separated preview and exported from style_switcher

src/components/export_import/export_import.vue

@@ -0,0 +1,75 @@
+<template>
+<div class="import-export">
+  <button class="btn" @click="exportData">{{ exportLabel }}</button>
+  <button class="btn" @click="importData">{{ importLabel }}</button>
+  <p v-if="importFailed" class="import-warning">{{ importFailedText }}</p>
+</div>
+</template>
+
+<script>
+export default {
+  props: [
+    'exportObject',
+    'importLabel',
+    'exportLabel',
+    'importFailedText',
+    'validator',
+    'onImport',
+    'onImportFailure'
+  ],
+  data () {
+    return {
+      importFailed: false
+    }
+  },
+  methods: {
+    exportData () {
+      const stringified = JSON.stringify(this.exportObject) // Pretty-print and indent with 2 spaces
+
+      // Create an invisible link with a data url and simulate a click
+      const e = document.createElement('a')
+      e.setAttribute('download', 'pleroma_theme.json')
+      e.setAttribute('href', 'data:application/json;base64,' + window.btoa(stringified))
+      e.style.display = 'none'
+
+      document.body.appendChild(e)
+      e.click()
+      document.body.removeChild(e)
+    },
+    importData () {
+      this.importFailed = false
+      const filePicker = document.createElement('input')
+      filePicker.setAttribute('type', 'file')
+      filePicker.setAttribute('accept', '.json')
+
+      filePicker.addEventListener('change', event => {
+        if (event.target.files[0]) {
+          // eslint-disable-next-line no-undef
+          const reader = new FileReader()
+          reader.onload = ({target}) => {
+            try {
+              const parsed = JSON.parse(target.result)
+              const valid = this.validator(parsed)
+              if (valid) {
+                this.onImport(parsed)
+              } else {
+                this.importFailed = true
+                // this.onImportFailure(valid)
+              }
+            } catch (e) {
+              // This will happen both if there is a JSON syntax error or the theme is missing components
+              this.importFailed = true
+              // this.onImportFailure(e)
+            }
+          }
+          reader.readAsText(event.target.files[0])
+        }
+      })
+
+      document.body.appendChild(filePicker)
+      filePicker.click()
+      document.body.removeChild(filePicker)
+    }
+  }
+}
+</script>