// 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 or at
// https://developers.google.com/open-source/licenses/bsd.

package gosrc

import (
	"encoding/json"
	"fmt"
	"net/http"
	"net/url"
	"regexp"
	"strings"
	"time"
)

func init() {
	addService(&service{
		pattern:         regexp.MustCompile(`^github\.com/(?P<owner>[a-z0-9A-Z_.\-]+)/(?P<repo>[a-z0-9A-Z_.\-]+)(?P<dir>/.*)?$`),
		prefix:          "github.com/",
		get:             getGitHubDir,
		getPresentation: getGitHubPresentation,
		getProject:      getGitHubProject,
	})

	addService(&service{
		pattern: regexp.MustCompile(`^gist\.github\.com/(?P<gist>[a-z0-9A-Z_.\-]+)\.git$`),
		prefix:  "gist.github.com/",
		get:     getGistDir,
	})
}

var (
	gitHubRawHeader     = http.Header{"Accept": {"application/vnd.github-blob.raw"}}
	gitHubPreviewHeader = http.Header{"Accept": {"application/vnd.github.preview"}}
	ownerRepoPat        = regexp.MustCompile(`^https://api.github.com/repos/([^/]+)/([^/]+)/`)
)

func gitHubError(resp *http.Response) error {
	var e struct {
		Message string `json:"message"`
	}
	if err := json.NewDecoder(resp.Body).Decode(&e); err == nil {
		return &RemoteError{resp.Request.URL.Host, fmt.Errorf("%d: %s (%s)", resp.StatusCode, e.Message, resp.Request.URL.String())}
	}
	return &RemoteError{resp.Request.URL.Host, fmt.Errorf("%d: (%s)", resp.StatusCode, resp.Request.URL.String())}
}

func getGitHubDir(client *http.Client, match map[string]string, savedEtag string) (*Directory, error) {

	c := &httpClient{client: client, errFn: gitHubError}

	type refJSON struct {
		Object struct {
			Type string
			Sha  string
			URL  string
		}
		Ref string
		URL string
	}
	var refs []*refJSON

	resp, err := c.getJSON(expand("https://api.github.com/repos/{owner}/{repo}/git/refs", match), &refs)
	if err != nil {
		return nil, err
	}

	// If the response contains a Link header, then fallback to requesting "master" and "go1" by name.
	if resp.Header.Get("Link") != "" {
		var masterRef refJSON
		if _, err := c.getJSON(expand("https://api.github.com/repos/{owner}/{repo}/git/refs/heads/master", match), &masterRef); err == nil {
			refs = append(refs, &masterRef)
		}

		var go1Ref refJSON
		if _, err := c.getJSON(expand("https://api.github.com/repos/{owner}/{repo}/git/refs/tags/go1", match), &go1Ref); err == nil {
			refs = append(refs, &go1Ref)
		}
	}

	tags := make(map[string]string)
	for _, ref := range refs {
		switch {
		case strings.HasPrefix(ref.Ref, "refs/heads/"):
			tags[ref.Ref[len("refs/heads/"):]] = ref.Object.Sha
		case strings.HasPrefix(ref.Ref, "refs/tags/"):
			tags[ref.Ref[len("refs/tags/"):]] = ref.Object.Sha
		}
	}

	var commit string
	match["tag"], commit, err = bestTag(tags, "master")
	if err != nil {
		return nil, err
	}

	if commit == savedEtag {
		return nil, ErrNotModified
	}

	var contents []*struct {
		Type    string
		Name    string
		GitURL  string `json:"git_url"`
		HTMLURL string `json:"html_url"`
	}

	if _, err := c.getJSON(expand("https://api.github.com/repos/{owner}/{repo}/contents{dir}?ref={tag}", match), &contents); err != nil {
		return nil, err
	}

	if len(contents) == 0 {
		return nil, NotFoundError{Message: "No files in directory."}
	}

	// GitHub owner and repo names are case-insensitive. Redirect if requested
	// names do not match the canonical names in API response.
	if m := ownerRepoPat.FindStringSubmatch(contents[0].GitURL); m != nil && (m[1] != match["owner"] || m[2] != match["repo"]) {
		match["owner"] = m[1]
		match["repo"] = m[2]
		return nil, NotFoundError{
			Message:  "Github import path has incorrect case.",
			Redirect: expand("github.com/{owner}/{repo}{dir}", match),
		}
	}

	var files []*File
	var dataURLs []string
	var subdirs []string

	for _, item := range contents {
		switch {
		case item.Type == "dir":
			if isValidPathElement(item.Name) {
				subdirs = append(subdirs, item.Name)
			}
		case isDocFile(item.Name):
			files = append(files, &File{Name: item.Name, BrowseURL: item.HTMLURL})
			dataURLs = append(dataURLs, item.GitURL)
		}
	}

	c.header = gitHubRawHeader
	if err := c.getFiles(dataURLs, files); err != nil {
		return nil, err
	}

	browseURL := expand("https://github.com/{owner}/{repo}", match)
	if match["dir"] != "" {
		browseURL = expand("https://github.com/{owner}/{repo}/tree/{tag}{dir}", match)
	}

	var repo = struct {
		Fork      bool      `json:"fork"`
		CreatedAt time.Time `json:"created_at"`
		PushedAt  time.Time `json:"pushed_at"`
	}{}

	if _, err := c.getJSON(expand("https://api.github.com/repos/{owner}/{repo}", match), &repo); err != nil {
		return nil, err
	}

	isDeadEndFork := repo.Fork && repo.PushedAt.Before(repo.CreatedAt)

	return &Directory{
		BrowseURL:      browseURL,
		Etag:           commit,
		Files:          files,
		LineFmt:        "%s#L%d",
		ProjectName:    match["repo"],
		ProjectRoot:    expand("github.com/{owner}/{repo}", match),
		ProjectURL:     expand("https://github.com/{owner}/{repo}", match),
		Subdirectories: subdirs,
		VCS:            "git",
		DeadEndFork:    isDeadEndFork,
	}, nil
}

func getGitHubPresentation(client *http.Client, match map[string]string) (*Presentation, error) {
	c := &httpClient{client: client, header: gitHubRawHeader}

	p, err := c.getBytes(expand("https://api.github.com/repos/{owner}/{repo}/contents{dir}/{file}", match))
	if err != nil {
		return nil, err
	}

	apiBase, err := url.Parse(expand("https://api.github.com/repos/{owner}/{repo}/contents{dir}/", match))
	if err != nil {
		return nil, err
	}
	rawBase, err := url.Parse(expand("https://raw.github.com/{owner}/{repo}/master{dir}/", match))
	if err != nil {
		return nil, err
	}

	c.header = gitHubRawHeader

	b := &presBuilder{
		data:     p,
		filename: match["file"],
		fetch: func(fnames []string) ([]*File, error) {
			var files []*File
			var dataURLs []string
			for _, fname := range fnames {
				u, err := apiBase.Parse(fname)
				if err != nil {
					return nil, err
				}
				u.RawQuery = apiBase.RawQuery
				files = append(files, &File{Name: fname})
				dataURLs = append(dataURLs, u.String())
			}
			err := c.getFiles(dataURLs, files)
			return files, err
		},
		resolveURL: func(fname string) string {
			u, err := rawBase.Parse(fname)
			if err != nil {
				return "/notfound"
			}
			if strings.HasSuffix(fname, ".svg") {
				u.Host = "rawgithub.com"
			}
			return u.String()
		},
	}

	return b.build()
}

// GetGitHubUpdates returns the full names ("owner/repo") of recently pushed GitHub repositories.
// by pushedAfter.
func GetGitHubUpdates(client *http.Client, pushedAfter string) (maxPushedAt string, names []string, err error) {
	c := httpClient{client: client, header: gitHubPreviewHeader}

	if pushedAfter == "" {
		pushedAfter = time.Now().Add(-24 * time.Hour).UTC().Format("2006-01-02T15:04:05Z")
	}
	u := "https://api.github.com/search/repositories?order=asc&sort=updated&q=fork:true+language:Go+pushed:>" + pushedAfter
	var updates struct {
		Items []struct {
			FullName string `json:"full_name"`
			PushedAt string `json:"pushed_at"`
		}
	}
	_, err = c.getJSON(u, &updates)
	if err != nil {
		return pushedAfter, nil, err
	}

	maxPushedAt = pushedAfter
	for _, item := range updates.Items {
		names = append(names, item.FullName)
		if item.PushedAt > maxPushedAt {
			maxPushedAt = item.PushedAt
		}
	}
	return maxPushedAt, names, nil
}

func getGitHubProject(client *http.Client, match map[string]string) (*Project, error) {
	c := &httpClient{client: client, errFn: gitHubError}

	var repo struct {
		Description string
	}

	if _, err := c.getJSON(expand("https://api.github.com/repos/{owner}/{repo}", match), &repo); err != nil {
		return nil, err
	}

	return &Project{
		Description: repo.Description,
	}, nil
}

func getGistDir(client *http.Client, match map[string]string, savedEtag string) (*Directory, error) {
	c := &httpClient{client: client, errFn: gitHubError}

	var gist struct {
		Files map[string]struct {
			Content string
		}
		HtmlUrl string `json:"html_url"`
		History []struct {
			Version string
		}
	}

	if _, err := c.getJSON(expand("https://api.github.com/gists/{gist}", match), &gist); err != nil {
		return nil, err
	}

	if len(gist.History) == 0 {
		return nil, NotFoundError{Message: "History not found."}
	}
	commit := gist.History[0].Version

	if commit == savedEtag {
		return nil, ErrNotModified
	}

	var files []*File

	for name, file := range gist.Files {
		if isDocFile(name) {
			files = append(files, &File{
				Name:      name,
				Data:      []byte(file.Content),
				BrowseURL: gist.HtmlUrl + "#file-" + strings.Replace(name, ".", "-", -1),
			})
		}
	}

	return &Directory{
		BrowseURL:      gist.HtmlUrl,
		Etag:           commit,
		Files:          files,
		LineFmt:        "%s-L%d",
		ProjectName:    match["gist"],
		ProjectRoot:    expand("gist.github.com/{gist}.git", match),
		ProjectURL:     gist.HtmlUrl,
		Subdirectories: nil,
		VCS:            "git",
	}, nil
}