package library

import (
	"encoding/json"
	"errors"
	"io/fs"
	"log"
	"os"
	"path/filepath"

	"gitbay.org/cmc/gallery/internal/format"
)

type metaEntry struct {
	ModTime int64       `json:"mtime"`
	Size    int64       `json:"size"`
	Meta    format.Meta `json:"meta"`
}

// MetaCache persists extracted metadata keyed by album-relative path.
type MetaCache struct {
	path    string
	entries map[string]metaEntry
}

func OpenMetaCache(path string) (*MetaCache, error) {
	c := &MetaCache{path: path, entries: map[string]metaEntry{}}
	data, err := os.ReadFile(path)
	if errors.Is(err, fs.ErrNotExist) {
		return c, nil
	}
	if err != nil {
		return nil, err
	}
	if err := json.Unmarshal(data, &c.entries); err != nil {
		log.Printf("meta cache %s unreadable, starting empty: %v", path, err)
		c.entries = map[string]metaEntry{}
	}
	return c, nil
}

func (c *MetaCache) get(rel string, fi fs.FileInfo) (format.Meta, bool) {
	e, ok := c.entries[rel]
	if !ok || e.ModTime != fi.ModTime().UnixNano() || e.Size != fi.Size() {
		return format.Meta{}, false
	}
	return e.Meta, true
}

func (c *MetaCache) put(rel string, fi fs.FileInfo, m format.Meta) {
	c.entries[rel] = metaEntry{ModTime: fi.ModTime().UnixNano(), Size: fi.Size(), Meta: m}
}

func (c *MetaCache) save(keep map[string]bool) error {
	for k := range c.entries {
		if !keep[k] {
			delete(c.entries, k)
		}
	}
	data, err := json.Marshal(c.entries)
	if err != nil {
		return err
	}
	if err := os.MkdirAll(filepath.Dir(c.path), 0o755); err != nil {
		return err
	}
	tmp := c.path + ".tmp"
	if err := os.WriteFile(tmp, data, 0o644); err != nil {
		return err
	}
	return os.Rename(tmp, c.path)
}