// Package server wires repospawner's HTTP surface: the request API, the health
// probes and the embedded UI, plus the reconcile loop that drives requests
// forward.
package server

import (
	"context"
	"encoding/json"
	"errors"
	"io"
	"io/fs"
	"log/slog"
	"net/http"
	"os"
	"strings"
	"time"

	"git.unkin.net/unkin/repospawner/internal/auth"
	"git.unkin.net/unkin/repospawner/internal/config"
	"git.unkin.net/unkin/repospawner/internal/gitea"
	"git.unkin.net/unkin/repospawner/internal/jobs"
	"git.unkin.net/unkin/repospawner/internal/repospec"
	"git.unkin.net/unkin/repospawner/internal/store"
)

// maxBodyBytes caps a submitted request body; the payload is four small fields.
const maxBodyBytes = 64 << 10

// Server holds the resolved dependencies of the app.
type Server struct {
	cfg     *config.Config
	store   *store.Store
	forge   *gitea.Client
	cluster Cluster
	gate    *auth.Middleware
	assets  fs.FS
	log     *slog.Logger
}

// New constructs a Server.
func New(cfg *config.Config, st *store.Store, forge *gitea.Client, cluster Cluster, assets fs.FS, log *slog.Logger) *Server {
	if log == nil {
		log = slog.Default()
	}
	return &Server{
		cfg:     cfg,
		store:   st,
		forge:   forge,
		cluster: cluster,
		gate:    auth.New(cfg.GroupsHeader, cfg.AllowedGroups),
		assets:  assets,
		log:     log,
	}
}

// Handler returns the root handler. Health probes are ungated (kubelet sends no
// identity header); everything else — API and UI alike — sits behind the group
// gate, so an unauthorized user cannot even load the page shell.
func (s *Server) Handler() http.Handler {
	mux := http.NewServeMux()
	mux.HandleFunc("GET /livez", func(w http.ResponseWriter, _ *http.Request) {
		_, _ = w.Write([]byte("ok"))
	})
	mux.HandleFunc("GET /readyz", s.readyz)

	gated := http.NewServeMux()
	gated.HandleFunc("POST /api/requests", s.handleCreate)
	gated.HandleFunc("GET /api/requests", s.handleList)
	gated.HandleFunc("GET /api/requests/{id}", s.handleGet)
	gated.HandleFunc("GET /api/capabilities", s.handleCapabilities)
	gated.HandleFunc("/", s.handleUI)

	mux.Handle("/", s.gate.Wrap(gated))
	return secureHeaders(mux)
}

// cspPolicy locks the page to same-origin code. The UI carries no inline script
// or style, so no unsafe-inline escape hatch is needed; data: is in img-src
// solely for the inline SVG favicon.
const cspPolicy = "default-src 'self'; img-src 'self' data:; style-src 'self'; script-src 'self'"

// secureHeaders stamps the browser-facing hardening headers onto every
// response — API, UI and probes alike — before the handler writes.
func secureHeaders(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		h := w.Header()
		h.Set("Content-Security-Policy", cspPolicy)
		h.Set("X-Content-Type-Options", "nosniff")
		h.Set("Referrer-Policy", "no-referrer")
		next.ServeHTTP(w, r)
	})
}

func (s *Server) readyz(w http.ResponseWriter, r *http.Request) {
	ctx, cancel := context.WithTimeout(r.Context(), 5*time.Second)
	defer cancel()
	if err := s.cluster.Ping(ctx); err != nil {
		s.log.Warn("readyz: kubernetes api unreachable", "err", err)
		http.Error(w, "kubernetes api unreachable", http.StatusServiceUnavailable)
		return
	}
	_, _ = w.Write([]byte("ok"))
}

// woodpeckerAvailable reports whether a Woodpecker API token is mounted. It is
// read per call so a later secret mount needs no restart.
func (s *Server) woodpeckerAvailable() bool {
	if s.cfg.WoodpeckerTokenFile == "" {
		return false
	}
	b, err := os.ReadFile(s.cfg.WoodpeckerTokenFile)
	return err == nil && strings.TrimSpace(string(b)) != ""
}

func (s *Server) handleCapabilities(w http.ResponseWriter, _ *http.Request) {
	writeJSON(w, http.StatusOK, map[string]any{
		"woodpecker": s.woodpeckerAvailable(),
		"tfgit_repo": s.cfg.TFGitRepo,
	})
}

func (s *Server) handleCreate(w http.ResponseWriter, r *http.Request) {
	var spec repospec.Request
	dec := json.NewDecoder(io.LimitReader(r.Body, maxBodyBytes))
	dec.DisallowUnknownFields()
	if err := dec.Decode(&spec); err != nil {
		writeErr(w, http.StatusBadRequest, "request body is not the expected JSON object")
		return
	}
	spec = spec.Normalize()
	if err := spec.Validate(); err != nil {
		var fe repospec.FieldErrors
		if errors.As(err, &fe) {
			writeJSON(w, http.StatusBadRequest, map[string]any{"error": "invalid request", "fields": fe})
			return
		}
		writeErr(w, http.StatusBadRequest, "invalid request")
		return
	}
	if spec.Woodpecker && !s.woodpeckerAvailable() {
		writeErr(w, http.StatusServiceUnavailable,
			"woodpecker enablement is unavailable: no woodpecker API token is mounted; resubmit with woodpecker disabled")
		return
	}
	if s.store.HasActiveName(spec.Name) {
		writeErr(w, http.StatusConflict, "a request for that repository name is already in flight")
		return
	}

	exists, err := s.forge.FileExists(r.Context(), s.cfg.TFGitRepo, spec.ConfigPath(), "main")
	if err != nil {
		s.log.Error("terraform-git name check failed", "name", spec.Name, "err", err)
		writeErr(w, http.StatusBadGateway, "cannot check the repository name against terraform-git")
		return
	}
	if exists {
		writeErr(w, http.StatusConflict, "that repository is already defined in terraform-git")
		return
	}

	req := store.NewRequest(store.NewID(), spec, s.store.Now())
	if err := s.cluster.CreateJob(r.Context(), jobs.PR(s.cfg, req)); err != nil {
		s.log.Error("create pull request job", "request", req.ID, "err", err)
		writeErr(w, http.StatusInternalServerError, "cannot start the pull request job")
		return
	}
	s.store.Put(req)
	s.log.Info("accepted repo request", "request", req.ID, "name", req.Name, "woodpecker", req.Woodpecker)

	w.Header().Set("Location", "/api/requests/"+req.ID)
	writeJSON(w, http.StatusAccepted, map[string]any{
		"id":         req.ID,
		"status_url": "/api/requests/" + req.ID,
		"state":      req.State,
	})
}

func (s *Server) handleList(w http.ResponseWriter, _ *http.Request) {
	writeJSON(w, http.StatusOK, map[string]any{"requests": s.store.List()})
}

func (s *Server) handleGet(w http.ResponseWriter, r *http.Request) {
	req, ok := s.store.Get(r.PathValue("id"))
	if !ok {
		writeErr(w, http.StatusNotFound, "no such request")
		return
	}
	writeJSON(w, http.StatusOK, req)
}

// handleUI serves the embedded assets, falling back to index.html so a reload
// on any path lands on the app.
func (s *Server) handleUI(w http.ResponseWriter, r *http.Request) {
	p := strings.TrimPrefix(r.URL.Path, "/")
	if strings.HasPrefix(p, "api/") {
		writeErr(w, http.StatusNotFound, "not found")
		return
	}
	if p != "" {
		if st, err := fs.Stat(s.assets, p); err == nil && !st.IsDir() {
			http.FileServerFS(s.assets).ServeHTTP(w, r)
			return
		}
	}
	b, err := fs.ReadFile(s.assets, "index.html")
	if err != nil {
		http.Error(w, "index missing", http.StatusInternalServerError)
		return
	}
	w.Header().Set("Content-Type", "text/html; charset=utf-8")
	_, _ = w.Write(b)
}

func writeJSON(w http.ResponseWriter, status int, v any) {
	w.Header().Set("Content-Type", "application/json; charset=utf-8")
	w.WriteHeader(status)
	_ = json.NewEncoder(w).Encode(v)
}

func writeErr(w http.ResponseWriter, status int, msg string) {
	writeJSON(w, status, map[string]string{"error": msg})
}