package dbx

import (
	"reflect"

	"github.com/go-jet/jet/v2/mysql"
	"golang.org/x/exp/constraints"
)

type ApplyInterface[T any] interface {
	Equal(T) bool
	IsZero() bool
}

// ApplyPtr compares the existing value with a new value and returns the updated value if they differ.
// If the new value is nil, the existing value is retained. If the new value is a zero-value, the
// existing value is NOT retained, it will be set to nil. If the value is changed, targetColumn is pushed
// to updatedColumns.
func ApplyPtr[T constraints.Float | constraints.Integer | string | bool](
	existing *T,
	newVal *T,
	updatedColumns *mysql.ColumnList,
	targetColumn mysql.Column,
) *T {
	if newVal == nil {
		return existing
	}
	if reflect.ValueOf(*newVal).IsZero() {
		newVal = nil
	}
	if newVal == nil && existing == nil || newVal != nil && existing != nil && *existing == *newVal {
		return existing
	}
	*updatedColumns = append(*updatedColumns, targetColumn)
	return newVal
}

// ApplyComplexPtr compares the existing value with a new value and returns the updated value if they differ.
// The new value may be of a different type (e.g. existing is uint16 and new is uint64), but it will be
// converted to match the current type resulting in potential loss of data. If the new value is nil, the
// existing value is retained. If the new value is a zero-value, the existing value is NOT retained, it
// will be set to nil. If the value is changed, targetColumn is pushed to updatedColumns.
func ApplyComplexPtr[
	Existing constraints.Float | constraints.Integer,
	New constraints.Float | constraints.Integer,
](
	existing *Existing,
	newVal *New,
	updatedColumns *mysql.ColumnList,
	targetColumn mysql.Column,
) *Existing {
	if newVal == nil {
		return existing
	}
	cast := Existing(*newVal)
	if existing != nil && *existing == cast {
		return existing
	}
	if reflect.ValueOf(cast).IsZero() {
		if existing != nil {
			*updatedColumns = append(*updatedColumns, targetColumn)
		}
		return nil
	}
	*updatedColumns = append(*updatedColumns, targetColumn)
	return &cast
}

// ApplyInterfacePtr compares the existing value with a new value and returns the updated value if
// they differ. Comparable types must have IsZero and Equal methods. If the new value is nil, the
// existing value is retained. If the new value is a zero-value, the existing value is NOT retained,
// it will be set to nil. If the value is changed, targetColumn is pushed to updatedColumns.
func ApplyInterfacePtr[T ApplyInterface[T]](
	existing *T,
	newVal *T,
	updatedColumns *mysql.ColumnList,
	targetColumn mysql.Column,
) *T {
	if newVal == nil {
		return existing
	}
	if existing != nil && (*existing).Equal(*newVal) {
		return existing
	}
	if (*newVal).IsZero() {
		if existing != nil {
			*updatedColumns = append(*updatedColumns, targetColumn)
		}
		return nil
	}
	*updatedColumns = append(*updatedColumns, targetColumn)
	return newVal
}

// ApplyVal compares the existing value with a pointer to a new value and returns the updated value if they
// differ. If the new value is nil, the existing value is retained. If the value is changed, targetColumn
// is pushed to updatedColumns
func ApplyVal[T constraints.Float | constraints.Integer | string | bool](
	existing T,
	newVal *T,
	updatedColumns *mysql.ColumnList,
	targetColumn mysql.Column,
) T {
	if newVal == nil {
		return existing
	}
	if existing == *newVal {
		return existing
	}
	*updatedColumns = append(*updatedColumns, targetColumn)
	return *newVal
}