package operations

import (
	"context"
	"encoding/json"
	"io/ioutil"
	"os"
	"path/filepath"

	"github.com/rclone/rclone/fs"
	"github.com/rclone/rclone/fs/config"
	"github.com/rclone/rclone/lib/cacheroot"
)

// Creates an OptionResume that will be passed to Put/Upload
func createResumeOpt(ctx context.Context, f fs.Fs, remote string, src fs.Object) (resumeOpt *fs.OptionResume) {
	ci := fs.GetConfig(ctx)
	cacheParent := config.GetCacheDir()
	resumeOpt = &fs.OptionResume{ID: "", Pos: 0, Src: src, F: f, Remote: remote, CacheCleaned: false, CacheDir: cacheParent}
	if ci.ResumeCutoff >= 0 {
		cacheDir, _, err := cacheroot.CreateCacheRoot(cacheParent, f.Name(), f.Root(), "resume")
		if err != nil {
			return nil
		}
		cacheFile := filepath.Join(cacheDir, remote)
		resumeID, hashName, hashState, attemptResume := readResumeCache(ctx, f, src, cacheFile)
		if attemptResume {
			fs.Debugf(f, "Existing resume cache file found: %s. A resume will now be attempted.", cacheFile)
			position, resumeErr := f.Features().Resume(ctx, remote, resumeID, hashName, hashState)
			if resumeErr != nil {
				fs.Errorf(src, "Resume canceled: %v", resumeErr)
			} else if position > int64(ci.ResumeCutoff) {
				resumeOpt.Pos = position
				resumeOpt.Hash = hashName
			}
		}
	}
	return resumeOpt
}

// readResumeCache checks to see if a resume ID has been cached for the source object.
// If it finds one it returns it along with true to signal a resume can be attempted
func readResumeCache(ctx context.Context, f fs.Fs, src fs.Object, cacheName string) (resumeID, hashName, hashState string, attemptResume bool) {
	existingCacheFile, statErr := os.Open(cacheName)
	defer func() {
		_ = existingCacheFile.Close()
	}()
	if !os.IsNotExist(statErr) {
		rawData, readErr := ioutil.ReadAll(existingCacheFile)
		if readErr == nil {
			existingFingerprint, resumeID, hashName, hashState, unmarshalErr := unmarshalResumeJSON(ctx, rawData)
			if unmarshalErr != nil {
				fs.Debugf(f, "Failed to unmarshal Resume JSON: %s. Resume will not be attempted.", unmarshalErr.Error())
			} else if existingFingerprint != "" {
				// Check if the src object has changed by comparing new Fingerprint to Fingerprint in cache file
				fingerprint := fs.Fingerprint(ctx, src, true)
				if existingFingerprint == fingerprint {
					return resumeID, hashName, hashState, true
				}
			}
		}
	}
	return "", "", "", false
}

func unmarshalResumeJSON(ctx context.Context, data []byte) (fprint, id, hashName, hashState string, err error) {
	var resumedata fs.ResumeJSON
	err = json.Unmarshal(data, &resumedata)
	if err != nil {
		return "", "", "", "", err
	}
	return resumedata.Fingerprint, resumedata.ID, resumedata.HashName, resumedata.HashState, nil
}