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

package main

import (
	"context"
	"fmt"
	"strings"
	"time"

	"github.com/chzyer/readline"

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

const completeTimeout = 1 * time.Second

// Completer implements readline.AutoCompleter for the command tree.
type Completer struct {
	root   *Node
	client grpcapi.MaglevClient
}

// Do implements readline.AutoCompleter.
// line is the full current line; pos is the cursor position.
// Returns (newLine [][]rune, length int) where length is how many rune bytes
// before pos should be replaced by each candidate in newLine.
func (co *Completer) Do(line []rune, pos int) (newLine [][]rune, length int) {
	before := string(line[:pos])
	tokens := splitTokens(before)

	// Determine the partial token being completed.
	var partial string
	var prefix []string
	if len(tokens) == 0 || (len(before) > 0 && before[len(before)-1] == ' ') {
		// Cursor is after a space — completing a new token.
		prefix = tokens
		partial = ""
	} else {
		// Cursor is within the last token.
		prefix = tokens[:len(tokens)-1]
		partial = tokens[len(tokens)-1]
	}

	ctx, cancel := context.WithTimeout(context.Background(), completeTimeout)
	defer cancel()

	candidates := Candidates(co.root, prefix, partial, ctx, co.client)

	var suffixes [][]rune
	for _, c := range candidates {
		suffix := c.Word[len(partial):]
		suffixes = append(suffixes, []rune(suffix+" "))
	}
	return suffixes, len([]rune(partial))
}

// questionListener intercepts the '?' key and prints inline help.
type questionListener struct {
	root   *Node
	client grpcapi.MaglevClient
	rl     *readline.Instance
}

func (ql *questionListener) OnChange(line []rune, pos int, key rune) (newLine []rune, newPos int, ok bool) {
	if key != '?' {
		return line, pos, false
	}

	// line[:pos] includes the '?' just typed — strip it before tokenizing.
	before := string(line[:pos])
	if len(before) > 0 && before[len(before)-1] == '?' {
		before = before[:len(before)-1]
	}
	tokens := splitTokens(before)

	var partial string
	var prefix []string
	if len(before) == 0 || before[len(before)-1] == ' ' {
		prefix = tokens
		partial = ""
	} else if len(tokens) > 0 {
		prefix = tokens[:len(tokens)-1]
		partial = tokens[len(tokens)-1]
	}

	ctx, cancel := context.WithTimeout(context.Background(), completeTimeout)
	defer cancel()

	candidates := Candidates(ql.root, prefix, partial, ctx, ql.client)

	fmt.Fprintf(ql.rl.Stderr(), "\r\n")
	if len(candidates) == 0 {
		fmt.Fprintf(ql.rl.Stderr(), "  <no completions>\r\n")
	} else {
		for _, c := range candidates {
			if c.Help != "" {
				fmt.Fprintf(ql.rl.Stderr(), "  %-20s  %s\r\n", c.Word, c.Help)
			} else {
				fmt.Fprintf(ql.rl.Stderr(), "  %s\r\n", c.Word)
			}
		}
	}

	// Remove the '?' from the line and return with cursor one step back.
	newLine = append(append([]rune{}, line[:pos-1]...), line[pos:]...)
	return newLine, pos - 1, true
}

// splitTokens splits a string into whitespace-separated tokens.
func splitTokens(s string) []string {
	return strings.Fields(s)
}