heroku-pg-extras/commands/mandelbrot.js

'use strict'

const co = require('co')
const cli = require('heroku-cli-util')
const pg = require('heroku-pg')

function * run (context, heroku) {
  let db = yield pg.fetcher(heroku).database(context.app, context.args.database)

  let query = `
  WITH RECURSIVE Z(IX, IY, CX, CY, X, Y, I) AS (
            SELECT IX, IY, X::float, Y::float, X::float, Y::float, 0
            FROM (select -2.2 + 0.031 * i, i from generate_series(0,101) as i) as xgen(x,ix),
                 (select -1.5 + 0.031 * i, i from generate_series(0,101) as i) as ygen(y,iy)
            UNION ALL
            SELECT IX, IY, CX, CY, X * X - Y * Y + CX AS X, Y * X * 2 + CY, I + 1
            FROM Z
            WHERE X * X + Y * Y < 16::float
            AND I < 100
      )
SELECT array_to_string(array_agg(SUBSTRING(' .,,,-----++++%%%%@@@@#### ', LEAST(GREATEST(I,1),27), 1)),'')
FROM (
      SELECT IX, IY, MAX(I) AS I
      FROM Z
      GROUP BY IY, IX
      ORDER BY IY, IX
     ) AS ZT
GROUP BY IY
ORDER BY IY
  `

  let output = yield pg.psql.exec(db, query)
  process.stdout.write(output)
}

const cmd = {
  topic: 'pg',
  description: 'show the mandelbrot set',
  needsApp: true,
  needsAuth: true,
  args: [{name: 'database', optional: true}],
  run: cli.command(co.wrap(run))
}

module.exports = [
  Object.assign({command: 'mandelbrot'}, cmd)
]