// Copyright 2018 The Hugo Authors. All rights reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

// Package templates contains functions for template processing of Resource objects.
package templates

import (
	"fmt"

	"github.com/gohugoio/hugo/helpers"
	"github.com/gohugoio/hugo/resource"
	"github.com/gohugoio/hugo/tpl"
)

// Client contains methods to perform template processing of Resource objects.
type Client struct {
	rs *resource.Spec

	textTemplate tpl.TemplateParseFinder
}

// New creates a new Client with the given specification.
func New(rs *resource.Spec, textTemplate tpl.TemplateParseFinder) *Client {
	if rs == nil {
		panic("must provice a resource Spec")
	}
	if textTemplate == nil {
		panic("must provide a textTemplate")
	}
	return &Client{rs: rs, textTemplate: textTemplate}
}

type executeAsTemplateTransform struct {
	rs           *resource.Spec
	textTemplate tpl.TemplateParseFinder
	targetPath   string
	data         interface{}
}

func (t *executeAsTemplateTransform) Key() resource.ResourceTransformationKey {
	return resource.NewResourceTransformationKey("execute-as-template", t.targetPath)
}

func (t *executeAsTemplateTransform) Transform(ctx *resource.ResourceTransformationCtx) error {
	tplStr := helpers.ReaderToString(ctx.From)
	templ, err := t.textTemplate.Parse(ctx.InPath, tplStr)
	if err != nil {
		return fmt.Errorf("failed to parse Resource %q as Template: %s", ctx.InPath, err)
	}

	ctx.OutPath = t.targetPath

	return templ.Execute(ctx.To, t.data)
}

func (c *Client) ExecuteAsTemplate(res resource.Resource, targetPath string, data interface{}) (resource.Resource, error) {
	return c.rs.Transform(
		res,
		&executeAsTemplateTransform{
			rs:           c.rs,
			targetPath:   helpers.ToSlashTrimLeading(targetPath),
			textTemplate: c.textTemplate,
			data:         data,
		},
	)
}