// This is Free Software under GNU Affero General Public License v >= 3.0
// without warranty, see README.md and license for details.
//
// SPDX-License-Identifier: AGPL-3.0-or-later
// License-Filename: LICENSES/AGPL-3.0.txt
//
// Copyright (C) 2019 by via donau
//   – Österreichische Wasserstraßen-Gesellschaft mbH
// Software engineering by Intevation GmbH
//
// Author(s):
//  * Sascha L. Teichmann <sascha.teichmann@intevation.de>

package wfs

import (
	"bufio"
	"fmt"
	"io"
	"io/ioutil"
	"os"
	"os/exec"
	"path/filepath"
	"sync"

	"gemma.intevation.de/gemma/pkg/config"
	"gemma.intevation.de/gemma/pkg/log"
)

var (
	// FormatGeoJSON is a list of MIME types of
	// GeoJSON documents.
	FormatGeoJSON = []string{"geojson", "application/json"}
	// FormatGML is a list of MIME types
	// GML documents.
	FormatGML = []string{
		"application/gml+xml; version=3.2",
		"gml2", "gml3", "gml32",
		"text/xml; subtype=gml/2.1.2",
		"text/xml; subtype=gml/3.1.1",
		"text/xml; subtype=gml/3.2",
	}
)

type (
	// Downloader abstracts the idea of a download function for WFS.
	Downloader interface {
		Download(user, password string, handler func(string, io.Reader) error) error
	}

	// GeoJSONDownloader is a Downloader for GeoJSON.
	GeoJSONDownloader []string
	// GMLDownloader is a Downloader for GML.
	GMLDownloader []string
)

var (
	getFeaturesOnce sync.Once
	getFeatures     func(*Capabilities, string, string) (Downloader, error)
)

func getFeaturesOnceFunc() {
	path, err := exec.LookPath("ogr2ogr")
	if err != nil {
		log.Infoln("ogr2ogr not installed. Using direct GeoJSON WFS download.")
		getFeatures = getFeaturesGeoJSON
	} else {
		log.Infof("ogr2ogr found at %s. Using GML WFS download.\n", path)
		getFeatures = getFeaturesGML
	}
}

// GetFeatures is the default Downloader in this Gemma server.
func GetFeatures(
	caps *Capabilities,
	featureTypeName string,
	sortBy string,
) (Downloader, error) {
	getFeaturesOnce.Do(getFeaturesOnceFunc)
	return getFeatures(caps, featureTypeName, sortBy)
}

func getFeaturesGeoJSON(
	caps *Capabilities,
	featureTypeName string,
	sortBy string,
) (Downloader, error) {
	urls, err := GetFeaturesGET(
		caps,
		featureTypeName,
		FormatGeoJSON,
		sortBy)
	return GeoJSONDownloader(urls), err
}

func getFeaturesGML(
	caps *Capabilities,
	featureTypeName string,
	sortBy string,
) (Downloader, error) {
	urls, err := GetFeaturesGET(
		caps,
		featureTypeName,
		FormatGML,
		sortBy)
	return GMLDownloader(urls), err
}

// Download is the GeoJSON implementation of the Downloader.
func (gjd GeoJSONDownloader) Download(user, password string, handler func(string, io.Reader) error) error {
	return DownloadURLs(user, password, []string(gjd), handler)
}

func places(n int) int {
	places := 1
	if n < 0 {
		places++
		n = -n
	}
	for value := 10; n >= value; value *= 10 {
		places++
	}
	return places
}

// Download is GML implementaion of the Downloader.
func (gmd GMLDownloader) Download(user, password string, handler func(string, io.Reader) error) error {

	if len(gmd) == 0 {
		return nil
	}

	tmpDir := config.TmpDir()
	dlDir, err := ioutil.TempDir(tmpDir, "wfs-downloads")
	if err != nil {
		return err
	}
	defer os.RemoveAll(dlDir)
	digits := places(len(gmd))

	var files []string

	for i, url := range gmd {
		fname := filepath.Join(dlDir, fmt.Sprintf("%0*d.gml", digits, i))
		if err := downloadURL(user, password, url, func(_ string, r io.Reader) error {
			f, err := os.Create(fname)
			if err != nil {
				return err
			}
			if _, err = io.Copy(f, r); err != nil {
				f.Close()
				return err
			}
			return f.Close()
		}); err != nil {
			return err
		}
		files = append(files, fname)
	}

	out := filepath.Join(dlDir, "out.geojson")

	cmd := exec.Command("ogr2ogr", append([]string{"-f", "GeoJSON", out}, files...)...)

	msg, err := cmd.CombinedOutput()
	if err != nil {
		return fmt.Errorf("ogr2ogr failed: %s", msg)
	}

	in, err := os.Open(out)
	if err != nil {
		return err
	}
	defer in.Close()

	return handler(gmd[0], bufio.NewReader(in))
}