package block

import (
	"fmt"
	"io/ioutil"
	"os"
	"path/filepath"
	"strings"
	"time"

	"github.com/kopia/kopia/internal/packindex"
	"golang.org/x/exp/mmap"
)

const (
	simpleIndexSuffix                    = ".sndx"
	unusedCommittedBlockIndexCleanupTime = 1 * time.Hour // delete unused committed index blocks after 1 hour
)

type diskCommittedBlockIndexCache struct {
	dirname string
}

func (c *diskCommittedBlockIndexCache) indexBlockPath(indexBlockID string) string {
	return filepath.Join(c.dirname, indexBlockID+simpleIndexSuffix)
}

func (c *diskCommittedBlockIndexCache) openIndex(indexBlockID string) (packindex.Index, error) {
	fullpath := c.indexBlockPath(indexBlockID)

	f, err := mmap.Open(fullpath)
	if err != nil {
		return nil, err
	}

	return packindex.Open(f)
}

func (c *diskCommittedBlockIndexCache) hasIndexBlockID(indexBlockID string) (bool, error) {
	_, err := os.Stat(c.indexBlockPath(indexBlockID))
	if err == nil {
		return true, nil
	}
	if os.IsNotExist(err) {
		return false, nil
	}

	return false, err
}

func (c *diskCommittedBlockIndexCache) addBlockToCache(indexBlockID string, data []byte) error {
	exists, err := c.hasIndexBlockID(indexBlockID)
	if err != nil {
		return err
	}

	if exists {
		return nil
	}

	tmpFile, err := writeTempFileAtomic(c.dirname, data)
	if err != nil {
		return err
	}

	// rename() is atomic, so one process will succeed, but the other will fail
	if err := os.Rename(tmpFile, c.indexBlockPath(indexBlockID)); err != nil {
		// verify that the block exists
		exists, err := c.hasIndexBlockID(indexBlockID)
		if err != nil {
			return err
		}
		if !exists {
			return fmt.Errorf("unsuccessful index write of block %q", indexBlockID)
		}
	}

	return nil
}

func writeTempFileAtomic(dirname string, data []byte) (string, error) {
	// write to a temp file to avoid race where two processes are writing at the same time.
	tf, err := ioutil.TempFile(dirname, "tmp")
	if err != nil {
		if os.IsNotExist(err) {
			os.MkdirAll(dirname, 0700) //nolint:errcheck
			tf, err = ioutil.TempFile(dirname, "tmp")
		}
	}
	if err != nil {
		return "", fmt.Errorf("can't create tmp file: %v", err)
	}

	if _, err := tf.Write(data); err != nil {
		return "", fmt.Errorf("can't write to temp file: %v", err)
	}
	if err := tf.Close(); err != nil {
		return "", fmt.Errorf("can't close tmp file")
	}

	return tf.Name(), nil
}

func (c *diskCommittedBlockIndexCache) expireUnused(used []string) error {
	entries, err := ioutil.ReadDir(c.dirname)
	if err != nil {
		return fmt.Errorf("can't list cache: %v", err)
	}

	remaining := map[string]os.FileInfo{}

	for _, ent := range entries {
		if strings.HasSuffix(ent.Name(), simpleIndexSuffix) {
			n := strings.TrimSuffix(ent.Name(), simpleIndexSuffix)
			remaining[n] = ent
		}
	}

	for _, u := range used {
		delete(remaining, u)
	}

	for _, rem := range remaining {
		if time.Since(rem.ModTime()) > unusedCommittedBlockIndexCleanupTime {
			log.Debugf("removing unused %v %v", rem.Name(), rem.ModTime())
			if err := os.Remove(filepath.Join(c.dirname, rem.Name())); err != nil {
				log.Warningf("unable to remove unused index file: %v", err)
			}
		} else {
			log.Debugf("keeping unused %v because it's too new %v", rem.Name(), rem.ModTime())
		}
	}

	return nil
}