// Copyright (c) 2012, 2013 Ugorji Nwoke. All rights reserved.
// Use of this source code is governed by a BSD-style license found in the LICENSE file.

package codec

// All non-std package dependencies live in this file,
// so porting to different environment is easy (just update functions).

import (
	"errors"
	"fmt"
	"math"
	"reflect"
)

func panicValToErr(panicVal interface{}, err *error) {
	if panicVal == nil {
		return
	}
	// case nil
	switch xerr := panicVal.(type) {
	case error:
		*err = xerr
	case string:
		*err = errors.New(xerr)
	default:
		*err = fmt.Errorf("%v", panicVal)
	}
	return
}

func hIsEmptyValue(v reflect.Value, deref, checkStruct bool) bool {
	switch v.Kind() {
	case reflect.Invalid:
		return true
	case reflect.Array, reflect.Map, reflect.Slice, reflect.String:
		return v.Len() == 0
	case reflect.Bool:
		return !v.Bool()
	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
		return v.Int() == 0
	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
		return v.Uint() == 0
	case reflect.Float32, reflect.Float64:
		return v.Float() == 0
	case reflect.Interface, reflect.Ptr:
		if deref {
			if v.IsNil() {
				return true
			}
			return hIsEmptyValue(v.Elem(), deref, checkStruct)
		} else {
			return v.IsNil()
		}
	case reflect.Struct:
		if !checkStruct {
			return false
		}
		// return true if all fields are empty. else return false.
		// we cannot use equality check, because some fields may be maps/slices/etc
		// and consequently the structs are not comparable.
		// return v.Interface() == reflect.Zero(v.Type()).Interface()
		for i, n := 0, v.NumField(); i < n; i++ {
			if !hIsEmptyValue(v.Field(i), deref, checkStruct) {
				return false
			}
		}
		return true
	}
	return false
}

func isEmptyValue(v reflect.Value) bool {
	return hIsEmptyValue(v, derefForIsEmptyValue, checkStructForEmptyValue)
}

func pruneSignExt(v []byte, pos bool) (n int) {
	if len(v) < 2 {
	} else if pos && v[0] == 0 {
		for ; v[n] == 0 && n+1 < len(v) && (v[n+1]&(1<<7) == 0); n++ {
		}
	} else if !pos && v[0] == 0xff {
		for ; v[n] == 0xff && n+1 < len(v) && (v[n+1]&(1<<7) != 0); n++ {
		}
	}
	return
}

func implementsIntf(typ, iTyp reflect.Type) (success bool, indir int8) {
	if typ == nil {
		return
	}
	rt := typ
	// The type might be a pointer and we need to keep
	// dereferencing to the base type until we find an implementation.
	for {
		if rt.Implements(iTyp) {
			return true, indir
		}
		if p := rt; p.Kind() == reflect.Ptr {
			indir++
			if indir >= math.MaxInt8 { // insane number of indirections
				return false, 0
			}
			rt = p.Elem()
			continue
		}
		break
	}
	// No luck yet, but if this is a base type (non-pointer), the pointer might satisfy.
	if typ.Kind() != reflect.Ptr {
		// Not a pointer, but does the pointer work?
		if reflect.PtrTo(typ).Implements(iTyp) {
			return true, -1
		}
	}
	return false, 0
}

// validate that this function is correct ...
// culled from OGRE (Object-Oriented Graphics Rendering Engine)
// function: halfToFloatI (http://stderr.org/doc/ogre-doc/api/OgreBitwise_8h-source.html)
func halfFloatToFloatBits(yy uint16) (d uint32) {
	y := uint32(yy)
	s := (y >> 15) & 0x01
	e := (y >> 10) & 0x1f
	m := y & 0x03ff

	if e == 0 {
		if m == 0 { // plu or minus 0
			return s << 31
		} else { // Denormalized number -- renormalize it
			for (m & 0x00000400) == 0 {
				m <<= 1
				e -= 1
			}
			e += 1
			const zz uint32 = 0x0400
			m &= ^zz
		}
	} else if e == 31 {
		if m == 0 { // Inf
			return (s << 31) | 0x7f800000
		} else { // NaN
			return (s << 31) | 0x7f800000 | (m << 13)
		}
	}
	e = e + (127 - 15)
	m = m << 13
	return (s << 31) | (e << 23) | m
}