exolve-from-text.js

/*
MIT License

Copyright (c) 2022 Viresh Ratnakar

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.

The latest code and documentation for Exolve can be found at:
https://github.com/viresh-ratnakar/exolve

Version: Exolve v1.61 February 22, 2025
*/

/**
 * exolveFromText() converts lines of text that mainly have the clues,
 * but may optionally have title/byline/preamble before the clues into
 * Exolve. The grid is inferred from clue numbers and enums. The clues
 * sections must have "Across" and "Down" headings. You can typically copy
 * such text from PDFs of crosswords, which is the main use-case enabled by
 * this in exolve-player.
 *
 * You shouldn't use this code to cheat on a crossword that has been presented
 * diagramlessly :-).
 *
 * The function returns a Worker object that does its core computations in
 * another thread (as these computations may take a long time, especially for
 * larger grid sizes). The Worker can be aborted at any time by calling its
 * terminate() function. While active, the Worker will send periodic update
 * messages to the main thread (with the .update field being a useful update
 * text to show) and will finally send a message containing a .results array
 * field. If the grid could not be inferred, the .results array is empty.
 *
 * Usually, only one grid gets matched, but occasionally, multiple grids may
 * match the pattern implied by the clues.
 *
 * Each matched grid is returned as an object (in the .results array in the
 * final posted message) that has fields .gridSpecLines and .exolve
 * that contain the grid specs and the full exolve specs, respectively.
 *
 * If there is error in parsing the text, then instead of a Worker, an
 * error string is returned.
 *
 * Usage:
 *   const worker = exolveFromText(w, h, text, filename);
 *   if (typeof worker == 'string') {
 *     alert(worker);
 *     return;
 *   }
 *   worker.onmessage = (e) => {
 *     if (e.data.update) {
 *       // Show e.data.update
 *       return;
 *     }
 *     const results = e.data.results;
 *     if (results.length == 0) {
 *       // Could not infer a grid.
 *     } else if (results.length == 1) {
 *       // Inferred 1 grid, use its full specs from results[0].exolve
 *     } else {
 *       // Multiple matches, ask the user to choose.
 *     }
 *   }
 *
 * This assumes that the grid is in a standard, blocked, UK-style format:
 *
 * - The grid is symmetric using one of 180/90/-90/hflip/vflip symmetries.
 * - Every 4x4 area has at least one black cell.
 * - No light is shorter than 3 letters.
 * - Enums are provided for all clues. The only exception is child clues
 *   in linked groups.
 * - For a linked group of clues, the component lights split the linked
 *   entry at exactly word-breaks or hyphens. Moreover (to keep the
 *   algorithm complexity in check), only one extra word-break/hyphen in the
 *   entry is supported (compared to the number of linked clues).
 */
exolveFromText = function(w, h, text, fname='') {
  let sections = {
    title: '',
    setter: '',
    preamble: '',
    copyright: '',
    across: [],
    down: [],
    acSols: [],
    dnSols: [],
    acAnnos: [],
    dnAnnos: [],
    file: fname || '[provided text]',
  };
  let seenClues = false;
  let seenDown = false;

  const lines = exolveFromTextClean(text).split('\n');

  const clueStartRE = /^\s*\d{1,2}(?!\d)([ ]*[,&][ ]*[aAdD][^ ]*)*/;
  const clueRE = /^\s*\d{1,2}(?!\d)([ ]*[,&][ ]*[aAdD][^ ]*)*.*\([0-9, '-]+\)/;
  const childRE = /^\s*\d{1,2}(?!\d)[\s\.:]*see /i;
  const wordsRE = /[a-zA-Z]+/;
  const copyrightRE = /^\s*(copyright|\(c\)|Ⓒ)/i;
  const titleAndSetterRE = /^\s*(.+)\sby\s(.+)/i; 
  const bylineRE = /^\s*(?:(?:set\sby)|(?:by))[^a-zA-Z0-9]*\s([a-zA-Z0-9].+)/i; 

  const acrossRE = /^[^a-zA-Z0-9]*across[^a-zA-Z0-9]*$/i;
  const downRE = /^[^a-zA-Z0-9]*down[^a-zA-Z0-9]*$/i; 

  const acSolsRE = /^[^a-zA-Z0-9]*across\s+solutions?[^a-zA-Z0-9]*$/i;
  const dnSolsRE = /^[^a-zA-Z0-9]*down\s+solutions?[^a-zA-Z0-9]*$/i; 
  const acAnnosRE = /^[^a-zA-Z0-9]*across\s+annotations?[^a-zA-Z0-9]*$/i;
  const dnAnnosRE = /^[^a-zA-Z0-9]*down\s+annotations?[^a-zA-Z0-9]*$/i; 

  let solannoArray = null;

  let joinedLine = '';
  for (let rawLine of lines) {
    let line = rawLine.replace(/\s/g, ' ').replace(/\s+/g, ' ').trim();
    if (seenDown) {
      if (acSolsRE.test(line)) {
        solannoArray = sections.acSols;
        continue;
      } else if (dnSolsRE.test(line)) {
        solannoArray = sections.dnSols;
        continue;
      } else if (acAnnosRE.test(line)) {
        solannoArray = sections.acAnnos;
        continue;
      } else if (dnAnnosRE.test(line)) {
        solannoArray = sections.dnAnnos;
        continue;
      }
    }
    if (solannoArray) {
      if (line) {
        solannoArray.push(line);
      }
      continue;
    }
    if (seenClues) {
      if (!seenDown && downRE.test(line)) {
        seenDown = true;
        joinedLine = '';
        continue;
      }
      if (clueRE.test(line) || childRE.test(line)) {
        if (joinedLine) {
          const tryLine = joinedLine + ' ' + line;
          if (clueRE.test(tryLine) || childRE.test(tryLine)) {
            line = tryLine;
          } else {
            console.log('Ignored potential clue start: ' + joinedLine);
          }
        }
        if (!seenDown) sections.across.push(line.trim());
        else sections.down.push(line.trim());
        joinedLine = '';
      } else if (clueStartRE.test(line)) {
        joinedLine = line;
      } else {
        joinedLine = joinedLine + ' ' + line;
        if (clueRE.test(joinedLine) || childRE.test(joinedLine)) {
          if (!seenDown) sections.across.push(joinedLine.trim());
          else sections.down.push(joinedLine.trim());
          joinedLine = '';
        }
      }
      continue;
    }
    /* !seenClues */
    if (acrossRE.test(line)) {
      seenClues = true;
      continue;
    }
    const tsMatch = line.match(titleAndSetterRE);
    if (tsMatch && tsMatch.length == 3) {
      sections.title = tsMatch[1].trim();
      if (sections.title.toLowerCase().endsWith(' set')) {
        sections.title = sections.title.substr(0, sections.title.length - 4);
      }
      sections.setter = tsMatch[2].trim();
      continue;
    }
    const byMatch = line.match(bylineRE);
    if (byMatch && byMatch.length == 2) {
      sections.setter = byMatch[1].trim();
      continue;
    }
    if (copyrightRE.test(line)) {
      sections.copyright = line.trim();
      continue;
    }
    if (wordsRE.test(line)) {
      if (!sections.title) {
        sections.title = line.trim();
      } else {
        if (sections.preamble) sections.preamble += ' ';
        sections.preamble += line;
      }
    }
  }
  const ret = exolveFromTextSections(w, h, sections);
  if (ret.error) {
    return ret.error;
  }
  return exolveFromTextCreateWorker(ret.candidates);
}

/**
 * Do lots of cleaning of the text.
 */
exolveFromTextClean = function(s) {
  /**
   * Normalize new-lines.
   */
  s = s.replace(/\r[\n]*/g, '\n');

  /**
   * Strip out non-alphanumeric weird characters preceding a number and after
   * some leading space after a newline ("bullets" are often found here).
   */
  s = s.replace(/\n\s+[^\w"',\.\(\)-]*([1-9][0-9]*)/g, '\n $1');

  /**
   * Remove end-of-line hyphenations.
   */
  s = s.replace(/([a-z])-\n\s*([a-z])/g, '$1$2');

  /**
   * Insert spaces before enums, if missing.
   */
  s = s.replace(/([^\s])\(([1-9])/g, '$1 ($2');

  /**
   * Insert newlines between clues that got stitched together (a common
   * PDF-to-text failure mode).
   */
  s = s.replace(/(\([1-9 ][0-9 ,'-]*\))\s*([1-9][0-9]*)/g, '$1\n$2');

  /**
   * If the word DOWN itself has been spliced to the preceding line, separate
   * it out. But be careful: only do it if it is clear that this is the
   * start of the down section. Heuristics used for that: a drop in clue
   * number, position of DOWN right after enum and before clue#.
   */
  const downSplicedMatch = s.match(
      /(.*)([^0-9])([1-9][0-9]*)(\s*[^()]*)(\([0-9 ,'-]*\))[ \t]*DOWN\s*([1-9][0-9]*)(.*)/i);
  if (downSplicedMatch && downSplicedMatch.length == 8) {
    const prevNum = parseInt(downSplicedMatch[3]);
    const nextNum = parseInt(downSplicedMatch[6]);
    if (nextNum < prevNum) {
      s = s.substr(0, downSplicedMatch.index) +
        downSplicedMatch[1] + downSplicedMatch[2] + downSplicedMatch[3] +
        downSplicedMatch[4] + '(' + downSplicedMatch[5] + ')\nDown\n' +
        downSplicedMatch[6] + downSplicedMatch[7] +
        s.substr(downSplicedMatch.index + downSplicedMatch[0].length);
    }
  }
  return s;
}

exolveFromTextAddChild = function(sections, par, child) {
  const parDir = par.charAt(0);
  const parNum = par.substr(1);
  const childDir = child.charAt(0);
  const childNum = child.substr(1);
  if (parDir != childDir || (parDir != 'A' && parDir != 'D')) {
    return false;
  }
  const arr = parDir == 'A' ? sections.across : sections.down;
  arr.push(`${childNum} See ${parNum}`);
  arr.sort((c1, c2) => {
    const c1i = parseInt(c1);
    const c2i = parseInt(c2);
    return c1i - c2i;
  });
  return true;
}

/**
 * Captures a candidate grid skeleton and the lights that need to be
 * placed in it. The lights array is indexed by the clue number (so
 * its 0-th entry is unused).
 */
function ExolveGridSkeleton(puz, specs) {
  this.puz = puz;
  this.specs = specs;
  this.w = puz.gridWidth;
  this.h = puz.gridHeight;
  this.no4x4 = true;
  this.grid = new Array(this.h);
  for (let r = 0; r < this.h; r++) {
    this.grid[r] = new Array(this.w);
  }
  this.parents = [];
  /* lights[x]['A'/'D'] (for x = 1,2,..) has the specs for that light */
  this.lights = [null];
  this.name = '';
  this.symName = ExolveGridSymmetryDefault;
}

ExolveGridSkeleton.prototype.clone = function(newLights=false) {
  const copy = new ExolveGridSkeleton(this.puz, this.specs);
  copy.parents = this.parents;
  copy.name = this.name;
  copy.symName = this.symName;
  copy.no4x4 = this.no4x4;

  copy.grid = new Array(this.h);
  for (let r = 0; r < this.h; r++) {
    copy.grid[r] = this.grid[r].slice();
  }
  // expandLinkedGroups() makes shallow copies of some lights[] objects.
  // But for other cloning, using the same lights is fine.
  if (newLights) {
    copy.lights = JSON.parse(JSON.stringify(this.lights));
  } else {
    copy.lights = this.lights;
  }
  return copy;
}

ExolveGridSkeleton.prototype.appendWithSyms = function(candidates) {
  for (let symName in ExolveGridSymmetries) {
    const candidate = this.clone();
    candidate.name = this.name + ': ' + symName + ' symmetry';
    candidate.symName = symName;
    candidates.push(candidate);
  }
  if (this.w == this.h) {
    for (let symName in ExolveSqGridSymmetries) {
      const candidate = this.clone();
      candidate.name = this.name + ': ' + symName + ' symmetry';
      candidate.symName = symName;
      candidates.push(candidate);
    }
  }
}

/**
 * For each linked group, split total length into chunks at word/hyphen
 * boundaries to infer component lengths. Allow at most one extra chunk,
 * to keep complexity in check. Handle some special cases too.
 */
ExolveGridSkeleton.prototype.expandLinkedGroups = function() {
  if (this.parents.length < 1) {
    return [this];
  }
  const choices = [];
  for (let par of this.parents) {
    const clue = this.lights[par[0]][par[1]].clue;
    const phParts = clue.placeholder.split(/[ -]/);
    const grp = par[2];
    if (grp.length > phParts.length) {
      /* See if this is still workable as a special case */
      const special = [];
      if (grp.length == 2 && phParts.length == 1) {
        if (clue.placeholder.length == 6) {
          special.push([3,3])
        } else if (clue.placeholder.length == 7) {
          special.push([3,4])
          special.push([4,3])
        } else if (clue.placeholder.length == 8) {
          special.push([3,5])
          special.push([4,4])
          special.push([5,3])
        }
      } else if (grp.length == 3 && phParts.length == 1 &&
                 clue.placeholder.length == 9) {
        special.push([3,3,3])
      }
      if (special.length > 0) {
        choices.push(special);
        continue;
      }
      console.log('Clue ' + par[1] + par[0] + ' has ' + grp.length + ' linked parts but enum only has ' + phParts.length);
      return [];
    }
    if (grp.length < phParts.length - 1) {
      console.log('Clue ' + par[1] + par[0] + ' has ' + grp.length + ' linked parts and enum has too many more parts: ' + phParts.length);
      return [];
    }
    const myChoices = [];
    const phPartsLens = [];
    for (let phPart of phParts) phPartsLens.push(phPart.length);
    if (grp.length == phPartsLens.length) {
      myChoices.push(phPartsLens);
    } else {
      console.assert(grp.length == phPartsLens.length - 1, grp.length, phPartsLens.length);
      /* We'll skip one of the boundaries in each split-choice. */
      for (let skip = 1; skip < phPartsLens.length; skip++) {
        const myChoicesEntry = [];
        for (let i = 0; i < phPartsLens.length; i++) {
          if (i == skip - 1) {
            continue;
          } else if (i == skip) {
            myChoicesEntry.push(phPartsLens[i - 1] + phPartsLens[i]);
          } else {
            myChoicesEntry.push(phPartsLens[i]);
          }
        }
        myChoices.push(myChoicesEntry);
      }
    }
    choices.push(myChoices);
  }
  let candidates = [this];
  for (let i = 0; i < this.parents.length; i++) {
    const par = this.parents[i];
    const grp = par[2];
    const updatedCandidates = [];
    for (let choice of choices[i]) {
      let usable = true;
      for (let l of choice) {
        if (l < 3) {
          usable = false;
          break;
        }
      }
      if (!usable) {
        continue;
      }
      for (let cand of candidates) {
        const updatedCand = cand.clone(true);
        for (let j = 0; j < grp.length; j++) {
          const cci = grp[j];
          const num = cci.substr(1);
          const dir = cci.substr(0, 1);
          const light = updatedCand.lights[num][dir];
          console.assert(light.len == 0, light);
          const lightCopy = {
            label: light.label,
            dir: light.dir,
            clue: light.clue,
            len: choice[j],
          };
          updatedCand.lights[num][dir] = lightCopy;
        }
        updatedCandidates.push(updatedCand);
      }
    }
    if (updatedCandidates.length < 1) {
      console.log('No linked group choice available for ' + grp[0]);
      return [];
    }
    candidates = updatedCandidates;
  }
  return candidates;
}

/**
 * Returns an object containing .candidates (and maybe .error).
 */
exolveFromTextSections = function(w, h, sections) {
  const ret = {
    candidates: []
  }
  if (w <= 0 || h <= 0) {
    ret.error = 'Width and height must both be at least 1';
    return ret;
  }
  if (!sections.across || sections.across.length <= 0 ||
      !sections.down || sections.down.length <= 0) {
    ret.error = 'Text has to contain at least one across clue and one down clue';
    return ret;
  }
  let specs = '';
  /**
   * Create an invisible Exolve puzzle with a fully blank and diagramless grid,
   * to parse just the clues.
   */
  const xlvpid = 'xlvp-from-text-temp';
  document.body.insertAdjacentHTML('beforeend',
      `<div id="${xlvpid}" style="display:none"/>`);
  const div = document.getElementById(xlvpid);

  specs = `
  exolve-begin
    exolve-width: ${w}
    exolve-height: ${h}
  `;
  if (sections.title) {
    specs += `
    exolve-title: ${sections.title}`;
  }
  if (sections.setter) {
    specs += `
    exolve-setter: ${sections.setter}`;
  }
  if (sections.copyright) {
    specs += `
    exolve-copyright: ${sections.copyright}`;
  }
  specs += `
    exolve-maker:
      Converted by exolve-from-text.js from ${sections.file}`
  if (sections.preamble) {
    specs += `
    exolve-preamble:
${sections.preamble}`;
  }

  let clueSpecLines = `
    exolve-across:`;
  for (let acrossClue of sections.across) {
    clueSpecLines += `
      ${acrossClue}`;
  }
  clueSpecLines += `
    exolve-down:`;
  for (let downClue of sections.down) {
    clueSpecLines += `
      ${downClue}`;
  }

  let gridSpecLines = `
    exolve-grid:`;
  for (let r = 0; r < h; r++) {
    let rowSpec = '';
    for (let c = 0; c < w; c++) {
      rowSpec += '0*';  /* diagramless, so lights are not inferred from grid */
    }
    gridSpecLines += `
      ${rowSpec}`;
  }

  const tempSpecs = specs + clueSpecLines + gridSpecLines + `
    exolve-option: ignore-unclued ignore-enum-mismatch
    exolve-id: ${xlvpid}
  exolve-end`;

  let puz;
  try {
    puz = new Exolve(tempSpecs, xlvpid, null, false, 0, 0, false);
  } catch (err) {
    const re = /^.*Invalid child ([AD][0-9][0-9]*) in ([AD][0-9][0-9]*)/i;
    const missingChild = err.toString().match(re);
    if (missingChild && missingChild.length == 3 &&
        exolveFromTextAddChild(sections, missingChild[2], missingChild[1])) {
      console.log('Adding ' + missingChild[1] +
          ' as child clue for ' + missingChild[2]);
      return exolveFromTextSections(w, h, sections);
    }
    console.log(err.stack);
    ret.error = 'Exolve had fatal errors in parsing clues: ' + err;
    return ret;
  }

  if (sections.acSols.length > 0 || sections.dnSols.length > 0 ||
      sections.acAnnos.length > 0 || sections.dnAnnos.length > 0) {
    const lineRE = /^\s*(\d+)\s*\.?\s*(.+)$/;
    const lineParser = (line) => {
      const matches = lineRE.exec(line);
      if (!matches || matches.length != 3) {
        console.log('Ignoring solution/annotation line: ' + line);
        return null;
      }
      return [matches[1], matches[2]];
    }
    for (const dir of ['A', 'D']) {
      const arrays = (dir == 'A') ? {
        sols: sections.acSols,
        annos: sections.acAnnos,
      } : {
        sols: sections.dnSols,
        annos: sections.dnAnnos,
      }
      for (const sa in arrays) {
        const arr = arrays[sa];
        for (const line of arr) {
          const numAndText = lineParser(line);
          if (!numAndText) continue;
          const ci = dir + numAndText[0];
          if (!puz.clues.hasOwnProperty(ci)) {
            console.log(sa + ' line has invalid index: ' + ci);
            continue;
          }
          const clue = puz.clues[ci];
          const anno = (sa == 'sols') ?
              '[' + numAndText[1] + ']' : numAndText[1];
          if (clue.anno) clue.anno += ' ';
          clue.anno += anno;
        }
      }
    }
    let acClues = '';
    let dnClues = '';
    for (const ci of puz.allClueIndices) {
      const clue = puz.clues[ci];
      const fullClue = '\n' + clue.label + ' ' + clue.clue + (
          clue.anno ? ' ' + clue.anno : '');
      if (clue.dir == 'A') acClues += fullClue;
      else dnClues += fullClue;
    }
    clueSpecLines = `
    exolve-across:${acClues}
    exolve-down:${dnClues}`;
  }
  specs += clueSpecLines;

  const skeleton = new ExolveGridSkeleton(puz, specs);
  if (exolvePuzzles && exolvePuzzles[xlvpid]) {
    delete exolvePuzzles[xlvpid];
  }
  div.remove();

  for (let r = 0; r < h; r++) {
    for (let c = 0; c < w; c++) {
      skeleton.grid[r][c] = '_';
    }
  }
  maxwh = Math.max(w, h);
  for (let ci of puz.allClueIndices) {
    let clue = puz.clues[ci];
    let num = parseInt(clue.label);
    if (isNaN(num) || num <= 0) {
      ret.error = 'Found non-positive-number clue label: ' + clue.label;
      return ret;
    }
    if (skeleton.lights.length <= num) {
      skeleton.lights.length = num + 1;
    }
    if (!skeleton.lights[num]) {
      skeleton.lights[num] = {};
    }
    if (clue.enumLen == 0 && !clue.parentClueIndex) {
      ret.error = 'Found no or zero enum in clue label: ' + clue.label;
      return ret;
    }
    skeleton.lights[num][clue.dir] = {
      label: num,
      dir: clue.dir,
      clue: clue,
      len: 0,
    };
  }
  if (skeleton.lights.length < 2) {
    ret.error = 'Did not find any clues';
    return ret;
  }

  let numLights = 0;
  for (let i = 1; i < skeleton.lights.length; i++) {
    if (!skeleton.lights[i]) {
      ret.error = 'Found missing clue ' + i;
      return ret;
    }
    if (!('A' in skeleton.lights[i]) && !('D' in skeleton.lights[i])) {
      ret.error = 'Found a hole at clue ' + i;
      return ret;
    }
    for (let dir of ['A', 'D']) {
      if (!(dir in skeleton.lights[i])) {
        continue;
      }
      numLights++;

      const light = skeleton.lights[i][dir];
      if (light.clue.childrenClueIndices && light.clue.childrenClueIndices.length > 0) {
        skeleton.parents.push([i, dir, puz.getLinkedClues(dir + i)]);
      } else if (!light.clue.parentClueIndex) {
        light.len = light.clue.enumLen;
      }
    }
  }
  console.log('There are ' + numLights + ' lights over ' +
              w + 'x' + h + ' = ' + (w * h) + ' cells.');

  const skeletons = skeleton.expandLinkedGroups();

  for (let rowpar = 0; rowpar < 2; rowpar++) {
    for (let colpar = 0; colpar < 2; colpar++) {
      for (const skeleton of skeletons) {
        const candidate = skeleton.clone();
        for (let r = 0; r < h; r++) {
          for (let c = 0; c < w; c++) {
            if (((r % 2) != rowpar) && ((c % 2) != colpar)) {
              candidate.grid[r][c] = '.';
            }
          }
        }
        candidate.name = 'Chequered ' + rowpar + '' + colpar;
        candidate.appendWithSyms(ret.candidates);
      }
    }
  }
  for (const skeleton of skeletons) {
    const candidate = skeleton.clone();
    candidate.name = 'Non-chequered';
    candidate.appendWithSyms(ret.candidates);
  }
  /**
   * no4x4 determines whether (in an unchequered skeleton), we allow
   * blocks of 2x2 white cells (false is tried as a last resort).
   */
  for (const skeleton of skeletons) {
    const candidate = skeleton.clone();
    candidate.no4x4 = false;
    candidate.name = 'Non-chequered-2x2-white-OK';
    candidate.appendWithSyms(ret.candidates);
  }
  return ret;
}

exolveFromTextCreateWorker = function(candidates) {
  let scriptSrc = '';
  for (let i = 0; i < document.scripts.length; i++) {
    const src = document.scripts[i].src;
    if (!src) continue;
    const srcUrl = new URL(src);
    if (srcUrl.pathname.endsWith('/exolve-from-text.js')) {
      scriptSrc = src;
      break;
    }
  }
  if (!scriptSrc) {
    return 'Could not find script with src "/exolve-from-text.js"';
  }
  const workerCode = `
    importScripts('${scriptSrc}');
    onmessage = (e) => {
      candidates = e.data || null;
      if (!candidates) {
        return;
      }
      const results = [];
      for (const skeleton of candidates) {
        const candidate = new ExolveGridInferrer(skeleton);
        candidate.infer(results);
        if (results.length > 0) {
          break;
        }
      }
      const seen = {};
      results.sort((r1, r2) => r1.score() - r2.score());
      const deduped = [];
      for (const result of results) {
        const gridSpecLines = result.gridSpecLines();
        if (seen[gridSpecLines]) continue;
        seen[gridSpecLines] = true;
        deduped.push({gridSpecLines: gridSpecLines, exolve: result.exolve()});
      }
      postMessage({results: deduped});
    }
  `;
  blob = new Blob([workerCode], {type: "text/javascript" });
  const worker = new Worker(window.URL.createObjectURL(blob));
  worker.postMessage(JSON.parse(JSON.stringify(candidates)));
  return worker;
}

function ExolveRowCol(h, w, row=0, col=0) {
  this.h = h;
  this.w = w;
  this.row = row;
  this.col = col;
}

ExolveRowCol.prototype.isValid = function() {
  return this.row >= 0 && this.row < this.h &&
         this.col >= 0 && this.col < this.w;
}

ExolveRowCol.prototype.incr = function(delta) {
  this.col += delta;
  if (delta > 0) {
    while (this.col >= this.w) {
      this.row++;
      this.col -= this.w;
    }
  } else if (delta < 0) {
    while (this.col < 0) {
      this.row--;
      this.col += this.w;
    }
  }
}
ExolveRowCol.prototype.clone = function() {
  return new ExolveRowCol(this.h, this.w, this.row, this.col);
}

ExolveRowCol.prototype.isLessThan = function(other) {
  return this.row < other.row ||
         (this.row == other.row && this.col < other.col);
}

/**
 * Captures a partially inferred candidate grid. Grid entries with '_' have not
 * been decided. The mapped and lights arrays are both indexed by 1-based clue
 * numbers (i.e., they have an unused element at index 0). The lights array
 * lists all the lights that need to be mapped, and the mapped array lists the
 * prefix of the lights that has been mapped so far.
 */
function ExolveGridInferrer(skeleton) {
  this.w = skeleton.w;
  this.h = skeleton.h;
  this.specs = skeleton.specs;
  this.no4x4 = skeleton.no4x4;
  /* The 'cursor': the next light will be placed at a cell here onwards */
  this.rowcol = new ExolveRowCol(this.h, this.w);

  this.grid = skeleton.grid;
  /* lights[x]['A'/'D'] (for x = 1,2,..) has the specs for that light */
  this.lights = skeleton.lights;
  /* mapped[x] (for x = 1,2,..) is the cell where label x has been placed */
  this.mapped = [null];
  this.parents = skeleton.parents;
  this.name = skeleton.name;
  this.symName = skeleton.symName;
  this.sym = ExolveGridSymmetries[this.symName] ||
             ExolveSqGridSymmetries[this.symName];
}

ExolveGridInferrer.prototype.clone = function() {
  const copy = new ExolveGridInferrer(this);
  copy.rowcol.row = this.rowcol.row;
  copy.rowcol.col = this.rowcol.col;
  copy.mapped = this.mapped.slice();

  copy.grid = new Array(this.h);
  for (let r = 0; r < this.h; r++) {
    copy.grid[r] = this.grid[r].slice();
  }
  copy.progress = this.progress || null;
  return copy;
}

ExolveGridInferrer.prototype.canStartA = function(rc) {
  if (!rc.isValid()) {
    return false;
  }
  const gcell = this.grid[rc.row][rc.col];
  if (gcell == '.') {
    return false;
  }
  if ((rc.col == 0 || this.grid[rc.row][rc.col - 1] == '.') &&
      rc.col < rc.w - 1 && this.grid[rc.row][rc.col + 1] != '.') {
    return true;
  }
  return false;
}

ExolveGridInferrer.prototype.canStartD = function(rc) {
  if (!rc.isValid()) {
    return false;
  }
  const gcell = this.grid[rc.row][rc.col];
  if (gcell == '.') {
    return false;
  }
  if ((rc.row == 0 || this.grid[rc.row - 1][rc.col] == '.') &&
      rc.row < rc.h - 1 && this.grid[rc.row + 1][rc.col] != '.') {
    return true;
  }
  return false;
}

ExolveGridInferrer.prototype.canStart = function(rc) {
  return this.canStartA(rc) || this.canStartD(rc);
}

ExolveGridInferrer.prototype.isViable = function(connectivity=false) {
  for (let par of this.parents) {
    const clue = this.lights[par[0]][par[1]].clue;
    const grp = par[2];
    let tot = 0;
    for (let cci of grp) {
      const light = this.lights[cci.substr(1)][cci.substr(0, 1)];
      if (light.len < 3) {
        return false;
      }
      tot += light.len;
    }
    if (tot != clue.enumLen) {
      return false;
    }
  }
  if (connectivity) {
    if (!this.isConnected()) {
      return false;
    }
  }
  return true;
}

/**
 * Default symmetry is 180 degrees.
 */
const ExolveGridSymmetryDefault = '180 deg.';

const ExolveGridSymmetries = {
  '180 deg.':
    (rc) => new ExolveRowCol(rc.h, rc.w, rc.h - 1 - rc.row, rc.w - 1 - rc.col),
  'Hor. flip': (rc) => new ExolveRowCol(rc.h, rc.w, rc.row, rc.w - 1 - rc.col),
  'Ver. flip': (rc) => new ExolveRowCol(rc.h, rc.w, rc.h - 1 - rc.row, rc.col),
};
const ExolveSqGridSymmetries = {
  '90-R deg.': (rc) => new ExolveRowCol(rc.w, rc.h, rc.w - 1 - rc.col, rc.h - 1 - rc.row),
  '90-L deg.': (rc) => new ExolveRowCol(rc.w, rc.h, rc.col, rc.row),
};

/**
 * Returns a list of rowcols rc2 such that rc-rc2 form a diagonal
 * with 0s in the two cross-diagonal cells.
 */
ExolveGridInferrer.prototype.threeZerosAll = function(rc) {
  console.assert(this.grid[rc.row][rc.col] == '0', rc);
  const ret = [];
  const row = rc.row;
  const col = rc.col;
  const prow = row - 1;
  const pcol = col - 1;
  const nrow = row + 1;
  const ncol = col + 1;
  if (prow >= 0 && pcol >= 0 &&
      this.grid[row][pcol] == '0' &&
      this.grid[prow][col] == '0') {
    ret.push(new ExolveRowCol(rc.h, rc.w, prow, pcol));
  }
  if (nrow < this.h && ncol < this.w &&
      this.grid[row][ncol] == '0' &&
      this.grid[nrow][col] == '0') {
    ret.push(new ExolveRowCol(rc.h, rc.w, nrow, ncol));
  }
  if (prow >= 0 && ncol < this.w &&
      this.grid[row][ncol] == '0' &&
      this.grid[prow][col] == '0') {
    ret.push(new ExolveRowCol(rc.h, rc.w, prow, ncol));
  }
  if (nrow < this.h && pcol >= 0 &&
      this.grid[nrow][col] == '0' &&
      this.grid[row][pcol] == '0') {
    ret.push(new ExolveRowCol(rc.h, rc.w, nrow, pcol));
  }
  return ret;
}

/**
 * Set entry at rc and its symmetric locaion to letter if possible. Return
 * false if either one is already set to something else.
 */
ExolveGridInferrer.prototype.setGrid = function(rc, letter) {
  if (!rc.isValid()) return false;
  if (this.grid[rc.row][rc.col] != '_' &&
      this.grid[rc.row][rc.col] != letter) {
    return false;
  }
  const sym = this.sym(rc);
  if (this.grid[sym.row][sym.col] != '_' &&
      this.grid[sym.row][sym.col] != letter) {
    return false;
  }
  this.grid[rc.row][rc.col] = letter;
  this.grid[sym.row][sym.col] = letter;
  if (letter == '0' && this.no4x4) {
    const mustBlock = this.threeZerosAll(rc);
    for (let rc2 of mustBlock) {
      if (!this.setGrid(rc2, '.')) {
        return false;
      }
    }
  }
  return true;
}


/**
 * Place a light along direction dir at the current this.rowcol cursor, making
 * sure no other light can start at any cell preceding that, starting at
 * cell rowcolStart.
 *
 * Return a new, updated ExolveGridInferrer object or null if there is a
 * conflict.
 */
ExolveGridInferrer.prototype.mapLight = function(dir, len, rowcolStart) {
  if (!this.rowcol.isValid() || len <= 1) {
    return null;
  }
  const mapped = this.clone();
  for (let rowcol = rowcolStart.clone();
       rowcol.isValid() && rowcol.isLessThan(this.rowcol); rowcol.incr(1)) {
    if (!mapped.canStart(rowcol)) {
      mapped.setGrid(rowcol, '.');
      continue;
    }
    if (mapped.setGrid(rowcol, '.')) {
      continue;
    }
    if (mapped.canStartA(rowcol)) {
      const nextA = rowcol.clone();
      nextA.incr(1);
      if (!mapped.setGrid(nextA, '.')) {
        return null;
      }
    }
    if (mapped.canStartD(rowcol)) {
      const nextD = rowcol.clone();
      nextD.incr(this.w);
      if (!mapped.setGrid(nextD, '.')) {
        return null;
      }
    }
  }
  if (dir == 'A') {
    if (!mapped.canStartA(this.rowcol)) {
      return null;
    }
    let rowcol = this.rowcol.clone();
    for (let l = 0; l < len; l++) {
      if (!rowcol.isValid() || rowcol.row != this.rowcol.row) {
        return null;
      }
      if (!mapped.setGrid(rowcol, '0')) {
        return null;
      }
      rowcol.incr(1);
    }
    if (rowcol.isValid() && rowcol.row == this.rowcol.row) {
      if (!mapped.setGrid(rowcol, '.')) {
        return null;
      }
    }
  }
  if (dir == 'D') {
    if (!mapped.canStartD(this.rowcol)) {
      return null;
    }
    let rowcol = this.rowcol.clone();
    for (let l = 0; l < len; l++) {
      if (!rowcol.isValid() || rowcol.col != this.rowcol.col) {
        return null;
      }
      if (!mapped.setGrid(rowcol, '0')) {
        return null;
      }
      rowcol.incr(this.w);
    }
    if (rowcol.isValid() && rowcol.col == this.rowcol.col) {
      if (!mapped.setGrid(rowcol, '.')) {
        return null;
      }
    }
  }
  return mapped;
}

/**
 * This does a postMessage(0 with an update on the status. We show this status
 * anchored to every new placement of the first 10 lights. For each such
 * combination, we show the max # of lights that could be placed (when this
 * max reaches the total number og lights, we're done).
 */
ExolveGridInferrer.prototype.inferShowProgress = function() {
  const LIGHTS_MAPPED_PREFIX = 10;
  if (!this.progress) {
    this.progress = {
      count: 0,
      max: LIGHTS_MAPPED_PREFIX,
    };
  }
  if (this.mapped.length == LIGHTS_MAPPED_PREFIX) {
    /* New placement combo for the first few lights */
    this.progress.count++;
    this.progress.max = LIGHTS_MAPPED_PREFIX;
  }
  if (this.mapped.length >= this.progress.max) {
    this.progress.max = this.mapped.length;
    postMessage({
        update: 'Trying: ' + this.name + ': First ' + LIGHTS_MAPPED_PREFIX +
                ' lights placement combo #' + this.progress.count +
                ' extends to ' + this.mapped.length + ' of ' +
                this.lights.length + ' lights'
    });
  } else if (this.mapped.length == 1) {
    postMessage({update: 'Trying: ' + this.name});
  }
}

/**
 * Infer the remaining grid recursively. Append any fully successfully
 * filled grids to results.
 */
ExolveGridInferrer.prototype.infer = function(results) {
  this.inferShowProgress();
  if (this.mapped.length == this.lights.length) {
    while (this.rowcol.isValid()) {
      this.setGrid(this.rowcol, '.');
      if (this.canStart(this.rowcol)) {
        return;
      }
      this.rowcol.incr(1);
    }
    if (!this.isViable(true)) {
      return;
    }
    results.push(this);
    return;
  }
  const lights = this.lights[this.mapped.length];
  const rowcolStart = this.rowcol.clone();
  let numUnsetCellsSet = 0;

  /* Only consider blackening up to these many cells */
  const maxToBlacken = 6;
  while (this.rowcol.isValid() && numUnsetCellsSet <= maxToBlacken) {
    const gridCell = this.grid[this.rowcol.row][this.rowcol.col];
    if (gridCell == '_') {
      numUnsetCellsSet++;
    }
    let candidate = this.clone();
    this.rowcol.incr(1);
    console.assert(('A' in lights) || ('D' in lights), lights);
    for (let dir of ['A', 'D']) {
      if (!(dir in lights)) {
        continue;
      }
      const light = lights[dir];
      console.assert(light.len >= 3, light);
      candidate = candidate.mapLight(dir, light.len, rowcolStart);
      if (!candidate) {
        break;
      }
    }
    if (!candidate) {
      continue;
    }
    candidate.mapped.push(candidate.rowcol.clone());
    candidate.rowcol.incr(1);
    if (!candidate.isViable()) {
      continue;
    }
    candidate.infer(results);
  }
}

ExolveGridInferrer.prototype.score = function() {
  let numUnches = 0;
  let num4x4 = 0;
  let maxRowBlack = 0;
  let maxColBlack = 0;
  for (let r = 0; r < this.h; r++) {
    for (let c = 0; c < this.w; c++) {
      if (this.grid[r][c] != '0') continue;
      if ((c < this.w - 1 && this.grid[r][c + 1] == '0') &&
          (r == 0 || this.grid[r - 1][c] == '.') &&
          (r == 0 || this.grid[r - 1][c + 1] == '.') &&
          (r == this.h - 1 || this.grid[r + 1][c] == '.') &&
          (r == this.h - 1 || this.grid[r + 1][c + 1] == '.')) {
        numUnches++;
      }
      if ((r < this.h - 1 && this.grid[r + 1][c] == '0') &&
          (c == 0 || this.grid[r][c - 1] == '.') &&
          (c == 0 || this.grid[r + 1][c - 1] == '.') &&
          (c == this.w - 1 || this.grid[r][c + 1] == '.') &&
          (c == this.w - 1 || this.grid[r + 1][c + 1] == '.')) {
        numUnches++;
      }
      if (r < this.h - 1 && c < this.w - 1 &&
          this.grid[r+1][c] == '0' &&
          this.grid[r][c+1] == '0' &&
          this.grid[r+1][c+1] == '0') {
        num4x4++;
      }
      /* horiz black span ending before this: */
      let span = 0;
      for (let c2 = c - 1; c2 >= 0; c2--) {
        if (this.grid[r][c2] == '.') {
          span++;
        } else {
          break;
        }
      }
      if (span > maxRowBlack) maxRowBlack = span;
      /* vert black span ending before this: */
      span = 0;
      for (let r2 = r - 1; r2 >= 0; r2--) {
        if (this.grid[r2][c] == '.') {
          span++;
        } else {
          break;
        }
      }
      if (span > maxColBlack) maxColBlack = span;
    }
  }
  return numUnches + num4x4 + maxRowBlack + maxColBlack;
}

ExolveGridInferrer.prototype.isConnected = function() {
  let cells = []
  let visited = new Array(this.h)
  for (let i = 0; i < this.h; i++) {
    visited[i] = new Array(this.w)
    for (let j = 0; j < this.w; j++) {
      visited[i][j] = false
      if (this.grid[i][j] != '.') {
        cells.push([i,j])
      }
    }
  }
  if (cells.length == 0) return false;
  let reachable = [cells[0]]
  visited[cells[0][0]][cells[0][1]] = true;
  let x = 0;
  while (x < reachable.length) {
    let r = reachable[x][0];
    let c = reachable[x][1];
    x++;
    if (c > 0 && this.grid[r][c-1] != '.' && !visited[r][c-1]) {
      visited[r][c-1] = true
      reachable.push([r,c-1])
    }
    if (c < this.w - 1 && this.grid[r][c+1] != '.' && !visited[r][c+1]) {
      visited[r][c+1] = true
      reachable.push([r,c+1])
    }
    if (r > 0 && this.grid[r-1][c] != '.' && !visited[r-1][c]) {
      visited[r-1][c] = true
      reachable.push([r-1,c])
    }
    if (r < this.h - 1 && this.grid[r+1][c] != '.' && !visited[r+1][c]) {
      visited[r+1][c] = true
      reachable.push([r+1,c])
    }
  }
  return reachable.length == cells.length;
}

/**
 * Return the grid in Exolve format. If a cell's blockiness
 * hasn't yet been determined, it is made diagramless.
 */
ExolveGridInferrer.prototype.gridSpecLines = function() {
  let lines = `
    exolve-grid:`;
  for (let r = 0; r < this.h; r++) {
    let rowLine = '';
    for (let c = 0; c < this.w; c++) {
      const gridCell = this.grid[r][c];
      rowLine += (gridCell == '_' ? '0*' : (gridCell + ' '));
    }
    lines += `
      ${rowLine}`;
  }
  return lines;
}
/**
 * Return the crossword in Exolve format, if fully filled. Otherwise return null.
 */
ExolveGridInferrer.prototype.exolve = function() {
  return this.specs + this.gridSpecLines() + '\n  exolve-end';
}