// Copyright 2012 Gary Burd
//
// Licensed under the Apache License, Version 2.0 (the "License"): you may
// not use this file except in compliance with the License. You may obtain
// a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
// WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
// License for the specific language governing permissions and limitations
// under the License.

package scan

import (
	"errors"
	"reflect"
	"strings"
	"sync"
)

type fieldSpec struct {
	name      string
	index     []int
	omitEmpty bool
}

type structSpec struct {
	m map[string]*fieldSpec
	l []*fieldSpec
}

func (ss *structSpec) fieldSpec(name []byte) *fieldSpec {
	return ss.m[string(name)]
}

func compileStructSpec(t reflect.Type, depth map[string]int, index []int, ss *structSpec) {
	for i := 0; i < t.NumField(); i++ {
		f := t.Field(i)
		switch {
		case f.PkgPath != "":
			// Ignore unexported fields.
		case f.Anonymous:
			// TODO: Handle pointers. Requires change to decoder and 
			// protection against infinite recursion.
			if f.Type.Kind() == reflect.Struct {
				compileStructSpec(f.Type, depth, append(index, i), ss)
			}
		default:
			fs := &fieldSpec{name: f.Name}
			tag := f.Tag.Get("redis")
			p := strings.Split(tag, ",")
			if len(p) > 0 && p[0] != "-" {
				if len(p[0]) > 0 {
					fs.name = p[0]
				}
				for _, s := range p[1:] {
					switch s {
					case "omitempty":
						fs.omitEmpty = true
					default:
						panic(errors.New("redigo: unknown field flag " + s + " for type " + t.Name()))
					}
				}
			}
			d, found := depth[fs.name]
			if !found {
				d = 1 << 30
			}
			switch {
			case len(index) == d:
				// At same depth, remove from result.
				delete(ss.m, fs.name)
				j := 0
				for i := 0; i < len(ss.l); i++ {
					if fs.name != ss.l[i].name {
						ss.l[j] = ss.l[i]
						j += 1
					}
				}
				ss.l = ss.l[:j]
			case len(index) < d:
				fs.index = make([]int, len(index)+1)
				copy(fs.index, index)
				fs.index[len(index)] = i
				depth[fs.name] = len(index)
				ss.m[fs.name] = fs
				ss.l = append(ss.l, fs)
			}
		}
	}
}

var (
	structSpecMutex  sync.RWMutex
	structSpecCache  = make(map[reflect.Type]*structSpec)
	defaultFieldSpec = &fieldSpec{}
)

func structSpecForType(t reflect.Type) *structSpec {

	structSpecMutex.RLock()
	ss, found := structSpecCache[t]
	structSpecMutex.RUnlock()
	if found {
		return ss
	}

	structSpecMutex.Lock()
	defer structSpecMutex.Unlock()
	ss, found = structSpecCache[t]
	if found {
		return ss
	}

	ss = &structSpec{m: make(map[string]*fieldSpec)}
	compileStructSpec(t, make(map[string]int), nil, ss)
	structSpecCache[t] = ss
	return ss
}