// Copyright 2022 Dolthub, Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package prolly

import (
	"bytes"
	"context"
	"encoding/binary"
	"errors"
	"fmt"
	"io"

	"github.com/dolthub/dolt/go/serial"

	"github.com/dolthub/dolt/go/store/hash"
	"github.com/dolthub/dolt/go/store/pool"
	"github.com/dolthub/dolt/go/store/prolly/message"
	"github.com/dolthub/dolt/go/store/prolly/tree"
	"github.com/dolthub/dolt/go/store/types"
)

// Closure values are a long (8 bytes) followed by a hash (20 bytes, hash.ByteLen).
const prefixWidth = 8

type CommitClosureValue []byte

type CommitClosure struct {
	closure tree.StaticMap[CommitClosureKey, CommitClosureValue, commitClosureKeyOrdering]
}

type commitClosureKeyOrdering struct{}

var _ tree.Ordering[CommitClosureKey] = commitClosureKeyOrdering{}

func (o commitClosureKeyOrdering) Compare(ctx context.Context, left, right CommitClosureKey) (int, error) {
	lh, rh := left.Height(), right.Height()
	if lh == rh {
		return bytes.Compare(left[prefixWidth:], right[prefixWidth:]), nil
	} else if lh < rh {
		return -1, nil
	}
	return 1, nil
}

func NewEmptyCommitClosure(ns tree.NodeStore) (CommitClosure, error) {
	// TODO: since this is constant, we should make a constant for it
	serializer := message.NewCommitClosureSerializer(ns.Pool())
	msg := serializer.Serialize(nil, nil, nil, 0)
	node, fileId, err := tree.NodeFromBytes(msg)
	if fileId != serial.CommitClosureFileID {
		return CommitClosure{}, fmt.Errorf("unexpected file ID for commit closure, expected %s, found %s", serial.CommitClosureFileID, fileId)
	}
	if err != nil {
		return CommitClosure{}, err
	}
	return NewCommitClosure(node, ns)
}

func NewCommitClosure(node *tree.Node, ns tree.NodeStore) (CommitClosure, error) {
	return CommitClosure{
		closure: tree.StaticMap[CommitClosureKey, CommitClosureValue, commitClosureKeyOrdering]{
			Root:      node,
			NodeStore: ns,
			Order:     commitClosureKeyOrdering{},
		},
	}, nil
}

func (c CommitClosure) Count() (int, error) {
	return c.closure.Count()
}

func (c CommitClosure) Height() int {
	return c.closure.Height()
}

func (c CommitClosure) Node() *tree.Node {
	return c.closure.Root
}

func (c CommitClosure) HashOf() hash.Hash {
	return c.closure.HashOf()
}

func (c CommitClosure) Format() *types.NomsBinFormat {
	return c.closure.NodeStore.Format()
}

func (c CommitClosure) Editor() CommitClosureEditor {
	return CommitClosureEditor{
		closure: c.closure.Mutate(),
	}
}

func (c CommitClosure) IterAllReverse(ctx context.Context) (CommitClosureIter, error) {
	return c.closure.IterAllReverse(ctx)
}

func (c CommitClosure) IterHeight(ctx context.Context, height uint64) (CommitClosureIter, error) {
	start := NewCommitClosureKey(c.closure.NodeStore.Pool(), height, hash.Hash{})
	stop := NewCommitClosureKey(c.closure.NodeStore.Pool(), height+1, hash.Hash{})
	return c.closure.IterKeyRange(ctx, start, stop)
}

func (c CommitClosure) IsEmpty() bool {
	return c.Node().Size() == 0
}

func (c CommitClosure) ContainsKey(ctx context.Context, h hash.Hash, height uint64) (bool, error) {
	k := NewCommitClosureKey(c.closure.NodeStore.Pool(), height, h)
	return c.closure.Has(ctx, k)
}

func (c CommitClosure) AsHashSet(ctx context.Context) (hash.HashSet, error) {
	closureIter, err := c.IterAllReverse(ctx)
	if err != nil {
		return hash.HashSet{}, err
	}

	skipCmts := hash.NewHashSet()
	for {
		key, _, err := closureIter.Next(ctx)
		if err != nil {
			if errors.Is(err, io.EOF) {
				break
			}
			return hash.HashSet{}, err

		}

		clsrHash := hash.New(key[prefixWidth:])
		skipCmts.Insert(clsrHash)
	}

	return skipCmts, nil
}

type CommitClosureEditor struct {
	closure tree.MutableMap[CommitClosureKey, CommitClosureValue, commitClosureKeyOrdering, tree.StaticMap[CommitClosureKey, CommitClosureValue, commitClosureKeyOrdering]]
}

type CommitClosureKey []byte

type CommitClosureIter tree.KvIter[CommitClosureKey, CommitClosureValue]

func NewCommitClosureKey(p pool.BuffPool, height uint64, addr hash.Hash) CommitClosureKey {
	r := p.Get(prefixWidth + hash.ByteLen)
	binary.LittleEndian.PutUint64(r, height)
	copy(r[prefixWidth:], addr[:])
	return CommitClosureKey(r)
}

func (k CommitClosureKey) Height() uint64 {
	return binary.LittleEndian.Uint64(k)
}

func (k CommitClosureKey) Addr() hash.Hash {
	return hash.New(k[prefixWidth:])
}

func (k CommitClosureKey) Less(ctx context.Context, other CommitClosureKey) bool {
	cmp, err := commitClosureKeyOrdering{}.Compare(ctx, k, other)
	if err != nil {
		panic(err)
	}
	return cmp < 0
}

var emptyCommitClosureValue CommitClosureValue = CommitClosureValue(make([]byte, 1))

func (wr CommitClosureEditor) Add(ctx context.Context, key CommitClosureKey) error {
	return wr.closure.Put(ctx, key, emptyCommitClosureValue)
}

func (wr CommitClosureEditor) Delete(ctx context.Context, key CommitClosureKey) error {
	return wr.closure.Delete(ctx, key)
}

func (wr CommitClosureEditor) Flush(ctx context.Context) (CommitClosure, error) {
	sm := wr.closure.Static
	serializer := message.NewCommitClosureSerializer(sm.NodeStore.Pool())
	fn := tree.ApplyMutations[CommitClosureKey, commitClosureKeyOrdering, message.CommitClosureSerializer]

	root, err := fn(ctx, sm.NodeStore, sm.Root, commitClosureKeyOrdering{}, serializer, wr.closure.Mutations())
	if err != nil {
		return CommitClosure{}, err
	}

	return CommitClosure{
		closure: tree.StaticMap[CommitClosureKey, CommitClosureValue, commitClosureKeyOrdering]{
			Root:      root,
			NodeStore: sm.NodeStore,
			Order:     sm.Order,
		},
	}, nil
}

func DiffCommitClosures(ctx context.Context, from, to CommitClosure, cb tree.DiffFn) error {
	considerAllRowsModified := false
	return tree.DiffOrderedTrees(ctx, from.closure, to.closure, considerAllRowsModified, cb)
}