package middleware

import (
	"github.com/gin-gonic/gin"
)

// CORS 返回一个允许指定来源跨域的中间件。
// 允许 origins 包含 "*" 时回显 *,否则回显请求 Origin 并放行对应来源。
func CORS(allowedOrigins []string) gin.HandlerFunc {
	allowAll := false
	originSet := make(map[string]struct{}, len(allowedOrigins))
	for _, o := range allowedOrigins {
		if o == "*" {
			allowAll = true
			continue
		}
		originSet[o] = struct{}{}
	}
	return func(c *gin.Context) {
		origin := c.GetHeader("Origin")
		if origin == "" {
			c.Next()
			return
		}
		if allowAll {
			c.Header("Access-Control-Allow-Origin", "*")
		} else if _, ok := originSet[origin]; ok {
			c.Header("Access-Control-Allow-Origin", origin)
			c.Header("Vary", "Origin")
		} else {
			c.Next()
			return
		}
		c.Header("Access-Control-Allow-Methods", "GET,POST,PUT,PATCH,DELETE,OPTIONS")
		c.Header("Access-Control-Allow-Headers", "Content-Type,Authorization,X-Requested-With")
		c.Header("Access-Control-Max-Age", "86400")

		if c.Request.Method == "OPTIONS" {
			c.AbortWithStatus(204)
			return
		}
		c.Next()
	}
}