package handler

import (
	"encoding/json"
	"log/slog"
	"net/http"
	"path/filepath"
	"strings"

	"codeberg.org/VARASYS/ZDDC/zddc/internal/apps"
	"codeberg.org/VARASYS/ZDDC/zddc/internal/archive"
	"codeberg.org/VARASYS/ZDDC/zddc/internal/config"
	"codeberg.org/VARASYS/ZDDC/zddc/internal/listing"
	"codeberg.org/VARASYS/ZDDC/zddc/internal/policy"
	"codeberg.org/VARASYS/ZDDC/zddc/internal/zddc"
)

// ServeArchive handles requests under a project's .archive virtual path.
//
// The dispatcher canonicalizes every .archive request to /<project>/.archive/...
// before reaching here (any deeper /<project>/sub/.../archive/... gets a 302
// to the project-rooted form), so this handler only ever sees one shape:
// project = first URL segment, filename = whatever follows .archive/.
//
// Permissions follow the FILE, not .archive itself. .archive is a virtual
// surface — it has no on-disk directory and no .zddc of its own. Two gates
// only:
//
//  1. Listing: returned entries are filtered by the per-target file's ACL
//     chain. If the project bucket is empty (or doesn't exist in the index)
//     the response is 404; if the user can read NO entries in a non-empty
//     bucket the response is 403, so existence of an inaccessible project's
//     archive does not leak.
//
//  2. Resolve: only the per-target file's ACL gates access. A user with
//     no project-root permission but an explicit allow on one transmittal
//     folder can fetch that file's tracking-number URL; conversely, a user
//     with broad project access but a narrower deny on a specific subtree
//     gets 404 (not 403) on its tracking numbers — existence must not leak.
//
// Listings serve the embedded `browse` SPA on Accept: text/html and the
// JSON entry array on Accept: application/json — same content negotiation
// as ServeDirectory, so the SPA's auto-detect path-fetch works at .archive
// URLs identically to real directories.
func ServeArchive(cfg config.Config, idx *archive.Index, w http.ResponseWriter, r *http.Request, project, filename string) {
	if project == "" {
		http.Error(w, "Not Found: .archive must be requested under a project directory (e.g. /<project>/.archive/)", http.StatusNotFound)
		return
	}

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

	if filename == "" {
		serveArchiveListing(cfg, idx, w, r, project, email, decider)
		return
	}

	target, ok := archive.Resolve(idx, project, filename)
	if !ok {
		http.Error(w, "Not Found", http.StatusNotFound)
		return
	}

	// Per-target ACL is the only gate. 404 (not 403) so the tracking
	// number's mere existence isn't disclosed to a caller who can't
	// actually read the resolved file.
	fileDir := filepath.Dir(filepath.Join(cfg.Root, filepath.FromSlash(target)))
	chain, err := zddc.EffectivePolicy(cfg.Root, fileDir)
	if err != nil {
		slog.Warn("ACL policy error on resolved file", "path", fileDir, "err", err)
	}
	if allowed, _ := policy.AllowFromChain(ctx, decider, chain, email, "/"+target); !allowed {
		http.Error(w, "Not Found", http.StatusNotFound)
		return
	}

	// Serve in place — DO NOT redirect to the resolved file's real path.
	// People share .archive/<tracking>.html#section URLs and expect the
	// link to keep tracking the latest revision; redirecting would pin
	// the bookmark to a specific transmittal-folder snapshot. The
	// canonicalization redirect (/<project>/<sub>/.archive/X → /<project>/.archive/X)
	// happens upstream in the dispatcher and is a different thing — it
	// only collapses the .archive prefix, not the resolved bytes.
	//
	// Cache-Control: no-cache forces conditional revalidation each load —
	// http.ServeFile sets Last-Modified/ETag from the on-disk file, so
	// when the resolver picks a newer target the ETag changes and the
	// browser refetches.
	absFile := filepath.Join(cfg.Root, filepath.FromSlash(target))
	w.Header().Set("Cache-Control", "no-cache")
	http.ServeFile(w, r, absFile)
}

func serveArchiveListing(cfg config.Config, idx *archive.Index, w http.ResponseWriter, r *http.Request, project, email string, decider policy.Decider) {
	ctx := r.Context()
	allEntries := idx.AllEntries(project)
	if len(allEntries) == 0 {
		// Project bucket missing or empty. 404 with no body distinction
		// from "unknown project" — a caller probing for project names
		// gets the same shape whether or not the project exists.
		http.Error(w, "Not Found", http.StatusNotFound)
		return
	}

	archiveBase := "/" + project + "/" + cfg.IndexPath + "/"

	// ACL chains are folder-keyed and the listing typically hits the same
	// few directories repeatedly (one per transmittal folder), so cache
	// the allow/deny decision per directory rather than re-walking .zddc
	// files for every entry.
	aclCache := make(map[string]bool)
	allowed := func(targetPath string) bool {
		fileDir := filepath.Dir(filepath.Join(cfg.Root, filepath.FromSlash(targetPath)))
		if v, ok := aclCache[fileDir]; ok {
			return v
		}
		chain, err := zddc.EffectivePolicy(cfg.Root, fileDir)
		if err != nil {
			aclCache[fileDir] = false
			return false
		}
		v, _ := policy.AllowFromChain(ctx, decider, chain, email, "/"+targetPath)
		aclCache[fileDir] = v
		return v
	}

	result := make([]listing.FileInfo, 0, len(allEntries))
	for _, e := range allEntries {
		if !allowed(e.TargetPath) {
			continue
		}
		result = append(result, listing.FileInfo{
			Name:  e.URLName,
			URL:   archiveBase + e.URLName,
			IsDir: false,
		})
	}

	// Existence-leak guard: if the user can read no entries in a
	// non-empty bucket, 403 — never confirm the project's archive
	// exists to a caller with no permissions in it.
	if len(result) == 0 {
		http.Error(w, "Forbidden", http.StatusForbidden)
		return
	}

	// Vary: Accept is critical because the same URL serves either the
	// JSON listing or the embedded browse SPA depending on Accept;
	// without it, browsers/CDNs may serve one Accept's body for the
	// other Accept value and break the SPA's JSON auto-fetch.
	w.Header().Set("Vary", "Accept")

	if strings.Contains(r.Header.Get("Accept"), "application/json") {
		body, err := json.Marshal(result)
		if err != nil {
			slog.Error("encoding archive 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
	}

	// HTML: serve the embedded `browse` SPA. The SPA auto-detects the
	// server-mode listing by re-fetching this same URL with
	// Accept: application/json — that path lands in the JSON branch
	// above and renders the archive entries as a sortable, filterable
	// flat list.
	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.
		jsonBody, err := json.Marshal(result)
		if err != nil {
			slog.Error("encoding archive listing (no-embed fallback)", "err", err)
			http.Error(w, "Internal Server Error", http.StatusInternalServerError)
			return
		}
		w.Header().Set("Content-Type", "application/json")
		w.Header().Set("Cache-Control", "no-cache")
		_, _ = w.Write(jsonBody)
		return
	}
	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)
}