1 files changed, 200 insertions, 0 deletions
diff --git a/src/regex.zig b/src/regex.zig
new file mode 100644
index 0000000..ed66df8
--- /dev/null
+++ b/src/regex.zig
@@ -0,0 +1,200 @@
+const std = @import("std");
+
+pub const Token = struct {
+    pub const Kind = enum { Literal, LParen, RParen, Class, Dot, Star, Plus, Question, Or };
+    pub const Value = union(Token.Kind) { Literal: u8, LParen, RParen, Class: RangeList, Dot, Star, Plus, Question, Or };
+
+    kind: Token.Kind,
+    value: ?Token.Value,
+    pos: usize,
+
+    pub fn format(self: *const Token, comptime fmt: []const u8, _: std.fmt.FormatOptions, writer: anytype) !void {
+        if (fmt.len != 0) { // must be {} or {any}
+            return std.invalidFmtError(fmt, self);
+        }
+
+        try writer.print("{{ kind: {s}", .{@tagName(self.kind)});
+
+        if (self.value) |val| {
+            switch (val) {
+                .Literal => |literal| try writer.print(", value: {c}", .{literal}),
+                .Class => |rl| try writer.print(", value: {}", .{rl}),
+                else => {},
+            }
+        }
+
+        try writer.print(" }}", .{});
+    }
+};
+
+pub const Lexer = struct {
+    start: usize,
+    cursor: usize,
+    regexp: []const u8,
+    allocator: *std.mem.Allocator,
+
+    pub const Error = error{ EndOfBuffer, InvalidCharacter, UnexpectedCharater };
+
+    pub fn init(regexp: []const u8, allocator: *std.mem.Allocator) Lexer {
+        return .{ .cursor = 0, .start = 0, .regexp = regexp, .allocator = allocator };
+    }
+
+    fn readChar(self: *Lexer) !u8 {
+        if (self.cursor >= self.regexp.len) {
+            return Error.EndOfBuffer;
+        }
+
+        return self.regexp[self.cursor];
+    }
+
+    pub fn advance(self: *Lexer) !Token {
+        self.start = self.cursor;
+
+        var c = try self.readChar();
+
+        const inferred_type: Token.Kind = switch (c) {
+            '(' => .LParen,
+            ')' => .RParen,
+            '[' => .Class,
+            '.' => .Dot,
+            '*' => .Star,
+            '+' => .Plus,
+            '?' => .Question,
+            '|' => .Or,
+            else => .Literal,
+        };
+
+        switch (inferred_type) {
+            .Literal => {
+                if (c == '\\') {
+                    self.cursor += 1;
+                    c = try self.readChar(); // needs more verbose error handling
+                    c = escapedChar(c);
+                }
+                self.cursor += 1;
+                return .{ .kind = inferred_type, .value = .{ .Literal = c }, .pos = self.start };
+            },
+            .Class => {
+                while (c != ']') { // needs more verbose error handling
+                    if (self.cursor >= self.regexp.len) {
+                        return Error.EndOfBuffer;
+                    }
+                    self.cursor += 1;
+                }
+                return .{ .kind = inferred_type, .value = .{ .Class = try RangeList.init(self.regexp[self.start + 1 .. self.cursor - 1], self.allocator) }, .pos = self.start };
+            },
+            else => {
+                self.cursor += 1;
+                return .{ .kind = inferred_type, .pos = self.start, .value = null };
+            },
+        }
+    }
+
+    fn escapedChar(c: u8) u8 {
+        return switch (c) {
+            'n' => '\n', // placeholder for now
+            't' => '\t',
+            'r' => '\r',
+            else => c,
+        };
+    }
+};
+
+// could use something like a bst, but thinking about what regex classes people actually write makes me think that a list is more efficient
+pub const RangeList = struct {
+    negated: bool,
+    head: ?*Node,
+    allocator: *std.mem.Allocator,
+
+    const Node = struct {
+        range: struct { min: u8, max: u8 },
+        next: ?*Node,
+    };
+
+    // need to do more error handling
+    pub fn init(str: []const u8, allocator: *std.mem.Allocator) !RangeList {
+        var rl = RangeList{
+            .negated = false,
+            .head = null,
+            .allocator = allocator,
+        };
+
+        var i: usize = 0;
+
+        if (str.len == 0) {
+            return rl;
+        }
+
+        if (str[0] == '^') {
+            rl.negated = true;
+            i += 1;
+        }
+
+        var p = rl.head;
+        while (i < str.len) : (i += 1) {
+            const node = try rl.allocator.create(Node);
+
+            const min = str[i];
+            var max = min;
+
+            i += 1;
+
+            if (i + 1 < str.len and str[i] == '-') {
+                i += 1;
+                max = str[i];
+                i += 1;
+            }
+
+            node.* = .{
+                .range = .{ .min = min, .max = max },
+                .next = null,
+            };
+
+            if (p) |tail| {
+                tail.next = node;
+                p = tail.next;
+            } else {
+                rl.head = node;
+                p = rl.head;
+            }
+        }
+        return rl;
+    }
+
+    pub fn deinit(self: *const RangeList) void {
+        var itr = self.head;
+
+        while (itr) |node| {
+            const prev = node;
+            itr = node.next;
+            self.allocator.destroy(prev);
+        }
+    }
+
+    pub fn format(self: *const RangeList, comptime fmt: []const u8, _: std.fmt.FormatOptions, writer: anytype) !void {
+        var itr = self.head;
+
+        if (fmt.len != 0) { // must be {} or {any}
+            return std.invalidFmtError(fmt, self);
+        }
+
+        if (self.negated) {
+            try writer.print("^", .{});
+        }
+
+        try writer.print("[", .{});
+
+        while (itr) |node| : (itr = node.next) {
+            if (node.range.min == node.range.max) {
+                try writer.print("{c}", .{node.range.min});
+            } else {
+                try writer.print("{c}-{c}", .{ node.range.min, node.range.max });
+            }
+
+            if (node.next) |_| {
+                try writer.print(", ", .{});
+            }
+        }
+        try writer.print("]", .{});
+    }
+};