// A small FlatBuffers builder.
//
// HyperHDR's image input speaks the hyperion.ng FlatBuffers schema. The
// upstream client generates code with flatcc and carries it as a submodule;
// that is a lot of build machinery for four message shapes, so this
// implements the builder algorithm directly. It follows the same back-to-front
// construction as the reference implementations, so buffers it produces are
// byte-comparable with flatc-generated output (minus vtable deduplication,
// which is an optimisation, not a format requirement).
#pragma once

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

#define FB_MAX_FIELDS 8

typedef struct {
    uint8_t* bytes; // full allocation; live data is bytes[head..cap)
    size_t cap;
    size_t head;
    size_t minalign;

    uint16_t vtable[FB_MAX_FIELDS];
    int vtable_count;
    size_t object_end; // fb_offset() captured at fb_start_table
    bool nested;
    bool failed;
} fb_t;

bool fb_init(fb_t* b, size_t initial_capacity);
void fb_free(fb_t* b);

// Offsets are distances from the end of the buffer, matching the reference
// builders. Zero means "absent".
uint32_t fb_create_uint8_vector(fb_t* b, const uint8_t* data, size_t count);
uint32_t fb_create_string(fb_t* b, const char* s);

void fb_start_table(fb_t* b, int num_fields);
void fb_add_offset(fb_t* b, int slot, uint32_t offset);
void fb_add_int32(fb_t* b, int slot, int32_t value, int32_t default_value);
void fb_add_uint8(fb_t* b, int slot, uint8_t value, uint8_t default_value);
uint32_t fb_end_table(fb_t* b);

void fb_finish(fb_t* b, uint32_t root);

// Valid until the next mutation or fb_free.
const uint8_t* fb_data(const fb_t* b, size_t* len);
bool fb_ok(const fb_t* b);