package command

import (
	"errors"
	"flag"
	"reflect"
	"strconv"
)

type FVSet struct {
	Name  string
	Value *any
	flags flag.FlagSet
}

func (f *FVSet) Parse(args []string) error {
	return f.flags.Parse(args)
}
func isPtr(v interface{}) bool {
	return reflect.TypeOf(v).Kind() == reflect.Ptr
}

// NewFVSet 创建一个新的FVSet实例，用于处理命令行标志。
// 参数v是一个指向结构体的指针，该结构体的字段将被用作命令行标志。
// 返回值是一个指向FVSet的指针和一个错误对象，如果操作成功，错误对象为nil。
// 如果v不是指向结构体的指针，函数将返回错误。
func NewFVSet(v interface{}) (*FVSet, error) {
	// 判断v是不是指针
	vv := reflect.ValueOf(v)
	if !isPtr(v) {
		return nil, errors.New("v must be a pointer")
	}
	// 判断指针指向的值是不是结构体
	vvv := vv.Elem()
	if vvv.Kind() != reflect.Struct {
		return nil, errors.New("v must be a pointer to a struct")
	}
	flags := flag.NewFlagSet(vvv.Type().Name(), flag.ContinueOnError)
	name := vvv.Type().Name()
	// 遍历结构体字段
	for i := 0; i < vvv.NumField(); i++ {
		//skip private field
		stField := vvv.Type().Field(i)
		if stField.PkgPath != "" {
			continue
		}
		// 获取字段名
		field := vvv.Field(i)
		nameTag := stField.Tag.Get("flag_name")
		flaName := nameTag
		if flaName == "" {
			flaName = stField.Name
		}
		defVal := stField.Tag.Get("flag_default")
		usageStr := stField.Tag.Get("flag_usage")
		if usageStr == "" {
			usageStr = "Set " + flaName + "(default " + defVal + ")"
		}

		if field.CanSet() {
			switch expression := field.Interface().(type) {
			case string:
				flags.StringVar(&expression, flaName, defVal, usageStr)
				break
			case int:
				v, _ := strconv.Atoi(defVal)
				flags.IntVar(&expression, flaName, v, usageStr)
				break
			case bool:
				flags.BoolVar(&expression, flaName, false, usageStr)
				break

			default:
				return nil, errors.New("unsupported type")
			}
		}
	}
	return &FVSet{
		Name:  name,
		Value: &v,
		flags: *flags,
	}, nil
}

// Parse is used to parse command line arguments based on one or more flag sets.
// args represents the list of command line arguments.
// flagSet is a variable-length parameter that contains the flag sets to be parsed.
// If no flag set is provided, it throws a panic exception.
// If only one flag set is provided, it directly parses the arguments with that flag set.
// If multiple flag sets are provided, it attempts to match and parse based on the first argument in args.
// If no matching flag set is found, it returns an error.
func Parse(args []string, flagSet ...*FVSet) error {
	// Check if the flag set is missing, if so, throw a panic exception.
	if len(flagSet) == 0 {
		panic("flag set missing")
	}
	// If only one flag set is provided, directly parse the arguments with that flag set.
	if len(flagSet) == 1 {
		return flagSet[0].Parse(args)
	}
	// Iterate through the flag sets to find a match for parsing.
	for _, f := range flagSet {
		// If a matching flag set is found, parse the remaining arguments with that flag set.
		if f.Name == args[0] {
			return f.Parse(args[1:])
		}
	}
	// If no matching flag set is found, return an error.
	return errors.New("flag set not found")
}