package getter

import (
	"context"
	"encoding/xml"
	"fmt"
	"io"
	"net/http"
	"net/url"
	"os"
	"path/filepath"
	"strings"

	safetemp "github.com/hashicorp/go-safetemp"
)

// HttpGetter is a Getter implementation that will download from an HTTP
// endpoint.
//
// For file downloads, HTTP is used directly.
//
// The protocol for downloading a directory from an HTTP endpoint is as follows:
//
// An HTTP GET request is made to the URL with the additional GET parameter
// "terraform-get=1". This lets you handle that scenario specially if you
// wish. The response must be a 2xx.
//
// First, a header is looked for "X-Terraform-Get" which should contain
// a source URL to download.
//
// If the header is not present, then a meta tag is searched for named
// "terraform-get" and the content should be a source URL.
//
// The source URL, whether from the header or meta tag, must be a fully
// formed URL. The shorthand syntax of "github.com/foo/bar" or relative
// paths are not allowed.
type HttpGetter struct {
	getter

	// Netrc, if true, will lookup and use auth information found
	// in the user's netrc file if available.
	Netrc bool

	// Client is the http.Client to use for Get requests.
	// This defaults to a cleanhttp.DefaultClient if left unset.
	Client *http.Client

	// Header contains optional request header fields that should be included
	// with every HTTP request. Note that the zero value of this field is nil,
	// and as such it needs to be initialized before use, via something like
	// make(http.Header).
	Header http.Header
}

func (g *HttpGetter) ClientMode(u *url.URL) (ClientMode, error) {
	if strings.HasSuffix(u.Path, "/") {
		return ClientModeDir, nil
	}
	return ClientModeFile, nil
}

func (g *HttpGetter) Get(dst string, u *url.URL) error {
	ctx := g.Context()
	// Copy the URL so we can modify it
	var newU url.URL = *u
	u = &newU

	if g.Netrc {
		// Add auth from netrc if we can
		if err := addAuthFromNetrc(u); err != nil {
			return err
		}
	}

	if g.Client == nil {
		g.Client = httpClient
	}

	// Add terraform-get to the parameter.
	q := u.Query()
	q.Add("terraform-get", "1")
	u.RawQuery = q.Encode()

	// Get the URL
	req, err := http.NewRequest("GET", u.String(), nil)
	if err != nil {
		return err
	}

	if g.Header != nil {
		req.Header = g.Header.Clone()
	}

	resp, err := g.Client.Do(req)
	if err != nil {
		return err
	}

	defer resp.Body.Close()
	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
		return fmt.Errorf("bad response code: %d", resp.StatusCode)
	}

	// Extract the source URL
	var source string
	if v := resp.Header.Get("X-Terraform-Get"); v != "" {
		source = v
	} else {
		source, err = g.parseMeta(resp.Body)
		if err != nil {
			return err
		}
	}
	if source == "" {
		return fmt.Errorf("no source URL was returned")
	}

	// If there is a subdir component, then we download the root separately
	// into a temporary directory, then copy over the proper subdir.
	source, subDir := SourceDirSubdir(source)
	if subDir == "" {
		var opts []ClientOption
		if g.client != nil {
			opts = g.client.Options
		}
		return Get(dst, source, opts...)
	}

	// We have a subdir, time to jump some hoops
	return g.getSubdir(ctx, dst, source, subDir)
}

// GetFile fetches the file from src and stores it at dst.
// If the server supports Accept-Range, HttpGetter will attempt a range
// request. This means it is the caller's responsibility to ensure that an
// older version of the destination file does not exist, else it will be either
// falsely identified as being replaced, or corrupted with extra bytes
// appended.
func (g *HttpGetter) GetFile(dst string, src *url.URL) error {
	ctx := g.Context()
	if g.Netrc {
		// Add auth from netrc if we can
		if err := addAuthFromNetrc(src); err != nil {
			return err
		}
	}
	// Create all the parent directories if needed
	if err := os.MkdirAll(filepath.Dir(dst), 0755); err != nil {
		return err
	}

	f, err := os.OpenFile(dst, os.O_RDWR|os.O_CREATE, os.FileMode(0666))
	if err != nil {
		return err
	}
	defer f.Close()

	if g.Client == nil {
		g.Client = httpClient
	}

	var currentFileSize int64

	// We first make a HEAD request so we can check
	// if the server supports range queries. If the server/URL doesn't
	// support HEAD requests, we just fall back to GET.
	req, err := http.NewRequest("HEAD", src.String(), nil)
	if err != nil {
		return err
	}
	if g.Header != nil {
		req.Header = g.Header.Clone()
	}
	headResp, err := g.Client.Do(req)
	if err == nil {
		headResp.Body.Close()
		if headResp.StatusCode == 200 {
			// If the HEAD request succeeded, then attempt to set the range
			// query if we can.
			if headResp.Header.Get("Accept-Ranges") == "bytes" && headResp.ContentLength >= 0 {
				if fi, err := f.Stat(); err == nil {
					if _, err = f.Seek(0, io.SeekEnd); err == nil {
						currentFileSize = fi.Size()
						req.Header.Set("Range", fmt.Sprintf("bytes=%d-", currentFileSize))
						if currentFileSize >= headResp.ContentLength {
							// file already present
							return nil
						}
					}
				}
			}
		}
	}
	req.Method = "GET"

	resp, err := g.Client.Do(req)
	if err != nil {
		return err
	}
	switch resp.StatusCode {
	case http.StatusOK, http.StatusPartialContent:
		// all good
	default:
		resp.Body.Close()
		return fmt.Errorf("bad response code: %d", resp.StatusCode)
	}

	body := resp.Body

	if g.client != nil && g.client.ProgressListener != nil {
		// track download
		fn := filepath.Base(src.EscapedPath())
		body = g.client.ProgressListener.TrackProgress(fn, currentFileSize, currentFileSize+resp.ContentLength, resp.Body)
	}
	defer body.Close()

	n, err := Copy(ctx, f, body)
	if err == nil && n < resp.ContentLength {
		err = io.ErrShortWrite
	}
	return err
}

// getSubdir downloads the source into the destination, but with
// the proper subdir.
func (g *HttpGetter) getSubdir(ctx context.Context, dst, source, subDir string) error {
	// Create a temporary directory to store the full source. This has to be
	// a non-existent directory.
	td, tdcloser, err := safetemp.Dir("", "getter")
	if err != nil {
		return err
	}
	defer tdcloser.Close()

	var opts []ClientOption
	if g.client != nil {
		opts = g.client.Options
	}
	// Download that into the given directory
	if err := Get(td, source, opts...); err != nil {
		return err
	}

	// Process any globbing
	sourcePath, err := SubdirGlob(td, subDir)
	if err != nil {
		return err
	}

	// Make sure the subdir path actually exists
	if _, err := os.Stat(sourcePath); err != nil {
		return fmt.Errorf(
			"Error downloading %s: %s", source, err)
	}

	// Copy the subdirectory into our actual destination.
	if err := os.RemoveAll(dst); err != nil {
		return err
	}

	// Make the final destination
	if err := os.MkdirAll(dst, 0755); err != nil {
		return err
	}

	return copyDir(ctx, dst, sourcePath, false)
}

// parseMeta looks for the first meta tag in the given reader that
// will give us the source URL.
func (g *HttpGetter) parseMeta(r io.Reader) (string, error) {
	d := xml.NewDecoder(r)
	d.CharsetReader = charsetReader
	d.Strict = false
	var err error
	var t xml.Token
	for {
		t, err = d.Token()
		if err != nil {
			if err == io.EOF {
				err = nil
			}
			return "", err
		}
		if e, ok := t.(xml.StartElement); ok && strings.EqualFold(e.Name.Local, "body") {
			return "", nil
		}
		if e, ok := t.(xml.EndElement); ok && strings.EqualFold(e.Name.Local, "head") {
			return "", nil
		}
		e, ok := t.(xml.StartElement)
		if !ok || !strings.EqualFold(e.Name.Local, "meta") {
			continue
		}
		if attrValue(e.Attr, "name") != "terraform-get" {
			continue
		}
		if f := attrValue(e.Attr, "content"); f != "" {
			return f, nil
		}
	}
}

// attrValue returns the attribute value for the case-insensitive key
// `name', or the empty string if nothing is found.
func attrValue(attrs []xml.Attr, name string) string {
	for _, a := range attrs {
		if strings.EqualFold(a.Name.Local, name) {
			return a.Value
		}
	}
	return ""
}

// charsetReader returns a reader for the given charset. Currently
// it only supports UTF-8 and ASCII. Otherwise, it returns a meaningful
// error which is printed by go get, so the user can find why the package
// wasn't downloaded if the encoding is not supported. Note that, in
// order to reduce potential errors, ASCII is treated as UTF-8 (i.e. characters
// greater than 0x7f are not rejected).
func charsetReader(charset string, input io.Reader) (io.Reader, error) {
	switch strings.ToLower(charset) {
	case "ascii":
		return input, nil
	default:
		return nil, fmt.Errorf("can't decode XML document using charset %q", charset)
	}
}
