// Package b1 reads data from b1 shards.
package b1 // import "github.com/influxdata/influxdb/cmd/influx_tsm/b1"

import (
	"encoding/binary"
	"math"
	"sort"
	"time"

	"github.com/boltdb/bolt"
	"github.com/influxdata/influxdb/cmd/influx_tsm/stats"
	"github.com/influxdata/influxdb/cmd/influx_tsm/tsdb"
	"github.com/influxdata/influxdb/tsdb/engine/tsm1"
)

// DefaultChunkSize is the size of chunks read from the b1 shard
const DefaultChunkSize int = 1000

var excludedBuckets = map[string]bool{
	"fields": true,
	"meta":   true,
	"series": true,
	"wal":    true,
}

// Reader is used to read all data from a b1 shard.
type Reader struct {
	path string
	db   *bolt.DB
	tx   *bolt.Tx

	cursors    []*cursor
	currCursor int

	keyBuf   string
	values   []tsm1.Value
	valuePos int

	fields map[string]*tsdb.MeasurementFields
	codecs map[string]*tsdb.FieldCodec

	stats *stats.Stats
}

// NewReader returns a reader for the b1 shard at path.
func NewReader(path string, stats *stats.Stats, chunkSize int) *Reader {
	r := &Reader{
		path:   path,
		fields: make(map[string]*tsdb.MeasurementFields),
		codecs: make(map[string]*tsdb.FieldCodec),
		stats:  stats,
	}

	if chunkSize <= 0 {
		chunkSize = DefaultChunkSize
	}

	r.values = make([]tsm1.Value, chunkSize)

	return r
}

// Open opens the reader.
func (r *Reader) Open() error {
	// Open underlying storage.
	db, err := bolt.Open(r.path, 0666, &bolt.Options{Timeout: 1 * time.Second})
	if err != nil {
		return err
	}
	r.db = db

	// Load fields.
	if err := r.db.View(func(tx *bolt.Tx) error {
		meta := tx.Bucket([]byte("fields"))
		c := meta.Cursor()

		for k, v := c.First(); k != nil; k, v = c.Next() {
			mf := &tsdb.MeasurementFields{}
			if err := mf.UnmarshalBinary(v); err != nil {
				return err
			}
			r.fields[string(k)] = mf
			r.codecs[string(k)] = tsdb.NewFieldCodec(mf.Fields)
		}
		return nil
	}); err != nil {
		return err
	}

	seriesSet := make(map[string]bool)

	// ignore series index and find all series in this shard
	if err := r.db.View(func(tx *bolt.Tx) error {
		tx.ForEach(func(name []byte, _ *bolt.Bucket) error {
			key := string(name)
			if !excludedBuckets[key] {
				seriesSet[key] = true
			}
			return nil
		})
		return nil
	}); err != nil {
		return err
	}

	r.tx, err = r.db.Begin(false)
	if err != nil {
		return err
	}

	// Create cursor for each field of each series.
	for s := range seriesSet {
		measurement := tsdb.MeasurementFromSeriesKey(s)
		fields := r.fields[measurement]
		if fields == nil {
			r.stats.IncrFiltered()
			continue
		}
		for _, f := range fields.Fields {
			c := newCursor(r.tx, s, f.Name, r.codecs[measurement])
			c.SeekTo(0)
			r.cursors = append(r.cursors, c)
		}
	}
	sort.Sort(cursors(r.cursors))

	return nil
}

// Next returns whether any data remains to be read. It must be called before
// the next call to Read().
func (r *Reader) Next() bool {
	r.valuePos = 0
OUTER:
	for {
		if r.currCursor >= len(r.cursors) {
			// All cursors drained. No more data remains.
			return false
		}

		cc := r.cursors[r.currCursor]
		r.keyBuf = tsm1.SeriesFieldKey(cc.series, cc.field)

		for {
			k, v := cc.Next()
			if k == -1 {
				// Go to next cursor and try again.
				r.currCursor++
				if r.valuePos == 0 {
					// The previous cursor had no data. Instead of returning
					// just go immediately to the next cursor.
					continue OUTER
				}
				// There is some data available. Indicate that it should be read.
				return true
			}

			if f, ok := v.(float64); ok {
				if math.IsInf(f, 0) {
					r.stats.AddPointsRead(1)
					r.stats.IncrInf()
					continue
				}

				if math.IsNaN(f) {
					r.stats.AddPointsRead(1)
					r.stats.IncrNaN()
					continue
				}
			}

			r.values[r.valuePos] = tsm1.NewValue(k, v)
			r.valuePos++

			if r.valuePos >= len(r.values) {
				return true
			}
		}
	}
}

// Read returns the next chunk of data in the shard, converted to tsm1 values. Data is
// emitted completely for every field, in every series, before the next field is processed.
// Data from Read() adheres to the requirements for writing to tsm1 shards
func (r *Reader) Read() (string, []tsm1.Value, error) {
	return r.keyBuf, r.values[:r.valuePos], nil
}

// Close closes the reader.
func (r *Reader) Close() error {
	r.tx.Rollback()
	return r.db.Close()
}

// cursor provides ordered iteration across a series.
type cursor struct {
	// Bolt cursor and readahead buffer.
	cursor *bolt.Cursor
	keyBuf int64
	valBuf interface{}

	series string
	field  string
	dec    *tsdb.FieldCodec
}

// Cursor returns an iterator for a key over a single field.
func newCursor(tx *bolt.Tx, series string, field string, dec *tsdb.FieldCodec) *cursor {
	cur := &cursor{
		keyBuf: -2,
		series: series,
		field:  field,
		dec:    dec,
	}

	// Retrieve series bucket.
	b := tx.Bucket([]byte(series))
	if b != nil {
		cur.cursor = b.Cursor()
	}

	return cur
}

// Seek moves the cursor to a position.
func (c *cursor) SeekTo(seek int64) {
	var seekBytes [8]byte
	binary.BigEndian.PutUint64(seekBytes[:], uint64(seek))
	k, v := c.cursor.Seek(seekBytes[:])
	c.keyBuf, c.valBuf = tsdb.DecodeKeyValue(c.field, c.dec, k, v)
}

// Next returns the next key/value pair from the cursor.
func (c *cursor) Next() (key int64, value interface{}) {
	for {
		k, v := func() (int64, interface{}) {
			if c.keyBuf != -2 {
				k, v := c.keyBuf, c.valBuf
				c.keyBuf = -2
				return k, v
			}

			k, v := c.cursor.Next()
			if k == nil {
				return -1, nil
			}
			return tsdb.DecodeKeyValue(c.field, c.dec, k, v)
		}()

		if k != -1 && v == nil {
			// There is a point in the series at the next timestamp,
			// but not for this cursor's field. Go to the next point.
			continue
		}
		return k, v
	}
}

// Sort b1 cursors in correct order for writing to TSM files.

type cursors []*cursor

func (a cursors) Len() int      { return len(a) }
func (a cursors) Swap(i, j int) { a[i], a[j] = a[j], a[i] }
func (a cursors) Less(i, j int) bool {
	if a[i].series == a[j].series {
		return a[i].field < a[j].field
	}
	return a[i].series < a[j].series
}
