// 缩略图懒生成：GET /uploads/thumb/{key}?w=960
//
// 首次请求从存储端读一次原图，缩放编码后落盘缓存（DataDir/.thumbnail_cache），
// 之后直接供缓存——时间线首屏不再拉原图。非图片 / 解码失败 / 冷却期内
// 一律 302 回原图：前端 <img> 拿 302 是无感的。
package api

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

	"oneblog/internal/httpx"
	"oneblog/internal/model"
	"oneblog/internal/storage"
	"oneblog/internal/store"
	"oneblog/internal/thumbs"
)

const (
	thumbDefaultW = 960
	thumbMinW     = 64
	thumbMaxW     = 1600
)

func (a *API) ThumbHandler() http.Handler {
	return http.HandlerFunc(a.thumb)
}

func (a *API) thumb(w http.ResponseWriter, r *http.Request) {
	if a.Thumbs == nil {
		httpx.NotFound(w)
		return
	}
	key := strings.TrimPrefix(r.URL.Path, "/uploads/thumb/")
	if key == "" || strings.Contains(key, "..") {
		httpx.NotFound(w)
		return
	}
	width := thumbDefaultW
	if s := r.URL.Query().Get("w"); s != "" {
		if n, err := strconv.Atoi(s); err == nil && n >= thumbMinW && n <= thumbMaxW {
			width = n
		}
	}

	f, err := a.Store.GetFileByKey(key)
	if errors.Is(err, store.ErrNotFound) {
		httpx.NotFound(w)
		return
	}
	if err != nil {
		httpx.ServerError(w, err)
		return
	}

	if !thumbs.Supported(f.Mime) || f.SHA256 == "" {
		a.thumbFallback(w, r, f)
		return
	}

	// 快路径：缓存命中直接供（锁外）
	if p := a.Thumbs.FindCached(f.SHA256, width); p != "" {
		a.serveThumbFile(w, r, p, f)
		return
	}
	// 冷却期：近期失败过，不再尝试
	if a.Thumbs.FailedRecently(f.SHA256) {
		a.thumbFallback(w, r, f)
		return
	}

	// 慢路径：同 key+宽度并发只生成一次，后来者等锁后读缓存
	lk := a.Thumbs.Lock(f.SHA256, width)
	lk.Lock()
	defer lk.Unlock()
	if p := a.Thumbs.FindCached(f.SHA256, width); p != "" {
		a.serveThumbFile(w, r, p, f)
		return
	}

	rc, _, err := a.Blobs.Open(r.Context(), f.Key)
	if err != nil {
		a.Thumbs.MarkFailed(f.SHA256)
		a.thumbFallback(w, r, f)
		return
	}
	src, err := thumbs.ReadAllLimited(rc, thumbs.MaxSrcBytes)
	rc.Close()
	if err != nil {
		a.Thumbs.MarkFailed(f.SHA256)
		a.thumbFallback(w, r, f)
		return
	}
	out, outMime, _, err := thumbs.Generate(src, f.Mime, width)
	if err != nil {
		a.Thumbs.MarkFailed(f.SHA256)
		a.thumbFallback(w, r, f)
		return
	}
	p, err := a.Thumbs.Put(f.SHA256, width, out, outMime)
	if err != nil {
		// 写缓存失败不拖累本次响应：产物就在内存里
		a.serveThumbBytes(w, outMime, out, f)
		return
	}
	a.serveThumbFile(w, r, p, f)
}

// thumbFallback 回原图：R2 + 公开域名是 302 直链，本地/未配域名回 /uploads/ 路由。
func (a *API) thumbFallback(w http.ResponseWriter, r *http.Request, f model.File) {
	http.Redirect(w, r, storage.FileURL(f.Store, f.Key, a.Cfg.UploadsPublicBase), http.StatusFound)
}

// serveThumbFile 用 ServeContent 供缓存文件：自带 Range/Last-Modified/304。
func (a *API) serveThumbFile(w http.ResponseWriter, r *http.Request, path string, f model.File) {
	fp, err := os.Open(path)
	if err != nil {
		a.thumbFallback(w, r, f)
		return
	}
	defer fp.Close()
	fi, err := fp.Stat()
	if err != nil {
		httpx.NotFound(w)
		return
	}
	a.Thumbs.Touch(path) // 记一次「最近用过」，供容量闸按 LRU 淘汰
	w.Header().Set("Cache-Control", "public, max-age=31536000, immutable")
	http.ServeContent(w, r, path, fi.ModTime(), fp)
}

func (a *API) serveThumbBytes(w http.ResponseWriter, mime string, data []byte, f model.File) {
	w.Header().Set("Content-Type", mime)
	w.Header().Set("Content-Length", strconv.Itoa(len(data)))
	w.Header().Set("ETag", `"`+f.SHA256+`"`)
	w.Header().Set("Cache-Control", "public, max-age=31536000, immutable")
	w.WriteHeader(http.StatusOK)
	_, _ = w.Write(data)
}