// SPDX-License-Identifier: AGPL-3.0-only
// Provenance-includes-location: https://github.com/cortexproject/cortex/blob/master/tools/doc-generator/parser.go
// Provenance-includes-license: Apache-2.0
// Provenance-includes-copyright: The Cortex Authors.

package parse

import (
	"flag"
	"fmt"
	"net/url"
	"reflect"
	"strings"
	"time"
	"unicode"

	"github.com/grafana/dskit/flagext"
	"github.com/grafana/regexp"
	"github.com/pkg/errors"
	"github.com/prometheus/common/model"
	prometheus_config "github.com/prometheus/prometheus/config"
	"github.com/prometheus/prometheus/model/relabel"
	"github.com/weaveworks/common/logging"

	"github.com/grafana/loki/pkg/ruler/util"
	storage_config "github.com/grafana/loki/pkg/storage/config"
	util_validation "github.com/grafana/loki/pkg/util/validation"
	"github.com/grafana/loki/pkg/validation"
)

var (
	yamlFieldNameParser   = regexp.MustCompile("^[^,]+")
	yamlFieldInlineParser = regexp.MustCompile("^[^,]*,inline$")
)

// ExamplerConfig can be implemented by configs to provide examples.
// If string is non-empty, it will be added as comment.
// If yaml value is non-empty, it will be marshaled as yaml under the same key as it would appear in config.
type ExamplerConfig interface {
	ExampleDoc() (comment string, yaml interface{})
}

type FieldExample struct {
	Comment string
	Yaml    interface{}
}

type ConfigBlock struct {
	Name          string
	Desc          string
	Entries       []*ConfigEntry
	FlagsPrefix   string
	FlagsPrefixes []string
}

func (b *ConfigBlock) Add(entry *ConfigEntry) {
	b.Entries = append(b.Entries, entry)
}

type EntryKind string

const (
	fieldString        = "string"
	fieldRelabelConfig = "relabel_config..."
)

const (
	KindBlock EntryKind = "block"
	KindField EntryKind = "field"
	KindSlice EntryKind = "slice"
	KindMap   EntryKind = "map"
)

type ConfigEntry struct {
	Kind     EntryKind
	Name     string
	Required bool

	// In case the Kind is KindBlock
	Block     *ConfigBlock
	BlockDesc string
	Root      bool

	// In case the Kind is KindField
	FieldFlag    string
	FieldDesc    string
	FieldType    string
	FieldDefault string
	FieldExample *FieldExample

	// In case the Kind is KindMap or KindSlice
	Element *ConfigBlock
}

func (e ConfigEntry) Description() string {
	return e.FieldDesc
}

type RootBlock struct {
	Name       string
	Desc       string
	StructType reflect.Type
}

func Flags(cfg flagext.Registerer) map[uintptr]*flag.Flag {
	fs := flag.NewFlagSet("", flag.PanicOnError)
	cfg.RegisterFlags(fs)

	flags := map[uintptr]*flag.Flag{}
	fs.VisitAll(func(f *flag.Flag) {
		// Skip deprecated flags
		if f.Value.String() == "deprecated" {
			return
		}

		ptr := reflect.ValueOf(f.Value).Pointer()
		flags[ptr] = f
	})

	return flags
}

// Config returns a slice of ConfigBlocks. The first ConfigBlock is a recursively expanded cfg.
// The remaining entries in the slice are all (root or not) ConfigBlocks.
func Config(cfg interface{}, flags map[uintptr]*flag.Flag, rootBlocks []RootBlock) ([]*ConfigBlock, error) {
	return config(nil, cfg, flags, rootBlocks)
}

func config(block *ConfigBlock, cfg interface{}, flags map[uintptr]*flag.Flag, rootBlocks []RootBlock) ([]*ConfigBlock, error) {
	var blocks []*ConfigBlock

	// If the input block is nil it means we're generating the doc for the top-level block
	if block == nil {
		block = &ConfigBlock{}
		blocks = append(blocks, block)
	}

	// The input config is expected to be addressable.
	if reflect.TypeOf(cfg).Kind() != reflect.Ptr {
		t := reflect.TypeOf(cfg)
		return nil, fmt.Errorf("%s is a %s while a %s is expected", t, t.Kind(), reflect.Ptr)
	}

	// The input config is expected to be a pointer to struct.
	v := reflect.ValueOf(cfg).Elem()
	t := v.Type()

	if v.Kind() != reflect.Struct {
		return nil, fmt.Errorf("%s is a %s while a %s is expected", v, v.Kind(), reflect.Struct)
	}

	for i := 0; i < t.NumField(); i++ {
		field := t.Field(i)
		fieldValue := v.FieldByIndex(field.Index)

		// Skip fields explicitly marked as "hidden" in the doc
		if isFieldHidden(field) {
			continue
		}

		// Skip fields not exported via yaml (unless they're inline)
		fieldName := getFieldName(field)
		if fieldName == "" && !isFieldInline(field) {
			continue
		}

		// Skip field types which are non-configurable
		if field.Type.Kind() == reflect.Func {
			continue
		}

		// Skip deprecated fields we're still keeping for backward compatibility
		// reasons (by convention we prefix them by UnusedFlag)
		if strings.HasPrefix(field.Name, "UnusedFlag") {
			continue
		}

		// Handle custom fields in vendored libs upon which we have no control.
		fieldEntry, err := getCustomFieldEntry(cfg, field, fieldValue, flags)
		if err != nil {
			return nil, err
		}
		if fieldEntry != nil {
			block.Add(fieldEntry)
			continue
		}

		// Recursively re-iterate if it's a struct, and it's not a custom type.
		if _, custom := getCustomFieldType(field.Type); (field.Type.Kind() == reflect.Struct || field.Type.Kind() == reflect.Ptr) && !custom {
			// Check whether the sub-block is a root config block
			rootName, rootDesc, isRoot := isRootBlock(field.Type, rootBlocks)

			// Since we're going to recursively iterate, we need to create a new sub
			// block and pass it to the doc generation function.
			var subBlock *ConfigBlock

			if !isFieldInline(field) {
				var blockName string
				var blockDesc string

				if isRoot {
					blockName = rootName

					// Honor the custom description if available.
					blockDesc = getFieldDescription(cfg, field, rootDesc)
				} else {
					blockName = fieldName
					blockDesc = getFieldDescription(cfg, field, "")
				}

				subBlock = &ConfigBlock{
					Name: blockName,
					Desc: blockDesc,
				}

				block.Add(&ConfigEntry{
					Kind:      KindBlock,
					Name:      fieldName,
					Required:  isFieldRequired(field),
					Block:     subBlock,
					BlockDesc: blockDesc,
					Root:      isRoot,
				})

				if isRoot {
					blocks = append(blocks, subBlock)
				}
			} else {
				subBlock = block
			}

			if field.Type.Kind() == reflect.Ptr {
				// If this is a pointer, it's probably nil, so we initialize it.
				fieldValue = reflect.New(field.Type.Elem())
			} else if field.Type.Kind() == reflect.Struct {
				fieldValue = fieldValue.Addr()
			}

			// Recursively generate the doc for the sub-block
			otherBlocks, err := config(subBlock, fieldValue.Interface(), flags, rootBlocks)
			if err != nil {
				return nil, err
			}

			blocks = append(blocks, otherBlocks...)
			continue
		}

		var (
			element *ConfigBlock
			kind    = KindField
		)
		{
			// Add ConfigBlock for slices only if the field isn't a custom type,
			// which shouldn't be inspected because doesn't have YAML tags, flag registrations, etc.
			_, isCustomType := getFieldCustomType(field.Type)
			isSliceOfStructs := field.Type.Kind() == reflect.Slice && (field.Type.Elem().Kind() == reflect.Struct || field.Type.Elem().Kind() == reflect.Ptr)
			if !isCustomType && isSliceOfStructs {
				// Check if slice element type is a root block
				// and add it to the blocks structure
				rootName, rootDesc, isRoot := isRootBlock(field.Type.Elem(), rootBlocks)
				if isRoot {
					sliceElementBlock, err := config(nil, reflect.New(field.Type.Elem()).Interface(), flags, rootBlocks)
					if err != nil {
						return nil, errors.Wrapf(err, "couldn't inspect slice, element_type=%s", field.Type.Elem())
					}
					if len(sliceElementBlock) == 1 {
						element = &ConfigBlock{
							Name:    rootName,
							Desc:    rootDesc,
							Entries: sliceElementBlock[0].Entries,
						}
						blocks = append(blocks, element)
					}
				}

				// Add slice element to current block
				element = &ConfigBlock{
					Name: fieldName,
					Desc: getFieldDescription(cfg, field, ""),
				}
				kind = KindSlice
			}
		}

		fieldType, err := getFieldType(field.Type, rootBlocks)
		if err != nil {
			return nil, errors.Wrapf(err, "config=%s.%s", t.PkgPath(), t.Name())
		}

		fieldFlag, err := getFieldFlag(field, fieldValue, flags)
		if err != nil {
			return nil, errors.Wrapf(err, "config=%s.%s", t.PkgPath(), t.Name())
		}
		if fieldFlag == nil {
			block.Add(&ConfigEntry{
				Kind:         kind,
				Name:         fieldName,
				Required:     isFieldRequired(field),
				FieldDesc:    getFieldDescription(cfg, field, ""),
				FieldType:    fieldType,
				FieldExample: getFieldExample(fieldName, field.Type),
				Element:      element,
			})
			continue
		}

		block.Add(&ConfigEntry{
			Kind:         kind,
			Name:         fieldName,
			Required:     isFieldRequired(field),
			FieldFlag:    fieldFlag.Name,
			FieldDesc:    getFieldDescription(cfg, field, fieldFlag.Usage),
			FieldType:    fieldType,
			FieldDefault: getFieldDefault(field, fieldFlag.DefValue),
			FieldExample: getFieldExample(fieldName, field.Type),
			Element:      element,
		})
	}

	return blocks, nil
}

func getFieldName(field reflect.StructField) string {
	name := field.Name
	tag := field.Tag.Get("yaml")

	// If the tag is not specified, then an exported field can be
	// configured via the field name (lowercase), while an unexported
	// field can't be configured.
	if tag == "" {
		if unicode.IsLower(rune(name[0])) {
			return ""
		}

		return strings.ToLower(name)
	}

	// Parse the field name
	fieldName := yamlFieldNameParser.FindString(tag)
	if fieldName == "-" {
		return ""
	}

	return fieldName
}

func getFieldCustomType(t reflect.Type) (string, bool) {
	// Handle custom data types used in the config
	switch t.String() {
	case reflect.TypeOf(&url.URL{}).String():
		return "url", true
	case reflect.TypeOf(time.Duration(0)).String():
		return "duration", true
	case reflect.TypeOf(storage_config.DayTime{}).String():
		return "daytime", true
	case reflect.TypeOf(flagext.StringSliceCSV{}).String():
		return fieldString, true
	case reflect.TypeOf(flagext.CIDRSliceCSV{}).String():
		return fieldString, true
	case reflect.TypeOf([]*util.RelabelConfig{}).String():
		return fieldRelabelConfig, true
	case reflect.TypeOf([]*relabel.Config{}).String():
		return fieldRelabelConfig, true
	case reflect.TypeOf([]*util_validation.BlockedQuery{}).String():
		return "blocked_query...", true
	case reflect.TypeOf([]*prometheus_config.RemoteWriteConfig{}).String():
		return "remote_write_config...", true
	case reflect.TypeOf(storage_config.PeriodConfig{}).String():
		return "period_config", true
	case reflect.TypeOf(validation.OverwriteMarshalingStringMap{}).String():
		return "headers", true
	default:
		return "", false
	}
}

func getFieldType(t reflect.Type, rootBlocks []RootBlock) (string, error) {
	if typ, isCustom := getFieldCustomType(t); isCustom {
		return typ, nil
	}

	if rootName, _, isRoot := isRootBlock(t, rootBlocks); isRoot {
		return rootName, nil
	}

	// Fallback to auto-detection of built-in data types
	switch t.Kind() {
	case reflect.Bool:
		return "boolean", nil
	case reflect.Int:
		fallthrough
	case reflect.Int8:
		fallthrough
	case reflect.Int16:
		fallthrough
	case reflect.Int32:
		fallthrough
	case reflect.Int64:
		fallthrough
	case reflect.Uint:
		fallthrough
	case reflect.Uint8:
		fallthrough
	case reflect.Uint16:
		fallthrough
	case reflect.Uint32:
		fallthrough
	case reflect.Uint64:
		return "int", nil
	case reflect.Float32:
		fallthrough
	case reflect.Float64:
		return "float", nil
	case reflect.String:
		return fieldString, nil
	case reflect.Slice:
		// Get the type of elements
		elemType, err := getFieldType(t.Elem(), rootBlocks)
		if err != nil {
			return "", err
		}
		return "list of " + elemType + "s", nil
	case reflect.Map:
		elemType, err := getFieldType(t.Elem(), rootBlocks)
		if err != nil {
			return "", err
		}
		return fmt.Sprintf("map of %s to %s", t.Key(), elemType), nil
	case reflect.Struct:
		return t.Name(), nil
	case reflect.Ptr:
		return getFieldType(t.Elem(), rootBlocks)
	case reflect.Interface:
		return t.Name(), nil
	default:
		return "", fmt.Errorf("unsupported data type %s", t.Kind())
	}
}

func getCustomFieldType(t reflect.Type) (string, bool) {
	// Handle custom data types used in the config
	switch t.String() {
	case reflect.TypeOf(&url.URL{}).String():
		return "url", true
	case reflect.TypeOf(time.Duration(0)).String():
		return "duration", true
	case reflect.TypeOf(storage_config.DayTime{}).String():
		return "daytime", true
	case reflect.TypeOf(flagext.StringSliceCSV{}).String():
		return fieldString, true
	case reflect.TypeOf(flagext.CIDRSliceCSV{}).String():
		return fieldString, true
	case reflect.TypeOf([]*relabel.Config{}).String():
		return fieldRelabelConfig, true
	case reflect.TypeOf([]*util.RelabelConfig{}).String():
		return fieldRelabelConfig, true
	case reflect.TypeOf(&prometheus_config.RemoteWriteConfig{}).String():
		return "remote_write_config...", true
	case reflect.TypeOf(validation.OverwriteMarshalingStringMap{}).String():
		return "headers", true
	default:
		return "", false
	}
}

func getFieldFlag(field reflect.StructField, fieldValue reflect.Value, flags map[uintptr]*flag.Flag) (*flag.Flag, error) {
	if isAbsentInCLI(field) {
		return nil, nil
	}
	fieldPtr := fieldValue.Addr().Pointer()
	fieldFlag, ok := flags[fieldPtr]
	if !ok {
		return nil, nil
	}

	return fieldFlag, nil
}

func getFieldExample(fieldKey string, fieldType reflect.Type) *FieldExample {
	ex, ok := reflect.New(fieldType).Interface().(ExamplerConfig)
	if !ok {
		return nil
	}
	comment, yml := ex.ExampleDoc()
	return &FieldExample{
		Comment: comment,
		Yaml:    map[string]interface{}{fieldKey: yml},
	}
}

func getCustomFieldEntry(cfg interface{}, field reflect.StructField, fieldValue reflect.Value, flags map[uintptr]*flag.Flag) (*ConfigEntry, error) {
	if field.Type == reflect.TypeOf(logging.Level{}) || field.Type == reflect.TypeOf(logging.Format{}) {
		fieldFlag, err := getFieldFlag(field, fieldValue, flags)
		if err != nil || fieldFlag == nil {
			return nil, err
		}

		return &ConfigEntry{
			Kind:         KindField,
			Name:         getFieldName(field),
			Required:     isFieldRequired(field),
			FieldFlag:    fieldFlag.Name,
			FieldDesc:    getFieldDescription(cfg, field, fieldFlag.Usage),
			FieldType:    fieldString,
			FieldDefault: getFieldDefault(field, fieldFlag.DefValue),
		}, nil
	}
	if field.Type == reflect.TypeOf(flagext.URLValue{}) {
		fieldFlag, err := getFieldFlag(field, fieldValue, flags)
		if err != nil || fieldFlag == nil {
			return nil, err
		}

		return &ConfigEntry{
			Kind:         KindField,
			Name:         getFieldName(field),
			Required:     isFieldRequired(field),
			FieldFlag:    fieldFlag.Name,
			FieldDesc:    getFieldDescription(cfg, field, fieldFlag.Usage),
			FieldType:    "url",
			FieldDefault: getFieldDefault(field, fieldFlag.DefValue),
		}, nil
	}
	if field.Type == reflect.TypeOf(flagext.Secret{}) {
		fieldFlag, err := getFieldFlag(field, fieldValue, flags)
		if err != nil || fieldFlag == nil {
			return nil, err
		}

		return &ConfigEntry{
			Kind:         KindField,
			Name:         getFieldName(field),
			Required:     isFieldRequired(field),
			FieldFlag:    fieldFlag.Name,
			FieldDesc:    getFieldDescription(cfg, field, fieldFlag.Usage),
			FieldType:    fieldString,
			FieldDefault: getFieldDefault(field, fieldFlag.DefValue),
		}, nil
	}
	if field.Type == reflect.TypeOf(model.Duration(0)) {
		fieldFlag, err := getFieldFlag(field, fieldValue, flags)
		if err != nil || fieldFlag == nil {
			return nil, err
		}

		return &ConfigEntry{
			Kind:         KindField,
			Name:         getFieldName(field),
			Required:     isFieldRequired(field),
			FieldFlag:    fieldFlag.Name,
			FieldDesc:    getFieldDescription(cfg, field, fieldFlag.Usage),
			FieldType:    "duration",
			FieldDefault: getFieldDefault(field, fieldFlag.DefValue),
		}, nil
	}
	if field.Type == reflect.TypeOf(flagext.Time{}) {
		fieldFlag, err := getFieldFlag(field, fieldValue, flags)
		if err != nil || fieldFlag == nil {
			return nil, err
		}

		return &ConfigEntry{
			Kind:         KindField,
			Name:         getFieldName(field),
			Required:     isFieldRequired(field),
			FieldFlag:    fieldFlag.Name,
			FieldDesc:    getFieldDescription(cfg, field, fieldFlag.Usage),
			FieldType:    "time",
			FieldDefault: getFieldDefault(field, fieldFlag.DefValue),
		}, nil
	}

	return nil, nil
}

func getFieldDefault(field reflect.StructField, fallback string) string {
	if v := getDocTagValue(field, "default"); v != "" {
		return v
	}

	return fallback
}

func isFieldDeprecated(f reflect.StructField) bool {
	return getDocTagFlag(f, "deprecated")
}

func isFieldHidden(f reflect.StructField) bool {
	return getDocTagFlag(f, "hidden")
}

func isAbsentInCLI(f reflect.StructField) bool {
	return getDocTagFlag(f, "nocli")
}

func isFieldRequired(f reflect.StructField) bool {
	return getDocTagFlag(f, "required")
}

func isFieldInline(f reflect.StructField) bool {
	return yamlFieldInlineParser.MatchString(f.Tag.Get("yaml"))
}

func getFieldDescription(cfg interface{}, field reflect.StructField, fallback string) string {
	// Set prefix
	prefix := ""
	if isFieldDeprecated(field) {
		prefix += "Deprecated: "
	}

	if desc := getDocTagValue(field, "description"); desc != "" {
		return prefix + desc
	}

	if methodName := getDocTagValue(field, "description_method"); methodName != "" {
		structRef := reflect.ValueOf(cfg)

		if method, ok := structRef.Type().MethodByName(methodName); ok {
			out := method.Func.Call([]reflect.Value{structRef})
			if len(out) == 1 {
				return prefix + out[0].String()
			}
		}
	}

	return prefix + fallback
}

func isRootBlock(t reflect.Type, rootBlocks []RootBlock) (string, string, bool) {
	for _, rootBlock := range rootBlocks {
		if t == rootBlock.StructType {
			return rootBlock.Name, rootBlock.Desc, true
		}
	}

	return "", "", false
}

func getDocTagFlag(f reflect.StructField, name string) bool {
	cfg := parseDocTag(f)
	_, ok := cfg[name]
	return ok
}

func getDocTagValue(f reflect.StructField, name string) string {
	cfg := parseDocTag(f)
	return cfg[name]
}

func parseDocTag(f reflect.StructField) map[string]string {
	cfg := map[string]string{}
	tag := f.Tag.Get("doc")

	if tag == "" {
		return cfg
	}

	for _, entry := range strings.Split(tag, "|") {
		parts := strings.SplitN(entry, "=", 2)

		switch len(parts) {
		case 1:
			cfg[parts[0]] = ""
		case 2:
			cfg[parts[0]] = parts[1]
		}
	}

	return cfg
}