git.scottworley.com Git - inverse-tax/blob - tax.js

   1 "use strict";
   2
   3 function parse_table(as_text) {
   4   function parse_line(line) {
   5     return line.trim().split(' ').filter(x => x !== '').map(x => parseFloat(x));
   6   }
   7   return as_text.trim().split('\n').map(parse_line);
   8 }
   9
  10 function parse_tax_table(as_text) {
  11   return parse_table(as_text).map(([start, rate], i, table) =>
  12     [start, i < table.length - 1 ? table[i+1][0] : Infinity, rate / 100.0]);
  13 }
  14
  15 function sum(nums) {
  16   return nums.reduce((total, num) => total + num, 0);
  17 }
  18
  19 function tax(table, income) {
  20   return sum(table.map(([start, end, rate]) =>
  21     Math.max(0, Math.min(income, end) - start) * rate));
  22 }
  23
  24 function apply_deductible(table, deductible) {
  25   return table.map(([start, end, rate]) => [start + deductible, end + deductible, rate]);
  26 }
  27
  28 function merge_tax_tables(t1, t2) {
  29   if (t1.length == 0) return t2;
  30   if (t2.length == 0) return t1;
  31   const [start1, end1, rate1] = t1[0];
  32   const [start2, end2, rate2] = t2[0];
  33   if (start1 == start2) {
  34     if (end1 == end2) {
  35       return [[start1, end1, rate1 + rate2]].concat(merge_tax_tables(t1.slice(1), t2.slice(1)));
  36     }
  37     if (end1 < end2) {
  38       return [[start1, end1, rate1 + rate2]].concat(merge_tax_tables(t1.slice(1), [[end1, end2, rate2]].concat(t2.slice(1))));
  39     }
  40     return merge_tax_tables(t2, t1);
  41   }
  42   if (start1 < start2) {
  43     if (end1 <= start2) {
  44       return [t1[0]].concat(merge_tax_tables(t1.slice(1), t2));
  45     }
  46     return [[start1, start2, rate1]].concat(merge_tax_tables([[start2, end1, rate1]].concat(t1.slice(1)), t2));
  47   }
  48   return merge_tax_tables(t2, t1);
  49 }