// SPDX-License-Identifier: GPL-2.0-only
/*
 * Line 6 Linux USB driver
 *
 * Copyright (C) 2004-2010 Markus Grabner (grabner@icg.tugraz.at)
 */

#include <linux/slab.h>

#include "midibuf.h"

static int midibuf_message_length(unsigned char code)
{
        int message_length;

        if (code < 0x80)
                message_length = -1;
        else if (code < 0xf0) {
                static const int length[] = { 3, 3, 3, 3, 2, 2, 3 };

                message_length = length[(code >> 4) - 8];
        } else {
                /*
                   Note that according to the MIDI specification 0xf2 is
                   the "Song Position Pointer", but this is used by Line 6
                   to send sysex messages to the host.
                 */
                static const int length[] = { -1, 2, -1, 2, -1, -1, 1, 1, 1, 1,
                        1, 1, 1, -1, 1, 1
                };
                message_length = length[code & 0x0f];
        }

        return message_length;
}

static int midibuf_is_empty(struct midi_buffer *this)
{
        return (this->pos_read == this->pos_write) && !this->full;
}

static int midibuf_is_full(struct midi_buffer *this)
{
        return this->full;
}

void line6_midibuf_reset(struct midi_buffer *this)
{
        this->pos_read = this->pos_write = this->full = 0;
        this->command_prev = -1;
}

int line6_midibuf_init(struct midi_buffer *this, int size, int split)
{
        this->buf = kmalloc(size, GFP_KERNEL);

        if (this->buf == NULL)
                return -ENOMEM;

        this->size = size;
        this->split = split;
        line6_midibuf_reset(this);
        return 0;
}

int line6_midibuf_bytes_free(struct midi_buffer *this)
{
        return
            midibuf_is_full(this) ?
            0 :
            (this->pos_read - this->pos_write + this->size - 1) % this->size +
            1;
}

int line6_midibuf_bytes_used(struct midi_buffer *this)
{
        return
            midibuf_is_empty(this) ?
            0 :
            (this->pos_write - this->pos_read + this->size - 1) % this->size +
            1;
}

int line6_midibuf_write(struct midi_buffer *this, unsigned char *data,
                        int length)
{
        int bytes_free;
        int length1, length2;
        int skip_active_sense = 0;

        if (midibuf_is_full(this) || (length <= 0))
                return 0;

        /* skip trailing active sense */
        if (data[length - 1] == 0xfe) {
                --length;
                skip_active_sense = 1;
        }

        bytes_free = line6_midibuf_bytes_free(this);

        if (length > bytes_free)
                length = bytes_free;

        if (length > 0) {
                length1 = this->size - this->pos_write;

                if (length < length1) {
                        /* no buffer wraparound */
                        memcpy(this->buf + this->pos_write, data, length);
                        this->pos_write += length;
                } else {
                        /* buffer wraparound */
                        length2 = length - length1;
                        memcpy(this->buf + this->pos_write, data, length1);
                        memcpy(this->buf, data + length1, length2);
                        this->pos_write = length2;
                }

                if (this->pos_write == this->pos_read)
                        this->full = 1;
        }

        return length + skip_active_sense;
}

int line6_midibuf_read(struct midi_buffer *this, unsigned char *data,
                       int length)
{
        int bytes_used;
        int length1, length2;
        int command;
        int midi_length;
        int repeat = 0;
        int i;

        /* we need to be able to store at least a 3 byte MIDI message */
        if (length < 3)
                return -EINVAL;

        if (midibuf_is_empty(this))
                return 0;

        bytes_used = line6_midibuf_bytes_used(this);

        if (length > bytes_used)
                length = bytes_used;

        length1 = this->size - this->pos_read;

        /* check MIDI command length */
        command = this->buf[this->pos_read];

        if (command & 0x80) {
                midi_length = midibuf_message_length(command);
                this->command_prev = command;
        } else {
                if (this->command_prev > 0) {
                        int midi_length_prev =
                            midibuf_message_length(this->command_prev);

                        if (midi_length_prev > 0) {
                                midi_length = midi_length_prev - 1;
                                repeat = 1;
                        } else
                                midi_length = -1;
                } else
                        midi_length = -1;
        }

        if (midi_length < 0) {
                /* search for end of message */
                if (length < length1) {
                        /* no buffer wraparound */
                        for (i = 1; i < length; ++i)
                                if (this->buf[this->pos_read + i] & 0x80)
                                        break;

                        midi_length = i;
                } else {
                        /* buffer wraparound */
                        length2 = length - length1;

                        for (i = 1; i < length1; ++i)
                                if (this->buf[this->pos_read + i] & 0x80)
                                        break;

                        if (i < length1)
                                midi_length = i;
                        else {
                                for (i = 0; i < length2; ++i)
                                        if (this->buf[i] & 0x80)
                                                break;

                                midi_length = length1 + i;
                        }
                }

                if (midi_length == length)
                        midi_length = -1;       /* end of message not found */
        }

        if (midi_length < 0) {
                if (!this->split)
                        return 0;       /* command is not yet complete */
        } else {
                if (length < midi_length)
                        return 0;       /* command is not yet complete */

                length = midi_length;
        }

        if (length < length1) {
                /* no buffer wraparound */
                memcpy(data + repeat, this->buf + this->pos_read, length);
                this->pos_read += length;
        } else {
                /* buffer wraparound */
                length2 = length - length1;
                memcpy(data + repeat, this->buf + this->pos_read, length1);
                memcpy(data + repeat + length1, this->buf, length2);
                this->pos_read = length2;
        }

        if (repeat)
                data[0] = this->command_prev;

        this->full = 0;
        return length + repeat;
}

int line6_midibuf_ignore(struct midi_buffer *this, int length)
{
        int bytes_used = line6_midibuf_bytes_used(this);

        if (length > bytes_used)
                length = bytes_used;

        this->pos_read = (this->pos_read + length) % this->size;
        this->full = 0;
        return length;
}

void line6_midibuf_destroy(struct midi_buffer *this)
{
        kfree(this->buf);
        this->buf = NULL;
}