package tsdb

import (
	"encoding/binary"
	"fmt"
	"strings"

	"github.com/fabxc/tsdb/chunks"
)

// SeriesReader provides reading access of serialized time series data.
type SeriesReader interface {
	// Chunk returns the series data chunk with the given reference.
	Chunk(ref uint32) (chunks.Chunk, error)
}

// seriesReader implements a SeriesReader for a serialized byte stream
// of series data.
type seriesReader struct {
	// The underlying byte slice holding the encoded series data.
	b []byte
}

func newSeriesReader(b []byte) (*seriesReader, error) {
	// Verify magic number.
	if m := binary.BigEndian.Uint32(b[:4]); m != MagicSeries {
		return nil, fmt.Errorf("invalid magic number %x", m)
	}
	return &seriesReader{b: b}, nil
}

func (s *seriesReader) Chunk(offset uint32) (chunks.Chunk, error) {
	b := s.b[offset:]

	l, n := binary.Uvarint(b)
	if n < 0 {
		return nil, fmt.Errorf("reading chunk length failed")
	}
	b = b[n:]
	enc := chunks.Encoding(b[0])

	c, err := chunks.FromData(enc, b[1:1+l])
	if err != nil {
		return nil, err
	}
	return c, nil
}

// IndexReader provides reading access of serialized index data.
type IndexReader interface {
	// Stats returns statisitics about the indexed data.
	Stats() (*BlockStats, error)

	// LabelValues returns the possible label values
	LabelValues(names ...string) (StringTuples, error)

	// Postings returns the postings list iteartor for the label pair.
	Postings(name, value string) (Iterator, error)

	// Series returns the series for the given reference.
	Series(ref uint32) (Series, error)
}

// StringTuple is a tuple of strings.
type StringTuple []string

// StringTuples provides access to a sorted list of string tuples.
type StringTuples interface {
	// Total number of tuples in the list.
	Len() int
	// At returns the tuple at position i.
	At(i int) (StringTuple, error)
}

type indexReader struct {
	// The underlying byte slice holding the encoded series data.
	b []byte

	// Cached hashmaps of section offsets.
	labels   map[string]uint32
	postings map[string]uint32
}

var (
	errInvalidSize = fmt.Errorf("invalid size")
	errInvalidFlag = fmt.Errorf("invalid flag")
)

func newIndexReader(b []byte) (*indexReader, error) {
	if len(b) < 16 {
		return nil, errInvalidSize
	}
	r := &indexReader{b: b}

	// Verify magic number.
	if m := binary.BigEndian.Uint32(b[:4]); m != MagicIndex {
		return nil, fmt.Errorf("invalid magic number %x", m)
	}

	var err error
	// The last two 4 bytes hold the pointers to the hashmaps.
	loff := binary.BigEndian.Uint32(b[len(b)-8 : len(b)-4])
	poff := binary.BigEndian.Uint32(b[len(b)-4:])

	if r.labels, err = readHashmap(r.section(loff)); err != nil {
		return nil, err
	}
	if r.postings, err = readHashmap(r.section(poff)); err != nil {
		return nil, err
	}

	return r, nil
}

func readHashmap(flag byte, b []byte, err error) (map[string]uint32, error) {
	if err != nil {
		return nil, err
	}
	if flag != flagStd {
		return nil, errInvalidFlag
	}
	h := make(map[string]uint32, 512)

	for len(b) > 0 {
		l, n := binary.Uvarint(b)
		if n < 1 {
			return nil, errInvalidSize
		}
		s := string(b[n : n+int(l)])
		b = b[n+int(l):]

		o, n := binary.Uvarint(b)
		if n < 1 {
			return nil, errInvalidSize
		}
		b = b[n:]

		h[s] = uint32(o)
	}

	return h, nil
}

func (r *indexReader) section(o uint32) (byte, []byte, error) {
	b := r.b[o:]

	if len(b) < 5 {
		return 0, nil, errInvalidSize
	}

	flag := r.b[0]
	l := binary.BigEndian.Uint32(b[1:5])

	b = b[5:]

	if len(b) < int(l) {
		return 0, nil, errInvalidSize
	}
	return flag, b, nil
}

func (r *indexReader) lookupSymbol(o uint32) ([]byte, error) {
	l, n := binary.Uvarint(r.b[o:])
	if n < 0 {
		return nil, fmt.Errorf("reading symbol length failed")
	}

	end := int(o) + n + int(l)
	if end > len(r.b) {
		return nil, fmt.Errorf("invalid length")
	}

	return r.b[int(o)+n : end], nil
}

func (r *indexReader) Stats() (*BlockStats, error) {
	return nil, nil
}

func (r *indexReader) LabelValues(names ...string) (StringTuples, error) {
	key := strings.Join(names, string(sep))
	off, ok := r.labels[key]
	if !ok {
		return nil, fmt.Errorf("label index doesn't exist")
	}

	flag, b, err := r.section(off)
	if err != nil {
		return nil, fmt.Errorf("section: %s", err)
	}
}