refactor: several improvements (#262)

- more tests
- file read in config
- reduce if depth
- reduce unnecessary requests

src/config.ts

@@ -1,13 +1,12 @@
 import * as core from '@actions/core'
 import {context} from '@actions/github'
+import {readFileSync} from 'fs'
 
 export const pullRequestNumber =
   context?.payload?.pull_request?.number ||
   +core.getInput('number', {required: false})
 
 export const repo = buildRepo()
-export const message = core.getInput('message', {required: false})
-export const path = core.getInput('path', {required: false})
 export const header = core.getInput('header', {required: false})
 export const append = core.getInput('append', {required: true}) === 'true'
 export const recreate = core.getInput('recreate', {required: true}) === 'true'
@@ -15,9 +14,25 @@ export const deleteOldComment =
   core.getInput('delete', {required: true}) === 'true'
 export const githubToken = core.getInput('GITHUB_TOKEN', {required: true})
 
+export const body = buildBody()
+
 function buildRepo(): {repo: string; owner: string} {
   return {
     owner: context.repo.owner,
     repo: core.getInput('repo', {required: false}) || context.repo.repo
   }
 }
+
+function buildBody(): string {
+  const path = core.getInput('path', {required: false})
+  if (path) {
+    try {
+      return readFileSync(path, 'utf-8')
+    } catch (error) {
+      core.setFailed(error.message)
+      return ''
+    }
+  } else {
+    return core.getInput('message', {required: false})
+  }
+}