// Package webdav is a built-in plugin that connects to a WebDAV server over
// HTTP(S). It offers the same capability surface as the filetransfer plugin
// (list/stat/download/upload/delete/mkdir) but speaks WebDAV verbs — PROPFIND,
// GET, PUT, DELETE, MKCOL — directly over net/http, so it needs no third-party
// client library and cross-compiles cleanly for the Linux container.
//
// Like filetransfer, nothing connects during Init; each capability (and the
// health probe) issues its own HTTP request against the configured base URL,
// authenticating with HTTP Basic auth. This suits WebDAV, which is stateless
// per request, and keeps the plugin free of long-lived connection state.
package webdav

import (
	"context"
	"crypto/tls"
	"encoding/base64"
	"encoding/json"
	"encoding/xml"
	"errors"
	"fmt"
	"io"
	"net"
	"net/http"
	"net/url"
	"path"
	"strconv"
	"strings"
	"sync"
	"time"

	"pilotvault/apiserver/internal/plugins"
)

const (
	dialTimeout = 12 * time.Second
	// maxReadBytes caps a download so a huge remote file can't exhaust memory;
	// the health probe and Invoke both honour it.
	maxReadBytes = 32 << 20 // 32 MiB

	// propfindBody requests just the properties we normalize into fileInfo.
	propfindBody = `<?xml version="1.0" encoding="utf-8"?>` +
		`<d:propfind xmlns:d="DAV:"><d:prop>` +
		`<d:displayname/><d:getcontentlength/><d:getlastmodified/><d:resourcetype/>` +
		`</d:prop></d:propfind>`
)

func init() {
	plugins.Register("webdav", func() plugins.Plugin { return &Plugin{} })
}

// Plugin is the WebDAV connector. All fields are guarded by mu because Init may
// run concurrently with a HealthCheck/Invoke from another request.
type Plugin struct {
	mu       sync.Mutex
	baseURL  string // e.g. https://cloud.example.com/remote.php/dav/files/alice/
	username string
	password string
	basePath string // working root, resolved under the base URL's path
	// insecureTLS skips HTTPS certificate verification when true.
	insecureTLS bool
	client      *http.Client
}

func (p *Plugin) Descriptor() plugins.Descriptor {
	return plugins.Descriptor{
		Name:     "webdav",
		Provider: "WebDAV",
		Version:  "1.0.0",
		Kind:     plugins.KindBuiltin,
		Category: plugins.CategoryDrivesExternal,
		AuthType: plugins.AuthBasic,
		Capabilities: []plugins.Capability{
			{ID: "list", Method: "PROPFIND", Endpoint: "/", Description: "List a remote directory. params: {path}"},
			{ID: "stat", Method: "PROPFIND", Endpoint: "/", Description: "Stat one remote path. params: {path}"},
			{ID: "download", Method: "GET", Endpoint: "/", Description: "Read a remote file (base64, ≤32 MiB). params: {path}"},
			{ID: "upload", Method: "PUT", Endpoint: "/", Description: "Write a remote file. params: {path, contentBase64}"},
			{ID: "delete", Method: "DELETE", Endpoint: "/", Description: "Delete a remote file or directory. params: {path}"},
			{ID: "mkdir", Method: "MKCOL", Endpoint: "/", Description: "Create a remote directory. params: {path}"},
		},
		ConfigFields: []plugins.ConfigField{
			// No field is Required: the plugin can be enabled as a master switch with
			// an empty global config, leaving each organization or user to supply
			// their own connection through the cascade (mirrors filetransfer). A
			// missing base URL is reported gracefully by the health probe.
			{Key: "baseURL", Label: "Server URL", Type: "text",
				Help: "WebDAV endpoint, e.g. https://cloud.example.com/remote.php/dav/files/alice/ — must include the scheme."},
			{Key: "username", Label: "Username", Type: "text"},
			{Key: "password", Label: "Password", Type: "password", Secret: true,
				Help: "Password or app-specific token for HTTP Basic auth. Leave blank for an anonymous/public share."},
			{Key: "basePath", Label: "Base path", Type: "text", Default: ".",
				Help: "Directory under the server URL used as the working root and probed by the health check, e.g. /Documents. Relative capability paths resolve under it."},
			{Key: "insecureSkipVerify", Label: "TLS verification", Type: "select", Default: "false",
				Options: []plugins.SelectOption{
					{Value: "false", Label: "Verify certificate (recommended)"},
					{Value: "true", Label: "Skip verification — accept any certificate"},
				},
				Help: "Only affects HTTPS. Skip verification only for self-signed test servers."},
		},
	}
}

func (p *Plugin) Init(_ context.Context, config map[string]string) error {
	p.mu.Lock()
	defer p.mu.Unlock()

	p.baseURL = strings.TrimSpace(config["baseURL"])
	p.username = strings.TrimSpace(config["username"])
	p.password = config["password"]
	p.basePath = strings.TrimSpace(config["basePath"])
	if p.basePath == "" {
		p.basePath = "."
	}
	p.insecureTLS = strings.EqualFold(strings.TrimSpace(config["insecureSkipVerify"]), "true")

	p.client = &http.Client{
		// No client-level timeout: request lifetime is bounded by the caller's
		// context so large downloads aren't cut off mid-stream.
		Transport: &http.Transport{
			DialContext:         (&net.Dialer{Timeout: dialTimeout}).DialContext,
			TLSHandshakeTimeout: dialTimeout,
			TLSClientConfig: &tls.Config{
				InsecureSkipVerify: p.insecureTLS, //nolint:gosec // opt-in for self-signed test servers
			},
		},
	}
	return nil
}

// resolve joins a caller-supplied path against the base path. A leading "/" is
// treated as relative to the server URL's own path root; an empty path becomes
// the base path itself. It never allows escaping above that root: the joined
// path is cleaned against a virtual "/" so "..", stray separators, and
// backslashes can't climb out.
func (p *Plugin) resolve(rel string) string {
	rel = strings.TrimSpace(rel)
	rel = strings.ReplaceAll(rel, "\\", "/")
	base := p.basePath
	if base == "." {
		base = ""
	}
	var joined string
	switch {
	case rel == "":
		joined = base
	case strings.HasPrefix(rel, "/"):
		joined = rel // relative to the server URL root, not the base path
	case base == "":
		joined = rel
	default:
		joined = base + "/" + rel
	}
	// Clean against a virtual root so nothing escapes above it.
	return strings.TrimPrefix(path.Clean("/"+joined), "/")
}

// requestURL builds the absolute request URL for a resolved path. When dir is
// true a trailing slash is kept, which WebDAV servers expect for collection
// operations (PROPFIND/MKCOL). url.URL.String() percent-escapes the path, so
// callers pass unescaped segments.
func (p *Plugin) requestURL(resolved string, dir bool) (string, error) {
	base, err := url.Parse(p.baseURL)
	if err != nil {
		return "", fmt.Errorf("invalid server URL: %w", err)
	}
	if base.Scheme == "" || base.Host == "" {
		return "", errors.New("server URL must include scheme and host")
	}
	full := *base
	full.Path = path.Join("/"+strings.Trim(base.Path, "/"), resolved)
	full.RawPath = "" // force re-escaping from Path
	if dir && !strings.HasSuffix(full.Path, "/") {
		full.Path += "/"
	}
	return full.String(), nil
}

// do issues one authenticated WebDAV request and returns the response. The
// caller is responsible for closing the body.
func (p *Plugin) do(ctx context.Context, method, rawURL string, body io.Reader, headers map[string]string) (*http.Response, error) {
	p.mu.Lock()
	client, user, pass := p.client, p.username, p.password
	p.mu.Unlock()
	if client == nil {
		return nil, errors.New("plugin not initialized")
	}
	req, err := http.NewRequestWithContext(ctx, method, rawURL, body)
	if err != nil {
		return nil, err
	}
	if user != "" || pass != "" {
		req.SetBasicAuth(user, pass)
	}
	for k, v := range headers {
		req.Header.Set(k, v)
	}
	return client.Do(req)
}

// HealthCheck issues a PROPFIND against the base path and classifies the
// outcome. A 401/403 means the server is reachable but auth failed (degraded);
// a transport error is down.
func (p *Plugin) HealthCheck(ctx context.Context) plugins.Health {
	start := time.Now()

	p.mu.Lock()
	base, baseURL := p.basePath, p.baseURL
	p.mu.Unlock()

	if baseURL == "" {
		return plugins.Health{Status: plugins.StatusDown, Detail: "no server URL configured"}
	}

	entries, err := p.propfind(ctx, p.resolve(""), 1)
	lat := time.Since(start).Milliseconds()
	if err != nil {
		var he *httpError
		if errors.As(err, &he) {
			return plugins.Health{Status: classifyStatus(he.code), LatencyMs: lat,
				Detail: fmt.Sprintf("connected but PROPFIND %q returned %d %s", base, he.code, http.StatusText(he.code))}
		}
		return plugins.Health{Status: plugins.StatusDown, LatencyMs: lat, Detail: err.Error()}
	}

	detail := fmt.Sprintf("WebDAV reachable — %d entr%s under %q", len(entries), plural(len(entries)), base)
	status := plugins.StatusOK
	if strings.HasPrefix(strings.ToLower(baseURL), "http://") {
		status = plugins.StatusDegraded
		detail += " · plaintext HTTP (no encryption)"
	}
	return plugins.Health{Status: status, LatencyMs: lat, Detail: detail}
}

// Invoke runs one capability against the WebDAV server.
func (p *Plugin) Invoke(ctx context.Context, action string, params json.RawMessage) (json.RawMessage, error) {
	switch action {
	case "list":
		var in pathParams
		_ = json.Unmarshal(params, &in)
		rp := p.resolve(in.Path)
		entries, err := p.propfind(ctx, rp, 1)
		if err != nil {
			return nil, err
		}
		return json.Marshal(map[string]any{"path": rp, "entries": entries})

	case "stat":
		var in pathParams
		_ = json.Unmarshal(params, &in)
		rp := p.resolve(in.Path)
		entries, err := p.propfind(ctx, rp, 0)
		if err != nil {
			return nil, err
		}
		if len(entries) == 0 {
			return nil, fmt.Errorf("not found: %s", rp)
		}
		return json.Marshal(entries[0])

	case "download":
		var in pathParams
		_ = json.Unmarshal(params, &in)
		rp := p.resolve(in.Path)
		data, err := p.read(ctx, rp)
		if err != nil {
			return nil, err
		}
		return json.Marshal(map[string]any{
			"path":          rp,
			"size":          len(data),
			"contentBase64": base64.StdEncoding.EncodeToString(data),
		})

	case "upload":
		var in writeParams
		if err := json.Unmarshal(params, &in); err != nil {
			return nil, fmt.Errorf("invalid params: %w", err)
		}
		data, err := base64.StdEncoding.DecodeString(in.ContentBase64)
		if err != nil {
			return nil, fmt.Errorf("contentBase64 is not valid base64: %w", err)
		}
		rp := p.resolve(in.Path)
		if err := p.write(ctx, rp, data); err != nil {
			return nil, err
		}
		return json.Marshal(map[string]any{"path": rp, "size": len(data), "ok": true})

	case "delete":
		var in pathParams
		_ = json.Unmarshal(params, &in)
		rp := p.resolve(in.Path)
		if err := p.remove(ctx, rp); err != nil {
			return nil, err
		}
		return json.Marshal(map[string]any{"path": rp, "ok": true})

	case "mkdir":
		var in pathParams
		_ = json.Unmarshal(params, &in)
		rp := p.resolve(in.Path)
		if err := p.mkdir(ctx, rp); err != nil {
			return nil, err
		}
		return json.Marshal(map[string]any{"path": rp, "ok": true})

	default:
		return nil, errors.New("unknown action: " + action)
	}
}

func (p *Plugin) Shutdown(context.Context) error { return nil }

// pathParams / writeParams are the Invoke request shapes.
type pathParams struct {
	Path string `json:"path"`
}
type writeParams struct {
	Path          string `json:"path"`
	ContentBase64 string `json:"contentBase64"`
}

// fileInfo is the normalized directory-entry shape returned by list/stat. It
// matches filetransfer's shape so callers can treat the drives uniformly.
type fileInfo struct {
	Name    string `json:"name"`
	Size    int64  `json:"size"`
	IsDir   bool   `json:"isDir"`
	ModTime string `json:"modTime,omitempty"`
}

// httpError carries a non-2xx status so HealthCheck can classify it.
type httpError struct {
	code   int
	method string
}

func (e *httpError) Error() string {
	return fmt.Sprintf("%s: %d %s", e.method, e.code, http.StatusText(e.code))
}

// ---------------------------------------------------------------------------
// WebDAV operations
// ---------------------------------------------------------------------------

// propfind lists (depth 1) or stats (depth 0) a path. For depth 1 the entry
// describing the collection itself is dropped so only children are returned.
func (p *Plugin) propfind(ctx context.Context, resolved string, depth int) ([]fileInfo, error) {
	u, err := p.requestURL(resolved, true)
	if err != nil {
		return nil, err
	}
	resp, err := p.do(ctx, "PROPFIND", u, strings.NewReader(propfindBody), map[string]string{
		"Depth":        strconv.Itoa(depth),
		"Content-Type": "application/xml; charset=utf-8",
	})
	if err != nil {
		return nil, err
	}
	defer drainClose(resp.Body)

	// 207 Multi-Status is the success case; 200 is tolerated for lenient servers.
	if resp.StatusCode != http.StatusMultiStatus && resp.StatusCode != http.StatusOK {
		return nil, &httpError{code: resp.StatusCode, method: "PROPFIND"}
	}

	var ms davMultistatus
	if err := xml.NewDecoder(io.LimitReader(resp.Body, maxReadBytes)).Decode(&ms); err != nil {
		return nil, fmt.Errorf("parse PROPFIND response: %w", err)
	}

	// The request path, cleaned, is used to recognise and drop the self entry.
	self := strings.Trim(resolved, "/")
	out := make([]fileInfo, 0, len(ms.Responses))
	for _, r := range ms.Responses {
		hrefPath := hrefToPath(r.Href)
		if depth == 1 && strings.Trim(hrefPath, "/") == self {
			continue // the collection itself
		}
		out = append(out, r.toFileInfo())
	}
	return out, nil
}

func (p *Plugin) read(ctx context.Context, resolved string) ([]byte, error) {
	u, err := p.requestURL(resolved, false)
	if err != nil {
		return nil, err
	}
	resp, err := p.do(ctx, http.MethodGet, u, nil, nil)
	if err != nil {
		return nil, err
	}
	defer drainClose(resp.Body)
	if resp.StatusCode/100 != 2 {
		return nil, &httpError{code: resp.StatusCode, method: "GET"}
	}
	return io.ReadAll(io.LimitReader(resp.Body, maxReadBytes))
}

func (p *Plugin) write(ctx context.Context, resolved string, data []byte) error {
	u, err := p.requestURL(resolved, false)
	if err != nil {
		return err
	}
	resp, err := p.do(ctx, http.MethodPut, u, strings.NewReader(string(data)),
		map[string]string{"Content-Type": "application/octet-stream"})
	if err != nil {
		return err
	}
	defer drainClose(resp.Body)
	if resp.StatusCode/100 != 2 {
		return &httpError{code: resp.StatusCode, method: "PUT"}
	}
	return nil
}

func (p *Plugin) remove(ctx context.Context, resolved string) error {
	u, err := p.requestURL(resolved, false)
	if err != nil {
		return err
	}
	resp, err := p.do(ctx, http.MethodDelete, u, nil, nil)
	if err != nil {
		return err
	}
	defer drainClose(resp.Body)
	// 404 is tolerated as already-gone.
	if resp.StatusCode/100 != 2 && resp.StatusCode != http.StatusNotFound {
		return &httpError{code: resp.StatusCode, method: "DELETE"}
	}
	return nil
}

func (p *Plugin) mkdir(ctx context.Context, resolved string) error {
	u, err := p.requestURL(resolved, true)
	if err != nil {
		return err
	}
	resp, err := p.do(ctx, "MKCOL", u, nil, nil)
	if err != nil {
		return err
	}
	defer drainClose(resp.Body)
	// 405 Method Not Allowed is what most servers return when the collection
	// already exists — treat it as success (idempotent mkdir).
	if resp.StatusCode/100 != 2 && resp.StatusCode != http.StatusMethodNotAllowed {
		return &httpError{code: resp.StatusCode, method: "MKCOL"}
	}
	return nil
}

// ---------------------------------------------------------------------------
// PROPFIND XML shapes and helpers
// ---------------------------------------------------------------------------

type davMultistatus struct {
	XMLName   xml.Name      `xml:"DAV: multistatus"`
	Responses []davResponse `xml:"DAV: response"`
}

type davResponse struct {
	Href      string        `xml:"DAV: href"`
	Propstats []davPropstat `xml:"DAV: propstat"`
}

type davPropstat struct {
	Status string  `xml:"DAV: status"`
	Prop   davProp `xml:"DAV: prop"`
}

type davProp struct {
	DisplayName  string          `xml:"DAV: displayname"`
	ContentLen   string          `xml:"DAV: getcontentlength"`
	LastModified string          `xml:"DAV: getlastmodified"`
	ResourceType davResourceType `xml:"DAV: resourcetype"`
}

type davResourceType struct {
	Collection *xml.Name `xml:"DAV: collection"`
}

// toFileInfo normalizes a PROPFIND <response>, preferring the 2xx propstat.
func (r davResponse) toFileInfo() fileInfo {
	fi := fileInfo{Name: nameFromHref(r.Href)}
	for _, ps := range r.Propstats {
		if !strings.Contains(ps.Status, " 2") { // "HTTP/1.1 200 OK"
			continue
		}
		if ps.Prop.ResourceType.Collection != nil {
			fi.IsDir = true
		}
		if n, err := strconv.ParseInt(strings.TrimSpace(ps.Prop.ContentLen), 10, 64); err == nil {
			fi.Size = n
		}
		if lm := strings.TrimSpace(ps.Prop.LastModified); lm != "" {
			if t, err := http.ParseTime(lm); err == nil {
				fi.ModTime = t.UTC().Format(time.RFC3339)
			}
		}
		if fi.Name == "" && strings.TrimSpace(ps.Prop.DisplayName) != "" {
			fi.Name = ps.Prop.DisplayName
		}
	}
	return fi
}

// hrefToPath extracts the URL path from an href, which may be absolute
// (http://host/a/b) or path-only (/a/b), and percent-decodes it.
func hrefToPath(href string) string {
	if u, err := url.Parse(href); err == nil && u.Path != "" {
		return u.Path
	}
	if dec, err := url.PathUnescape(href); err == nil {
		return dec
	}
	return href
}

// nameFromHref returns the last path segment of an href, percent-decoded.
func nameFromHref(href string) string {
	p := strings.TrimRight(hrefToPath(href), "/")
	if i := strings.LastIndex(p, "/"); i >= 0 {
		p = p[i+1:]
	}
	return p
}

// classifyStatus maps an HTTP status to a health status: an auth rejection means
// the server is reachable but credentials are wrong (degraded); anything else is
// down.
func classifyStatus(code int) string {
	switch code {
	case http.StatusUnauthorized, http.StatusForbidden:
		return plugins.StatusDegraded
	default:
		return plugins.StatusDown
	}
}

// drainClose drains and closes a response body so the connection can be reused.
func drainClose(body io.ReadCloser) {
	_, _ = io.Copy(io.Discard, io.LimitReader(body, 4<<10))
	_ = body.Close()
}

func plural(n int) string {
	if n == 1 {
		return "y"
	}
	return "ies"
}