package handlers

import (
	"errors"
	"io/fs"
	"net/http"
	"os"
	"path/filepath"
	"strconv"
	"strings"

	"github.com/gin-gonic/gin"

	"booklib/internal/bookfile"
	"booklib/internal/store"
)

const defaultCover = `<svg xmlns="http://www.w3.org/2000/svg" width="120" height="170"><rect width="120" height="170" rx="6" fill="#2a2a33"/><path d="M30 25h60v120H30z" fill="#3a3a45"/><path d="M30 25h60M60 25v120" stroke="#555" stroke-width="2"/></svg>`

func (h *H) bookRoot(c *gin.Context, b store.Book) (string, bool) {
	lib, ok := h.getLib(c, b.LibraryID)
	if !ok {
		return "", false
	}
	return h.libRoot(c, lib)
}

func (h *H) immutable(c *gin.Context) {
	c.Header("Cache-Control", "public, max-age=31536000, immutable")
}

// checkPath 纵深防御:path 越界 → 403,与原契约一致。
func checkPath(c *gin.Context, root string, b store.Book) (string, bool) {
	abs, perr := absBookPath(root, b)
	if perr != nil {
		err(c, http.StatusForbidden, "forbidden", "unsafe path")
		return "", false
	}
	return abs, true
}

// mapContentErr 把 media/bookfile 的文件级失败映射回原契约状态码:
// 文件不在盘上 → 404,其余(坏包等)由调用方决定 422/500。
func mapContentErr(c *gin.Context, e error) bool {
	if errors.Is(e, fs.ErrNotExist) {
		err(c, http.StatusNotFound, "not_found", "file missing on disk")
		return true
	}
	return false
}

func (h *H) ServeCover(c *gin.Context) {
	b, ok := h.bookFromParam(c)
	if !ok {
		return
	}
	h.immutable(c)
	dir := bookfile.CoverDir(h.cfg.CacheDir, bookfile.DirKey(b.ID, bookfile.Hash(b.FileSize, b.ModTS)))
	if entries, e := os.ReadDir(dir); e == nil {
		for _, en := range entries { // 跳过写一半的 .tmp 落盘中间态
			if !strings.Contains(en.Name(), ".tmp") {
				http.ServeFile(c.Writer, c.Request, filepath.Join(dir, en.Name()))
				return
			}
		}
	}
	if b.Format == "cbz" || b.Format == "epub" { // 自愈:缓存丢了就地抽封面(重启/卷漂移/扫描器还没跑到)
		if root, ok := h.bookRoot(c, b); ok {
			if _, ok := checkPath(c, root, b); ok {
				e := h.med.EnsureCover(c, b.ID, b.Format, b.FileSize, b.ModTS, root, b.Path)
				switch {
				case e == nil:
					if entries, re := os.ReadDir(dir); re == nil {
						for _, en := range entries {
							if !strings.Contains(en.Name(), ".tmp") {
								http.ServeFile(c.Writer, c.Request, filepath.Join(dir, en.Name()))
								return
							}
						}
					}
				case mapContentErr(c, e):
					return // 404 已回复
				}
				// 抽取失败(坏包)→ 落到占位 SVG,与原契约一致
			} else {
				return // 403 已回复
			}
		} else {
			return // 404/503 已回复
		}
	}
	if c.Writer.Written() {
		return
	}
	c.Data(http.StatusOK, "image/svg+xml", []byte(defaultCover))
}

func (h *H) ServeFile(c *gin.Context) {
	b, ok := h.bookFromParam(c)
	if !ok {
		return
	}
	root, ok := h.bookRoot(c, b)
	if !ok {
		return
	}
	abs, ok := checkPath(c, root, b)
	if !ok {
		return
	}
	if _, e := os.Stat(abs); e != nil {
		err(c, http.StatusNotFound, "not_found", "file missing on disk")
		return
	}
	c.Header("ETag", `"`+h.med.CacheBuster(b.FileSize, b.ModTS)+`"`)
	c.Header("Cache-Control", "private, must-revalidate")
	http.ServeFile(c.Writer, c.Request, abs)
}

// pageIndex 走 media(redis 缓存 + 索引提取);路径校验仍在 handler,保住 403 契约。
func (h *H) pageIndex(c *gin.Context, b store.Book, root string) ([]string, bool) {
	if _, ok := checkPath(c, root, b); !ok {
		return nil, false
	}
	idx, e := h.med.PageIndex(c, b.ID, b.FileSize, b.ModTS, root, b.Path)
	if e != nil {
		if !mapContentErr(c, e) {
			err(c, http.StatusUnprocessableEntity, "broken", e.Error())
		}
		return nil, false
	}
	return idx, true
}

func (h *H) PagesCount(c *gin.Context) {
	b, ok := h.bookFromParam(c)
	if !ok {
		return
	}
	if b.Format != "cbz" {
		err(c, http.StatusBadRequest, "bad_request", "pages only for cbz")
		return
	}
	root, ok := h.bookRoot(c, b)
	if !ok {
		return
	}
	idx, ok := h.pageIndex(c, b, root)
	if !ok {
		return
	}
	c.JSON(http.StatusOK, gin.H{"count": len(idx), "chapters": h.med.ChaptersOf(idx)})
}

func (h *H) Page(c *gin.Context) {
	b, ok := h.bookFromParam(c)
	if !ok {
		return
	}
	if b.Format != "cbz" {
		err(c, http.StatusBadRequest, "bad_request", "pages only for cbz")
		return
	}
	n, e := strconv.Atoi(c.Param("n"))
	if e != nil || n < 0 {
		err(c, http.StatusBadRequest, "bad_request", "bad page number")
		return
	}
	root, ok := h.bookRoot(c, b)
	if !ok {
		return
	}
	idx, ok := h.pageIndex(c, b, root)
	if !ok {
		return
	}
	if n >= len(idx) {
		err(c, http.StatusNotFound, "not_found", "no such page")
		return
	}
	// miss → 解压落盘(media 内部唯一 tmp 名 + rename 原子,并发重做同页幂等)
	dst, e := h.med.EnsurePage(c, b.ID, b.FileSize, b.ModTS, root, b.Path, n, idx)
	if e != nil {
		if mapContentErr(c, e) {
			return
		}
		err(c, http.StatusInternalServerError, "internal", "extract page")
		return
	}
	h.immutable(c)
	http.ServeFile(c.Writer, c.Request, dst)
}