package sms

import (
	"bytes"
	"context"
	"fmt"
	"io"
	"net/http"
	"os"
	"strings"
	"time"

	"doormile/utils"
)

// A provider-agnostic HTTP gateway, and the wiring that installs it.
//
// This package called itself "the seam, not the integration", with a logging
// sink standing in until a gateway was plugged in. The sink was never replaced:
// sms.Register had no callers anywhere in the tree, so every customer
// verification code since this surface shipped has gone to the application log
// and nowhere else. Two consequences, both live in production:
//
//  1. No customer can complete sign-in without somebody reading the server log
//     to them. That is the single blocker on the customer app, and it is why
//     the app's offline dev mode became the only practical way in — which in
//     turn is why bookings "made" in it never reached the admin console.
//  2. Every OTP ever issued is sitting in log storage as plaintext. A
//     credential in a log file is a credential in the wrong place.
//
// Rather than hard-coding one vendor, this posts to whatever gateway the
// deployment names. The Indian providers this would plausibly use — MSG91,
// Gupshup, Textlocal, Fast2SMS — all accept an authenticated POST carrying a
// destination and a body, so one templated request covers them and swapping
// vendors is configuration rather than a release.
//
// Configuration, all read once at startup. An absent SMS_GATEWAY_URL leaves the
// log sink exactly where it is, so this change cannot break a deployment that
// has not been configured yet:
//
//	SMS_GATEWAY_URL     endpoint to POST to; absent means "stay on the log sink"
//	SMS_GATEWAY_METHOD  HTTP method, default POST
//	SMS_GATEWAY_AUTH    Authorization header value, for vendors that use one
//	SMS_GATEWAY_HEADER  one extra "Name: value" header, for vendors with their own key header
//	SMS_GATEWAY_BODY    body template; {{phone}}, {{message}} and {{sender}} are substituted
//	SMS_GATEWAY_TYPE    content type, default application/json
//	SMS_SENDER_ID       the registered sender id, substituted as {{sender}}

const gatewayTimeout = 10 * time.Second

type httpSender struct {
	url         string
	method      string
	auth        string
	headerName  string
	headerValue string
	bodyTmpl    string
	contentType string
	senderID    string
	client      *http.Client
}

func (httpSender) Name() string { return "http-gateway" }

func (s httpSender) Send(phone, message string) error {
	body := s.bodyTmpl
	body = strings.ReplaceAll(body, "{{phone}}", phone)
	body = strings.ReplaceAll(body, "{{message}}", jsonEscape(message))
	body = strings.ReplaceAll(body, "{{sender}}", s.senderID)

	ctx, cancel := context.WithTimeout(context.Background(), gatewayTimeout)
	defer cancel()

	req, err := http.NewRequestWithContext(ctx, s.method, s.url, bytes.NewReader([]byte(body)))
	if err != nil {
		return fmt.Errorf("sms: build gateway request: %w", err)
	}
	req.Header.Set("Content-Type", s.contentType)
	if s.auth != "" {
		req.Header.Set("Authorization", s.auth)
	}
	if s.headerName != "" {
		req.Header.Set(s.headerName, s.headerValue)
	}

	resp, err := s.client.Do(req)
	if err != nil {
		return fmt.Errorf("sms: gateway unreachable: %w", err)
	}
	defer resp.Body.Close()

	// Read a bounded slice of the response for the log. The gateway's reason
	// for refusing — "insufficient balance", "DLT template not approved" — is
	// the entire diagnosis, and it only ever appears in the body.
	snippet, _ := io.ReadAll(io.LimitReader(resp.Body, 512))

	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
		// The number is masked and the message is NOT logged: the message
		// contains the code, which is the thing this whole file exists to keep
		// out of the log.
		utils.Error("sms: gateway rejected the send",
			"status", resp.StatusCode,
			"phone", maskPhone(phone),
			"response", strings.TrimSpace(string(snippet)))
		return fmt.Errorf("sms: gateway returned %d", resp.StatusCode)
	}

	utils.Info("sms: code delivered", "phone", maskPhone(phone))
	return nil
}

// jsonEscape makes a message safe to interpolate into a JSON body template.
// The OTP text carries no quotes today, but a template is a template and the
// next message to go through here will not be this one.
func jsonEscape(s string) string {
	var b strings.Builder
	for _, r := range s {
		switch r {
		case '"':
			b.WriteString(`\"`)
		case '\\':
			b.WriteString(`\\`)
		case '\n':
			b.WriteString(`\n`)
		case '\r':
			b.WriteString(`\r`)
		case '\t':
			b.WriteString(`\t`)
		default:
			b.WriteRune(r)
		}
	}
	return b.String()
}

// Configure installs a real gateway when one is configured, and says plainly
// which transport the process ended up with.
//
// Called once from main() after config load. Deliberately loud in both
// directions: a deployment that believes it can send texts and cannot is the
// exact failure that has been live in this service since the customer surface
// shipped, so it must not be possible to start without the answer appearing in
// the boot log.
func Configure() {
	url := strings.TrimSpace(os.Getenv("SMS_GATEWAY_URL"))
	if url == "" {
		utils.Warn("SMS: no gateway configured (SMS_GATEWAY_URL is unset). " +
			"Verification codes are written to THIS LOG and no text is sent. " +
			"Customer sign-in cannot complete unless somebody reads the code out " +
			"of here, or CX_STAGING_OTP is set on a non-production deployment.")
		return
	}

	method := strings.ToUpper(strings.TrimSpace(os.Getenv("SMS_GATEWAY_METHOD")))
	if method == "" {
		method = http.MethodPost
	}

	bodyTmpl := os.Getenv("SMS_GATEWAY_BODY")
	if strings.TrimSpace(bodyTmpl) == "" {
		bodyTmpl = `{"to":"{{phone}}","message":"{{message}}","sender":"{{sender}}"}`
	}

	contentType := strings.TrimSpace(os.Getenv("SMS_GATEWAY_TYPE"))
	if contentType == "" {
		contentType = "application/json"
	}

	var headerName, headerValue string
	if raw := strings.TrimSpace(os.Getenv("SMS_GATEWAY_HEADER")); raw != "" {
		if name, value, ok := strings.Cut(raw, ":"); ok {
			headerName = strings.TrimSpace(name)
			headerValue = strings.TrimSpace(value)
		} else {
			utils.Warn("SMS: SMS_GATEWAY_HEADER is not in 'Name: value' form and was ignored",
				"value", raw)
		}
	}

	Register(httpSender{
		url:         url,
		method:      method,
		auth:        strings.TrimSpace(os.Getenv("SMS_GATEWAY_AUTH")),
		headerName:  headerName,
		headerValue: headerValue,
		bodyTmpl:    bodyTmpl,
		contentType: contentType,
		senderID:    strings.TrimSpace(os.Getenv("SMS_SENDER_ID")),
		client:      &http.Client{Timeout: gatewayTimeout},
	})
}