feat: add limit-commits option

Adds a new option that can be used to set a maximum number of commits
that branch-diff should work with prior to starting requesting GitHub
APIs.

This is an essential feature to help releasers avoid exceeding
GitHub API secondary rate limit.

README.md

@@ -42,6 +42,12 @@ But the comparison isn't quite as strict, generally leading to a shorter list of
 * `--commit-url`:A URL template which will be used to generate commit URLs for a repository not hosted in GitHub. `{ref}` is the placeholder that will be replaced with the commit, i.e. `--commit-url=https://gitlab.com/myUser/myRepo/commit/{ref}`. `{ghUser}` and `{ghRepo}` are available if they can be derived from package.json (Gitlab and Bitbucket URLs should be understood in package.json).
 * `--user`: Override the auto-detected GitHub user/org derived from package.json
 * `--repo`: Override the auto-detected GitHub repository name derived from package.json
+* `--limit-commits`: `number` Limits the number of commits for branch-diff to work with, e.g: `--limit-commits=500`. Note that this limit is set prior to applying all filters, this number does not represent the number of resulting commits.
+* `--skip-commits`: `number` Defines an amount of commits to be skipped from the initial difference list built between `base-branch` and `comparison-branch`, e.g: `--skip-commits=400`.
+
+### Reducing the amount of commits to avoid hitting GitHub rate limits
+
+Using the `limit-commits` and `skip-commits` options allow users to reduce the amount of commits that branch-diff will work with in order to avoid hitting GitHub API rate limits.
 
 ## License
 

branch-diff.js

@@ -75,6 +75,16 @@ async function diffCollected (options, branchCommits) {
 
   let list = branchCommits[1].filter((commit) => !isInList(commit))
 
+  if (options.limitCommits > 0) {
+    list = list.slice(-options.limitCommits)
+  }
+
+  // TODO: finish clean up the transition to skipCommits
+  // TODO: branch-diff should error with exit code on GitHub API error
+  if (options.skipCommits > 0) {
+    list = list.slice(options.skipCommits)
+  }
+
   await collectCommitLabels(list)
 
   if (options.excludeLabels.length > 0) {
@@ -125,6 +135,8 @@ async function main () {
   const endRef = argv['end-ref']
   let excludeLabels = []
   let requireLabels = []
+  let limitCommits;
+  let skipCommits;
 
   if (argv.version || argv.v) {
     return console.log(`v ${require('./package.json').version}`)
@@ -148,6 +160,14 @@ async function main () {
     requireLabels = requireLabels.concat(argv['require-label'])
   }
 
+  if (argv['limit-commits']) {
+    limitCommits = parseInt(argv['limit-commits'], 10);
+  }
+
+  if (argv['skip-commits']) {
+    skipCommits = parseInt(argv['skip-commits'], 10);
+  }
+
   if (argv.user) {
     ghId.user = argv.user
   }
@@ -160,6 +180,8 @@ async function main () {
     group,
     excludeLabels,
     requireLabels,
+    limitCommits,
+    skipCommits,
     endRef
   }