// Copyright 2013 The Go Authors.  All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// This is a blog server for articles written in present format.
// It powers blog.golang.org.
package main

import (
	"bytes"
	"html/template"
	"log"
	"net/http"
	"os"
	"path"
	"path/filepath"
	"sort"
	"strings"

	_ "code.google.com/p/go.talks/pkg/playground"
	"code.google.com/p/go.talks/pkg/present"
)

const (
	baseURL      = "http://blog.golang.org"
	homeArticles = 5 // number of articles to display on the home page
)

// Doc represents an article, adorned with presentation data:
// its absolute path and related articles.
type Doc struct {
	*present.Doc
	Permalink    string
	Path         string
	Related      []*Doc
	Newer, Older *Doc
	HTML         template.HTML // rendered article
}

// Server implements an http.Handler that serves blog articles.
type Server struct {
	pathPrefix string
	docs       []*Doc
	tags       []string
	docPaths   map[string]*Doc
	docTags    map[string][]*Doc
	template   struct {
		home, index, article, doc *template.Template
	}
	content http.Handler
}

// NewServer constructs a new Server, serving articles from the specified
// contentPath generated from templates from templatePath, under the prefix
// specified by pathPrefix.
func NewServer(pathPrefix, contentPath, templatePath string) (*Server, error) {
	present.PlayEnabled = true

	root := filepath.Join(templatePath, "root.tmpl")
	parse := func(name string) (*template.Template, error) {
		t := template.New("").Funcs(funcMap)
		return t.ParseFiles(root, filepath.Join(templatePath, name))
	}

	s := &Server{pathPrefix: pathPrefix}

	// Parse templates.
	var err error
	s.template.home, err = parse("home.tmpl")
	if err != nil {
		return nil, err
	}
	s.template.index, err = parse("index.tmpl")
	if err != nil {
		return nil, err
	}
	s.template.article, err = parse("article.tmpl")
	if err != nil {
		return nil, err
	}
	p := present.Template().Funcs(funcMap)
	s.template.doc, err = p.ParseFiles(filepath.Join(templatePath, "doc.tmpl"))
	if err != nil {
		return nil, err
	}

	// Load content.
	err = s.loadDocs(filepath.Clean(contentPath))
	if err != nil {
		return nil, err
	}

	// Set up content file server.
	s.content = http.StripPrefix(pathPrefix, http.FileServer(http.Dir(contentPath)))

	return s, nil
}

var funcMap = template.FuncMap{
	"sectioned": sectioned,
	"authors":   authors,
}

// sectioned returns true if the provided Doc contains more than one section.
// This is used to control whether to display the table of contents and headings.
func sectioned(d *present.Doc) bool {
	return len(d.Sections) > 1
}

// authors returns a comma-separated list of author names.
func authors(authors []present.Author) string {
	var b bytes.Buffer
	last := len(authors) - 1
	for i, a := range authors {
		if i > 0 {
			if i == last {
				b.WriteString(" and ")
			} else {
				b.WriteString(", ")
			}
		}
		b.WriteString(authorName(a))
	}
	return b.String()
}

// authorName returns the first line of the Author text: the author's name.
func authorName(a present.Author) string {
	el := a.TextElem()
	if len(el) == 0 {
		return ""
	}
	text, ok := el[0].(present.Text)
	if !ok || len(text.Lines) == 0 {
		return ""
	}
	return text.Lines[0]
}

// loadDocs reads all content from the provided file system root, renders all
// the articles it finds, adds them to the Server's docs field, computes the
// denormalized docPaths, docTags, and tags fields, and populates the various
// helper fields (Next, Previous, Related) for each Doc.
func (s *Server) loadDocs(root string) error {
	// Read content into docs field.
	const ext = ".article"
	fn := func(p string, info os.FileInfo, err error) error {
		if filepath.Ext(p) != ext {
			return nil
		}
		f, err := os.Open(p)
		if err != nil {
			return err
		}
		defer f.Close()
		d, err := present.Parse(f, p, 0)
		if err != nil {
			return err
		}
		html := new(bytes.Buffer)
		err = d.Render(html, s.template.doc)
		if err != nil {
			return err
		}
		p = p[len(root) : len(p)-len(ext)] // trim root and extension
		s.docs = append(s.docs, &Doc{
			Doc:  d,
			Path: path.Join(s.pathPrefix, p),
			HTML: template.HTML(html.String()),
		})
		return nil
	}
	err := filepath.Walk(root, fn)
	if err != nil {
		return err
	}
	sort.Sort(docsByTime(s.docs))

	// Pull out doc paths and tags and put in reverse-associating maps.
	s.docPaths = make(map[string]*Doc)
	s.docTags = make(map[string][]*Doc)
	for _, d := range s.docs {
		s.docPaths[d.Path] = d
		for _, t := range d.Tags {
			s.docTags[t] = append(s.docTags[t], d)
		}
	}

	// Pull out unique sorted list of tags.
	for t := range s.docTags {
		s.tags = append(s.tags, t)
	}
	sort.Strings(s.tags)

	// Set up presentation-related fields, Newer, Older, and Related.
	for _, doc := range s.docs {
		// Newer, Older: docs adjacent to doc
		for i := range s.docs {
			if s.docs[i] != doc {
				continue
			}
			if i > 0 {
				doc.Newer = s.docs[i-1]
			}
			if i+1 < len(s.docs) {
				doc.Older = s.docs[i+1]
			}
			break
		}

		// Related: all docs that share tags with doc.
		related := make(map[*Doc]bool)
		for _, t := range doc.Tags {
			for _, d := range s.docTags[t] {
				if d != doc {
					related[d] = true
				}
			}
		}
		for d := range related {
			doc.Related = append(doc.Related, d)
		}
		sort.Sort(docsByTime(doc.Related))
	}

	return nil
}

// rootData encapsulates data destined for the root template.
type rootData struct {
	Doc  *Doc
	Data interface{}
}

// ServeHTTP servers either an article list or a single article.
func (s *Server) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	p := r.URL.Path
	if !strings.HasPrefix(p, s.pathPrefix) {
		http.Error(w, "not found", http.StatusNotFound)
		return
	}
	var (
		d rootData
		t *template.Template
	)
	switch p[len(s.pathPrefix):] {
	case "":
		d.Data = s.docs
		if len(s.docs) > homeArticles {
			d.Data = s.docs[:homeArticles]
		}
		t = s.template.home
	case "index":
		d.Data = s.docs
		t = s.template.index
	default:
		doc, ok := s.docPaths[p]
		if !ok {
			// Not a doc; try to just serve static content.
			s.content.ServeHTTP(w, r)
			return
		}
		d.Doc = doc
		t = s.template.article
	}
	err := t.ExecuteTemplate(w, "root", d)
	if err != nil {
		log.Println(err)
	}
}

// docsByTime implements sort.Interface, sorting Docs by their Time field.
type docsByTime []*Doc

func (s docsByTime) Len() int           { return len(s) }
func (s docsByTime) Swap(i, j int)      { s[i], s[j] = s[j], s[i] }
func (s docsByTime) Less(i, j int) bool { return s[i].Time.After(s[j].Time) }