/* AILang Str runtime primitives.
 *
 * Provides ABI-stable string operations against the existing
 * constant-Str layout (NUL-terminated byte buffer, passed as
 * `ptr` in LLVM IR). Lives separately from runtime/rc.c so that
 * a future heap-Str ABI milestone can swap the implementations
 * without touching the RC runtime.
 *
 * Linked unconditionally by `ail build` (Gc, Bump, Rc) so that
 * any program that monomorphises `eq__Str` (auto-loaded from
 * the prelude) finds the symbol. Programs that never call
 * `eq` on Str leave @ail_str_eq as a dead-stripped no-op at
 * link time under clang -O2.
 */

#include <stdbool.h>
#include <string.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <math.h>

/* Defined in runtime/rc.c — exposed with default external linkage.
 * Returns a zero-initialised payload whose `rc_header` sits at
 * `payload - 8` and is initialised to refcount 1. str.c's heap-Str
 * helpers call this regardless of the program's --alloc strategy,
 * because heap-Str values are always refcounted (the global
 * `--alloc` flag governs ADT allocation, not Str allocation).
 *
 * Declared `__attribute__((weak))` in hs.3 so the publicly-visible
 * `ailang_int_to_str` / `ailang_float_to_str` symbols can link into
 * binaries that do not pull in `runtime/rc.c` (i.e. `--alloc=bump`
 * bench builds, where `rc.c` is not linked). Under
 * such targets the reference resolves to NULL; the heap-Str helpers
 * are not yet called from any IR site (hs.4 wires the lowering), so
 * the NULL is never dereferenced at runtime. Under `--alloc=rc` the
 * strong definition in `rc.c` wins as usual. Once hs.4 lands the
 * unconditional `rc.c` link the `weak` attribute becomes a no-op
 * (strong definitions always satisfy weak references); the attribute
 * is intentionally retained so str.c remains link-safe in isolation.
 */
extern void *ailang_rc_alloc(size_t size) __attribute__((weak));

/* Byte-equality on NUL-terminated strings. Mirrors strcmp(...) == 0
 * but exposed under a stable AILang-namespaced ABI so the codegen
 * caller does not assume libc's strcmp shape. Heap-Str ABI milestone
 * will replace the body with length-prefixed comparison without
 * changing the signature. */
bool ail_str_eq(const char *a, const char *b) {
    return strcmp(a, b) == 0;
}

/* Three-way comparison of NUL-terminated strings. Normalises libc
 * strcmp's signed-int output to exactly -1 / 0 / +1 so the codegen
 * caller can branch on `icmp slt i32 result, 0` and
 * `icmp eq i32 result, 0` against constants directly without
 * worrying about strcmp implementations that return values outside
 * {-1, 0, +1}. Heap-Str ABI milestone will replace the body with
 * length-prefixed comparison without changing the signature. */
int ail_str_compare(const char *a, const char *b) {
    int r = strcmp(a, b);
    if (r < 0) return -1;
    if (r > 0) return 1;
    return 0;
}

/* Heap-Str slab allocator. Lays out:
 *
 *     [ rc_header (8B) | len (8B) | bytes... | NUL ]
 *     ^                ^
 *     payload-8        payload (returned)
 *
 * Calls `ailang_rc_alloc(8 + len + 1)`. The +8 is the len field;
 * the +1 is the trailing NUL byte that keeps `@strcmp` and `@fputs`
 * happy under the shared consumer ABI. Writes `len` into the first
 * 8 bytes of the payload and returns the payload pointer; the
 * caller is responsible for filling bytes [8 .. 8 + len) and the
 * `NUL` byte at offset `8 + len`.
 *
 * Private (static linkage) — callers within this TU only.
 */
static char *str_alloc(uint64_t len) {
    char *payload = (char *)ailang_rc_alloc(8 + len + 1);
    *(uint64_t *)payload = len;
    return payload;
}

/* Convert an i64 into a heap-allocated Str. Format `"%lld"`. The
 * worst-case width is 20 chars (i64::MIN = "-9223372036854775808");
 * a 64-byte stack buffer is comfortably oversized. `snprintf`'s
 * return tells us how many bytes *would* have been written; if that
 * exceeds the buffer we abort() defensively — this should be
 * unreachable for any valid i64 input but survives format-string
 * widening if a future change ever swaps `%lld` for something more
 * verbose without re-sizing the buffer.
 *
 * Returns the payload pointer of a fresh heap-Str slab. Caller owns
 * the refcount (init to 1 by `ailang_rc_alloc`); standard RC
 * discipline (`ailang_rc_inc` / `ailang_rc_dec`) applies.
 */
char *ailang_int_to_str(int64_t n) {
    char buf[64];
    int written = snprintf(buf, sizeof(buf), "%lld", (long long)n);
    if (written < 0 || (size_t)written >= sizeof(buf)) {
        fprintf(stderr,
                "ailang_int_to_str: snprintf truncation/error "
                "(written=%d, buffer=%zu) — should be unreachable for any valid i64; aborting\n",
                written, sizeof(buf));
        abort();
    }
    uint64_t len = (uint64_t)written;
    char *payload = str_alloc(len);
    memcpy(payload + 8, buf, len);
    payload[8 + len] = '\0';
    return payload;
}

/* Convert a double into a heap-allocated Str. Format `"%g"` —
 * the same libc rendering used throughout the runtime for Float
 * text output (post-iter-rpe.1 polymorphic `print` for Float
 * routes here via `Show Float.show`).
 * NaN renders as libc-default (`nan`/`-nan`/etc.); ±Inf as `inf`
 * /`-inf`. Worst-case width for `%g` on a `double` is bounded by
 * the libc default precision (`%.6g` ⇒ at most ~13 chars including
 * sign and exponent); the 64-byte stack buffer is comfortably
 * oversized. Defensive `abort()` on truncation, same shape as
 * `ailang_int_to_str`.
 *
 * `.0`-fallback (Gitea #7): if `x` is finite and `%g`'s output
 * contains neither `.` nor `e`/`E`, append `.0` so a whole-valued
 * Float renders with a Float-shaped suffix instead of Int-shaped
 * text. Mirrors the surface printer's `write_float_lit` fallback
 * at `crates/ailang-surface/src/print.rs` lines 624-637, keeping
 * the surface/runtime round-trip-on-lex symmetry intact. The
 * `isfinite(x)` fence skips the fallback for `nan`/`inf`/`-inf`,
 * which would otherwise match the no-`.`-no-`e` predicate and
 * render as `nan.0`/`inf.0`.
 *
 * Returns the payload pointer of a fresh heap-Str slab.
 */
char *ailang_float_to_str(double x) {
    char buf[64];
    int written = snprintf(buf, sizeof(buf), "%g", x);
    if (written < 0 || (size_t)written >= sizeof(buf)) {
        fprintf(stderr,
                "ailang_float_to_str: snprintf truncation/error "
                "(written=%d, buffer=%zu) — should be unreachable for any finite double; aborting\n",
                written, sizeof(buf));
        abort();
    }
    uint64_t len = (uint64_t)written;
    /* `.0`-fallback — see block comment above and the surface
     * counterpart at crates/ailang-surface/src/print.rs lines
     * 624-637. `%g` output is ASCII, so plain `memchr` suffices. */
    if (isfinite(x)
        && memchr(buf, '.', len) == NULL
        && memchr(buf, 'e', len) == NULL
        && memchr(buf, 'E', len) == NULL) {
        if (len + 2 >= sizeof(buf)) {
            fprintf(stderr,
                    "ailang_float_to_str: .0-fallback would overflow buffer "
                    "(len=%llu, buffer=%zu) — should be unreachable for any finite double; aborting\n",
                    (unsigned long long)len, sizeof(buf));
            abort();
        }
        buf[len] = '.';
        buf[len + 1] = '0';
        len += 2;
    }
    char *payload = str_alloc(len);
    memcpy(payload + 8, buf, len);
    payload[8 + len] = '\0';
    return payload;
}

/* Convert a bool into a heap-allocated Str — "true" (4 bytes) or
 * "false" (5 bytes). Heap-allocates every call; the static-Str
 * literal alternative (used by a hypothetical `\x -> if x then "true"
 * else "false"` schema body) would require phi-of-static-Str
 * through the drop-elision pipeline which is not load-bearing-
 * ratified today (see parent spec §"Out of scope" / `bool_to_str` as
 * schema-if).
 *
 * Returns the payload pointer of a fresh heap-Str slab.
 */
char *ailang_bool_to_str(bool b) {
    const char *lit = b ? "true" : "false";
    uint64_t len = b ? 4 : 5;
    char *payload = str_alloc(len);
    memcpy(payload + 8, lit, len);
    payload[8 + len] = '\0';
    return payload;
}

/* Clone a Str into a fresh heap-Str slab. Reads `len` from the
 * first 8 bytes of the source payload, allocates a new slab of the
 * same length via `str_alloc`, and memcpy's the payload bytes plus
 * the trailing NUL. Works uniformly on static-Str and heap-Str
 * inputs because the consumer ABI (i64 len at offset 0, bytes
 * starting at offset 8, NUL at offset 8 + len) is identical
 * between realisations (see design/contracts/0011-str-abi.md); the rc_header at
 * offset -8 — present only on heap-Str — is never consulted.
 *
 * Used by `show__Str` (parent spec milestone 24): converts a
 * borrowed Str input into an Owned heap-Str output, preserving
 * the uniform `show : forall a. Show a => (a borrow) -> Str Own`
 * signature.
 *
 * Returns the payload pointer of a fresh heap-Str slab.
 */
char *ailang_str_clone(const char *src) {
    uint64_t len = *(const uint64_t *)src;
    char *payload = str_alloc(len);
    memcpy(payload + 8, src + 8, len);
    payload[8 + len] = '\0';
    return payload;
}

/*
 * `ailang_str_concat(a, b)` — heap-Str concatenation primitive
 * shipped in iter str-concat (2026-05-13). Reads `len` headers from
 * both source Str payloads (offset 0 of each), allocates a fresh
 * heap-Str slab sized for the combined bytes via `str_alloc`,
 * memcpys both payloads in order, NUL-terminates, returns the new
 * payload pointer. Like `str_clone`, this works uniformly on static-
 * Str and heap-Str inputs because the consumer ABI is identical
 * between realisations (see design/contracts/0011-str-abi.md).
 *
 * Used by Show bodies that want labelled output (e.g.
 * `"Item " ++ int_to_str n`) and by any caller that needs to
 * combine two existing Str values into a new owned Str.
 *
 * Returns the payload pointer of a fresh heap-Str slab. The rc
 * header is initialised to 1 by `str_alloc`.
 */
char *ailang_str_concat(const char *a, const char *b) {
    uint64_t la = *(const uint64_t *)a;
    uint64_t lb = *(const uint64_t *)b;
    char *payload = str_alloc(la + lb);
    memcpy(payload + 8, a + 8, la);
    memcpy(payload + 8 + la, b + 8, lb);
    payload[8 + la + lb] = '\0';
    return payload;
}
