//                           _       _
// __      _____  __ ___   ___  __ _| |_ ___
// \ \ /\ / / _ \/ _` \ \ / / |/ _` | __/ _ \
//  \ V  V /  __/ (_| |\ V /| | (_| | ||  __/
//   \_/\_/ \___|\__,_| \_/ |_|\__,_|\__\___|
//
//  Copyright © 2016 - 2026 Weaviate B.V. All rights reserved.
//
//  CONTACT: hello@weaviate.io
//

package schema

import (
	"bytes"
	"encoding/json"
	"fmt"

	"github.com/weaviate/weaviate/entities/models"
	"github.com/weaviate/weaviate/usecases/sharding"
)

// Diff creates human-readable information about the difference in two schemas,
// returns a len=0 slice if schemas are identical
func Diff(
	leftLabel string, left *State,
	rightLabel string, right *State,
) []string {
	var msgs []string

	if len(left.ObjectSchema.Classes) != len(right.ObjectSchema.Classes) {
		msg := fmt.Sprintf("%s has %d classes, but %s has %d classes",
			leftLabel, len(left.ObjectSchema.Classes),
			rightLabel, len(right.ObjectSchema.Classes))
		msgs = append(msgs, msg)
	}

	leftClasses := map[string]*models.Class{}
	rightClasses := map[string]*models.Class{}

	for _, class := range right.ObjectSchema.Classes {
		rightClasses[class.Class] = class
	}

	for _, classLeft := range left.ObjectSchema.Classes {
		className := classLeft.Class
		leftClasses[className] = classLeft
		if classRight, ok := rightClasses[className]; !ok {
			msg := fmt.Sprintf("class %s exists in %s, but not in %s",
				className, leftLabel, rightLabel)
			msgs = append(msgs, msg)
		} else {
			cc := classComparison{
				left:       classLeft,
				right:      classRight,
				leftLabel:  leftLabel,
				rightLabel: rightLabel,
			}
			msgs = append(msgs, cc.diff()...)

			ssc := shardingStateComparison{
				left:       left.ShardingState[className],
				right:      right.ShardingState[className],
				leftLabel:  leftLabel,
				rightLabel: rightLabel,
				className:  className,
			}
			msgs = append(msgs, ssc.diff()...)
		}
	}

	for className := range rightClasses {
		if _, ok := leftClasses[className]; !ok {
			msg := fmt.Sprintf("class %s exists in %s, but not in %s",
				className, rightLabel, leftLabel)
			msgs = append(msgs, msg)
		}
	}

	return msgs
}

type classComparison struct {
	left, right           *models.Class
	leftLabel, rightLabel string
	msgs                  []string
}

func (cc *classComparison) addMsg(msg ...string) {
	cc.msgs = append(cc.msgs, msg...)
}

func (cc *classComparison) diff() []string {
	lj, _ := json.Marshal(cc.left)
	rj, _ := json.Marshal(cc.right)

	if bytes.Equal(lj, rj) {
		// classes are identical, we are done
		return nil
	}

	// classes are not identical, log this fact, then dig deeper to find the diff
	msg := fmt.Sprintf("class %s exists in both, but is not identical: "+
		"size %d vs %d", cc.left.Class, len(lj), len(rj))
	cc.addMsg(msg)

	pc := propsComparison{
		left:       cc.left.Properties,
		right:      cc.right.Properties,
		leftLabel:  cc.leftLabel,
		rightLabel: cc.rightLabel,
		className:  cc.left.Class,
	}
	cc.addMsg(pc.diff()...)

	ccc := classConfigComparison{
		left:       cc.left,
		right:      cc.right,
		leftLabel:  cc.leftLabel,
		rightLabel: cc.rightLabel,
		className:  cc.left.Class,
	}
	cc.addMsg(ccc.diff()...)

	return cc.msgs
}

type propsComparison struct {
	left, right           []*models.Property
	leftLabel, rightLabel string
	className             string
	msgs                  []string
}

func (pc *propsComparison) addMsg(msg ...string) {
	pc.msgs = append(pc.msgs, msg...)
}

func (pc *propsComparison) diff() []string {
	containedLeft := map[string]*models.Property{}
	containedRight := map[string]*models.Property{}

	for _, prop := range pc.left {
		containedLeft[prop.Name] = prop
	}
	for _, prop := range pc.right {
		if leftProp, ok := containedLeft[prop.Name]; !ok {
			msg := fmt.Sprintf("class %s: property %s exists in %s, but not in %s",
				pc.className, prop.Name, pc.rightLabel, pc.leftLabel)
			pc.addMsg(msg)
		} else {
			pc.compareProp(leftProp, prop)
		}
		containedRight[prop.Name] = prop
	}

	for _, prop := range pc.left {
		if _, ok := containedRight[prop.Name]; !ok {
			msg := fmt.Sprintf("class %s: property %s exists in %s, but not in %s",
				pc.className, prop.Name, pc.leftLabel, pc.rightLabel)
			pc.addMsg(msg)
		}
	}

	return pc.msgs
}

func (pc *propsComparison) compareProp(left, right *models.Property) {
	lj, _ := json.Marshal(left)
	rj, _ := json.Marshal(right)

	if bytes.Equal(lj, rj) {
		return
	}

	msg := fmt.Sprintf("class %s: property %s: mismatch: %s has %s, but %s has %s",
		pc.className, left.Name, pc.leftLabel, lj, pc.rightLabel, rj)
	pc.addMsg(msg)
}

type classConfigComparison struct {
	left, right           *models.Class
	leftLabel, rightLabel string
	className             string
	msgs                  []string
}

func (ccc *classConfigComparison) addMsg(msg ...string) {
	ccc.msgs = append(ccc.msgs, msg...)
}

func (ccc *classConfigComparison) diff() []string {
	ccc.compare(ccc.left.Description, ccc.right.Description, "description")
	ccc.compare(ccc.left.InvertedIndexConfig,
		ccc.right.InvertedIndexConfig, "inverted index config")
	ccc.compare(ccc.left.ModuleConfig,
		ccc.right.ModuleConfig, "module config")
	ccc.compare(ccc.left.ReplicationConfig,
		ccc.right.ReplicationConfig, "replication config")
	ccc.compare(ccc.left.ShardingConfig,
		ccc.right.ShardingConfig, "sharding config")
	ccc.compare(ccc.left.VectorIndexConfig,
		ccc.right.VectorIndexConfig, "vector index config")
	ccc.compare(ccc.left.VectorIndexType,
		ccc.right.VectorIndexType, "vector index type")
	ccc.compare(ccc.left.Vectorizer,
		ccc.right.Vectorizer, "vectorizer")
	ccc.compare(ccc.left.VectorConfig,
		ccc.right.VectorConfig, "vector config")
	return ccc.msgs
}

func (ccc *classConfigComparison) compare(
	left, right any, label string,
) {
	lj, _ := json.Marshal(left)
	rj, _ := json.Marshal(right)

	if bytes.Equal(lj, rj) {
		return
	}

	msg := fmt.Sprintf("class %s: %s mismatch: %s has %s, but %s has %s",
		ccc.className, label, ccc.leftLabel, lj, ccc.rightLabel, rj)
	ccc.addMsg(msg)
}

type shardingStateComparison struct {
	left, right           *sharding.State
	leftLabel, rightLabel string
	className             string
	msgs                  []string
}

func (ssc *shardingStateComparison) addMsg(msg ...string) {
	ssc.msgs = append(ssc.msgs, msg...)
}

func (ssc *shardingStateComparison) diff() []string {
	if ssc.left == nil && ssc.right != nil {
		msg := fmt.Sprintf("class %s: missing sharding state in %s",
			ssc.className, ssc.leftLabel)
		ssc.addMsg(msg)
		return ssc.msgs
	}

	if ssc.left != nil && ssc.right == nil {
		msg := fmt.Sprintf("class %s: missing sharding state in %s",
			ssc.className, ssc.rightLabel)
		ssc.addMsg(msg)
		return ssc.msgs
	}

	lj, _ := json.Marshal(ssc.left)
	rj, _ := json.Marshal(ssc.right)

	if bytes.Equal(lj, rj) {
		return ssc.msgs
	}

	msg := fmt.Sprintf("class %s: sharding state mismatch: "+
		"%s has %s, but %s has %s",
		ssc.className, ssc.leftLabel, lj, ssc.rightLabel, rj)
	ssc.addMsg(msg)

	return ssc.msgs
}
