archivist: initial Go implementation of the written user stories (US-01..US-23)

archivist/internal/config/render.go

@@ -0,0 +1,95 @@
+package config
+
+import (
+	"fmt"
+	"regexp"
+	"strconv"
+	"strings"
+	"time"
+
+	"github.com/expr-lang/expr"
+)
+
+var placeholderRe = regexp.MustCompile(`\{([^{}]+)\}`)
+
+type tplPart struct {
+	literal string
+	program expr.Node
+	hasExpr bool
+}
+
+// CompiledTemplate is a naming template with pre-compiled {expr} placeholders.
+type CompiledTemplate struct {
+	Name  string
+	parts []tplPart
+}
+
+// CompileTemplate parses and compiles every placeholder expression (US-02).
+func CompileTemplate(name, src string) (*CompiledTemplate, error) {
+	ct := &CompiledTemplate{Name: name}
+	last := 0
+	for _, loc := range placeholderRe.FindAllStringSubmatchIndex(src, -1) {
+		if loc[0] > last {
+			ct.parts = append(ct.parts, tplPart{literal: src[last:loc[0]]})
+		}
+		inner := src[loc[2]:loc[3]]
+		prog, err := CompileExpr(inner)
+		if err != nil {
+			return nil, fmt.Errorf("placeholder {%s}: %w", inner, err)
+		}
+		ct.parts = append(ct.parts, tplPart{program: prog, hasExpr: true})
+		last = loc[1]
+	}
+	if last < len(src) {
+		ct.parts = append(ct.parts, tplPart{literal: src[last:]})
+	}
+	return ct, nil
+}
+
+// Render evaluates the placeholders in the document context and concatenates
+// the result. Unset optional fields render as an empty string; a rendered
+// value containing "/" is invalid (it is the S3 key delimiter) (US-15).
+func (ct *CompiledTemplate) Render(fields map[string]any, pages []string) (string, error) {
+	env := ExprEnv(pages, fields)
+	var b strings.Builder
+	for _, p := range ct.parts {
+		if !p.hasExpr {
+			b.WriteString(p.literal)
+			continue
+		}
+		v, err := expr.Run(p.program, env)
+		if err != nil {
+			return "", fmt.Errorf("template render error: %v", err)
+		}
+		s, err := renderValue(v)
+		if err != nil {
+			return "", err
+		}
+		if strings.Contains(s, "/") {
+			return "", fmt.Errorf("rendered value %q must not contain '/'", s)
+		}
+		b.WriteString(s)
+	}
+	return b.String(), nil
+}
+
+func renderValue(v any) (string, error) {
+	switch t := v.(type) {
+	case nil:
+		return "", nil
+	case string:
+		return t, nil
+	case time.Time:
+		return t.Format("2006-01-02"), nil
+	case float64:
+		return strconv.FormatFloat(t, 'f', -1, 64), nil
+	case int:
+		return strconv.Itoa(t), nil
+	case int64:
+		return strconv.FormatInt(t, 10), nil
+	case bool:
+		return strconv.FormatBool(t), nil
+	default:
+		return "", fmt.Errorf("cannot render value of type %T", v)
+	}
+}