package keeper

import (
	"fmt"

	sdk "github.com/cosmos/cosmos-sdk/types"

	"github.com/oy/openyield/x/bearers/types"
)

// transport.go holds the store-backed BearerTransport impl (P2-02-01,
// REQ-034, A-522). The v0.2 BearerTransport Go interface (Send, Receive,
// Status) gains a store-backed runtime impl: the keeper IS the transport
// for simtest purposes — no hardware/RF Go libraries (D-054).
//
// The transport wraps the keeper's session store. Send appends a frame to
// the session's Frames slice. Receive marks the frame received (and
// transitions the session Open → Active on first ack). Status reports
// whether the session is Open or Active (i.e., still carrying traffic).
//
// Surveillance-resistant invariant (A-522): the transport carries NO
// geolocation / sender physical location fields. The surveillance-resistant
// locked const on OYSATLink/OYLRLink is a runtime invariant — the transport
// MUST NOT emit geolocation in events. A negative simtest asserts the event
// set contains NO geolocation fields.

// StoreTransport is the store-backed BearerTransport impl. It wraps a
// Keeper + the sdk.Context (bound at construction so the BearerTransport
// interface methods can stay parameterless per the v0.2 interface contract).
// The transport operates on a single session-id (a transport instance is
// scoped to one session — the bearer is a per-session handle in the simtest
// runtime).
type StoreTransport struct {
	keeper    Keeper
	ctx       sdk.Context
	sessionID string
}

// NewStoreTransport constructs a store-backed BearerTransport scoped to the
// named session. The session must already exist (Open or Active). The
// transport reads/writes the session's Frames slice via the keeper store.
func NewStoreTransport(k Keeper, ctx sdk.Context, sessionID string) *StoreTransport {
	return &StoreTransport{keeper: k, ctx: ctx, sessionID: sessionID}
}

// Compile-time assertion: StoreTransport satisfies the v0.2 BearerTransport
// interface (D-029, REQ-034). The interface contract is Send/Receive/Status
// (parameterless except Send takes a payload).
var _ types.BearerTransport = (*StoreTransport)(nil)

// Send dispatches a payload via the bearer. The store-backed impl appends
// the payload as a new Frame on the session's Frames slice. Returns an
// error if the session is not found or is terminal (Closed/Revoked) — a
// terminal session rejects further Send calls.
func (t *StoreTransport) Send(payload []byte) error {
	s, ok := t.keeper.GetSession(t.ctx, t.sessionID)
	if !ok {
		return fmt.Errorf("bearers: session %q not found", t.sessionID)
	}
	if s.IsTerminal() {
		return fmt.Errorf("bearers: session %q is terminal (%s), rejects Send", t.sessionID, s.Status)
	}
	frame := types.Frame{
		FrameID:      fmt.Sprintf("%s-frame-%d", t.sessionID, len(s.Frames)+1),
		SenderReach:  s.InitiatorReach,
		PayloadBytes: payload,
		SentAt:       t.ctx.BlockTime().Unix(),
	}
	s.Frames = append(s.Frames, frame)
	t.keeper.SetSession(t.ctx, s)
	t.ctx.EventManager().EmitEvent(sdk.NewEvent(
		"bearers.frame_sent",
		sdk.NewAttribute("session_id", t.sessionID),
		sdk.NewAttribute("frame_id", frame.FrameID),
		sdk.NewAttribute("sender_reach", frame.SenderReach),
		// NO geolocation (A-522 surveillance-resistant invariant).
	))
	return nil
}

// Receive accepts an inbound payload from the bearer. The store-backed impl
// marks the first unreceived frame as Received and transitions the session
// Open → Active on the first ack. Returns the payload and an error if the
// bearer has no inbound (unreceived) payload or the session is terminal.
func (t *StoreTransport) Receive() ([]byte, error) {
	s, ok := t.keeper.GetSession(t.ctx, t.sessionID)
	if !ok {
		return nil, fmt.Errorf("bearers: session %q not found", t.sessionID)
	}
	if s.IsTerminal() {
		return nil, fmt.Errorf("bearers: session %q is terminal (%s), rejects Receive", t.sessionID, s.Status)
	}
	// Find the first unreceived frame.
	var received *types.Frame
	for i := range s.Frames {
		if !s.Frames[i].Received {
			s.Frames[i].Received = true
			received = &s.Frames[i]
			break
		}
	}
	if received == nil {
		return nil, fmt.Errorf("bearers: no inbound frame on session %q", t.sessionID)
	}
	// Open → Active on the first ack.
	if s.Status == types.SessionOpen {
		s.Status = types.SessionActive
	}
	t.keeper.SetSession(t.ctx, s)
	t.ctx.EventManager().EmitEvent(sdk.NewEvent(
		"bearers.frame_received",
		sdk.NewAttribute("session_id", t.sessionID),
		sdk.NewAttribute("frame_id", received.FrameID),
		sdk.NewAttribute("status", string(s.Status)),
		// NO geolocation (A-522 surveillance-resistant invariant).
	))
	return received.PayloadBytes, nil
}

// Status reports the bearer's current reachability (true = reachable). The
// store-backed impl reports true iff the session exists and is Open or
// Active (still carrying traffic). A terminal or missing session is
// unreachable.
func (t *StoreTransport) Status() bool {
	s, ok := t.keeper.GetSession(t.ctx, t.sessionID)
	if !ok {
		return false
	}
	return s.Status == types.SessionOpen || s.Status == types.SessionActive
}