/* test_pack_overlay.c — overlay backend: copy-up, whiteout deletion of a
 * lower-layer entry (Section 4.2), compaction (Section 4.1/5.3),
 * cross-restart durability via journal replay (Section 4.4), and pack
 * integrity validation rejecting a corrupted file (Section 7). */

#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#include "packfs.h"
#include "test_harness.h"

static char *tmp_pack_path(void) {
    static char path[512];
    snprintf(path, sizeof(path), "/tmp/packfs_test_pack_%d.img", (int)getpid());
    return path;
}

int main(void) {
    char *pack_path = tmp_pack_path();
    unlink(pack_path);
    char jpath[600];
    snprintf(jpath, sizeof(jpath), "%s.jnl", pack_path);
    unlink(jpath);

    /* --- phase 1: build an initial pack directly (as if shipped) --- */
    Vfs *v = vfs_new();
    Backend *mem = backend_mem_new();
    int oerr = 0;
    Backend *ov = backend_overlay_new(pack_path, mem, &oerr);
    CHECK(ov != NULL);
    CHECK_EQ_INT(vfs_mount(v, "/", ov), VFS_OK);

    int err = 0;
    VfsFile *f = vfs_open(v, "/a.txt", VFS_O_WRONLY | VFS_O_CREAT, &err);
    CHECK(f != NULL);
    CHECK_EQ_INT(vfs_write(f, "AAAA", 4), 4);
    CHECK_EQ_INT(vfs_close(f), VFS_OK);

    f = vfs_open(v, "/dup.txt", VFS_O_WRONLY | VFS_O_CREAT, &err);
    CHECK(f != NULL);
    CHECK_EQ_INT(vfs_write(f, "AAAA", 4), 4); /* same content as a.txt: exercises dedup (Section 9.2) */
    CHECK_EQ_INT(vfs_close(f), VFS_OK);

    f = vfs_open(v, "/b.txt", VFS_O_WRONLY | VFS_O_CREAT, &err);
    CHECK(f != NULL);
    CHECK_EQ_INT(vfs_write(f, "BBBBBB", 6), 6);
    CHECK_EQ_INT(vfs_close(f), VFS_OK);

    CHECK_EQ_INT(vfs_sync(v, "/"), VFS_OK); /* compaction */

    /* read-only open straight from the freshly-compacted pack */
    f = vfs_open(v, "/a.txt", VFS_O_RDONLY, &err);
    CHECK(f != NULL);
    char buf[16] = {0};
    CHECK_EQ_INT(vfs_read(f, buf, sizeof(buf)), 4);
    CHECK_STR_EQ(buf, "AAAA");
    CHECK_EQ_INT(vfs_close(f), VFS_OK);

    /* --- copy-up on write intent, whiteout on delete (Section 4.2) --- */
    f = vfs_open(v, "/a.txt", VFS_O_RDWR, &err); /* triggers copy-up */
    CHECK(f != NULL);
    CHECK_EQ_INT(vfs_write(f, "ZZZZ", 4), 4);
    CHECK_EQ_INT(vfs_close(f), VFS_OK);
    f = vfs_open(v, "/a.txt", VFS_O_RDONLY, &err);
    memset(buf, 0, sizeof(buf));
    CHECK_EQ_INT(vfs_read(f, buf, sizeof(buf)), 4);
    CHECK_STR_EQ(buf, "ZZZZ");
    CHECK_EQ_INT(vfs_close(f), VFS_OK);

    CHECK_EQ_INT(vfs_unlink(v, "/b.txt"), VFS_OK); /* whiteout: b.txt only existed in the pack */
    VfsStat st;
    CHECK_EQ_INT(vfs_stat(v, "/b.txt", &st), VFS_ERR_NOENT);

    /* --- durability: a fresh Vfs replays the journal without compacting --- */
    vfs_unmount(v, "/");
    backend_free(ov);
    backend_free(mem);
    vfs_free(v);

    Vfs *v2 = vfs_new();
    Backend *mem2 = backend_mem_new();
    Backend *ov2 = backend_overlay_new(pack_path, mem2, &oerr);
    CHECK(ov2 != NULL);
    CHECK_EQ_INT(vfs_mount(v2, "/", ov2), VFS_OK);

    CHECK_EQ_INT(vfs_stat(v2, "/b.txt", &st), VFS_ERR_NOENT); /* whiteout replayed */
    f = vfs_open(v2, "/a.txt", VFS_O_RDONLY, &err);
    CHECK(f != NULL);
    memset(buf, 0, sizeof(buf));
    CHECK_EQ_INT(vfs_read(f, buf, sizeof(buf)), 4);
    CHECK_STR_EQ(buf, "ZZZZ"); /* the post-compaction write survived via the journal */
    CHECK_EQ_INT(vfs_close(f), VFS_OK);

    CHECK_EQ_INT(vfs_sync(v2, "/"), VFS_OK); /* compact again to fold the journal in */
    vfs_unmount(v2, "/");
    backend_free(ov2);
    backend_free(mem2);
    vfs_free(v2);

    /* --- pack integrity validation (Section 7): a corrupted pack is rejected --- */
    int fd = open(pack_path, O_RDWR);
    CHECK(fd >= 0);
    unsigned char one;
    CHECK_EQ_INT(pread(fd, &one, 1, 40), 1); /* somewhere inside the header/offsets region */
    one = (unsigned char)(one ^ 0xFF);
    CHECK_EQ_INT(pwrite(fd, &one, 1, 40), 1);
    close(fd);

    Vfs *v3 = vfs_new();
    Backend *mem3 = backend_mem_new();
    int oerr3 = 0;
    Backend *ov3 = backend_overlay_new(pack_path, mem3, &oerr3);
    CHECK(ov3 == NULL);
    CHECK_EQ_INT(oerr3, VFS_ERR_CORRUPT);
    backend_free(mem3);
    vfs_free(v3);

    unlink(pack_path);
    unlink(jpath);
    TEST_MAIN_END();
}