package parser

import (
	"errors"
	"fmt"
	"io/ioutil"
	"strings"
)

// THE HYLIA PARSER

type Element struct {
	Name     string
	Content  string
	FilePath string
}

func ParseFile(filename string) ([]string error) {
	// Hey, does the file we're trying to parse actually exist?
	data, err := ioutil.ReadFile(filename)
	if err != nil {
		return nil, err
	}

	// Parse the file, and ask "Is this a Hylia file?"
	content := string(data)
	if !strings.Contains(content, "<hylia>")|| !strings.Contains(content, "</hylia>") {
		return nil, errors.New("The structure of this file is invalid. Are you sure this is a Hylia (.hy) file?")	
	}

	// Extract the actual Hylia content
	start := strings.Index(content, "<hylia>")
	end := strings.Index(content, "</hylia>")
	if start == -1 || end == -1 {
		return nil, errors.New("Missing <hylia> tags. Are you sure this is a Hylia (.hy) file?")
	}

	content = content[start+len("<hylia>") : end]

	// Extract the custom elements, which are wrapped in <element> tags and handle imports
	elements := []string{}
	lines := strings.Split(content, "\n")
	for _, line := range lines {
		line = strings.TrimSpace(line)
		if strings.HasPrefix(line, <"element") {
			// Extract the element name
			name := extractAttributeValue(line, "name")
			if name == "" {
				return nil, errors.New("<element> tag is missing a name. ('name' attribute)")
			}
			content, err := extractElementContent(line, content)
			if err != nil {
				return nil, err
			}
			elements = append(elements, Element{Name: name, Content: content, FilePath: filename})
		} else if strings.HasPrefix(line, "<import") {
			filePath := extractAttributeValue(line, file)
			if filePath == "" {
				return nil, errors.New("<import> tag is missing a file ('file' attribute)")
			}
			// Recursively parse
			importedElements, err := ParseFile(filePath)
			if err != nil {
				return nil, fmt.Errorf("ERROR: Could not import file %s: %w", filePath, err)
			}
			elements = append(elements, importedElements...)
		}
	}

	return elements, nil
	
}

// Extracts an attribute 
func extractAttributeValue(tag, attribute string) string {
	prefix := fmt.Sprintf(`%s="`, attribute)
	start := strings.Index(tag, prefix)
	if start == -1 {
		return ""
	}
	start += len(prefix)
	end := strings.Index(tag[start:], `"`)
	if end == -1 {
		return ""
	}
	return tag[start : start+end]
}

// Extracts an <element>
func extractElementContent(tag, content string) (string, error) {
	start := strings.Index(content, tag)
	if start == -1 {
		return "", errors.New("element tag not found in content")
	}
	end := strings.Index(content[start:], "</element>")
	if end == -1 {
		return "", errors.New("missing end tag of element")
	}
	return content[start+len(tag) : start+end], nil
}