package s3migrate

import (
	"context"
	"fmt"
	"io"
	"net/http"
	"time"

	"github.com/aws/aws-sdk-go-v2/aws"
	"github.com/aws/aws-sdk-go-v2/credentials"
	"github.com/aws/aws-sdk-go-v2/service/s3"
	"go.mongodb.org/mongo-driver/bson"
	"go.mongodb.org/mongo-driver/mongo"
	"go.mongodb.org/mongo-driver/mongo/options"
)

const (
	collectionName = "s3"
	presignExpiry  = time.Hour
)

type Params struct {
	SourceEngine    string `json:"sourceEngine"`
	SourceEndpoint  string `json:"sourceEndpoint"`
	SourceBucket    string `json:"sourceBucket"`
	SourceAccessKey string `json:"sourceAccessKey"`
	SourceSecretKey string `json:"sourceSecretKey"`
	SourceRegion    string `json:"sourceRegion"`

	DestEngine    string `json:"destEngine"`
	DestEndpoint  string `json:"destEndpoint"`
	DestBucket    string `json:"destBucket"`
	DestAccessKey string `json:"destAccessKey"`
	DestSecretKey string `json:"destSecretKey"`
	DestRegion    string `json:"destRegion"`
}

type objectRecord struct {
	Name        string `bson:"name"`
	Engine      string `bson:"engine"`
	Key         string `bson:"key"`
	Size        int64  `bson:"size"`
	ContentType string `bson:"content_type"`
}

type LogFunc func(msg string, args ...any)

func Run(ctx context.Context, db *mongo.Database, params Params, logf LogFunc) error {
	if err := validateParams(params); err != nil {
		return err
	}
	if params.SourceRegion == "" {
		params.SourceRegion = "us-east-1"
	}
	if params.DestRegion == "" {
		params.DestRegion = "us-east-1"
	}

	srcPresign := newPresignClient(params.SourceEndpoint, params.SourceAccessKey, params.SourceSecretKey, params.SourceRegion)
	dstPresign := newPresignClient(params.DestEndpoint, params.DestAccessKey, params.DestSecretKey, params.DestRegion)

	coll := db.Collection(collectionName)
	count, err := coll.CountDocuments(ctx, bson.M{"engine": params.SourceEngine})
	if err != nil {
		return fmt.Errorf("count source objects: %w", err)
	}
	logf("source engine=%s count=%d", params.SourceEngine, count)

	if count == 0 {
		logf("no objects to migrate")
		return nil
	}

	cursor, err := coll.Find(ctx, bson.M{"engine": params.SourceEngine}, options.Find().SetBatchSize(100))
	if err != nil {
		return fmt.Errorf("find source objects: %w", err)
	}
	defer cursor.Close(ctx)

	var migrated, skipped, failed int64
	for cursor.Next(ctx) {
		var obj objectRecord
		if err := cursor.Decode(&obj); err != nil {
			logf("decode error: %v", err)
			failed++
			continue
		}

		exists, err := objectExistsInDest(ctx, coll, params.DestEngine, obj.Name)
		if err != nil {
			logf("check dest error name=%s: %v", obj.Name, err)
			failed++
			continue
		}
		if exists {
			skipped++
			continue
		}

		if err := copyObject(ctx, srcPresign, params.SourceBucket, dstPresign, params.DestBucket, obj); err != nil {
			logf("copy error name=%s: %v", obj.Name, err)
			failed++
			continue
		}

		if _, err := coll.UpdateOne(ctx,
			bson.M{"engine": params.SourceEngine, "name": obj.Name},
			bson.M{"$set": bson.M{"engine": params.DestEngine}},
		); err != nil {
			logf("update engine error name=%s: %v", obj.Name, err)
			failed++
			continue
		}

		migrated++
		if migrated%100 == 0 {
			logf("progress: migrated=%d skipped=%d failed=%d", migrated, skipped, failed)
		}
	}

	logf("complete: migrated=%d skipped=%d failed=%d total=%d", migrated, skipped, failed, count)
	return nil
}

func validateParams(p Params) error {
	if p.SourceEngine == "" {
		return fmt.Errorf("sourceEngine is required")
	}
	if p.DestEngine == "" {
		return fmt.Errorf("destEngine is required")
	}
	if p.SourceEngine == p.DestEngine {
		return fmt.Errorf("sourceEngine and destEngine must be different")
	}
	if p.SourceEndpoint == "" || p.SourceBucket == "" || p.SourceAccessKey == "" || p.SourceSecretKey == "" {
		return fmt.Errorf("source S3 config (endpoint, bucket, accessKey, secretKey) is required")
	}
	if p.DestEndpoint == "" || p.DestBucket == "" || p.DestAccessKey == "" || p.DestSecretKey == "" {
		return fmt.Errorf("dest S3 config (endpoint, bucket, accessKey, secretKey) is required")
	}
	return nil
}

func newPresignClient(endpoint, accessKey, secretKey, region string) *s3.PresignClient {
	cfg := aws.Config{
		Region:      region,
		Credentials: credentials.NewStaticCredentialsProvider(accessKey, secretKey, ""),
		BaseEndpoint: &endpoint,
	}
	client := s3.NewFromConfig(cfg, func(o *s3.Options) {
		o.UsePathStyle = true
	})
	return s3.NewPresignClient(client)
}

func objectExistsInDest(ctx context.Context, coll *mongo.Collection, destEngine, name string) (bool, error) {
	count, err := coll.CountDocuments(ctx, bson.M{"engine": destEngine, "name": name}, options.Count().SetLimit(1))
	if err != nil {
		return false, err
	}
	return count > 0, nil
}

func copyObject(ctx context.Context, srcPresign *s3.PresignClient, srcBucket string, dstPresign *s3.PresignClient, dstBucket string, obj objectRecord) error {
	getReq, err := srcPresign.PresignGetObject(ctx, &s3.GetObjectInput{
		Bucket: &srcBucket,
		Key:    &obj.Key,
	}, s3.WithPresignExpires(presignExpiry))
	if err != nil {
		return fmt.Errorf("presign get: %w", err)
	}

	contentType := obj.ContentType
	putReq, err := dstPresign.PresignPutObject(ctx, &s3.PutObjectInput{
		Bucket:      &dstBucket,
		Key:         &obj.Key,
		ContentType: &contentType,
	}, s3.WithPresignExpires(presignExpiry))
	if err != nil {
		return fmt.Errorf("presign put: %w", err)
	}

	downloadResp, err := http.Get(getReq.URL)
	if err != nil {
		return fmt.Errorf("download: %w", err)
	}
	defer downloadResp.Body.Close()

	if downloadResp.StatusCode == http.StatusNotFound {
		return fmt.Errorf("source object not found: %s", obj.Key)
	}
	if downloadResp.StatusCode != http.StatusOK {
		return fmt.Errorf("download status: %s", downloadResp.Status)
	}

	uploadReq, err := http.NewRequestWithContext(ctx, http.MethodPut, putReq.URL, downloadResp.Body)
	if err != nil {
		return fmt.Errorf("create upload request: %w", err)
	}
	if downloadResp.ContentLength > 0 {
		uploadReq.ContentLength = downloadResp.ContentLength
	} else {
		uploadReq.ContentLength = obj.Size
	}
	if contentType != "" {
		uploadReq.Header.Set("Content-Type", contentType)
	}

	uploadResp, err := http.DefaultClient.Do(uploadReq)
	if err != nil {
		return fmt.Errorf("upload: %w", err)
	}
	defer func() { _, _ = io.Copy(io.Discard, uploadResp.Body); uploadResp.Body.Close() }()

	if uploadResp.StatusCode != http.StatusOK {
		return fmt.Errorf("upload status: %s", uploadResp.Status)
	}
	return nil
}