/*
 * autovars.c -- xce_test auto-variable substitution (see include/autovars.h).
 */
#include <errno.h>
#include <stdio.h>
#include <string.h>

#include "autovars.h"

static void set_err(char* errbuf, size_t errlen, const char* msg)
{
    if ((errbuf != NULL) && (errlen > 0)) {
        snprintf(errbuf, errlen, "%s", msg);
    }
}

int autovar_substitute(const char* line, const autovar_ctx_t* ctx, char* out,
                       size_t outlen, char* errbuf, size_t errlen)
{
    const char* p = line;
    const char* first;
    size_t      o = 0;

    if ((errbuf != NULL) && (errlen > 0)) {
        errbuf[0] = '\0';
    }
    if ((line == NULL) || (ctx == NULL) || (out == NULL) || (outlen == 0)) {
        return -EINVAL;
    }

    /* `!` shell-escape and `#` comment lines are left untouched. */
    first = line;
    while ((*first == ' ') || (*first == '\t')) {
        first++;
    }
    if ((*first == '!') || (*first == '#')) {
        size_t len = strlen(line);

        if (len >= outlen) {
            return -ENOSPC;
        }
        memcpy(out, line, len + 1);
        return 0;
    }

    while (*p != '\0') {
        /* A `$` starts a candidate auto-var only when it begins a token, i.e.
         * the previous char is the line start or whitespace. */
        int at_token_start
            = (p == line) || (*(p - 1) == ' ') || (*(p - 1) == '\t');

        if ((*p == '$') && at_token_start) {
            const char* name = p + 1;
            const char* end  = name;
            const char* repl = NULL;
            const char* stop; /* where the replaced text ends */
            char        numbuf[32];

            /* Scan to the token end (whitespace or NUL). */
            while ((*end != '\0') && (*end != ' ') && (*end != '\t')) {
                end++;
            }

            size_t namelen = (size_t)(end - name);
            /* `$jobid[...]` (Req 4.10): only `$jobid` is replaced; the rest
             * of the token, from the `[`, is copied unchanged. */
            int jobid_index
                = (namelen > 5) && (strncmp(name, "jobid[", 6) == 0);

            stop = end;
            if ((namelen == 1) && (name[0] == '?')) {
                snprintf(numbuf, sizeof(numbuf), "%d", ctx->last_status);
                repl = numbuf;
            } else if (jobid_index
                       || ((namelen == 5)
                           && (strncmp(name, "jobid", 5) == 0))) {
                /* Req 4.11: an unset $jobid fails `$jobid[...]` the same
                 * way as `$jobid`. */
                if ((ctx->jobid == NULL) || (ctx->jobid[0] == '\0')) {
                    set_err(errbuf, errlen,
                            "autovar: $jobid referenced before set");
                    return -EINVAL;
                }
                repl = ctx->jobid;
                stop = name + 5;
            } else if ((namelen == 8) && (strncmp(name, "jobcount", 8) == 0)) {
                if (ctx->jobcount < 0) {
                    set_err(errbuf, errlen,
                            "autovar: $jobcount referenced before set");
                    return -EINVAL;
                }
                snprintf(numbuf, sizeof(numbuf), "%d", ctx->jobcount);
                repl = numbuf;
            }

            if (repl != NULL) {
                size_t rlen = strlen(repl);

                if ((o + rlen) >= outlen) {
                    return -ENOSPC;
                }
                memcpy(out + o, repl, rlen);
                o += rlen;
                p = stop; /* consume `$name`; a `[...]` rest is copied */
                continue;
            }

            /* Not a recognized auto-var: copy the whole token verbatim. */
            while (p < end) {
                if ((o + 1) >= outlen) {
                    return -ENOSPC;
                }
                out[o++] = *p++;
            }
            continue;
        }

        if ((o + 1) >= outlen) {
            return -ENOSPC;
        }
        out[o++] = *p++;
    }

    out[o] = '\0';
    return 0;
}