// Copyright (c) 2026 Storm Dragon
// SPDX-License-Identifier: GPL-3.0-or-later

// Package tentacle implements the experimental command, presentation and interaction SDK.
// It has no reader, input, or output backend dependencies.
package tentacle

import (
	"bufio"
	"context"
	"encoding/json"
	"errors"
	"io"
	"strconv"
	"sync"

	"git.stormux.org/storm/cthulhu/internal/interaction"
	"git.stormux.org/storm/cthulhu/internal/tentaclewire"
)

type Binding struct {
	Layout string `json:"layout"`
	Scope  string `json:"scope"`
	Key    string `json:"key"`
}

// Presentation returns independent plain-text speech and braille messages.
// Declare Command.Presentation and obtain the local host grant before using it.
// Uninterruptible protects accepted speech through ordinary input/focus changes;
// session revocation and core lifecycle/output policy still take precedence.
type Presentation = tentaclewire.Presentation

// Interaction requires the explicit interaction grant as well as presentation.
type Interaction = tentaclewire.Interaction
type Submission = tentaclewire.Submission
type Item = tentaclewire.Item
type Form = interaction.Form
type Element = interaction.Element
type ListItem = interaction.Item
type Value = interaction.Value

const (
	List     = interaction.List
	Entry    = interaction.Entry
	CheckBox = interaction.CheckBox
	Button   = interaction.Button
)

// Handlers may run concurrently. Cancellation applies to the entire session;
// check ctx before side effects. Returning an error produces a generic RPC error,
// never the error text (which may contain private data).
type Handler func(ctx context.Context, arguments json.RawMessage) (any, error)

type Command struct {
	ID           string    `json:"id"`
	Title        string    `json:"title"`
	Description  string    `json:"description"`
	Bindings     []Binding `json:"bindings,omitempty"`
	Presentation bool      `json:"presentation,omitempty"`
	Interaction  bool      `json:"interaction,omitempty"`
	// Settings exposes this interactive command through global Preferences.
	// Register at most one; its handler opens a form without requiring arguments.
	Settings bool    `json:"settings,omitempty"`
	Handle   Handler `json:"-"`
}

var ErrProtocol = tentaclewire.ErrProtocol

type request struct {
	JSONRPC string          `json:"jsonrpc"`
	ID      string          `json:"id,omitempty"`
	Method  string          `json:"method"`
	Params  json.RawMessage `json:"params"`
}

// Serve owns the streams and closes them on return. Use stdin/stdout in a
// dedicated child process and exit when Serve returns. Shutdown/EOF cancels all
// handlers and waits for them; the host kills a child that ignores cancellation.
// Never print to stdout. Command declarations must remain unchanged during Serve.
func Serve(input io.ReadCloser, output io.WriteCloser, commands []Command) error {
	ctx, cancel := context.WithCancel(context.Background())
	var workers sync.WaitGroup
	var writeMutex sync.Mutex
	defer func() { cancel(); input.Close(); output.Close(); workers.Wait() }()
	handlers := make(map[string]Handler)
	if len(commands) == 0 || len(commands) > 32 {
		return ErrProtocol
	}
	settings := false
	for _, command := range commands {
		if command.Settings && (!command.Interaction || !command.Presentation || settings) || command.ID == "" || command.Handle == nil || handlers[command.ID] != nil {
			return ErrProtocol
		}
		settings = settings || command.Settings
		handlers[command.ID] = command.Handle
	}
	writeReply := func(id string, value any, failed bool, release func()) error {
		reply := map[string]any{"jsonrpc": "2.0", "id": id, "result": value}
		if failed {
			delete(reply, "result")
			reply["error"] = map[string]any{"code": -32603, "message": "Command failed"}
		}
		frame, err := json.Marshal(reply)
		if err != nil || len(frame) > tentaclewire.MaxFrameBytes || tentaclewire.ValidateJSON(frame) != nil {
			frame, _ = json.Marshal(map[string]any{"jsonrpc": "2.0", "id": id,
				"error": map[string]any{"code": -32603, "message": "Invalid or oversized result"}})
		}
		writeMutex.Lock()
		defer writeMutex.Unlock()
		// A completed reply may reach the host before Write returns. Release
		// its handler slot first, with at most one additional serialized writer.
		if release != nil {
			release()
		}
		if ctx.Err() != nil {
			return ctx.Err()
		}
		_, err = output.Write(append(frame, '\n'))
		return err
	}
	reader := bufio.NewReader(input)
	var sequence uint64
	session := ""
	active := false
	slots := make(chan struct{}, 8)
	for {
		frame, err := tentaclewire.ReadFrame(reader)
		if errors.Is(err, io.EOF) {
			return nil
		}
		if err != nil {
			return err
		}
		var message request
		if tentaclewire.DecodeStrict(frame, &message) != nil || message.JSONRPC != "2.0" {
			return ErrProtocol
		}
		var fields map[string]json.RawMessage
		_ = json.Unmarshal(frame, &fields)
		for key := range fields {
			if key != "jsonrpc" && key != "id" && key != "method" && key != "params" {
				return ErrProtocol
			}
		}
		if _, present := fields["id"]; present && message.ID == "" {
			return ErrProtocol
		}
		if message.ID != "" {
			number, err := strconv.ParseUint(message.ID, 10, 64)
			if err != nil || number <= sequence || strconv.FormatUint(number, 10) != message.ID {
				return ErrProtocol
			}
			sequence = number
		}
		switch message.Method {
		case "initialize":
			var params struct {
				Protocol struct {
					Major *int `json:"major"`
					Minor *int `json:"minor"`
				} `json:"protocol"`
				Session      string   `json:"session"`
				APIs         []string `json:"apis"`
				Capabilities []string `json:"capabilities"`
			}
			if session != "" || message.ID == "" || tentaclewire.DecodeStrict(message.Params, &params) != nil ||
				params.Protocol.Major == nil || params.Protocol.Minor == nil || *params.Protocol.Major != 1 || *params.Protocol.Minor != 0 || params.Session == "" || len(params.Session) > 128 ||
				!tentaclewire.ValidAPIs(params.APIs, params.Capabilities) {
				return ErrProtocol
			}
			for _, command := range commands {
				if command.Presentation && len(params.APIs) < 2 || command.Interaction && (!command.Presentation || len(params.APIs) != 3) {
					return ErrProtocol
				}
			}
			session = params.Session
			if err := writeReply(message.ID, map[string]any{"protocol": params.Protocol, "session": session, "commands": commands}, false, nil); err != nil {
				return err
			}
		case "initialized":
			var params struct {
				Session string `json:"session"`
			}
			if session == "" || active || message.ID != "" || tentaclewire.DecodeStrict(message.Params, &params) != nil || params.Session != session {
				return ErrProtocol
			}
			active = true
		case "command.invoke":
			var params struct {
				Command   string          `json:"command"`
				Arguments json.RawMessage `json:"arguments"`
			}
			if !active || message.ID == "" || tentaclewire.DecodeStrict(message.Params, &params) != nil || len(params.Arguments) == 0 || len(params.Arguments) > 16*1024 || handlers[params.Command] == nil {
				return ErrProtocol
			}
			select {
			case slots <- struct{}{}:
			default:
				return tentaclewire.ErrLimit
			}
			workers.Add(1)
			go func(id string, handler Handler, arguments json.RawMessage) {
				defer workers.Done()
				released := false
				release := func() {
					if !released {
						<-slots
						released = true
					}
				}
				defer release()
				value, err := call_handler(ctx, handler, arguments)
				if writeReply(id, value, err != nil, release) != nil {
					cancel()
					input.Close()
				}
			}(message.ID, handlers[params.Command], params.Arguments)
		case "shutdown":
			if message.ID != "" || (len(message.Params) != 0 && string(message.Params) != "null") {
				return ErrProtocol
			}
			return nil
		default:
			return ErrProtocol
		}
	}
}

func call_handler(ctx context.Context, handler Handler, arguments json.RawMessage) (value any, err error) {
	defer func() {
		if recover() != nil {
			value = nil
			err = errors.New("command panicked")
		}
	}()
	return handler(ctx, arguments)
}