From 26bbb05777dbbb6d2f3c7485b53ebeba4b41ecc2 Mon Sep 17 00:00:00 2001
From: mars <mars@tebibyte.media>
Date: Wed, 30 Aug 2023 19:09:53 -0600
Subject: [PATCH] tail(1p): tail -n

---
 src/tail.c | 69 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 69 insertions(+)

diff --git a/src/tail.c b/src/tail.c
index d576dfa..f798eb3 100644
--- a/src/tail.c
+++ b/src/tail.c
@@ -28,6 +28,75 @@
 
 #include "yac.h"
 
+typedef struct string_t {
+  char *mem;
+  int len;
+  int capacity;
+} string_t;
+
+string_t *string_new() {
+  string_t *string = calloc(1, sizeof(string_t));
+  string->capacity = 1024;
+  string->len = 0;
+  string->mem = calloc(string->capacity, sizeof(char));
+  return string;
+}
+
+void string_putc(string_t *string, char c) {
+  string->mem[string->len] = c;
+  string->len++;
+  if (string->len >= string->capacity) {
+    string->capacity *= 2;
+    string->mem = realloc(string->mem, string->capacity * sizeof(char));
+  }
+}
+
+void tailc(FILE *f, long num) {}
+
+void tailn(FILE *f, long num) {
+  string_t *lines[num];
+  int cursor = 0;
+  int looped = 0;
+
+  lines[cursor] = string_new();
+
+  int c = fgetc(f);
+  for (;;) {
+    if (c == EOF) {
+      string_putc(lines[cursor], '\0');
+      break;
+    }
+
+    string_putc(lines[cursor], c);
+
+    if (c == '\n') {
+      string_putc(lines[cursor], '\0');
+
+      if ((c = fgetc(f)) == EOF) {
+        break;
+      }
+
+      if (++cursor >= num) {
+        looped = 1;
+        cursor = 0;
+      }
+
+      lines[cursor] = string_new();
+    } else {
+      c = fgetc(f);
+    }
+  }
+
+  int read = looped ? cursor + 1 : 0;
+  do {
+    if (read >= num) {
+      read = 0;
+    }
+
+    fputs(lines[read]->mem, stdout);
+  } while (read++ != cursor);
+}
+
 void tailf(FILE *file) {
 	int byte;