#pragma once
/*
 * snapdiff.h — byte-level comparator for two checkpoint files
 * (bug-1389 triage: OPCode_snapshotTransfer chunk-content corruption).
 *
 * Compares a locally-generated source checkpoint (snap-*.capnp) against a
 * received one (snap-*.bin, ha_handle_snapshot_chunk) byte-for-byte, and
 * reports the first divergent offset plus whether it lands exactly on an
 * OPCode_snapshotTransfer chunk boundary (SNAPSHOT_CHUNK_SIZE, config_repl.c)
 * — the decisive signal separating "chunk transport corrupted this specific
 * chunk" from "the two files were never going to match" (different content
 * entirely, unrelated to chunking).
 *
 * Strictly read-only: opens both files O_RDONLY, mutates nothing.
 */
#include <stdio.h>
#include <sys/types.h>

/* Mirrors config_repl.c's SNAPSHOT_CHUNK_SIZE (the OPCode_snapshotTransfer
 * wire chunk size) — kept in sync manually; both are compile-time constants
 * for the same wire protocol, not expected to change independently. */
#define SNAPDIFF_CHUNK_SIZE 65536

typedef struct {
    off_t size1;
    off_t size2;
    int   size_mismatch; /* 1 if size1 != size2 (diff_offset unset in that case) */
    int   identical;     /* 1 if same size and byte-for-byte identical */
    off_t diff_offset;   /* -1 if identical or size_mismatch; else first
                          * differing byte offset */
    int   at_chunk_boundary; /* 1 if diff_offset is the first byte of a
                              * SNAPDIFF_CHUNK_SIZE-aligned chunk, i.e.
                              * diff_offset % SNAPDIFF_CHUNK_SIZE == 0 */
    off_t chunk_index;   /* diff_offset / SNAPDIFF_CHUNK_SIZE, valid only
                          * when diff_offset >= 0 */
} snapdiff_report_t;

/* Compare `path1` (source of truth) against `path2` (candidate, e.g. a
 * received copy). Prints a human-readable report to `out` (may be NULL) and
 * fills `*rep` (may be NULL). Returns 0 if identical, 1 if they differ (see
 * `*rep` for detail), or a negative errno on open/fstat failure. */
int snapdiff_paths(const char* path1, const char* path2, FILE* out,
                   snapdiff_report_t* rep);