// Copyright 2020 The LevelDB-Go and Pebble Authors. All rights reserved. Use
// of this source code is governed by a BSD-style license that can be found in
// the LICENSE file.

package manifest

import (
	"bytes"
	"fmt"

	"github.com/cockroachdb/pebble/internal/base"
)

// LevelMetadata contains metadata for all of the files within
// a level of the LSM.
type LevelMetadata struct {
	level int
	tree  btree
}

// clone makes a copy of the level metadata, implicitly increasing the ref
// count of every file contained within lm.
func (lm *LevelMetadata) clone() LevelMetadata {
	return LevelMetadata{
		level: lm.level,
		tree:  lm.tree.clone(),
	}
}

func (lm *LevelMetadata) release() (obsolete []*FileMetadata) {
	return lm.tree.release()
}

func makeLevelMetadata(cmp Compare, level int, files []*FileMetadata) LevelMetadata {
	bcmp := btreeCmpSeqNum
	if level > 0 {
		bcmp = btreeCmpSmallestKey(cmp)
	}
	var lm LevelMetadata
	lm.level = level
	lm.tree, _ = makeBTree(bcmp, files)
	return lm
}

func makeBTree(cmp btreeCmp, files []*FileMetadata) (btree, LevelSlice) {
	var t btree
	t.cmp = cmp
	for _, f := range files {
		t.insert(f)
	}
	return t, LevelSlice{iter: t.iter(), length: t.length}
}

// Empty indicates whether there are any files in the level.
func (lm *LevelMetadata) Empty() bool {
	return lm.tree.length == 0
}

// Len returns the number of files within the level.
func (lm *LevelMetadata) Len() int {
	return lm.tree.length
}

// Iter constructs a LevelIterator over the entire level.
func (lm *LevelMetadata) Iter() LevelIterator {
	return LevelIterator{iter: lm.tree.iter()}
}

// Slice constructs a slice containing the entire level.
func (lm *LevelMetadata) Slice() LevelSlice {
	return LevelSlice{iter: lm.tree.iter(), length: lm.tree.length}
}

// Find finds the provided file in the level if it exists.
func (lm *LevelMetadata) Find(cmp base.Compare, m *FileMetadata) *LevelFile {
	iter := lm.Iter()
	if lm.level != 0 {
		// If lm holds files for levels >0, we can narrow our search by binary
		// searching by bounds.
		o := overlaps(iter, cmp, m.Smallest.UserKey,
			m.Largest.UserKey, m.Largest.IsExclusiveSentinel())
		iter = o.Iter()
	}
	for f := iter.First(); f != nil; f = iter.Next() {
		if f == m {
			lf := iter.Take()
			return &lf
		}
	}
	return nil
}

// Annotation lazily calculates and returns the annotation defined by
// Annotator. The Annotator is used as the key for pre-calculated
// values, so equal Annotators must be used to avoid duplicate computations
// and cached annotations. Annotation must not be called concurrently, and in
// practice this is achieved by requiring callers to hold DB.mu.
func (lm *LevelMetadata) Annotation(annotator Annotator) interface{} {
	if lm.Empty() {
		return annotator.Zero(nil)
	}
	v, _ := lm.tree.root.annotation(annotator)
	return v
}

// InvalidateAnnotation clears any cached annotations defined by Annotator. The
// Annotator is used as the key for pre-calculated values, so equal Annotators
// must be used to clear the appropriate cached annotation. InvalidateAnnotation
// must not be called concurrently, and in practice this is achieved by
// requiring callers to hold DB.mu.
func (lm *LevelMetadata) InvalidateAnnotation(annotator Annotator) {
	if lm.Empty() {
		return
	}
	lm.tree.root.invalidateAnnotation(annotator)
}

// LevelFile holds a file's metadata along with its position
// within a level of the LSM.
type LevelFile struct {
	*FileMetadata
	slice LevelSlice
}

// Slice constructs a LevelSlice containing only this file.
func (lf LevelFile) Slice() LevelSlice {
	return lf.slice
}

// NewLevelSliceSeqSorted constructs a LevelSlice over the provided files,
// sorted by the L0 sequence number sort order.
// TODO(jackson): Can we improve this interface or avoid needing to export
// a slice constructor like this?
func NewLevelSliceSeqSorted(files []*FileMetadata) LevelSlice {
	tr, slice := makeBTree(btreeCmpSeqNum, files)
	tr.release()
	return slice
}

// NewLevelSliceKeySorted constructs a LevelSlice over the provided files,
// sorted by the files smallest keys.
// TODO(jackson): Can we improve this interface or avoid needing to export
// a slice constructor like this?
func NewLevelSliceKeySorted(cmp base.Compare, files []*FileMetadata) LevelSlice {
	tr, slice := makeBTree(btreeCmpSmallestKey(cmp), files)
	tr.release()
	return slice
}

// NewLevelSliceSpecificOrder constructs a LevelSlice over the provided files,
// ordering the files by their order in the provided slice. It's used in
// tests.
// TODO(jackson): Update tests to avoid requiring this and remove it.
func NewLevelSliceSpecificOrder(files []*FileMetadata) LevelSlice {
	tr, slice := makeBTree(btreeCmpSpecificOrder(files), files)
	tr.release()
	return slice
}

// LevelSlice contains a slice of the files within a level of the LSM.
// A LevelSlice is immutable once created, but may be used to construct a
// mutable LevelIterator over the slice's files.
type LevelSlice struct {
	iter   iterator
	length int
	// start and end form the inclusive bounds of a slice of files within a
	// level of the LSM. They may be nil if the entire B-Tree backing iter is
	// accessible.
	start *iterator
	end   *iterator
}

// Each invokes fn for each element in the slice.
func (ls LevelSlice) Each(fn func(*FileMetadata)) {
	iter := ls.Iter()
	for f := iter.First(); f != nil; f = iter.Next() {
		fn(f)
	}
}

// String implements fmt.Stringer.
func (ls LevelSlice) String() string {
	var buf bytes.Buffer
	ls.Each(func(f *FileMetadata) {
		if buf.Len() > 0 {
			fmt.Fprintf(&buf, " ")
		}
		fmt.Fprint(&buf, f)
	})
	return buf.String()
}

// Empty indicates whether the slice contains any files.
func (ls *LevelSlice) Empty() bool {
	return emptyWithBounds(ls.iter, ls.start, ls.end)
}

// Iter constructs a LevelIterator that iterates over the slice.
func (ls *LevelSlice) Iter() LevelIterator {
	return LevelIterator{
		start: ls.start,
		end:   ls.end,
		iter:  ls.iter.clone(),
	}
}

// Len returns the number of files in the slice. Its runtime is constant.
func (ls *LevelSlice) Len() int {
	return ls.length
}

// SizeSum sums the size of all files in the slice. Its runtime is linear in
// the length of the slice.
func (ls *LevelSlice) SizeSum() uint64 {
	var sum uint64
	iter := ls.Iter()
	for f := iter.First(); f != nil; f = iter.Next() {
		sum += f.Size
	}
	return sum
}

// Reslice constructs a new slice backed by the same underlying level, with
// new start and end positions. Reslice invokes the provided function, passing
// two LevelIterators: one positioned to i's inclusive start and one
// positioned to i's inclusive end. The resliceFunc may move either iterator
// forward or backwards, including beyond the callee's original bounds to
// capture additional files from the underlying level. Reslice constructs and
// returns a new LevelSlice with the final bounds of the iterators after
// calling resliceFunc.
func (ls LevelSlice) Reslice(resliceFunc func(start, end *LevelIterator)) LevelSlice {
	if ls.iter.r == nil {
		return ls
	}
	var start, end LevelIterator
	if ls.start == nil {
		start.iter = ls.iter.clone()
		start.iter.first()
	} else {
		start.iter = ls.start.clone()
	}
	if ls.end == nil {
		end.iter = ls.iter.clone()
		end.iter.last()
	} else {
		end.iter = ls.end.clone()
	}
	resliceFunc(&start, &end)

	s := LevelSlice{
		iter:  start.iter.clone(),
		start: &start.iter,
		end:   &end.iter,
	}
	// Calculate the new slice's length.
	iter := s.Iter()
	for f := iter.First(); f != nil; f = iter.Next() {
		s.length++
	}
	return s
}

// KeyType is used to specify the type of keys we're looking for in
// LevelIterator positioning operations. Files not containing any keys of the
// desired type are skipped.
type KeyType int8

const (
	// KeyTypePointAndRange denotes a search among the entire keyspace, including
	// both point keys and range keys. No sstables are skipped.
	KeyTypePointAndRange KeyType = iota
	// KeyTypePoint denotes a search among the point keyspace. SSTables with no
	// point keys will be skipped. Note that the point keyspace includes rangedels.
	KeyTypePoint
	// KeyTypeRange denotes a search among the range keyspace. SSTables with no
	// range keys will be skipped.
	KeyTypeRange
)

type keyTypeAnnotator struct{}

var _ Annotator = keyTypeAnnotator{}

func (k keyTypeAnnotator) Zero(dst interface{}) interface{} {
	var val *KeyType
	if dst != nil {
		val = dst.(*KeyType)
	} else {
		val = new(KeyType)
	}
	*val = KeyTypePoint
	return val
}

func (k keyTypeAnnotator) Accumulate(m *FileMetadata, dst interface{}) (interface{}, bool) {
	v := dst.(*KeyType)
	switch *v {
	case KeyTypePoint:
		if m.HasRangeKeys {
			*v = KeyTypePointAndRange
		}
	case KeyTypePointAndRange:
		// Do nothing.
	default:
		panic("unexpected key type")
	}
	return v, true
}

func (k keyTypeAnnotator) Merge(src interface{}, dst interface{}) interface{} {
	v := dst.(*KeyType)
	srcVal := src.(*KeyType)
	switch *v {
	case KeyTypePoint:
		if *srcVal == KeyTypePointAndRange {
			*v = KeyTypePointAndRange
		}
	case KeyTypePointAndRange:
		// Do nothing.
	default:
		panic("unexpected key type")
	}
	return v
}

// LevelIterator iterates over a set of files' metadata. Its zero value is an
// empty iterator.
type LevelIterator struct {
	iter   iterator
	start  *iterator
	end    *iterator
	filter KeyType
}

func (i LevelIterator) String() string {
	var buf bytes.Buffer
	iter := i.iter.clone()
	iter.first()
	iter.prev()
	if i.iter.pos == -1 {
		fmt.Fprint(&buf, "(<start>)*")
	}
	iter.next()
	for ; iter.valid(); iter.next() {
		if buf.Len() > 0 {
			fmt.Fprint(&buf, "   ")
		}

		if i.start != nil && cmpIter(iter, *i.start) == 0 {
			fmt.Fprintf(&buf, " [ ")
		}
		isCurrentPos := cmpIter(iter, i.iter) == 0
		if isCurrentPos {
			fmt.Fprint(&buf, " ( ")
		}
		fmt.Fprint(&buf, iter.cur().String())
		if isCurrentPos {
			fmt.Fprint(&buf, " )*")
		}
		if i.end != nil && cmpIter(iter, *i.end) == 0 {
			fmt.Fprintf(&buf, " ]")
		}
	}
	if i.iter.n != nil && i.iter.pos >= i.iter.n.count {
		if buf.Len() > 0 {
			fmt.Fprint(&buf, "   ")
		}
		fmt.Fprint(&buf, "(<end>)*")
	}
	return buf.String()
}

// Clone copies the iterator, returning an independent iterator at the same
// position.
func (i *LevelIterator) Clone() LevelIterator {
	if i.iter.r == nil {
		return *i
	}
	// The start and end iterators are not cloned and are treated as
	// immutable.
	return LevelIterator{
		iter:   i.iter.clone(),
		start:  i.start,
		end:    i.end,
		filter: i.filter,
	}
}

// Current returns the item at the current iterator position.
func (i *LevelIterator) Current() *FileMetadata {
	if !i.iter.valid() {
		return nil
	}
	return i.iter.cur()
}

func (i *LevelIterator) empty() bool {
	return emptyWithBounds(i.iter, i.start, i.end)
}

// Filter clones the iterator and sets the desired KeyType as the key to filter
// files on.
func (i *LevelIterator) Filter(keyType KeyType) LevelIterator {
	l := i.Clone()
	l.filter = keyType
	return l
}

func emptyWithBounds(i iterator, start, end *iterator) bool {
	// If i.r is nil, the iterator was constructed from an empty btree.
	// If the end bound is before the start bound, the bounds represent an
	// empty slice of the B-Tree.
	return i.r == nil || (start != nil && end != nil && cmpIter(*end, *start) < 0)
}

// First seeks to the first file in the iterator and returns it.
func (i *LevelIterator) First() *FileMetadata {
	if i.empty() {
		return nil
	}
	if i.start != nil {
		i.iter = i.start.clone()
	} else {
		i.iter.first()
	}
	if !i.iter.valid() {
		return nil
	}
	return i.filteredNextFile(i.iter.cur())
}

// Last seeks to the last file in the iterator and returns it.
func (i *LevelIterator) Last() *FileMetadata {
	if i.empty() {
		return nil
	}
	if i.end != nil {
		i.iter = i.end.clone()
	} else {
		i.iter.last()
	}
	if !i.iter.valid() {
		return nil
	}
	return i.filteredPrevFile(i.iter.cur())
}

// Next advances the iterator to the next file and returns it.
func (i *LevelIterator) Next() *FileMetadata {
	i.iter.next()
	if !i.iter.valid() {
		return nil
	}
	if i.end != nil && cmpIter(i.iter, *i.end) > 0 {
		return nil
	}
	return i.filteredNextFile(i.iter.cur())
}

// Prev moves the iterator the previous file and returns it.
func (i *LevelIterator) Prev() *FileMetadata {
	i.iter.prev()
	if !i.iter.valid() {
		return nil
	}
	if i.start != nil && cmpIter(i.iter, *i.start) < 0 {
		return nil
	}
	return i.filteredPrevFile(i.iter.cur())
}

// SeekGE seeks to the first file in the iterator's file set with a largest
// user key greater than or equal to the provided user key. The iterator must
// have been constructed from L1+, because it requires the underlying files to
// be sorted by user keys and non-overlapping.
func (i *LevelIterator) SeekGE(cmp Compare, userKey []byte) *FileMetadata {
	// TODO(jackson): Assert that i.iter.cmp == btreeCmpSmallestKey.
	if i.empty() {
		return nil
	}
	meta := i.seek(func(m *FileMetadata) bool {
		return cmp(m.Largest.UserKey, userKey) >= 0
	})
	for meta != nil {
		switch i.filter {
		case KeyTypePointAndRange:
			return meta
		case KeyTypePoint:
			if meta.HasPointKeys && cmp(meta.LargestPointKey.UserKey, userKey) >= 0 {
				return meta
			}
		case KeyTypeRange:
			if meta.HasRangeKeys && cmp(meta.LargestRangeKey.UserKey, userKey) >= 0 {
				return meta
			}
		}
		meta = i.Next()
	}
	return i.filteredNextFile(meta)
}

// SeekLT seeks to the last file in the iterator's file set with a smallest
// user key less than the provided user key. The iterator must have been
// constructed from L1+, because it requires the underlying files to be sorted
// by user keys and non-overlapping.
func (i *LevelIterator) SeekLT(cmp Compare, userKey []byte) *FileMetadata {
	// TODO(jackson): Assert that i.iter.cmp == btreeCmpSmallestKey.
	if i.empty() {
		return nil
	}
	i.seek(func(m *FileMetadata) bool {
		return cmp(m.Smallest.UserKey, userKey) >= 0
	})
	meta := i.Prev()
	for meta != nil {
		switch i.filter {
		case KeyTypePointAndRange:
			return meta
		case KeyTypePoint:
			if meta.HasPointKeys && cmp(meta.SmallestPointKey.UserKey, userKey) < 0 {
				return meta
			}
		case KeyTypeRange:
			if meta.HasRangeKeys && cmp(meta.SmallestRangeKey.UserKey, userKey) < 0 {
				return meta
			}
		}
		meta = i.Prev()
	}
	return i.filteredPrevFile(meta)
}

func (i *LevelIterator) filteredNextFile(meta *FileMetadata) *FileMetadata {
	switch i.filter {
	case KeyTypePoint:
		for meta != nil && !meta.HasPointKeys {
			meta = i.Next()
		}
		return meta
	case KeyTypeRange:
		// TODO(bilal): Range keys are expected to be rare and sparse. Add an
		// optimization to annotate the tree and efficiently skip over files that
		// do not contain range keys right at the seek step, to reduce iterations
		// here.
		for meta != nil && !meta.HasRangeKeys {
			meta = i.Next()
		}
		return meta
	default:
		return meta
	}
}

func (i *LevelIterator) filteredPrevFile(meta *FileMetadata) *FileMetadata {
	switch i.filter {
	case KeyTypePoint:
		for meta != nil && !meta.HasPointKeys {
			meta = i.Prev()
		}
		return meta
	case KeyTypeRange:
		// TODO(bilal): Range keys are expected to be rare and sparse. Add an
		// optimization to annotate the tree and efficiently skip over files that
		// do not contain range keys right at the seek step, to reduce iterations
		// here.
		for meta != nil && !meta.HasRangeKeys {
			meta = i.Prev()
		}
		return meta
	default:
		return meta
	}
}

func (i *LevelIterator) seek(fn func(*FileMetadata) bool) *FileMetadata {
	i.iter.seek(fn)

	// i.iter.seek seeked in the unbounded underlying B-Tree. If the iterator
	// has start or end bounds, we may have exceeded them. Reset to the bounds
	// if necessary.
	//
	// NB: The LevelIterator and LevelSlice semantics require that a bounded
	// LevelIterator/LevelSlice containing files x0, x1, ..., xn behave
	// identically to an unbounded LevelIterator/LevelSlice of a B-Tree
	// containing x0, x1, ..., xn. In other words, any files outside the
	// LevelIterator's bounds should not influence the iterator's behavior.
	// When seeking, this means a SeekGE that seeks beyond the end bound,
	// followed by a Prev should return the last element within bounds.
	if i.end != nil && cmpIter(i.iter, *i.end) > 0 {
		i.iter = i.end.clone()
		// Since seek(fn) positioned beyond i.end, we know there is nothing to
		// return within bounds.
		i.iter.next()
		return nil
	} else if i.start != nil && cmpIter(i.iter, *i.start) < 0 {
		i.iter = i.start.clone()
		return i.iter.cur()
	}
	if !i.iter.valid() {
		return nil
	}
	return i.iter.cur()
}

// Take constructs a LevelFile containing the file at the iterator's current
// position. Take panics if the iterator is not currently positioned over a
// file.
func (i *LevelIterator) Take() LevelFile {
	m := i.Current()
	if m == nil {
		panic("Take called on invalid LevelIterator")
	}
	// LevelSlice's start and end fields are immutable and are positioned to
	// the same position for a LevelFile because they're inclusive, so we can
	// share one iterator stack between the two bounds.
	boundsIter := i.iter.clone()
	return LevelFile{
		FileMetadata: m,
		slice: LevelSlice{
			iter:   i.iter.clone(),
			start:  &boundsIter,
			end:    &boundsIter,
			length: 1,
		},
	}
}