// Package application defines the application record domain model, status
// machine, and sentinel errors owned by Game Lobby Service for public-game
// enrollment requests.
package application

import (
	"fmt"
	"strings"
	"time"

	"galaxy/lobby/internal/domain/common"
)

// Application stores one durable application record owned by Game Lobby
// Service. Applications are used exclusively by public games; private
// games use the invite flow instead.
type Application struct {
	// ApplicationID identifies the record.
	ApplicationID common.ApplicationID

	// GameID identifies the game this application belongs to.
	GameID common.GameID

	// ApplicantUserID stores the platform user id of the applicant.
	ApplicantUserID string

	// RaceName stores the desired in-game name submitted with the
	// application.
	RaceName string

	// Status stores the current lifecycle state.
	Status Status

	// CreatedAt stores when the record was created.
	CreatedAt time.Time

	// DecidedAt stores when the record transitioned out of submitted. It
	// is nil while the application is still submitted.
	DecidedAt *time.Time
}

// NewApplicationInput groups all fields required to create a submitted
// application record.
type NewApplicationInput struct {
	// ApplicationID identifies the new record.
	ApplicationID common.ApplicationID

	// GameID identifies the game the applicant is applying to.
	GameID common.GameID

	// ApplicantUserID stores the platform user id of the applicant.
	ApplicantUserID string

	// RaceName stores the desired in-game name submitted by the
	// applicant.
	RaceName string

	// Now stores the creation wall-clock used for CreatedAt.
	Now time.Time
}

// New validates input and returns a submitted Application record.
// Validation errors are returned verbatim so callers can surface them as
// invalid_request.
func New(input NewApplicationInput) (Application, error) {
	if err := input.Validate(); err != nil {
		return Application{}, err
	}

	record := Application{
		ApplicationID:   input.ApplicationID,
		GameID:          input.GameID,
		ApplicantUserID: strings.TrimSpace(input.ApplicantUserID),
		RaceName:        strings.TrimSpace(input.RaceName),
		Status:          StatusSubmitted,
		CreatedAt:       input.Now.UTC(),
	}

	if err := record.Validate(); err != nil {
		return Application{}, err
	}

	return record, nil
}

// Validate reports whether input satisfies the frozen application-record
// invariants required to construct a submitted record.
func (input NewApplicationInput) Validate() error {
	if err := input.ApplicationID.Validate(); err != nil {
		return fmt.Errorf("application id: %w", err)
	}
	if err := input.GameID.Validate(); err != nil {
		return fmt.Errorf("game id: %w", err)
	}
	if strings.TrimSpace(input.ApplicantUserID) == "" {
		return fmt.Errorf("applicant user id must not be empty")
	}
	if strings.TrimSpace(input.RaceName) == "" {
		return fmt.Errorf("race name must not be empty")
	}
	if input.Now.IsZero() {
		return fmt.Errorf("now must not be zero")
	}

	return nil
}

// Validate reports whether record satisfies the full invariants.
// Every marshal and unmarshal round-trip calls Validate to guarantee that
// the Redis store never exposes malformed records.
func (record Application) Validate() error {
	if err := record.ApplicationID.Validate(); err != nil {
		return fmt.Errorf("application id: %w", err)
	}
	if err := record.GameID.Validate(); err != nil {
		return fmt.Errorf("game id: %w", err)
	}
	if strings.TrimSpace(record.ApplicantUserID) == "" {
		return fmt.Errorf("applicant user id must not be empty")
	}
	if strings.TrimSpace(record.RaceName) == "" {
		return fmt.Errorf("race name must not be empty")
	}
	if !record.Status.IsKnown() {
		return fmt.Errorf("status %q is unsupported", record.Status)
	}
	if record.CreatedAt.IsZero() {
		return fmt.Errorf("created at must not be zero")
	}
	if record.Status == StatusSubmitted {
		if record.DecidedAt != nil {
			return fmt.Errorf("decided at must be nil for submitted applications")
		}
	} else {
		if record.DecidedAt == nil {
			return fmt.Errorf("decided at must not be nil for %q applications", record.Status)
		}
		if record.DecidedAt.IsZero() {
			return fmt.Errorf("decided at must not be zero when present")
		}
		if record.DecidedAt.Before(record.CreatedAt) {
			return fmt.Errorf("decided at must not be before created at")
		}
	}

	return nil
}