package transformers

import (
	"context"
	"errors"
	"sync"
	"time"

	"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"
)

type MssqlTransformer struct{}

func NewMssqlTransformer() etl.Transformer {
	return &MssqlTransformer{}
}

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
}

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
			}
		}

		if rowValues == nil {
			continue
		}

		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)

	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)
		}
	}
}