// Copyright 2019 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.
//
// This file incorporates work covered by the following copyright and
// permission notice:
//
// Copyright 2016 Attic Labs, Inc. All rights reserved.
// Licensed under the Apache License, version 2.0:
// http://www.apache.org/licenses/LICENSE-2.0

package diff

import (
	"bytes"
	"context"

	"github.com/dolthub/dolt/go/store/types"
)

// Patch is a list of difference objects that can be applied to a graph
// using ApplyPatch(). Patch implements a sort order that is useful for
// applying the patch in an efficient way.
type Patch []Difference

type PatchSort struct {
	patch Patch
}

func (ps PatchSort) Swap(i, j int) {
	ps.patch[i], ps.patch[j] = ps.patch[j], ps.patch[i]
}

func (ps PatchSort) Len() int {
	return len(ps.patch)
}

var vals = map[types.DiffChangeType]int{types.DiffChangeRemoved: 0, types.DiffChangeModified: 1, types.DiffChangeAdded: 2}

func (ps PatchSort) Less(ctx context.Context, nbf *types.NomsBinFormat, i, j int) (bool, error) {
	if ps.patch[i].Path.Equals(ps.patch[j].Path) {
		return vals[ps.patch[i].ChangeType] < vals[ps.patch[j].ChangeType], nil
	}
	return pathIsLess(ctx, nbf, ps.patch[i].Path, ps.patch[j].Path)
}

// Utility methods on path
// TODO: Should these be on types.Path & types.PathPart?
func pathIsLess(ctx context.Context, nbf *types.NomsBinFormat, p1, p2 types.Path) (bool, error) {
	for i, pp1 := range p1 {
		if len(p2) == i {
			return false, nil // p1 > p2
		}

		idx, err := pathPartCompare(ctx, nbf, pp1, p2[i])

		if err != nil {
			return false, err
		}

		switch idx {
		case -1:
			return true, nil // p1 < p2
		case 1:
			return false, nil // p1 > p2
		}
	}

	return len(p2) > len(p1), nil // if true p1 < p2, else p1 == p2
}

func fieldPathCompare(pp types.FieldPath, o types.PathPart) int {
	switch opp := o.(type) {
	case types.FieldPath:
		if pp.Name == opp.Name {
			return 0
		}
		if pp.Name < opp.Name {
			return -1
		}
		return 1
	case types.IndexPath:
		return -1
	case types.HashIndexPath:
		return -1
	}
	panic("unreachable")
}

func indexPathCompare(ctx context.Context, nbf *types.NomsBinFormat, pp types.IndexPath, o types.PathPart) (int, error) {
	switch opp := o.(type) {
	case types.FieldPath:
		return 1, nil
	case types.IndexPath:
		if pp.Index.Equals(opp.Index) {
			if pp.IntoKey == opp.IntoKey {
				return 0, nil
			}
			if pp.IntoKey {
				return -1, nil
			}
			return 1, nil
		}
		if isLess, err := pp.Index.Less(ctx, nbf, opp.Index); err != nil {
			return 0, err
		} else if isLess {
			return -1, nil
		}
		return 1, nil
	case types.HashIndexPath:
		return -1, nil
	}
	panic("unreachable")
}

func hashIndexPathCompare(pp types.HashIndexPath, o types.PathPart) int {
	switch opp := o.(type) {
	case types.FieldPath:
		return 1
	case types.IndexPath:
		return 1
	case types.HashIndexPath:
		switch bytes.Compare(pp.Hash[:], opp.Hash[:]) {
		case -1:
			return -1
		case 0:
			if pp.IntoKey == opp.IntoKey {
				return 0
			}
			if pp.IntoKey {
				return -1
			}
			return 1
		case 1:
			return 1
		}
	}
	panic("unreachable")
}

func pathPartCompare(ctx context.Context, nbf *types.NomsBinFormat, pp, pp2 types.PathPart) (int, error) {
	switch pp1 := pp.(type) {
	case types.FieldPath:
		return fieldPathCompare(pp1, pp2), nil
	case types.IndexPath:
		return indexPathCompare(ctx, nbf, pp1, pp2)
	case types.HashIndexPath:
		return hashIndexPathCompare(pp1, pp2), nil
	}
	panic("unreachable")
}