  weather: WeatherSample | null; capturedAt: string; sunrise: string; url: string; test: boolean;
}) {
  const condition = weatherKey(capture.weather, config);
  const date = new Date(capture.capturedAt);
  const values: Record<string, string> = {
    message: config.messages[condition].join('\n'), date: kstFields(date).date,
    dateDots: kstFields(date).date.replaceAll('-', '.'), hostname: new URL(capture.url).hostname,
    time: kstClock(date).slice(0, 5), sunrise: kstClock(new Date(capture.sunrise)).slice(0, 5), url: capture.url,
  };
  const text = (capture.test ? config.testPrefix : '') + config.template.join('\n').replace(/\{(\w+)\}/g, (_, key: string) => {
    if (!(key in values)) throw new Error(`Unknown caption placeholder: ${key}`);
    return values[key];
  });
  if (!text.trim() || [...text].length > THREADS.captionMaxLength) throw new Error('Caption must contain 1–500 characters');
  return { text, condition };
}