package handler

import (
	"crypto/sha256"
	"encoding/hex"
	"encoding/json"
	"log/slog"
	"net/http"
	"os"
	"path/filepath"
	"strings"

	"codeberg.org/VARASYS/ZDDC/zddc/internal/apps"
	"codeberg.org/VARASYS/ZDDC/zddc/internal/config"
	appfs "codeberg.org/VARASYS/ZDDC/zddc/internal/fs"
	"codeberg.org/VARASYS/ZDDC/zddc/internal/policy"
	"codeberg.org/VARASYS/ZDDC/zddc/internal/zddc"
)

// listingETag returns a hex-encoded SHA-256 prefix of the rendered JSON
// listing body. Truncated to 16 chars (64 bits) — collisions on a
// listing of any realistic size are vanishingly unlikely, and the short
// header keeps the wire footprint trim.
func listingETag(body []byte) string {
	h := sha256.Sum256(body)
	return hex.EncodeToString(h[:8])
}

// safeJoin joins fsRoot and relPath, then verifies the result is under fsRoot.
// Returns ("", false) if relPath would escape fsRoot.
func safeJoin(fsRoot, relPath string) (string, bool) {
	abs := filepath.Join(fsRoot, filepath.FromSlash(relPath))
	if !strings.HasPrefix(abs, fsRoot+string(filepath.Separator)) && abs != fsRoot {
		return "", false
	}
	return abs, true
}

// ServeDirectory handles a request for a directory path.
// If Accept: application/json → return Caddy-compatible JSON listing.
// Otherwise → return minimal HTML.
//
// appsSrv is optional: when non-nil, HTML responses resolve the
// `browse` tool through the apps subsystem so a `.zddc apps:` cascade
// entry can override the embedded bytes (handy for live alpha-dev
// iteration: point apps.browse: at a path source and every ./build is
// served from disk without recompiling the binary). When nil, the
// embedded copy is served directly — same behavior as before the
// cascade hook was added.
func ServeDirectory(cfg config.Config, appsSrv *apps.Server, w http.ResponseWriter, r *http.Request) {
	urlPath := r.URL.Path
	if !strings.HasSuffix(urlPath, "/") {
		http.Redirect(w, r, urlPath+"/", http.StatusFound)
		return
	}

	email := EmailFromContext(r)
	decider := DeciderFromContext(r)
	ctx := r.Context()

	// Compute relative dir path (no leading or trailing slash)
	dirPath := strings.TrimPrefix(urlPath, "/")
	dirPath = strings.TrimSuffix(dirPath, "/")

	// ACL check on this directory itself.
	// Bypassed at the root path: the landing page is a public project
	// picker. Per-project filtering inside fs.ListDirectory still hides
	// directories the caller can't reach.
	absDir, ok := safeJoin(cfg.Root, dirPath)
	if !ok {
		http.Error(w, "Not Found", http.StatusNotFound)
		return
	}
	chain, err := zddc.EffectivePolicy(cfg.Root, absDir)
	if err != nil {
		slog.Warn("ACL policy error", "path", absDir, "err", err)
	}
	isRoot := dirPath == ""
	if !isRoot {
		if allowed, _ := policy.AllowFromChain(ctx, decider, chain, email, urlPath); !allowed {
			http.Error(w, "Forbidden", http.StatusForbidden)
			return
		}
	}

	accept := r.Header.Get("Accept")

	// For HTML requests, serve index.html if present (landing page convention)
	if !strings.Contains(accept, "application/json") {
		indexPath := filepath.Join(absDir, "index.html")
		if info, err := os.Stat(indexPath); err == nil && !info.IsDir() {
			ServeFile(w, r, indexPath)
			return
		}

		// Tables redirect: when this directory is the rows directory of
		// a registered table — i.e. the parent declares
		// `tables: { <name>: ... }` with a valid spec, OR the default-MDL
		// fallback kicks in at archive/<party>/mdl/ — bounce HTML
		// requests to the canonical <parent>/<name>.table.html URL so
		// users land on the table view instead of a bare folder listing.
		// JSON requests fall through unchanged so the table client can
		// still enumerate row files.
		if redirect := tableRowsRedirect(cfg.Root, urlPath); redirect != "" {
			http.Redirect(w, r, redirect, http.StatusFound)
			return
		}
	}

	// Build base URL for listing entries
	baseURL := urlPath // relative URLs suffice for JSON listings

	// ?hidden=1 surfaces dot- and underscore-prefixed entries. ACL is
	// still the only real gate — anyone who can't read this dir sees
	// nothing regardless. browse pipes the flag through when its
	// "Show hidden" toggle is on. Matches the bare-flag convention
	// used by ?zip and ?convert= elsewhere in the dispatcher.
	includeHidden := r.URL.Query().Has("hidden")

	entries, err := appfs.ListDirectory(ctx, decider, cfg.Root, dirPath, email, baseURL, includeHidden)
	if err != nil {
		if os.IsNotExist(err) {
			http.Error(w, "Not Found", http.StatusNotFound)
		} else {
			slog.Error("listing directory", "path", dirPath, "err", err)
			http.Error(w, "Internal Server Error", http.StatusInternalServerError)
		}
		return
	}

	// Vary: Accept is critical — the same URL serves either the JSON
	// listing or the embedded browse.html depending on the Accept
	// header. Without Vary, browsers/CDNs cache one response and
	// serve it for the other Accept value, breaking browse.html's
	// auto-detect (which fetches the same URL with Accept: JSON).
	w.Header().Set("Vary", "Accept")

	// Surface cascade-resolved scope flags via response headers so
	// the browse SPA can render scope-aware UI (drop-zone overlay,
	// grid-mode auto-activation, future affordances) without
	// re-implementing the cascade client-side. Keep the header
	// surface tight — only routing-shape signals go here; ACL
	// details stay server-side.
	if zddc.DropTargetAt(cfg.Root, absDir) {
		w.Header().Set("X-ZDDC-Drop-Target", "true")
	}
	if dt := zddc.DefaultToolAt(cfg.Root, absDir); dt != "" {
		w.Header().Set("X-ZDDC-Default-Tool", dt)
	}
	// X-ZDDC-On-Plan-Review surfaces whether the cascade above this
	// path has an on_plan_review block configured. Browse uses it to
	// show/hide the "Plan Review" right-click menu item without
	// re-implementing the cascade client-side. Boolean; absent header
	// = false.
	if zddc.OnPlanReviewAt(cfg.Root, absDir) != nil {
		w.Header().Set("X-ZDDC-On-Plan-Review", "true")
	}
	// X-ZDDC-Canonical-Folder names the canonical project-layout slot
	// this directory occupies — "incoming", "received", "working",
	// "staging", etc. Drives scope-aware context-menu visibility for
	// Accept Transmittal, Stage/Unstage, and Create Transmittal folder.
	// Absent header means the directory is not at a canonical slot.
	if cf := zddc.CanonicalFolderAt(cfg.Root, absDir); cf != "" {
		w.Header().Set("X-ZDDC-Canonical-Folder", cf)
	}

	if strings.Contains(accept, "application/json") {
		// Content-hash ETag on the listing payload. Re-fetched on every
		// request (the cascade is walked, ACL filter applied, JSON
		// rendered, hashed) — that's the same server work the previous
		// no-cache version did. The win is on the *response*: identical
		// listings (e.g. the same vendor refreshing their archive page)
		// short-circuit to 304 with no body.
		//
		// Crucially, this scheme tolerates unreliable filesystem
		// watching (Azure SMB, network shares with delayed inotify):
		// the ETag is the actual response hash, not a watcher-derived
		// invalidation token, so it can never lie about content.
		body, err := json.Marshal(entries)
		if err != nil {
			slog.Error("encoding directory listing", "err", err)
			http.Error(w, "Internal Server Error", http.StatusInternalServerError)
			return
		}
		etag := `"` + listingETag(body) + `"`
		w.Header().Set("Content-Type", "application/json")
		w.Header().Set("ETag", etag)
		w.Header().Set("Cache-Control", "private, max-age=0, must-revalidate")
		if match := r.Header.Get("If-None-Match"); match != "" && match == etag {
			w.WriteHeader(http.StatusNotModified)
			return
		}
		_, _ = w.Write(body)
		return
	}

	// Browser HTML fallback: serve the directory's DirTool — the
	// trailing-slash half of the slash/no-slash convention. It
	// resolves to "browse" by default (the single-file file-tree SPA
	// whose autoDetectServerMode loads the JSON listing for the
	// current directory and renders it as a sortable, filterable
	// tree); an operator's `.zddc dir_tool:` can point a subtree's
	// slash form at another directory-oriented tool. Either way it
	// goes through the apps subsystem when wired up, so `.zddc apps:`
	// source overrides are honored at directory URLs too (not just
	// /<dir>/<tool>.html). When appsSrv is nil we serve the embedded
	// browse copy directly — same behavior as before the hook.
	dirTool := zddc.DirToolAt(cfg.Root, absDir)
	if appsSrv != nil && zddc.IsKnownApp(dirTool) {
		appsSrv.Serve(w, r, dirTool, chain, absDir)
		return
	}
	body := apps.EmbeddedBytes("browse")
	if len(body) == 0 {
		// Bootstrap state: a fresh build hasn't populated browse.html
		// into the embed yet. Fall through to JSON for clients that
		// will still parse it.
		w.Header().Set("Content-Type", "application/json")
		w.Header().Set("Cache-Control", "no-cache")
		if err := json.NewEncoder(w).Encode(entries); err != nil {
			slog.Error("encoding directory listing (no-embed fallback)", "err", err)
		}
		return
	}
	// ETag + max-age=0 + must-revalidate: every request re-validates and
	// gets a 304 unless the binary has been redeployed (the ETag is a
	// content hash, computed once at startup and memoized in apps.embed).
	// Saves re-transmitting ~230 KB of browse.html on every page load
	// while still picking up redeploys immediately.
	etag := `"` + apps.EmbeddedETag("browse") + `"`
	w.Header().Set("ETag", etag)
	w.Header().Set("Cache-Control", "public, max-age=0, must-revalidate")
	w.Header().Set("Content-Type", "text/html; charset=utf-8")
	w.Header().Set("X-ZDDC-Source", "embedded:browse")
	if match := r.Header.Get("If-None-Match"); match != "" && match == etag {
		w.WriteHeader(http.StatusNotModified)
		return
	}
	_, _ = w.Write(body)
}