feh: the wallpaper as a module, its image an archive of its own (hq ADR 0208, ADR 0205)

~/.fehbg stops pointing into the predecessor's tree; the session's xinitrc slot runs it once; Go tools set (for the session) and current.
2026-10-04 13:15:39 +02:00
parent c42cd285e2
commit 91c6fa6fce
15 changed files with 1401 additions and 0 deletions
@@ -0,0 +1,174 @@
+package main
+
+import (
+	"encoding/json"
+	"errors"
+	"fmt"
+	"os"
+	"path/filepath"
+	"regexp"
+	"strings"
+	"time"
+)
+
+// modes are feh's background modes, by the word feh_set takes.
+var modes = []string{"fill", "center", "max", "scale", "tile"}
+
+// Wallpaper is images and how they are laid on the screens.
+type Wallpaper struct {
+	Images []string `json:"images"`
+	Mode   string   `json:"mode"`
+	At     string   `json:"at,omitempty"`
+}
+
+func fehbg() string { return filepath.Join(operatorHome(), ".fehbg") }
+
+// sessionRecord is where feh_set notes what it put up, for feh_current: in the runtime directory,
+// so it lasts exactly as long as the login, like the wallpaper itself.
+func sessionRecord(s Session) string {
+	if s.RuntimeDir == "" {
+		return ""
+	}
+	return filepath.Join(s.RuntimeDir, "feh", "current.json")
+}
+
+// SetResult is what feh_set answers.
+type SetResult struct {
+	Wallpaper
+	Note string `json:"note"`
+}
+
+// Set puts images up as the wallpaper for this session.
+func Set(images []string, mode string) (SetResult, error) {
+	if mode == "" {
+		mode = "fill"
+	}
+	known := false
+	for _, m := range modes {
+		known = known || m == mode
+	}
+	if !known {
+		return SetResult{}, fmt.Errorf("mode %q is one of %s", mode, strings.Join(modes, ", "))
+	}
+	if len(images) == 0 {
+		return SetResult{}, errors.New("images is required: at least one image")
+	}
+	var paths []string
+	for _, img := range images {
+		p := img
+		if strings.HasPrefix(p, "~/") {
+			p = filepath.Join(operatorHome(), p[2:])
+		}
+		if !filepath.IsAbs(p) {
+			p = filepath.Join(operatorHome(), p)
+		}
+		info, err := os.Stat(p)
+		if err != nil {
+			return SetResult{}, fmt.Errorf("image %s: %w", img, err)
+		}
+		if info.IsDir() {
+			return SetResult{}, fmt.Errorf("image %s is a directory", img)
+		}
+		paths = append(paths, p)
+	}
+	s, err := findSession()
+	if err != nil {
+		return SetResult{}, err
+	}
+	args := append([]string{"--no-fehbg", "--bg-" + mode}, paths...)
+	r, err := s.run(15*time.Second, "", "feh", args...)
+	if err != nil {
+		return SetResult{}, err
+	}
+	if r.Code != 0 {
+		return SetResult{}, fmt.Errorf("feh: %s", strings.TrimSpace(r.Stderr))
+	}
+	w := Wallpaper{Images: paths, Mode: mode, At: time.Now().Format(time.RFC3339)}
+	if rec := sessionRecord(s); rec != "" {
+		if err := os.MkdirAll(filepath.Dir(rec), 0o700); err == nil {
+			raw, _ := json.Marshal(w)
+			_ = os.WriteFile(rec, raw, 0o600)
+		}
+	}
+	return SetResult{Wallpaper: w, Note: "for this session; the declared wallpaper returns at the next login"}, nil
+}
+
+// CurrentResult is what feh_current answers.
+type CurrentResult struct {
+	Declared *Wallpaper `json:"declared"`
+	Session  *Wallpaper `json:"session,omitempty"`
+}
+
+var bgMode = regexp.MustCompile(`--bg-(fill|center|max|scale|tile)\b`)
+
+// Current is the declared wallpaper and the one set in this session.
+func Current() (CurrentResult, error) {
+	var out CurrentResult
+	if raw, err := os.ReadFile(fehbg()); err == nil {
+		out.Declared = parseFehbg(string(raw), operatorHome())
+	}
+	if rec := sessionRecord(findEnvironment()); rec != "" {
+		if raw, err := os.ReadFile(rec); err == nil {
+			var w Wallpaper
+			if json.Unmarshal(raw, &w) == nil {
+				out.Session = &w
+			}
+		}
+	}
+	return out, nil
+}
+
+// parseFehbg reads the feh line of a ~/.fehbg: its mode and its images, with $HOME expanded.
+func parseFehbg(script, home string) *Wallpaper {
+	for _, line := range strings.Split(script, "\n") {
+		line = strings.TrimSpace(line)
+		if !strings.HasPrefix(line, "feh ") {
+			continue
+		}
+		w := &Wallpaper{Images: []string{}}
+		if m := bgMode.FindStringSubmatch(line); m != nil {
+			w.Mode = m[1]
+		}
+		for _, word := range shellWords(line)[1:] {
+			if strings.HasPrefix(word, "-") {
+				continue
+			}
+			word = strings.ReplaceAll(strings.ReplaceAll(word, "${HOME}", home), "$HOME", home)
+			w.Images = append(w.Images, word)
+		}
+		return w
+	}
+	return nil
+}
+
+// shellWords splits a simple command line on blanks, honouring single and double quotes.
+func shellWords(line string) []string {
+	var words []string
+	var cur strings.Builder
+	var quote byte
+	in := false
+	for i := 0; i < len(line); i++ {
+		c := line[i]
+		switch {
+		case quote != 0 && c == quote:
+			quote = 0
+		case quote != 0:
+			cur.WriteByte(c)
+		case c == '\'' || c == '"':
+			quote, in = c, true
+		case c == ' ' || c == '\t':
+			if in {
+				words = append(words, cur.String())
+				cur.Reset()
+				in = false
+			}
+		default:
+			cur.WriteByte(c)
+			in = true
+		}
+	}
+	if in {
+		words = append(words, cur.String())
+	}
+	return words
+}