package main

import (
	"bufio"
	"bytes"
	"fmt"
	"go/format"
	"io/ioutil"
	"log"
	"os"
	"strings"
)

const (
	inputPath   = "elements.txt"
	outputPath  = "elements.go"
	packageName = "hatmill"

	parentType = "parent"
	emptyType  = "empty"

	parentTemplate = `func %s(attribs ...Attrib) func(children ...Term) *ParentElement {
        return func(children ...Term) *ParentElement {
            return &ParentElement{
    			EmptyElement: EmptyElement{
    				TagName: "%s",
    				Attribs: attribs,
    			},
    			Children: children,
    		}
        }
    }
    `
	emptyTemplate = `func %s(attribs ...Attrib) EmptyElement {
        return EmptyElement{
			TagName: "%s",
			Attribs: attribs,
		}
    }
    `
)

func main() {
	inputFile, err := os.Open(inputPath)
	if err != nil {
		log.Fatal(err)
	}
	defer inputFile.Close()

	var output bytes.Buffer

	fmt.Fprintln(&output, "// GENERATED BY gitlab.codemonkeysoftware.net/b/hatmill/internal/elementgen")
	fmt.Fprintln(&output, "// DO NOT EDIT!\n")
	fmt.Fprintln(&output, "package ", packageName, "\n")

	scanner := bufio.NewScanner(inputFile)
	for scanner.Scan() {
		line := scanner.Text()
		if line == "" {
			continue
		}

		var tagName, elemType string
		_, err = fmt.Sscanf(line, "%s %s", &tagName, &elemType)
		if err != nil {
			log.Fatalf("error parsing input line: %s", err)
		}

		var template string
		switch elemType {
		case parentType:
			template = parentTemplate
		case emptyType:
			template = emptyTemplate
		default:
			log.Fatal("unknown element type: ", elemType)
		}
		fmt.Fprintf(&output, template, strings.Title(tagName), tagName)
	}
	if err := scanner.Err(); err != nil {
		log.Fatalf("error scanning input: %s", err)
	}

	formatted, err := format.Source(output.Bytes())
	if err != nil {
		log.Fatalf("error formatting output: %s", err)
	}

	err = ioutil.WriteFile(outputPath, formatted, 0644)
	if err != nil {
		log.Fatalf("error writing output: %s", err)
	}
}