Sunsetter improvements

Improve sunsetter output and behavior, especially in
positions close to mate.

- fix eval sign in "analyze" mode, which is
  used after sunsetter plays a forced move
- enter analyze mode if sunsetter quickly picks an obvious move
  without fully evaluating. For example, if alternatives allow
  mate in 1, sunsetter might move with only depth 1 evaluation,
  giving the best move but an incorrect eval score.
- approximate depth when sunsetter finds mate but doesn't give
  a depth.

Fixes lichess-org#2198 and lichess-org#2199.

ui/analyse/src/ceval/sunsetterWorker.js

@@ -8,7 +8,9 @@ module.exports = function(opts, name) {
 
  // Sunsetter always plays only moves right away. Count the number of played
  // moves to show the correct mate in #n.
- var onlyMoves = 0;
+ // When aiMoves is >0, sunsetter is in analysis mode, which uses an absolute
+ // eval score instead of relative to current color :-\.
+ var aiMoves = 0;
  var best;
 
  var send = function(text) {
@@ -19,14 +21,14 @@ module.exports = function(opts, name) {
  if (text === 'tellics stopped') {
  busy = false;
  stopping = false;
- onlyMoves = 0;
+ aiMoves = 0;
  best = undefined;
  return;
  }
  if (stopping) return;
 
  if (text.indexOf('move ') == 0) {
- onlyMoves++;
+ aiMoves++;
  best = text.split(' ')[1];
  send('analyze');
  return;
@@ -38,46 +40,45 @@ module.exports = function(opts, name) {
  if (matches) {
  depth = parseInt(matches[1], 10);
  cp = parseInt(matches[2], 10);
- if (!onlyMoves) best = matches[5];
+ if (!aiMoves) {
+ best = matches[5];
+ if (depth < opts.minDepth) return;
+ }
  } else {
  matches = text.match(/Found move:\s+([a-h1-8=@PNBRQK]+)\s+([-+]?\d+)\s.*/);
  if (matches) {
- depth = work.maxDepth;
  cp = parseInt(matches[2], 10);
- if (!onlyMoves) best = matches[1];
- stopping = true;
- send('force');
- send('tellics stopped');
+ if (!aiMoves) best = matches[1];
+ send('analyze');
  } else {
  return;
  }
  }
 
- if (!onlyMoves && depth < opts.minDepth) return;
-
- if (work.ply % 2 == 1) {
- if (cp) cp = -cp;
- if (mate) mate = -mate;
+ if (cp && !aiMoves && work.ply % 2) {
+ cp = -cp;
  }
 
  // transform mate scores
- if (cp > 20000) {
- mate = Math.floor((30000 - cp) / 10);
- cp = undefined;
- } else if (cp < -20000) {
- mate = Math.floor((-30000 - cp) / 10);
+ if (Math.abs(cp) > 20000) {
+ mate = Math.floor((30000 - Math.abs(cp)) / 10);
+ // approx depth for searches that end early with mate.
+ depth = Math.max(depth || 0, mate * 2 - 1);
+ // correct sign and add sunsetter played moves
+ mate = Math.sign(cp) * (mate + aiMoves)
  cp = undefined;
  }
 
  if (mate) {
- if (mate > 0) mate += onlyMoves;
- else mate -= onlyMoves;
+ stopping = true
+ send('force');
+ send('tellics stopped');
  }
 
  work.emit({
  work: work,
  eval: {
- depth: depth,
+ depth: depth + aiMoves,
  cp: cp,
  mate: mate,
  best: best
@@ -91,7 +92,7 @@ module.exports = function(opts, name) {
  instance = new Worker('/assets/vendor/Sunsetter/sunsetter.js');
  busy = false;
  stopping = false;
- onlyMoves = 0;
+ aiMoves = 0;
  send('xboard');
  };
 
@@ -107,7 +108,6 @@ module.exports = function(opts, name) {
  for (var i = 0; i < work.moves.length; i++) {
  send(work.moves[i]);
  }
- send('analyze');
  send('go');
  instance.onmessage = function(msg) {
  processOutput(msg.data, work);
@@ -116,7 +116,7 @@ module.exports = function(opts, name) {
  stop: function() {
  if (!busy) return;
  stopping = true;
- onlyMoves = 0;
+ aiMoves = 0;
  best = undefined;
  send('exit');
  send('tellics stopped');