package fs

import (
	"context"
	"net/url"
	"os"
	"path/filepath"
	"strings"

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

// 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
}

// ListDirectory returns a Caddy-compatible JSON listing for the directory at
// filepath.Join(fsRoot, dirPath), filtered by ACL for userEmail.
//
// Rules:
//   - Hidden files and .zddc files are excluded
//   - *.portfolio files appear as virtual directories (stem + "/")
//   - Subdirectories for which the user lacks access are omitted (not 403'd inline)
//   - dirPath="" means the root of the served tree
//
// baseURL should end with "/" and is the URL prefix for this directory.
//
// The decider is queried per subdirectory; nil falls back to the internal
// Go evaluator (policy.InternalDecider) for tests that don't wire up
// an explicit decider.
func ListDirectory(ctx context.Context, decider policy.Decider, fsRoot, dirPath, userEmail, baseURL string) ([]listing.FileInfo, error) {
	if decider == nil {
		decider = &policy.InternalDecider{}
	}
	absDir, ok := safeJoin(fsRoot, dirPath)
	if !ok {
		return nil, os.ErrNotExist
	}

	entries, err := os.ReadDir(absDir)
	if err != nil {
		// Empty-listing fallback for canonical project folders. A fresh
		// project doesn't have working/, staging/, reviewing/, or even
		// archive/ on disk until something is written into them
		// (EnsureCanonicalAncestors materialises lazily). The stage-strip
		// nav links into these folders unconditionally; without this
		// fallback, a click on "Working" against a fresh project 404s.
		// Returning [] makes the click land on a usable empty view; the
		// virtualUserHomeEntry below still fires for working/ so the
		// user sees their own home placeholder.
		if os.IsNotExist(err) &&
			(zddc.IsProjectRootFolder(dirPath) || zddc.IsArchivePartyFolder(dirPath)) {
			entries = nil
		} else {
			return nil, err
		}
	}

	// Empty (not nil) so the JSON encoder emits [] rather than null
	// when no entries match — clients (browse, archive) expect an array.
	result := make([]listing.FileInfo, 0, len(entries))

	// Display overrides for this directory's children, sourced from
	// THIS directory's .zddc `display:` map. Built once and looked up
	// case-insensitively per entry. Empty map = no overrides.
	displayMap := readDisplayMap(absDir)

	for _, entry := range entries {
		name := entry.Name()

		// Skip hidden files and dotfiles (including .zddc)
		if strings.HasPrefix(name, ".") {
			continue
		}

		info, err := entry.Info()
		if err != nil {
			continue
		}

		isDir := entry.IsDir()
		displayName := lookupDisplay(displayMap, name)

		if isDir {
			// ACL check for subdirectory
			subAbs := filepath.Join(absDir, name)
			chain, err := zddc.EffectivePolicy(fsRoot, subAbs)
			if err != nil {
				continue
			}
			subURLPath := baseURL + name + "/"
			allowed, _ := policy.AllowFromChain(ctx, decider, chain, userEmail, subURLPath)
			if !allowed {
				continue // omit denied directories silently
			}
			fi := listing.FileInfo{
				Name:        name + "/",
				Size:        info.Size(),
				URL:         baseURL + url.PathEscape(name) + "/",
				ModTime:     info.ModTime(),
				Mode:        uint32(info.Mode()),
				IsDir:       true,
				DisplayName: displayName,
			}
			result = append(result, fi)
			continue
		}

		// Regular file
		fi := listing.FileInfo{
			Name:        name,
			Size:        info.Size(),
			URL:         baseURL + url.PathEscape(name),
			ModTime:     info.ModTime(),
			Mode:        uint32(info.Mode()),
			IsDir:       false,
			DisplayName: displayName,
		}
		result = append(result, fi)
	}

	// Per-user virtual home: when listing <project>/working/ for an
	// authenticated viewer, surface a synthetic <viewer-email>/ entry if
	// no real folder of any case variant already exists for them. A
	// first write to that path materialises a real folder with auto-own
	// .zddc; subsequent listings drop the synthetic entry naturally.
	if syn, ok := virtualUserHomeEntry(fsRoot, dirPath, userEmail, baseURL, result); ok {
		result = append(result, syn)
	}

	// At a project root, surface the four canonical project folders
	// (archive/working/staging/reviewing) as virtual entries when no
	// on-disk variant exists in any case. The browse client previously
	// did this client-side; moving it server-side lets the directory's
	// `display:` map apply to virtual entries the same way it applies
	// to real ones.
	result = append(result, virtualCanonicalFolders(fsRoot, dirPath, baseURL, result, displayMap)...)

	return result, nil
}

// virtualCanonicalFolders returns synthetic entries for any canonical
// project-root folder absent from real. Fires only when dirPath is a
// depth-1 directory under fsRoot (the project root); other depths get
// an empty slice. Case-insensitive presence check so an on-disk
// "Archive" suppresses the lowercase "archive" virtual entry.
func virtualCanonicalFolders(fsRoot, dirPath, baseURL string,
	real []listing.FileInfo, displayMap map[string]string) []listing.FileInfo {

	rel := strings.Trim(filepath.ToSlash(dirPath), "/")
	if rel == "" {
		return nil
	}
	parts := strings.Split(rel, "/")
	if len(parts) != 1 {
		return nil // not a project root
	}

	present := make(map[string]bool, len(real))
	for _, fi := range real {
		if !fi.IsDir {
			continue
		}
		bare := strings.TrimSuffix(fi.Name, "/")
		present[strings.ToLower(bare)] = true
	}

	var synth []listing.FileInfo
	for _, name := range zddc.ProjectRootFolders {
		if present[name] {
			continue
		}
		synth = append(synth, listing.FileInfo{
			Name:        name + "/",
			URL:         baseURL + url.PathEscape(name) + "/",
			IsDir:       true,
			Virtual:     true,
			DisplayName: lookupDisplay(displayMap, name),
		})
	}
	return synth
}

// virtualUserHomeEntry returns the synthetic <viewer-email>/ entry that
// should be appended to a working/ listing, or (zero, false) when no
// synthetic entry applies.
//
// Conditions for the entry to fire:
//   - dirPath case-folds to <project>/working at depth-2 of fsRoot
//   - viewerEmail is non-empty
//   - real does not already contain a directory entry that case-folds
//     to viewerEmail (so a materialised home doesn't get duplicated)
func virtualUserHomeEntry(fsRoot, dirPath, viewerEmail, baseURL string, real []listing.FileInfo) (listing.FileInfo, bool) {
	if viewerEmail == "" {
		return listing.FileInfo{}, false
	}
	rel := strings.Trim(filepath.ToSlash(dirPath), "/")
	parts := strings.Split(rel, "/")
	if len(parts) != 2 || !strings.EqualFold(parts[1], "working") {
		return listing.FileInfo{}, false
	}
	for _, fi := range real {
		if !fi.IsDir {
			continue
		}
		// fi.Name carries a trailing slash for dirs.
		bare := strings.TrimSuffix(fi.Name, "/")
		if strings.EqualFold(bare, viewerEmail) {
			return listing.FileInfo{}, false
		}
	}
	return listing.FileInfo{
		Name:    viewerEmail + "/",
		URL:     baseURL + url.PathEscape(viewerEmail) + "/",
		IsDir:   true,
		Virtual: true,
	}, true
}

// readDisplayMap parses dirAbs/.zddc and returns its Display map (or
// nil when the file doesn't exist or has no display block). All keys
// are case-folded to lowercase so lookupDisplay's case-insensitive
// match is a simple map read.
func readDisplayMap(dirAbs string) map[string]string {
	zf, err := zddc.ParseFile(filepath.Join(dirAbs, ".zddc"))
	if err != nil || len(zf.Display) == 0 {
		return nil
	}
	out := make(map[string]string, len(zf.Display))
	for k, v := range zf.Display {
		if v == "" {
			continue
		}
		out[strings.ToLower(strings.TrimSpace(k))] = v
	}
	return out
}

// lookupDisplay returns the custom display label for name (matched
// case-insensitively against displayMap's keys), or "" when no
// override applies.
func lookupDisplay(displayMap map[string]string, name string) string {
	if len(displayMap) == 0 {
		return ""
	}
	return displayMap[strings.ToLower(name)]
}