// Options for Open

package fs

import (
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"net/http"
	"os"
	"path/filepath"
	"sort"
	"strconv"
	"strings"

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

// OpenOption is an interface describing options for Open
type OpenOption interface {
	fmt.Stringer

	// Header returns the option as an HTTP header
	Header() (key string, value string)

	// Mandatory returns whether this option can be ignored or not
	Mandatory() bool
}

// RangeOption defines an HTTP Range option with start and end.  If
// either start or end are < 0 then they will be omitted.
//
// End may be bigger than the Size of the object in which case it will
// be capped to the size of the object.
//
// Note that the End is inclusive, so to fetch 100 bytes you would use
// RangeOption{Start: 0, End: 99}
//
// If Start is specified but End is not then it will fetch from Start
// to the end of the file.
//
// If End is specified, but Start is not then it will fetch the last
// End bytes.
//
// Examples:
//
//     RangeOption{Start: 0, End: 99} - fetch the first 100 bytes
//     RangeOption{Start: 100, End: 199} - fetch the second 100 bytes
//     RangeOption{Start: 100, End: -1} - fetch bytes from offset 100 to the end
//     RangeOption{Start: -1, End: 100} - fetch the last 100 bytes
//
// A RangeOption implements a single byte-range-spec from
// https://tools.ietf.org/html/rfc7233#section-2.1
type RangeOption struct {
	Start int64
	End   int64
}

// Header formats the option as an http header
func (o *RangeOption) Header() (key string, value string) {
	key = "Range"
	value = "bytes="
	if o.Start >= 0 {
		value += strconv.FormatInt(o.Start, 10)

	}
	value += "-"
	if o.End >= 0 {
		value += strconv.FormatInt(o.End, 10)
	}
	return key, value
}

// ParseRangeOption parses a RangeOption from a Range: header.
// It only accepts single ranges.
func ParseRangeOption(s string) (po *RangeOption, err error) {
	const preamble = "bytes="
	if !strings.HasPrefix(s, preamble) {
		return nil, errors.New("Range: header invalid: doesn't start with " + preamble)
	}
	s = s[len(preamble):]
	if strings.IndexRune(s, ',') >= 0 {
		return nil, errors.New("Range: header invalid: contains multiple ranges which isn't supported")
	}
	dash := strings.IndexRune(s, '-')
	if dash < 0 {
		return nil, errors.New("Range: header invalid: contains no '-'")
	}
	start, end := strings.TrimSpace(s[:dash]), strings.TrimSpace(s[dash+1:])
	o := RangeOption{Start: -1, End: -1}
	if start != "" {
		o.Start, err = strconv.ParseInt(start, 10, 64)
		if err != nil || o.Start < 0 {
			return nil, errors.New("Range: header invalid: bad start")
		}
	}
	if end != "" {
		o.End, err = strconv.ParseInt(end, 10, 64)
		if err != nil || o.End < 0 {
			return nil, errors.New("Range: header invalid: bad end")
		}
	}
	return &o, nil
}

// String formats the option into human-readable form
func (o *RangeOption) String() string {
	return fmt.Sprintf("RangeOption(%d,%d)", o.Start, o.End)
}

// Mandatory returns whether the option must be parsed or can be ignored
func (o *RangeOption) Mandatory() bool {
	return true
}

// Decode interprets the RangeOption into an offset and a limit
//
// The offset is the start of the stream and the limit is how many
// bytes should be read from it.  If the limit is -1 then the stream
// should be read to the end.
func (o *RangeOption) Decode(size int64) (offset, limit int64) {
	if o.Start >= 0 {
		offset = o.Start
		if o.End >= 0 {
			limit = o.End - o.Start + 1
		} else {
			limit = -1
		}
	} else {
		if o.End >= 0 {
			offset = size - o.End
		} else {
			offset = 0
		}
		limit = -1
	}
	return offset, limit
}

// FixRangeOption looks through the slice of options and adjusts any
// RangeOption~s found that request a fetch from the end into an
// absolute fetch using the size passed in and makes sure the range does
// not exceed filesize. Some remotes (e.g. Onedrive, Box) don't support
// range requests which index from the end.
func FixRangeOption(options []OpenOption, size int64) {
	if size == 0 {
		// if size 0 then remove RangeOption~s
		// replacing with a NullOptions~s which won't be rendered
		for i := range options {
			if _, ok := options[i].(*RangeOption); ok {
				options[i] = NullOption{}

			}
		}
		return
	}
	for i := range options {
		option := options[i]
		if x, ok := option.(*RangeOption); ok {
			// If start is < 0 then fetch from the end
			if x.Start < 0 {
				x = &RangeOption{Start: size - x.End, End: -1}
				options[i] = x
			}
			if x.End > size {
				x = &RangeOption{Start: x.Start, End: size - 1}
				options[i] = x
			}
		}
	}
}

// SeekOption defines an HTTP Range option with start only.
type SeekOption struct {
	Offset int64
}

// Header formats the option as an http header
func (o *SeekOption) Header() (key string, value string) {
	key = "Range"
	value = fmt.Sprintf("bytes=%d-", o.Offset)
	return key, value
}

// String formats the option into human-readable form
func (o *SeekOption) String() string {
	return fmt.Sprintf("SeekOption(%d)", o.Offset)
}

// Mandatory returns whether the option must be parsed or can be ignored
func (o *SeekOption) Mandatory() bool {
	return true
}

// HTTPOption defines a general purpose HTTP option
type HTTPOption struct {
	Key   string
	Value string
}

// Header formats the option as an http header
func (o *HTTPOption) Header() (key string, value string) {
	return o.Key, o.Value
}

// String formats the option into human-readable form
func (o *HTTPOption) String() string {
	return fmt.Sprintf("HTTPOption(%q,%q)", o.Key, o.Value)
}

// Mandatory returns whether the option must be parsed or can be ignored
func (o *HTTPOption) Mandatory() bool {
	return false
}

// HashesOption defines an option used to tell the local fs to limit
// the number of hashes it calculates.
type HashesOption struct {
	Hashes hash.Set
}

// Header formats the option as an http header
func (o *HashesOption) Header() (key string, value string) {
	return "", ""
}

// String formats the option into human-readable form
func (o *HashesOption) String() string {
	return fmt.Sprintf("HashesOption(%v)", o.Hashes)
}

// Mandatory returns whether the option must be parsed or can be ignored
func (o *HashesOption) Mandatory() bool {
	return false
}

// OptionResume defines a Put/Upload for doing resumes
type OptionResume struct {
	ID           string // resume this ID if set
	Pos          int64  // and resume from this position
	Hash         string
	Src          Object
	F            Fs
	Remote       string
	CacheCleaned bool
	CacheDir     string
}

// SetID will be called by backend's Put/Update function if the object's upload
// could be resumed upon failure
//
// SetID takes the passed resume ID, hash state, hash name and Fingerprint of the object and stores it in
// --cache-dir so that future Copy operations can resume the upload if it fails
func (o *OptionResume) SetID(ctx context.Context, ID, hashName, hashState string) error {
	ci := GetConfig(ctx)
	// Get the Fingerprint of the src object so that future Copy operations can ensure the
	// object hasn't changed before resuming an upload
	fingerprint := Fingerprint(ctx, o.Src, true)
	data, err := marshalResumeJSON(ctx, fingerprint, ID, hashName, hashState)
	if err != nil {
		return fmt.Errorf("failed to marshal data JSON: %w", err)
	}
	if len(data) < int(ci.MaxResumeCacheSize) {
		// Each remote will have its own directory for cached resume files
		dirPath, _, err := cacheroot.CreateCacheRoot(o.CacheDir, o.F.Name(), o.F.Root(), "resume")
		if err != nil {
			return err
		}
		err = os.MkdirAll(dirPath, os.ModePerm)
		if err != nil {
			return fmt.Errorf("failed to create cache directory %v: %w", dirPath, err)
		}
		// Write resume data to disk
		cachePath := filepath.Join(dirPath, o.Remote)
		cacheFile, err := os.Create(cachePath)
		if err != nil {
			return fmt.Errorf("failed to create cache file %v: %w", cachePath, err)
		}
		defer func() {
			_ = cacheFile.Close()
		}()
		_, errWrite := cacheFile.Write(data)
		if errWrite != nil {
			return fmt.Errorf("failed to write JSON to file: %w", errWrite)
		}
	}
	if !o.CacheCleaned {
		rootCacheDir := filepath.Join(o.CacheDir, "resume")
		if err := cleanResumeCache(ctx, rootCacheDir); err != nil {
			return fmt.Errorf("failed to clean resume cache: %w", err)
		}
	}
	o.CacheCleaned = true
	return nil
}

// ResumeJSON is a struct for storing resume info in cache
type ResumeJSON struct {
	Fingerprint string `json:"fprint"`
	ID          string `json:"id"`
	HashName    string `json:"hname"`
	HashState   string `json:"hstate"`
}

func marshalResumeJSON(ctx context.Context, fprint, id, hashName, hashState string) ([]byte, error) {
	resumedata := ResumeJSON{
		Fingerprint: fprint,
		ID:          id,
		HashName:    hashName,
		HashState:   hashState,
	}
	data, err := json.Marshal(&resumedata)
	return data, err
}

// cleanCache checks the size of the resume cache and removes the oldest resume files if more than limit
func cleanResumeCache(ctx context.Context, rootCacheDir string) error {
	ci := GetConfig(ctx)
	var paths []string
	pathsWithInfo := make(map[string]os.FileInfo)
	totalCacheSize := int64(0)
	walkErr := filepath.Walk(rootCacheDir,
		func(path string, info os.FileInfo, err error) error {
			if err != nil {
				return err
			}
			if info.IsDir() {
				// Empty subdirectories in the resume cache dir can be removed
				removeErr := os.Remove(path)
				if err != nil && !os.IsNotExist(removeErr) {
					return fmt.Errorf("failed to remove empty subdirectory: %s: %w", path, err)
				}
				return nil
			}
			paths = append(paths, path)
			pathsWithInfo[path] = info
			totalCacheSize += info.Size()
			return nil
		})
	if walkErr != nil {
		return fmt.Errorf("error walking through cache when cleaning cache dir: %w", walkErr)
	}
	if totalCacheSize > int64(ci.MaxResumeCacheSize) {
		sort.Slice(paths, func(i, j int) bool {
			return pathsWithInfo[paths[i]].ModTime().Before(pathsWithInfo[paths[j]].ModTime())
		})
		for _, p := range paths {
			if totalCacheSize < int64(ci.MaxResumeCacheSize) {
				break
			}
			if err := os.Remove(p); err != nil {
				return fmt.Errorf("error removing oldest cache file: %s: %w", p, err)
			}
			totalCacheSize -= pathsWithInfo[p].Size()
			Debugf(p, "Successfully removed oldest cache file")
		}
	}
	return nil
}

// Header formats the option as an http header
func (o *OptionResume) Header() (key string, value string) {
	return "", ""
}

// String formats the option into human readable form
func (o *OptionResume) String() string {
	return fmt.Sprintf("OptionResume(ID:%v, Pos:%v)", o.ID, o.Pos)
}

// Mandatory returns whether the option must be parsed or can be ignored
func (o *OptionResume) Mandatory() bool {
	return false
}

// NullOption defines an Option which does nothing
type NullOption struct {
}

// Header formats the option as an http header
func (o NullOption) Header() (key string, value string) {
	return "", ""
}

// String formats the option into human-readable form
func (o NullOption) String() string {
	return fmt.Sprintf("NullOption()")
}

// Mandatory returns whether the option must be parsed or can be ignored
func (o NullOption) Mandatory() bool {
	return false
}

// OpenOptionAddHeaders adds each header found in options to the
// headers map provided the key was non empty.
func OpenOptionAddHeaders(options []OpenOption, headers map[string]string) {
	for _, option := range options {
		key, value := option.Header()
		if key != "" && value != "" {
			headers[key] = value
		}
	}
}

// OpenOptionHeaders adds each header found in options to the
// headers map provided the key was non empty.
//
// It returns a nil map if options was empty
func OpenOptionHeaders(options []OpenOption) (headers map[string]string) {
	if len(options) == 0 {
		return nil
	}
	headers = make(map[string]string, len(options))
	OpenOptionAddHeaders(options, headers)
	return headers
}

// OpenOptionAddHTTPHeaders Sets each header found in options to the
// http.Header map provided the key was non empty.
func OpenOptionAddHTTPHeaders(headers http.Header, options []OpenOption) {
	for _, option := range options {
		key, value := option.Header()
		if key != "" && value != "" {
			headers.Set(key, value)
		}
	}
}