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

// Package tentacle implements the experimental process host used by explicit
// local reader launches. Start and Invoke never wait for child pipe I/O.
package tentacle

import (
	"bufio"
	"bytes"
	"encoding/json"
	"errors"
	"fmt"
	"git.stormux.org/storm/cthulhu/internal/tentaclewire"
	"strings"
)

const (
	MaxFrameBytes      = tentaclewire.MaxFrameBytes // Excludes the mandatory newline.
	MaxArgumentBytes   = 16 * 1024
	MaxCommands        = 32
	MaxDiagnosticBytes = 64 * 1024 // Lifetime budget; diagnostics are discarded.
)

var (
	ErrBusy        = errors.New("tentacle host capacity exhausted")
	ErrUnavailable = errors.New("tentacle is not active")
	ErrDisabled    = errors.New("tentacle disabled")
	ErrProtocol    = tentaclewire.ErrProtocol
	ErrLimit       = tentaclewire.ErrLimit
	ErrExited      = errors.New("tentacle process exited")
)

type Version struct {
	Major int `json:"major"`
	Minor int `json:"minor"`
}

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     bool      `json:"settings,omitempty"` // Opens settings; never a continuation handler.
}

type Initialization struct {
	Protocol     Version  `json:"protocol"`
	Session      string   `json:"session"`
	APIs         []string `json:"apis"`
	Capabilities []string `json:"capabilities"`
}

type Registration struct {
	Protocol Version   `json:"protocol"`
	Session  string    `json:"session"`
	Commands []Command `json:"commands"`
}

// RPCError retains the bounded remote message for a future accessible details
// view. Error deliberately omits child-supplied text from normal diagnostics.
type RPCError struct {
	Code    int    `json:"code"`
	Message string `json:"message"`
}

func (failure *RPCError) Error() string {
	return fmt.Sprintf("tentacle RPC error %d", failure.Code)
}

type response struct {
	JSONRPC string          `json:"jsonrpc"`
	ID      string          `json:"id"`
	Result  json.RawMessage `json:"result"`
	Error   *RPCError       `json:"error"`
}

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

func encode_request(id, method string, params any) ([]byte, error) {
	data, err := json.Marshal(request{JSONRPC: "2.0", ID: id, Method: method, Params: params})
	if err != nil {
		return nil, ErrProtocol
	}
	if len(data) > MaxFrameBytes {
		return nil, ErrLimit
	}
	return append(data, '\n'), nil
}

func read_frame(reader *bufio.Reader) ([]byte, error) { return tentaclewire.ReadFrame(reader) }
func validate_json(data []byte) error                 { return tentaclewire.ValidateJSON(data) }
func decode_strict(data []byte, target any) error     { return tentaclewire.DecodeStrict(data, target) }

func decode_response(data []byte) (response, error) {
	var reply response
	if err := decode_strict(data, &reply); err != nil {
		return reply, err
	}
	// Presence matters: a null result is valid; a null error is not.
	var fields map[string]json.RawMessage
	_ = json.Unmarshal(data, &fields)
	for key := range fields {
		if key != "jsonrpc" && key != "id" && key != "result" && key != "error" {
			return reply, ErrProtocol
		}
	}
	_, hasResult := fields["result"]
	_, hasError := fields["error"]
	if reply.JSONRPC != "2.0" || reply.ID == "" || len(reply.ID) > 32 || hasResult == hasError ||
		(hasError && (reply.Error == nil || len(reply.Error.Message) > 1024)) {
		return reply, ErrProtocol
	}
	if hasError {
		var errorFields map[string]json.RawMessage
		_ = json.Unmarshal(fields["error"], &errorFields)
		if errorFields["code"] == nil || bytes.Equal(errorFields["code"], []byte("null")) ||
			errorFields["message"] == nil || bytes.Equal(errorFields["message"], []byte("null")) {
			return reply, ErrProtocol
		}
	}
	return reply, nil
}

func valid_id(value string) bool {
	if len(value) == 0 || len(value) > 128 || value[0] < 'a' || value[0] > 'z' {
		return false
	}
	for _, char := range value {
		if !(char >= 'a' && char <= 'z' || char >= '0' && char <= '9' || char == '-' || char == '.') {
			return false
		}
	}
	return true
}

func validate_registration(registration Registration, session string) error {
	if registration.Protocol != (Version{Major: 1, Minor: 0}) || registration.Session != session ||
		len(registration.Commands) == 0 || len(registration.Commands) > MaxCommands {
		return ErrProtocol
	}
	seen := make(map[string]bool)
	settings := false
	for _, command := range registration.Commands {
		if command.Settings && (!command.Interaction || settings) || command.Interaction && !command.Presentation || !valid_id(command.ID) || seen[command.ID] || strings.TrimSpace(command.Title) == "" ||
			len(command.Title) > 256 || len(command.Description) > 1024 {
			return ErrProtocol
		}
		seen[command.ID] = true
		settings = settings || command.Settings
		if len(command.Bindings) > 4 {
			return ErrLimit
		}
		for _, binding := range command.Bindings {
			if err := validate_binding(binding); err != nil {
				return err
			}
		}
	}
	return nil
}

func clone_commands(commands []Command) []Command {
	result := append([]Command(nil), commands...)
	for index := range result {
		result[index].Bindings = append([]Binding(nil), result[index].Bindings...)
	}
	return result
}