// ─── parseDate (C# DateTime.ParseExact style) ───
// Parses a date string using an exact format pattern.
// Supported tokens:
//   yyyy — 4-digit year
//   yy   — 2-digit year (assumes 2000+)
//   MM   — 2-digit month (01–12)
//   M    — 1 or 2-digit month
//   dd   — 2-digit day (01–31)
//   d    — 1 or 2-digit day
//   HH   — 2-digit hour 24h (00–23)
//   H    — 1 or 2-digit hour 24h
//   hh   — 2-digit hour 12h (01–12)
//   h    — 1 or 2-digit hour 12h
//   mm   — 2-digit minute (00–59)
//   m    — 1 or 2-digit minute
//   ss   — 2-digit second (00–59)
//   s    — 1 or 2-digit second
//   fff  — 3-digit milliseconds
//   ff   — 2-digit (tenths + hundredths)
//   f    — 1-digit (tenths)
//   tt   — AM/PM
//   t    — A/P
//   Z    — literal 'Z' (UTC marker)
//   K    — timezone offset (+HH:mm, -HH:mm, or Z)
//
// All other characters are matched literally.
// Returns Date on success, null on failure.

const TOKEN_ORDER = [
  "yyyy", "yy",
  "MM", "M",
  "dd", "d",
  "HH", "H", "hh", "h",
  "mm", "m",
  "ss", "s",
  "fff", "ff", "f",
  "tt", "t",
  "K", "Z",
];

const TOKEN_PATTERNS = {
  yyyy: "(\\d{4})",
  yy: "(\\d{2})",
  MM: "(\\d{2})",
  M: "(\\d{1,2})",
  dd: "(\\d{2})",
  d: "(\\d{1,2})",
  HH: "(\\d{2})",
  H: "(\\d{1,2})",
  hh: "(\\d{2})",
  h: "(\\d{1,2})",
  mm: "(\\d{2})",
  m: "(\\d{1,2})",
  ss: "(\\d{2})",
  s: "(\\d{1,2})",
  fff: "(\\d{3})",
  ff: "(\\d{2})",
  f: "(\\d{1})",
  tt: "(AM|PM|am|pm)",
  t: "([AaPp])",
  K: "(Z|[+-]\\d{2}:\\d{2})",
  Z: "(Z)",
};

function buildFormatRegex(format) {
  const groups = [];
  let regexStr = "";
  let i = 0;

  while (i < format.length) {
    let matched = false;
    for (const token of TOKEN_ORDER) {
      if (format.startsWith(token, i)) {
        groups.push(token);
        regexStr += TOKEN_PATTERNS[token];
        i += token.length;
        matched = true;
        break;
      }
    }
    if (!matched) {
      // Escape literal character
      regexStr += format[i].replace(/[.*+?^${}()|[\]\\]/g, "\\$&");
      i++;
    }
  }

  return { regex: new RegExp("^" + regexStr + "$"), groups };
}

export function parseDate(input, format) {
  if (input == null || format == null) return null;
  if (input instanceof Date) return input;

  const str = String(input);
  const { regex, groups } = buildFormatRegex(format);
  const match = str.match(regex);
  if (!match) return null;

  let year = 0, month = 1, day = 1;
  let hour = 0, minute = 0, second = 0, ms = 0;
  let isPM = false, isAM = false;
  let tzOffset = null; // minutes

  for (let g = 0; g < groups.length; g++) {
    const token = groups[g];
    const val = match[g + 1];

    switch (token) {
      case "yyyy": year = parseInt(val, 10); break;
      case "yy": year = 2000 + parseInt(val, 10); break;
      case "MM":
      case "M": month = parseInt(val, 10); break;
      case "dd":
      case "d": day = parseInt(val, 10); break;
      case "HH":
      case "H": hour = parseInt(val, 10); break;
      case "hh":
      case "h": hour = parseInt(val, 10); break;
      case "mm":
      case "m": minute = parseInt(val, 10); break;
      case "ss":
      case "s": second = parseInt(val, 10); break;
      case "fff": ms = parseInt(val, 10); break;
      case "ff": ms = parseInt(val, 10) * 10; break;
      case "f": ms = parseInt(val, 10) * 100; break;
      case "tt": isPM = val.toUpperCase() === "PM"; isAM = val.toUpperCase() === "AM"; break;
      case "t": isPM = val.toUpperCase() === "P"; isAM = val.toUpperCase() === "A"; break;
      case "Z": tzOffset = 0; break;
      case "K":
        if (val === "Z") {
          tzOffset = 0;
        } else {
          const sign = val[0] === "+" ? 1 : -1;
          const [h, m] = val.substring(1).split(":").map(Number);
          tzOffset = sign * (h * 60 + m);
        }
        break;
    }
  }

  // 12h → 24h conversion
  if (isPM && hour < 12) hour += 12;
  if (isAM && hour === 12) hour = 0;

  if (tzOffset !== null) {
    // Build UTC date, apply offset
    const utcMs = Date.UTC(year, month - 1, day, hour, minute, second, ms);
    return new Date(utcMs - tzOffset * 60000);
  }

  return new Date(year, month - 1, day, hour, minute, second, ms);
}

// ─── Input transform presets ───

export const IntInput = { transform: parseInt };
export const FloatInput = { transform: parseFloat };
export const BoolInput = {
  transform: (v) => {
    if (typeof v === "boolean") return v;
    if (typeof v === "string") {
      if (v.toLowerCase() === "true") return true;
      if (v.toLowerCase() === "false") return false;
    }
    return Boolean(v);
  },
};

export function DateInput(format) {
  return {
    transform: (v) => parseDate(v, format),
  };
}

export const IsoDateInput = DateInput("yyyy-MM-ddTHH:mm:ssK");