// SPDX-FileCopyrightText: 2026 Stefan Majewsky <majewsky@gmx.net>
// SPDX-License-Identifier: Apache-2.0

package oblast

import (
	"database/sql"
	"errors"
	"fmt"
	"reflect"
)

// PrepareThreshold is a tuning parameter for the strategy used by all methods of [Store] operating on batches of records provided by the caller
// (specifically, [Store.Insert], [Store.Update] and [Store.Delete]).
//
// For large amounts of records, it is obviously advantageous to build a prepared statement for the one query that will be used repeatedly on all of them.
// However, building a prepared statement is associated with some amount of bookkeeping on the level of the database/sql library.
// When operating on individual records or small amounts of records at a time (that is, in OLTP rather than OLAP workloads), this overhead becomes a measurable performance burden.
//
// This tuning parameter defines the minimum number of records that will justify maintaining a prepared statement.
// Our benchmarking with the mattn/go-sqlite3 driver (and last checked with Go 1.26.2 on x86_64) indicates that this becomes a worthwhile investment at 8 or more records, so this is our default.
// If your benchmarking indicates a different tradeoff depending on your choice of Go version or SQL driver, you may adjust this variable accordingly.
var PrepareThreshold int = 8

// Insert executes an SQL INSERT statement for each of the provided records.
//
// Fields that are declared with the "auto" tag will not be written into the DB,
// and instead their value (as auto-generated by the DB on insert) will be placed in the record.
// On success, returns the original set of records, updated thusly.
//
// Returns an error if [NewStore] was called without the [TableNameIs] option, which is required to generate a query for this method.
func (s Store[R]) Insert(db Handle, records ...R) (returnedRecords []R, returnedError error) {
	// NOTE: This function body should be as short as possible to reduce the binary size after monomorphization.
	//       Any expression that does not depend on type R should be factored out into a reusable function.
	// TODO: minimize

	if s.plan.Insert.Query == "" {
		return nil, errors.New("cannot execute Insert() because query could not be autogenerated")
	}

	var (
		argumentIndexes = s.plan.Insert.ArgumentIndexes
		argumentSlots   = make([]any, len(argumentIndexes))
		scanIndexes     = s.plan.Insert.ScanIndexes
		scanSlots       []any
	)
	if len(scanIndexes) > 0 {
		scanSlots = make([]any, len(scanIndexes))
	}

	var stmt *sql.Stmt
	if len(records) >= PrepareThreshold {
		var err error
		stmt, err = db.Prepare(s.plan.Insert.Query)
		if err != nil {
			return nil, fmt.Errorf("during Prepare(): %w", err)
		}
		defer func() {
			returnedError = newIOError(returnedError, "Stmt.Close", stmt.Close())
		}()
	}

	for idx := range records {
		v := reflect.ValueOf(&records[idx]).Elem()
		for idx, index := range argumentIndexes {
			argumentSlots[idx] = v.FieldByIndex(index).Interface()
		}

		if s.dialect.UsesLastInsertID() {
			var (
				result sql.Result
				err    error
			)
			if stmt == nil {
				result, err = db.Exec(s.plan.Insert.Query, argumentSlots...)
			} else {
				result, err = stmt.Exec(argumentSlots...)
			}
			if err != nil {
				return nil, fmt.Errorf("during Exec() for record with idx = %d: %w", idx, err)
			}
			id, err := result.LastInsertId()
			if err != nil {
				return nil, fmt.Errorf("during LastInsertId() for record with idx = %d: %w", idx, err)
			}
			if s.plan.FillIDWithSetInt {
				v.FieldByIndex(scanIndexes[0]).SetInt(id)
			} else if s.plan.FillIDWithSetUint {
				if id < 0 {
					return nil, fmt.Errorf("LastInsertId() = %d for record with idx = %d cannot be converted to uint", id, idx)
				}
				v.FieldByIndex(scanIndexes[0]).SetUint(uint64(id))
			}
		} else {
			for idx, index := range scanIndexes {
				scanSlots[idx] = v.FieldByIndex(index).Addr().Interface()
			}
			var err error
			if stmt == nil {
				err = db.QueryRow(s.plan.Insert.Query, argumentSlots...).Scan(scanSlots...)
			} else {
				err = stmt.QueryRow(argumentSlots...).Scan(scanSlots...)
			}
			if err != nil {
				return nil, fmt.Errorf("during QueryRow() for record with idx = %d: %w", idx, err)
			}
		}
	}

	return records, nil
}

// Update executes an SQL UPDATE statement for each of the provided records, updating all non-primary-key columns with the values in the records.
// Returns [MissingRecordError] if any of the records does not exist in the database, that is, if for any of the records, the database contains no row with the same primary key values.
//
// Returns an error if [NewStore] was called without the [TableNameIs] or [PrimaryKeyIs] options, which are both required to generate a query for this method.
func (s Store[R]) Update(db Handle, records ...R) (returnedError error) {
	if s.plan.Update.Query == "" {
		return errors.New("cannot execute Update() because query could not be autogenerated")
	}

	var (
		argumentIndexes = s.plan.Update.ArgumentIndexes
		argumentSlots   = make([]any, len(argumentIndexes))
	)

	var stmt *sql.Stmt
	if len(records) >= PrepareThreshold {
		var err error
		stmt, err = db.Prepare(s.plan.Update.Query)
		if err != nil {
			return fmt.Errorf("during Prepare(): %w", err)
		}
		defer func() {
			returnedError = newIOError(returnedError, "Stmt.Close", stmt.Close())
		}()
	}

	for idx, r := range records {
		v := reflect.ValueOf(&r).Elem()
		for idx, index := range argumentIndexes {
			argumentSlots[idx] = v.FieldByIndex(index).Addr().Interface()
		}
		var (
			result sql.Result
			err    error
		)
		if stmt == nil {
			result, err = db.Exec(s.plan.Update.Query, argumentSlots...)
		} else {
			result, err = stmt.Exec(argumentSlots...)
		}
		if err != nil {
			return fmt.Errorf("during Exec() for record with idx = %d: %w", idx, err)
		}
		rowsAffected, err := result.RowsAffected()
		if err != nil {
			return fmt.Errorf("during RowsAffected() for record with idx = %d: %w", idx, err)
		}
		if rowsAffected == 0 {
			return MissingRecordError[R]{r, s.plan}
		}
	}
	return nil
}

// Delete executes an SQL DELETE statement for each of the provided records, using their primary keys to locate the respective table rows.
//
// Returns an error if [NewStore] was called without the [TableNameIs] or [PrimaryKeyIs] options, which are both required to generate a query for this method.
func (s Store[R]) Delete(db Handle, records ...R) (returnedError error) {
	// NOTE: This function body should be as short as possible to reduce the binary size after monomorphization.
	//       Any expression that does not depend on type R should be factored out into a reusable function.
	// TODO: minimize

	if s.plan.Delete.Query == "" {
		return errors.New("cannot execute Delete() because query could not be autogenerated")
	}

	var (
		argumentIndexes = s.plan.Delete.ArgumentIndexes
		argumentSlots   = make([]any, len(argumentIndexes))
	)

	var stmt *sql.Stmt
	if len(records) >= PrepareThreshold {
		var err error
		stmt, err = db.Prepare(s.plan.Delete.Query)
		if err != nil {
			return fmt.Errorf("during Prepare(): %w", err)
		}
		defer func() {
			returnedError = newIOError(returnedError, "Stmt.Close", stmt.Close())
		}()
	}

	for idx, r := range records {
		v := reflect.ValueOf(&r).Elem()
		for idx, index := range argumentIndexes {
			argumentSlots[idx] = v.FieldByIndex(index).Addr().Interface()
		}
		var err error
		if stmt == nil {
			_, err = db.Exec(s.plan.Delete.Query, argumentSlots...)
		} else {
			_, err = stmt.Exec(argumentSlots...)
		}
		if err != nil {
			return fmt.Errorf("during Exec() for record with idx = %d: %w", idx, err)
		}
	}
	return nil
}