package env

import (
	"encoding"
	"fmt"
	"net/url"
	"os"
	"reflect"
	"strconv"
	"strings"
	"time"
	"unicode"
)

// nolint: gochecknoglobals
var (
	defaultBuiltInParsers = map[reflect.Kind]ParserFunc{
		reflect.Bool: func(v string) (interface{}, error) {
			return strconv.ParseBool(v)
		},
		reflect.String: func(v string) (interface{}, error) {
			return v, nil
		},
		reflect.Int: func(v string) (interface{}, error) {
			i, err := strconv.ParseInt(v, 10, 32)
			return int(i), err
		},
		reflect.Int16: func(v string) (interface{}, error) {
			i, err := strconv.ParseInt(v, 10, 16)
			return int16(i), err
		},
		reflect.Int32: func(v string) (interface{}, error) {
			i, err := strconv.ParseInt(v, 10, 32)
			return int32(i), err
		},
		reflect.Int64: func(v string) (interface{}, error) {
			return strconv.ParseInt(v, 10, 64)
		},
		reflect.Int8: func(v string) (interface{}, error) {
			i, err := strconv.ParseInt(v, 10, 8)
			return int8(i), err
		},
		reflect.Uint: func(v string) (interface{}, error) {
			i, err := strconv.ParseUint(v, 10, 32)
			return uint(i), err
		},
		reflect.Uint16: func(v string) (interface{}, error) {
			i, err := strconv.ParseUint(v, 10, 16)
			return uint16(i), err
		},
		reflect.Uint32: func(v string) (interface{}, error) {
			i, err := strconv.ParseUint(v, 10, 32)
			return uint32(i), err
		},
		reflect.Uint64: func(v string) (interface{}, error) {
			i, err := strconv.ParseUint(v, 10, 64)
			return i, err
		},
		reflect.Uint8: func(v string) (interface{}, error) {
			i, err := strconv.ParseUint(v, 10, 8)
			return uint8(i), err
		},
		reflect.Float64: func(v string) (interface{}, error) {
			return strconv.ParseFloat(v, 64)
		},
		reflect.Float32: func(v string) (interface{}, error) {
			f, err := strconv.ParseFloat(v, 32)
			return float32(f), err
		},
	}
)

func defaultTypeParsers() map[reflect.Type]ParserFunc {
	return map[reflect.Type]ParserFunc{
		reflect.TypeOf(url.URL{}): func(v string) (interface{}, error) {
			u, err := url.Parse(v)
			if err != nil {
				return nil, newParseValueError("unable to parse URL", err)
			}
			return *u, nil
		},
		reflect.TypeOf(time.Nanosecond): func(v string) (interface{}, error) {
			s, err := time.ParseDuration(v)
			if err != nil {
				return nil, newParseValueError("unable to parse duration", err)
			}
			return s, err
		},
	}
}

// ParserFunc defines the signature of a function that can be used within `CustomParsers`.
type ParserFunc func(v string) (interface{}, error)

// OnSetFn is a hook that can be run when a value is set.
type OnSetFn func(tag string, value interface{}, isDefault bool)

// Options for the parser.
type Options struct {
	// Environment keys and values that will be accessible for the service.
	Environment map[string]string

	// TagName specifies another tagname to use rather than the default env.
	TagName string

	// RequiredIfNoDef automatically sets all env as required if they do not
	// declare 'envDefault'.
	RequiredIfNoDef bool

	// OnSet allows to run a function when a value is set.
	OnSet OnSetFn

	// Prefix define a prefix for each key.
	Prefix string

	// UseFieldNameByDefault defines whether or not env should use the field
	// name by default if the `env` key is missing.
	UseFieldNameByDefault bool

	// Custom parse functions for different types.
	FuncMap map[reflect.Type]ParserFunc
}

func defaultOptions() Options {
	return Options{
		TagName:     "env",
		Environment: toMap(os.Environ()),
		FuncMap:     defaultTypeParsers(),
	}
}

func customOptions(opt Options) Options {
	defOpts := defaultOptions()
	if opt.TagName == "" {
		opt.TagName = defOpts.TagName
	}
	if opt.Environment == nil {
		opt.Environment = defOpts.Environment
	}
	if opt.FuncMap == nil {
		opt.FuncMap = map[reflect.Type]ParserFunc{}
	}
	for k, v := range defOpts.FuncMap {
		opt.FuncMap[k] = v
	}
	return opt
}

func optionsWithEnvPrefix(field reflect.StructField, opts Options) Options {
	return Options{
		Environment:           opts.Environment,
		TagName:               opts.TagName,
		RequiredIfNoDef:       opts.RequiredIfNoDef,
		OnSet:                 opts.OnSet,
		Prefix:                opts.Prefix + field.Tag.Get("envPrefix"),
		UseFieldNameByDefault: opts.UseFieldNameByDefault,
		FuncMap:               opts.FuncMap,
	}
}

// Parse parses a struct containing `env` tags and loads its values from
// environment variables.
func Parse(v interface{}) error {
	return parseInternal(v, defaultOptions())
}

// Parse parses a struct containing `env` tags and loads its values from
// environment variables.
func ParseWithOptions(v interface{}, opts Options) error {
	return parseInternal(v, customOptions(opts))
}

func parseInternal(v interface{}, opts Options) error {
	ptrRef := reflect.ValueOf(v)
	if ptrRef.Kind() != reflect.Ptr {
		return newAggregateError(NotStructPtrError{})
	}
	ref := ptrRef.Elem()
	if ref.Kind() != reflect.Struct {
		return newAggregateError(NotStructPtrError{})
	}
	return doParse(ref, opts)
}

func doParse(ref reflect.Value, opts Options) error {
	refType := ref.Type()

	var agrErr AggregateError

	for i := 0; i < refType.NumField(); i++ {
		refField := ref.Field(i)
		refTypeField := refType.Field(i)

		if err := doParseField(refField, refTypeField, opts); err != nil {
			if val, ok := err.(AggregateError); ok {
				agrErr.Errors = append(agrErr.Errors, val.Errors...)
			} else {
				agrErr.Errors = append(agrErr.Errors, err)
			}
		}
	}

	if len(agrErr.Errors) == 0 {
		return nil
	}

	return agrErr
}

func doParseField(refField reflect.Value, refTypeField reflect.StructField, opts Options) error {
	if !refField.CanSet() {
		return nil
	}
	if reflect.Ptr == refField.Kind() && !refField.IsNil() {
		return parseInternal(refField.Interface(), optionsWithEnvPrefix(refTypeField, opts))
	}
	if reflect.Struct == refField.Kind() && refField.CanAddr() && refField.Type().Name() == "" {
		return parseInternal(refField.Addr().Interface(), optionsWithEnvPrefix(refTypeField, opts))
	}
	value, err := get(refTypeField, opts)
	if err != nil {
		return err
	}

	if value != "" {
		return set(refField, refTypeField, value, opts.FuncMap)
	}

	if reflect.Struct == refField.Kind() {
		return doParse(refField, optionsWithEnvPrefix(refTypeField, opts))
	}

	return nil
}

const underscore rune = '_'

func toEnvName(input string) string {
	var output []rune
	for i, c := range input {
		if i > 0 && output[i-1] != underscore && c != underscore && unicode.ToUpper(c) == c {
			output = append(output, underscore)
		}
		output = append(output, unicode.ToUpper(c))
	}
	return string(output)
}

func get(field reflect.StructField, opts Options) (val string, err error) {
	var exists bool
	var isDefault bool
	var loadFile bool
	var unset bool
	var notEmpty bool
	var expand bool

	required := opts.RequiredIfNoDef
	ownKey, tags := parseKeyForOption(field.Tag.Get(opts.TagName))
	if ownKey == "" && opts.UseFieldNameByDefault {
		ownKey = toEnvName(field.Name)
	}

	for _, tag := range tags {
		switch tag {
		case "":
			continue
		case "file":
			loadFile = true
		case "required":
			required = true
		case "unset":
			unset = true
		case "notEmpty":
			notEmpty = true
		case "expand":
			expand = true
		default:
			return "", newNoSupportedTagOptionError(tag)
		}
	}

	prefix := opts.Prefix
	key := prefix + ownKey
	defaultValue, defExists := field.Tag.Lookup("envDefault")
	val, exists, isDefault = getOr(key, defaultValue, defExists, opts.Environment)

	if expand {
		val = os.ExpandEnv(val)
	}

	if unset {
		defer os.Unsetenv(key)
	}

	if required && !exists && len(ownKey) > 0 {
		return "", newEnvVarIsNotSet(key)
	}

	if notEmpty && val == "" {
		return "", newEmptyEnvVarError(key)
	}

	if loadFile && val != "" {
		filename := val
		val, err = getFromFile(filename)
		if err != nil {
			return "", newLoadFileContentError(filename, key, err)
		}
	}

	if opts.OnSet != nil {
		if ownKey != "" {
			opts.OnSet(key, val, isDefault)
		}
	}
	return val, err
}

// split the env tag's key into the expected key and desired option, if any.
func parseKeyForOption(key string) (string, []string) {
	opts := strings.Split(key, ",")
	return opts[0], opts[1:]
}

func getFromFile(filename string) (value string, err error) {
	b, err := os.ReadFile(filename)
	return string(b), err
}

func getOr(key, defaultValue string, defExists bool, envs map[string]string) (string, bool, bool) {
	value, exists := envs[key]
	switch {
	case (!exists || key == "") && defExists:
		return defaultValue, true, true
	case exists && value == "" && defExists:
		return defaultValue, true, true
	case !exists:
		return "", false, false
	}

	return value, true, false
}

func set(field reflect.Value, sf reflect.StructField, value string, funcMap map[reflect.Type]ParserFunc) error {
	if tm := asTextUnmarshaler(field); tm != nil {
		if err := tm.UnmarshalText([]byte(value)); err != nil {
			return newParseError(sf, err)
		}
		return nil
	}

	typee := sf.Type
	fieldee := field
	if typee.Kind() == reflect.Ptr {
		typee = typee.Elem()
		fieldee = field.Elem()
	}

	parserFunc, ok := funcMap[typee]
	if ok {
		val, err := parserFunc(value)
		if err != nil {
			return newParseError(sf, err)
		}

		fieldee.Set(reflect.ValueOf(val))
		return nil
	}

	parserFunc, ok = defaultBuiltInParsers[typee.Kind()]
	if ok {
		val, err := parserFunc(value)
		if err != nil {
			return newParseError(sf, err)
		}

		fieldee.Set(reflect.ValueOf(val).Convert(typee))
		return nil
	}

	switch field.Kind() {
	case reflect.Slice:
		return handleSlice(field, value, sf, funcMap)
	case reflect.Map:
		return handleMap(field, value, sf, funcMap)
	}

	return newNoParserError(sf)
}

func handleSlice(field reflect.Value, value string, sf reflect.StructField, funcMap map[reflect.Type]ParserFunc) error {
	separator := sf.Tag.Get("envSeparator")
	if separator == "" {
		separator = ","
	}
	parts := strings.Split(value, separator)

	typee := sf.Type.Elem()
	if typee.Kind() == reflect.Ptr {
		typee = typee.Elem()
	}

	if _, ok := reflect.New(typee).Interface().(encoding.TextUnmarshaler); ok {
		return parseTextUnmarshalers(field, parts, sf)
	}

	parserFunc, ok := funcMap[typee]
	if !ok {
		parserFunc, ok = defaultBuiltInParsers[typee.Kind()]
		if !ok {
			return newNoParserError(sf)
		}
	}

	result := reflect.MakeSlice(sf.Type, 0, len(parts))
	for _, part := range parts {
		r, err := parserFunc(part)
		if err != nil {
			return newParseError(sf, err)
		}
		v := reflect.ValueOf(r).Convert(typee)
		if sf.Type.Elem().Kind() == reflect.Ptr {
			v = reflect.New(typee)
			v.Elem().Set(reflect.ValueOf(r).Convert(typee))
		}
		result = reflect.Append(result, v)
	}
	field.Set(result)
	return nil
}

func handleMap(field reflect.Value, value string, sf reflect.StructField, funcMap map[reflect.Type]ParserFunc) error {
	keyType := sf.Type.Key()
	keyParserFunc, ok := funcMap[keyType]
	if !ok {
		keyParserFunc, ok = defaultBuiltInParsers[keyType.Kind()]
		if !ok {
			return newNoParserError(sf)
		}
	}

	elemType := sf.Type.Elem()
	elemParserFunc, ok := funcMap[elemType]
	if !ok {
		elemParserFunc, ok = defaultBuiltInParsers[elemType.Kind()]
		if !ok {
			return newNoParserError(sf)
		}
	}

	separator := sf.Tag.Get("envSeparator")
	if separator == "" {
		separator = ","
	}

	result := reflect.MakeMap(sf.Type)
	for _, part := range strings.Split(value, separator) {
		pairs := strings.Split(part, ":")
		if len(pairs) != 2 {
			return newParseError(sf, fmt.Errorf(`%q should be in "key:value" format`, part))
		}

		key, err := keyParserFunc(pairs[0])
		if err != nil {
			return newParseError(sf, err)
		}

		elem, err := elemParserFunc(pairs[1])
		if err != nil {
			return newParseError(sf, err)
		}

		result.SetMapIndex(reflect.ValueOf(key).Convert(keyType), reflect.ValueOf(elem).Convert(elemType))
	}

	field.Set(result)
	return nil
}

func asTextUnmarshaler(field reflect.Value) encoding.TextUnmarshaler {
	if reflect.Ptr == field.Kind() {
		if field.IsNil() {
			field.Set(reflect.New(field.Type().Elem()))
		}
	} else if field.CanAddr() {
		field = field.Addr()
	}

	tm, ok := field.Interface().(encoding.TextUnmarshaler)
	if !ok {
		return nil
	}
	return tm
}

func parseTextUnmarshalers(field reflect.Value, data []string, sf reflect.StructField) error {
	s := len(data)
	elemType := field.Type().Elem()
	slice := reflect.MakeSlice(reflect.SliceOf(elemType), s, s)
	for i, v := range data {
		sv := slice.Index(i)
		kind := sv.Kind()
		if kind == reflect.Ptr {
			sv = reflect.New(elemType.Elem())
		} else {
			sv = sv.Addr()
		}
		tm := sv.Interface().(encoding.TextUnmarshaler)
		if err := tm.UnmarshalText([]byte(v)); err != nil {
			return newParseError(sf, err)
		}
		if kind == reflect.Ptr {
			slice.Index(i).Set(sv)
		}
	}

	field.Set(slice)

	return nil
}