package datatypes

import (
	"database/sql"
	"database/sql/driver"
	"errors"
	"fmt"
	"reflect"
	"strconv"
	"time"
)

// NullString represents a string that may be null.
// NullString implements the [Scanner] interface so
// it can be used as a scan destination:
//
//	var s NullString
//	err := db.QueryRow("SELECT name FROM foo WHERE id=?", id).Scan(&s)
//	...
//	if s.Valid {
//	   // use s.String
//	} else {
//	   // NULL value
//	}
type NullString = Null[string]

// NullInt64 represents an int64 that may be null.
// NullInt64 implements the [Scanner] interface so
// it can be used as a scan destination, similar to [NullString].
type NullInt64 = Null[int64]

// NullInt32 represents an int32 that may be null.
// NullInt32 implements the [Scanner] interface so
// it can be used as a scan destination, similar to [NullString].
type NullInt32 = Null[int32]

// NullInt16 represents an int16 that may be null.
// NullInt16 implements the [Scanner] interface so
// it can be used as a scan destination, similar to [NullString].
type NullInt16 = Null[int16]

// NullByte represents a byte that may be null.
// NullByte implements the [Scanner] interface so
// it can be used as a scan destination, similar to [NullString].
type NullByte = Null[byte]

// NullFloat64 represents a float64 that may be null.
// NullFloat64 implements the [Scanner] interface so
// it can be used as a scan destination, similar to [NullString].
type NullFloat64 = Null[float64]

// NullBool represents a bool that may be null.
// NullBool implements the [Scanner] interface so
// it can be used as a scan destination, similar to [NullString].
type NullBool = Null[bool]

// NullTime represents a [time.Time] that may be null.
// NullTime implements the [Scanner] interface so
// it can be used as a scan destination, similar to [NullString].
type NullTime = Null[time.Time]

// Null represents a value that may be null.
// Null implements the [Scanner] interface so
// it can be used as a scan destination:
//
//	var s Null[string]
//	err := db.QueryRow("SELECT name FROM foo WHERE id=?", id).Scan(&s)
//	...
//	if s.Valid {
//	   // use s.V
//	} else {
//	   // NULL value
//	}
type Null[T any] struct {
	V     T
	Valid bool
}

func (n *Null[T]) Scan(value any) error {
	if value == nil {
		n.V, n.Valid = *new(T), false
		return nil
	}
	n.Valid = true
	return convertAssign(&n.V, value)
}

func (n Null[T]) Value() (driver.Value, error) {
	if !n.Valid {
		return nil, nil
	}
	return n.V, nil
}

// NewNull returns a new, non-null Null.
func NewNull[T any](v T) Null[T] {
	return Null[T]{V: v, Valid: true}
}

var errNilPtr = errors.New("destination pointer is nil") // embedded in descriptive error

// convertAssign is the same as convertAssignRows, but without the optional
// rows argument.
func convertAssign(dest, src any) error {
	return convertAssignRows(dest, src, nil)
}

// convertAssignRows copies to dest the value in src, converting it if possible.
// An error is returned if the copy would result in loss of information.
// dest should be a pointer type. If rows is passed in, the rows will
// be used as the parent for any cursor values converted from a
// driver.Rows to a *Rows.
func convertAssignRows(dest, src any, rows *sql.Rows) error {
	// Common cases, without reflect.
	switch s := src.(type) {
	case string:
		switch d := dest.(type) {
		case *string:
			if d == nil {
				return errNilPtr
			}
			*d = s
			return nil
		case *[]byte:
			if d == nil {
				return errNilPtr
			}
			*d = []byte(s)
			return nil
		case *sql.RawBytes:
			if d == nil {
				return errNilPtr
			}
			*d = append((*d)[:0], s...)
			return nil
		}
	case []byte:
		switch d := dest.(type) {
		case *string:
			if d == nil {
				return errNilPtr
			}
			*d = string(s)
			return nil
		case *any:
			if d == nil {
				return errNilPtr
			}
			*d = cloneBytes(s)
			return nil
		case *[]byte:
			if d == nil {
				return errNilPtr
			}
			*d = cloneBytes(s)
			return nil
		case *sql.RawBytes:
			if d == nil {
				return errNilPtr
			}
			*d = s
			return nil
		}
	case time.Time:
		switch d := dest.(type) {
		case *time.Time:
			*d = s
			return nil
		case *string:
			*d = s.Format(time.RFC3339Nano)
			return nil
		case *[]byte:
			if d == nil {
				return errNilPtr
			}
			*d = []byte(s.Format(time.RFC3339Nano))
			return nil
		case *sql.RawBytes:
			if d == nil {
				return errNilPtr
			}
			*d = s.AppendFormat((*d)[:0], time.RFC3339Nano)
			return nil
		}
	case decimalDecompose:
		switch d := dest.(type) {
		case decimalCompose:
			return d.Compose(s.Decompose(nil))
		}
	case nil:
		switch d := dest.(type) {
		case *any:
			if d == nil {
				return errNilPtr
			}
			*d = nil
			return nil
		case *[]byte:
			if d == nil {
				return errNilPtr
			}
			*d = nil
			return nil
		case *sql.RawBytes:
			if d == nil {
				return errNilPtr
			}
			*d = nil
			return nil
		}
	}

	var sv reflect.Value

	switch d := dest.(type) {
	case *string:
		sv = reflect.ValueOf(src)
		switch sv.Kind() {
		case reflect.Bool,
			reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64,
			reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64,
			reflect.Float32, reflect.Float64:
			*d = asString(src)
			return nil
		}
	case *[]byte:
		sv = reflect.ValueOf(src)
		if b, ok := asBytes(nil, sv); ok {
			*d = b
			return nil
		}
	case *sql.RawBytes:
		sv = reflect.ValueOf(src)
		if b, ok := asBytes([]byte(*d)[:0], sv); ok {
			*d = sql.RawBytes(b)
			return nil
		}
	case *bool:
		bv, err := driver.Bool.ConvertValue(src)
		if err == nil {
			*d = bv.(bool)
		}
		return err
	case *any:
		*d = src
		return nil
	}

	if scanner, ok := dest.(sql.Scanner); ok {
		return scanner.Scan(src)
	}

	dpv := reflect.ValueOf(dest)
	if dpv.Kind() != reflect.Pointer {
		return errors.New("destination not a pointer")
	}
	if dpv.IsNil() {
		return errNilPtr
	}

	if !sv.IsValid() {
		sv = reflect.ValueOf(src)
	}

	dv := reflect.Indirect(dpv)
	if sv.IsValid() && sv.Type().AssignableTo(dv.Type()) {
		switch b := src.(type) {
		case []byte:
			dv.Set(reflect.ValueOf(cloneBytes(b)))
		default:
			dv.Set(sv)
		}
		return nil
	}

	if dv.Kind() == sv.Kind() && sv.Type().ConvertibleTo(dv.Type()) {
		dv.Set(sv.Convert(dv.Type()))
		return nil
	}

	// The following conversions use a string value as an intermediate representation
	// to convert between various numeric types.
	//
	// This also allows scanning into user defined types such as "type Int int64".
	// For symmetry, also check for string destination types.
	switch dv.Kind() {
	case reflect.Pointer:
		if src == nil {
			dv.Set(reflect.Zero(dv.Type()))
			return nil
		}
		dv.Set(reflect.New(dv.Type().Elem()))
		return convertAssignRows(dv.Interface(), src, rows)
	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
		if src == nil {
			return fmt.Errorf("converting NULL to %s is unsupported", dv.Kind())
		}
		s := asString(src)
		i64, err := strconv.ParseInt(s, 10, dv.Type().Bits())
		if err != nil {
			err = strconvErr(err)
			return fmt.Errorf("converting driver.Value type %T (%q) to a %s: %v", src, s, dv.Kind(), err)
		}
		dv.SetInt(i64)
		return nil
	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64:
		if src == nil {
			return fmt.Errorf("converting NULL to %s is unsupported", dv.Kind())
		}
		s := asString(src)
		u64, err := strconv.ParseUint(s, 10, dv.Type().Bits())
		if err != nil {
			err = strconvErr(err)
			return fmt.Errorf("converting driver.Value type %T (%q) to a %s: %v", src, s, dv.Kind(), err)
		}
		dv.SetUint(u64)
		return nil
	case reflect.Float32, reflect.Float64:
		if src == nil {
			return fmt.Errorf("converting NULL to %s is unsupported", dv.Kind())
		}
		s := asString(src)
		f64, err := strconv.ParseFloat(s, dv.Type().Bits())
		if err != nil {
			err = strconvErr(err)
			return fmt.Errorf("converting driver.Value type %T (%q) to a %s: %v", src, s, dv.Kind(), err)
		}
		dv.SetFloat(f64)
		return nil
	case reflect.String:
		if src == nil {
			return fmt.Errorf("converting NULL to %s is unsupported", dv.Kind())
		}
		switch v := src.(type) {
		case string:
			dv.SetString(v)
			return nil
		case []byte:
			dv.SetString(string(v))
			return nil
		}
	}

	return fmt.Errorf("unsupported Scan, storing driver.Value type %T into type %T", src, dest)
}

func strconvErr(err error) error {
	if ne, ok := err.(*strconv.NumError); ok {
		return ne.Err
	}
	return err
}

func asString(src any) string {
	switch v := src.(type) {
	case string:
		return v
	case []byte:
		return string(v)
	}
	rv := reflect.ValueOf(src)
	switch rv.Kind() {
	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
		return strconv.FormatInt(rv.Int(), 10)
	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64:
		return strconv.FormatUint(rv.Uint(), 10)
	case reflect.Float64:
		return strconv.FormatFloat(rv.Float(), 'g', -1, 64)
	case reflect.Float32:
		return strconv.FormatFloat(rv.Float(), 'g', -1, 32)
	case reflect.Bool:
		return strconv.FormatBool(rv.Bool())
	}
	return fmt.Sprintf("%v", src)
}

func asBytes(buf []byte, rv reflect.Value) (b []byte, ok bool) {
	switch rv.Kind() {
	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
		return strconv.AppendInt(buf, rv.Int(), 10), true
	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64:
		return strconv.AppendUint(buf, rv.Uint(), 10), true
	case reflect.Float32:
		return strconv.AppendFloat(buf, rv.Float(), 'g', -1, 32), true
	case reflect.Float64:
		return strconv.AppendFloat(buf, rv.Float(), 'g', -1, 64), true
	case reflect.Bool:
		return strconv.AppendBool(buf, rv.Bool()), true
	case reflect.String:
		s := rv.String()
		return append(buf, s...), true
	}
	return
}

type decimalDecompose interface {
	// Decompose returns the internal decimal state in parts.
	// If the provided buf has sufficient capacity, buf may be returned as the coefficient with
	// the value set and length set as appropriate.
	Decompose(buf []byte) (form byte, negative bool, coefficient []byte, exponent int32)
}

type decimalCompose interface {
	// Compose sets the internal decimal value from parts. If the value cannot be
	// represented then an error should be returned.
	Compose(form byte, negative bool, coefficient []byte, exponent int32) error
}

// cloneBytes returns a copy of b[:len(b)].
// The result may have additional unused capacity.
// cloneBytes(nil) returns nil.
func cloneBytes(b []byte) []byte {
	if b == nil {
		return nil
	}
	return append([]byte{}, b...)
}