// configcheck exercises the calibration and config-persistence WebSocket frames
// against a StreamHub (either the Go hub or the C++ StreamHub) and exits
// non-zero if the hub's replies do not match the protocol.
package main

import (
	"encoding/json"
	"flag"
	"fmt"
	"os"
	"time"

	"github.com/gorilla/websocket"
)

type calEntry struct {
	Source string  `json:"source"`
	Signal string  `json:"signal"`
	Scale  float64 `json:"scale"`
	Offset float64 `json:"offset"`
	Unit   string  `json:"unit"`
}

type frame struct {
	Type  string     `json:"type"`
	Cal   []calEntry `json:"cal"`
	OK    bool       `json:"ok"`
	Path  string     `json:"path"`
	Error string     `json:"error"`
}

type conn struct {
	ws      *websocket.Conn
	timeout time.Duration
	// readCh is a long-lived goroutine that forwards frames; nil until startReader.
	readCh chan readResult
}

type readResult struct {
	f   frame
	err error
}

// startReader launches a background goroutine that reads all text frames from
// the WebSocket and forwards them on readCh.  This avoids setting a read
// deadline on the underlying connection, which permanently poisons gorilla
// websocket after a timeout fires.
func (c *conn) startReader() {
	c.readCh = make(chan readResult, 32)
	go func() {
		for {
			mt, data, err := c.ws.ReadMessage()
			if err != nil {
				c.readCh <- readResult{err: fmt.Errorf("ws read: %w", err)}
				return
			}
			if mt != websocket.TextMessage {
				continue
			}
			var f frame
			if jsonErr := json.Unmarshal(data, &f); jsonErr != nil {
				continue
			}
			c.readCh <- readResult{f: f}
		}
	}()
}

// next reads from the background reader until a frame with the wanted type
// arrives, or the per-frame deadline passes.
func (c *conn) next(want string) (frame, error) {
	deadline := time.NewTimer(c.timeout)
	defer deadline.Stop()
	for {
		select {
		case <-deadline.C:
			return frame{}, fmt.Errorf("timeout waiting for %q", want)
		case r, ok := <-c.readCh:
			if !ok {
				return frame{}, fmt.Errorf("reader closed while waiting for %q", want)
			}
			if r.err != nil {
				return frame{}, fmt.Errorf("read while waiting for %q: %w", want, r.err)
			}
			if r.f.Type == want {
				return r.f, nil
			}
		}
	}
}

// nextWithin reads from the background reader until a frame with the wanted
// type arrives within d, returning (frame, true) or (frame{}, false).  Unlike
// next() it does NOT return an error on timeout, making it suitable for the
// "must NOT arrive" assertion.
func (c *conn) nextWithin(want string, d time.Duration) (frame, bool) {
	deadline := time.NewTimer(d)
	defer deadline.Stop()
	for {
		select {
		case <-deadline.C:
			return frame{}, false
		case r, ok := <-c.readCh:
			if !ok || r.err != nil {
				return frame{}, false
			}
			if r.f.Type == want {
				return r.f, true
			}
		}
	}
}

func (c *conn) send(v interface{}) error {
	data, err := json.Marshal(v)
	if err != nil {
		return err
	}
	return c.ws.WriteMessage(websocket.TextMessage, data)
}

func findCal(list []calEntry, source, signal string) (calEntry, bool) {
	for _, e := range list {
		if e.Source == source && e.Signal == signal {
			return e, true
		}
	}
	return calEntry{}, false
}

func run(url, source, signal string, timeout time.Duration) error {
	ws, _, err := websocket.DefaultDialer.Dial(url, nil)
	if err != nil {
		return fmt.Errorf("dial %s: %w", url, err)
	}
	defer ws.Close()
	c := &conn{ws: ws, timeout: timeout}
	c.startReader()

	// 1. The hub sends a calibration frame on connect, even when empty.
	if _, err := c.next("calibration"); err != nil {
		return fmt.Errorf("on connect: %w", err)
	}

	// 2. setCalibration is accepted and echoed back to every client.
	want := calEntry{Source: source, Signal: signal, Scale: 0.5, Offset: -1.25, Unit: "V"}
	if err := c.send(map[string]interface{}{
		"type":   "setCalibration",
		"source": want.Source,
		"signal": want.Signal,
		"scale":  want.Scale,
		"offset": want.Offset,
		"unit":   want.Unit,
	}); err != nil {
		return err
	}
	f, err := c.next("calibration")
	if err != nil {
		return fmt.Errorf("after setCalibration: %w", err)
	}
	got, ok := findCal(f.Cal, source, signal)
	if !ok {
		return fmt.Errorf("setCalibration: entry %s/%s missing from broadcast", source, signal)
	}
	if got != want {
		return fmt.Errorf("setCalibration: got %+v, want %+v", got, want)
	}

	// 3. An invalid entry (scale = 0) must be rejected: no broadcast follows.
	if err := c.send(map[string]interface{}{
		"type": "setCalibration", "source": source, "signal": signal,
		"scale": 0.0, "offset": 0.0, "unit": "",
	}); err != nil {
		return err
	}
	if _, accepted := c.nextWithin("calibration", 500*time.Millisecond); accepted {
		return fmt.Errorf("setCalibration with scale=0 was accepted, must be rejected")
	}

	// 4. saveSources acknowledges with configSaved.
	if err := c.send(map[string]string{"type": "saveSources"}); err != nil {
		return err
	}
	f, err = c.next("configSaved")
	if err != nil {
		return err
	}
	if !f.OK {
		return fmt.Errorf("configSaved: ok=false, error=%q", f.Error)
	}
	if f.Path == "" {
		return fmt.Errorf("configSaved: ok=true but path is empty")
	}

	// 5. reloadConfig acknowledges and re-broadcasts the saved calibration.
	if err := c.send(map[string]string{"type": "reloadConfig"}); err != nil {
		return err
	}
	f, err = c.next("configReloaded")
	if err != nil {
		return err
	}
	if !f.OK {
		return fmt.Errorf("configReloaded: ok=false, error=%q", f.Error)
	}
	f, err = c.next("calibration")
	if err != nil {
		return fmt.Errorf("after reloadConfig: %w", err)
	}
	got, ok = findCal(f.Cal, source, signal)
	if !ok {
		return fmt.Errorf("reloadConfig: entry %s/%s did not survive the round-trip", source, signal)
	}
	if got != want {
		return fmt.Errorf("reloadConfig: got %+v, want %+v", got, want)
	}
	return nil
}

func main() {
	url := flag.String("url", "ws://127.0.0.1:8090/ws", "hub WebSocket URL")
	source := flag.String("source", "cfgcheck", "calibration source label to use")
	signal := flag.String("signal", "Probe", "calibration signal name to use")
	timeout := flag.Duration("timeout", 5*time.Second, "per-frame timeout")
	flag.Parse()

	if err := run(*url, *source, *signal, *timeout); err != nil {
		fmt.Fprintf(os.Stderr, "configcheck FAIL: %v\n", err)
		os.Exit(1)
	}
	fmt.Println("configcheck OK")
}