package serviceapi

import (
	"context"
	"encoding/json"
	"errors"
	"net/http"
	"sort"
	"strconv"
	"strings"
	"time"

	"github.com/itworx/pulse/internal/auth"
	"github.com/itworx/pulse/internal/probe"
	"github.com/itworx/pulse/internal/problem"
	"github.com/itworx/pulse/internal/reverseproxy"
	"github.com/itworx/pulse/internal/service"
)

type Handler struct {
	Provider     service.Provider
	Dependencies interface {
		List(context.Context, string, int) ([]service.Dependency, error)
	}
	MaxPageSize  int
	MaxHistory   int
	ReverseProxy reverseproxy.Provider
}

func (h Handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	if r.Method != http.MethodGet || (r.URL.Path != "/api/v1/services" && !strings.HasPrefix(r.URL.Path, "/api/v1/services/") && r.URL.Path != "/api/v1/topology") {
		http.NotFound(w, r)
		return
	}
	if _, ok := auth.PrincipalFromContext(r.Context()); !ok {
		problem.Write(w, r, http.StatusUnauthorized, "UNAUTHORIZED", "Authentication required", "Authentication is required to read services.", nil)
		return
	}
	if err := r.Context().Err(); err != nil {
		return
	}
	if r.URL.Path == "/api/v1/topology" {
		h.serveTopology(w, r)
		return
	}
	if strings.HasSuffix(r.URL.Path, "/dependencies") {
		h.serveDependencies(w, r)
		return
	}
	snapshot, err := h.snapshot(r)
	if err != nil {
		if errors.Is(err, context.Canceled) || errors.Is(err, context.DeadlineExceeded) {
			return
		}
		problem.Write(w, r, http.StatusServiceUnavailable, "SERVICES_UNAVAILABLE", "Servicegegevens niet beschikbaar", "De servicegegevens konden niet worden gelezen.", nil)
		return
	}
	if r.URL.Path == "/api/v1/services" {
		limit, parseErr := h.limit(r.URL.Query().Get("limit"), h.pageLimit())
		if parseErr != nil {
			problem.Write(w, r, http.StatusBadRequest, "SERVICE_QUERY_INVALID", "Invalid service query", "De servicelimiet is ongeldig.", nil)
			return
		}
		response := boundedSnapshot(snapshot, limit, h.historyLimit())
		writeJSON(w, response)
		return
	}
	path := strings.TrimPrefix(r.URL.Path, "/api/v1/services/")
	historyRequest := strings.HasSuffix(path, "/history")
	if strings.Contains(path, "/") && !historyRequest {
		http.NotFound(w, r)
		return
	}
	id := strings.TrimSuffix(path, "/history")
	id = strings.TrimSuffix(id, "/")
	if id == "" {
		http.NotFound(w, r)
		return
	}
	for _, item := range snapshot.Services {
		if item.ID != id {
			continue
		}
		item = boundedStatus(item, h.historyLimit())
		if historyRequest {
			limit, parseErr := h.limit(r.URL.Query().Get("limit"), h.historyLimit())
			if parseErr != nil {
				problem.Write(w, r, http.StatusBadRequest, "SERVICE_HISTORY_QUERY_INVALID", "Invalid service history query", "De historielimiet is ongeldig.", nil)
				return
			}
			if len(item.History) > limit {
				item.History = item.History[:limit]
			}
			writeJSON(w, struct {
				ServiceID string         `json:"serviceId"`
				History   []probe.Result `json:"history"`
			}{ServiceID: item.ID, History: item.History})
			return
		}
		writeJSON(w, struct {
			Service service.ServiceStatus `json:"service"`
		}{Service: item})
		return
	}
	http.NotFound(w, r)
}

func (h Handler) serveTopology(w http.ResponseWriter, r *http.Request) {
	if h.Dependencies == nil {
		problem.Write(w, r, http.StatusServiceUnavailable, "TOPOLOGY_UNAVAILABLE", "Topology not available", "De topologygegevens zijn niet beschikbaar.", nil)
		return
	}
	limit, err := h.limit(r.URL.Query().Get("limit"), 100)
	if err != nil {
		problem.Write(w, r, http.StatusBadRequest, "TOPOLOGY_QUERY_INVALID", "Invalid topology query", "De topologylimiet is ongeldig.", nil)
		return
	}
	snapshot, err := h.snapshot(r)
	if err != nil {
		if errors.Is(err, context.Canceled) || errors.Is(err, context.DeadlineExceeded) {
			return
		}
		problem.Write(w, r, http.StatusServiceUnavailable, "TOPOLOGY_UNAVAILABLE", "Topology not available", "De topologygegevens konden niet worden gelezen.", nil)
		return
	}
	dependencies, err := h.Dependencies.List(r.Context(), "", minTopologyEdges(limit))
	if err != nil {
		if errors.Is(err, context.Canceled) || errors.Is(err, context.DeadlineExceeded) {
			return
		}
		problem.Write(w, r, http.StatusServiceUnavailable, "TOPOLOGY_UNAVAILABLE", "Topology not available", "De afhankelijkheden konden niet worden gelezen.", nil)
		return
	}
	var routes []reverseproxy.Route
	if h.ReverseProxy != nil {
		proxySnapshot, proxyErr := h.ReverseProxy.Snapshot(r.Context())
		if proxyErr != nil {
			if errors.Is(proxyErr, context.Canceled) || errors.Is(proxyErr, context.DeadlineExceeded) {
				return
			}
		} else if proxySnapshot.Source.State == reverseproxy.StateEnabled {
			routes = proxySnapshot.Routes
		}
	}
	sourceTruncated := len(snapshot.Services) > limit
	topology, err := service.BuildTopologyWithRoutes(boundedSnapshot(snapshot, limit, h.historyLimit()), dependencies, routes, limit, minTopologyEdges(limit))
	if err != nil {
		problem.Write(w, r, http.StatusServiceUnavailable, "TOPOLOGY_UNAVAILABLE", "Topology not available", "De topology kon niet veilig worden samengesteld.", nil)
		return
	}
	topology.Truncated = topology.Truncated || sourceTruncated
	writeJSON(w, topology)
}

func minTopologyEdges(limit int) int {
	if limit > 250 {
		return 500
	}
	return limit * 2
}
func (h Handler) serveDependencies(w http.ResponseWriter, r *http.Request) {
	if h.Dependencies == nil {
		problem.Write(w, r, http.StatusServiceUnavailable, "DEPENDENCIES_UNAVAILABLE", "Dependencies not available", "Afhankelijkheden zijn niet beschikbaar.", nil)
		return
	}
	id := strings.TrimSuffix(strings.TrimPrefix(r.URL.Path, "/api/v1/services/"), "/dependencies")
	if id == "" || strings.Contains(id, "/") {
		http.NotFound(w, r)
		return
	}
	limit, err := h.limit(r.URL.Query().Get("limit"), 100)
	if err != nil {
		problem.Write(w, r, http.StatusBadRequest, "DEPENDENCY_QUERY_INVALID", "Invalid dependency query", "De afhankelijkheidslimiet is ongeldig.", nil)
		return
	}
	items, err := h.Dependencies.List(r.Context(), id, limit)
	if err != nil {
		if errors.Is(err, context.Canceled) || errors.Is(err, context.DeadlineExceeded) {
			return
		}
		problem.Write(w, r, http.StatusServiceUnavailable, "DEPENDENCIES_UNAVAILABLE", "Dependencies not available", "Afhankelijkheden konden niet worden gelezen.", nil)
		return
	}
	service.SortDependencies(items)
	writeJSON(w, struct {
		ServiceID    string               `json:"serviceId"`
		Dependencies []service.Dependency `json:"dependencies"`
	}{ServiceID: id, Dependencies: items})
}
func (h Handler) snapshot(r *http.Request) (service.Snapshot, error) {
	if h.Provider == nil {
		return service.UnknownSnapshot(time.Now().UTC(), "source_unavailable"), nil
	}
	return h.Provider.Snapshot(r.Context())
}

func (h Handler) pageLimit() int {
	if h.MaxPageSize == 0 {
		return 100
	}
	return h.MaxPageSize
}

func (h Handler) historyLimit() int {
	if h.MaxHistory == 0 {
		return 100
	}
	return h.MaxHistory
}

func (h Handler) limit(raw string, fallback int) (int, error) {
	if raw == "" {
		return fallback, nil
	}
	value, err := strconv.Atoi(raw)
	if err != nil || value < 1 || value > fallback {
		return 0, errors.New("limit outside bounds")
	}
	return value, nil
}

func boundedSnapshot(snapshot service.Snapshot, maxServices, maxHistory int) service.Snapshot {
	snapshot.Services = append([]service.ServiceStatus(nil), snapshot.Services...)
	sort.Slice(snapshot.Services, func(i, j int) bool { return snapshot.Services[i].ID < snapshot.Services[j].ID })
	if len(snapshot.Services) > maxServices {
		snapshot.Services = snapshot.Services[:maxServices]
	}
	for index := range snapshot.Services {
		snapshot.Services[index] = boundedStatus(snapshot.Services[index], maxHistory)
	}
	if len(snapshot.Events) > 100 {
		snapshot.Events = snapshot.Events[:100]
	}
	return snapshot
}

func boundedStatus(status service.ServiceStatus, maxHistory int) service.ServiceStatus {
	status.History = append([]probe.Result(nil), status.History...)
	if len(status.History) > maxHistory {
		status.History = status.History[:maxHistory]
	}
	if len(status.Probes) > 100 {
		status.Probes = status.Probes[:100]
	}
	return status
}

func writeJSON(w http.ResponseWriter, value any) {
	w.Header().Set("Content-Type", "application/json")
	w.Header().Set("Cache-Control", "private, max-age=5")
	_ = json.NewEncoder(w).Encode(value)
}