package cors

import (
	"net/http"
	"strconv"
	"strings"

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

type Options struct {
	Origin               *[]string //传入空指针，表示允许"*",  传入空数组表示禁止跨域
	Methods              []string  //Methods
	AllowedHeaders       []string  //AllowHeaders
	ExposedHeaders       []string  //exposeHeader
	Credentials          bool      //cookie
	MaxAge               int64     //缓存MaxAge
	PreflightContinue    bool      //在遇到Options的时候，继续，而不是返回请求
	OptionsSuccessStatus int       //Options时，返回的状态码，默认204
}

func configureOrigin(o *Options, c *gin.Context) map[string]string {
	reqOrigin := c.GetHeader("Origin")
	if o.Origin == nil {
		return map[string]string{"Access-Control-Allow-Origin": "*"}
	}
	headers := make(map[string]string)
	isAllowed := false
	for _, allowed := range *o.Origin {
		if allowed == reqOrigin {
			isAllowed = true
			break
		}
	}
	if isAllowed {
		headers["Access-Control-Allow-Origin"] = reqOrigin
	} else {
		headers["Access-Control-Allow-Origin"] = strconv.FormatBool(false)
	}
	headers["Vary"] = "Origin"
	return headers
}

func configureMethods(o *Options) map[string]string {
	headers := make(map[string]string)
	if len(o.Methods) > 0 {
		headers["Access-Control-Allow-Methods"] = strings.ToUpper(strings.Join(o.Methods, ","))
	}
	return headers
}

func configureCredentials(o *Options) map[string]string {
	headers := make(map[string]string)
	if o.Credentials {
		headers["Access-Control-Allow-Credentials"] = strconv.FormatBool(true)
	}
	return headers
}

func configureAllowedHeaders(o *Options, c *gin.Context) map[string]string {
	headers := make(map[string]string)
	if len(o.AllowedHeaders) > 0 {
		headers["Access-Control-Allow-Headers"] = strings.Join(o.AllowedHeaders, ",")
	}
	return headers
}

func configureExposedHeaders(o *Options) map[string]string {
	var headers = make(map[string]string)
	if len(o.ExposedHeaders) > 0 {
		headers["Access-Control-Expose-Headers"] = strings.Join(o.ExposedHeaders, ",")
	}
	return headers
}

func configureMaxAge(o *Options) map[string]string {
	var headers = make(map[string]string)
	if o.MaxAge >= 0 {
		headers["Access-Control-Max-Age"] = strconv.FormatInt(o.MaxAge, 10)
	}
	return headers
}

func mergeMap(m ...map[string]string) map[string]string {
	r := make(map[string]string)
	for _, t := range m {
		for k, v := range t {
			r[k] = v
		}
	}
	return r
}

func applyHeader(c *gin.Context, h map[string]string) {
	for k, v := range h {
		c.Header(k, v)
	}
}

// Cors 跨域处理
func Cors(o *Options) gin.HandlerFunc {
	if o.OptionsSuccessStatus == 0 {
		o.OptionsSuccessStatus = http.StatusNoContent
	}
	return func(c *gin.Context) {
		method := c.Request.Method
		//c.Header("Access-Control-Allow-Origin", "*")
		//c.Header("Access-Control-Allow-Headers", "Content-Type,AccessToken,X-CSRF-Token,Authorization,Token,Content-Length,Etag,Content-Range,Accept-Ranges,User-Agent,Range,Bucket,Content-Disposition,Signature,X-Forwarded-For,X-Real-Ip")
		if method == "OPTIONS" {
			h := mergeMap(
				configureOrigin(o, c),
				configureCredentials(o),
				configureMethods(o),
				configureAllowedHeaders(o, c),
				configureMaxAge(o),
				configureExposedHeaders(o),
			)
			applyHeader(c, h)
			if o.PreflightContinue {
				return
			}
			c.Header("Content-Length", "0")
			c.AbortWithStatus(o.OptionsSuccessStatus)
			return
		}
		h := mergeMap(
			configureOrigin(o, c),
			configureCredentials(o),
			configureExposedHeaders(o),
		)
		applyHeader(c, h)
	}
}