// Copyright 2014 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.

// +build ignore

// The gendebug program takes gl.go and generates a version of it
// where each function includes tracing code that writes its arguments
// to the standard log.
package main

import (
	"bytes"
	"flag"
	"fmt"
	"go/ast"
	"go/format"
	"go/parser"
	"go/printer"
	"go/token"
	"io/ioutil"
	"log"
	"os"
	"strconv"
)

var outfile = flag.String("o", "", "result will be written to the file instead of stdout.")

var fset = new(token.FileSet)

func typeString(t ast.Expr) string {
	buf := new(bytes.Buffer)
	printer.Fprint(buf, fset, t)
	return buf.String()
}

func typePrinter(t string) string {
	switch t {
	case "[]float32", "[]byte":
		return "len(%d)"
	}
	return "%v"
}

func typePrinterArg(t, name string) string {
	switch t {
	case "[]float32", "[]byte":
		return "len(" + name + ")"
	}
	return name
}

func die(err error) {
	fmt.Fprintf(os.Stderr, err.Error())
	os.Exit(1)
}

func main() {
	flag.Parse()

	f, err := parser.ParseFile(fset, "consts.go", nil, parser.ParseComments)
	if err != nil {
		die(err)
	}
	entries := enum(f)

	f, err = parser.ParseFile(fset, "gl.go", nil, parser.ParseComments)
	if err != nil {
		die(err)
	}

	buf := new(bytes.Buffer)

	fmt.Fprint(buf, preamble)

	fmt.Fprintf(buf, "func (v Enum) String() string {\n")
	fmt.Fprintf(buf, "\tswitch v {\n")
	for _, e := range dedup(entries) {
		fmt.Fprintf(buf, "\tcase 0x%x: return %q\n", e.value, e.name)
	}
	fmt.Fprintf(buf, "\t%s\n", `default: return fmt.Sprintf("gl.Enum(0x%x)", uint32(v))`)
	fmt.Fprintf(buf, "\t}\n")
	fmt.Fprintf(buf, "}\n\n")

	for _, d := range f.Decls {
		// Before:
		// func StencilMask(mask uint32) {
		//	C.glStencilMask(C.GLuint(mask))
		// }
		//
		// After:
		// func StencilMask(mask uint32) {
		// 	defer func() {
		// 		errstr := errDrain()
		// 		log.Printf("gl.StencilMask(%v) %v", mask, errstr)
		//	}()
		//	C.glStencilMask(C.GLuint(mask))
		// }
		fn, ok := d.(*ast.FuncDecl)
		if !ok {
			continue
		}
		if fn.Recv != nil {
			continue
		}

		var (
			params      []string
			paramTypes  []string
			results     []string
			resultTypes []string
		)

		// Print function signature.
		fmt.Fprintf(buf, "func %s(", fn.Name.Name)
		for i, p := range fn.Type.Params.List {
			if i > 0 {
				fmt.Fprint(buf, ", ")
			}
			ty := typeString(p.Type)
			for i, n := range p.Names {
				if i > 0 {
					fmt.Fprint(buf, ", ")
				}
				fmt.Fprintf(buf, "%s ", n.Name)
				params = append(params, n.Name)
				paramTypes = append(paramTypes, ty)
			}
			fmt.Fprint(buf, ty)
		}
		fmt.Fprintf(buf, ") (")
		if fn.Type.Results != nil {
			for i, r := range fn.Type.Results.List {
				if i > 0 {
					fmt.Fprint(buf, ", ")
				}
				ty := typeString(r.Type)
				if len(r.Names) == 0 {
					name := fmt.Sprintf("r%d", i)
					fmt.Fprintf(buf, "%s ", name)
					results = append(results, name)
					resultTypes = append(resultTypes, ty)
				}
				for i, n := range r.Names {
					if i > 0 {
						fmt.Fprint(buf, ", ")
					}
					fmt.Fprintf(buf, "%s ", n.Name)
					results = append(results, n.Name)
					resultTypes = append(resultTypes, ty)
				}
				fmt.Fprint(buf, ty)
			}
		}
		fmt.Fprintf(buf, ") {\n")

		// gl.GetError is used by errDrain, which will be made part of
		// all functions. So do not apply it to gl.GetError to avoid
		// infinite recursion.
		skip := fn.Name.Name == "GetError"

		if !skip {
			// Insert a defer block for tracing.
			fmt.Fprintf(buf, "defer func() {\n")
			fmt.Fprintf(buf, "\terrstr := errDrain()\n")
			switch fn.Name.Name {
			case "GetUniformLocation", "GetAttribLocation":
				fmt.Fprintf(buf, "\tr0.name = name\n")
			}
			fmt.Fprintf(buf, "\tlog.Printf(\"gl.%s(", fn.Name.Name)
			for i, p := range paramTypes {
				if i > 0 {
					fmt.Fprint(buf, ", ")
				}
				fmt.Fprint(buf, typePrinter(p))
			}
			fmt.Fprintf(buf, ") ")
			if len(resultTypes) > 1 {
				fmt.Fprint(buf, "(")
			}
			for i, r := range resultTypes {
				if i > 0 {
					fmt.Fprint(buf, ", ")
				}
				fmt.Fprint(buf, typePrinter(r))
			}
			if len(resultTypes) > 1 {
				fmt.Fprint(buf, ") ")
			}
			fmt.Fprintf(buf, "%%v\"")
			for i, p := range paramTypes {
				fmt.Fprintf(buf, ", %s", typePrinterArg(p, params[i]))
			}
			for i, r := range resultTypes {
				fmt.Fprintf(buf, ", %s", typePrinterArg(r, results[i]))
			}
			fmt.Fprintf(buf, ", errstr)\n")
			fmt.Fprintf(buf, "}()\n")
		}

		// Print original body of function.
		for _, s := range fn.Body.List {
			printer.Fprint(buf, fset, s)
			fmt.Fprintf(buf, "\n")
		}
		fmt.Fprintf(buf, "}\n\n")
	}

	b, err := format.Source(buf.Bytes())
	if err != nil {
		os.Stdout.Write(buf.Bytes())
		die(err)
	}

	if *outfile == "" {
		os.Stdout.Write(b)
		return
	}
	if err := ioutil.WriteFile(*outfile, b, 0666); err != nil {
		die(err)
	}
}

const preamble = `// Copyright 2014 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.

// Generated from gl.go using go generate. DO NOT EDIT.
// See doc.go for details.

// +build linux darwin
// +build gldebug

package gl

// #include "work.h"
import "C"

import (
	"fmt"
	"log"
	"math"
	"unsafe"
)

func errDrain() string {
	var errs []Enum
	for {
		e := GetError()
		if e == 0 {
			break
		}
		errs = append(errs, e)
	}
	if len(errs) > 0 {
		return fmt.Sprintf(" error: %v", errs)
	}
	return ""
}

`

type entry struct {
	name  string
	value int
}

// enum builds a list of all GL constants that make up the gl.Enum type.
func enum(f *ast.File) []entry {
	var entries []entry
	for _, d := range f.Decls {
		gendecl, ok := d.(*ast.GenDecl)
		if !ok {
			continue
		}
		if gendecl.Tok != token.CONST {
			continue
		}
		for _, s := range gendecl.Specs {
			v, ok := s.(*ast.ValueSpec)
			if !ok {
				continue
			}
			if len(v.Names) != 1 || len(v.Values) != 1 {
				continue
			}
			val, err := strconv.ParseInt(v.Values[0].(*ast.BasicLit).Value, 0, 32)
			if err != nil {
				log.Fatalf("enum %s: %v", v.Names[0].Name, err)
			}
			entries = append(entries, entry{v.Names[0].Name, int(val)})
		}
	}
	return entries
}

func dedup(entries []entry) []entry {
	// Find all duplicates. Use "%d" as the name of any value with duplicates.
	seen := make(map[int]int)
	for _, e := range entries {
		seen[e.value]++
	}
	var dedup []entry
	for _, e := range entries {
		switch seen[e.value] {
		case 0: // skip, already here
		case 1:
			dedup = append(dedup, e)
		default:
			// value is duplicated
			dedup = append(dedup, entry{fmt.Sprintf("%d", e.value), e.value})
			seen[e.value] = 0
		}
	}
	return dedup
}