package multi

import (
	"io"
	"os"

	"github.com/CloudyKit/jet/v6"
)

var _ jet.Loader = (*Multi)(nil)

// Multi implements jet.Loader interface and tries to load templates from a list of custom loaders.
// Caution: When multiple loaders have templates with the same name, the order in which you pass loaders
// to NewLoader/AddLoaders dictates which template will be returned by Open when you request it!
type Multi struct {
	loaders []jet.Loader
}

// NewLoader returns a new multi loader. The order of the loaders passed as parameters
// will define the order in which templates are loaded.
func NewLoader(loaders ...jet.Loader) *Multi {
	return &Multi{loaders: loaders}
}

// AddLoaders adds the passed loaders to the list of loaders.
func (m *Multi) AddLoaders(loaders ...jet.Loader) {
	m.loaders = append(m.loaders, loaders...)
}

// ClearLoaders clears the list of loaders.
func (m *Multi) ClearLoaders() {
	m.loaders = nil
}

// Open will open the file passed by trying all loaders in succession.
func (m *Multi) Open(name string) (io.ReadCloser, error) {
	for _, loader := range m.loaders {
		if f, err := loader.Open(name); err == nil {
			return f, nil
		}
	}
	return nil, &os.PathError{Op: "open", Path: name, Err: os.ErrNotExist}
}

// Exists checks all loaders in succession, returning true if the template file was found or false
// if no loader can provide the file.
func (m *Multi) Exists(name string) bool {
	for _, loader := range m.loaders {
		if ok := loader.Exists(name); ok {
			return true
		}
	}
	return false
}