refactor: add useFilePreview composable for shared preview logic

web/frontend/src/composables/useFilePreview.ts

@@ -0,0 +1,47 @@
+import { ref } from 'vue'
+import { ElMessage } from 'element-plus'
+
+export function useFilePreview() {
+  const showPreview = ref(false)
+  const previewType = ref<'image' | 'excel' | ''>('')
+  const previewSrc = ref('')
+  const previewRows = ref<string[][]>([])
+
+  async function openPreview(dir: string, fname: string) {
+    const token = localStorage.getItem('token')
+    try {
+      const resp = await fetch(`/api/files/preview/${dir}/${encodeURIComponent(fname)}`, {
+        headers: { Authorization: `Bearer ${token}` }
+      })
+      const ct = resp.headers.get('content-type') || ''
+      if (ct.includes('image')) {
+        previewType.value = 'image'
+        const blob = await resp.blob()
+        previewSrc.value = URL.createObjectURL(blob)
+      } else {
+        const data = await resp.json()
+        if (data.type === 'excel') {
+          previewType.value = 'excel'
+          previewRows.value = data.rows
+        }
+      }
+      showPreview.value = true
+    } catch {
+      ElMessage.error('预览失败')
+    }
+  }
+
+  function cleanupPreview() {
+    if (previewSrc.value && previewSrc.value.startsWith('blob:')) {
+      URL.revokeObjectURL(previewSrc.value)
+    }
+    previewSrc.value = ''
+    previewType.value = ''
+    previewRows.value = []
+  }
+
+  return {
+    showPreview, previewType, previewSrc, previewRows,
+    openPreview, cleanupPreview
+  }
+}