// Copyright 2019 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 rst converts content to HTML using the RST external helper.
package rst

import (
	"bytes"
	"os/exec"
	"runtime"

	"github.com/gohugoio/hugo/markup/internal"

	"github.com/gohugoio/hugo/markup/converter"
)

// Provider is the package entry point.
var Provider converter.ProviderProvider = provider{}

type provider struct {
}

func (p provider) New(cfg converter.ProviderConfig) (converter.Provider, error) {
	return converter.NewProvider("rst", func(ctx converter.DocumentContext) (converter.Converter, error) {
		return &rstConverter{
			ctx: ctx,
			cfg: cfg,
		}, nil
	}), nil
}

type rstConverter struct {
	ctx converter.DocumentContext
	cfg converter.ProviderConfig
}

func (c *rstConverter) Convert(ctx converter.RenderContext) (converter.Result, error) {
	return converter.Bytes(c.getRstContent(ctx.Src, c.ctx)), nil
}

// getRstContent calls the Python script rst2html as an external helper
// to convert reStructuredText content to HTML.
func (c *rstConverter) getRstContent(src []byte, ctx converter.DocumentContext) []byte {
	logger := c.cfg.Logger
	path := getRstExecPath()

	if path == "" {
		logger.ERROR.Println("rst2html / rst2html.py not found in $PATH: Please install.\n",
			"                 Leaving reStructuredText content unrendered.")
		return src
	}
	logger.INFO.Println("Rendering", ctx.DocumentName, "with", path, "...")
	var result []byte
	// certain *nix based OSs wrap executables in scripted launchers
	// invoking binaries on these OSs via python interpreter causes SyntaxError
	// invoke directly so that shebangs work as expected
	// handle Windows manually because it doesn't do shebangs
	if runtime.GOOS == "windows" {
		python := internal.GetPythonExecPath()
		args := []string{path, "--leave-comments", "--initial-header-level=2"}
		result = internal.ExternallyRenderContent(c.cfg, ctx, src, python, args)
	} else {
		args := []string{"--leave-comments", "--initial-header-level=2"}
		result = internal.ExternallyRenderContent(c.cfg, ctx, src, path, args)
	}
	// TODO(bep) check if rst2html has a body only option.
	bodyStart := bytes.Index(result, []byte("<body>\n"))
	if bodyStart < 0 {
		bodyStart = -7 //compensate for length
	}

	bodyEnd := bytes.Index(result, []byte("\n</body>"))
	if bodyEnd < 0 || bodyEnd >= len(result) {
		bodyEnd = len(result) - 1
		if bodyEnd < 0 {
			bodyEnd = 0
		}
	}

	return result[bodyStart+7 : bodyEnd]
}

func getRstExecPath() string {
	path, err := exec.LookPath("rst2html")
	if err != nil {
		path, err = exec.LookPath("rst2html.py")
		if err != nil {
			return ""
		}
	}
	return path
}

// Supports returns whether rst is installed on this computer.
func Supports() bool {
	return getRstExecPath() != ""
}
