feat: implement cel_crsf_param_set_power

Enumerate parameters until TX Power entry is found, match
requested mW against TEXT_SELECT options, and write the
selected option index.

Added:
- str_contains_ci() for case-insensitive substring matching
- is_power_param() to detect power-related parameters
- match_power_option() to find mW in option strings
- 4 new tests: null port, frame roundtrip, success, not found

celrs/crsf_param.c

@@ -1,7 +1,70 @@
-#include "celrs/crsf_param.h"
+#include <ctype.h>
+#include <stdio.h>
 #include <string.h>
 #include <time.h>
 
+#include "celrs/crsf_param.h"
+
+/* --------------------------------------------------------------------------- */
+/* Helpers for power matching                                                 */
+/* --------------------------------------------------------------------------- */
+
+/* Case-insensitive string contains */
+static int str_contains_ci(char const* haystack, char const* needle) {
+    size_t hlen = strlen(haystack);
+    size_t nlen = strlen(needle);
+    if (nlen > hlen) return 0;
+    for (size_t i = 0; i <= hlen - nlen; i++) {
+        int match = 1;
+        for (size_t j = 0; j < nlen; j++) {
+            if (tolower((unsigned char)haystack[i + j])
+                != tolower((unsigned char)needle[j]))
+            {
+                match = 0;
+                break;
+            }
+        }
+        if (match) return 1;
+    }
+    return 0;
+}
+
+/* Check if param name contains "power" (case-insensitive) */
+static int is_power_param(cel_crsf_param const* param) {
+    return str_contains_ci(param->name, "power");
+}
+
+/* Match requested power (mW) against a TEXT_SELECT option string.
+ * Returns option index (0-based) or -1 if no match. */
+static int match_power_option(cel_crsf_param const* param, int mw) {
+    char const* opts = param->options;
+    char opt_buf[64];
+    int index = 0;
+
+    while (*opts) {
+        /* Extract option up to ';' or '\0' */
+        size_t i = 0;
+        while (*opts && *opts != ';' && i < sizeof(opt_buf) - 1) {
+            opt_buf[i++] = *opts++;
+        }
+        opt_buf[i] = '\0';
+        if (*opts == ';') opts++; /* skip separator */
+
+        /* Check if option starts with the requested mW value */
+        char req_buf[16];
+        sprintf(req_buf, "%d", mw);
+        if (str_contains_ci(opt_buf, req_buf)) {
+            return index;
+        }
+        index++;
+    }
+    return -1;
+}
+
+/* --------------------------------------------------------------------------- */
+/* Public API                                                                 */
+/* --------------------------------------------------------------------------- */
+
 int cel_crsf_param_ping(cel_serial_port* port, float timeout_sec) {
     if (port == NULL) return -1;
 
@@ -101,22 +164,31 @@ int cel_crsf_param_write(cel_serial_port* port, uint8_t index,
 
 int cel_crsf_param_set_power(cel_serial_port* port, int mw,
                               float timeout_sec) {
-    /* TODO: enumerate parameters until TX Power entry is found.
-     * 1. Send ping, verify DEVICE_INFO response (call cel_crsf_param_ping).
-     * 2. For index 0..31:
-     *    a. Send param read frame for index.
-     *    b. Wait for PARAM_ENTRY response (timeout per param).
-     *    c. If no response, stop (end of parameter list).
-     *    d. If param name contains "power" (case-insensitive)
-     *       and type is CEL_PARAM_TEXT_SELECT:
-     *       - Search options for matching power level string
-     *         (e.g. "10" matches "10 mW", "dynamic" matches "dynamic").
-     *       - Send param write frame with matching option index.
-     *       - Return 0.
-     * 3. If loop completes without finding power param, return -1. */
-    (void)port;
-    (void)mw;
-    (void)timeout_sec;
+    if (port == NULL) return -1;
+
+    /* 1. Ping to verify connection */
+    if (cel_crsf_param_ping(port, timeout_sec) != 0) return -1;
+
+    /* 2. Enumerate params until power entry is found */
+    for (uint8_t idx = 0; idx < 32; idx++) {
+        cel_crsf_param param;
+        if (cel_crsf_param_read(port, idx, &param, timeout_sec) != 0) {
+            /* No response = end of parameter list */
+            break;
+        }
+
+        /* Check if this is the power parameter */
+        if (is_power_param(&param) && param.type == CEL_PARAM_TEXT_SELECT) {
+            /* Find matching option */
+            int opt_index = match_power_option(&param, mw);
+            if (opt_index >= 0) {
+                /* Write the selected option */
+                return cel_crsf_param_write(port, idx, (uint8_t)opt_index);
+            }
+        }
+    }
+
+    /* 3. Power param not found */
     return -1;
 }
 

celrs/crsf_param.h

@@ -1,6 +1,7 @@
 #pragma once
-#include <stdint.h>
 #include <stddef.h>
+#include <stdint.h>
+
 #include "celrs/crsf.h"
 #include "celrs/serial.h"