package transformers

import (
	"context"
	"errors"
	"fmt"
	"strings"
	"sync"
	"time"

	"git.ksdemosapps.com/kylesoda/go-migrate/internal/app/azure"
	"git.ksdemosapps.com/kylesoda/go-migrate/internal/app/config"
	"git.ksdemosapps.com/kylesoda/go-migrate/internal/app/custom_errors"
	"git.ksdemosapps.com/kylesoda/go-migrate/internal/app/etl"
	"git.ksdemosapps.com/kylesoda/go-migrate/internal/app/models"
	"github.com/google/uuid"
	log "github.com/sirupsen/logrus"
)

type MssqlTransformer struct {
	toStorage   config.ToStorageConfig
	sourceTable config.SourceTableInfo
	azureClient *azure.Client
}

func NewMssqlTransformer(toStorage config.ToStorageConfig, sourceTable config.SourceTableInfo, azureClient *azure.Client) etl.Transformer {
	return &MssqlTransformer{
		toStorage:   toStorage,
		sourceTable: sourceTable,
		azureClient: azureClient,
	}
}

func computeTransformationPlan(columns []models.ColumnType) []etl.ColumnTransformPlan {
	var plan []etl.ColumnTransformPlan

	for i, col := range columns {
		switch col.SystemType() {
		case "uniqueidentifier":
			plan = append(plan, etl.ColumnTransformPlan{
				Index: i,
				Fn: func(v any) (any, error) {
					if b, ok := v.([]byte); ok && b != nil {
						return mssqlUuidToBigEndian(b)
					}
					return v, nil
				},
			})

		case "geometry", "geography":
			plan = append(plan, etl.ColumnTransformPlan{
				Index: i,
				Fn: func(v any) (any, error) {
					if b, ok := v.([]byte); ok && b != nil {
						return wkbToEwkbWithSrid(b, 4326)
					}
					return v, nil
				},
			})

		case "datetime", "datetime2":
			plan = append(plan, etl.ColumnTransformPlan{
				Index: i,
				Fn: func(v any) (any, error) {
					if t, ok := v.(time.Time); ok {
						return ensureUTC(t), nil
					}
					return v, nil
				},
			})
		}
	}

	return plan
}

func computeStorageTransformationPlan(
	ctx context.Context,
	azureClient *azure.Client,
	toStorage config.ToStorageConfig,
	sourceColumns []models.ColumnType,
	sourceTable config.SourceTableInfo,
) []etl.ColumnTransformPlan {
	if azureClient == nil || len(toStorage.Columns) == 0 {
		return nil
	}

	colIndex := make(map[string]int, len(sourceColumns))
	for i, col := range sourceColumns {
		colIndex[strings.ToUpper(col.Name())] = i
	}

	var plan []etl.ColumnTransformPlan
	for _, storageCol := range toStorage.Columns {
		if storageCol.Mode != "REFERENCE_ONLY" {
			log.Warnf("to_storage: unsupported mode %q for column %s — skipping", storageCol.Mode, storageCol.Source)
			continue
		}

		idx, ok := colIndex[strings.ToUpper(storageCol.Source)]
		if !ok {
			log.Warnf("to_storage: source column %q not found in source schema — skipping", storageCol.Source)
			continue
		}

		sourceColName := storageCol.Source
		schema := sourceTable.Schema
		table := sourceTable.Table

		plan = append(plan, etl.ColumnTransformPlan{
			Index: idx,
			Fn: func(v any) (any, error) {
				if v == nil {
					return nil, nil
				}
				b, ok := v.([]byte)
				if !ok {
					log.Warnf("to_storage: expected []byte for %s.%s.%s, got %T — passing through",
						schema, table, sourceColName, v)
					return v, nil
				}
				start := time.Now()
				blobPath := fmt.Sprintf("%s/%s/%s", schema, table, uuid.New().String())
				blobURL, err := azureClient.UploadAndGetURL(ctx, blobPath, b)
				if err != nil {
					return nil, fmt.Errorf("uploading %s.%s.%s: %w", schema, table, sourceColName, err)
				}
				log.Debugf(`Succesfully uploaded "%s", (%vms)`, blobURL, time.Since(start).Milliseconds())
				return blobURL, nil
			},
		})
	}
	return plan
}

const processBatchCtxCheck = 4096

func (mssqlTr *MssqlTransformer) ProcessBatch(
	ctx context.Context,
	batch *models.Batch,
	transformationPlan []etl.ColumnTransformPlan,
) error {
	for i, rowValues := range batch.Rows {
		if i%processBatchCtxCheck == 0 {
			if err := ctx.Err(); err != nil {
				return err
			}
		}

		for _, task := range transformationPlan {
			val := rowValues[task.Index]
			if val == nil {
				continue
			}

			transformed, err := task.Fn(val)
			if err != nil {
				return err
			}
			rowValues[task.Index] = transformed
		}
	}

	return nil
}

func (mssqlTr *MssqlTransformer) Exec(
	ctx context.Context,
	columns []models.ColumnType,
	chBatchesIn <-chan models.Batch,
	chBatchesOut chan<- models.Batch,
	chJobErrorsOut chan<- custom_errors.JobError,
	wgActiveBatches *sync.WaitGroup,
) {
	transformationPlan := computeTransformationPlan(columns)
	storagePlan := computeStorageTransformationPlan(ctx, mssqlTr.azureClient, mssqlTr.toStorage, columns, mssqlTr.sourceTable)
	transformationPlan = append(transformationPlan, storagePlan...)

	for {
		if ctx.Err() != nil {
			return
		}

		select {
		case <-ctx.Done():
			return

		case batch, ok := <-chBatchesIn:
			if !ok {
				return
			}

			if len(transformationPlan) == 0 {
				select {
				case chBatchesOut <- batch:
					wgActiveBatches.Add(1)
					continue
				case <-ctx.Done():
					return
				}
			}

			err := mssqlTr.ProcessBatch(ctx, &batch, transformationPlan)
			if err != nil {
				if errors.Is(err, ctx.Err()) {
					return
				}

				select {
				case chJobErrorsOut <- custom_errors.JobError{ShouldCancelJob: true, Msg: "Transformation failed", Prev: err}:
				case <-ctx.Done():
				}
				return
			}

			select {
			case chBatchesOut <- batch:
			case <-ctx.Done():
				return
			}

			wgActiveBatches.Add(1)
		}
	}
}