#ifndef _PB_H_
#define _PB_H_

#include <stdint.h>
#include <stddef.h> // size_t
#include <stdbool.h>

#ifdef __GNUC__
// This just reduces memory requirements, but is not required.
#define pb_packed __attribute__((packed))
#else
#define pb_packed
#endif

/* Lightweight input stream.
 * If buf is NULL, read but don't store bytes.
 * You have to provide a callback function for reading.
 * You can use state to store your own data (e.g. buffer pointer),
 * and rely on pb_read to verify that no-body reads past bytes_left.
 * However, substreams may change bytes_left so don't use that to
 * compute any pointers.
 */
typedef struct _pb_istream_t pb_istream_t;
struct _pb_istream_t
{
    bool (*callback)(pb_istream_t *stream, uint8_t *buf, size_t count);
    void *state; // Free field for use by callback implementation
    size_t bytes_left;
};

static inline bool pb_read(pb_istream_t *stream, uint8_t *buf, size_t count)
{
    if (stream->bytes_left < count)
        return false;
    
    bool status = stream->callback(stream, buf, count);
    stream->bytes_left -= count;
    return status;
}

/* Lightweight output stream. */
typedef struct _pb_ostream_t pb_ostream_t;
struct _pb_ostream_t
{
    bool (*callback)(pb_ostream_t *stream, const uint8_t *buf, size_t count);
    void *state; // Free field for use by callback implementation
    size_t bytes_written;
};

static inline bool pb_write(pb_ostream_t *stream, const uint8_t *buf, size_t count)
{
    bool status = stream->callback(stream, buf, count);
    stream->bytes_written += count;
    return status;
}

/* List of possible field types
 * Least-significant 4 bits tell the scalar type
 * Most-significant 4 bits specify repeated/required/packed etc.
 * 
 * INT32 and UINT32 are treated the same, as are (U)INT64 and (S)FIXED*
 * These types are simply casted to correct field type when they are
 * assigned to the memory pointer.
 * SINT* is different, though, because it is zig-zag coded.
 */

typedef enum {
    // Standard integer types
    PB_LTYPE_UINT32 = 0x00,
    PB_LTYPE_INT32 = 0x00,
    PB_LTYPE_SINT32 = 0x01,
    PB_LTYPE_FIXED32 = 0x02,
    PB_LTYPE_SFIXED32 = 0x02,
    PB_LTYPE_UINT64 = 0x03,
    PB_LTYPE_INT64 = 0x03,
    PB_LTYPE_SINT64 = 0x04,
    PB_LTYPE_FIXED64 = 0x05,
    PB_LTYPE_SFIXED64 = 0x05,
    PB_LTYPE_BOOL = 0x06,
    PB_LTYPE_ENUM = 0x07,
    
    // Standard float types
    PB_LTYPE_FLOAT = 0x08,
    PB_LTYPE_DOUBLE = 0x09,
    
    // Byte array with pre-allocated buffer.
    // data_size is the length of the allocated PB_BYTES_ARRAY structure.
    PB_LTYPE_BYTES = 0x0A,
    
    // String with pre-allocated buffer.
    // data_size is the maximum length.
    PB_LTYPE_STRING = 0x0B,
    
    // Submessage
    // submsg_fields is pointer to field descriptions
    PB_LTYPE_SUBMESSAGE = 0x0C,
    
    /////////////
    // Modifier flags
    
    // Just the basic, write data at data_offset
    PB_HTYPE_REQUIRED = 0x00,
    
    // Write true at size_offset
    PB_HTYPE_OPTIONAL = 0x10,
    
    // Read to pre-allocated array
    // Maximum number of entries is array_size,
    // actual number is stored at size_offset
    PB_HTYPE_ARRAY = 0x20,
    
    // Works for all required/optional/repeated fields.
    // data_offset points to pb_callback_t structure.
    // LTYPE is ignored.
    PB_HTYPE_CALLBACK = 0x30
} pb_packed pb_type_t;

#define PB_HTYPE(x) ((x) & 0xF0)
#define PB_LTYPE(x) ((x) & 0x0F)

/* This structure is used in auto-generated constants
 * to specify struct fields.
 * You can change field sizes here if you need structures
 * larger than 256 bytes or field tags larger than 256.
 * The compiler should complain if your .proto has such
 * structures ("initializer too large for type").
 */
typedef struct _pb_field_t pb_field_t;
struct _pb_field_t {
    uint8_t tag;
    pb_type_t type;
    uint8_t data_offset; // Offset of actual data or array start
    uint8_t size_offset; // Offset of array size or has-boolean
    uint8_t data_size; // Data size in bytes for a single item
    uint8_t array_size; // Maximum number of entries in array
    
    // Field definitions for submessage
    // OR default value for all other non-array, non-callback types
    // If null, then field will zeroed.
    const void *ptr;
} pb_packed;

#define PB_LAST_FIELD {0,0,0,0}

// This structure is used for 'bytes' arrays.
// It has the number of bytes in the beginning, and after that an array.
#define PB_BYTES_ARRAY(buffersize) \
struct { \
    size_t size; \
    uint8_t bytes[buffersize]; \
}

typedef PB_BYTES_ARRAY(1) pb_bytes_array_t;

// This structure is used for giving the callback function.
//
// The decoding callback will be given a limited-length stream
// If the wire type was string, the length is the length of the string.
// If the wire type was a varint/fixed32/fixed64, the length is the length
// of the actual value.
// The function may be called multiple times (especially for repeated types,
// but also otherwise if the message happens to contain the field multiple
// times.)
//
// The encoding callback will receive the actual output stream.
// It should write all the data in one call, including the field tag and
// wire type. It can write multiple fields.
typedef struct _pb_callback_t pb_callback_t;
struct _pb_callback_t {
    union {
        bool (*decode)(pb_istream_t *stream, const pb_field_t *field, void *arg);
        bool (*encode)(pb_ostream_t *stream, const pb_field_t *field, void *arg);
    } funcs;
    
    // Free arg for use by callback
    void *arg;
};

#endif