package lagoon

import (
	"database/sql"
	"encoding/json"
	"fmt"
	"log/slog"
	"reflect"
	"strconv"
	"strings"
	"sync"
)

// HasFillable is the Go form of Eloquent $fillable: the model's backstop
// allow-list for mass assignment (D-05).
type HasFillable interface {
	Fillable() []string
}

// HasHidden is the Go form of Eloquent $hidden: column names that must not
// appear in an accidental JSON marshal (D-08).
type HasHidden interface {
	Hidden() []string
}

var droppedKeys sync.Map

// FillTypeError reports a requested value that cannot be stored in its
// column: a fraction, an exponent or an overflow for an integer field, or a
// value of the wrong type. Key is the column the value was requested for, so
// a caller can answer it as a validation failure on that field. Fill returns
// any other failure, such as a model that is not a struct pointer, as a
// plain error.
type FillTypeError struct {
	Key string
	Err error
}

func (e *FillTypeError) Error() string { return "lagoon: fill " + e.Key + ": " + e.Err.Error() }

func (e *FillTypeError) Unwrap() error { return e.Err }

// Fill copies requested keys onto model only when they are also in allowed.
// Unknown and non-fillable keys are dropped with no error (D-06). In
// non-production, each type+key pair is logged once. A value that does not
// fit its column is a *FillTypeError.
func Fill(model any, allowed []string, requested map[string]any, production bool) error {
	if model == nil {
		return fmt.Errorf("lagoon: fill model is nil")
	}
	rv := reflect.ValueOf(model)
	if rv.Kind() != reflect.Ptr || rv.IsNil() {
		return fmt.Errorf("lagoon: fill model must be a non-nil pointer")
	}
	rv = rv.Elem()
	if rv.Kind() != reflect.Struct {
		return fmt.Errorf("lagoon: fill model must point to a struct")
	}
	rt := rv.Type()
	typeName := rt.String()
	for key, val := range requested {
		if !allowListed(key, allowed) {
			logDroppedKeyOnce(production, typeName, key)
			continue
		}
		field, ok := fieldByColumn(rv, rt, key)
		if !ok {
			logDroppedKeyOnce(production, typeName, key)
			continue
		}
		if err := setField(field, val); err != nil {
			return &FillTypeError{Key: key, Err: err}
		}
	}
	return nil
}

func logDroppedKeyOnce(production bool, typeName, key string) {
	if production {
		return
	}
	k := typeName + "." + key
	if _, loaded := droppedKeys.LoadOrStore(k, struct{}{}); loaded {
		return
	}
	slog.Warn("lagoon: dropped non-fillable key", "type", typeName, "key", key)
}

func fieldByColumn(rv reflect.Value, rt reflect.Type, column string) (reflect.Value, bool) {
	for i := 0; i < rt.NumField(); i++ {
		f := rt.Field(i)
		if !f.IsExported() {
			continue
		}
		if gormColumn(f.Tag.Get("gorm")) == column {
			return rv.Field(i), true
		}
	}
	return reflect.Value{}, false
}

func gormColumn(tag string) string {
	for _, part := range strings.Split(tag, ";") {
		part = strings.TrimSpace(part)
		if after, ok := strings.CutPrefix(part, "column:"); ok {
			return after
		}
	}
	return ""
}

func setField(field reflect.Value, val any) error {
	if !field.CanSet() {
		return fmt.Errorf("field cannot be set")
	}
	if val == nil {
		field.Set(reflect.Zero(field.Type()))
		if field.CanAddr() {
			if scanner, ok := field.Addr().Interface().(sql.Scanner); ok {
				return scanner.Scan(nil)
			}
		}
		return nil
	}
	src := reflect.ValueOf(val)
	if field.Kind() == reflect.Ptr {
		elemType := field.Type().Elem()
		converted, err := convertValue(src, elemType)
		if err != nil {
			return err
		}
		ptr := reflect.New(elemType)
		ptr.Elem().Set(converted)
		field.Set(ptr)
		return nil
	}
	converted, err := convertValue(src, field.Type())
	if err == nil {
		field.Set(converted)
		return nil
	}
	if field.Type() == encryptedType {
		return err
	}
	if field.CanAddr() {
		if scanner, ok := field.Addr().Interface().(sql.Scanner); ok {
			scanSrc, scanErr := fillScanSource(val)
			if scanErr != nil {
				return scanErr
			}
			return scanner.Scan(scanSrc)
		}
	}
	return err
}

func fillScanSource(val any) (any, error) {
	switch v := val.(type) {
	case string, []byte:
		return v, nil
	default:
		b, err := json.Marshal(v)
		if err != nil {
			return nil, err
		}
		return b, nil
	}
}

var encryptedType = reflect.TypeOf(Encrypted{})

func convertValue(src reflect.Value, destType reflect.Type) (reflect.Value, error) {
	if destType == encryptedType {
		return encryptedFromRequest(src)
	}
	if src.Type().AssignableTo(destType) {
		return src, nil
	}
	if n, ok := src.Interface().(json.Number); ok {
		if out, handled, err := convertNumber(n, destType); handled {
			return out, err
		}
	}
	if src.Type().ConvertibleTo(destType) {
		return src.Convert(destType), nil
	}
	return reflect.Value{}, fmt.Errorf("cannot assign %s to %s", src.Type(), destType)
}

// convertNumber parses a json.Number, which a request decoder using
// UseNumber produces, into an integer, unsigned or float field. A value that
// does not parse as that kind or overflows it is an error. handled is false
// for any other destination kind, so a string field still takes the number's
// text through the ordinary conversion.
func convertNumber(n json.Number, destType reflect.Type) (reflect.Value, bool, error) {
	out := reflect.New(destType).Elem()
	switch destType.Kind() {
	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
		i, err := strconv.ParseInt(n.String(), 10, 64)
		if err != nil || out.OverflowInt(i) {
			return reflect.Value{}, true, fmt.Errorf("cannot assign number %s to %s", n, destType)
		}
		out.SetInt(i)
	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64:
		u, err := strconv.ParseUint(n.String(), 10, 64)
		if err != nil || out.OverflowUint(u) {
			return reflect.Value{}, true, fmt.Errorf("cannot assign number %s to %s", n, destType)
		}
		out.SetUint(u)
	case reflect.Float32, reflect.Float64:
		f, err := strconv.ParseFloat(n.String(), 64)
		if err != nil || out.OverflowFloat(f) {
			return reflect.Value{}, true, fmt.Errorf("cannot assign number %s to %s", n, destType)
		}
		out.SetFloat(f)
	default:
		return reflect.Value{}, false, nil
	}
	return out, true, nil
}

// encryptedFromRequest treats request input for an Encrypted column as
// plaintext. It never falls through to Encrypted.Scan: Scan decrypts, so a
// write path that scanned request input would reject real secrets and accept
// another row's ciphertext, copying that row's secret.
func encryptedFromRequest(src reflect.Value) (reflect.Value, error) {
	if src.Type() == encryptedType {
		return src, nil
	}
	if src.Kind() != reflect.String {
		return reflect.Value{}, fmt.Errorf("encrypted value must be a string")
	}
	return reflect.ValueOf(NewEncrypted(src.String())), nil
}