// Copyright 2014 Alvaro J. Genial. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package form

import (
	"fmt"
	"io"
	"io/ioutil"
	"net/url"
	"reflect"
	"strconv"
	"time"
)

// NewDecoder returns a new form Decoder.
func NewDecoder(r io.Reader) *Decoder {
	return &Decoder{r, defaultDelimiter, defaultEscape, false, false}
}

// Decoder decodes data from a form (application/x-www-form-urlencoded).
type Decoder struct {
	r             io.Reader
	d             rune
	e             rune
	ignoreUnknown bool
	ignoreCase    bool
}

// DelimitWith sets r as the delimiter used for composite keys by Decoder d and returns the latter; it is '.' by default.
func (d *Decoder) DelimitWith(r rune) *Decoder {
	d.d = r
	return d
}

// EscapeWith sets r as the escape used for delimiters (and to escape itself) by Decoder d and returns the latter; it is '\\' by default.
func (d *Decoder) EscapeWith(r rune) *Decoder {
	d.e = r
	return d
}

// Decode reads in and decodes form-encoded data into dst.
func (d Decoder) Decode(dst interface{}) error {
	bs, err := ioutil.ReadAll(d.r)
	if err != nil {
		return err
	}
	vs, err := url.ParseQuery(string(bs))
	if err != nil {
		return err
	}
	v := reflect.ValueOf(dst)
	return d.decodeNode(v, parseValues(d.d, d.e, vs, canIndexOrdinally(v)))
}

// IgnoreUnknownKeys if set to true it will make the Decoder ignore values
// that are not found in the destination object instead of returning an error.
func (d *Decoder) IgnoreUnknownKeys(ignoreUnknown bool) {
	d.ignoreUnknown = ignoreUnknown
}

// IgnoreCase if set to true it will make the Decoder try to set values in the
// destination object even if the case does not match.
func (d *Decoder) IgnoreCase(ignoreCase bool) {
	d.ignoreCase = ignoreCase
}

// DecodeString decodes src into dst.
func (d Decoder) DecodeString(dst interface{}, src string) error {
	vs, err := url.ParseQuery(src)
	if err != nil {
		return err
	}
	v := reflect.ValueOf(dst)
	return d.decodeNode(v, parseValues(d.d, d.e, vs, canIndexOrdinally(v)))
}

// DecodeValues decodes vs into dst.
func (d Decoder) DecodeValues(dst interface{}, vs url.Values) error {
	v := reflect.ValueOf(dst)
	return d.decodeNode(v, parseValues(d.d, d.e, vs, canIndexOrdinally(v)))
}

// DecodeString decodes src into dst.
func DecodeString(dst interface{}, src string) error {
	return NewDecoder(nil).DecodeString(dst, src)
}

// DecodeValues decodes vs into dst.
func DecodeValues(dst interface{}, vs url.Values) error {
	return NewDecoder(nil).DecodeValues(dst, vs)
}

func (d Decoder) decodeNode(v reflect.Value, n node) (err error) {
	defer func() {
		if e := recover(); e != nil {
			err = fmt.Errorf("%v", e)
		}
	}()

	if v.Kind() == reflect.Slice {
		return fmt.Errorf("could not decode directly into slice; use pointer to slice")
	}
	d.decodeValue(v, n)
	return nil
}

func (d Decoder) decodeValue(v reflect.Value, x interface{}) {
	t := v.Type()
	k := v.Kind()

	if k == reflect.Ptr && v.IsNil() {
		v.Set(reflect.New(t.Elem()))
	}

	if unmarshalValue(v, x) {
		return
	}

	empty := isEmpty(x)

	switch k {
	case reflect.Ptr:
		d.decodeValue(v.Elem(), x)
		return
	case reflect.Interface:
		if !v.IsNil() {
			d.decodeValue(v.Elem(), x)
			return

		} else if empty {
			return // Allow nil interfaces only if empty.
		} else {
			panic("form: cannot decode non-empty value into into nil interface")
		}
	}

	if empty {
		v.Set(reflect.Zero(t)) // Treat the empty string as the zero value.
		return
	}

	switch k {
	case reflect.Struct:
		if t.ConvertibleTo(timeType) {
			d.decodeTime(v, x)
		} else if t.ConvertibleTo(urlType) {
			d.decodeURL(v, x)
		} else {
			d.decodeStruct(v, x)
		}
	case reflect.Slice:
		d.decodeSlice(v, x)
	case reflect.Array:
		d.decodeArray(v, x)
	case reflect.Map:
		d.decodeMap(v, x)
	case reflect.Invalid, reflect.Uintptr, reflect.UnsafePointer, reflect.Chan, reflect.Func:
		panic(t.String() + " has unsupported kind " + k.String())
	default:
		d.decodeBasic(v, x)
	}
}

func (d Decoder) decodeStruct(v reflect.Value, x interface{}) {
	t := v.Type()
	for k, c := range getNode(x) {
		if f, ok := findField(v, k, d.ignoreCase); !ok && k == "" {
			panic(getString(x) + " cannot be decoded as " + t.String())
		} else if !ok {
			if !d.ignoreUnknown {
				panic(k + " doesn't exist in " + t.String())
			}
		} else if !f.CanSet() {
			panic(k + " cannot be set in " + t.String())
		} else {
			d.decodeValue(f, c)
		}
	}
}

func (d Decoder) decodeMap(v reflect.Value, x interface{}) {
	t := v.Type()
	if v.IsNil() {
		v.Set(reflect.MakeMap(t))
	}
	for k, c := range getNode(x) {
		i := reflect.New(t.Key()).Elem()
		d.decodeValue(i, k)

		w := v.MapIndex(i)
		if w.IsValid() { // We have an actual element value to decode into.
			if w.Kind() == reflect.Interface {
				w = w.Elem()
			}
			w = reflect.New(w.Type()).Elem()
		} else if t.Elem().Kind() != reflect.Interface { // The map's element type is concrete.
			w = reflect.New(t.Elem()).Elem()
		} else {
			// The best we can do here is to decode as either a string (for scalars) or a map[string]interface {} (for the rest).
			// We could try to guess the type based on the string (e.g. true/false => bool) but that'll get ugly fast,
			// especially if we have to guess the kind (slice vs. array vs. map) and index type (e.g. string, int, etc.)
			switch c.(type) {
			case node:
				w = reflect.MakeMap(stringMapType)
			case string:
				w = reflect.New(stringType).Elem()
			default:
				panic("value is neither node nor string")
			}
		}

		d.decodeValue(w, c)
		v.SetMapIndex(i, w)
	}
}

func (d Decoder) decodeArray(v reflect.Value, x interface{}) {
	t := v.Type()
	for k, c := range getNode(x) {
		i, err := strconv.Atoi(k)
		if err != nil {
			panic(k + " is not a valid index for type " + t.String())
		}
		if l := v.Len(); i >= l {
			panic("index is above array size")
		}
		d.decodeValue(v.Index(i), c)
	}
}

func (d Decoder) decodeSlice(v reflect.Value, x interface{}) {
	t := v.Type()
	if t.Elem().Kind() == reflect.Uint8 {
		// Allow, but don't require, byte slices to be encoded as a single string.
		if s, ok := x.(string); ok {
			v.SetBytes([]byte(s))
			return
		}
	}

	// NOTE: Implicit indexing is currently done at the parseValues level,
	//       so if if an implicitKey reaches here it will always replace the last.
	implicit := 0
	for k, c := range getNode(x) {
		var i int
		if k == implicitKey {
			i = implicit
			implicit++
		} else {
			explicit, err := strconv.Atoi(k)
			if err != nil {
				panic(k + " is not a valid index for type " + t.String())
			}
			i = explicit
			implicit = explicit + 1
		}
		// "Extend" the slice if it's too short.
		if l := v.Len(); i >= l {
			delta := i - l + 1
			v.Set(reflect.AppendSlice(v, reflect.MakeSlice(t, delta, delta)))
		}
		d.decodeValue(v.Index(i), c)
	}
}

func (d Decoder) decodeBasic(v reflect.Value, x interface{}) {
	t := v.Type()
	switch k, s := t.Kind(), getString(x); k {
	case reflect.Bool:
		if b, e := strconv.ParseBool(s); e == nil {
			v.SetBool(b)
		} else {
			panic("could not parse bool from " + strconv.Quote(s))
		}
	case reflect.Int,
		reflect.Int8,
		reflect.Int16,
		reflect.Int32,
		reflect.Int64:
		if i, e := strconv.ParseInt(s, 10, 64); e == nil {
			v.SetInt(i)
		} else {
			panic("could not parse int from " + strconv.Quote(s))
		}
	case reflect.Uint,
		reflect.Uint8,
		reflect.Uint16,
		reflect.Uint32,
		reflect.Uint64:
		if u, e := strconv.ParseUint(s, 10, 64); e == nil {
			v.SetUint(u)
		} else {
			panic("could not parse uint from " + strconv.Quote(s))
		}
	case reflect.Float32,
		reflect.Float64:
		if f, e := strconv.ParseFloat(s, 64); e == nil {
			v.SetFloat(f)
		} else {
			panic("could not parse float from " + strconv.Quote(s))
		}
	case reflect.Complex64,
		reflect.Complex128:
		var c complex128
		if n, err := fmt.Sscanf(s, "%g", &c); n == 1 && err == nil {
			v.SetComplex(c)
		} else {
			panic("could not parse complex from " + strconv.Quote(s))
		}
	case reflect.String:
		v.SetString(s)
	default:
		panic(t.String() + " has unsupported kind " + k.String())
	}
}

func (d Decoder) decodeTime(v reflect.Value, x interface{}) {
	t := v.Type()
	s := getString(x)
	// TODO: Find a more efficient way to do this.
	for _, f := range allowedTimeFormats {
		if p, err := time.Parse(f, s); err == nil {
			v.Set(reflect.ValueOf(p).Convert(v.Type()))
			return
		}
	}
	panic("cannot decode string `" + s + "` as " + t.String())
}

func (d Decoder) decodeURL(v reflect.Value, x interface{}) {
	t := v.Type()
	s := getString(x)
	if u, err := url.Parse(s); err == nil {
		v.Set(reflect.ValueOf(*u).Convert(v.Type()))
		return
	}
	panic("cannot decode string `" + s + "` as " + t.String())
}

var allowedTimeFormats = []string{
	"2006-01-02T15:04:05.999999999Z07:00",
	"2006-01-02T15:04:05.999999999Z07",
	"2006-01-02T15:04:05.999999999Z",
	"2006-01-02T15:04:05.999999999",
	"2006-01-02T15:04:05Z07:00",
	"2006-01-02T15:04:05Z07",
	"2006-01-02T15:04:05Z",
	"2006-01-02T15:04:05",
	"2006-01-02T15:04Z",
	"2006-01-02T15:04",
	"2006-01-02T15Z",
	"2006-01-02T15",
	"2006-01-02",
	"2006-01",
	"2006",
	"15:04:05.999999999Z07:00",
	"15:04:05.999999999Z07",
	"15:04:05.999999999Z",
	"15:04:05.999999999",
	"15:04:05Z07:00",
	"15:04:05Z07",
	"15:04:05Z",
	"15:04:05",
	"15:04Z",
	"15:04",
	"15Z",
	"15",
}