// Parses X-Plane's CIFP procedure data (SIDs / STARs / approaches) on demand —
// one small file per airport in Resources/default data/CIFP/<ICAO>.dat, in the
// ARINC-424-derived "XP CIFP" format. Fix idents are resolved to coordinates
// via the shared navdata index; runway thresholds come from the RWY records.
//
// Used by the G1000 PROC page: list a destination's procedures, then load a
// chosen procedure+transition's leg fixes into the active flight plan.

import fs from 'node:fs';
import path from 'node:path';
import { lookup, xplaneRoot } from './navdata.js';

// "N47274972" -> 47.4638..  /  "W122183954" -> -122.3109..
function parseCoord(s) {
  if (!s || s.length < 8) return null;
  const hemi = s[0];
  const neg = hemi === 'S' || hemi === 'W';
  const digits = s.slice(1);
  // lat = DDMMSSss (8) ; lon = DDDMMSSss (9)
  const degLen = (hemi === 'E' || hemi === 'W') ? 3 : 2;
  const dd = parseInt(digits.slice(0, degLen), 10);
  const mm = parseInt(digits.slice(degLen, degLen + 2), 10);
  const ss = parseInt(digits.slice(degLen + 2, degLen + 4), 10);
  const hh = parseInt(digits.slice(degLen + 4, degLen + 6) || '0', 10);
  if (!isFinite(dd) || !isFinite(mm)) return null;
  const val = dd + mm / 60 + (ss + hh / 100) / 3600;
  return neg ? -val : val;
}

function cifpFile(icao) {
  const root = xplaneRoot();
  if (!root) return null;
  const f = path.join(root, 'Resources', 'default data', 'CIFP', `${icao.toUpperCase()}.dat`);
  return fs.existsSync(f) ? f : null;
}

// Parse one airport's procedures into a structured summary + leg store.
// Returns null if the airport has no CIFP file.
export function parseProcedures(icao) {
  const file = cifpFile(icao);
  if (!file) return null;

  const runways = {};                 // RW16C -> { lat, lon, elev }
  const groups = { SID: {}, STAR: {}, APPCH: {} };
  // groups[type][procName] = { order:[trans...], legs:{ trans:[{fix,term,alt}] } }

  const ensure = (type, name, trans) => {
    const g = groups[type];
    if (!g[name]) g[name] = { order: [], legs: {} };
    if (!(trans in g[name].legs)) { g[name].legs[trans] = []; g[name].order.push(trans); }
    return g[name].legs[trans];
  };

  for (const raw of fs.readFileSync(file, 'utf8').split('\n')) {
    const line = raw.trim().replace(/;$/, '');
    if (!line) continue;
    const colon = line.indexOf(':');
    if (colon < 0) continue;
    const type = line.slice(0, colon);
    const f = line.slice(colon + 1).split(',');

    if (type === 'RWY') {
      // RWY:RW16C, , ,00429, ,ISZI,3, ;N47274972,W122183954,0000
      const id = f[0];
      const tail = line.split(';')[1] || '';      // "N47274972,W122183954,0000"
      const [latS, lonS] = tail.split(',');
      const lat = parseCoord(latS), lon = parseCoord(lonS);
      if (lat != null && lon != null) runways[id] = { lat, lon, elev: parseInt(f[3], 10) || 0 };
      continue;
    }
    if (type !== 'SID' && type !== 'STAR' && type !== 'APPCH') continue;

    // f[0]=seqno, f[1]=route type, f[2]=proc, f[3]=transition, f[4]=fix,
    // f[11]=path/termination, f[22]=alt flag (+/-), f[23]=altitude.
    const procName = f[2];               // BANGR9 / CHINS5 / I16C
    const trans = (f[3] || '').trim();   // RW16C / PDT / ERYKA / '' (common)
    const fix = (f[4] || '').trim();     // OTLIE / ANVIL / RW16C
    const term = (f[11] || '').trim();   // path/termination: IF TF CF DF VA CA ...
    const altFlag = (f[22] || '').trim();
    const altVal = parseInt((f[23] || '').trim(), 10);
    const alt = isFinite(altVal) && altVal > 0 ? altVal : null;

    const legs = ensure(type, procName, trans || '(common)');
    legs.push({ fix, term, alt, altFlag });
  }

  // Build the client-facing summary (names + their transitions).
  const summarize = (g) => Object.entries(g).map(([name, v]) => ({
    name, transitions: v.order.filter((t) => t !== '(common)'),
  }));

  return {
    icao: icao.toUpperCase(),
    runways: Object.keys(runways),
    sids: summarize(groups.SID),
    stars: summarize(groups.STAR),
    approaches: summarize(groups.APPCH),
    _groups: groups,
    _rwy: runways,
  };
}

// Resolve a chosen procedure+transition to a list of waypoints with coordinates.
// type: 'sid' | 'star' | 'approach'. Fixes are resolved via the navdata index;
// runway "fixes" (RWxx) and unresolved fixes fall back to the RWY threshold.
export function procedureLegs(icao, type, name, trans) {
  const parsed = parseProcedures(icao);
  if (!parsed) return [];
  const TYPE = { sid: 'SID', star: 'STAR', approach: 'APPCH' }[String(type).toLowerCase()];
  const g = parsed._groups[TYPE];
  if (!g || !g[name]) return [];
  const node = g[name];

  // Compose the leg list: chosen transition first, then the common segment.
  // (SID: runway/enroute transition then common climb-out; STAR: enroute entry
  // then common arrival; approach: IAF transition then final-approach segment.)
  const seq = [];
  const wantTrans = trans && node.legs[trans] ? trans : node.order.find((t) => t !== '(common)');
  if (wantTrans && node.legs[wantTrans]) seq.push(...node.legs[wantTrans]);
  if (node.legs['(common)']) seq.push(...node.legs['(common)']);

  const out = [];
  const seen = new Set();
  for (const leg of seq) {
    if (!leg.fix) continue;                          // heading/altitude legs w/o a fix
    if (seen.has(leg.fix)) continue;                 // de-dupe repeated fixes
    let pt = null;
    const isRwy = /^RW/.test(leg.fix);
    if (isRwy && parsed._rwy[leg.fix]) pt = parsed._rwy[leg.fix];
    else {
      const hit = lookup(leg.fix);
      if (hit) pt = { lat: hit.lat, lon: hit.lon };
    }
    if (!pt) continue;                               // unresolved fix → skip
    seen.add(leg.fix);
    out.push({ id: leg.fix, lat: pt.lat, lon: pt.lon, type: isRwy ? 'APT' : 'WPT', alt: leg.alt });
    // An approach ends at the runway threshold — drop the missed-approach legs.
    if (TYPE === 'APPCH' && isRwy) break;
  }
  return out;
}