From 9f7bf8ddf255f06a3c27c13dad87e34a70356d58 Mon Sep 17 00:00:00 2001
From: Stefan Zabka <zabkaste@hu-berlin.de>
Date: Wed, 20 May 2020 18:07:43 +0200
Subject: First implementation of prompt

---
 02_exercise/prompt_utils.c | 90 ++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 90 insertions(+)
 create mode 100644 02_exercise/prompt_utils.c

(limited to '02_exercise/prompt_utils.c')

diff --git a/02_exercise/prompt_utils.c b/02_exercise/prompt_utils.c
new file mode 100644
index 0000000..819509d
--- /dev/null
+++ b/02_exercise/prompt_utils.c
@@ -0,0 +1,90 @@
+#include "prompt_utils.h"
+
+#include "array.h"
+#include <errno.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+char const *const relative_path(char const *const from_dir, char const *const to_dir) {
+    // easiest cases first
+    {
+        int result = strcmp(from_dir, to_dir);
+        if (result == 0) {
+            char *return_value = malloc(2);
+            strcpy(return_value, ".");
+            return return_value;
+        }
+    }
+    {
+        if (strcmp("/", from_dir) == 0) {
+            char *return_value = malloc(strlen(to_dir) + 2);
+            return_value[0] = '.';
+            memcpy(return_value + 1, to_dir, strlen(to_dir) + 1);
+            return return_value;
+        }
+    }
+    // Splitting path into pieces so we can do strcmp on each of them
+    size_t const *const from_dir_indeces = get_seperator_indeces(from_dir, '/');
+    size_t const *const to_dir_indeces = get_seperator_indeces(to_dir, '/');
+
+    size_t from_dir_len = arrayLen(from_dir_indeces);
+    size_t to_dir_len = arrayLen(to_dir_indeces);
+
+    // finding the longest common substring
+    size_t array_len = from_dir_len < to_dir_len ? from_dir_len : to_dir_len;
+    size_t i = 0;
+    size_t common_position = 0;
+    for (; i < array_len - 1; i++) {
+        if (from_dir_indeces[i + 1] != to_dir_indeces[i + 1]) {
+            break;
+        }
+        size_t index = from_dir_indeces[i];
+        size_t count = from_dir_indeces[i + 1] - from_dir_indeces[i];
+        if (strncmp(from_dir + index, to_dir + index, count) != 0) {
+            break;
+        }
+        common_position = from_dir_indeces[i + 1];
+    }
+
+    size_t levels_up = from_dir_len - i - 1;
+    char *return_value;
+    if (levels_up == 0) {
+        // Equal dirs for whole length of path and not equal => subdir
+        size_t length = strlen(to_dir + common_position) + strlen("./") + 1;
+        return_value = malloc(length * sizeof(char));
+        strcpy(return_value, ".");
+        strcat(return_value, to_dir + common_position);
+    } else {
+        char const *const go_up = "/..";
+        size_t length = strlen(to_dir + common_position) + strlen("..") +
+                        strlen(go_up) * (levels_up - 1);
+        return_value = malloc(length * sizeof(char));
+        strcpy(return_value, "..");
+        for (size_t j = 0; j < levels_up - 1; j++) {
+            strcat(return_value, go_up);
+        }
+        strcat(return_value, to_dir + common_position);
+    }
+
+    arrayRelease((void *)from_dir_indeces);
+    arrayRelease((void *)to_dir_indeces);
+
+    return return_value;
+}
+
+size_t *get_seperator_indeces(char const *const text, char seperator) {
+    size_t *indeces;
+    arrayInit(indeces);
+    char const *current = text;
+    if (strchr(current, seperator) == NULL) {
+        arrayRelease(indeces);
+        return NULL;
+    }
+    while ((current = strchr(current, seperator)) != NULL) {
+        arrayPush(indeces) = current - text;
+        ++current;
+    }
+    arrayPush(indeces) = strlen(text);
+    return indeces;
+}
-- 
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