package darwingests3

import (
	"compress/gzip"
	"context"
	"encoding/xml"
	"errors"
	"fmt"
	"io"
	"log"
	"regexp"
	"sort"
	"strconv"
	"time"

	"gocloud.dev/blob"
	"hg.lukegb.com/lukegb/depot/go/trains/darwin"
)

var (
	blobRegex = regexp.MustCompile(`^(?P<datetime>[0-9]{14})(_ref)?_v(?P<version>[0-9]+)\.xml\.gz$`)
)

const (
	understoodVersionTimetable = 8
	understoodVersionReference = 3
)

type fileType int

const (
	fileTypeWantAny fileType = iota
	fileTypeTimetable
	fileTypeReference
)

func (ft fileType) IsA(wantFileType fileType) bool {
	switch wantFileType {
	case fileTypeWantAny:
		return true
	case ft:
		return true
	default:
		return false
	}
}

type fileInfo struct {
	filename     string
	fileType     fileType
	version      int
	filenameDate time.Time
}

func parseFilename(fn string) (fileInfo, error) {
	m := blobRegex.FindStringSubmatch(fn)
	if m == nil {
		return fileInfo{}, fmt.Errorf("couldn't parse filename %q: regex didn't match", fn)
	}

	filenameDateStr := m[1]
	filenameDate, err := time.ParseInLocation("20060102150405", filenameDateStr, darwin.London)
	if err != nil {
		return fileInfo{}, fmt.Errorf("couldn't parse blob filename %q: datetime part %q unparsable: %v", fn, filenameDateStr, err)
	}

	versionStr := m[3]
	version, err := strconv.Atoi(versionStr)
	if err != nil {
		return fileInfo{}, fmt.Errorf("couldn't parse blob filename %q: version part %q unparsable: %v", fn, versionStr, err)
	}

	fileType := fileTypeTimetable
	if m[2] != "" {
		fileType = fileTypeReference
	}

	return fileInfo{
		filename:     fn,
		fileType:     fileType,
		version:      version,
		filenameDate: filenameDate,
	}, nil
}

func filesInBucket(ctx context.Context, bucket *blob.Bucket, wantFileType fileType) ([]fileInfo, error) {
	var fis []fileInfo

	iter := bucket.List(nil)
	for {
		obj, err := iter.Next(ctx)
		if err == io.EOF {
			break
		}
		if err != nil {
			return nil, fmt.Errorf("listing objects in bucket: %w", err)
		}

		fi, err := parseFilename(obj.Key)
		if err != nil {
			log.Print(err)
			continue
		}

		if !fi.fileType.IsA(wantFileType) {
			continue
		}

		fis = append(fis, fi)
	}

	return fis, nil
}

func LoadTimetableForDate(ctx context.Context, bucket *blob.Bucket, ts time.Time) (*darwin.PushPortTimetable, error) {
	// Find the latest filename that covers "today".
	// This is a little tricky, and probably wrong, but we'll try and be good enough.
	fis, err := filesInBucket(ctx, bucket, fileTypeTimetable)
	if err != nil {
		return nil, fmt.Errorf("filesInBucket: %w", err)
	}

	// OK, find one where the date matches...
	wanty, wantm, wantd := ts.Date()
	var got *fileInfo
	for _, fi := range fis {
		if fi.version != understoodVersionTimetable {
			continue
		}
		fiy, fim, fid := fi.filenameDate.Date()
		if wanty == fiy && wantm == fim && wantd == fid {
			fi := fi
			got = &fi
			break
		}
	}
	if got == nil {
		return nil, fmt.Errorf("unable to find matching timetable for %v")
	}

	return LoadTimetable(ctx, bucket, got.filename)
}

func decodeFromBucket(ctx context.Context, bucket *blob.Bucket, filename string, out interface{}) error {
	r, err := bucket.NewReader(ctx, filename, nil)
	if err != nil {
		return fmt.Errorf("NewReader(%q): %w", filename, err)
	}
	defer r.Close()

	gzr, err := gzip.NewReader(r)
	if err != nil {
		return fmt.Errorf("gzip.NewReader(fn=%q): %w", filename, err)
	}
	defer gzr.Close()

	if err := xml.NewDecoder(gzr).Decode(out); err != nil {
		return fmt.Errorf("decoding XML from %q: %w", filename, err)
	}

	return nil
}

var ErrBadVersion = errors.New("darwingests3: bad version, ignoring request")

func LoadTimetable(ctx context.Context, bucket *blob.Bucket, filename string) (*darwin.PushPortTimetable, error) {
	log.Printf("loading timetable from S3 file %q", filename)
	fi, err := parseFilename(filename)
	if err != nil {
		return nil, err
	}
	if fi.version != understoodVersionTimetable {
		return nil, ErrBadVersion
	}
	var ppt darwin.PushPortTimetable
	if err := decodeFromBucket(ctx, bucket, filename, &ppt); err != nil {
		return nil, err
	}
	return &ppt, nil
}

func LoadLatestReferenceData(ctx context.Context, bucket *blob.Bucket) (*darwin.PushPortReferenceData, error) {
	fis, err := filesInBucket(ctx, bucket, fileTypeReference)
	if err != nil {
		return nil, fmt.Errorf("filesInBucket: %w", err)
	}

	sort.Slice(fis, func(i, j int) bool {
		if fis[i].version == understoodVersionReference && fis[j].version != understoodVersionReference {
			return true
		} else if fis[i].version != understoodVersionReference && fis[j].version == understoodVersionReference {
			return false
		}
		return fis[i].filenameDate.Before(fis[j].filenameDate)
	})

	return LoadReferenceData(ctx, bucket, fis[0].filename)
}

func LoadReferenceData(ctx context.Context, bucket *blob.Bucket, filename string) (*darwin.PushPortReferenceData, error) {
	log.Printf("loading reference data from S3 file %q", filename)
	fi, err := parseFilename(filename)
	if err != nil {
		return nil, err
	}
	if fi.version != understoodVersionReference {
		return nil, ErrBadVersion
	}
	var pprd darwin.PushPortReferenceData
	if err := decodeFromBucket(ctx, bucket, filename, &pprd); err != nil {
		return nil, err
	}
	return &pprd, nil
}