package main

import (
	"bytes"
	"go/ast"
	"go/format"
	"go/parser"
	"go/token"
	"os"
	"sort"
	"strconv"
	"text/template"
)

const codeTemplate = `// Code generated by internal/generator/c2c_switcher DO NOT EDIT.

package client

import (
{{range .Imports}}	{{.}}
{{end}}
)

const (
	UnknownDecoder = iota
{{range .Consts}}	{{.}}
{{end}}
)

func peekC2CDecoder(msgType int32) (decoder func(*QQClient, *msg.Message, *network.IncomingPacketInfo), decoderType uint8) {
    switch msgType {
{{range .Decoders}}	case {{.Id}}:
		return {{.Func}}, {{.DecoderType}}
{{end}}	default:
        return nil, UnknownDecoder
    }
}`

type decoder struct {
	Id          int64
	Func        string
	DecoderType string
}
type DecoderSort []decoder

func (d DecoderSort) Len() int           { return len(d) }
func (d DecoderSort) Swap(i, j int)      { d[i], d[j] = d[j], d[i] }
func (d DecoderSort) Less(i, j int) bool { return d[i].Id < d[j].Id }

func main() {
	type switchFile struct {
		Imports  []string
		Consts   []string
		Decoders DecoderSort
	}
	var sf switchFile

	fset := token.NewFileSet()
	astF, err := parser.ParseFile(fset, "_c2c_decoders.go", nil, parser.AllErrors|parser.ParseComments)
	if err != nil {
		panic(err)
	}

	sf.Imports = make([]string, 0, len(astF.Imports))
	for _, imp := range astF.Imports {
		sf.Imports = append(sf.Imports, imp.Path.Value)
	}

	sf.Consts = make([]string, 0, len(astF.Scope.Objects))
	for _, obj := range astF.Scope.Objects {
		if obj.Kind != ast.Var {
			panic(`unknown non-variable in "_c2c_decoders.go"`)
		}
		value := obj.Decl.(*ast.ValueSpec)
		sf.Consts = append(sf.Consts, obj.Name)
		for _, value := range value.Values {
			if value, ok := value.(*ast.CompositeLit); ok {
				for _, kv := range value.Elts {
					if kv, ok := kv.(*ast.KeyValueExpr); ok {
						k := kv.Key.(*ast.BasicLit)
						v := kv.Value.(*ast.Ident)
						sf.Decoders = append(sf.Decoders, decoder{
							Id:          mustParseInt(k.Value),
							Func:        v.Name,
							DecoderType: obj.Name,
						})
					} else {
						panic(`unknown key value in ` + obj.Name + ` in "_c2c_decoders.go"`)
					}
				}
			} else {
				panic(`unknown non-map value in "_c2c_decoders.go"`)
			}
		}
	}
	sort.Slice(sf.Consts, func(i, j int) bool {
		return sf.Consts[i] < sf.Consts[j]
	})
	sort.Sort(sf.Decoders)

	f, _ := os.OpenFile("c2c_switch.go", os.O_WRONLY|os.O_CREATE|os.O_SYNC|os.O_TRUNC, 0o644)
	tmpl, err := template.New("template").Parse(codeTemplate)
	if err != nil {
		panic(err)
	}
	buffer := &bytes.Buffer{}
	err = tmpl.Execute(buffer, &sf)
	if err != nil {
		panic(err)
	}
	source, _ := format.Source(buffer.Bytes())
	_, _ = f.Write(source)
	_ = f.Close()
}

func mustParseInt(s string) int64 {
	i, err := strconv.ParseInt(s, 10, 32)
	if err != nil {
		panic(err)
	}
	return i
}