package provision

import (
	"bytes"
	"encoding/json"
	"errors"
	"io"
	"strings"

	"github.com/carlosframework/platform/internal/maintenanceguard"
)

var ErrMaintenanceProjection = errors.New("provision: invalid maintenance projection or protected fields")

// MaintenanceProjection retains a present projection, including invalid input.
// Its value receiver validates on marshal, so an ignored decode error cannot
// turn a present invalid projection into an absent one. An empty slice is absent.
type MaintenanceProjection []byte

func (p *MaintenanceProjection) UnmarshalJSON(raw []byte) error {
	*p = append((*p)[:0], raw...)
	_, err := maintenanceguard.DecodeProjection(raw)
	if err != nil {
		return ErrMaintenanceProjection
	}
	return nil
}
func (p MaintenanceProjection) MarshalJSON() ([]byte, error) {
	if _, err := maintenanceguard.DecodeProjection(p); err != nil {
		return nil, ErrMaintenanceProjection
	}
	return append([]byte(nil), p...), nil
}

// DecodeRecord is the bucket-record parser. API response views may use ordinary
// JSON decoding; they do not authorize writes. Keep this off Record's method
// set so embedding Record cannot swallow a wrapper's fields or Gate shadow.
func DecodeRecord(raw []byte) (Record, error) {
	invalid := Record{Maintenance: MaintenanceProjection("null")}
	dec := json.NewDecoder(bytes.NewReader(raw))
	first, e := dec.Token()
	if e != nil || first != json.Delim('{') {
		return invalid, ErrMaintenanceProjection
	}
	seen := false
	for dec.More() {
		key, e := dec.Token()
		if e != nil {
			return invalid, ErrMaintenanceProjection
		}
		name, ok := key.(string)
		if !ok {
			return invalid, ErrMaintenanceProjection
		}
		if strings.EqualFold(name, "maintenance") {
			if name != "maintenance" || seen {
				return invalid, ErrMaintenanceProjection
			}
			seen = true
		}
		var value json.RawMessage
		if dec.Decode(&value) != nil {
			return invalid, ErrMaintenanceProjection
		}
	}
	if end, e := dec.Token(); e != nil || end != json.Delim('}') {
		return invalid, ErrMaintenanceProjection
	}
	if _, e = dec.Token(); e != io.EOF {
		return invalid, ErrMaintenanceProjection
	}
	var rec Record
	if json.Unmarshal(raw, &rec) != nil {
		return invalid, ErrMaintenanceProjection
	}
	return rec, nil
}

// Equality preserves the projection, not permission to change a fenced record.
// Durable guard and lifecycle checks belong to the maintenance integration.
func protectedFieldsEqual(before, after Record) bool {
	if before.RecordSeq != after.RecordSeq || before.Account != after.Account || before.App != after.App || before.Host != after.Host || !before.CreatedAt.Equal(after.CreatedAt) {
		return false
	}
	if len(before.Maintenance) == 0 || len(after.Maintenance) == 0 {
		return len(before.Maintenance) == len(after.Maintenance)
	}
	a, e := maintenanceguard.DecodeProjection(before.Maintenance)
	if e != nil {
		return false
	}
	b, e := maintenanceguard.DecodeProjection(after.Maintenance)
	return e == nil && a == b
}