/* startup_validation.c — Startup pre-flight validation functions.
 *
 * Implements validate_vcpus(), validate_startup_config(),
 * validate_peer_count(), validate_cert_files(), and
 * validate_heartbeat_config() for use in main.c and the controller
 * unit test suite.
 *
 * Requirements: 4.1 (peer count), 4.2 (cert pre-flight),
 *               4.3 (vcpus), 4.4 (vcpus key deprecation warn),
 *               2.4 (heartbeat timing validation)
 */
#define _GNU_SOURCE
#include <errno.h>
#include <stdint.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>

/* ── Req 4.3: --vcpus validation ─────────────────────────────────────── */

/*
 * validate_vcpus: returns 0 if vcpus >= 1, -EINVAL otherwise.
 * Called from main.c after argp_parse() sets arguments.vcpus.
 */
int validate_vcpus(int vcpus)
{
    if (vcpus <= 0) {
        return -EINVAL;
    }
    return 0;
}

/* ── Req 4.4: vcpus key in config file — warn only ───────────────────── */

/*
 * validate_startup_config: scan config_path for a "vcpus" key.
 * If found, write a deprecation warning into warn_buf (must contain "vcpus").
 * Always returns 0 — the presence of a vcpus key is not a fatal error.
 * warn_buf is left empty (first byte = '\0') when no vcpus key is found.
 *
 * The scan is line-based: a line contains the vcpus key if it starts with
 * optional whitespace followed by the literal string "vcpus".
 */
int validate_startup_config(const char *config_path,
                            char *warn_buf, size_t warn_len)
{
    if (warn_buf && warn_len > 0) {
        warn_buf[0] = '\0';
    }

    if (!config_path) {
        return 0;
    }

    FILE *fp = fopen(config_path, "r");
    if (!fp) {
        return 0; /* can't open — not a fatal error at this stage */
    }

    char line[1024];
    while (fgets(line, sizeof(line), fp)) {
        /* skip leading whitespace */
        const char *p = line;
        while (*p == ' ' || *p == '\t') {
            p++;
        }
        if (strncmp(p, "vcpus", 5) == 0) {
            /* Found a vcpus key — write deprecation warning */
            if (warn_buf && warn_len > 0) {
                snprintf(warn_buf, warn_len,
                         "config file contains deprecated 'vcpus' key; "
                         "use --vcpus CLI parameter instead");
            }
            break;
        }
    }

    fclose(fp);
    return 0;
}

/* ── Req 4.1: even-N peer count rejection ─────────────────────────────── */

/*
 * validate_peer_count: returns 0 for valid odd counts (1, 3, 5, ...),
 * -EINVAL for even counts > 1.
 * n_peers == 1 is single-node mode — always valid.
 * Even counts > 1 cannot form a safe majority partition.
 */
int validate_peer_count(int n_peers)
{
    if (n_peers > 1 && (n_peers % 2) == 0) {
        return -EINVAL;
    }
    return 0;
}

/* ── Req 4.2: TLS cert pre-flight ─────────────────────────────────────── */

/*
 * validate_cert_files: check that cert_path and key_path are readable.
 * On the first missing/unreadable file, sets err_buf to a message
 * containing the full file path and returns -ENOENT.
 * Returns 0 if both files are accessible.
 */
int validate_cert_files(const char *cert_path, const char *key_path,
                        char *err_buf, size_t err_len)
{
    if (access(cert_path, R_OK) != 0) {
        if (err_buf && err_len > 0) {
            snprintf(err_buf, err_len,
                     "TLS certificate not found or unreadable: %s",
                     cert_path);
        }
        return -ENOENT;
    }

    if (access(key_path, R_OK) != 0) {
        if (err_buf && err_len > 0) {
            snprintf(err_buf, err_len,
                     "TLS key not found or unreadable: %s",
                     key_path);
        }
        return -ENOENT;
    }

    return 0;
}

/* ── Req 2.4: heartbeat timing validation ─────────────────────────────── */

/*
 * validate_heartbeat_config: enforce heartbeat_timeout_ms >= 2 * heartbeat_interval_ms.
 *
 * A timeout smaller than two intervals means the standby could declare the
 * primary dead before a single missed heartbeat has elapsed — that is an
 * operator misconfiguration that must be caught at startup.
 *
 * Returns 0 when the relationship holds (valid config).
 * Returns -EINVAL when heartbeat_timeout_ms < 2 * heartbeat_interval_ms;
 * writes a human-readable error message into err_buf.
 */
int validate_heartbeat_config(uint32_t heartbeat_timeout_ms,
                              uint32_t heartbeat_interval_ms,
                              char *err_buf, size_t err_len)
{
    if (err_buf && err_len > 0) {
        err_buf[0] = '\0';
    }

    if (heartbeat_timeout_ms < 2 * heartbeat_interval_ms) {
        if (err_buf && err_len > 0) {
            snprintf(err_buf, err_len,
                     "heartbeat_timeout_ms (%u) must be >= 2 * heartbeat_interval_ms (%u); "
                     "current ratio %.2f is below the minimum of 2.0 — "
                     "set heartbeat_timeout_ms >= %u",
                     heartbeat_timeout_ms,
                     heartbeat_interval_ms,
                     heartbeat_interval_ms > 0
                         ? (double)heartbeat_timeout_ms / (double)heartbeat_interval_ms
                         : 0.0,
                     2 * heartbeat_interval_ms);
        }
        return -EINVAL;
    }

    return 0;
}