package api

import (
	"fmt"
	"net/http"
	"os"
	"path/filepath"
	"strconv"
	"strings"
	"time"

	"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 (a *api) bookRoot(c *gin.Context, b store.Book) (string, bool) {
	lib, ok := a.getLibRow(c, b.LibraryID)
	if !ok {
		return "", false
	}
	return a.libRoot(c, lib)
}

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

func (a *api) serveCover(c *gin.Context) {
	b, ok := a.bookFromParam(c)
	if !ok {
		return
	}
	a.immutable(c)
	dir := bookfile.CoverDir(a.cfg.CacheDir, bookfile.DirKey(b.ID, bookfile.Hash(b.FileSize, b.ModTS)))
	if entries, e := os.ReadDir(dir); e == nil && len(entries) > 0 {
		http.ServeFile(c.Writer, c.Request, filepath.Join(dir, entries[0].Name()))
		return
	}
	c.Data(http.StatusOK, "image/svg+xml", []byte(defaultCover))
}

func (a *api) serveFile(c *gin.Context) {
	b, ok := a.bookFromParam(c)
	if !ok {
		return
	}
	root, ok := a.bookRoot(c, b)
	if !ok {
		return
	}
	abs, perr := absBookPath(root, b)
	if perr != nil {
		err(c, http.StatusForbidden, "forbidden", "unsafe path")
		return
	}
	c.Header("ETag", `"`+bookfile.Hash(b.FileSize, b.ModTS)+`"`)
	c.Header("Cache-Control", "private, must-revalidate")
	http.ServeFile(c.Writer, c.Request, abs)
}

func (a *api) openBook(c *gin.Context, b store.Book, root string) (*os.File, int64, bool) {
	abs, perr := absBookPath(root, b)
	if perr != nil {
		err(c, http.StatusForbidden, "forbidden", "unsafe path")
		return nil, 0, false
	}
	f, perr := os.Open(abs)
	if perr != nil {
		err(c, http.StatusNotFound, "not_found", "file missing on disk")
		return nil, 0, false
	}
	st, perr := f.Stat()
	if perr != nil {
		f.Close()
		err(c, http.StatusInternalServerError, "internal", "stat")
		return nil, 0, false
	}
	return f, st.Size(), true
}

func (a *api) pageIndex(c *gin.Context, b store.Book, root string) ([]string, error) {
	hash := bookfile.Hash(b.FileSize, b.ModTS)
	key := fmt.Sprintf("pagesidx:%d:%s", b.ID, hash)
	if v, ok := a.rdb.Get(c, key); ok && v != "" {
		return strings.Split(v, "\n"), nil
	}
	f, size, ok := a.openBook(c, b, root)
	if !ok {
		return nil, os.ErrNotExist
	}
	defer f.Close()
	idx, e := bookfile.PageIndex(f, size)
	if e != nil {
		return nil, e
	}
	if len(idx) > 0 { // 空索引不缓存,否则 warm 命中 "" 会 Split 出幽灵页
		a.rdb.Set(c, key, strings.Join(idx, "\n"), 7*24*time.Hour)
	}
	return idx, nil
}

func (a *api) pagesCount(c *gin.Context) {
	b, ok := a.bookFromParam(c)
	if !ok {
		return
	}
	if b.Format != "cbz" {
		err(c, http.StatusBadRequest, "bad_request", "pages only for cbz")
		return
	}
	root, ok := a.bookRoot(c, b)
	if !ok {
		return
	}
	idx, e := a.pageIndex(c, b, root)
	if e != nil {
		if c.Writer.Written() {
			return // openBook 已写 403/404,不再叠加 422
		}
		err(c, http.StatusUnprocessableEntity, "broken", e.Error())
		return
	}
	c.JSON(http.StatusOK, gin.H{"count": len(idx)})
}

func (a *api) page(c *gin.Context) {
	b, ok := a.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 := a.bookRoot(c, b)
	if !ok {
		return
	}
	idx, e := a.pageIndex(c, b, root)
	if e != nil {
		if c.Writer.Written() {
			return // openBook 已写 403/404,不再叠加 422
		}
		err(c, http.StatusUnprocessableEntity, "broken", e.Error())
		return
	}
	if n >= len(idx) {
		err(c, http.StatusNotFound, "not_found", "no such page")
		return
	}
	ext := strings.ToLower(filepath.Ext(idx[n]))
	dir := bookfile.PagesDir(a.cfg.CacheDir, bookfile.DirKey(b.ID, bookfile.Hash(b.FileSize, b.ModTS)))
	dst := filepath.Join(dir, strconv.Itoa(n)+ext)
	if _, e := os.Stat(dst); e != nil { // miss → 解压落盘(并发重做同页幂等,唯一 tmp 名 + rename 原子)
		f, size, ok := a.openBook(c, b, root)
		if !ok {
			return
		}
		defer f.Close()
		data, e := bookfile.ReadEntry(f, size, idx[n])
		if e != nil {
			err(c, http.StatusInternalServerError, "internal", "extract page")
			return
		}
		if e := os.MkdirAll(dir, 0o755); e != nil {
			err(c, http.StatusInternalServerError, "internal", "cache dir")
			return
		}
		tmp := fmt.Sprintf("%s.tmp-%d", dst, time.Now().UnixNano())
		if e := os.WriteFile(tmp, data, 0o644); e != nil {
			os.Remove(tmp)
			err(c, http.StatusInternalServerError, "internal", "write cache")
			return
		}
		if e := os.Rename(tmp, dst); e != nil {
			os.Remove(tmp)
			err(c, http.StatusInternalServerError, "internal", "rename cache")
			return
		}
	}
	a.immutable(c)
	http.ServeFile(c.Writer, c.Request, dst)
}