// Package page implements the website backed by a local filesystem.
//
// Reading the base template off the disk, then any markdown files which are
// split into two sections by the DocumentSplit global variable.  The first
// section is parsed as yaml to populate the Page struct.  The second portion is
// markdown, first executed as part of the text/template then rendered by
// blackfriday.
//
// This package is designed to only be run with ***TRUSTED INPUT***
//
// Usage:
//
//	import (
//		"fmt"
//		"os"
//		site "riedstra.dev/mitch/go-website/page"
//	)
//	// Where some/path.md exists
//	p := site.NewPage("/some/path")
//	// Dump the rendered HTML to stdout
//	err := p.Render(os.Stdout)
//	if err != nil {
//		fmt.Fprintln(os.Stderr, err)
//	}
package page

import (
	"bufio"
	"bytes"
	"errors"
	"fmt"
	"io"
	"log"
	"os"
	"path/filepath"
	"text/template"

	"github.com/russross/blackfriday"
	"gopkg.in/yaml.v3"
)

// Page should not be created directly as it will not set the interal path
// properly. Use NewPage instead.
//
// The exported fields can be filled in the yaml at the top of a page and
// utilized within.
type Page struct {
	path               string
	DefaultTitle       string `yaml:"title"`
	DefaultDescription string `yaml:"description"`
	AuthorName         string
	AuthorEmail        string
	// Tags to apply to the page in question. Useful for Index()
	Tags      map[string]interface{}
	Date      *PageTime
	Published bool
	Vars      map[string]interface{}
	// Keys of vars to be included when RenderJson is called, all vars are
	// omitted if empty.
	JsonVars []string
	markdown []byte
}

// Global is meant to be supplied by external users of this package to populate
// globally accessible information across all of the templates accessiable via
// .Global care must be taken when utilizing this functionality.
var Global interface{}

// Funcs accessible to the templates.
var Funcs template.FuncMap

// CacheIndex determines whether or not the index will be cached in memory
// or rebuilt on each call.
var CacheIndex = true

// TemplateDirectory is the parent directory which templates are stored,
// usually the BaseTemplate is stored here as well, though it does not
// have to be. Currently this is used for the 4xx and 5xx pages. ( 4xx.md
// and 5xx.md respectively.
var TemplateDirectory = "tpl"

// BaseTemplate can be adjusted to change the base template used in rendering.
var BaseTemplate = "tpl/base.md"

// Suffix is applied to all pages for reading off of the disk.
var Suffix = ".md"

// DocumentSplit is used to split the .md files into yaml and markdown.
var DocumentSplit = "|---\n"

// Logger is the default logger used throughout this package, feel
// free to override.
var Logger = log.New(os.Stderr, "PAGE: ", log.LstdFlags)

// NewPage returns a page struct with the path populated.
func NewPage(pth string) *Page {
	return &Page{path: filepath.FromSlash(filepath.Clean(pth))}
}

// NewPage Allow for the creation of a new page from the current page, does
// not inlcude any information about the current page.
func (p Page) NewPage(pth string) *Page {
	return NewPage(pth)
}

// Path gets the current path set on the struct for the page in question
// Useful if you're say iterating across tags to print out a list of
// relevant posts on a blog or so by topic.
func (p Page) Path() string {
	return filepath.ToSlash(p.path)
}

// Title returns `DefaultTitle` unless `.Vars.Title` is
// set, then it returns that instead.
func (p Page) Title() string {
	if p.Vars == nil {
		return p.DefaultTitle
	}

	t, ok := p.Vars["Title"]
	if !ok {
		return p.DefaultTitle
	}

	nt, ok := t.(string)
	if !ok {
		return p.DefaultTitle
	}

	return nt
}

// Description returns `DefaultDescription` unless `.Vars.Description` is
// set, then it returns that instead.
func (p Page) Description() string {
	if p.Vars == nil {
		return p.DefaultDescription
	}

	t, ok := p.Vars["Description"]
	if !ok {
		return p.DefaultDescription
	}

	nt, ok := t.(string)
	if !ok {
		return p.DefaultDescription
	}

	return nt
}

// Global is specifically for use inside of a page markdown file or
// in a base template. This simply returns the package Global variable.
func (p *Page) Global() interface{} {
	return Global
}

// Render a page.
func (p *Page) Render(wr io.Writer) error {
	if err := p.Read(); err != nil {
		return err
	}

	templateContent, err := os.ReadFile(BaseTemplate)
	if err != nil {
		return fmt.Errorf("reading base template: %w", err)
	}

	t, err := template.New("baseTemplate").Funcs(Funcs).Parse(string(templateContent))
	if err != nil {
		return fmt.Errorf("parsing: %w", err)
	}

	t = t.Funcs(Funcs)

	return t.Execute(wr, p)
}

// Read in the special markdown file format for the website off of the disk.
func (p *Page) Read() error {
	yamlBuf := bytes.NewBuffer(nil)
	markdownBuf := bytes.NewBuffer(nil)

	fh, err := os.Open(p.path + Suffix)
	if err != nil {
		return fmt.Errorf("opening markdown: %w", err)
	}

	defer func() {
		err := fh.Close()
		if err != nil {
			Logger.Println(err)
		}
	}()

	rdr := bufio.NewReader(fh)

	// Read in the file and split between markdown and yaml buffers
	yamlDone := false

	for {
		bytes, err := rdr.ReadBytes('\n')
		if errors.Is(err, io.EOF) {
			break
		} else if err != nil {
			return fmt.Errorf("reading markdown: %w", err)
		}

		// Is this the line where we stop reading the yaml and start reading markdown?
		if DocumentSplit == string(bytes) && !yamlDone {
			yamlDone = true

			continue
		}

		if !yamlDone {
			yamlBuf.Write(bytes)
		} else {
			markdownBuf.Write(bytes)
		}
	}

	err = yaml.Unmarshal(yamlBuf.Bytes(), p)
	if err != nil {
		return fmt.Errorf("reading yaml: %w", err)
	}

	p.markdown = markdownBuf.Bytes()

	return nil
}

// RenderBody renders and executes a template from the body of the
// markdown file, then runs it through the markdown parser. Typically
// this is called in the base template.
func (p *Page) RenderBody() (string, error) {
	s, err := p.GetMarkdown()
	return string(blackfriday.Run([]byte(s))), err
}

// GetMarkdown renders and executes a template from the body of the
// markdown file, then simply returns the unrendered markdown.
func (p *Page) GetMarkdown() (string, error) {
	buf := &bytes.Buffer{}

	t, err := template.New("Body").Funcs(Funcs).Parse(string(p.markdown))
	if err != nil {
		return "", fmt.Errorf("render body: %w", err)
	}

	err = t.Execute(buf, p)

	if err != nil {
		return "", fmt.Errorf("template execute; %w", err)
	}

	return buf.String(), nil
}

func (p Page) String() string {
	return fmt.Sprintf("Page: %s", p.path)
}