// gmail — 透過 Gmail API 發送 Email
// 透過 host function 呼叫 Gmail API
//
//go:build tinygo

package main

import (
	"encoding/json"
	"io"
	"os"
	"strings"
	"unsafe"
)

//go:wasmimport u6u http_request
func hostHttpRequest(
	urlPtr uintptr, urlLen uint32,
	methodPtr uintptr, methodLen uint32,
	headersPtr uintptr, headersLen uint32,
	bodyPtr uintptr, bodyLen uint32,
	outPtr uintptr, outLenPtr uintptr,
) uint32

type Input struct {
	To          string `json:"to"`
	Subject     string `json:"subject"`
	Body        string `json:"body"`
	AccessToken string `json:"access_token"`
}

func main() {
	raw, err := io.ReadAll(os.Stdin)
	if err != nil {
		writeError("failed to read stdin: " + err.Error())
		return
	}
	var input Input
	if err := json.Unmarshal(raw, &input); err != nil {
		writeError("invalid input JSON: " + err.Error())
		return
	}
	if input.To == "" {
		writeError("to 必填")
		return
	}
	if input.Subject == "" {
		writeError("subject 必填")
		return
	}
	if input.AccessToken == "" {
		writeError("access_token 必填")
		return
	}

	// 建立 RFC 2822 格式的 email，base64url 編碼
	emailLines := []string{
		"To: " + input.To,
		"Subject: " + input.Subject,
		"Content-Type: text/plain; charset=UTF-8",
		"",
		input.Body,
	}
	emailRaw := strings.Join(emailLines, "\r\n")
	encoded := base64URLEncode([]byte(emailRaw))

	bodyData, _ := json.Marshal(map[string]string{"raw": encoded})

	apiURL := "https://gmail.googleapis.com/gmail/v1/users/me/messages/send"
	method := "POST"
	headers := map[string]string{
		"Authorization": "Bearer " + input.AccessToken,
		"Content-Type":  "application/json",
	}
	headersJSON, _ := json.Marshal(headers)

	urlBytes := []byte(apiURL)
	methodBytes := []byte(method)
	bodyBytes := bodyData

	outBuf := make([]byte, 65536)
	var outLen uint32

	result := hostHttpRequest(
		uintptr(unsafe.Pointer(&urlBytes[0])), uint32(len(urlBytes)),
		uintptr(unsafe.Pointer(&methodBytes[0])), uint32(len(methodBytes)),
		uintptr(unsafe.Pointer(&headersJSON[0])), uint32(len(headersJSON)),
		uintptr(unsafe.Pointer(&bodyBytes[0])), uint32(len(bodyBytes)),
		uintptr(unsafe.Pointer(&outBuf[0])), uintptr(unsafe.Pointer(&outLen)),
	)

	if result != 0 {
		writeError("Gmail API 呼叫失敗")
		return
	}

	responseStr := string(outBuf[:outLen])
	var responseData map[string]interface{}
	if err := json.Unmarshal([]byte(responseStr), &responseData); err != nil {
		responseData = map[string]interface{}{"raw": responseStr}
	}

	messageID, _ := responseData["id"].(string)
	out, _ := json.Marshal(map[string]interface{}{
		"success": true,
		"data":    map[string]interface{}{"message_id": messageID},
	})
	os.Stdout.Write(out)
}

// base64URLEncode — 不依賴 encoding/base64（TinyGo 相容）
func base64URLEncode(data []byte) string {
	const chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_"
	var sb strings.Builder
	for i := 0; i < len(data); i += 3 {
		b0 := data[i]
		var b1, b2 byte
		if i+1 < len(data) {
			b1 = data[i+1]
		}
		if i+2 < len(data) {
			b2 = data[i+2]
		}
		sb.WriteByte(chars[b0>>2])
		sb.WriteByte(chars[((b0&0x3)<<4)|(b1>>4)])
		if i+1 < len(data) {
			sb.WriteByte(chars[((b1&0xf)<<2)|(b2>>6)])
		}
		if i+2 < len(data) {
			sb.WriteByte(chars[b2&0x3f])
		}
	}
	return sb.String()
}

func writeError(msg string) {
	out, _ := json.Marshal(map[string]interface{}{"success": false, "error": msg})
	os.Stdout.Write(out)
}