package parser

import (
	"github.com/a-h/parse"
	"github.com/a-h/templ/parser/v2/goexpression"
)

var callTemplateExpression callTemplateExpressionParser

var callTemplateExpressionStart = parse.Or(parse.String("{! "), parse.String("{!"))

type callTemplateExpressionParser struct{}

func (p callTemplateExpressionParser) Parse(pi *parse.Input) (n Node, ok bool, err error) {
	start := pi.Position()

	// Check the prefix first.
	if _, ok, err = callTemplateExpressionStart.Parse(pi); err != nil || !ok {
		return
	}

	// Once we have a prefix, we must have an expression that returns a template.
	r := &CallTemplateExpression{}
	if r.Expression, err = parseGo("call template expression", pi, goexpression.Expression); err != nil {
		return
	}

	// Eat the final brace.
	if _, ok, err = closeBraceWithOptionalPadding.Parse(pi); err != nil || !ok {
		err = parse.Error("call template expression: missing closing brace", pi.Position())
		return
	}

	r.Range = NewRange(start, pi.Position())

	return r, true, nil
}