package main

import (
	"bytes"
	"encoding/json"
	"flag"
	"fmt"
	"go/format"
	"io/ioutil"
	"log"
	"strings"
)

func identifier(s string) string {
	words := strings.Split(s, "-")
	for i, word := range words {
		words[i] = strings.Title(word)
	}
	return strings.Join(words, "")
}

func formatComment(s string) string {
	return "// " + strings.TrimSpace(s) + "\n"
}

type AttribTypeInfo struct {
	Template string
	Imports  []string
}

func simpleTemplate(paramType, convertExpr string) string {
	conversion := fmt.Sprintf(convertExpr, "value")
	return fmt.Sprintf(`func %%s(value %s) hatmill.Attrib {
		return hatmill.Attrib{
			Key: "%%s",
			Value: %s,
		}
	}
	`, paramType, conversion)
}

var attribTypes = map[string]AttribTypeInfo{
	"string": {Template: simpleTemplate("string", "%s")},
	"bool": {
		Template: `func %s() hatmill.Attrib {
			return hatmill.Attrib{
				Key: "%s",
			}
		}
		`,
	},
	"explicit bool": {
		Template: simpleTemplate("bool", "strconv.FormatBool(%s)"),
		Imports:  []string{"strconv"},
	},
	"int": {
		Template: simpleTemplate("int", "strconv.FormatInt(int64(%s), 10)"),
		Imports:  []string{"strconv"},
	},
	"float": {
		Template: simpleTemplate("float32", "strconv.FormatFloat(float64(%s), 'G', -1, 32)"),
		Imports:  []string{"strconv"},
	},
}

// Def represents a top-level definition and its required imports.
type Def struct {
	Source  string
	Imports []string
}

type Spec interface {
	Generate() Def
}

type AttribSpec struct {
	Name    string `json:"name"`
	Type    string `json:"type"`
	Comment string `json:"comment"`
}

func (spec AttribSpec) Generate() Def {
	name := spec.Name
	ident := identifier(spec.Name)
	var comment string
	if spec.Comment != "" {
		comment = spec.Comment
	} else {
		comment = fmt.Sprintf("%s creates a \"%s\" attribute", ident, name)
	}
	template := attribTypes[spec.Type].Template
	return Def{
		Source:  formatComment(comment) + fmt.Sprintf(template, ident, name),
		Imports: attribTypes[spec.Type].Imports,
	}
}

type ElemSpec struct {
	Name    string `json:"name"`
	Void    bool   `json:"void"`
	Comment string `json:"comment"`
}

func (spec ElemSpec) Generate() Def {
	const (
		parentTemplate = `func %s(attribs ...hatmill.Attrib) func(children ...hatmill.Term) hatmill.ParentElement {
            return func(children ...hatmill.Term) hatmill.ParentElement {
                return hatmill.ParentElement{
                    VoidElement: hatmill.VoidElement{
                        TagName: "%s",
                        Attribs: attribs,
                    },
                    Children: children,
                }
            }
        }
        `
		voidTemplate = `func %s(attribs ...hatmill.Attrib) hatmill.VoidElement {
            return hatmill.VoidElement{
                TagName: "%s",
                Attribs: attribs,
            }
        }
        `
	)

	name := spec.Name
	ident := identifier(spec.Name)
	var comment string
	if spec.Comment != "" {
		comment = spec.Comment
	} else {
		comment = fmt.Sprintf("%s creates a <%s> element.", ident, name)
	}
	template := parentTemplate
	if spec.Void {
		template = voidTemplate
	}
	return Def{
		Source: formatComment(comment) + fmt.Sprintf(template, ident, name),
	}
}

func Render(defs []Def, pkgName string) ([]byte, error) {
	buf := new(bytes.Buffer)
	buf.WriteString(`// GENERATED BY gitlab.codemonkeysoftware.net/b/hatmill/internal/codegen
	// DO NOT EDIT!

	`)
	fmt.Fprintln(buf, "package ", pkgName)
	buf.WriteString(`import "gitlab.codemonkeysoftware.net/b/hatmill"
	`)

	// Print each import only once.
	imports := make(map[string]struct{})
	for _, def := range defs {
		for _, imp := range def.Imports {
			imports[imp] = struct{}{}
		}
	}
	for imp := range imports {
		fmt.Fprintf(buf, "import \"%s\"\n", imp)
	}

	for _, def := range defs {
		buf.WriteString(def.Source)
	}

	formatted, err := format.Source(buf.Bytes())
	if err != nil {
		err = fmt.Errorf("generated invalid code: %s\nSource code:\n%s", err, buf)
	}
	return formatted, err
}

func WriteCodeFile(specs []Spec, path, pkgName string) error {
	var defs []Def
	for _, spec := range specs {
		defs = append(defs, spec.Generate())
	}
	b, err := Render(defs, pkgName)
	if err != nil {
		return err
	}
	return ioutil.WriteFile(path, b, 0644)
}

func main() {
	inputPath := flag.String("input", "", "JSON input file")
	elemPath := flag.String("elemfile", "", "generated element .go file")
	elemPkg := flag.String("elempkg", "", "generated element package name")
	attribPath := flag.String("attribfile", "", "generated attribute .go file")
	attribPkg := flag.String("attribpkg", "", "generated attribute package name")
	flag.Parse()

	input, err := ioutil.ReadFile(*inputPath)
	if err != nil {
		log.Fatal(err)
	}

	var specs struct {
		AttribSpecs []AttribSpec `json:"attributes"`
		ElemSpecs   []ElemSpec   `json:"elements"`
	}

	err = json.Unmarshal(input, &specs)
	if err != nil {
		log.Fatal(err)
	}

	var attribSpecs []Spec
	for _, spec := range specs.AttribSpecs {
		attribSpecs = append(attribSpecs, spec)
	}
	err = WriteCodeFile(attribSpecs, *attribPath, *attribPkg)
	if err != nil {
		log.Fatal(err)
	}

	var elemSpecs []Spec
	for _, spec := range specs.ElemSpecs {
		elemSpecs = append(elemSpecs, spec)
	}
	err = WriteCodeFile(elemSpecs, *elemPath, *elemPkg)
	if err != nil {
		log.Fatal(err)
	}

}