package v1

import (
	"errors"
	"fmt"
)

var (
	errStandByLongerThanSuspendTime = errors.New("stand-by time cannot be longer than suspend time")
	errSuspendLongerThanOffTime     = errors.New("suspend time cannot be longer than off time")
)

// Validates the DisplayConfig, checking:
//   - Supported resolutions are not configured in spec.
//   - Only one display is configured as the primary.
//   - DPMS configuration is valid (standby-time < suspend-time < off-time).
func (displayConfig *DisplayConfig) Validate() error {
	if displayConfig == nil {
		return nil
	}

	if err := validateNonSettableFields(displayConfig); err != nil {
		return err
	}

	if err := validatePrimary(displayConfig); err != nil {
		return err
	}

	return validateDPMS(displayConfig)
}

// Displays cannot configure supported resolution.
func validateNonSettableFields(displayConfig *DisplayConfig) error {
	for mpid, display := range displayConfig.Displays {
		if display.SupportedResolutions != nil {
			return fmt.Errorf("display %s specified 'supportedResolutions': resolution should be configured via the 'resolution' field", mpid)
		}
	}
	return nil
}

// Only one display can be the primary.
func validatePrimary(displayConfig *DisplayConfig) error {
	primaries := []MPID{}
	for mpid, display := range displayConfig.Displays {
		if display.IsPrimary() {
			primaries = append(primaries, mpid)
		}
	}

	if len(primaries) > 1 {
		return fmt.Errorf("there can only be one primary, found %d: %v", len(primaries), primaries)
	}

	return nil
}

// Validates DPMS configuration.
//
// Where these fields are set, they must be configured so
// standby-time < suspend-time < off-time.
//
// If a field is not set, it is assumed to be 0.
func validateDPMS(displayConfig *DisplayConfig) error {
	if displayConfig.DPMS == nil {
		return nil
	}

	var standybyTime, suspendTimeTime, offTimeTime int
	if displayConfig.DPMS.StandbyTime != nil {
		standybyTime = *displayConfig.DPMS.StandbyTime
	}
	if displayConfig.DPMS.SuspendTime != nil {
		suspendTimeTime = *displayConfig.DPMS.SuspendTime
	}
	if displayConfig.DPMS.OffTime != nil {
		offTimeTime = *displayConfig.DPMS.OffTime
	}

	if standybyTime > suspendTimeTime {
		return errStandByLongerThanSuspendTime
	} else if suspendTimeTime > offTimeTime {
		return errSuspendLongerThanOffTime
	}

	return nil
}