package service

import (
	"errors"
	"fmt"
	"sort"
)

type DependencySuppressionInput struct {
	DependencyID       string  `json:"dependencyId"`
	ServiceID          string  `json:"serviceId"`
	DependsOnServiceID string  `json:"dependsOnServiceId"`
	SourceID           string  `json:"sourceId,omitempty"`
	Confidence         float64 `json:"confidence"`
	Confirmed          bool    `json:"confirmed"`
	UpstreamState      string  `json:"upstreamState"`
	Suppress           bool    `json:"suppress"`
	Reason             string  `json:"reason"`
}

// ValidateDependencyGraph rejects dependency cycles deterministically. Only
// depends_on edges participate in propagation; backs/exposes remain visible
// topology links without changing service state.
func ValidateDependencyGraph(dependencies []Dependency) error {
	edges := append([]Dependency(nil), dependencies...)
	SortDependencies(edges)
	seen := make(map[string]struct{}, len(edges))
	adjacency := make(map[string][]string)
	for _, dependency := range edges {
		if err := dependency.Validate(); err != nil {
			return err
		}
		key := dependencyKey(dependency)
		if _, exists := seen[key]; exists {
			return fmt.Errorf("duplicate service dependency: %s", key)
		}
		seen[key] = struct{}{}
		if dependency.RelationType == RelationDependsOn {
			adjacency[dependency.ServiceID] = append(adjacency[dependency.ServiceID], dependency.DependsOnServiceID)
		}
	}
	for source := range adjacency {
		sort.Strings(adjacency[source])
	}
	colors := make(map[string]uint8)
	var visit func(string) error
	visit = func(node string) error {
		switch colors[node] {
		case 1:
			return fmt.Errorf("%w includes %s", ErrDependencyCycle, node)
		case 2:
			return nil
		}
		colors[node] = 1
		for _, target := range adjacency[node] {
			if err := visit(target); err != nil {
				return err
			}
		}
		colors[node] = 2
		return nil
	}
	nodes := make([]string, 0, len(adjacency))
	for node := range adjacency {
		nodes = append(nodes, node)
	}
	sort.Strings(nodes)
	for _, node := range nodes {
		if err := visit(node); err != nil {
			return err
		}
	}
	return nil
}

func SortDependencies(dependencies []Dependency) {
	sort.SliceStable(dependencies, func(i, j int) bool {
		left, right := dependencies[i], dependencies[j]
		if left.ServiceID != right.ServiceID {
			return left.ServiceID < right.ServiceID
		}
		if left.DependsOnServiceID != right.DependsOnServiceID {
			return left.DependsOnServiceID < right.DependsOnServiceID
		}
		if left.RelationType != right.RelationType {
			return left.RelationType < right.RelationType
		}
		if left.SourceID != right.SourceID {
			return left.SourceID < right.SourceID
		}
		return left.ID < right.ID
	})
}

func BuildSuppressionInputs(dependencies []Dependency, states map[string]string) ([]DependencySuppressionInput, error) {
	if states == nil {
		states = map[string]string{}
	}
	if err := ValidateDependencyGraph(dependencies); err != nil {
		return nil, err
	}
	ordered := append([]Dependency(nil), dependencies...)
	SortDependencies(ordered)
	inputs := make([]DependencySuppressionInput, 0, len(ordered))
	for _, dependency := range ordered {
		if dependency.RelationType != RelationDependsOn {
			continue
		}
		state := states[dependency.DependsOnServiceID]
		input := DependencySuppressionInput{DependencyID: dependency.ID, ServiceID: dependency.ServiceID, DependsOnServiceID: dependency.DependsOnServiceID, SourceID: dependency.SourceID, Confidence: dependency.Confidence, Confirmed: dependency.Confirmed, UpstreamState: state}
		switch state {
		case StateDown, StateDegraded:
			input.Suppress = dependency.Confirmed || dependency.Confidence >= .75
			if input.Suppress && dependency.Confirmed {
				input.Reason = "confirmed_dependency_failure"
			} else if input.Suppress {
				input.Reason = "inferred_dependency_failure"
			} else {
				input.Reason = "low_confidence_dependency_failure"
			}
		case StateUnknown:
			input.Reason = "dependency_unknown"
		default:
			input.Reason = "dependency_healthy"
		}
		inputs = append(inputs, input)
	}
	return inputs, nil
}

func dependencyKey(dependency Dependency) string {
	return dependency.ServiceID + "|" + dependency.DependsOnServiceID + "|" + dependency.RelationType + "|" + dependency.SourceID
}

var ErrDependencyCycle = errors.New("service dependency cycle")