// Licensed under the Apache License, Version 2.0 (the "License"); you may not
// use this file except in compliance with the License. You may obtain a copy of
// the License at
//
//  http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
// WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
// License for the specific language governing permissions and limitations under
// the License.

// Changes feed support
//
// At present, this driver provides only rudimentary Changes feed support. It
// supports only one-off changes feeds (no continuous support), and this is
// implemented by scanning the database directory, and returning each document
// and its most recent revision only.

package fs

import (
	"context"
	"io"
	"os"
	"strings"

	"github.com/go-kivik/kivik/v4/driver"
	"github.com/go-kivik/kivik/v4/x/fsdb/cdb/decode"
)

type changes struct {
	db    *db
	ctx   context.Context
	infos []os.FileInfo
}

var _ driver.Changes = &changes{}

func (c *changes) ETag() string    { return "" }
func (c *changes) LastSeq() string { return "" }
func (c *changes) Pending() int64  { return 0 }

func ignoreDocID(name string) bool {
	if name[0] != '_' {
		return false
	}
	if strings.HasPrefix(name, "_design/") {
		return false
	}
	if strings.HasPrefix(name, "_local/") {
		return false
	}
	return true
}

func (c *changes) Next(ch *driver.Change) error {
	for {
		if len(c.infos) == 0 {
			return io.EOF
		}
		candidate := c.infos[len(c.infos)-1]
		c.infos = c.infos[:len(c.infos)-1]
		if candidate.IsDir() {
			continue
		}
		for _, ext := range decode.Extensions() {
			if strings.HasSuffix(candidate.Name(), "."+ext) {
				base := strings.TrimSuffix(candidate.Name(), "."+ext)
				docid, err := filename2id(base)
				if err != nil {
					// ignore unrecognized files
					continue
				}
				if ignoreDocID(docid) {
					continue
				}
				rev, deleted, err := c.db.metadata(candidate.Name(), ext)
				if err != nil {
					return err
				}
				if rev == "" {
					rev = "1-"
				}
				ch.ID = docid
				ch.Deleted = deleted
				ch.Changes = []string{rev}
				return nil
			}
		}
	}
}

func (c *changes) Close() error {
	return nil
}

func (d *db) Changes(ctx context.Context, _ driver.Options) (driver.Changes, error) {
	f, err := os.Open(d.path())
	if err != nil {
		return nil, err
	}
	dir, err := f.Readdir(-1)
	if err != nil {
		return nil, err
	}
	return &changes{
		db:    d,
		ctx:   ctx,
		infos: dir,
	}, nil
}