// 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 main

import (
	"context"
	"fmt"

	"github.com/dolthub/dolt/go/store/d"

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

type CommitIterator struct {
	vr       types.ValueReader
	branches branchList
}

// NewCommitIterator initializes a new CommitIterator with the first commit to be printed.
func NewCommitIterator(vr types.ValueReader, commit types.Value) *CommitIterator {
	cr, err := types.NewRef(commit, vr.Format())
	d.PanicIfError(err)
	return &CommitIterator{vr: vr, branches: branchList{branch{addr: cr.TargetHash(), height: cr.Height(), commit: commit}}}
}

// Next returns information about the next commit to be printed. LogNode contains enough contextual
// info that the commit and associated graph can be correctly printed.
// This works by traversing the "commit" di-graph in a breadth-first manner. Each time it is called,
// the commit in the branchlist with the greatest height is returned. If that commit has multiple
// parents, new branches are added to the branchlist so that they can be traversed in order. When
// more than one branch contains the same node, that indicates that the branches are converging and so
// the branchlist will have branches removed to reflect that.
func (iter *CommitIterator) Next(ctx context.Context) (LogNode, bool) {
	if iter.branches.IsEmpty() {
		return LogNode{}, false
	}

	// Float of branches present when printing this commit
	startingColCount := len(iter.branches)

	branchIndexes := iter.branches.HighestBranchIndexes()
	col := branchIndexes[0]
	br := iter.branches[col]

	// Any additional indexes, represent other branches with the same ancestor. So they are merging
	// into a common ancestor and are no longer graphed.
	iter.branches = iter.branches.RemoveBranches(branchIndexes[1:])

	// If this commit has parents, then a branch is splitting. Create a branch for each of the parents
	// and splice that into the iterators list of branches.
	branches := branchList{}

	parents, err := datas.GetCommitParents(ctx, iter.vr, br.commit)
	d.PanicIfError(err)
	for _, p := range parents {
		v := p.NomsValue()
		b := branch{height: p.Height(), addr: p.Addr(), commit: v}
		branches = append(branches, b)
	}
	iter.branches = iter.branches.Splice(col, 1, branches...)

	// Collect the indexes for any newly created branches.
	newCols := []int{}
	for cnt := 1; cnt < len(parents); cnt++ {
		newCols = append(newCols, col+cnt)
	}

	// Now that the branchlist has been adjusted, check to see if there are branches with common
	// ancestors that will be folded together on this commit's graph.
	foldedCols := iter.branches.HighestBranchIndexes()
	node := LogNode{
		height:           br.height,
		addr:             br.addr,
		commit:           br.commit,
		startingColCount: startingColCount,
		endingColCount:   len(iter.branches),
		col:              col,
		newCols:          newCols,
		foldedCols:       foldedCols,
		lastCommit:       iter.branches.IsEmpty(),
	}
	return node, true
}

type LogNode struct {
	commit           types.Value // commit that needs to be printed
	newCols          []int       // col to start using '\' in graph
	foldedCols       []int       // cols with common ancestors, that will get folded together
	height           uint64
	startingColCount int // how many branches are being tracked when this commit is printed
	endingColCount   int // home many branches will be tracked when next commit is printed
	col              int // col to put the '*' character in graph
	addr             hash.Hash
	lastCommit       bool // this is the last commit that will be returned by iterator
}

func (n LogNode) String() string {
	return fmt.Sprintf("cr: %s(%d), startingColCount: %d, endingColCount: %d, col: %d, newCols: %v, foldedCols: %v, expanding: %t, shrunk: %t, shrinking: %t", n.addr.String()[0:9], n.height, n.startingColCount, n.endingColCount, n.col, n.newCols, n.foldedCols, n.Expanding(), n.Shrunk(), n.Shrinking())
}

// Expanding reports whether this commit's graph will expand to show an additional branch
func (n LogNode) Expanding() bool {
	return n.startingColCount < n.endingColCount
}

// Shrinking reports whether this commit's graph will show a branch being folded into another branch
func (n LogNode) Shrinking() bool {
	return len(n.foldedCols) > 1
}

// Shrunk reports whether the previous commit showed a branch being folded into another branch.
func (n LogNode) Shrunk() bool {
	return n.startingColCount > n.endingColCount
}

type branch struct {
	commit types.Value
	height uint64
	addr   hash.Hash
}

func (b branch) String() string {
	return fmt.Sprintf("%s(%d)", b.addr.String()[0:9], b.height)
}

type branchList []branch

func (bl branchList) IsEmpty() bool {
	return len(bl) == 0
}

// look through this list of branches and return the one(s) with the max height.
// If there are multiple nodes with max height, the result will contain a list of all nodes with
// maxHeight that are duplicates of the first one found.
// This indicates that two or more branches or converging.
func (bl branchList) HighestBranchIndexes() []int {
	maxHeight := uint64(0)
	var br branch
	cols := []int{}
	for i, b := range bl {
		if b.height > maxHeight {
			maxHeight = b.height
			br = b
			cols = []int{i}
		} else if b.height == maxHeight && b.addr == br.addr {
			cols = append(cols, i)
		}
	}
	return cols
}

func (bl branchList) Splice(start int, deleteCount int, branches ...branch) branchList {
	res := append(branchList{}, bl[:start]...)
	res = append(res, branches...)
	return append(res, bl[start+deleteCount:]...)
}

func (bl branchList) RemoveBranches(indexes []int) branchList {
	for i := len(indexes) - 1; i >= 0; i-- {
		bl = bl.Splice(indexes[i], 1)
	}
	return bl
}