package handler

import (
	"context"
	"encoding/json"
	"net/http"
	"net/url"
	"os"
	"path/filepath"
	"sort"
	"strings"
	"time"

	"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"
)

// IsReviewingPath classifies a URL as a reviewing-aggregator path and
// extracts (project, tracking). The aggregator is a virtual view at:
//
//	<project>/reviewing/                 → depth 0: list pending submittals
//	<project>/reviewing/<tracking>/      → depth 1: list received/ + staged/
//
// Anything deeper than depth 1 returns ok=false; the depth-1 listing
// emits canonical URLs (under archive/ and staging/) so navigation past
// that point goes through the regular file-tree handlers, not back into
// the virtual reviewing/ subtree.
//
// Trailing slash on either depth is required and tolerated. Match on
// "reviewing" is case-insensitive.
func IsReviewingPath(urlPath string) (project, tracking string, ok bool) {
	parts := strings.Split(strings.Trim(urlPath, "/"), "/")
	if len(parts) < 2 || !strings.EqualFold(parts[1], "reviewing") {
		return "", "", false
	}
	switch len(parts) {
	case 2:
		return parts[0], "", true
	case 3:
		return parts[0], parts[2], true
	default:
		return "", "", false
	}
}

// pendingSubmittal is one row of the aggregator's view: a submittal in
// archive/<party>/received/ that doesn't yet have a matching entry in
// archive/<party>/issued/, optionally paired with an in-progress
// response folder under staging/.
type pendingSubmittal struct {
	tracking     string    // canonical tracking number, e.g. "123456-ST-SUB-0026"
	party        string    // party folder name, e.g. "Acme"
	receivedURL  string    // /<project>/archive/<party>/received/<folder>/
	stagedURL    string    // /<project>/staging/<folder>/  or "" if no draft yet
	lastModified time.Time // newer of the two folders' mtimes
}

// computePending walks the project's archive/ and staging/ subtrees to
// build the virtual reviewing-aggregator view.
//
// Algorithm:
//
//  1. Index staging/<folder>/ by tracking number.
//  2. For each party under archive/<party>/:
//     a. Index archive/<party>/issued/ by tracking number.
//     b. For each archive/<party>/received/<folder>:
//     - skip folders that don't parse as transmittal folders.
//     - skip if tracking already in issued (response complete).
//     - emit a pendingSubmittal pointing at the canonical received
//     URL and (if found) the matching staging URL.
//
// ACL: per-party. The caller's email + decider are consulted on the
// archive/<party>/received/ subtree before reading its contents — a
// party the caller can't see at upstream is omitted entirely (no info
// leak via tracking-number listing).
//
// Missing intermediate folders (archive/, party/issued/, staging/) are
// not errors; they just produce empty intermediate sets. This matches
// the lazy-instantiation pattern of the canonical project folders.
func computePending(ctx context.Context, decider policy.Decider,
	fsRoot, project, email string) ([]pendingSubmittal, error) {

	projectAbs := filepath.Join(fsRoot, project)
	archiveAbs := filepath.Join(projectAbs, "archive")
	stagingAbs := filepath.Join(projectAbs, "staging")

	// Index staging by tracking → folder name.
	stagedByTracking := map[string]string{}
	if entries, err := os.ReadDir(stagingAbs); err == nil {
		for _, e := range entries {
			if !e.IsDir() || strings.HasPrefix(e.Name(), ".") {
				continue
			}
			if _, tracking, _, _, ok := zddc.ParseTransmittalFolder(e.Name()); ok {
				stagedByTracking[tracking] = e.Name()
			}
		}
	}

	parties, err := os.ReadDir(archiveAbs)
	if err != nil {
		if os.IsNotExist(err) {
			return nil, nil
		}
		return nil, err
	}

	var result []pendingSubmittal
	for _, p := range parties {
		if !p.IsDir() || strings.HasPrefix(p.Name(), ".") {
			continue
		}
		party := p.Name()
		partyAbs := filepath.Join(archiveAbs, party)
		receivedAbs := filepath.Join(partyAbs, "received")

		// ACL: skip parties whose received/ subtree the caller can't read.
		// Filtering at the party level is cheaper than per-entry and matches
		// fs.ListDirectory's omit-denied-subdirs convention.
		chain, err := zddc.EffectivePolicy(fsRoot, receivedAbs)
		if err != nil {
			continue
		}
		receivedURLPrefix := "/" + project + "/archive/" + party + "/received/"
		if allowed, _ := policy.AllowFromChain(ctx, decider, chain, email, receivedURLPrefix); !allowed {
			continue
		}

		// Index this party's issued/ trackings (no ACL filter — issued/
		// is WORM-readable to anyone with party access by design, and
		// we just need the set membership for matching).
		issuedTrackings := map[string]bool{}
		if entries, err := os.ReadDir(filepath.Join(partyAbs, "issued")); err == nil {
			for _, e := range entries {
				if !e.IsDir() {
					continue
				}
				if _, tracking, _, _, ok := zddc.ParseTransmittalFolder(e.Name()); ok {
					issuedTrackings[tracking] = true
				}
			}
		}

		receivedEntries, err := os.ReadDir(receivedAbs)
		if err != nil {
			continue
		}
		for _, e := range receivedEntries {
			if !e.IsDir() || strings.HasPrefix(e.Name(), ".") {
				continue
			}
			_, tracking, _, _, ok := zddc.ParseTransmittalFolder(e.Name())
			if !ok {
				continue
			}
			if issuedTrackings[tracking] {
				continue // response complete; not pending
			}

			info, err := e.Info()
			if err != nil {
				continue
			}
			modTime := info.ModTime()

			sub := pendingSubmittal{
				tracking:     tracking,
				party:        party,
				receivedURL:  receivedURLPrefix + url.PathEscape(e.Name()) + "/",
				lastModified: modTime,
			}
			if stagedFolder, hasDraft := stagedByTracking[tracking]; hasDraft {
				sub.stagedURL = "/" + project + "/staging/" + url.PathEscape(stagedFolder) + "/"
				if stagedInfo, err := os.Stat(filepath.Join(stagingAbs, stagedFolder)); err == nil {
					if stagedInfo.ModTime().After(modTime) {
						sub.lastModified = stagedInfo.ModTime()
					}
				}
			}
			result = append(result, sub)
		}
	}

	sort.Slice(result, func(i, j int) bool {
		return result[i].tracking < result[j].tracking
	})
	return result, nil
}

// ServeReviewing emits the aggregator JSON listing for either depth 0
// (project's full pending list) or depth 1 (one submittal's
// received/ + staged/ pair). The HTML branch is handled separately by
// the apps subsystem (mdedit served at the URL); only requests that
// accept JSON reach here.
func ServeReviewing(cfg config.Config, w http.ResponseWriter, r *http.Request,
	project, tracking string) {

	pending, err := computePending(r.Context(), DeciderFromContext(r),
		cfg.Root, project, EmailFromContext(r))
	if err != nil {
		http.Error(w, "Internal Server Error", http.StatusInternalServerError)
		return
	}

	var entries []listing.FileInfo
	switch tracking {
	case "":
		// Depth 0: list pending submittals as virtual <tracking>/ folders.
		// The URLs stay under reviewing/ so the user can drill into a
		// per-submittal view.
		urlPrefix := "/" + project + "/reviewing/"
		for _, s := range pending {
			entries = append(entries, listing.FileInfo{
				Name:    s.tracking + "/",
				URL:     urlPrefix + url.PathEscape(s.tracking) + "/",
				ModTime: s.lastModified,
				IsDir:   true,
				Virtual: true,
			})
		}
	default:
		// Depth 1: find the matching pending entry; emit received/ +
		// staged/ pointing at canonical archive/staging URLs. Clients
		// using the polyfill follow these URLs out of the virtual
		// subtree into the real file paths underneath.
		var match *pendingSubmittal
		for i := range pending {
			if pending[i].tracking == tracking {
				match = &pending[i]
				break
			}
		}
		if match == nil {
			http.Error(w, "Not Found", http.StatusNotFound)
			return
		}
		entries = append(entries, listing.FileInfo{
			Name:    "received/",
			URL:     match.receivedURL,
			ModTime: match.lastModified,
			IsDir:   true,
			Virtual: true,
		})
		if match.stagedURL != "" {
			entries = append(entries, listing.FileInfo{
				Name:    "staged/",
				URL:     match.stagedURL,
				ModTime: match.lastModified,
				IsDir:   true,
				Virtual: true,
			})
		}
	}

	if entries == nil {
		entries = []listing.FileInfo{}
	}
	w.Header().Set("Content-Type", "application/json; charset=utf-8")
	w.Header().Set("Cache-Control", "no-store") // virtual; recompute every time
	w.Header().Set("X-ZDDC-Source", "reviewing-aggregator")
	_ = json.NewEncoder(w).Encode(entries)
}