// Package api exposes the small authenticated HTTP boundary around domain
// policies. Persistent adapters can replace the in-memory dependencies without
// changing request authentication or validation rules.
package api

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

	"github.com/cosmic-clash/cosmic-clash/server/domain"
)

const maxBodyBytes = 8 << 10

type CandidateProvider func(playerID, ticketID string) (domain.Candidate, error)
type CandidateProviderV2 func(playerID, ticketID string, spec domain.QueueSpec) (domain.Candidate, error)
type ProbeProvider func(playerID, region string, opaqueLocation, nonce []byte, receivedAt time.Time) (domain.ProbeEvidence, []byte, error)

type QueueBackend interface {
	Create(context.Context, string, string, string, domain.QueueSpec, time.Time) (domain.QueueTicket, error)
	Heartbeat(context.Context, string, string, string, uint64, time.Time) (domain.QueueTicket, error)
	Cancel(context.Context, string, string, string, uint64, time.Time) (domain.QueueTicket, error)
	Get(context.Context, string, string, time.Time) (domain.QueueTicket, error)
}

type SessionBackend interface {
	Authenticate(context.Context, string, string, time.Time) (domain.Session, error)
}
type SteamLoginProvider interface {
	Authenticate(context.Context, string, time.Time) (domain.VerifiedIdentity, error)
}
type SessionIssuer interface {
	Issue(context.Context, string, time.Duration, time.Time) (domain.Session, string, error)
}

type Service struct {
	Sessions       *domain.SessionStore
	SessionBackend SessionBackend
	SessionIssuer  SessionIssuer
	SteamLogin     SteamLoginProvider
	Queue          *domain.Queue
	Candidate      CandidateProvider
	CandidateV2    CandidateProviderV2
	QueueBackend   QueueBackend
	Probe          ProbeProvider
	Now            func() time.Time
	Proposals      map[string]*domain.Proposal
	RankedProfiles map[string]domain.RankedProfile
	TierPolicy     domain.TierPolicy
	proposalMu     sync.Mutex
}

func (s *Service) Handler() http.Handler {
	mux := http.NewServeMux()
	mux.HandleFunc("/healthz", s.health)
	mux.HandleFunc("/v1/session/steam", s.steamSession)
	mux.HandleFunc("/v1/queue", s.queueCreate)
	mux.HandleFunc("/v1/queue/", s.queueMutation)
	mux.HandleFunc("/v1/proposals/", s.proposalMutation)
	mux.HandleFunc("/v1/profile/ranked", s.rankedProfile)
	mux.HandleFunc("/v1/probes/", s.probe)
	return mux
}

type steamSessionRequest struct {
	WebAPITicket string `json:"web_api_ticket"`
}

func (s *Service) steamSession(w http.ResponseWriter, r *http.Request) {
	if r.Method != http.MethodPost {
		writeError(w, http.StatusMethodNotAllowed, "method_not_allowed")
		return
	}
	if s.SteamLogin == nil {
		writeError(w, http.StatusServiceUnavailable, "auth_unavailable")
		return
	}
	var input steamSessionRequest
	if !decodeBody(w, r, &input) {
		return
	}
	if input.WebAPITicket == "" || len(input.WebAPITicket) > 4096 {
		writeError(w, http.StatusBadRequest, "invalid_request")
		return
	}
	now := s.now()
	identity, err := s.SteamLogin.Authenticate(r.Context(), input.WebAPITicket, now)
	if err != nil || identity.PlayerID == "" || identity.SteamID == "" {
		writeError(w, http.StatusUnauthorized, "unauthorized")
		return
	}
	var session domain.Session
	var token string
	if s.SessionIssuer != nil {
		session, token, err = s.SessionIssuer.Issue(r.Context(), identity.PlayerID, time.Hour, now)
	} else if s.Sessions != nil {
		session, token, err = s.Sessions.Issue(identity.PlayerID, time.Hour, now)
	} else {
		writeError(w, http.StatusServiceUnavailable, "auth_unavailable")
		return
	}
	if err != nil {
		writeError(w, http.StatusServiceUnavailable, "auth_unavailable")
		return
	}
	writeJSON(w, http.StatusOK, map[string]any{"player_id": session.PlayerID, "expires_at": session.ExpiresAt, "access_token": session.SessionID + ":" + token})
}

func (s *Service) health(w http.ResponseWriter, _ *http.Request) {
	writeJSON(w, http.StatusOK, map[string]string{"status": "ok"})
}

type queueCreateRequest struct {
	TicketID        string `json:"ticket_id"`
	Playlist        string `json:"playlist"`
	ClientBuild     string `json:"client_build"`
	ProtocolVersion int    `json:"protocol_version"`
}
type queueResponse struct {
	TicketID   string    `json:"ticket_id"`
	PlayerID   string    `json:"player_id"`
	State      string    `json:"state"`
	Revision   uint64    `json:"revision"`
	EnqueuedAt time.Time `json:"enqueued_at"`
	ExpiresAt  time.Time `json:"expires_at"`
	Playlist   string    `json:"playlist"`
}

func (s *Service) queueCreate(w http.ResponseWriter, r *http.Request) {
	if r.Method != http.MethodPost {
		writeError(w, http.StatusMethodNotAllowed, "method_not_allowed")
		return
	}
	playerID, ok := s.authenticate(w, r)
	if !ok {
		return
	}
	if (s.Queue == nil && s.QueueBackend == nil) || (s.QueueBackend == nil && s.Candidate == nil && s.CandidateV2 == nil) {
		writeError(w, http.StatusServiceUnavailable, "queue_unavailable")
		return
	}
	var input queueCreateRequest
	if !decodeBody(w, r, &input) {
		return
	}
	if input.TicketID == "" || (input.Playlist != string(domain.Casual) && input.Playlist != string(domain.Ranked)) || input.ClientBuild == "" || len(input.ClientBuild) > 128 || input.ProtocolVersion < 1 {
		writeError(w, http.StatusBadRequest, "invalid_request")
		return
	}
	key := r.Header.Get("Idempotency-Key")
	if len(key) < 16 || len(key) > 128 {
		writeError(w, http.StatusBadRequest, "invalid_idempotency_key")
		return
	}
	now := s.now()
	spec := domain.QueueSpec{Playlist: domain.Playlist(input.Playlist), ClientBuild: input.ClientBuild, ProtocolVersion: input.ProtocolVersion}
	if s.QueueBackend != nil {
		ticket, err := s.QueueBackend.Create(r.Context(), playerID, input.TicketID, key, spec, now)
		if err != nil {
			writeDomainError(w, err)
			return
		}
		writeJSON(w, http.StatusCreated, toQueueResponse(ticket))
		return
	}
	var candidate domain.Candidate
	var err error
	if s.CandidateV2 != nil {
		candidate, err = s.CandidateV2(playerID, input.TicketID, spec)
	} else {
		candidate, err = s.Candidate(playerID, input.TicketID)
		// Legacy providers predate queue compatibility metadata. The API has
		// validated the request; keep the resulting projection self-describing.
		candidate.Playlist = spec.Playlist
		candidate.ClientBuild = spec.ClientBuild
		candidate.ProtocolVersion = spec.ProtocolVersion
	}
	if err != nil {
		writeError(w, http.StatusUnprocessableEntity, "candidate_unavailable")
		return
	}
	if candidate.PlayerID != playerID || candidate.TicketID != input.TicketID || candidate.Playlist != spec.Playlist || candidate.ClientBuild != spec.ClientBuild || candidate.ProtocolVersion != spec.ProtocolVersion {
		writeError(w, http.StatusUnprocessableEntity, "candidate_mismatch")
		return
	}
	ticket, err := s.Queue.Create(playerID, input.TicketID, key, candidate, now)
	if err != nil {
		writeDomainError(w, err)
		return
	}
	writeJSON(w, http.StatusCreated, toQueueResponse(ticket))
}

func (s *Service) queueMutation(w http.ResponseWriter, r *http.Request) {
	if r.Method != http.MethodPost && r.Method != http.MethodGet {
		writeError(w, http.StatusMethodNotAllowed, "method_not_allowed")
		return
	}
	playerID, ok := s.authenticate(w, r)
	if !ok {
		return
	}
	if s.Queue == nil && s.QueueBackend == nil {
		writeError(w, http.StatusServiceUnavailable, "queue_unavailable")
		return
	}
	parts := strings.Split(strings.TrimPrefix(r.URL.Path, "/v1/queue/"), "/")
	if r.Method == http.MethodGet {
		if len(parts) != 1 || parts[0] == "" {
			writeError(w, http.StatusNotFound, "not_found")
			return
		}
		var ticket domain.QueueTicket
		var err error
		if s.QueueBackend != nil {
			ticket, err = s.QueueBackend.Get(r.Context(), playerID, parts[0], s.now())
		} else {
			ticket, err = s.Queue.Get(playerID, parts[0], s.now())
		}
		if err != nil {
			writeDomainError(w, err)
			return
		}
		writeJSON(w, http.StatusOK, toQueueResponse(ticket))
		return
	}
	if len(parts) != 2 || parts[0] == "" || (parts[1] != "heartbeat" && parts[1] != "cancel") {
		writeError(w, http.StatusNotFound, "not_found")
		return
	}
	ticketID, key := parts[0], r.Header.Get("Idempotency-Key")
	if len(key) < 16 || len(key) > 128 {
		writeError(w, http.StatusBadRequest, "invalid_idempotency_key")
		return
	}
	revision, err := strconv.ParseUint(r.Header.Get("If-Match-Revision"), 10, 64)
	if err != nil {
		writeError(w, http.StatusBadRequest, "invalid_revision")
		return
	}
	now := s.now()
	var ticket domain.QueueTicket
	if parts[1] == "heartbeat" {
		if s.QueueBackend != nil {
			ticket, err = s.QueueBackend.Heartbeat(r.Context(), playerID, ticketID, key, revision, now)
		} else {
			ticket, err = s.Queue.Heartbeat(playerID, ticketID, key, revision, now)
		}
	} else {
		if s.QueueBackend != nil {
			ticket, err = s.QueueBackend.Cancel(r.Context(), playerID, ticketID, key, revision, now)
		} else {
			ticket, err = s.Queue.Cancel(playerID, ticketID, key, revision, now)
		}
	}
	if err != nil {
		writeDomainError(w, err)
		return
	}
	writeJSON(w, http.StatusOK, toQueueResponse(ticket))
}

type proposalResponse struct {
	ProposalID   string                       `json:"proposal_id"`
	Playlist     string                       `json:"playlist"`
	State        string                       `json:"state"`
	Revision     uint64                       `json:"revision"`
	ExpiresAt    time.Time                    `json:"expires_at"`
	Participants []domain.ProposalParticipant `json:"participants"`
}

func (s *Service) proposalMutation(w http.ResponseWriter, r *http.Request) {
	if r.Method != http.MethodPost && r.Method != http.MethodGet {
		writeError(w, http.StatusMethodNotAllowed, "method_not_allowed")
		return
	}
	playerID, ok := s.authenticate(w, r)
	if !ok {
		return
	}
	parts := strings.Split(strings.TrimPrefix(r.URL.Path, "/v1/proposals/"), "/")
	if r.Method == http.MethodGet {
		if len(parts) != 1 || parts[0] == "" {
			writeError(w, http.StatusNotFound, "not_found")
			return
		}
		s.proposalMu.Lock()
		defer s.proposalMu.Unlock()
		proposal, exists := s.Proposals[parts[0]]
		if !exists || proposal == nil || !proposal.HasParticipant(playerID) {
			writeError(w, http.StatusNotFound, "not_found")
			return
		}
		proposal.Expire(s.now())
		writeJSON(w, http.StatusOK, toProposalResponse(*proposal))
		return
	}
	if len(parts) != 2 || parts[0] == "" || (parts[1] != "accept" && parts[1] != "decline") {
		writeError(w, http.StatusNotFound, "not_found")
		return
	}
	key := r.Header.Get("Idempotency-Key")
	if len(key) < 16 || len(key) > 128 {
		writeError(w, http.StatusBadRequest, "invalid_idempotency_key")
		return
	}
	revision, err := strconv.ParseUint(r.Header.Get("If-Match-Revision"), 10, 64)
	if err != nil {
		writeError(w, http.StatusBadRequest, "invalid_revision")
		return
	}
	s.proposalMu.Lock()
	defer s.proposalMu.Unlock()
	proposal, exists := s.Proposals[parts[0]]
	if !exists || proposal == nil {
		writeError(w, http.StatusNotFound, "not_found")
		return
	}
	updated, err := proposal.Respond(playerID, key, parts[1] == "accept", revision, s.now())
	if err != nil {
		writeDomainError(w, err)
		return
	}
	writeJSON(w, http.StatusOK, toProposalResponse(updated))
}

type rankedProfileResponse struct {
	Rating      float64 `json:"rating"`
	RD          float64 `json:"rd"`
	Volatility  float64 `json:"volatility"`
	RankedGames int     `json:"ranked_games"`
	Tier        string  `json:"tier"`
	Provisional bool    `json:"provisional"`
	SeasonID    string  `json:"season_id,omitempty"`
}

func (s *Service) rankedProfile(w http.ResponseWriter, r *http.Request) {
	if r.Method != http.MethodGet {
		writeError(w, http.StatusMethodNotAllowed, "method_not_allowed")
		return
	}
	playerID, ok := s.authenticate(w, r)
	if !ok {
		return
	}
	profile, exists := s.RankedProfiles[playerID]
	if !exists {
		writeError(w, http.StatusNotFound, "not_found")
		return
	}
	tier, err := domain.RankedTier(profile, s.TierPolicy)
	if err != nil {
		writeError(w, http.StatusServiceUnavailable, "ranked_profile_unavailable")
		return
	}
	writeJSON(w, http.StatusOK, rankedProfileResponse{Rating: profile.Value, RD: profile.RD, Volatility: profile.Volatility, RankedGames: profile.RankedGames, Tier: string(tier), Provisional: domain.RankedIsProvisional(profile), SeasonID: profile.LastSeasonID})
}

type probeRequest struct {
	OpaqueLocation []byte `json:"opaque_location"`
	Nonce          []byte `json:"nonce"`
}

func (s *Service) probe(w http.ResponseWriter, r *http.Request) {
	if r.Method != http.MethodPost {
		writeError(w, http.StatusMethodNotAllowed, "method_not_allowed")
		return
	}
	playerID, ok := s.authenticate(w, r)
	if !ok {
		return
	}
	region := strings.TrimPrefix(r.URL.Path, "/v1/probes/")
	if (region != "EU" && region != "NA") || strings.Contains(region, "/") {
		writeError(w, http.StatusNotFound, "not_found")
		return
	}
	if s.Probe == nil {
		writeError(w, http.StatusServiceUnavailable, "probe_unavailable")
		return
	}
	var input probeRequest
	if !decodeBody(w, r, &input) {
		return
	}
	receivedAt := s.now()
	evidence, expectedNonce, err := s.Probe(playerID, region, input.OpaqueLocation, input.Nonce, receivedAt)
	if err != nil {
		writeError(w, http.StatusUnprocessableEntity, "probe_unavailable")
		return
	}
	if evidence.Region != region || domain.ValidateProbe(evidence, expectedNonce, receivedAt) != nil {
		writeError(w, http.StatusUnprocessableEntity, "invalid_probe")
		return
	}
	writeJSON(w, http.StatusAccepted, map[string]any{"region": region, "server_rtt_ms": evidence.ServerRTT.Milliseconds(), "status": "accepted"})
}

func (s *Service) authenticate(w http.ResponseWriter, r *http.Request) (string, bool) {
	if s.Sessions == nil && s.SessionBackend == nil {
		writeError(w, http.StatusServiceUnavailable, "auth_unavailable")
		return "", false
	}
	parts := strings.Fields(r.Header.Get("Authorization"))
	if len(parts) != 2 || parts[0] != "Bearer" {
		writeError(w, http.StatusUnauthorized, "unauthorized")
		return "", false
	}
	separator := strings.IndexByte(parts[1], ':')
	if separator <= 0 || separator == len(parts[1])-1 {
		writeError(w, http.StatusUnauthorized, "unauthorized")
		return "", false
	}
	var session domain.Session
	var err error
	if s.SessionBackend != nil {
		session, err = s.SessionBackend.Authenticate(r.Context(), parts[1][:separator], parts[1][separator+1:], s.now())
	} else {
		session, err = s.Sessions.Authenticate(parts[1][:separator], parts[1][separator+1:], s.now())
	}
	if err != nil {
		writeError(w, http.StatusUnauthorized, "unauthorized")
		return "", false
	}
	return session.PlayerID, true
}

func (s *Service) now() time.Time {
	if s.Now != nil {
		return s.Now()
	}
	return time.Now().UTC()
}

func decodeBody(w http.ResponseWriter, r *http.Request, target any) bool {
	r.Body = http.MaxBytesReader(w, r.Body, maxBodyBytes)
	decoder := json.NewDecoder(r.Body)
	decoder.DisallowUnknownFields()
	if err := decoder.Decode(target); err != nil {
		writeError(w, http.StatusBadRequest, "invalid_request")
		return false
	}
	var extra any
	if err := decoder.Decode(&extra); err != io.EOF {
		writeError(w, http.StatusBadRequest, "invalid_request")
		return false
	}
	return true
}

func toQueueResponse(ticket domain.QueueTicket) queueResponse {
	return queueResponse{TicketID: ticket.TicketID, PlayerID: ticket.PlayerID, Playlist: string(ticket.Playlist), State: string(ticket.State), Revision: ticket.Revision, EnqueuedAt: ticket.EnqueuedAt, ExpiresAt: ticket.ExpiresAt}
}

func toProposalResponse(proposal domain.Proposal) proposalResponse {
	return proposalResponse{ProposalID: proposal.ProposalID, Playlist: string(proposal.Playlist), State: string(proposal.State), Revision: proposal.Revision, ExpiresAt: proposal.ExpiresAt, Participants: proposal.Participants}
}

func writeDomainError(w http.ResponseWriter, err error) {
	switch {
	case errors.Is(err, domain.ErrPlayerQueued), errors.Is(err, domain.ErrConflict), errors.Is(err, domain.ErrStaleRevision):
		writeError(w, http.StatusConflict, "conflict")
	case errors.Is(err, domain.ErrTicketExpired):
		writeError(w, http.StatusGone, "expired")
	case errors.Is(err, domain.ErrNotTicketOwner):
		writeError(w, http.StatusForbidden, "forbidden")
	case errors.Is(err, domain.ErrTicketNotFound):
		writeError(w, http.StatusNotFound, "not_found")
	default:
		writeError(w, http.StatusUnprocessableEntity, "invalid_request")
	}
}

func writeError(w http.ResponseWriter, status int, code string) {
	writeJSON(w, status, map[string]string{"error": code})
}

func writeJSON(w http.ResponseWriter, status int, value any) {
	w.Header().Set("Content-Type", "application/json")
	w.WriteHeader(status)
	_ = json.NewEncoder(w).Encode(value)
}