package web

import (
	"bytes"
	"image/png"
	"net/http"
	"strconv"
	"sync"
	"time"

	"rond-with-you/internal/fog"
)

// 差异瓦片要反复读同一份快照、同一份库内迷雾，单槽缓存住两边的块集即可——
// 站长一次只会看一份预览。缓存里的 map 加载完就只读，渲染时并发遍历是安全的。
var (
	diffSetsMu    sync.Mutex
	diffSetsToken string
	diffSetsAt    time.Time
	diffSetsCur   map[[2]int][]byte
	diffSetsInc   map[[2]int][]byte
)

// diffSetsTTL 短于暂存的 2 小时：库内迷雾随时可能被别的操作改掉，
// 缓存太久会让差异图与页面上那组数字对不上。
const diffSetsTTL = 10 * time.Minute

func (s *Server) fogDiffSets(token string) (cur, inc map[[2]int][]byte, err error) {
	diffSetsMu.Lock()
	defer diffSetsMu.Unlock()
	if token == diffSetsToken && time.Since(diffSetsAt) < diffSetsTTL {
		return diffSetsCur, diffSetsInc, nil
	}
	data, err := s.loadStashedFog(token)
	if err != nil {
		return nil, nil, err
	}
	blocks, _, err := fog.Decode(data)
	if err != nil {
		return nil, nil, err
	}
	ix, err := s.fogIndex()
	if err != nil {
		return nil, nil, err
	}
	cur = map[[2]int][]byte{}
	ix.View(func(m map[[2]int][]byte) {
		for k, bm := range m {
			cur[k] = bm
		}
	})
	inc = make(map[[2]int][]byte, len(blocks))
	for _, b := range blocks {
		inc[[2]int{b.GX, b.GY}] = b.Bitmap
	}
	diffSetsToken, diffSetsCur, diffSetsInc, diffSetsAt = token, cur, inc, time.Now()
	return cur, inc, nil
}

// adminFogDiffTile 渲染一张差异瓦片：绿=叠加会新增、灰=两边都有、红=整体替换会丢。
// 只给站长看，不涉及遮罩。
func (s *Server) adminFogDiffTile(w http.ResponseWriter, r *http.Request) {
	z, err1 := strconv.Atoi(r.PathValue("z"))
	x, err2 := strconv.Atoi(r.PathValue("x"))
	y, err3 := strconv.Atoi(r.PathValue("y"))
	if err1 != nil || err2 != nil || err3 != nil || z < 0 || z > 22 ||
		x < 0 || y < 0 || x >= 1<<uint(z) || y >= 1<<uint(z) {
		http.NotFound(w, r)
		return
	}
	cur, inc, err := s.fogDiffSets(r.PathValue("token"))
	if err != nil {
		http.NotFound(w, r)
		return
	}
	crs := r.URL.Query().Get("crs")
	if crs != "gcj02" && crs != "wgs84" {
		crs = s.cfg.MapCRS
	}
	img := fog.RenderDiffTile(cur, inc, z, x, y, crs)
	if img == nil {
		http.NotFound(w, r)
		return
	}
	var buf bytes.Buffer
	if err := png.Encode(&buf, img); err != nil {
		s.serverError(w, r, err)
		return
	}
	w.Header().Set("Content-Type", "image/png")
	// 令牌是一次性的，内容也只给站长看，不落共享缓存
	w.Header().Set("Cache-Control", "private, max-age=300")
	w.Write(buf.Bytes())
}