package config

import (
	"reflect"
	"strconv"
	"strings"
)

// Suggest only a unique, nearby declared field. Input values are never used.
func unknownFieldReason(name string, fields map[string]reflect.StructField) string {
	if len(name) < 3 || len(name) > 128 {
		return "unknown field"
	}
	best, match, tied := 3, "", false
	for candidate := range fields {
		if len(candidate) > 128 {
			continue
		}
		d := fieldDistance(strings.ToLower(name), strings.ToLower(candidate))
		if d < best {
			best, match, tied = d, candidate, false
		} else if d == best {
			tied = true
		}
	}
	if match != "" && !tied && best <= 2 {
		return "unknown field; did you mean " + strconv.Quote(match) + "?"
	}
	return "unknown field"
}
func fieldDistance(a, b string) int {
	prev := make([]int, len(b)+1)
	for i := range prev {
		prev[i] = i
	}
	for i := 0; i < len(a); i++ {
		left, diagonal := i+1, prev[0]
		prev[0] = left
		for j := 0; j < len(b); j++ {
			cost := 0
			if a[i] != b[j] {
				cost = 1
			}
			old := prev[j+1]
			left = min(left+1, old+1, diagonal+cost)
			prev[j+1] = left
			diagonal = old
		}
	}
	return prev[len(b)]
}