What is the earliest prose collection of pre-Qin philosophers?

The earliest collection of essays by pre-Qin philosophers is Shangshu, and the earliest collection of essays by China is said to have been selected by Confucius. As a historical classic, Shangshu has always been called the earliest collection of essays in China by literary historians, and it is a genre juxtaposed with The Book of Songs. But by today's standards, most of this essay should belong to the official document of the government dealing with state affairs at that time. Accurately speaking, it should be a relatively complete collection of official documents.