// Package webhook implements POST /update, the endpoint CI calls after
// pushing an image. It records the pushed tag as "available" on every service
// that uses the image, starts an update for the services in auto mode and
// waits for those updates to finish.
package webhook

import (
	"context"
	"crypto/rand"
	"crypto/sha256"
	"crypto/subtle"
	"encoding/hex"
	"encoding/json"
	"errors"
	"log/slog"
	"net/http"
	"regexp"
	"strconv"
	"strings"
	"time"

	"github.com/shcizo/package-updater/internal/imageref"
	"github.com/shcizo/package-updater/internal/logging"
	"github.com/shcizo/package-updater/internal/master/events"
	"github.com/shcizo/package-updater/internal/master/jobs"
	"github.com/shcizo/package-updater/internal/master/model"
)

// maxBodyBytes caps the request body; a valid request is a few hundred bytes.
const maxBodyBytes = 64 << 10

// defaultPollEvery is how often pending jobs are re-read from the store when
// no broker signal arrives (signals to a slow subscriber can be dropped).
const defaultPollEvery = 5 * time.Second

// tagPattern is Docker's tag grammar. It keeps spaces, colons and "@" out of
// the ref the agent is asked to deploy.
var tagPattern = regexp.MustCompile(`^[A-Za-z0-9_][A-Za-z0-9_.-]{0,127}$`)

// Result statuses.
const (
	statusSucceeded = "succeeded"
	statusFailed    = "failed"
	statusTimeout   = "timeout"
	statusMarked    = "marked"
	statusBusy      = "busy"
	statusRefused   = "refused"
)

// Store is the storage the webhook needs. *store.Store satisfies it.
type Store interface {
	ServicesByRepo(ctx context.Context, repo string) ([]model.Service, error)
	SetAvailable(ctx context.Context, id int64, a model.Available) error
	GetJob(ctx context.Context, id int64) (model.Job, error)
}

// Jobs starts updates. *jobs.Service satisfies it.
type Jobs interface {
	Start(ctx context.Context, svc model.Service, req jobs.StartRequest) (model.Job, error)
}

// Broker delivers change signals. *events.Broker satisfies it.
type Broker interface {
	Subscribe() (<-chan events.Topic, func())
	Publish(t events.Topic)
}

// Config holds the webhook settings.
type Config struct {
	Token     string        // bearer token; empty disables the webhook
	Timeout   time.Duration // bounds the whole wait of one request
	PublicURL string        // base of job_url, without trailing slash
}

// Handler serves POST /update.
type Handler struct {
	store  Store
	jobs   Jobs
	broker Broker
	cfg    Config
	log    *slog.Logger

	now       func() time.Time
	pollEvery time.Duration
}

// New returns the handler for POST /update. It does its own bearer-token
// check, so mount it outside the OIDC login.
func New(store Store, jobs Jobs, broker Broker, cfg Config, log *slog.Logger) *Handler {
	return &Handler{store: store, jobs: jobs, broker: broker, cfg: cfg, log: log,
		now: time.Now, pollEvery: defaultPollEvery}
}

type request struct {
	Image string `json:"image"`
	Tag   string `json:"tag"`
}

type result struct {
	ServiceID  int64  `json:"service_id"`
	Service    string `json:"service"`
	Kind       string `json:"kind"`
	Mode       string `json:"mode"`
	Status     string `json:"status"`
	JobID      int64  `json:"job_id,omitempty"`
	JobURL     string `json:"job_url,omitempty"`
	ToRef      string `json:"to_ref,omitempty"`
	Error      string `json:"error,omitempty"`
	DurationMS int64  `json:"duration_ms"`
}

type response struct {
	RequestID string   `json:"request_id"`
	Image     string   `json:"image"`
	Tag       string   `json:"tag,omitempty"`
	Matched   int      `json:"matched"`
	Results   []result `json:"results"`
}

// ServeHTTP handles one webhook call. See the README for the contract.
func (h *Handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	started := h.now()
	requestID := r.Header.Get("X-Request-ID")
	if requestID == "" {
		requestID = newRequestID()
	}
	w.Header().Set("X-Request-ID", requestID)

	if h.cfg.Token == "" {
		writeJSON(w, http.StatusServiceUnavailable, map[string]string{"error": "webhook disabled: UPDATER_API_KEY not set"})
		return
	}
	if !h.authorized(r) {
		writeJSON(w, http.StatusUnauthorized, map[string]string{"error": "unauthorized"})
		return
	}

	var req request
	r.Body = http.MaxBytesReader(w, r.Body, maxBodyBytes)
	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
		writeJSON(w, http.StatusBadRequest, map[string]string{"error": "invalid JSON body"})
		return
	}
	if req.Image == "" {
		writeJSON(w, http.StatusBadRequest, map[string]string{"error": "image is required"})
		return
	}
	if req.Tag != "" && !tagPattern.MatchString(req.Tag) {
		writeJSON(w, http.StatusBadRequest, map[string]string{"error": "invalid tag"})
		return
	}

	log := logging.FromContext(logging.WithRequestID(r.Context(), requestID), h.log)
	repo := imageref.Parse(req.Image).Repo
	// A client that disconnects must not abort marking or starting: that
	// could leave a queued job no agent knows about.
	work := context.WithoutCancel(r.Context())

	services, err := h.store.ServicesByRepo(work, repo)
	if err != nil {
		log.Error("webhook_lookup_failed", "image", req.Image, "error", err)
		writeJSON(w, http.StatusInternalServerError, map[string]string{"error": "internal error"})
		return
	}
	if len(services) == 0 {
		writeJSON(w, http.StatusNotFound, map[string]string{
			"error": "no service uses image " + repo, "request_id": requestID})
		return
	}

	// Subscribe before any job exists so no completion signal is missed.
	sub, cancel := h.broker.Subscribe()
	defer cancel()

	resp := response{RequestID: requestID, Image: req.Image, Tag: req.Tag, Matched: len(services)}
	pending := map[int]int64{} // index into resp.Results -> job ID
	for _, svc := range services {
		res, job := h.handle(work, svc, req.Tag, started)
		resp.Results = append(resp.Results, res)
		if job != nil {
			pending[len(resp.Results)-1] = job.ID
		}
	}
	h.broker.Publish(events.Services)

	h.wait(r.Context(), sub, &resp, pending, started, log)

	status := http.StatusOK
	counts := map[string]int{}
	for _, res := range resp.Results {
		counts[res.Status]++
		if res.Status == statusFailed || res.Status == statusTimeout {
			status = http.StatusInternalServerError
		}
	}
	log.Info("webhook_request", "image", req.Image, "tag", req.Tag, "matched", resp.Matched,
		"succeeded", counts[statusSucceeded], "failed", counts[statusFailed], "timeout", counts[statusTimeout],
		"marked", counts[statusMarked], "busy", counts[statusBusy], "refused", counts[statusRefused])
	writeJSON(w, status, resp)
}

// handle records the available ref on svc and, in auto mode, starts an update.
// It returns the result and, if the job is still active, that job.
func (h *Handler) handle(ctx context.Context, svc model.Service, tag string, started time.Time) (result, *model.Job) {
	res := result{ServiceID: svc.ID, Service: svc.DisplayName(), Kind: string(svc.Kind), Mode: svc.UpdateMode}

	// The ref is built from the service's own repo, never from the request
	// string, so a request cannot point a service at another registry.
	var ref string
	if tag != "" {
		ref = svc.ImageRepo + ":" + tag
	} else {
		ref = jobs.FollowedRef(svc.ActualRef)
	}
	res.ToRef = ref
	if ref != "" {
		err := h.store.SetAvailable(ctx, svc.ID, model.Available{Ref: ref, Source: model.SourceWebhook, At: h.now()})
		if err != nil {
			h.log.Error("webhook_set_available_failed", "service_id", svc.ID, "error", err)
			return h.finish(res, statusFailed, "could not record available version: "+err.Error(), started), nil
		}
	}
	if svc.UpdateMode != model.ModeAuto {
		return h.finish(res, statusMarked, "", started), nil
	}

	job, err := h.jobs.Start(ctx, svc, jobs.StartRequest{Trigger: model.TriggerWebhook, Ref: ref})
	var notUpdatable *model.NotUpdatableError
	switch {
	case errors.As(err, &notUpdatable):
		return h.finish(res, statusRefused, notUpdatable.Reason, started), nil
	case errors.Is(err, model.ErrJobActive):
		h.setJob(&res, job)
		return h.finish(res, statusBusy, err.Error(), started), nil
	case err != nil:
		h.log.Error("webhook_start_failed", "service_id", svc.ID, "error", err)
		return h.finish(res, statusFailed, err.Error(), started), nil
	}
	h.setJob(&res, job)
	if job.Active() {
		return res, &job
	}
	h.resolveJob(&res, job, started)
	return res, nil
}

func (h *Handler) setJob(res *result, job model.Job) {
	res.JobID = job.ID
	res.JobURL = h.cfg.PublicURL + "/jobs/" + strconv.FormatInt(job.ID, 10)
}

func (h *Handler) finish(res result, status, msg string, started time.Time) result {
	res.Status, res.Error = status, msg
	res.DurationMS = h.now().Sub(started).Milliseconds()
	return res
}

// resolveJob sets the result from a job that is no longer active.
func (h *Handler) resolveJob(res *result, job model.Job, started time.Time) {
	if job.Status == model.JobSucceeded {
		*res = h.finish(*res, statusSucceeded, "", started)
		return
	}
	*res = h.finish(*res, statusFailed, job.Error, started)
}

// wait blocks until every pending job has finished, the timeout passes or
// the client goes away. Jobs still pending then get status "timeout"; the
// master never cancels or fails them.
func (h *Handler) wait(parent context.Context, sub <-chan events.Topic, resp *response,
	pending map[int]int64, started time.Time, log *slog.Logger) {
	if len(pending) == 0 {
		return
	}
	ctx, cancel := context.WithTimeout(parent, h.cfg.Timeout)
	defer cancel()
	ticker := time.NewTicker(h.pollEvery)
	defer ticker.Stop()

	for len(pending) > 0 {
		select {
		case <-ctx.Done():
			for i := range pending {
				resp.Results[i] = h.finish(resp.Results[i], statusTimeout, "still running when the request timed out", started)
			}
			return
		case t := <-sub:
			if t != events.Jobs {
				continue
			}
		case <-ticker.C:
		}
		for i, id := range pending {
			job, err := h.store.GetJob(ctx, id)
			if err != nil {
				log.Warn("webhook_get_job_failed", "job_id", id, "error", err)
				continue
			}
			if !job.Active() {
				h.resolveJob(&resp.Results[i], job, started)
				delete(pending, i)
			}
		}
	}
}

// authorized reports whether the request carries the configured bearer token.
// Both sides are hashed so the comparison takes the same time whatever the
// length of the supplied token.
func (h *Handler) authorized(r *http.Request) bool {
	const prefix = "Bearer "
	got, ok := strings.CutPrefix(r.Header.Get("Authorization"), prefix)
	if !ok || got == "" {
		return false
	}
	a, b := sha256.Sum256([]byte(got)), sha256.Sum256([]byte(h.cfg.Token))
	return subtle.ConstantTimeCompare(a[:], b[:]) == 1
}

func writeJSON(w http.ResponseWriter, status int, body any) {
	w.Header().Set("Content-Type", "application/json")
	w.WriteHeader(status)
	_ = json.NewEncoder(w).Encode(body)
}

// newRequestID returns a random 128-bit hex ID.
func newRequestID() string {
	var b [16]byte
	_, _ = rand.Read(b[:])
	return hex.EncodeToString(b[:])
}