templating/render/render.go

package render

import (
	"context"
	"errors"
	"fmt"
	"io"
)

var ErrNotFound = errors.New("not found")

func New(parser Parser, engines ...Engine) *Render {
	return &Render{
		parser:  parser,
		engines: engines,
	}
}

type Render struct {
	engines []Engine
	parser  Parser
}

type Execute func(ctx context.Context, wr io.Writer, data interface{}, params Params) error

type Engine interface {
	Support(context.Context, Reference) bool
	Load(ctx context.Context, reference Reference) (Execute, error)
}

type Parser func(ctx context.Context, name string, opts ...Option) (Reference, error)

// Add add engine. This function is not thread-safe.
func (e *Render) Add(engine ...Engine) {
	e.engines = append(e.engines, engine...)
}

func (e *Render) WithParser(parser Parser) *Render {
	return New(parser, e.engines...)
}

func (e *Render) Load(ctx context.Context, reference Reference) (Execute, error) {
	for _, engine := range e.engines {
		if engine.Support(ctx, reference) {
			exec, err := engine.Load(ctx, reference)
			if err != nil {
				return nil, fmt.Errorf("render load:%w", err)
			}

			return exec, nil
		}
	}

	return nil, fmt.Errorf("loader:%w", ErrNotFound)
}

func (e *Render) Parse(ctx context.Context, name string, opts ...Option) (Reference, error) {
	return e.parser(ctx, name, opts...)
}

func (e *Render) Execute(ctx context.Context, wr io.Writer, name string, data interface{}, opts ...Option) error {
	reference, rerr := e.parser(ctx, name, opts...)
	if rerr != nil {
		return fmt.Errorf("parse: %w", rerr)
	}

	execute, err := e.Load(ctx, reference)
	if err != nil {
		return fmt.Errorf("engine load:%w", err)
	}

	if err := execute(ctx, wr, data, reference.Params); err != nil {
		return fmt.Errorf("render execute:%w", err)
	}

	return nil
}