package main

import (
	"bytes"
	"flag"
	"fmt"
	"go/ast"
	"go/format"
	"go/parser"
	"go/token"
	"io"
	"os"
	"sort"
	"strconv"
	"strings"
)

type Param struct {
	Name    string
	Type    string
	Default string
}

type Router struct {
	Func   string
	Path   []string
	Params []Param
}

type generator struct {
	out io.Writer
}

func (g *generator) WriteString(s string) {
	io.WriteString(g.out, s)
}

func (g *generator) generate(routers []Router) {
	g.WriteString("// Code generated by cmd/api-generator. DO NOT EDIT.\n\n")
	g.WriteString("package api\n\nimport (\n\n")
	g.WriteString("\"github.com/Mrs4s/go-cqhttp/coolq\"\n")
	g.WriteString("\"github.com/Mrs4s/go-cqhttp/global\"\n")
	g.WriteString(")\n\n")
	g.WriteString(`func (c *Caller) call(action string, p Getter) global.MSG {
	switch action {
	default:
		return coolq.Failed(404, "API_NOT_FOUND", "API不存在")` + "\n")
	for _, router := range routers {
		g.router(router)
	}
	io.WriteString(g.out, `	}}`)
}

func (g *generator) router(router Router) {
	g.WriteString(`case `)
	for i, p := range router.Path {
		if i != 0 {
			g.WriteString(`, `)
		}
		g.WriteString(strconv.Quote(p))
	}
	g.WriteString(":\n")

	for i, p := range router.Params {
		if p.Default == "" {
			v := "p.Get(" + strconv.Quote(p.Name) + ")"
			fmt.Fprintf(g.out, "p%d := %s\n", i, conv(v, p.Type))
		} else {
			fmt.Fprintf(g.out, "p%d := %s\n", i, p.Default)
			fmt.Fprintf(g.out, "if pt := p.Get(%s); pt.Exists() {\n", strconv.Quote(p.Name))
			fmt.Fprintf(g.out, "p%d = %s\n}\n", i, conv("pt", p.Type))
		}
	}

	g.WriteString("\t\treturn c.bot." + router.Func + "(")
	for i := range router.Params {
		if i != 0 {
			g.WriteString(", ")
		}
		fmt.Fprintf(g.out, "p%d", i)
	}
	g.WriteString(")\n")
}

func conv(v, t string) string {
	switch t {
	default:
		panic("unknown type: " + t)
	case "gjson.Result":
		return v
	case "int64":
		return v + ".Int()"
	case "bool":
		return v + ".Bool()"
	case "string":
		return v + ".String()"
	case "int32", "int":
		return t + "(" + v + ".Int())"
	case "uint64":
		return v + ".Uint()"
	case "uint32":
		return "uint32(" + v + ".Uint())"
	}
}

func main() {
	var routers []Router
	src := flag.String("path", "", "source file")
	flag.Parse()
	fset := token.NewFileSet()
	file, err := parser.ParseFile(fset, *src, nil, parser.ParseComments)
	if err != nil {
		panic(err)
	}

	for _, decl := range file.Decls {
		switch decl := decl.(type) {
		case *ast.FuncDecl:
			if !decl.Name.IsExported() || decl.Recv == nil {
				continue
			}
			if st, ok := decl.Recv.List[0].Type.(*ast.StarExpr); !ok || st.X.(*ast.Ident).Name != "CQBot" {
				continue
			}
			router := Router{Func: decl.Name.Name}

			// compute params
			for _, p := range decl.Type.Params.List {
				var typ string
				switch t := p.Type.(type) {
				case *ast.Ident:
					typ = t.Name
				case *ast.SelectorExpr:
					typ = t.X.(*ast.Ident).Name + "." + t.Sel.Name
				}
				for _, name := range p.Names {
					router.Params = append(router.Params, Param{Name: snakecase(name.Name), Type: typ})
				}
			}

			for _, comment := range decl.Doc.List {
				annotation, args := match(comment.Text)
				switch annotation {
				case "route":
					for _, route := range strings.Split(args, ",") {
						router.Path = append(router.Path, unquote(route))
					}
				case "default":
					for name, value := range parseMap(args, "=") {
						for i, p := range router.Params {
							if p.Name == name {
								router.Params[i].Default = convDefault(value, p.Type)
							}
						}
					}
				case "rename":
					for name, value := range parseMap(args, "->") {
						for i, p := range router.Params {
							if p.Name == name {
								router.Params[i].Name = value
							}
						}
					}
				}
				sort.Slice(router.Path, func(i, j int) bool {
					return router.Path[i] < router.Path[j]
				})
			}
			if router.Path != nil {
				routers = append(routers, router)
			} else {
				println(decl.Name.Name)
			}
		}
	}

	sort.Slice(routers, func(i, j int) bool {
		return routers[i].Path[0] < routers[j].Path[0]
	})

	out := new(bytes.Buffer)
	g := &generator{out: out}
	g.generate(routers)
	source, err := format.Source(out.Bytes())
	if err != nil {
		panic(err)
	}
	err = os.WriteFile("api.go", source, 0o644)
	if err != nil {
		panic(err)
	}
}

func unquote(s string) string {
	switch s[0] {
	case '"':
		s, _ = strconv.Unquote(s)
	case '`':
		s = strings.Trim(s, "`")
	}
	return s
}

func parseMap(input string, sep string) map[string]string {
	out := make(map[string]string)
	for _, arg := range strings.Split(input, ",") {
		k, v, ok := cut(arg, sep)
		if !ok {
			out[k] = "true"
		}
		k = strings.TrimSpace(k)
		v = unquote(strings.TrimSpace(v))
		out[k] = v
	}
	return out
}

func match(text string) (string, string) {
	text = strings.TrimPrefix(text, "//")
	text = strings.TrimSpace(text)
	if !strings.HasPrefix(text, "@") || !strings.HasSuffix(text, ")") {
		return "", ""
	}
	text = strings.Trim(text, "@)")
	cmd, args, ok := cut(text, "(")
	if !ok {
		return "", ""
	}
	return cmd, unquote(args)
}

func cut(s, sep string) (before, after string, found bool) {
	if i := strings.Index(s, sep); i >= 0 {
		return s[:i], s[i+len(sep):], true
	}
	return s, "", false
}

// some abbreviations need translation before transforming ro snake case
var replacer = strings.NewReplacer("ID", "Id")

func snakecase(s string) string {
	s = replacer.Replace(s)
	t := make([]byte, 0, 32)
	for i := 0; i < len(s); i++ {
		c := s[i]
		if ('a' <= c && c <= 'z') || ('0' <= c && c <= '9') {
			t = append(t, c)
		} else {
			t = append(t, '_')
			t = append(t, c^0x20)
		}
	}
	return string(t)
}

func convDefault(s string, t string) string {
	switch t {
	case "bool":
		if s == "true" {
			return s
		}
	case "uint32":
		if s != "0" {
			return t + "(" + s + ")"
		}
	default:
		panic("unhandled default value type:" + t)
	}
	return ""
}