Add statistics function with average closed time

Add conditional check if post.md already exists

main.js

@@ -41,7 +41,10 @@ for (const arg of process.argv) {
 }
 
 if (!args.includes('--no-download')) download()
-else createTable()
+else {
+  createTable()
+  createStatistics()
+}
 
 function download() {
   api.Projects
@@ -62,6 +65,7 @@ function download() {
           }
         })
         .then(createTable)
+        .then(createStatistics)
     })
 }
 
@@ -143,6 +147,42 @@ function createTable() {
     table += ` ${closedAt} |\n`
   }
 
-  fs.copyFileSync(path.join(__dirname, 'template.md'), path.join(__dirname, year, month, 'post.md'))
+  if (!fs.existsSync(path.join(__dirname, year, month, 'post.md')))
+    fs.copyFileSync(path.join(__dirname, 'template.md'), path.join(__dirname, year, month, 'post.md'))
   fs.writeFileSync(path.join(__dirname, year, month, 'table.md'), table, {encoding: 'UTF-8'})
 }
+
+function createStatistics() {
+  let opened = klaw(openedPath)
+  let closed = klaw(closedPath)
+
+  let statistics = '## Statistics\n\n'
+
+  statistics += `In the month of ${month} `
+  statistics += `${opened.length} issues were opened and `
+  statistics += `${closed.length} issues were closed.\n\n`
+
+  let averageClosedDays
+  let averageClosedHours
+  for (const file of closed) {
+    const issue = require(file.path)
+    const openedAt = new Date(issue.created_at)
+    const closedAt = new Date(issue.closed_at)
+    const diffDays = Math.floor((closedAt - openedAt) / (1000 * 60 * 60 * 24))
+    const diffHours = Math.floor((closedAt - openedAt) / (1000 * 60 * 60))
+
+    averageClosedDays = (typeof averageClosedDays === 'undefined')
+      ? averageClosedDays = diffDays
+      : averageClosedDays += diffDays
+    averageClosedHours = (typeof averageClosedHours === 'undefined')
+      ? averageClosedHours = diffHours
+      : averageClosedHours += diffHours
+  }
+  averageClosedDays = Math.floor(averageClosedDays / closed.length)
+  averageClosedHours = Math.floor(averageClosedHours / closed.length)
+
+  statistics += `The average time to close issues was ${averageClosedDays} days `
+  statistics += `or ${averageClosedHours} hours.\n\n`
+
+  fs.writeFileSync(path.join(__dirname, year, month, 'statistics.md'), statistics, {encoding: 'UTF-8'})
+}