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// Copyright 2011 The Go Authors.  All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package xml

import (
        "fmt"
        "reflect"
        "strings"
        "sync"
)

// typeInfo holds details for the xml representation of a type.
type typeInfo struct {
        xmlname *fieldInfo
        fields  []fieldInfo
}

// fieldInfo holds details for the xml representation of a single field.
type fieldInfo struct {
        idx     []int
        name    string
        xmlns   string
        flags   fieldFlags
        parents []string
}

type fieldFlags int

const (
        fElement fieldFlags = 1 << iota
        fAttr
        fCharData
        fInnerXml
        fComment
        fAny

        // TODO:
        //fOmitEmpty

        fMode = fElement | fAttr | fCharData | fInnerXml | fComment | fAny
)

var tinfoMap = make(map[reflect.Type]*typeInfo)
var tinfoLock sync.RWMutex

var nameType = reflect.TypeOf(Name{})

// getTypeInfo returns the typeInfo structure with details necessary
// for marshalling and unmarshalling typ.
func getTypeInfo(typ reflect.Type) (*typeInfo, error) {
        tinfoLock.RLock()
        tinfo, ok := tinfoMap[typ]
        tinfoLock.RUnlock()
        if ok {
                return tinfo, nil
        }
        tinfo = &typeInfo{}
        if typ.Kind() == reflect.Struct && typ != nameType {
                n := typ.NumField()
                for i := 0; i < n; i++ {
                        f := typ.Field(i)
                        if f.PkgPath != "" || f.Tag.Get("xml") == "-" {
                                continue // Private field
                        }

                        // For embedded structs, embed its fields.
                        if f.Anonymous {
                                if f.Type.Kind() != reflect.Struct {
                                        continue
                                }
                                inner, err := getTypeInfo(f.Type)
                                if err != nil {
                                        return nil, err
                                }
                                for _, finfo := range inner.fields {
                                        finfo.idx = append([]int{i}, finfo.idx...)
                                        if err := addFieldInfo(typ, tinfo, &finfo); err != nil {
                                                return nil, err
                                        }
                                }
                                continue
                        }

                        finfo, err := structFieldInfo(typ, &f)
                        if err != nil {
                                return nil, err
                        }

                        if f.Name == "XMLName" {
                                tinfo.xmlname = finfo
                                continue
                        }

                        // Add the field if it doesn't conflict with other fields.
                        if err := addFieldInfo(typ, tinfo, finfo); err != nil {
                                return nil, err
                        }
                }
        }
        tinfoLock.Lock()
        tinfoMap[typ] = tinfo
        tinfoLock.Unlock()
        return tinfo, nil
}

// structFieldInfo builds and returns a fieldInfo for f.
func structFieldInfo(typ reflect.Type, f *reflect.StructField) (*fieldInfo, error) {
        finfo := &fieldInfo{idx: f.Index}

        // Split the tag from the xml namespace if necessary.
        tag := f.Tag.Get("xml")
        if i := strings.Index(tag, " "); i >= 0 {
                finfo.xmlns, tag = tag[:i], tag[i+1:]
        }

        // Parse flags.
        tokens := strings.Split(tag, ",")
        if len(tokens) == 1 {
                finfo.flags = fElement
        } else {
                tag = tokens[0]
                for _, flag := range tokens[1:] {
                        switch flag {
                        case "attr":
                                finfo.flags |= fAttr
                        case "chardata":
                                finfo.flags |= fCharData
                        case "innerxml":
                                finfo.flags |= fInnerXml
                        case "comment":
                                finfo.flags |= fComment
                        case "any":
                                finfo.flags |= fAny
                        }
                }

                // Validate the flags used.
                switch mode := finfo.flags & fMode; mode {
                case 0:
                        finfo.flags |= fElement
                case fAttr, fCharData, fInnerXml, fComment, fAny:
                        if f.Name != "XMLName" && (tag == "" || mode == fAttr) {
                                break
                        }
                        fallthrough
                default:
                        // This will also catch multiple modes in a single field.
                        return nil, fmt.Errorf("xml: invalid tag in field %s of type %s: %q",
                                f.Name, typ, f.Tag.Get("xml"))
                }
        }

        // Use of xmlns without a name is not allowed.
        if finfo.xmlns != "" && tag == "" {
                return nil, fmt.Errorf("xml: namespace without name in field %s of type %s: %q",
                        f.Name, typ, f.Tag.Get("xml"))
        }

        if f.Name == "XMLName" {
                // The XMLName field records the XML element name. Don't
                // process it as usual because its name should default to
                // empty rather than to the field name.
                finfo.name = tag
                return finfo, nil
        }

        if tag == "" {
                // If the name part of the tag is completely empty, get
                // default from XMLName of underlying struct if feasible,
                // or field name otherwise.
                if xmlname := lookupXMLName(f.Type); xmlname != nil {
                        finfo.xmlns, finfo.name = xmlname.xmlns, xmlname.name
                } else {
                        finfo.name = f.Name
                }
                return finfo, nil
        }

        // Prepare field name and parents.
        tokens = strings.Split(tag, ">")
        if tokens[0] == "" {
                tokens[0] = f.Name
        }
        if tokens[len(tokens)-1] == "" {
                return nil, fmt.Errorf("xml: trailing '>' in field %s of type %s", f.Name, typ)
        }
        finfo.name = tokens[len(tokens)-1]
        if len(tokens) > 1 {
                finfo.parents = tokens[:len(tokens)-1]
        }

        // If the field type has an XMLName field, the names must match
        // so that the behavior of both marshalling and unmarshalling
        // is straightforward and unambiguous.
        if finfo.flags&fElement != 0 {
                ftyp := f.Type
                xmlname := lookupXMLName(ftyp)
                if xmlname != nil && xmlname.name != finfo.name {
                        return nil, fmt.Errorf("xml: name %q in tag of %s.%s conflicts with name %q in %s.XMLName",
                                finfo.name, typ, f.Name, xmlname.name, ftyp)
                }
        }
        return finfo, nil
}

// lookupXMLName returns the fieldInfo for typ's XMLName field
// in case it exists and has a valid xml field tag, otherwise
// it returns nil.
func lookupXMLName(typ reflect.Type) (xmlname *fieldInfo) {
        for typ.Kind() == reflect.Ptr {
                typ = typ.Elem()
        }
        if typ.Kind() != reflect.Struct {
                return nil
        }
        for i, n := 0, typ.NumField(); i < n; i++ {
                f := typ.Field(i)
                if f.Name != "XMLName" {
                        continue
                }
                finfo, err := structFieldInfo(typ, &f)
                if finfo.name != "" && err == nil {
                        return finfo
                }
                // Also consider errors as a non-existent field tag
                // and let getTypeInfo itself report the error.
                break
        }
        return nil
}

func min(a, b int) int {
        if a <= b {
                return a
        }
        return b
}

// addFieldInfo adds finfo to tinfo.fields if there are no
// conflicts, or if conflicts arise from previous fields that were
// obtained from deeper embedded structures than finfo. In the latter
// case, the conflicting entries are dropped.
// A conflict occurs when the path (parent + name) to a field is
// itself a prefix of another path, or when two paths match exactly.
// It is okay for field paths to share a common, shorter prefix.
func addFieldInfo(typ reflect.Type, tinfo *typeInfo, newf *fieldInfo) error {
        var conflicts []int
Loop:
        // First, figure all conflicts. Most working code will have none.
        for i := range tinfo.fields {
                oldf := &tinfo.fields[i]
                if oldf.flags&fMode != newf.flags&fMode {
                        continue
                }
                minl := min(len(newf.parents), len(oldf.parents))
                for p := 0; p < minl; p++ {
                        if oldf.parents[p] != newf.parents[p] {
                                continue Loop
                        }
                }
                if len(oldf.parents) > len(newf.parents) {
                        if oldf.parents[len(newf.parents)] == newf.name {
                                conflicts = append(conflicts, i)
                        }
                } else if len(oldf.parents) < len(newf.parents) {
                        if newf.parents[len(oldf.parents)] == oldf.name {
                                conflicts = append(conflicts, i)
                        }
                } else {
                        if newf.name == oldf.name {
                                conflicts = append(conflicts, i)
                        }
                }
        }
        // Without conflicts, add the new field and return.
        if conflicts == nil {
                tinfo.fields = append(tinfo.fields, *newf)
                return nil
        }

        // If any conflict is shallower, ignore the new field.
        // This matches the Go field resolution on embedding.
        for _, i := range conflicts {
                if len(tinfo.fields[i].idx) < len(newf.idx) {
                        return nil
                }
        }

        // Otherwise, if any of them is at the same depth level, it's an error.
        for _, i := range conflicts {
                oldf := &tinfo.fields[i]
                if len(oldf.idx) == len(newf.idx) {
                        f1 := typ.FieldByIndex(oldf.idx)
                        f2 := typ.FieldByIndex(newf.idx)
                        return &TagPathError{typ, f1.Name, f1.Tag.Get("xml"), f2.Name, f2.Tag.Get("xml")}
                }
        }

        // Otherwise, the new field is shallower, and thus takes precedence,
        // so drop the conflicting fields from tinfo and append the new one.
        for c := len(conflicts) - 1; c >= 0; c-- {
                i := conflicts[c]
                copy(tinfo.fields[i:], tinfo.fields[i+1:])
                tinfo.fields = tinfo.fields[:len(tinfo.fields)-1]
        }
        tinfo.fields = append(tinfo.fields, *newf)
        return nil
}

// A TagPathError represents an error in the unmarshalling process
// caused by the use of field tags with conflicting paths.
type TagPathError struct {
        Struct       reflect.Type
        Field1, Tag1 string
        Field2, Tag2 string
}

func (e *TagPathError) Error() string {
        return fmt.Sprintf("%s field %q with tag %q conflicts with field %q with tag %q", e.Struct, e.Field1, e.Tag1, e.Field2, e.Tag2)
}