/* P0-15a: WAL integrity end-to-end smoke tests
 *
 * Exercises cross-phase interactions:
 *   - WAL writer (P0-B) produces segment files that can be read back
 *   - Torn-write simulation (ftruncate) + persist_recover() (P0-C)
 *   - Chained-CRC corruption detection during recovery replay
 */
#define _GNU_SOURCE
#include <dirent.h>
#include <errno.h>
#include <fcntl.h>
#include <inttypes.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/stat.h>
#include <unistd.h>
#include <zlib.h>

#include <unity/unity.h>

#include "config.h"
#include "persist.h"

/* ------------------------------------------------------------------ */
/* Helpers                                                              */
/* ------------------------------------------------------------------ */

static char g_e2e_wal_tmpdir[256];

static persist_t* make_e2e_wal_persist(void)
{
    strcpy(g_e2e_wal_tmpdir, "/tmp/xce_e2e_wal_XXXXXX");
    if (!mkdtemp(g_e2e_wal_tmpdir)) return NULL;

    persist_t* p = calloc(1, sizeof(persist_t));
    if (!p) return NULL;

    persist_config_t cfg = persist_config_defaults();
    cfg.wal_sync_ms = 5000; /* suppress background fsync races */

    persist_set_workdir(p, g_e2e_wal_tmpdir, "e2e-wal");

    if (persist_init(p, &cfg, NULL) != 0) { free(p); return NULL; }
    if (persist_start(p) != 0) { persist_fini(p); free(p); return NULL; }
    return p;
}

static void teardown_e2e_wal(persist_t* p)
{
    persist_stop(p);
    persist_fini(p);
    free(p);
}

/* Return the path to the first .wal segment in the WAL directory. */
static int find_first_wal_segment(const char* wal_dir, char* out, size_t outsz)
{
    DIR* d = opendir(wal_dir);
    if (!d) return -1;

    struct dirent* e;
    while ((e = readdir(d)) != NULL) {
        size_t len = strlen(e->d_name);
        if (len > 4 && strcmp(e->d_name + len - 4, ".wal") == 0) {
            snprintf(out, outsz, "%s/%s", wal_dir, e->d_name);
            closedir(d);
            return 0;
        }
    }
    closedir(d);
    return -1;
}

/* Count valid wal_entry_hdr_t records in a segment file by reading
 * sequentially and checking header CRC (first 32 bytes of header). */
static int count_valid_wal_entries(const char* seg_path)
{
    int fd = open(seg_path, O_RDONLY);
    if (fd < 0) return -1;

    int count = 0;
    off_t offset = 0;

    for (;;) {
        wal_entry_hdr_t hdr;
        ssize_t n = pread(fd, &hdr, sizeof(hdr), offset);
        if (n != (ssize_t)sizeof(hdr)) break;

        /* Verify header CRC (first WAL_HDR_CRC_SIZE bytes) */
        uint32_t expected_crc = (uint32_t)crc32(0L,
            (const unsigned char*)&hdr, WAL_HDR_CRC_SIZE);
        if (hdr.payload_len > 0) {
            unsigned char* payload = malloc(hdr.payload_len);
            if (!payload) break;
            ssize_t pn = pread(fd, payload, hdr.payload_len,
                               offset + (off_t)sizeof(hdr));
            if (pn == (ssize_t)hdr.payload_len)
                expected_crc = (uint32_t)crc32(expected_crc,
                                               payload, hdr.payload_len);
            free(payload);
        }

        if (expected_crc != hdr.crc) break;

        count++;
        offset += (off_t)(sizeof(hdr) + hdr.payload_len);
    }

    close(fd);
    return count;
}

/* ------------------------------------------------------------------ */
/* Test 1: write 10 WAL entries and verify they appear in segment file */
/* ------------------------------------------------------------------ */

static void test_wal_write_and_verify_entry_count(void)
{
    persist_t* p = make_e2e_wal_persist();
    TEST_ASSERT_NOT_NULL(p);

    const char payload[] = "e2e-entry";
    for (int i = 0; i < 10; i++) {
        int rc = persist_wal_async(p, WAL_JOB_UPDATE, payload,
                                   (uint32_t)strlen(payload));
        TEST_ASSERT_EQUAL_INT(0, rc);
    }

    TEST_ASSERT_EQUAL_INT(0, persist_flush(p));

    char seg_path[512];
    TEST_ASSERT_EQUAL_INT(0,
        find_first_wal_segment(p->wal_path, seg_path, sizeof(seg_path)));

    int count = count_valid_wal_entries(seg_path);
    TEST_ASSERT_EQUAL_INT(10, count);

    teardown_e2e_wal(p);
    printf("test_wal_write_and_verify_entry_count: PASS\n");
}

/* ------------------------------------------------------------------ */
/* Test 2: torn-write recovery — truncate last entry, recover, check   */
/* ------------------------------------------------------------------ */

static void test_wal_torn_write_recovery(void)
{
    /* Phase 1: write 5 entries and flush */
    persist_t* p = make_e2e_wal_persist();
    TEST_ASSERT_NOT_NULL(p);

    const char payload[] = "torn";
    for (int i = 0; i < 5; i++) {
        TEST_ASSERT_EQUAL_INT(0,
            persist_wal_async(p, WAL_JOB_UPDATE, payload,
                              (uint32_t)strlen(payload)));
    }
    TEST_ASSERT_EQUAL_INT(0, persist_flush(p));

    /* Locate segment file and determine size of 4 complete entries */
    char seg_path[512];
    TEST_ASSERT_EQUAL_INT(0,
        find_first_wal_segment(p->wal_path, seg_path, sizeof(seg_path)));

    /* One entry = sizeof(wal_entry_hdr_t) + payload_len */
    off_t entry_size = (off_t)(sizeof(wal_entry_hdr_t) + strlen(payload));
    off_t trunc_offset = entry_size * 4; /* keep only 4 complete entries */

    /* Truncate: simulate torn write on entry 5 */
    int fd = open(seg_path, O_RDWR);
    TEST_ASSERT_TRUE(fd >= 0);
    TEST_ASSERT_EQUAL_INT(0, ftruncate(fd, trunc_offset));
    close(fd);

    uint64_t lsn_before = p->current_lsn;

    teardown_e2e_wal(p); /* stop / destroy the first instance */

    /* Phase 2: fresh persist_t pointing at the same directory */
    persist_t* p2 = calloc(1, sizeof(persist_t));
    TEST_ASSERT_NOT_NULL(p2);

    persist_config_t cfg = persist_config_defaults();
    cfg.wal_sync_ms = 5000;
    persist_set_workdir(p2, g_e2e_wal_tmpdir, "e2e-wal");

    TEST_ASSERT_EQUAL_INT(0, persist_init(p2, &cfg, NULL));
    TEST_ASSERT_EQUAL_INT(0, persist_start(p2));

    int rc = persist_recover(p2);
    TEST_ASSERT_EQUAL_INT(0, rc);

    /* Recovery must have replayed at most 4 entries (not 5 — torn write) */
    TEST_ASSERT_TRUE(p2->current_lsn < lsn_before);

    teardown_e2e_wal(p2);
    printf("test_wal_torn_write_recovery: PASS\n");
}

/* ------------------------------------------------------------------ */
/* Test 3: chained CRC corruption stops replay at last valid entry     */
/* ------------------------------------------------------------------ */

static void test_wal_chained_crc_detects_corruption(void)
{
    /* Phase 1: write 5 entries and flush */
    persist_t* p = make_e2e_wal_persist();
    TEST_ASSERT_NOT_NULL(p);

    const char payload[] = "crc-chain";
    for (int i = 0; i < 5; i++) {
        TEST_ASSERT_EQUAL_INT(0,
            persist_wal_async(p, WAL_JOB_UPDATE, payload,
                              (uint32_t)strlen(payload)));
    }
    TEST_ASSERT_EQUAL_INT(0, persist_flush(p));

    char seg_path[512];
    TEST_ASSERT_EQUAL_INT(0,
        find_first_wal_segment(p->wal_path, seg_path, sizeof(seg_path)));

    /* Corrupt payload of entry 3 (zero-indexed: entries 0,1 valid; entry 2
     * corrupted; entries 3,4 unreachable via CRC chain). */
    off_t entry_size = (off_t)(sizeof(wal_entry_hdr_t) + strlen(payload));
    off_t corrupt_offset = entry_size * 2 + (off_t)sizeof(wal_entry_hdr_t);
    /* Write garbage over the payload of entry 2 */
    int fd = open(seg_path, O_RDWR);
    TEST_ASSERT_TRUE(fd >= 0);
    const char garbage[] = "\xFF\xFF\xFF\xFF";
    pwrite(fd, garbage, sizeof(garbage) - 1, corrupt_offset);
    close(fd);

    uint64_t lsn_before = p->current_lsn;
    teardown_e2e_wal(p);

    /* Phase 2: fresh persist_t — recover must stop before the corrupt entry */
    persist_t* p2 = calloc(1, sizeof(persist_t));
    TEST_ASSERT_NOT_NULL(p2);

    persist_config_t cfg = persist_config_defaults();
    cfg.wal_sync_ms = 5000;
    persist_set_workdir(p2, g_e2e_wal_tmpdir, "e2e-wal");

    TEST_ASSERT_EQUAL_INT(0, persist_init(p2, &cfg, NULL));
    TEST_ASSERT_EQUAL_INT(0, persist_start(p2));

    int rc = persist_recover(p2);
    TEST_ASSERT_EQUAL_INT(0, rc);

    /* Must have replayed fewer than 5 entries — stopped at corruption */
    TEST_ASSERT_TRUE(p2->current_lsn < lsn_before);

    teardown_e2e_wal(p2);
    printf("test_wal_chained_crc_detects_corruption: PASS\n");
}

/* ------------------------------------------------------------------ */
/* Suite entry point                                                    */
/* ------------------------------------------------------------------ */

void test_e2e_wal(void)
{
    printf("\n>> P0-15a: WAL E2E — torn write + CRC corruption recovery\n\n");

    RUN_TEST(test_wal_write_and_verify_entry_count);
    RUN_TEST(test_wal_torn_write_recovery);
    RUN_TEST(test_wal_chained_crc_detects_corruption);
}