Feat: add character card support

pngmeta/metareader.go

@@ -0,0 +1,107 @@
+package pngmeta
+
+import (
+	"bytes"
+	"elefant/models"
+	"encoding/base64"
+	"encoding/json"
+	"errors"
+	"io"
+	"os"
+	"path"
+	"strings"
+)
+
+const (
+	embType = "tEXt"
+)
+
+type PngEmbed struct {
+	Key   string
+	Value string
+}
+
+func (c PngEmbed) GetDecodedValue() (*models.CharCardSpec, error) {
+	data, err := base64.StdEncoding.DecodeString(c.Value)
+	if err != nil {
+		return nil, err
+	}
+	card := &models.CharCardSpec{}
+	if err := json.Unmarshal(data, &card); err != nil {
+		return nil, err
+	}
+	return card, nil
+}
+
+func extractChar(fname string) (*PngEmbed, error) {
+	data, err := os.ReadFile(fname)
+	if err != nil {
+		return nil, err
+	}
+	reader := bytes.NewReader(data)
+	pr, err := NewPNGStepReader(reader)
+	if err != nil {
+		return nil, err
+	}
+	for {
+		step, err := pr.Next()
+		if err != nil {
+			if errors.Is(err, io.EOF) {
+				break
+			}
+		}
+		if step.Type() != embType {
+			if _, err := io.Copy(io.Discard, step); err != nil {
+				return nil, err
+			}
+		} else {
+			buf, err := io.ReadAll(step)
+			if err != nil {
+				return nil, err
+			}
+			dataInstep := string(buf)
+			values := strings.Split(dataInstep, "\x00")
+			if len(values) == 2 {
+				return &PngEmbed{Key: values[0], Value: values[1]}, nil
+			}
+		}
+		if err := step.Close(); err != nil {
+			return nil, err
+		}
+	}
+	return nil, errors.New("failed to find embedded char in png: " + fname)
+}
+
+func ReadCard(fname, uname string) (*models.CharCard, error) {
+	pe, err := extractChar(fname)
+	if err != nil {
+		return nil, err
+	}
+	charSpec, err := pe.GetDecodedValue()
+	if err != nil {
+		return nil, err
+	}
+	return charSpec.Simplify(uname, fname), nil
+}
+
+func ReadDirCards(dirname, uname string) ([]*models.CharCard, error) {
+	files, err := os.ReadDir(dirname)
+	if err != nil {
+		return nil, err
+	}
+	resp := []*models.CharCard{}
+	for _, f := range files {
+		if !strings.HasSuffix(f.Name(), ".png") {
+			continue
+		}
+		fpath := path.Join(dirname, f.Name())
+		cc, err := ReadCard(fpath, uname)
+		if err != nil {
+			// log err
+			return nil, err
+			// continue
+		}
+		resp = append(resp, cc)
+	}
+	return resp, nil
+}