// Package config simplifies the declaration of configuration options.
//
// Forked from https://github.com/kubernetes/kubernetes/blob/master/test/edge/e2e/framework/config/config.go
// because the K8s repo is intentionally set up in a way that allows you to
// import it.
//
// Right now the implementation maps them directly to command line
// flags. When combined with test/edge/e2e/framework/viperconfig in a test
// suite, those flags then can also be read from a config file.
//
// The command line flags all get stored in a private flag set. The
// developer of the E2E test suite decides how they are exposed. Options
// include:
//   - exposing as normal flags in the actual command line:
//     CopyFlags(Flags, flag.CommandLine)
//   - populate via test/edge/e2e/framework/viperconfig:
//     viperconfig.ViperizeFlags("my-config.yaml", "", Flags)
//   - a combination of both:
//     CopyFlags(Flags, flag.CommandLine)
//     viperconfig.ViperizeFlags("my-config.yaml", "", flag.CommandLine)
//
// Instead of defining flags one-by-one, test developers annotate a
// structure with tags and then call a single function. This is the
// same approach as in https://godoc.org/github.com/jessevdk/go-flags,
// but implemented so that a test suite can continue to use the normal
// "flag" package.
//
// For example, a file storage/csi.go might define:
//
//	var scaling struct {
//	        NumNodes int  `default:"1" description:"number of nodes to run on"`
//	        Master string
//	}
//	_ = config.AddOptions(&scaling, "storage.csi.scaling")
//
// This defines the following command line flags:
//
//	-storage.csi.scaling.numNodes=<int>  - number of nodes to run on (default: 1)
//	-storage.csi.scaling.master=<string>
//
// All fields in the structure must be exported and have one of the following
// types (same as in the `flag` package):
// - bool
// - time.Duration
// - float64
// - string
// - int
// - int64
// - uint
// - uint64
// - and/or nested or embedded structures containing those basic types.
//
// Each basic entry may have a tag with these optional keys:
//
//	    usage:   additional explanation of the option
//	    default: the default value, in the same format as it would
//	             be given on the command line and true/false for
//	             a boolean
//	    name:    explicit flag name, defaults to the struct field name, lower
//							  case
//
// The names of the final configuration options are a combination of an
// optional common prefix for all options in the structure and the
// name of the fields, concatenated with a dot. To get names that are
// consistent with the command line flags defined by `ginkgo`, the
// initial character of each field name is converted to lower case.
//
// There is currently no support for aliases, so renaming the fields
// or the common prefix will be visible to users of the test suite and
// may breaks scripts which use the old names.
//
// The variable will be filled with the actual values by the test
// suite before running tests. Beware that the code which registers
// Ginkgo tests cannot use those config options, because registering
// tests and options both run before the E2E test suite handles
// parameters.
package config

import (
	"flag"
	"fmt"
	"reflect"
	"strconv"
	"strings"
	"time"
)

// Flags is the flag set that AddOptions adds to. Test authors should
// also use it instead of directly adding to the global command line.
var Flags = flag.NewFlagSet("", flag.ContinueOnError)

// CopyFlags ensures that all flags that are defined in the source flag
// set appear in the target flag set as if they had been defined there
// directly. From the flag package it inherits the behavior that there
// is a panic if the target already contains a flag from the source.
func CopyFlags(source *flag.FlagSet, target *flag.FlagSet) {
	source.VisitAll(func(flag *flag.Flag) {
		// We don't need to copy flag.DefValue. The original
		// default (from, say, flag.String) was stored in
		// the value and gets extracted by Var for the help
		// message.
		target.Var(flag.Value, flag.Name, flag.Usage)
	})
}

// AddOptions analyzes the options value and creates the necessary
// flags to populate it.
//
// The prefix can be used to root the options deeper in the overall
// set of options, with a dot separating different levels.
//
// The function always returns true, to enable this simplified
// registration of options:
// _ = AddOptions(...)
//
// It panics when it encounters an error, like unsupported types
// or option name conflicts.
func AddOptions(options interface{}, prefix string) bool {
	return AddOptionsToSet(Flags, options, prefix)
}

// AddOptionsToSet is the same as AddOption, except that it allows choosing the flag set.
func AddOptionsToSet(flags *flag.FlagSet, options interface{}, prefix string) bool {
	optionsType := reflect.TypeOf(options)
	if optionsType == nil {
		panic("options parameter without a type - nil?!")
	}
	if optionsType.Kind() != reflect.Ptr || optionsType.Elem().Kind() != reflect.Struct {
		panic(fmt.Sprintf("need a pointer to a struct, got instead: %T", options))
	}
	addStructFields(flags, optionsType.Elem(), reflect.Indirect(reflect.ValueOf(options)), prefix)
	return true
}

func addStructFields(flags *flag.FlagSet, structType reflect.Type, structValue reflect.Value, prefix string) {
	for i := 0; i < structValue.NumField(); i++ {
		entry := structValue.Field(i)
		addr := entry.Addr()
		structField := structType.Field(i)
		usage := structField.Tag.Get("usage")
		def := structField.Tag.Get("default")
		name := structField.Tag.Get("name")
		if name == "" {
			name = strings.ToLower(structField.Name)
		}
		if prefix != "" {
			name = prefix + "." + name
		}
		if structField.PkgPath != "" {
			panic(fmt.Sprintf("struct entry %q not exported", name))
		}
		ptr := addr.Interface()
		if structField.Anonymous {
			// Entries in embedded fields are treated like
			// entries, in the struct itself, i.e. we add
			// them with the same prefix.
			addStructFields(flags, structField.Type, entry, prefix)
			continue
		}
		if structField.Type.Kind() == reflect.Struct {
			// Add nested options.
			addStructFields(flags, structField.Type, entry, name)
			continue
		}
		// We could switch based on structField.Type. Doing a
		// switch after getting an interface holding the
		// pointer to the entry has the advantage that we
		// immediately have something that we can add as flag
		// variable.
		//
		// Perhaps generics will make this entire switch redundant someday...
		switch ptr := ptr.(type) {
		case *bool:
			var defValue bool
			parseDefault(&defValue, name, def)
			flags.BoolVar(ptr, name, defValue, usage)
		case *time.Duration:
			var defValue time.Duration
			parseDefault(&defValue, name, def)
			flags.DurationVar(ptr, name, defValue, usage)
		case *float64:
			var defValue float64
			parseDefault(&defValue, name, def)
			flags.Float64Var(ptr, name, defValue, usage)
		case *string:
			flags.StringVar(ptr, name, def, usage)
		case *int:
			var defValue int
			parseDefault(&defValue, name, def)
			flags.IntVar(ptr, name, defValue, usage)
		case *int64:
			var defValue int64
			parseDefault(&defValue, name, def)
			flags.Int64Var(ptr, name, defValue, usage)
		case *uint:
			var defValue uint
			parseDefault(&defValue, name, def)
			flags.UintVar(ptr, name, defValue, usage)
		case *uint64:
			var defValue uint64
			parseDefault(&defValue, name, def)
			flags.Uint64Var(ptr, name, defValue, usage)
		default:
			panic(fmt.Sprintf("unsupported struct entry type %q: %T", name, entry.Interface()))
		}
	}
}

// parseDefault is necessary because "flag" wants the default in the
// actual type and cannot take a string. It would be nice to reuse the
// existing code for parsing from the "flag" package, but it isn't
// exported.
func parseDefault(value interface{}, name, def string) {
	if def == "" {
		return
	}
	checkErr := func(err error, value interface{}) {
		if err != nil {
			panic(fmt.Sprintf("invalid default %q for %T entry %s: %s", def, value, name, err))
		}
	}
	switch value := value.(type) {
	case *bool:
		v, err := strconv.ParseBool(def)
		checkErr(err, *value)
		*value = v
	case *time.Duration:
		v, err := time.ParseDuration(def)
		checkErr(err, *value)
		*value = v
	case *float64:
		v, err := strconv.ParseFloat(def, 64)
		checkErr(err, *value)
		*value = v
	case *int:
		v, err := strconv.Atoi(def)
		checkErr(err, *value)
		*value = v
	case *int64:
		v, err := strconv.ParseInt(def, 0, 64)
		checkErr(err, *value)
		*value = v
	case *uint:
		v, err := strconv.ParseUint(def, 0, strconv.IntSize)
		checkErr(err, *value)
		*value = uint(v)
	case *uint64:
		v, err := strconv.ParseUint(def, 0, 64)
		checkErr(err, *value)
		*value = v
	default:
		panic(fmt.Sprintf("%q: setting defaults not supported for type %T", name, value))
	}
}