Add functions for seeking lines and getting line counts in functions (t…

…gstation#95)

dds rustg_file_get_line_count for getting the line count of a given filename, and rustg_file_seek_line for getting a specific line.

These are useful as to not load the entire file into memory in DM, which is useful for very large files like dictionaries.

build.rs

@@ -28,7 +28,7 @@ fn main() {
     for (key, _value) in std::env::vars() {
         // CARGO_FEATURE_<name> — For each activated feature of the package being built, this environment variable will be present where <name> is the name of the feature uppercased and having - translated to _.
         if let Some(uprfeature) = key.strip_prefix("CARGO_FEATURE_") {
-            let feature = uprfeature.to_lowercase().replace("_", "-"); // actual proper name of the enabled feature
+            let feature = uprfeature.to_lowercase().replace('_', "-"); // actual proper name of the enabled feature
             if feature_dm_exists!(&feature) {
                 writeln!(
                     f,

dmsrc/file.dm

@@ -2,6 +2,8 @@
 #define rustg_file_exists(fname) call(RUST_G, "file_exists")(fname)
 #define rustg_file_write(text, fname) call(RUST_G, "file_write")(text, fname)
 #define rustg_file_append(text, fname) call(RUST_G, "file_append")(text, fname)
+#define rustg_file_get_line_count(fname) text2num(call(RUST_G, "file_get_line_count")(fname))
+#define rustg_file_seek_line(fname, line) call(RUST_G, "file_seek_line")(fname, "[line]")
 
 #ifdef RUSTG_OVERRIDE_BUILTINS
 	#define file2text(fname) rustg_file_read("[fname]")

src/file.rs

@@ -1,7 +1,7 @@
 use crate::error::Result;
 use std::{
     fs::{File, OpenOptions},
-    io::{BufReader, BufWriter, Read, Write},
+    io::{BufRead, BufReader, BufWriter, Read, Write},
 };
 
 byond_fn!(fn file_read(path) {
@@ -20,14 +20,25 @@ byond_fn!(fn file_append(data, path) {
     append(data, path).err()
 });
 
+byond_fn!(fn file_get_line_count(path) {
+    Some(get_line_count(path).ok()?.to_string())
+});
+
+byond_fn!(fn file_seek_line(path, line) {
+    seek_line(path, match line.parse::<usize>() {
+        Ok(line) => line,
+        Err(_) => return None,
+    })
+});
+
 fn read(path: &str) -> Result<String> {
     let file = File::open(path)?;
     let metadata = file.metadata()?;
     let mut file = BufReader::new(file);
 
     let mut content = String::with_capacity(metadata.len() as usize);
     file.read_to_string(&mut content)?;
-    let content = content.replace("\r", "");
+    let content = content.replace('\r', "");
 
     Ok(content)
 }
@@ -70,3 +81,13 @@ fn append(data: &str, path: &str) -> Result<usize> {
 
     Ok(written)
 }
+
+fn get_line_count(path: &str) -> Result<u32> {
+    let file = BufReader::new(File::open(path)?);
+    Ok(file.lines().count() as u32)
+}
+
+fn seek_line(path: &str, line: usize) -> Option<String> {
+    let file = BufReader::new(File::open(path).ok()?);
+    file.lines().nth(line).and_then(|line| line.ok())
+}