// Package server serves the pre-rendered Mode A site out of a build directory.
//
// Everything a visitor reads is a file the build wrote: the server renders a
// page only for a keyword search that carries a query, and for the streamed
// panel demonstration. Nothing here calls a model, opens a socket to another
// service or reads the content tree, so stopping Qdrant, OmniRoute or any query
// service cannot change what a visitor sees (acceptance test A1).
//
// The two pieces that are not files are the two things the static build cannot
// pre-render:
//
//	GET /search?q=…          keyword search over the FTS5 index
//	GET /api/stage/stream    the stage panel bound to an event stream
package server

import (
	"bytes"
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"log/slog"
	"net/http"
	"os"
	"path"
	"path/filepath"
	"strconv"
	"strings"
	"time"

	"gitea.lab.audasmedia.com.au/sam/ai-resume/internal/search"
	"gitea.lab.audasmedia.com.au/sam/ai-resume/internal/site"
	"gitea.lab.audasmedia.com.au/sam/ai-resume/internal/stage"
	"gitea.lab.audasmedia.com.au/sam/ai-resume/internal/web/templates"
)

// Default configuration. The address is loopback on purpose: Caddy is the only
// public listener (AGENTS.md §5).
const (
	DefaultAddr        = "127.0.0.1:8096"
	DefaultDist        = "dist"
	DefaultStreamDelay = 350 * time.Millisecond
)

// Cache policies. Pages are rebuilt on deploy and must not be stale across a
// release, so HTML is revalidated. Unhashed assets get an hour at the origin;
// Phase 3's Caddy block sets the long immutable cache for the public edge.
const (
	pageCache  = "no-cache"
	assetCache = "public, max-age=3600"
	fragCache  = "public, max-age=300"
)

// Config is what the server needs to start. Every field has a usable default so
// that the same binary runs under systemd, compose and `make dev`.
type Config struct {
	// Addr is the listen address. Default 127.0.0.1:8096.
	Addr string
	// DistDir is a directory written by cmd/build. Default "dist".
	DistDir string
	// StreamDelay paces the streamed panel demonstration. Default 350ms.
	StreamDelay time.Duration
	// Logger receives one line per request. Default: JSON to stdout.
	Logger *slog.Logger
}

func (c *Config) defaults() {
	if c.Addr == "" {
		c.Addr = DefaultAddr
	}
	if c.DistDir == "" {
		c.DistDir = DefaultDist
	}
	if c.StreamDelay <= 0 {
		c.StreamDelay = DefaultStreamDelay
	}
	if c.Logger == nil {
		c.Logger = slog.New(slog.NewJSONHandler(os.Stdout, &slog.HandlerOptions{Level: slog.LevelInfo}))
	}
}

// Server serves one build directory.
type Server struct {
	cfg   Config
	dist  string
	shell site.Shell
	log   *slog.Logger

	// built is nil when the directory has no readable build.json; the site is
	// still served, but /healthz reports static as not ready.
	built    *site.BuildInfo
	builtErr error

	// manifest is nil when the build has no stage fragments. Only the streamed
	// demonstration needs it.
	manifest    *stage.Manifest
	manifestErr error

	// index is nil when the FTS5 index could not be opened. Search then says so
	// and the rest of the site is unaffected.
	index    *search.Index
	indexErr error

	handler http.Handler
}

// New opens a build directory. It does not fail when the directory is
// incomplete: it starts, serves whatever is there and lets /healthz report why
// it is not ready, which is what a deploy script needs to see.
func New(cfg Config) (*Server, error) {
	cfg.defaults()
	abs, err := filepath.Abs(cfg.DistDir)
	if err != nil {
		return nil, err
	}
	cfg.DistDir = abs
	st, err := os.Stat(abs)
	if err != nil {
		return nil, fmt.Errorf("build directory %s: %w", abs, err)
	}
	if !st.IsDir() {
		return nil, fmt.Errorf("build directory %s is not a directory", abs)
	}

	s := &Server{
		cfg:   cfg,
		dist:  abs,
		shell: site.NewShell(),
		log:   cfg.Logger,
	}

	s.built, s.builtErr = site.LoadBuildInfo(abs)
	if s.built == nil && s.builtErr == nil {
		s.builtErr = errors.New("build.json is missing")
	}
	if s.builtErr != nil {
		s.log.Warn("build metadata unavailable", "dist", abs, "error", s.builtErr)
	}

	if raw, err := os.ReadFile(filepath.Join(abs, filepath.FromSlash(site.ManifestFile))); err != nil {
		s.manifestErr = err
		s.log.Warn("stage manifest unavailable", "dist", abs, "error", err)
	} else if m, err := stage.LoadManifest(raw); err != nil {
		s.manifestErr = err
		s.log.Warn("stage manifest is not readable", "dist", abs, "error", err)
	} else {
		s.manifest = m
	}

	s.index, s.indexErr = search.Open(filepath.Join(abs, site.IndexFile))
	if s.indexErr != nil {
		s.log.Warn("search index unavailable", "dist", abs, "error", s.indexErr)
	}

	s.handler = s.routes()
	return s, nil
}

// Handler is the whole site behind one http.Handler.
func (s *Server) Handler() http.Handler { return s.handler }

// Close releases the search index handle.
func (s *Server) Close() error {
	if s.index != nil {
		return s.index.Close()
	}
	return nil
}

func (s *Server) routes() http.Handler {
	mux := http.NewServeMux()

	// Liveness and readiness. The AI field is separate and deliberately false:
	// Mode A never needs a model (docs/phase-2-static-site.md §2.1).
	mux.HandleFunc("GET /healthz", s.handleHealth)

	// The two things that are not pre-rendered files.
	mux.HandleFunc("GET /search", s.handleSearch)
	mux.HandleFunc("GET /api/stage/stream", s.handleStream)

	// Route driver: one pre-rendered fragment per click.
	mux.HandleFunc("GET /stage/{id}", s.handleFragment)

	// Assets the build copied out of the repository.
	mux.Handle("GET /static/", s.assetHandler("static"))
	mux.Handle("GET /assets/", s.assetHandler("assets"))

	// Every other path is a page. "GET /" is the fallback pattern.
	mux.HandleFunc("GET /", s.handlePage)

	return s.middleware(s.rejectDotSegments(mux))
}

// rejectDotSegments refuses a request whose path has a "." or ".." segment
// before http.ServeMux cleans it and answers with a redirect. Without this,
// "/static/../build.json" is redirected to "/build.json" and served from outside
// the asset directory. The check runs on URL.Path, which is already percent-
// decoded, so an encoded "%2e%2e" is caught as well.
func (s *Server) rejectDotSegments(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		if hasDotSegment(r.URL.Path) {
			s.notFound(w, r)
			return
		}
		next.ServeHTTP(w, r)
	})
}

// hasDotSegment reports whether any segment of p is "." or "..".
func hasDotSegment(p string) bool {
	for _, seg := range strings.Split(p, "/") {
		if seg == "." || seg == ".." {
			return true
		}
	}
	return false
}

// middleware adds the security headers, one log line per request, and a panic
// guard that keeps one bad request from taking the process down.
func (s *Server) middleware(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		h := w.Header()
		// The policy mirrors the Caddy block in docs/phase-3-deploy.md, so the
		// browser sees the same rules whether it reaches the origin or the edge.
		h.Set("Content-Security-Policy", "default-src 'self'; img-src 'self' data:; script-src 'self'; style-src 'self' 'unsafe-inline'; connect-src 'self'; frame-ancestors 'none'; base-uri 'none'; form-action 'self'")
		h.Set("X-Content-Type-Options", "nosniff")
		h.Set("Referrer-Policy", "strict-origin-when-cross-origin")
		h.Set("X-Frame-Options", "DENY")
		h.Set("Permissions-Policy", "geolocation=(), microphone=(), camera=()")

		rec := &statusWriter{ResponseWriter: w}
		started := time.Now()
		defer func() {
			if p := recover(); p != nil {
				s.log.Error("request panic", "method", r.Method, "path", r.URL.Path, "panic", fmt.Sprint(p))
				if rec.status == 0 {
					http.Error(rec, "internal error", http.StatusInternalServerError)
				}
			}
			s.log.Info("request",
				"method", r.Method,
				"path", r.URL.Path,
				"status", rec.statusOf(),
				"bytes", rec.bytes,
				"duration_ms", time.Since(started).Milliseconds(),
			)
		}()
		next.ServeHTTP(rec, r)
	})
}

// handleHealth reports static and AI readiness separately. Static readiness is
// the only thing that decides the status code, because static readiness is what
// a deploy needs; the AI field says plainly that Mode A does not use one.
func (s *Server) handleHealth(w http.ResponseWriter, r *http.Request) {
	indexReady := s.index != nil
	documents := 0
	if indexReady {
		if n, err := s.index.Count(); err == nil {
			documents = n
		}
	}
	if documents == 0 && s.built != nil {
		documents = s.built.Indexed
	}

	static := struct {
		Ready bool   `json:"ready"`
		Pages int    `json:"pages,omitempty"`
		Built string `json:"built,omitempty"`
		Error string `json:"error,omitempty"`
	}{Ready: s.staticReady()}
	if s.built != nil {
		static.Pages = s.built.Pages
		static.Built = s.built.Built.Format(time.RFC3339)
	}
	if !static.Ready && s.builtErr != nil {
		static.Error = s.builtErr.Error()
	} else if !static.Ready {
		static.Error = "index.html is missing from the build directory"
	}

	body := struct {
		Status string `json:"status"`
		Static any    `json:"static"`
		AI     struct {
			Ready  bool   `json:"ready"`
			Reason string `json:"reason"`
		} `json:"ai"`
		Search struct {
			Ready     bool   `json:"ready"`
			Documents int    `json:"documents,omitempty"`
			Error     string `json:"error,omitempty"`
		} `json:"search"`
	}{Static: static}
	body.AI.Ready = false
	body.AI.Reason = "Mode A serves pre-rendered pages and calls no model; Mode B reports its own readiness in Phase 5."
	body.Search.Ready = indexReady
	body.Search.Documents = documents
	if s.indexErr != nil {
		body.Search.Error = s.indexErr.Error()
	}

	code := http.StatusOK
	body.Status = "ok"
	if !static.Ready {
		code = http.StatusServiceUnavailable
		body.Status = "static-unavailable"
	}

	w.Header().Set("Content-Type", "application/json; charset=utf-8")
	w.Header().Set("Cache-Control", "no-store")
	w.WriteHeader(code)
	enc := json.NewEncoder(w)
	enc.SetIndent("", "  ")
	_ = enc.Encode(body)
}

// staticReady is true when the build actually produced a landing page.
func (s *Server) staticReady() bool {
	if s.built == nil {
		return false
	}
	st, err := os.Stat(filepath.Join(s.dist, "index.html"))
	return err == nil && !st.IsDir()
}

// handlePage serves a pre-rendered page by URL. Directory URLs map to
// index.html so the same tree works under any plain file server.
func (s *Server) handlePage(w http.ResponseWriter, r *http.Request) {
	rel := strings.TrimPrefix(path.Clean("/"+r.URL.Path), "/")
	file, ok := s.resolvePage(rel)
	if !ok {
		s.notFound(w, r)
		return
	}
	if !s.serveFile(w, r, file, "text/html; charset=utf-8", pageCache) {
		s.notFound(w, r)
	}
}

// resolvePage maps a cleaned URL path onto a file inside the build directory.
// A file that is not there is not an error: the caller serves the 404 page.
func (s *Server) resolvePage(rel string) (string, bool) {
	candidates := make([]string, 0, 3)
	switch {
	case rel == "" || strings.HasSuffix(rel, "/"):
		candidates = append(candidates, rel+"index.html")
	case path.Ext(rel) == "":
		candidates = append(candidates, rel, rel+"/index.html", rel+".html")
	default:
		candidates = append(candidates, rel)
	}
	for _, c := range candidates {
		full := filepath.Join(s.dist, filepath.FromSlash(c))
		if !within(s.dist, full) {
			continue
		}
		if st, err := os.Stat(full); err == nil && !st.IsDir() {
			return full, true
		}
	}
	return "", false
}

// handleFragment serves the route driver's payload: one pre-rendered stage
// fragment, selected by the evidence table's hx-get. It is the same bytes the
// stream driver sends as an event.
func (s *Server) handleFragment(w http.ResponseWriter, r *http.Request) {
	id := r.PathValue("id")
	if !validFragmentID(id) {
		s.fragmentNotFound(w, "That fragment is not part of this build.")
		return
	}
	file := filepath.Join(s.dist, "stage", id+".html")
	if !within(s.dist, file) {
		s.fragmentNotFound(w, "That fragment is not part of this build.")
		return
	}
	if _, err := os.Stat(file); err != nil {
		s.fragmentNotFound(w, "That fragment is not part of this build.")
		return
	}
	if !s.serveFile(w, r, file, "text/html; charset=utf-8", fragCache) {
		s.fragmentNotFound(w, "That fragment could not be read.")
	}
}

// validFragmentID keeps ids to the alphabet the build produces, so a request
// can never build a path of its own.
func validFragmentID(id string) bool {
	if id == "" || len(id) > 128 {
		return false
	}
	for _, r := range id {
		switch {
		case r >= 'a' && r <= 'z', r >= '0' && r <= '9', r == '-', r == '_':
		default:
			return false
		}
	}
	return true
}

// fragmentNotFound returns a small HTML fragment, because the panel swaps the
// response into the page and a full document would nest inside it.
func (s *Server) fragmentNotFound(w http.ResponseWriter, msg string) {
	w.Header().Set("Content-Type", "text/html; charset=utf-8")
	w.Header().Set("Cache-Control", "no-store")
	w.WriteHeader(http.StatusNotFound)
	_, _ = io.WriteString(w, `<div class="stage-empty"><p class="stage-empty-title">`+msg+`</p><p class="stage-hint">The <a href="/evidence/">evidence index</a> lists every fragment in this build.</p></div>`)
}

// handleSearch runs a keyword search. With HTMX it returns just the contents of
// the results block, which the search page's own form swaps into #search-results;
// without JavaScript the same handler returns the whole page, so the form works
// in both cases.
func (s *Server) handleSearch(w http.ResponseWriter, r *http.Request) {
	q := strings.TrimSpace(r.URL.Query().Get("q"))
	failed := false
	indexed := 0
	if s.built != nil {
		indexed = s.built.Indexed
	}
	var results []search.Result
	if s.index != nil {
		if n, err := s.index.Count(); err == nil {
			indexed = n
		}
	}
	if q != "" {
		if s.index == nil {
			failed = true
		} else {
			var err error
			results, err = s.index.Query(q, 20)
			if err != nil {
				failed = true
				s.log.Warn("search failed", "query_length", len(q), "error", err)
			}
		}
	}

	view := s.shell.SearchView(indexed, q, results, failed)
	w.Header().Set("Cache-Control", "no-store")
	w.Header().Set("Vary", "HX-Request")

	var buf bytes.Buffer
	var c interface {
		Render(context.Context, io.Writer) error
	} = templates.SearchPage(view)
	if r.Header.Get("HX-Request") == "true" {
		// The element that holds #search-results stays where it is, so the
		// fragment carries the contents and not the wrapper.
		c = templates.SearchResultsBody(view)
	}
	if err := c.Render(r.Context(), &buf); err != nil {
		s.log.Error("render search", "error", err)
		http.Error(w, "search is unavailable", http.StatusInternalServerError)
		return
	}
	w.Header().Set("Content-Type", "text/html; charset=utf-8")
	w.Header().Set("Content-Length", strconv.Itoa(buf.Len()))
	w.WriteHeader(http.StatusOK)
	if r.Method != http.MethodHead {
		_, _ = w.Write(buf.Bytes())
	}
}

// notFound serves the pre-rendered 404 page with a 404 status.
func (s *Server) notFound(w http.ResponseWriter, r *http.Request) {
	file := filepath.Join(s.dist, "404.html")
	if raw, err := os.ReadFile(file); err == nil && within(s.dist, file) {
		w.Header().Set("Content-Type", "text/html; charset=utf-8")
		w.Header().Set("Cache-Control", "no-store")
		w.WriteHeader(http.StatusNotFound)
		if r.Method != http.MethodHead {
			_, _ = w.Write(raw)
		}
		return
	}
	http.Error(w, "not found", http.StatusNotFound)
}

// assetHandler serves a directory of build output (/static/, /assets/).
func (s *Server) assetHandler(dir string) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		if r.Method != http.MethodGet && r.Method != http.MethodHead {
			w.Header().Set("Allow", "GET, HEAD")
			http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
			return
		}
		prefix := "/" + dir + "/"
		rel := strings.TrimPrefix(path.Clean("/"+strings.TrimPrefix(r.URL.Path, prefix)), "/")
		if rel == "" || strings.HasPrefix(rel, "..") {
			s.notFound(w, r)
			return
		}
		file := filepath.Join(s.dist, dir, filepath.FromSlash(rel))
		if !within(filepath.Join(s.dist, dir), file) {
			s.notFound(w, r)
			return
		}
		ctype := contentTypeFor(file)
		if !s.serveFile(w, r, file, ctype, assetCache) {
			s.notFound(w, r)
		}
	})
}

// serveFile writes one file, with Range and HEAD support. It returns false when
// the file is missing or unreadable, so the caller can choose the error page.
func (s *Server) serveFile(w http.ResponseWriter, r *http.Request, file, ctype, cache string) bool {
	f, err := os.Open(file)
	if err != nil {
		return false
	}
	defer f.Close()
	st, err := f.Stat()
	if err != nil || st.IsDir() {
		return false
	}
	h := w.Header()
	h.Set("Content-Type", ctype)
	h.Set("Cache-Control", cache)
	h.Set("Content-Length", strconv.FormatInt(st.Size(), 10))
	http.ServeContent(w, r, st.Name(), st.ModTime(), f)
	return true
}

// within reports whether target is inside root, after cleaning both. Every path
// built from a request goes through here before it reaches the filesystem.
func within(root, target string) bool {
	rel, err := filepath.Rel(root, target)
	if err != nil {
		return false
	}
	return rel != ".." && !strings.HasPrefix(rel, ".."+string(filepath.Separator)) && !filepath.IsAbs(rel)
}

// contentTypeFor is the small set of types this site publishes.
func contentTypeFor(file string) string {
	switch strings.ToLower(filepath.Ext(file)) {
	case ".css":
		return "text/css; charset=utf-8"
	case ".js":
		return "text/javascript; charset=utf-8"
	case ".svg":
		return "image/svg+xml"
	case ".png":
		return "image/png"
	case ".jpg", ".jpeg":
		return "image/jpeg"
	case ".webp":
		return "image/webp"
	case ".woff2":
		return "font/woff2"
	case ".json":
		return "application/json; charset=utf-8"
	case ".html":
		return "text/html; charset=utf-8"
	}
	return "application/octet-stream"
}

// statusWriter records the status and size for the request log, and forwards
// Flush so an event stream is not buffered by the middleware.
type statusWriter struct {
	http.ResponseWriter
	status int
	bytes  int
}

func (w *statusWriter) WriteHeader(code int) {
	if w.status == 0 {
		w.status = code
	}
	w.ResponseWriter.WriteHeader(code)
}

func (w *statusWriter) Write(b []byte) (int, error) {
	if w.status == 0 {
		w.status = http.StatusOK
	}
	n, err := w.ResponseWriter.Write(b)
	w.bytes += n
	return n, err
}

func (w *statusWriter) Flush() {
	if f, ok := w.ResponseWriter.(http.Flusher); ok {
		f.Flush()
	}
}

func (w *statusWriter) Unwrap() http.ResponseWriter { return w.ResponseWriter }

func (w *statusWriter) statusOf() int {
	if w.status == 0 {
		return http.StatusOK
	}
	return w.status
}