vpp-maglev/cmd/maglevc/shell.go

// Copyright (c) 2026, Pim van Pelt <pim@ipng.ch>

package main

import (
	"context"
	"errors"
	"fmt"
	"io"
	"strings"

	"github.com/chzyer/readline"

	"git.ipng.ch/ipng/vpp-maglev/internal/grpcapi"
)

// errQuit is a sentinel returned by runQuit to exit the REPL.
var errQuit = errors.New("quit")

// runShell runs the interactive REPL until the user types quit/exit or EOF.
func runShell(ctx context.Context, client grpcapi.MaglevClient) error {
	root := buildTree()

	comp := &Completer{root: root, client: client}
	ql := &questionListener{root: root, client: client}

	cfg := &readline.Config{
		Prompt:          "maglev> ",
		AutoComplete:    comp,
		InterruptPrompt: "^C",
		EOFPrompt:       "exit",
		Listener:        ql,
	}
	rl, err := readline.NewEx(cfg)
	if err != nil {
		return fmt.Errorf("readline init: %w", err)
	}
	ql.rl = rl
	defer rl.Close()

	for {
		line, err := rl.Readline()
		if err == readline.ErrInterrupt {
			continue
		}
		if err == io.EOF {
			return nil
		}
		if err != nil {
			return err
		}

		tokens := splitTokens(line)
		if len(tokens) == 0 {
			continue
		}

		if err := dispatch(ctx, root, client, tokens); err != nil {
			if errors.Is(err, errQuit) {
				return nil
			}
			fmt.Fprintf(rl.Stderr(), "%s\n", formatError(err))
		}
	}
}

// dispatch walks the tree and executes the matched command.
func dispatch(ctx context.Context, root *Node, client grpcapi.MaglevClient, tokens []string) error {
	node, args, remaining := Walk(root, tokens)

	if len(remaining) > 0 {
		// One or more tokens couldn't be matched. Report the first
		// offending token with the consumed prefix for context; don't
		// dump the full command tree prefixed with garbage, which is
		// what the previous code did and what prompted this fix.
		consumed := tokens[:len(tokens)-len(remaining)]
		return unknownCommandError(consumed, remaining[0])
	}

	if node.Run == nil {
		showHelpAt(node, strings.Join(tokens, " "))
		return nil
	}

	return node.Run(ctx, client, args)
}

// unknownCommandError builds the error returned by dispatch when the
// tree walk couldn't consume the full token list. The format differs
// slightly depending on whether any tokens were consumed, so the
// message always points at the first unknown token and its context.
func unknownCommandError(consumed []string, bad string) error {
	if len(consumed) == 0 {
		return fmt.Errorf("unknown command: %s", bad)
	}
	return fmt.Errorf("unknown subcommand %q after %q", bad, strings.Join(consumed, " "))
}

// showHelpAt prints the reachable leaves below node, each displayed
// with the given prefix. Split from dispatch so the caller can decide
// which node to anchor the help at without re-walking the tree.
func showHelpAt(node *Node, prefix string) {
	lines := expandPaths(node, prefix, make(map[*Node]bool))

	maxLen := 0
	for _, l := range lines {
		if len(l.path) > maxLen {
			maxLen = len(l.path)
		}
	}

	if len(lines) == 0 {
		fmt.Println("  <no completions>")
		return
	}
	for _, l := range lines {
		if l.help != "" {
			fmt.Printf("%-*s  %s\n", maxLen+2, l.path, l.help)
		} else {
			fmt.Printf("%s\n", l.path)
		}
	}
}