// Copyright 2024, Command Line Inc.
// SPDX-License-Identifier: Apache-2.0

package wshutil

import (
	"bytes"
	"encoding/base64"
	"encoding/json"
	"fmt"
	"reflect"
)

const WaveOSC = "23198"
const WaveOSCPrefix = "\x1b]" + WaveOSC + ";"
const HexChars = "0123456789ABCDEF"
const BEL = 0x07

var waveOSCPrefixBytes = []byte(WaveOSCPrefix)

// OSC escape types
// OSC 23198 ; (JSON | base64-JSON) ST
// JSON = must escape all ASCII control characters ([\x00-\x1F\x7F])
// we can tell the difference between JSON and base64-JSON by the first character: '{' or not

func EncodeWaveOSCMessage(cmd Command) ([]byte, error) {
	if cmd.GetCommand() == "" {
		return nil, fmt.Errorf("Command field not set in struct")
	}
	ctype, ok := CommandToTypeMap[cmd.GetCommand()]
	if !ok {
		return nil, fmt.Errorf("unknown command type %q", cmd.GetCommand())
	}
	cmdType := reflect.TypeOf(cmd)
	if cmdType != ctype && (cmdType.Kind() == reflect.Pointer && cmdType.Elem() != ctype) {
		return nil, fmt.Errorf("command type does not match %q", cmd.GetCommand())
	}
	barr, err := json.Marshal(cmd)
	if err != nil {
		return nil, fmt.Errorf("error marshalling message to json: %w", err)
	}
	hasControlChars := false
	for _, b := range barr {
		if b < 0x20 || b == 0x7F {
			hasControlChars = true
			break
		}
	}
	if !hasControlChars {
		// If no control characters, directly construct the output
		// \x1b] (2) + WaveOSC + ; (1) + message + \x07 (1)
		output := make([]byte, len(WaveOSCPrefix)+len(barr)+1)
		copy(output, waveOSCPrefixBytes)
		copy(output[len(WaveOSCPrefix):], barr)
		output[len(output)-1] = BEL
		return output, nil
	}

	var buf bytes.Buffer
	buf.Write(waveOSCPrefixBytes)
	escSeq := [6]byte{'\\', 'u', '0', '0', '0', '0'}
	for _, b := range barr {
		if b < 0x20 || b == 0x7f {
			escSeq[4] = HexChars[b>>4]
			escSeq[5] = HexChars[b&0x0f]
			buf.Write(escSeq[:])
		} else {
			buf.WriteByte(b)
		}
	}
	buf.WriteByte(BEL)
	return buf.Bytes(), nil
}

func decodeWaveOSCMessage(data []byte) (Command, error) {
	var baseCmd baseCommand
	err := json.Unmarshal(data, &baseCmd)
	if err != nil {
		return nil, fmt.Errorf("error unmarshalling json: %w", err)
	}
	rtnCmd := reflect.New(CommandToTypeMap[baseCmd.Command]).Interface()
	err = json.Unmarshal(data, rtnCmd)
	if err != nil {
		return nil, fmt.Errorf("error unmarshalling json: %w", err)
	}
	return rtnCmd.(Command), nil
}

// data does not contain the escape sequence, just the innards
// this function implements the switch between JSON and base64-JSON
func DecodeWaveOSCMessage(data []byte) (Command, error) {
	if len(data) == 0 {
		return nil, fmt.Errorf("empty data")
	}
	if data[0] != '{' {
		// decode base64
		rtnLen := base64.StdEncoding.DecodedLen(len(data))
		rtn := make([]byte, rtnLen)
		nw, err := base64.StdEncoding.Decode(rtn, data)
		if err != nil {
			return nil, fmt.Errorf("error decoding base64: %w", err)
		}
		return decodeWaveOSCMessage(rtn[:nw])
	}
	return decodeWaveOSCMessage(data)
}