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package main
import (
"bytes"
"encoding/base64"
"encoding/json"
"fmt"
"net/http"
"os"
"os/exec"
"strings"
"time"
)
const geminiAPI = "https://generativelanguage.googleapis.com/v1beta/models/gemini-2.5-flash:generateContent"
const altTextPrompt = "Write alt text for this image suitable for Mastodon. Be descriptive but concise (max 1500 chars). Output only the alt text, no preamble or explanation."
type requestBody struct {
Contents []content `json:"contents"`
GenerationConfig *generationConfig `json:"generationConfig,omitempty"`
}
type generationConfig struct {
ThinkingConfig *thinkingConfig `json:"thinkingConfig,omitempty"`
}
type thinkingConfig struct {
ThinkingBudget int `json:"thinkingBudget"`
}
type content struct {
Parts []part `json:"parts"`
}
type part struct {
Text string `json:"text,omitempty"`
InlineData *inlineData `json:"inline_data,omitempty"`
}
type inlineData struct {
MimeType string `json:"mime_type"`
Data string `json:"data"`
}
type response struct {
Candidates []struct {
Content struct {
Parts []struct {
Text string `json:"text"`
} `json:"parts"`
} `json:"content"`
} `json:"candidates"`
Error *struct {
Message string `json:"message"`
} `json:"error"`
}
func readImageFromClipboard() ([]byte, error) {
for _, mimeType := range []string{"image/png", "image/jpeg"} {
cmd := exec.Command("xclip", "-selection", "clipboard", "-t", mimeType, "-o")
out, err := cmd.Output()
if err == nil && len(out) > 0 {
return out, nil
}
}
return nil, fmt.Errorf("no image found in X11 clipboard (tried image/png and image/jpeg)")
}
func convertToWebP(imageBytes []byte) ([]byte, error) {
cmd := exec.Command("magick", "-", "webp:-")
cmd.Stdin = bytes.NewReader(imageBytes)
out, err := cmd.Output()
if err != nil {
return nil, fmt.Errorf("magick convert: %w", err)
}
return out, nil
}
func generateAltText(apiKey string, imageBytes []byte, mimeType string) (string, error) {
encoded := base64.StdEncoding.EncodeToString(imageBytes)
body := requestBody{
Contents: []content{
{
Parts: []part{
{InlineData: &inlineData{MimeType: mimeType, Data: encoded}},
{Text: altTextPrompt},
},
},
},
GenerationConfig: &generationConfig{
ThinkingConfig: &thinkingConfig{ThinkingBudget: 0},
},
}
bodyJSON, err := json.Marshal(body)
if err != nil {
return "", fmt.Errorf("marshal request: %w", err)
}
req, err := http.NewRequest("POST", geminiAPI, bytes.NewReader(bodyJSON))
if err != nil {
return "", fmt.Errorf("create request: %w", err)
}
req.Header.Set("Content-Type", "application/json")
req.Header.Set("x-goog-api-key", apiKey)
resp, err := http.DefaultClient.Do(req)
if err != nil {
return "", fmt.Errorf("http request: %w", err)
}
defer resp.Body.Close()
var result response
if err := json.NewDecoder(resp.Body).Decode(&result); err != nil {
return "", fmt.Errorf("decode response: %w", err)
}
if result.Error != nil {
return "", fmt.Errorf("gemini API error: %s", result.Error.Message)
}
if len(result.Candidates) == 0 || len(result.Candidates[0].Content.Parts) == 0 {
return "", fmt.Errorf("no content in response")
}
return strings.TrimSpace(result.Candidates[0].Content.Parts[0].Text), nil
}
func apiKeyFromPass() (string, error) {
out, err := exec.Command("pass", "internet/ai.google.dev/gemini/api-keys/gemini-2.5-flash").Output()
if err != nil {
return "", fmt.Errorf("pass: %w", err)
}
// pass outputs the key on the first line
key := strings.SplitN(strings.TrimSpace(string(out)), "\n", 2)[0]
return key, nil
}
func launch() {
self, err := os.Executable()
if err != nil {
fmt.Fprintf(os.Stderr, "error: %s\n", err)
os.Exit(1)
}
cmd := exec.Command("alacritty",
"--class", "mastodon-alt-text,floating",
"--title", "mastodon-alt-text",
"-o", "window.dimensions.columns=90",
"-o", "window.dimensions.lines=12",
"--hold",
"-e", self, "run",
)
cmd.Stdin = os.Stdin
cmd.Stdout = os.Stdout
cmd.Stderr = os.Stderr
if err := cmd.Start(); err != nil {
fmt.Fprintf(os.Stderr, "error: %s\n", err)
os.Exit(1)
}
// don't wait — detach and let alacritty manage its own lifecycle
}
func main() {
if len(os.Args) > 1 && os.Args[1] == "run" {
run()
return
}
launch()
}
func run() {
apiKey := os.Getenv("GEMINI_API_KEY")
if apiKey == "" {
var err error
apiKey, err = apiKeyFromPass()
if err != nil {
fmt.Fprintf(os.Stderr, "error: GEMINI_API_KEY not set and pass failed: %s\n", err)
os.Exit(1)
}
}
t0 := time.Now()
imageBytes, err := readImageFromClipboard()
if err != nil {
fmt.Fprintf(os.Stderr, "error: %s\n", err)
os.Exit(1)
}
fmt.Fprintf(os.Stderr, "clipboard read: %s\n", time.Since(t0).Round(time.Millisecond))
t1 := time.Now()
webpBytes, err := convertToWebP(imageBytes)
if err != nil {
fmt.Fprintf(os.Stderr, "error: %s\n", err)
os.Exit(1)
}
fmt.Fprintf(os.Stderr, "webp convert: %s (%d KB → %d KB)\n", time.Since(t1).Round(time.Millisecond), len(imageBytes)/1024, len(webpBytes)/1024)
t2 := time.Now()
altText, err := generateAltText(apiKey, webpBytes, "image/webp")
if err != nil {
fmt.Fprintf(os.Stderr, "error: %s\n", err)
os.Exit(1)
}
fmt.Fprintf(os.Stderr, "gemini: %s\n", time.Since(t2).Round(time.Millisecond))
fmt.Fprintf(os.Stderr, "total: %s\n", time.Since(t0).Round(time.Millisecond))
fmt.Println(altText)
cmd := exec.Command("xclip", "-selection", "primary")
cmd.Stdin = strings.NewReader(altText)
if err := cmd.Run(); err != nil {
fmt.Fprintf(os.Stderr, "warning: failed to copy to primary selection: %s\n", err)
}
}
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