// Package enrol links a PC to a shop, using the one-shot code an operator is
// given.
//
// It existed only inside the desktop app, which meant a HEADLESS install - a
// back-office PC with no window, the configuration the agent binary is for -
// could not be claimed at all. The only route was hand-editing agent.json,
// which is exactly the state the desktop's Setup screen was built to end.
//
// The endpoint behind this is deliberately unauthenticated: the PC doing it has
// nobody signed in yet, and requiring a login would mean shipping a password to
// every shop that installs the software.
package enrol

import (
	"bytes"
	"context"
	"encoding/json"
	"fmt"
	"io"
	"net/http"
	"strings"
	"time"
)

// Bootstrap is what the server hands back: which shop this PC is, and the
// credentials it needs to say so.
type Bootstrap struct {
	ClientSlug string `json:"client_slug"`
	SiteSlug   string `json:"site_slug"`
	SiteName   string `json:"site_name"`
	MQTTURL    string `json:"mqtt_url"`
	MQTTUser   string `json:"mqtt_username"`
	MQTTPass   string `json:"mqtt_password"`
	CAPem      string `json:"ca_pem,omitempty"`
	AgentToken string `json:"agent_token"`
}

// Claim redeems an installation code.
//
// The code is read aloud down a phone and photographed off screens, so what is
// typed here can be as untidy as it needs to be: the server strips spaces,
// dashes and case at its end. Sending it as typed keeps ONE implementation of
// that normalisation, on the side that also issued the code - two would
// eventually disagree and hash to something the redeemer never produces.
func Claim(ctx context.Context, base, code string) (Bootstrap, error) {
	var out Bootstrap
	base = strings.TrimRight(base, "/")
	if base == "" {
		return out, fmt.Errorf("no server address configured (set cloud_base or BEHAVISION_CLOUD)")
	}
	body, err := json.Marshal(map[string]string{"site_token": code})
	if err != nil {
		return out, err
	}
	ctx, cancel := context.WithTimeout(ctx, 30*time.Second)
	defer cancel()

	req, err := http.NewRequestWithContext(ctx, http.MethodPost,
		base+"/api/agent/enrol", bytes.NewReader(body))
	if err != nil {
		return out, err
	}
	req.Header.Set("Content-Type", "application/json")

	resp, err := http.DefaultClient.Do(req)
	if err != nil {
		return out, fmt.Errorf("could not reach %s: %w", base, err)
	}
	defer resp.Body.Close()
	blob, _ := io.ReadAll(io.LimitReader(resp.Body, 64<<10))
	if resp.StatusCode != http.StatusOK {
		// The server answers unknown, expired and already-used identically on
		// purpose - the difference only helps somebody guessing codes, and the
		// operator's next step is the same in all three cases. Its own words
		// are passed through rather than reworded here.
		var e struct {
			Message string `json:"message"`
		}
		_ = json.Unmarshal(blob, &e)
		if e.Message != "" {
			return out, fmt.Errorf("%s", e.Message)
		}
		return out, fmt.Errorf("head office: %s", resp.Status)
	}
	if err := json.Unmarshal(blob, &out); err != nil {
		return out, err
	}
	if out.SiteSlug == "" || out.MQTTURL == "" {
		return out, fmt.Errorf("head office returned an incomplete setup")
	}
	return out, nil
}