// Copyright (c) Tailscale Inc & contributors
// SPDX-License-Identifier: BSD-3-Clause

//go:build !ts_omit_drive

package main

import (
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"net/http"
	"sync"
	"syscall/js"

	"tailscale.com/drive"
	"tailscale.com/tailcfg"
	"tailscale.com/tsd"
)

// Compile-time check that jsFileSystemForRemote implements drive.FileSystemForRemote.
var _ drive.FileSystemForRemote = (*jsFileSystemForRemote)(nil)

// jsFileSystemForRemote implements drive.FileSystemForRemote by bridging
// incoming WebDAV requests to a JS handler function. Auth and permission
// parsing are handled upstream by handleServeDrive before this is called.
type jsFileSystemForRemote struct {
	mu sync.RWMutex
	fn js.Value
}

func (fs *jsFileSystemForRemote) setHandler(fn js.Value) {
	fs.mu.Lock()
	fs.fn = fn
	fs.mu.Unlock()
}

// SetFileServerAddr is a no-op: the JS handler owns its own storage.
func (fs *jsFileSystemForRemote) SetFileServerAddr(_ string) {}

// SetShares is a no-op: the JS handler controls which shares it exposes.
func (fs *jsFileSystemForRemote) SetShares(_ []*drive.Share) {}

// Close is a no-op.
func (fs *jsFileSystemForRemote) Close() error { return nil }

// ServeHTTPWithPerms handles a WebDAV request by bridging it to the JS handler.
// It streams the request body to JS via readBodyChunk() and streams the
// response body back via write()/end() callbacks, so no full-body buffering
// occurs regardless of file size.
//
// The call blocks until JS calls end() (or a write error occurs).
func (fs *jsFileSystemForRemote) ServeHTTPWithPerms(
	perms drive.Permissions, w http.ResponseWriter, r *http.Request,
) {
	fs.mu.RLock()
	fn := fs.fn
	fs.mu.RUnlock()

	if fn.IsUndefined() || fn.IsNull() {
		http.NotFound(w, r)
		return
	}

	// readBodyChunk is exposed to JS as req.readBodyChunk().
	// Each call returns a Promise<Uint8Array|null>: null signals EOF.
	readBodyChunk := js.FuncOf(func(_ js.Value, _ []js.Value) any {
		return makePromise(func() (any, error) {
			buf := make([]byte, 65536)
			n, err := r.Body.Read(buf)
			if n > 0 {
				arr := js.Global().Get("Uint8Array").New(n)
				js.CopyBytesToJS(arr, buf[:n])
				return arr, nil
			}
			if errors.Is(err, io.EOF) {
				return js.Null(), nil
			}
			return nil, err
		})
	})

	// doneCh receives nil when JS calls end(), or a write error if Write fails.
	doneCh := make(chan error, 1)

	// writeHead sets response headers and status code. Must be called before write().
	writeHead := js.FuncOf(func(_ js.Value, args []js.Value) any {
		if len(args) < 1 {
			return nil
		}
		status := args[0].Int()
		if len(args) > 1 && !args[1].IsUndefined() && !args[1].IsNull() {
			for k, vs := range jsHeadersToGo(args[1]) {
				for _, v := range vs {
					w.Header().Add(k, v)
				}
			}
		}
		w.WriteHeader(status)
		return nil
	})

	// write streams a single response body chunk to the client.
	write := js.FuncOf(func(_ js.Value, args []js.Value) any {
		if len(args) < 1 {
			return nil
		}
		data := args[0]
		buf := make([]byte, data.Get("length").Int())
		js.CopyBytesToGo(buf, data)
		if _, werr := w.Write(buf); werr != nil {
			select {
			case doneCh <- werr:
			default:
			}
			return nil
		}
		if f, ok := w.(http.Flusher); ok {
			f.Flush()
		}
		return nil
	})

	// end signals that the response is complete.
	end := js.FuncOf(func(_ js.Value, _ []js.Value) any {
		select {
		case doneCh <- nil:
		default:
		}
		return nil
	})

	defer func() {
		readBodyChunk.Release()
		writeHead.Release()
		write.Release()
		end.Release()
	}()

	jsReq := map[string]any{
		"method":        r.Method,
		"path":          r.URL.Path,
		"rawQuery":      r.URL.RawQuery,
		"headers":       goHeadersToJS(r.Header),
		"readBodyChunk": readBodyChunk,
	}
	jsRes := map[string]any{
		"writeHead": writeHead,
		"write":     write,
		"end":       end,
	}

	fn.Invoke(jsReq, jsRes, drivePermsToJS(perms))

	// Block this goroutine until JS calls end() or a write error occurs.
	// The Go WASM scheduler yields back to JS while we wait.
	<-doneCh
}

// drivePermsToJS converts drive.Permissions to a plain JS-friendly object.
// Each share name maps to a numeric permission: 0=none, 1=read-only, 2=read-write.
// The wildcard share name "*" is included if present.
func drivePermsToJS(p drive.Permissions) map[string]any {
	result := make(map[string]any, len(p))
	for name, perm := range p {
		result[name] = int(perm)
	}
	return result
}

// goHeadersToJS converts an http.Header to a map[string]any suitable for JS.
// Single-value headers become a string; multi-value headers become a []any.
func goHeadersToJS(h http.Header) map[string]any {
	result := make(map[string]any, len(h))
	for k, vs := range h {
		if len(vs) == 1 {
			result[k] = vs[0]
		} else {
			arr := make([]any, len(vs))
			for i, v := range vs {
				arr[i] = v
			}
			result[k] = arr
		}
	}
	return result
}

// jsHeadersToGo parses a JS headers object into an http.Header map.
// Values may be a string or an array of strings.
func jsHeadersToGo(jsHeaders js.Value) http.Header {
	h := make(http.Header)
	keys := js.Global().Get("Object").Call("keys", jsHeaders)
	for i := 0; i < keys.Length(); i++ {
		key := keys.Index(i).String()
		val := jsHeaders.Get(key)
		switch val.Type() {
		case js.TypeString:
			h.Set(key, val.String())
		case js.TypeObject:
			if val.InstanceOf(js.Global().Get("Array")) {
				for j := 0; j < val.Length(); j++ {
					h.Add(key, val.Index(j).String())
				}
			}
		}
	}
	return h
}

// initDriveForRemote creates the JS-backed FileSystemForRemote and registers
// it with sys. Must be called before NewLocalBackend (SubSystem is set-once).
func initDriveForRemote(sys *tsd.System) *jsFileSystemForRemote {
	driveFS := &jsFileSystemForRemote{}
	sys.Set(driveFS)
	return driveFS
}

// wireDriveJS adds drive-related methods to the IPN JS methods map.
// driveFS must be the value returned by initDriveForRemote.
func wireDriveJS(i *jsIPN, driveFS *jsFileSystemForRemote, m map[string]any) {
	m["setDriveHandler"] = js.FuncOf(func(_ js.Value, args []js.Value) any {
		if len(args) < 1 {
			return nil
		}
		driveFS.setHandler(args[0])
		return nil
	})

	m["listDrivePeers"] = js.FuncOf(func(_ js.Value, _ []js.Value) any {
		return i.listDrivePeers()
	})
}

type jsDrivePeer struct {
	Name         string  `json:"name"`
	PeerAPIURL   string  `json:"peerAPIURL"`
	StableNodeID string  `json:"stableNodeID"`
	Online       *bool   `json:"online,omitempty"`
}

// listDrivePeers returns a JSON array of peers that carry
// PeerCapabilityTaildriveSharer. Returns an empty array if the local node
// does not have drive:access in its ACL (DriveAccessEnabled). This mirrors
// the filtering in LocalBackend.driveRemotesFromPeers.
func (i *jsIPN) listDrivePeers() js.Value {
	return makePromise(func() (any, error) {
		if !i.lb.DriveAccessEnabled() {
			return "[]", nil
		}

		nm := i.lb.NetMap()
		if nm == nil {
			return nil, errors.New("listDrivePeers: no network map available")
		}

		var selfHave4, selfHave6 bool
		for _, a := range nm.GetAddresses().All() {
			if !a.IsSingleIP() {
				continue
			}
			if a.Addr().Is4() {
				selfHave4 = true
			} else if a.Addr().Is6() {
				selfHave6 = true
			}
		}

		peers := make([]jsDrivePeer, 0)
		for _, p := range nm.Peers {
			// Check PeerCapabilityTaildriveSharer via the live PeerCaps map
			// (derived from ACL rules), mirroring driveRemotesFromPeers.
			hasCap := false
			for _, a := range p.Addresses().All() {
				if a.IsSingleIP() && i.lb.PeerCaps(a.Addr()).HasCapability(tailcfg.PeerCapabilityTaildriveSharer) {
					hasCap = true
					break
				}
			}
			if !hasCap {
				continue
			}
			peerURL := buildPeerAPIURL(p, selfHave4, selfHave6)
			online := p.Online().Clone()
			peers = append(peers, jsDrivePeer{
				Name:         p.DisplayName(false),
				PeerAPIURL:   peerURL,
				StableNodeID: string(p.StableID()),
				Online:       online,
			})
		}

		b, err := json.Marshal(peers)
		if err != nil {
			return nil, fmt.Errorf("listDrivePeers: marshal: %w", err)
		}
		return string(b), nil
	})
}