const std = @import("std");

const token = @import("token.zig");
const main = @import("main.zig");

const TokenList = std.ArrayList(token.Token);

pub const Scanner = struct {
    source: []u8,
    tokens: TokenList,

    start: usize = 0,
    current: usize = 0,
    line: usize = 1,

    pub fn init(allocator: *std.mem.Allocator, data: []u8) Scanner {
        return Scanner{
            .source = data,
            .tokens = TokenList.init(allocator),
        };
    }

    fn isAtEnd(self: *Scanner) bool {
        return self.current >= self.source.len;
    }

    fn advance(self: *Scanner) u8 {
        self.current += 1;
        return self.source[self.current - 1];
    }

    fn currentLexeme(self: *Scanner) []u8 {
        return self.source[self.start..self.current];
    }

    fn addSimpleToken(self: *Scanner, ttype: token.TokenType) !void {
        try self.addToken(token.Token{
            .Simple = token.SimpleToken.init(
                ttype,
                self.currentLexeme(),
                self.line,
                {},
            ),
        });
    }

    fn addToken(
        self: *Scanner,
        tok: token.Token,
    ) !void {
        try self.tokens.append(tok);
    }

    fn scanToken(self: *Scanner) !void {
        var c = self.advance();

        switch (c) {
            '(' => try self.addSimpleToken(.LEFT_PAREN),
            ')' => try self.addSimpleToken(.RIGHT_PAREN),
            '{' => try self.addSimpleToken(.LEFT_BRACE),
            '}' => try self.addSimpleToken(.RIGHT_BRACE),
            ',' => try self.addSimpleToken(.COMMA),
            '.' => try self.addSimpleToken(.DOT),
            '-' => try self.addSimpleToken(.MINUS),
            '+' => try self.addSimpleToken(.PLUS),
            ';' => try self.addSimpleToken(.SEMICOLON),
            '*' => try self.addSimpleToken(.STAR),
            else => {
                try main.doError(self.line, "Unexpected character");
            },
        }
    }

    pub fn scanTokens(self: *Scanner) !TokenList {
        // while we aren't at the end, we're still consuming
        // tokens.
        while (!self.isAtEnd()) {
            self.start = self.current;
            try self.scanToken();
        }

        try self.addToken(token.Token{
            .Simple = token.SimpleToken.init(
                .EOF,
                "",
                self.line,
                {},
            ),
        });

        return self.tokens;
    }
};