// Package server 定义采购服务当前拥有的 HTTP 端点。
package server

import (
	"crypto/subtle"
	"errors"
	"net/http"
	"net/url"
	"strings"

	"cmbuyer/admin/internal/auth"
	"cmbuyer/admin/internal/transport/webui"

	"github.com/gin-gonic/gin"
	"golang.org/x/crypto/bcrypt"
)

const maxFormBytes = 8 << 10

// Options 是路由层需要的安全依赖。凭据由启动配置注入，不能在路由中设置默认值。
type Options struct {
	AdminUsername       string
	AdminPasswordBcrypt string
	Sessions            *auth.Manager
}

// NewRouter 返回当前服务范围内的完整 HTTP 路由。
func NewRouter(options Options) (*gin.Engine, error) {
	if options.AdminUsername == "" || options.AdminPasswordBcrypt == "" || options.Sessions == nil {
		return nil, errors.New("server authentication options are incomplete")
	}

	router := gin.New()
	router.Use(gin.Recovery())
	router.Use(securityHeaders())
	router.GET("/healthz", healthz)
	router.GET("/login", loginPage(options))
	router.POST("/login", login(options))
	router.POST("/logout", logout(options))
	router.GET("/tasks", tasksPage(options))

	return router, nil
}

func healthz(context *gin.Context) {
	context.JSON(http.StatusOK, gin.H{"status": "ok"})
}

func securityHeaders() gin.HandlerFunc {
	return func(context *gin.Context) {
		context.Header("Cache-Control", "no-store")
		context.Header("X-Content-Type-Options", "nosniff")
		context.Header("Referrer-Policy", "no-referrer")
		context.Header("Content-Security-Policy", "default-src 'self'; style-src 'self' 'unsafe-inline'; script-src 'none'; object-src 'none'; base-uri 'none'; frame-ancestors 'none'; form-action 'self'")
		context.Next()
	}
}

func loginPage(options Options) gin.HandlerFunc {
	return func(context *gin.Context) {
		csrfToken, authenticated := options.Sessions.Ensure(context.Writer, context.Request)
		if authenticated {
			context.Redirect(http.StatusSeeOther, "/tasks")
			return
		}

		renderLogin(context, http.StatusOK, csrfToken, returnTo(context.Query("return_to")), "", "")
	}
}

func login(options Options) gin.HandlerFunc {
	return func(context *gin.Context) {
		limitFormBody(context)
		csrfToken := context.PostForm("csrf_token")
		returnPath := returnTo(context.PostForm("return_to"))
		username := context.PostForm("username")
		password := context.PostForm("password")

		if _, ok := options.Sessions.VerifyCSRF(context.Request, csrfToken); !ok {
			newCSRF, _ := options.Sessions.Ensure(context.Writer, context.Request)
			renderLogin(context, http.StatusForbidden, newCSRF, returnPath, "", "请求已过期，请重新登录。")
			return
		}

		usernameMatches := subtle.ConstantTimeCompare([]byte(options.AdminUsername), []byte(username)) == 1
		passwordMatches := bcrypt.CompareHashAndPassword([]byte(options.AdminPasswordBcrypt), []byte(password)) == nil
		if !usernameMatches || !passwordMatches {
			csrf, _ := options.Sessions.Ensure(context.Writer, context.Request)
			renderLogin(context, http.StatusUnauthorized, csrf, returnPath, "", "账号或密码不正确，请检查后重试。")
			return
		}

		options.Sessions.RotateAuthenticated(context.Writer, context.Request)
		context.Redirect(http.StatusSeeOther, returnPath)
	}
}

func logout(options Options) gin.HandlerFunc {
	return func(context *gin.Context) {
		limitFormBody(context)
		authenticated, ok := options.Sessions.VerifyCSRF(context.Request, context.PostForm("csrf_token"))
		if !ok || !authenticated {
			context.Status(http.StatusForbidden)
			return
		}

		options.Sessions.Logout(context.Writer, context.Request)
		context.Redirect(http.StatusSeeOther, "/login")
	}
}

func tasksPage(options Options) gin.HandlerFunc {
	return func(context *gin.Context) {
		csrfToken, authenticated := options.Sessions.Ensure(context.Writer, context.Request)
		if !authenticated {
			context.Redirect(http.StatusSeeOther, "/login?return_to="+url.QueryEscape(context.Request.URL.RequestURI()))
			return
		}

		context.Header("Content-Type", "text/html; charset=utf-8")
		if err := webui.RenderTasks(context.Writer, webui.TasksData{CSRFToken: csrfToken}); err != nil {
			_ = context.Error(err)
		}
	}
}

func renderLogin(context *gin.Context, status int, csrfToken, returnPath, username, message string) {
	context.Header("Content-Type", "text/html; charset=utf-8")
	context.Status(status)
	if err := webui.RenderLogin(context.Writer, webui.LoginData{
		CSRFToken: csrfToken,
		ReturnTo:  returnPath,
		Username:  username,
		Error:     message,
	}); err != nil {
		_ = context.Error(err)
	}
}

func limitFormBody(context *gin.Context) {
	context.Request.Body = http.MaxBytesReader(context.Writer, context.Request.Body, maxFormBytes)
}

func returnTo(value string) string {
	if value == "/tasks" || strings.HasPrefix(value, "/tasks/") || strings.HasPrefix(value, "/tasks?") {
		if strings.Contains(value, "\\") || strings.Contains(value, "%") || strings.HasPrefix(value, "//") {
			return "/tasks"
		}
		parsed, err := url.ParseRequestURI(value)
		if err == nil && parsed.IsAbs() == false && parsed.Host == "" && hasSafeTaskPath(parsed.Path) {
			return value
		}
	}

	return "/tasks"
}

func hasSafeTaskPath(path string) bool {
	for _, segment := range strings.Split(path, "/") {
		if segment == "." || segment == ".." {
			return false
		}
	}
	return true
}