// Copyright 2020 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 asciidocext converts AsciiDoc to HTML using Asciidoctor
// external binary. The `asciidoc` module is reserved for a future golang
// implementation.
package asciidocext

import (
	"bytes"
	"os/exec"
	"path/filepath"

	"github.com/gohugoio/hugo/identity"
	"github.com/gohugoio/hugo/markup/asciidocext/asciidocext_config"
	"github.com/gohugoio/hugo/markup/converter"
	"github.com/gohugoio/hugo/markup/internal"
	"github.com/gohugoio/hugo/markup/tableofcontents"
	"golang.org/x/net/html"
)

/* ToDo: RelPermalink patch for svg posts not working*/
type pageSubset interface {
	RelPermalink() string
}

// 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("asciidocext", func(ctx converter.DocumentContext) (converter.Converter, error) {
		return &asciidocConverter{
			ctx: ctx,
			cfg: cfg,
		}, nil
	}), nil
}

type asciidocResult struct {
	converter.Result
	toc tableofcontents.Root
}

func (r asciidocResult) TableOfContents() tableofcontents.Root {
	return r.toc
}

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

func (a *asciidocConverter) Convert(ctx converter.RenderContext) (converter.Result, error) {
	content, toc, err := a.extractTOC(a.getAsciidocContent(ctx.Src, a.ctx))
	if err != nil {
		return nil, err
	}
	return asciidocResult{
		Result: converter.Bytes(content),
		toc:    toc,
	}, nil
}

func (a *asciidocConverter) Supports(_ identity.Identity) bool {
	return false
}

// getAsciidocContent calls asciidoctor as an external helper
// to convert AsciiDoc content to HTML.
func (a *asciidocConverter) getAsciidocContent(src []byte, ctx converter.DocumentContext) []byte {
	path := getAsciidoctorExecPath()
	if path == "" {
		a.cfg.Logger.ERROR.Println("asciidoctor not found in $PATH: Please install.\n",
			"                 Leaving AsciiDoc content unrendered.")
		return src
	}

	args := a.parseArgs(ctx)
	args = append(args, "-")

	a.cfg.Logger.INFO.Println("Rendering", ctx.DocumentName, "with", path, "using asciidoctor args", args, "...")

	return internal.ExternallyRenderContent(a.cfg, ctx, src, path, args)
}

func (a *asciidocConverter) parseArgs(ctx converter.DocumentContext) []string {
	var cfg = a.cfg.MarkupConfig.AsciidocExt
	args := []string{}

	args = a.appendArg(args, "-b", cfg.Backend, asciidocext_config.CliDefault.Backend, asciidocext_config.AllowedBackend)

	for _, extension := range cfg.Extensions {
		if !asciidocext_config.AllowedExtensions[extension] {
			a.cfg.Logger.ERROR.Println("Unsupported asciidoctor extension was passed in. Extension `" + extension + "` ignored.")
			continue
		}

		args = append(args, "-r", extension)
	}

	for attributeKey, attributeValue := range cfg.Attributes {
		if asciidocext_config.DisallowedAttributes[attributeKey] {
			a.cfg.Logger.ERROR.Println("Unsupported asciidoctor attribute was passed in. Attribute `" + attributeKey + "` ignored.")
			continue
		}

		args = append(args, "-a", attributeKey+"="+attributeValue)
	}

	if cfg.WorkingFolderCurrent {
		contentDir := filepath.Dir(ctx.Filename)
		sourceDir := a.cfg.Cfg.GetString("source")
		destinationDir := a.cfg.Cfg.GetString("destination")

		if destinationDir == "" {
			a.cfg.Logger.ERROR.Println("markup.asciidocext.workingFolderCurrent requires hugo command option --destination to be set")
		}
		if !filepath.IsAbs(destinationDir) && sourceDir != "" {
			destinationDir = filepath.Join(sourceDir, destinationDir)
		}

		var outDir string
		var err error

		file := filepath.Base(ctx.Filename)
		if a.cfg.Cfg.GetBool("uglyUrls") || file == "_index.adoc" || file == "index.adoc" {
			outDir, err = filepath.Abs(filepath.Dir(filepath.Join(destinationDir, ctx.DocumentName)))

		} else {
			postDir := ""
			page, ok := ctx.Document.(pageSubset)
			if ok {
				postDir = filepath.Base(page.RelPermalink())
			} else {
				a.cfg.Logger.ERROR.Println("unable to cast interface to pageSubset")
			}

			outDir, err = filepath.Abs(filepath.Join(destinationDir, filepath.Dir(ctx.DocumentName), postDir))
		}

		if err != nil {
			a.cfg.Logger.ERROR.Println("asciidoctor outDir: ", err)
		}

		args = append(args, "--base-dir", contentDir, "-a", "outdir="+outDir)
	}

	if cfg.NoHeaderOrFooter {
		args = append(args, "--no-header-footer")
	} else {
		a.cfg.Logger.WARN.Println("asciidoctor parameter NoHeaderOrFooter is expected for correct html rendering")
	}

	if cfg.SectionNumbers {
		args = append(args, "--section-numbers")
	}

	if cfg.Verbose {
		args = append(args, "--verbose")
	}

	if cfg.Trace {
		args = append(args, "--trace")
	}

	args = a.appendArg(args, "--failure-level", cfg.FailureLevel, asciidocext_config.CliDefault.FailureLevel, asciidocext_config.AllowedFailureLevel)

	args = a.appendArg(args, "--safe-mode", cfg.SafeMode, asciidocext_config.CliDefault.SafeMode, asciidocext_config.AllowedSafeMode)

	return args
}

func (a *asciidocConverter) appendArg(args []string, option, value, defaultValue string, allowedValues map[string]bool) []string {
	if value != defaultValue {
		if allowedValues[value] {
			args = append(args, option, value)
		} else {
			a.cfg.Logger.ERROR.Println("Unsupported asciidoctor value `" + value + "` for option " + option + " was passed in and will be ignored.")
		}
	}
	return args
}

func getAsciidoctorExecPath() string {
	path, err := exec.LookPath("asciidoctor")
	if err != nil {
		return ""
	}
	return path
}

// extractTOC extracts the toc from the given src html.
// It returns the html without the TOC, and the TOC data
func (a *asciidocConverter) extractTOC(src []byte) ([]byte, tableofcontents.Root, error) {
	var buf bytes.Buffer
	buf.Write(src)
	node, err := html.Parse(&buf)
	if err != nil {
		return nil, tableofcontents.Root{}, err
	}
	var (
		f       func(*html.Node) bool
		toc     tableofcontents.Root
		toVisit []*html.Node
	)
	f = func(n *html.Node) bool {
		if n.Type == html.ElementNode && n.Data == "div" && attr(n, "id") == "toc" {
			toc = parseTOC(n)
			if !a.cfg.MarkupConfig.AsciidocExt.PreserveTOC {
				n.Parent.RemoveChild(n)
			}
			return true
		}
		if n.FirstChild != nil {
			toVisit = append(toVisit, n.FirstChild)
		}
		if n.NextSibling != nil && f(n.NextSibling) {
			return true
		}
		for len(toVisit) > 0 {
			nv := toVisit[0]
			toVisit = toVisit[1:]
			if f(nv) {
				return true
			}
		}
		return false
	}
	f(node)
	if err != nil {
		return nil, tableofcontents.Root{}, err
	}
	buf.Reset()
	err = html.Render(&buf, node)
	if err != nil {
		return nil, tableofcontents.Root{}, err
	}
	// ltrim <html><head></head><body> and rtrim </body></html> which are added by html.Render
	res := buf.Bytes()[25:]
	res = res[:len(res)-14]
	return res, toc, nil
}

// parseTOC returns a TOC root from the given toc Node
func parseTOC(doc *html.Node) tableofcontents.Root {
	var (
		toc tableofcontents.Root
		f   func(*html.Node, int, int)
	)
	f = func(n *html.Node, row, level int) {
		if n.Type == html.ElementNode {
			switch n.Data {
			case "ul":
				if level == 0 {
					row++
				}
				level++
				f(n.FirstChild, row, level)
			case "li":
				for c := n.FirstChild; c != nil; c = c.NextSibling {
					if c.Type != html.ElementNode || c.Data != "a" {
						continue
					}
					href := attr(c, "href")[1:]
					toc.AddAt(tableofcontents.Header{
						Text: nodeContent(c),
						ID:   href,
					}, row, level)
				}
				f(n.FirstChild, row, level)
			}
		}
		if n.NextSibling != nil {
			f(n.NextSibling, row, level)
		}
	}
	f(doc.FirstChild, -1, 0)
	return toc
}

func attr(node *html.Node, key string) string {
	for _, a := range node.Attr {
		if a.Key == key {
			return a.Val
		}
	}
	return ""
}

func nodeContent(node *html.Node) string {
	var buf bytes.Buffer
	for c := node.FirstChild; c != nil; c = c.NextSibling {
		html.Render(&buf, c)
	}
	return buf.String()
}

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