Added help command

repl/docs.go

@@ -1,6 +1,93 @@
 package repl
 
+import (
+	"context"
+	"errors"
+	"fmt"
+	"github.com/lmika/gopkgs/fp/maps"
+	"os"
+	"sort"
+	"strings"
+	"text/tabwriter"
+	"ucl.lmika.dev/ucl"
+	"unicode"
+)
+
 type Doc struct {
 	Brief    string
 	Detailed string
 }
+
+func (d Doc) config(cmdName string, r *REPL) {
+	r.commandDocs[cmdName] = d
+}
+
+func (r *REPL) helpBuiltin(ctx context.Context, args ucl.CallArgs) (any, error) {
+	switch {
+	case args.NArgs() == 0:
+		names := maps.Keys(r.commandDocs)
+		sort.Strings(names)
+
+		tabWriter := tabwriter.NewWriter(os.Stdout, 0, 0, 1, ' ', 0)
+
+		for _, name := range names {
+			cdoc := r.commandDocs[name]
+			if cdoc.Brief != "" {
+				fmt.Fprintf(tabWriter, "%v\t  %v\n", name, r.commandDocs[name].Brief)
+			} else {
+				fmt.Fprintf(tabWriter, "%v\n", name)
+			}
+		}
+
+		tabWriter.Flush()
+	default:
+		var cmdName string
+		if err := args.Bind(&cmdName); err != nil {
+			return nil, err
+		}
+
+		docs, ok := r.commandDocs[cmdName]
+		if !ok {
+			return nil, errors.New("no help docs found for command")
+		}
+
+		fmt.Printf("%v\n", cmdName)
+		fmt.Printf("  %v\n", docs.Brief)
+
+		if docs.Detailed != "" {
+			fmt.Println("")
+			fmt.Println("Details:")
+
+			lines := strings.Split(docs.Detailed, "\n")
+
+			trimLeft := 0
+			if len(lines) == 0 {
+				return nil, nil
+			} else if len(strings.TrimSpace(lines[0])) == 0 && len(lines) > 1 {
+				// indicates that the next line should indicate the indentation
+				trimLeft = len(lines[1]) - len(strings.TrimLeftFunc(lines[1], unicode.IsSpace))
+				lines = lines[1:]
+			}
+
+			for _, line := range lines {
+				fmt.Printf("  %v\n", trimSpaceLeftUpto(line, trimLeft))
+			}
+		}
+	}
+	return NoResults{}, nil
+}
+
+func trimSpaceLeftUpto(s string, n int) string {
+	if n == 0 {
+		return s
+	}
+
+	for i, c := range s {
+		if i >= n {
+			return s[i:]
+		} else if !unicode.IsSpace(c) {
+			return s[i:]
+		}
+	}
+	return s
+}