package upwatch

import (
	"bytes"
	"context"
	"encoding/base64"
	"encoding/json"
	"fmt"
	"io"
	"net/http"
	"net/url"
	"regexp"
	"strings"
	"time"
)

// Report is what one app says about its own work right now.
type Report struct {
	// UploadCounter is the app's own cumulative count of bytes it uploaded (qBittorrent `up_info_data`, Transmission
	// `current-stats.uploadedBytes`). It restarts at zero with the app; the watcher treats a drop as a restart.
	UploadCounter    uint64
	HasUploadCounter bool
	// Viewers is the number of playing sessions (Plex `/status/sessions` size). A viewer EXPLAINS upload of any size:
	// the per-session bandwidth was not measured in the spike (no claimed server with a remote player tonight), so
	// the rule is deliberately the conservative half — no viewer and a big upload is the Plex2Shell signature.
	Viewers        int
	HasViewerCount bool
	// Transcodes is CPU work the app reports (Plex `/transcode/sessions` size). Any transcode explains the CPU.
	Transcodes        int
	HasTranscodeCount bool
	// Limit is the app's current global upload limit in bytes/s (0 = none); HasLimit when the app has one to read.
	Limit    int64
	HasLimit bool
}

// Explainer asks one app about its own work.
type Explainer interface {
	Stack() string
	Ask(ctx context.Context) (Report, error)
}

// Box is what an explainer needs outside HTTP — the mediawire seams (`docker exec printenv`, the Plex token read at
// use). Production: mediawire.DockerBox.
type Box interface {
	Env(container, name string) (string, error)
	Running(container string) bool
}

// httpDo is one request to an app's own container. Small and local on purpose: mediawire's helpers are methods of
// its Wirer, which also writes; this package only reads (and sets one limit, qblimit.go).
func httpDo(ctx context.Context, c *http.Client, method, u string, hdr map[string]string, body []byte, ctype string) (int, []byte, http.Header, error) {
	req, err := http.NewRequestWithContext(ctx, method, u, bytes.NewReader(body))
	if err != nil {
		return 0, nil, nil, err
	}
	for k, v := range hdr {
		if strings.EqualFold(k, "Host") {
			req.Host = v
			continue
		}
		req.Header.Set(k, v)
	}
	if ctype != "" {
		req.Header.Set("Content-Type", ctype)
	}
	resp, err := c.Do(req)
	if err != nil {
		return 0, nil, nil, err
	}
	defer resp.Body.Close()
	b, _ := io.ReadAll(io.LimitReader(resp.Body, 4<<20))
	return resp.StatusCode, b, resp.Header, nil
}

// ── qBittorrent ──────────────────────────────────────────────────────────────────────────────────────────────────

// QBittorrent asks qBittorrent's Web API. Measured on 9202 (qBittorrent 5.2.4, WebAPI 2.15.1): while seeding, the
// container sent 1.03–1.07 × what `up_info_data` counted (protocol overhead); `transfer/uploadLimit` and
// `app/preferences.up_limit` are the same value, persisted across a restart (`Session\GlobalUPSpeedLimit`, KiB/s).
type QBittorrent struct {
	Box  Box
	URL  string // default http://qbittorrent:8080 (the container's name on the docker network, as mediawire calls it)
	HTTP *http.Client

	sess map[string]string // the session cookie, kept between minutes (a login a minute would fill qBittorrent's log)
}

func (q *QBittorrent) Stack() string { return "qbittorrent" }

func (q *QBittorrent) base() string {
	if q.URL != "" {
		return q.URL
	}
	return "http://qbittorrent:8080"
}

func (q *QBittorrent) client() *http.Client {
	if q.HTTP != nil {
		return q.HTTP
	}
	return &http.Client{Timeout: 20 * time.Second}
}

var qbCookieRE = regexp.MustCompile(`((?:QBT_)?SID[A-Za-z0-9_]*)=([^;]+)`)

// login returns the headers of an authenticated session. The password is the catalog's QBT_ADMIN_PASSWORD, read at
// use; Referer must equal the base (qBittorrent's CSRF check — a mismatch is a 401, measured).
func (q *QBittorrent) login(ctx context.Context) (map[string]string, error) {
	pw, err := q.Box.Env("qbittorrent", "QBT_ADMIN_PASSWORD")
	if err != nil {
		return nil, err
	}
	form := url.Values{"username": {"admin"}, "password": {pw}}.Encode()
	code, _, hd, err := httpDo(ctx, q.client(), "POST", q.base()+"/api/v2/auth/login", map[string]string{"Referer": q.base()}, []byte(form), "application/x-www-form-urlencoded")
	if err != nil {
		return nil, err
	}
	m := qbCookieRE.FindStringSubmatch(strings.Join(hd.Values("Set-Cookie"), "; "))
	if (code != 200 && code != 204) || m == nil { // 5.x answers a good login 204
		return nil, fmt.Errorf("qBittorrent login: HTTP %d", code)
	}
	return map[string]string{"Referer": q.base(), "Cookie": m[1] + "=" + m[2]}, nil
}

// session returns the kept session, logging in when there is none or when fresh is set.
func (q *QBittorrent) session(ctx context.Context, fresh bool) (map[string]string, error) {
	if q.sess != nil && !fresh {
		return q.sess, nil
	}
	h, err := q.login(ctx)
	if err != nil {
		q.sess = nil
		return nil, err
	}
	q.sess = h
	return h, nil
}

func (q *QBittorrent) Ask(ctx context.Context) (Report, error) {
	h, err := q.session(ctx, false)
	if err != nil {
		return Report{}, err
	}
	code, b, _, err := httpDo(ctx, q.client(), "GET", q.base()+"/api/v2/transfer/info", h, nil, "")
	if err == nil && code == 403 { // the session expired (qBittorrent restarted, or its 1-hour timeout): once more
		if h, err = q.session(ctx, true); err != nil {
			return Report{}, err
		}
		code, b, _, err = httpDo(ctx, q.client(), "GET", q.base()+"/api/v2/transfer/info", h, nil, "")
	}
	if err != nil || code != 200 {
		return Report{}, fmt.Errorf("qBittorrent transfer/info: HTTP %d %v", code, err)
	}
	var ti struct {
		UpInfoData uint64 `json:"up_info_data"`
	}
	if err := json.Unmarshal(b, &ti); err != nil {
		return Report{}, err
	}
	r := Report{UploadCounter: ti.UpInfoData, HasUploadCounter: true}
	if lim, err := q.UploadLimit(ctx, h); err == nil {
		r.Limit, r.HasLimit = lim, true
	}
	return r, nil
}

// UploadLimit reads the global upload limit (bytes/s, 0 = none). h nil → logs in.
func (q *QBittorrent) UploadLimit(ctx context.Context, h map[string]string) (int64, error) {
	if h == nil {
		var err error
		if h, err = q.session(ctx, true); err != nil {
			return 0, err
		}
	}
	code, b, _, err := httpDo(ctx, q.client(), "GET", q.base()+"/api/v2/transfer/uploadLimit", h, nil, "")
	if err != nil || code != 200 {
		return 0, fmt.Errorf("qBittorrent uploadLimit: HTTP %d %v", code, err)
	}
	var v int64
	if _, err := fmt.Sscan(strings.TrimSpace(string(b)), &v); err != nil {
		return 0, fmt.Errorf("qBittorrent uploadLimit: %q", strings.TrimSpace(string(b)))
	}
	return v, nil
}

// SetUploadLimit sets the global upload limit (bytes/s) and returns the value qBittorrent stored (it keeps KiB/s, so
// 2 500 000 reads back as 2 499 584 — measured).
func (q *QBittorrent) SetUploadLimit(ctx context.Context, bytesPerSec int64) (int64, error) {
	h, err := q.session(ctx, true)
	if err != nil {
		return 0, err
	}
	form := url.Values{"limit": {fmt.Sprint(bytesPerSec)}}.Encode()
	code, _, _, err := httpDo(ctx, q.client(), "POST", q.base()+"/api/v2/transfer/setUploadLimit", h, []byte(form), "application/x-www-form-urlencoded")
	if err != nil || code != 200 {
		return 0, fmt.Errorf("qBittorrent setUploadLimit: HTTP %d %v", code, err)
	}
	return q.UploadLimit(ctx, h)
}

// ── Transmission ─────────────────────────────────────────────────────────────────────────────────────────────────

// Transmission asks Transmission's RPC (4.1.3 on 9202): `session-stats.current-stats.uploadedBytes` matched the
// container's sent bytes within 0.1–2 % while seeding (measured).
type Transmission struct {
	Box  Box
	URL  string // default http://transmission:9091
	HTTP *http.Client
}

func (t *Transmission) Stack() string { return "transmission" }

func (t *Transmission) Ask(ctx context.Context) (Report, error) {
	pw, err := t.Box.Env("transmission", "PASS")
	if err != nil {
		return Report{}, err
	}
	base := t.URL
	if base == "" {
		base = "http://transmission:9091"
	}
	c := t.HTTP
	if c == nil {
		c = &http.Client{Timeout: 20 * time.Second}
	}
	h := map[string]string{"Authorization": "Basic " + base64.StdEncoding.EncodeToString([]byte("admin:"+pw)), "Host": "transmission:9091"}
	body := []byte(`{"method":"session-stats"}`)
	for i := 0; i < 2; i++ {
		code, b, hd, err := httpDo(ctx, c, "POST", base+"/transmission/rpc", h, body, "application/json")
		if err != nil {
			return Report{}, err
		}
		if code == 409 {
			h["X-Transmission-Session-Id"] = hd.Get("X-Transmission-Session-Id")
			continue
		}
		if code != 200 {
			return Report{}, fmt.Errorf("transmission session-stats: HTTP %d", code)
		}
		var st struct {
			Arguments struct {
				Current struct {
					UploadedBytes uint64 `json:"uploadedBytes"`
				} `json:"current-stats"`
			} `json:"arguments"`
		}
		if err := json.Unmarshal(b, &st); err != nil {
			return Report{}, err
		}
		return Report{UploadCounter: st.Arguments.Current.UploadedBytes, HasUploadCounter: true}, nil
	}
	return Report{}, fmt.Errorf("transmission session-stats: no session id")
}

// ── Plex ─────────────────────────────────────────────────────────────────────────────────────────────────────────

// Plex asks Plex Media Server for its playing and transcoding sessions. Measured on 9202 (1.43.5, unclaimed): both
// answer `{"MediaContainer":{"size":0}}` without a token from the docker network; a CLAIMED server needs its own
// PlexOnlineToken, read from Preferences.xml at use exactly as mediawire does (`09` §3 decision 248).
type Plex struct {
	Token func() string                  // mediawire.PlexToken(box); "" for an unclaimed server
	URL   func(port int) (string, error) // mediawire.PlexURL (Plex refuses a call by NAME as non-local, R-1060)
	HTTP  *http.Client
}

func (p *Plex) Stack() string { return "plex" }

func (p *Plex) Ask(ctx context.Context) (Report, error) {
	base, err := p.URL(32400)
	if err != nil {
		return Report{}, err
	}
	c := p.HTTP
	if c == nil {
		c = &http.Client{Timeout: 20 * time.Second}
	}
	h := map[string]string{"Accept": "application/json"}
	if tok := p.Token(); tok != "" {
		h["X-Plex-Token"] = tok
	}
	size := func(path string) (int, error) {
		code, b, _, err := httpDo(ctx, c, "GET", base+path, h, nil, "")
		if err != nil || code != 200 {
			return 0, fmt.Errorf("plex %s: HTTP %d %v", path, code, err)
		}
		var mc struct {
			MediaContainer struct {
				Size int `json:"size"`
			} `json:"MediaContainer"`
		}
		if err := json.Unmarshal(b, &mc); err != nil {
			return 0, err
		}
		return mc.MediaContainer.Size, nil
	}
	v, err := size("/status/sessions")
	if err != nil {
		return Report{}, err
	}
	tr, err := size("/transcode/sessions")
	if err != nil {
		return Report{}, err
	}
	return Report{Viewers: v, HasViewerCount: true, Transcodes: tr, HasTranscodeCount: true}, nil
}