- move fromTag resolving to main.ts and remove dependency on checks from ReleaseNotes.ts

- require fromTag for ReleaseNotes
- adjust tests, split into according test classes
- simplify transform.ts

src/main.ts

@@ -8,6 +8,8 @@ import {ReleaseNotes} from './releaseNotes'
 import {createCommandManager} from './gitHelper'
 import * as github from '@actions/github'
 import {DefaultConfiguration} from './configuration'
+import {Octokit} from '@octokit/rest'
+import {Tags} from './tags'
 
 async function run(): Promise<void> {
   core.setOutput('failed', false) // mark the action not failed by default
@@ -30,7 +32,7 @@ async function run(): Promise<void> {
     const owner = core.getInput('owner') || github.context.repo.owner
     const repo = core.getInput('repo') || github.context.repo.repo
     // read in from, to tag inputs
-    const fromTag = core.getInput('fromTag')
+    let fromTag = core.getInput('fromTag')
     let toTag = core.getInput('toTag')
     // read in flags
     const ignorePreReleases = core.getInput('ignorePreReleases') === 'true'
@@ -80,19 +82,49 @@ async function run(): Promise<void> {
     }
     core.endGroup()
 
-    const releaseNotes = new ReleaseNotes({
+    // load octokit instance
+    const octokit = new Octokit({
+      auth: `token ${token || process.env.GITHUB_TOKEN}`
+    })
+
+    // ensure to resolve the fromTag if it was not provided specifically
+    if (!fromTag) {
+      core.startGroup(`🔖 Resolve previous tag`)
+      core.debug(`fromTag undefined, trying to resolve via API`)
+      const tagsApi = new Tags(octokit)
+
+      const previousTag = await tagsApi.findPredecessorTag(
+        owner,
+        repo,
+        toTag,
+        ignorePreReleases,
+        configuration.max_tags_to_fetch ||
+          DefaultConfiguration.max_tags_to_fetch
+      )
+      if (previousTag == null) {
+        failOrError(
+          `💥 Unable to retrieve previous tag given ${toTag}`,
+          failOnError
+        )
+        return
+      }
+      fromTag = previousTag.name
+      core.debug(`fromTag resolved via previousTag as: ${previousTag.name}`)
+      core.endGroup()
+    }
+
+    const releaseNotes = new ReleaseNotes(octokit, {
       owner,
       repo,
       fromTag,
       toTag,
-      ignorePreReleases,
       failOnError,
       configuration
     })
 
     core.setOutput(
       'changelog',
-      (await releaseNotes.pull(token)) ||
+      (await releaseNotes.pull()) ||
         configuration.empty_template ||
         DefaultConfiguration.empty_template
     )