package domain

import (
	"errors"
	"slices"
	"sort"

	"git.cin.su/m/Assistant/contracts/capability"
)

var ErrInvalidFleetReadiness = errors.New("invalid fleet readiness")

func BuildFleetReadiness(observedAt int64, members []capability.FleetMember) (capability.FleetReadiness, error) {
	if observedAt < 1 || len(members) == 0 {
		return capability.FleetReadiness{}, ErrInvalidFleetReadiness
	}
	result := capability.FleetReadiness{ObservedAtUnixMillis: observedAt, Members: append([]capability.FleetMember(nil), members...), FallbackTier: capability.FleetTierLifeboat}
	seen := map[capability.FleetTier]bool{}
	for i := range result.Members {
		member := &result.Members[i]
		if member.ProviderInstanceID == "" || member.ModelDescriptorID == "" || !validFleetTier(member.Tier) || seen[member.Tier] && member.Ready {
			return capability.FleetReadiness{}, ErrInvalidFleetReadiness
		}
		if member.Ready {
			seen[member.Tier] = true
		}
	}
	for _, tier := range []capability.FleetTier{capability.FleetTierFast, capability.FleetTierMedium, capability.FleetTierHeavy, capability.FleetTierLifeboat} {
		if seen[tier] {
			result.ReadyTiers = append(result.ReadyTiers, tier)
		}
	}
	return result, nil
}

func SelectFleetTier(readiness capability.FleetReadiness, preferred capability.FleetTier) (capability.FleetTier, error) {
	if readiness.ObservedAtUnixMillis < 1 || len(readiness.Members) == 0 || !validFleetTier(readiness.FallbackTier) {
		return "", ErrInvalidFleetReadiness
	}
	if !validFleetTier(preferred) {
		return "", ErrInvalidFleetReadiness
	}
	for _, tier := range fleetFailoverOrder(preferred) {
		if slices.Contains(readiness.ReadyTiers, tier) {
			return tier, nil
		}
	}
	if slices.Contains(readiness.ReadyTiers, readiness.FallbackTier) {
		return readiness.FallbackTier, nil
	}
	return "", ErrInvalidFleetReadiness
}

func fleetFailoverOrder(preferred capability.FleetTier) []capability.FleetTier {
	switch preferred {
	case capability.FleetTierHeavy:
		return []capability.FleetTier{capability.FleetTierHeavy, capability.FleetTierMedium, capability.FleetTierFast}
	case capability.FleetTierMedium:
		return []capability.FleetTier{capability.FleetTierMedium, capability.FleetTierFast}
	case capability.FleetTierFast:
		return []capability.FleetTier{capability.FleetTierFast}
	case capability.FleetTierLifeboat:
		return []capability.FleetTier{capability.FleetTierLifeboat}
	default:
		return nil
	}
}

func validFleetTier(value capability.FleetTier) bool {
	return value == capability.FleetTierFast || value == capability.FleetTierMedium || value == capability.FleetTierHeavy || value == capability.FleetTierLifeboat
}

func SortFleetMembers(members []capability.FleetMember) {
	sort.SliceStable(members, func(i, j int) bool {
		if members[i].Tier != members[j].Tier {
			return members[i].Tier < members[j].Tier
		}
		return members[i].ProviderInstanceID < members[j].ProviderInstanceID
	})
}