Gable board calculator.

index.js

#!/usr/bin/env node

const gabbleWidth = 22*12;
const boardCoverage = 6.375;
const boardLength = 144;
const nBoards = Math.ceil(gabbleWidth/boardCoverage);

const narray = (n, v) => {
  let arr = [...Array(Math.ceil(n+1)).keys()];
  arr.shift();
  if (v) arr = arr.map(i => v);
  return arr;
}

const xarray = (arr, x) => {
  let result;
  for (let i = 0; i < x; i++) {
    result = arr.concat(arr);
  }
  return result;
}

const placements = narray(nBoards/2);

const lengths = placements.map((b) => {
  return Math.tan(27 * Math.PI / 180) * (b*boardCoverage);
});

const totalLengths = xarray(lengths, 4);

// add existing cutoffs
const cuttoffs = []
  .concat(narray(4, 56))
  .concat(narray(2, 25))
  .concat(narray(10, 32))
  .concat(narray(8, 35));

let boards = 0;
do {
  let cutoff, candidate, candidates;
  const length = totalLengths.pop();
  console.log(`Need a board of ${length} inches.`);

  console.log(`Checking cutoffs...`);
  candidates = cuttoffs.filter((c) => c > length);
  console.log(`Found ${candidates.length} cutoffs that would work.`);

  if (candidates.length > 0) {
    console.log(`Looking for shortest cutoff...`);
    candidate = candidates.reduce((m,c) => m < c ? m : c);
    console.log(`Found a cutoff of ${candidate} inches.`);
    cuttoffs.splice(cuttoffs.indexOf(candidate), 1);
    cuttoffs.push(candidate-length);
  } else {
    console.log(`No cutoff found, cutting into a new board...`);
    boards++;
    cutoff = boardLength-length;
    cuttoffs.push(cutoff);
  }
}
while (totalLengths.length > 0);

console.log(`You will need ${boards} boards.`);