// Package push uploads locally-downloaded audio to a remote podkit server.
//
// This exists because the download and the hosting do not have to happen on the
// same machine, and usually shouldn't. Downloading is something a person does
// from their own connection; hosting is something a server does. Splitting them
// means the server never needs credentials for, or a working route to, whatever
// the audio came from.
package push

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

	"podkit/internal/feed"
)

// Options configure an upload run.
type Options struct {
	Dir    string // local directory holding the audio
	Server string // base URL of the remote podkit server
	Token  string // the remote server's token
	Force  bool   // upload even when the server already has a matching file
	Client *http.Client
}

// Result describes what happened to one file.
type Result struct {
	Name    string
	Bytes   int64
	Skipped bool
	Err     error
}

// Run uploads every audio file in Dir that the server does not already have.
func Run(ctx context.Context, opts Options) ([]Result, error) {
	if opts.Server == "" {
		return nil, fmt.Errorf("a server URL is required")
	}
	base, err := url.Parse(opts.Server)
	if err != nil || base.Scheme == "" || base.Host == "" {
		return nil, fmt.Errorf("server %q needs a scheme and host, e.g. https://host/podkit", opts.Server)
	}

	client := opts.Client
	if client == nil {
		// No overall timeout: a large episode on a slow uplink is a legitimate
		// long request. Cancellation comes from ctx instead.
		client = &http.Client{Timeout: 0}
	}

	local, err := localFiles(opts.Dir)
	if err != nil {
		return nil, err
	}
	if len(local) == 0 {
		return nil, fmt.Errorf("no audio files in %s", opts.Dir)
	}

	remote := map[string]int64{}
	if !opts.Force {
		remote, err = fetchManifest(ctx, client, base, opts.Token)
		if err != nil {
			return nil, err
		}
	}

	var results []Result
	for _, f := range local {
		if size, ok := remote[f.name]; ok && size == f.size {
			results = append(results, Result{Name: f.name, Bytes: f.size, Skipped: true})
			continue
		}
		err := upload(ctx, client, base, opts.Token, opts.Dir, f.name, f.size)
		results = append(results, Result{Name: f.name, Bytes: f.size, Err: err})
		if err != nil && ctx.Err() != nil {
			// Interrupted rather than rejected; stop instead of hammering
			// through the rest of the list with a dead context.
			break
		}
	}
	return results, nil
}

type localFile struct {
	name string
	size int64
}

func localFiles(dir string) ([]localFile, error) {
	entries, err := os.ReadDir(dir)
	if err != nil {
		return nil, fmt.Errorf("reading %s: %w", dir, err)
	}
	var out []localFile
	for _, e := range entries {
		if e.IsDir() || !feed.IsAudio(e.Name()) {
			continue
		}
		info, err := e.Info()
		if err != nil {
			return nil, fmt.Errorf("stat %s: %w", e.Name(), err)
		}
		out = append(out, localFile{e.Name(), info.Size()})
	}
	sort.Slice(out, func(i, j int) bool { return out[i].name < out[j].name })
	return out, nil
}

func fetchManifest(ctx context.Context, c *http.Client, base *url.URL, token string) (map[string]int64, error) {
	u := *base
	u.Path = path.Join(u.Path, "manifest")
	req, err := http.NewRequestWithContext(ctx, http.MethodGet, u.String(), nil)
	if err != nil {
		return nil, err
	}
	auth(req, token)

	resp, err := c.Do(req)
	if err != nil {
		return nil, fmt.Errorf("contacting %s: %w", u.String(), err)
	}
	defer resp.Body.Close()

	if resp.StatusCode != http.StatusOK {
		// The server 404s both a wrong token and a server without --ingest, on
		// purpose. Say so, rather than reporting a bare 404 the user then has
		// to guess the meaning of.
		return nil, fmt.Errorf("manifest request returned %s — check the token, and that the server was started with --ingest",
			resp.Status)
	}

	var m struct {
		Files map[string]int64 `json:"files"`
	}
	if err := json.NewDecoder(resp.Body).Decode(&m); err != nil {
		return nil, fmt.Errorf("parsing manifest from %s: %w", u.String(), err)
	}
	if m.Files == nil {
		m.Files = map[string]int64{}
	}
	return m.Files, nil
}

func upload(ctx context.Context, c *http.Client, base *url.URL, token, dir, name string, size int64) error {
	f, err := os.Open(filepath.Join(dir, name))
	if err != nil {
		return err
	}
	defer f.Close()

	u := *base
	u.Path = path.Join(u.Path, "ingest")
	q := u.Query()
	q.Set("name", name)
	u.RawQuery = q.Encode()

	req, err := http.NewRequestWithContext(ctx, http.MethodPost, u.String(), f)
	if err != nil {
		return err
	}
	auth(req, token)
	req.Header.Set("Content-Type", feed.MIMEType(name))
	// Set explicitly so the server sees a length rather than a chunked body,
	// and so MaxBytesReader can reject an oversized file before the transfer.
	req.ContentLength = size

	resp, err := c.Do(req)
	if err != nil {
		return fmt.Errorf("uploading %s: %w", name, err)
	}
	defer resp.Body.Close()

	if resp.StatusCode != http.StatusOK {
		body, _ := io.ReadAll(io.LimitReader(resp.Body, 512))
		msg := strings.TrimSpace(string(body))
		if msg == "" {
			msg = resp.Status
		}
		return fmt.Errorf("uploading %s: %s", name, msg)
	}
	_, _ = io.Copy(io.Discard, resp.Body)
	return nil
}

func auth(req *http.Request, token string) {
	if token == "" {
		return
	}
	// Header rather than query string: it keeps the secret out of the server's
	// access log, and push is not a podcast client so it has the choice.
	req.Header.Set("Authorization", "Bearer "+token)
}

// Summarise renders results for the terminal.
func Summarise(results []Result) (uploaded, skipped, failed int) {
	for _, r := range results {
		switch {
		case r.Err != nil:
			failed++
		case r.Skipped:
			skipped++
		default:
			uploaded++
		}
	}
	return
}