From 3efb1a26e0e6c4ad9c3e7f9cf37cd29d20f47225 Mon Sep 17 00:00:00 2001
From: Joscha <joscha@plugh.de>
Date: Sun, 7 Nov 2021 21:59:20 +0000
Subject: [PATCH] Start implementing parser

---
 README.md     |  12 ++++++
 src/main.rs   |   1 +
 src/parser.rs | 107 ++++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 120 insertions(+)
 create mode 100644 src/parser.rs

diff --git a/README.md b/README.md
index 279fd14..f8d645c 100644
--- a/README.md
+++ b/README.md
@@ -112,4 +112,16 @@ BDATE 1987-05-14
 
 BIRTHDAY Martha
 BDATE ?-09-21
+
+NOTE Physics lecture
+DATE wed 14:00 -- 15:30
+DATE 2021-05-07 14:00 -- 15:30
+FROM 2021-04-14
+UNTIL 2021-07-28
+EXCEPT 2021-05-06
+	This is a description of the event. It might mention further information
+	that doesn't fit into the title.
+
+	It may even contain multiple paragraphs, separated by an arbitrary amount
+	of empty lines, as long as every non-empty line is indented.
 ```
diff --git a/src/main.rs b/src/main.rs
index 7590a92..48a0c19 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -3,6 +3,7 @@ use std::path::PathBuf;
 use structopt::StructOpt;
 
 mod commands;
+mod parser;
 mod source;
 
 #[derive(Debug, StructOpt)]
diff --git a/src/parser.rs b/src/parser.rs
new file mode 100644
index 0000000..f3da2ce
--- /dev/null
+++ b/src/parser.rs
@@ -0,0 +1,107 @@
+use std::cmp::min;
+use std::process::Command;
+
+use crate::source::{SourceFile, SourceSpan};
+
+#[derive(Debug)]
+pub struct ParseError(SourceSpan, String);
+
+type ParseResult<T> = Result<T, ParseError>;
+
+#[derive(Debug)]
+pub struct Parser<'a> {
+    file: SourceFile,
+    content: &'a str,
+    offset: usize,
+    errors: Vec<ParseError>,
+}
+
+impl<'a> Parser<'a> {
+    pub fn new(file: SourceFile, content: &'a str) -> Self {
+        Self {
+            file,
+            content,
+            offset: 0,
+            errors: vec![],
+        }
+    }
+
+    fn peek(&self, amount: usize) -> &'a str {
+        let end = min(self.content.len(), self.offset + amount);
+        &self.content[self.offset..end]
+    }
+
+    fn peek_rest(&self) -> &'a str {
+        &self.content[self.offset..]
+    }
+
+    fn at_eof(&self) -> bool {
+        self.offset >= self.content.len()
+    }
+
+    fn take(&mut self, amount: usize) {
+        self.offset += amount;
+    }
+
+    fn error(&self, at: usize, error: impl ToString) -> ParseError {
+        ParseError(self.file.span(at..at), error.to_string())
+    }
+
+    fn uncritical(&mut self, at: usize, error: impl ToString) {
+        self.errors.push(self.error(at, error));
+    }
+
+    fn critical(&self, at: usize, error: impl ToString) -> ParseResult<()> {
+        Err(self.error(at, error))
+    }
+
+    pub fn parse(&mut self) -> Result<Vec<Command>, Vec<ParseError>> {
+        match self.parse_commands() {
+            Ok(commands) => {
+                if self.errors.is_empty() {
+                    return Ok(commands);
+                }
+            }
+            Err(error) => {
+                self.errors.push(error);
+            }
+        };
+
+        Err(self.errors.split_off(0))
+    }
+
+    fn parse_commands(&mut self) -> ParseResult<Vec<Command>> {
+        let mut commands = vec![];
+
+        self.skip_empty_lines();
+        while !self.at_eof() {
+            commands.push(self.parse_command()?);
+        }
+
+        if !self.at_eof() {
+            self.uncritical(self.offset, "expected EOF");
+        }
+
+        Ok(commands)
+    }
+
+    fn skip_empty_lines(&mut self) {
+        loop {
+            if let Some(i) = self.peek_rest().find('\n') {
+                if self.peek(i).chars().all(|c| c.is_whitespace()) {
+                    self.take(i + 1); // Include the newline
+                } else {
+                    break;
+                }
+            } else if self.peek_rest().chars().all(|c| c.is_whitespace()) {
+                self.take(self.peek_rest().len());
+            } else {
+                break;
+            }
+        }
+    }
+
+    fn parse_command(&mut self) -> ParseResult<Command> {
+        todo!()
+    }
+}