package webhook

import (
	"context"
	"crypto/hmac"
	"crypto/sha256"
	"encoding/hex"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"log/slog"
	"net/http"
	"strings"
	"sync"

	"github.com/go-chi/chi/v5"

	"github.com/alexei/tinyforge/internal/store"
)

// signatureHeader is the canonical Gitea/GitHub-compatible header name for
// HMAC-SHA256 signatures over the raw request body. Tinyforge accepts the
// same header so existing CI integrations work unchanged.
const signatureHeader = "X-Hub-Signature-256"

// verifyHMAC validates the X-Hub-Signature-256 header against the raw body
// using HMAC-SHA256. The function does the comparison in constant time.
//
// Behavior:
//   - signingSecret == "": signing not configured for this entity. The
//     function returns (false, false) — the caller decides whether to
//     enforce based on the require_signature flag.
//   - header missing: returns (false, true) — caller-decided.
//   - header malformed or signature mismatch: returns (false, true).
//   - signature valid: returns (true, true).
//
// First return: whether the signature was successfully verified.
// Second return: whether the verification was attempted (i.e., a header was
// present or signing is configured). The caller uses this to distinguish
// "no signature submitted" from "wrong signature submitted".
func verifyHMAC(signingSecret string, body []byte, headerValue string) (verified, attempted bool) {
	if signingSecret == "" {
		return false, false
	}
	if headerValue == "" {
		return false, false
	}
	const prefix = "sha256="
	if !strings.HasPrefix(headerValue, prefix) {
		return false, true
	}
	provided, err := hex.DecodeString(headerValue[len(prefix):])
	if err != nil {
		return false, true
	}
	mac := hmac.New(sha256.New, []byte(signingSecret))
	mac.Write(body)
	expected := mac.Sum(nil)
	return hmac.Equal(provided, expected), true
}

// maxSiteConcurrentSyncs caps fan-out of background site syncs triggered by
// webhooks. Above this limit, requests are rejected with 503.
const maxSiteConcurrentSyncs = 4

// maxWebhookBodyBytes caps the request body size for webhook payloads. The
// /api routes already wrap the body with MaxBytesReader, but the webhook
// router relies on its own limit so changes to the parent middleware can't
// silently increase the cap.
const maxWebhookBodyBytes = 256 * 1024 // 256 KiB

// DeployTriggerer is called when a webhook determines a deploy should happen.
// Same interface as registry.DeployTriggerer — kept separate to avoid import cycles.
type DeployTriggerer interface {
	TriggerDeploy(ctx context.Context, projectID, stageID, imageTag string) error
}

// SiteSyncTriggerer is called when a static-site webhook determines a sync
// should happen. The manager handles the actual git-pull + redeploy.
type SiteSyncTriggerer interface {
	Deploy(ctx context.Context, siteID string, force bool) error
}

// Payload is the expected JSON body for a project webhook request.
type Payload struct {
	// Image is the full image reference including tag, e.g.
	// "git.dolgolyov-family.by/alexei/web-app-launcher:dev-abc123".
	Image string `json:"image"`
}

// SitePayload is the expected JSON body for a static-site webhook request.
// Callers point Gitea/GitHub/GitLab webhooks at the site URL; only the ref
// matters for branch filtering. Body is optional — an empty body triggers
// a sync using the site's configured branch.
type SitePayload struct {
	Ref string `json:"ref"` // e.g. "refs/heads/main"; optional
}

// ParsedImage holds the components extracted from a full image reference string.
type ParsedImage struct {
	// Registry is the hostname, e.g. "git.dolgolyov-family.by".
	Registry string
	// Owner is the namespace/org, e.g. "alexei".
	Owner string
	// Name is the repository name, e.g. "web-app-launcher".
	Name string
	// Tag is the image tag, e.g. "dev-abc123". Empty string means "latest".
	Tag string
}

// FullName returns "owner/name" (the image path without registry and tag).
func (p ParsedImage) FullName() string {
	if p.Owner != "" {
		return p.Owner + "/" + p.Name
	}
	return p.Name
}

// ParseImageRef splits a full image reference into its components.
// Accepted formats:
//
//	registry.example.com/owner/name:tag
//	registry.example.com/owner/name
//	owner/name:tag
//	name:tag
func ParseImageRef(ref string) (ParsedImage, error) {
	ref = strings.TrimSpace(ref)
	if ref == "" {
		return ParsedImage{}, fmt.Errorf("empty image reference")
	}

	var parsed ParsedImage

	// Split off tag.
	if idx := strings.LastIndex(ref, ":"); idx != -1 {
		// Make sure the colon is not inside the registry host (e.g. "localhost:5000/img").
		afterColon := ref[idx+1:]
		if !strings.Contains(afterColon, "/") {
			parsed.Tag = afterColon
			ref = ref[:idx]
		}
	}

	parts := strings.Split(ref, "/")
	switch len(parts) {
	case 1:
		// "name"
		parsed.Name = parts[0]
	case 2:
		// "owner/name"
		parsed.Owner = parts[0]
		parsed.Name = parts[1]
	default:
		// "registry/owner/name" or "registry/owner/sub/name" — first segment is registry.
		parsed.Registry = parts[0]
		parsed.Owner = strings.Join(parts[1:len(parts)-1], "/")
		parsed.Name = parts[len(parts)-1]
	}

	if parsed.Name == "" {
		return ParsedImage{}, fmt.Errorf("invalid image reference: missing name in %q", ref)
	}

	return parsed, nil
}

// Handler is the HTTP handler for webhook requests.
type Handler struct {
	store    *store.Store
	deployer DeployTriggerer
	sites    SiteSyncTriggerer

	// Site sync coordination — webhooks fire syncs in the background; Drain
	// blocks until those goroutines finish, so a graceful shutdown does not
	// kill an in-flight git fetch + container rebuild.
	siteSyncCtx    context.Context
	siteSyncCancel context.CancelFunc
	siteSyncWG     sync.WaitGroup
	siteSyncSem    chan struct{}
}

// NewHandler creates a new webhook Handler. The sites triggerer is optional
// and may be nil (site webhooks will return 404).
func NewHandler(st *store.Store, deployer DeployTriggerer, sites SiteSyncTriggerer) *Handler {
	ctx, cancel := context.WithCancel(context.Background())
	return &Handler{
		store:          st,
		deployer:       deployer,
		sites:          sites,
		siteSyncCtx:    ctx,
		siteSyncCancel: cancel,
		siteSyncSem:    make(chan struct{}, maxSiteConcurrentSyncs),
	}
}

// SetSiteSyncTriggerer injects the static-site manager after construction.
// The site manager depends on the store + docker client, which are wired up
// in the same startup path as the handler; this setter lets callers defer the
// dependency if needed.
func (h *Handler) SetSiteSyncTriggerer(s SiteSyncTriggerer) {
	h.sites = s
}

// Drain cancels in-flight site syncs and waits for their goroutines to exit.
// Safe to call from a graceful-shutdown path.
func (h *Handler) Drain() {
	h.siteSyncCancel()
	h.siteSyncWG.Wait()
}

// Route returns a chi router with the webhook endpoints mounted.
//
// Routes:
//
//	POST /{secret}          — per-project deploy trigger
//	POST /sites/{secret}    — per-site sync trigger
func (h *Handler) Route() chi.Router {
	r := chi.NewRouter()
	r.Post("/sites/{secret}", h.handleSiteWebhook)
	r.Post("/{secret}", h.handleWebhook)
	return r
}

// respondWebhookJSON writes a JSON response for webhook handlers.
func respondWebhookJSON(w http.ResponseWriter, status int, data any) {
	w.Header().Set("Content-Type", "application/json")
	w.WriteHeader(status)
	json.NewEncoder(w).Encode(data) //nolint:errcheck
}

// respondWebhookError writes a JSON error response for webhook handlers.
func respondWebhookError(w http.ResponseWriter, status int, msg string) {
	respondWebhookJSON(w, status, map[string]any{"success": false, "error": msg})
}

// handleWebhook processes an incoming project webhook request.
//
// URL: POST /api/webhook/{secret}
//
// The secret identifies exactly one project. Stage routing is delegated to
// the project's configured stages (tag_pattern match). Returns 404 for
// unknown secrets (no information leak).
func (h *Handler) handleWebhook(w http.ResponseWriter, r *http.Request) {
	ctx := r.Context()

	secret := chi.URLParam(r, "secret")
	if secret == "" {
		http.NotFound(w, r)
		return
	}

	project, err := h.store.GetProjectByWebhookSecret(secret)
	if err != nil {
		if errors.Is(err, store.ErrNotFound) {
			http.NotFound(w, r)
			return
		}
		slog.Error("webhook: project lookup failed", "error", err)
		http.NotFound(w, r)
		return
	}

	// Read body once so we can both verify HMAC and decode JSON.
	body, err := io.ReadAll(io.LimitReader(r.Body, maxWebhookBodyBytes))
	if err != nil {
		respondWebhookError(w, http.StatusBadRequest, "failed to read request body")
		return
	}

	// HMAC enforcement: a configured signing secret + the require_signature
	// flag together produce a hard reject on missing/invalid signatures.
	// When the flag is off we still verify any submitted signature so a
	// CI misconfiguration surfaces as a 401 rather than silent acceptance.
	verified, attempted := verifyHMAC(project.WebhookSigningSecret, body, r.Header.Get(signatureHeader))
	if project.WebhookRequireSignature && !verified {
		slog.Warn("webhook: signature required but invalid/missing", "project", project.Name)
		respondWebhookError(w, http.StatusUnauthorized, "invalid or missing signature")
		return
	}
	if attempted && !verified {
		slog.Warn("webhook: bad signature", "project", project.Name)
		respondWebhookError(w, http.StatusUnauthorized, "invalid signature")
		return
	}

	var payload Payload
	if err := json.Unmarshal(body, &payload); err != nil {
		respondWebhookError(w, http.StatusBadRequest, "invalid JSON payload")
		return
	}

	if payload.Image == "" {
		respondWebhookError(w, http.StatusBadRequest, "missing image field")
		return
	}

	parsed, err := ParseImageRef(payload.Image)
	if err != nil {
		respondWebhookError(w, http.StatusBadRequest, "invalid image reference")
		return
	}

	if parsed.Tag == "" {
		parsed.Tag = "latest"
	}

	// Guardrail: refuse payloads whose image doesn't match the project's
	// configured image. Not a security control (the secret already scopes
	// access) — just a misconfiguration check that prevents accidental
	// cross-project deploys from a misaimed CI pipeline.
	if project.Image != "" && !imageMatches(project.Image, parsed.FullName()) {
		slog.Warn("webhook: image mismatch",
			"project", project.Name, "expected", project.Image, "received", parsed.FullName())
		respondWebhookError(w, http.StatusBadRequest,
			fmt.Sprintf("image %q does not match project image %q", parsed.FullName(), project.Image))
		return
	}

	slog.Info("webhook: received push",
		"project", project.Name, "image", parsed.FullName(), "tag", parsed.Tag)

	stage, found, err := matchStage(h.store, project.ID, parsed.Tag)
	if err != nil {
		slog.Error("webhook: stage match failed", "project", project.Name, "error", err)
		respondWebhookError(w, http.StatusInternalServerError, "internal error")
		return
	}
	if !found {
		slog.Info("webhook: no stage matches tag",
			"project", project.Name, "tag", parsed.Tag)
		respondWebhookJSON(w, http.StatusOK, map[string]any{
			"success": true, "deploy": false, "project": project.Name,
			"reason": "no stage pattern matched tag",
		})
		return
	}

	if !stage.AutoDeploy {
		slog.Info("webhook: auto_deploy disabled, skipping",
			"project", project.Name, "stage", stage.Name)
		respondWebhookJSON(w, http.StatusOK, map[string]any{
			"success": true, "deploy": false,
			"project": project.Name, "stage": stage.Name,
		})
		return
	}

	if err := h.deployer.TriggerDeploy(ctx, project.ID, stage.ID, parsed.Tag); err != nil {
		slog.Error("webhook: deploy trigger failed", "error", err)
		respondWebhookError(w, http.StatusInternalServerError, "deploy trigger failed")
		return
	}

	slog.Info("webhook: triggered deploy",
		"project", project.Name, "stage", stage.Name, "tag", parsed.Tag)
	respondWebhookJSON(w, http.StatusOK, map[string]any{
		"success": true, "deploy": true,
		"project": project.Name, "stage": stage.Name, "tag": parsed.Tag,
	})
}

// handleSiteWebhook processes an incoming static-site webhook request.
//
// URL: POST /api/webhook/sites/{secret}
//
// The secret identifies exactly one static site. If the payload includes a
// ref (Git push event), it must match the site's configured branch (when the
// site's sync_trigger is "push"). For tag-based sync, the ref must match the
// stored tag pattern. Manual-trigger sites ignore webhooks entirely.
func (h *Handler) handleSiteWebhook(w http.ResponseWriter, r *http.Request) {
	ctx := r.Context()

	if h.sites == nil {
		http.NotFound(w, r)
		return
	}

	secret := chi.URLParam(r, "secret")
	if secret == "" {
		http.NotFound(w, r)
		return
	}

	site, err := h.store.GetStaticSiteByWebhookSecret(secret)
	if err != nil {
		if errors.Is(err, store.ErrNotFound) {
			http.NotFound(w, r)
			return
		}
		slog.Error("webhook: site lookup failed", "error", err)
		http.NotFound(w, r)
		return
	}

	// Manual sites do not auto-sync via webhook. Return success but skip.
	if site.SyncTrigger == "manual" {
		slog.Info("webhook: site sync_trigger=manual, skipping",
			"site", site.Name)
		respondWebhookJSON(w, http.StatusOK, map[string]any{
			"success": true, "sync": false, "site": site.Name,
			"reason": "sync_trigger is manual",
		})
		return
	}

	// Body is optional. We attempt to decode but accept an empty body (no Ref
	// filter); a malformed non-empty body is treated as bad-request to avoid
	// silently bypassing the branch/tag filter.
	var payload SitePayload
	body, err := io.ReadAll(io.LimitReader(r.Body, maxWebhookBodyBytes))
	if err != nil {
		respondWebhookError(w, http.StatusBadRequest, "failed to read request body")
		return
	}

	// HMAC enforcement matches the project flow: hard reject when required,
	// soft reject when an invalid signature is supplied without enforcement.
	verified, attempted := verifyHMAC(site.WebhookSigningSecret, body, r.Header.Get(signatureHeader))
	if site.WebhookRequireSignature && !verified {
		slog.Warn("webhook: site signature required but invalid/missing", "site", site.Name)
		respondWebhookError(w, http.StatusUnauthorized, "invalid or missing signature")
		return
	}
	if attempted && !verified {
		slog.Warn("webhook: site bad signature", "site", site.Name)
		respondWebhookError(w, http.StatusUnauthorized, "invalid signature")
		return
	}

	if len(body) > 0 {
		if err := json.Unmarshal(body, &payload); err != nil {
			respondWebhookError(w, http.StatusBadRequest, "invalid JSON payload")
			return
		}
	}

	if payload.Ref != "" && !siteRefMatches(site, payload.Ref) {
		slog.Info("webhook: site ref does not match configured branch/tag",
			"site", site.Name, "ref", payload.Ref,
			"branch", site.Branch, "tag_pattern", site.TagPattern,
			"trigger", site.SyncTrigger)
		respondWebhookJSON(w, http.StatusOK, map[string]any{
			"success": true, "sync": false, "site": site.Name,
			"reason": "ref does not match configured branch or tag pattern",
		})
		return
	}

	// Cap concurrent syncs so a runaway CI cannot fan out unbounded
	// git-clone goroutines.
	select {
	case h.siteSyncSem <- struct{}{}:
	default:
		respondWebhookError(w, http.StatusServiceUnavailable, "site sync queue full")
		return
	}

	h.siteSyncWG.Add(1)
	go func(siteID, siteName string) {
		defer h.siteSyncWG.Done()
		defer func() { <-h.siteSyncSem }()
		if err := h.sites.Deploy(h.siteSyncCtx, siteID, false); err != nil {
			slog.Error("webhook: site sync failed", "site", siteName, "error", err)
		}
	}(site.ID, site.Name)

	_ = ctx
	slog.Info("webhook: triggered site sync", "site", site.Name, "ref", payload.Ref)
	respondWebhookJSON(w, http.StatusOK, map[string]any{
		"success": true, "sync": true, "site": site.Name,
	})
}