const std = @import("std");
const scanners = @import("scanner.zig");
const main = @import("main.zig");
const ast = @import("ast.zig");
const tokens = @import("tokens.zig");
const err = @import("errors.zig");

const Allocator = std.mem.Allocator;
const Scanner = scanners.Scanner;
const Token = tokens.Token;
const TokenType = tokens.TokenType;
const Result = main.Result;

const Expr = ast.Expr;

pub const Parser = struct {
    allocator: *Allocator,
    scanner: *Scanner,

    tokens: []Token = undefined,
    current: usize = 0,

    pub fn init(allocator: *Allocator, scanner: *Scanner) Parser {
        return Parser{ .allocator = allocator, .scanner = scanner };
    }

    fn doError(self: *Parser, comptime fmt: []const u8, args: ...) !void {
        std.debug.warn("parser error at line {}\n\t", self.scanner.line);
        std.debug.warn(fmt, args);
        std.debug.warn("\n");

        return Result.CompileError;
    }

    fn peek(self: *Parser) Token {
        return self.tokens[self.current];
    }

    fn previous(self: *Parser) Token {
        return self.tokens[self.current - 1];
    }

    fn tokenError(self: *Parser, token: Token, msg: []const u8) Result!void {
        if (token.ttype == .EOF) {
            err.report(token.line, " at end", msg);
        } else {
            err.reportFmt(token.line, " at '{}': {}", token.lexeme, msg);
        }

        return Result.CompileError;
    }

    fn synchronize(self: *Parser) void {
        _ = self.advance();
        while (!self.isAtEnd()) {
            if (self.previous().ttype == .Semicolon) return;

            switch (self.peek().ttype) {
                .Struct, .Fn, .For, .If, .Return => return,
                else => {},
            }

            _ = self.advance();
        }
    }

    fn isAtEnd(self: *Parser) bool {
        return self.peek().ttype == .EOF;
    }

    fn advance(self: *Parser) Token {
        if (!self.isAtEnd()) self.current += 1;
        return self.previous();
    }

    fn check(self: *Parser, ttype: TokenType) bool {
        if (self.isAtEnd()) return false;
        return self.peek().ttype == ttype;
    }

    fn match(self: *Parser, ttypes: []TokenType) bool {
        for (ttypes) |ttype| {
            if (self.check(ttype)) {
                _ = self.advance();
                return true;
            }
        }

        return false;
    }

    fn matchSingle(self: *Parser, ttype: TokenType) bool {
        if (self.check(ttype)) {
            _ = self.advance();
            return true;
        }

        return false;
    }

    fn consume(self: *Parser, ttype: TokenType, comptime msg: []const u8) Result!Token {
        if (self.check(ttype)) return self.advance();

        try self.tokenError(self.peek(), msg);
        return Result.CompileError;
    }

    fn equality(self: *Parser) !Expr {
        var expr = try self.comparison();

        while (self.match(&[_]TokenType{ TokenType.BangEqual, TokenType.EqualEqual })) {
            var operator = self.previous();
            var right = try self.comparison();

            expr = ast.mkBinary(&expr, operator, &right);
        }

        return expr;
    }

    fn comparison(self: *Parser) !Expr {
        var expr = try self.addition();

        while (self.match(&[_]TokenType{
            TokenType.Greater,
            TokenType.GreaterEqual,
            TokenType.Less,
            TokenType.LessEqual,
        })) {
            var operator = self.previous();
            var right = try self.addition();
            expr = ast.mkBinary(&expr, operator, &right);
        }

        return expr;
    }

    fn addition(self: *Parser) !Expr {
        var expr = try self.multiplication();

        while (self.match(&[_]TokenType{ TokenType.Minus, TokenType.Plus })) {
            var operator = self.previous();
            var right = try self.multiplication();
            expr = ast.mkBinary(&expr, operator, &right);
        }

        return expr;
    }

    fn multiplication(self: *Parser) anyerror!Expr {
        var expr = try self.unary();

        while (self.match(&[_]TokenType{ TokenType.Slash, TokenType.Star })) {
            var operator = self.previous();
            var right = try self.unary();
            expr = ast.mkBinary(&expr, operator, &right);
        }

        return expr;
    }

    fn unary(self: *Parser) anyerror!Expr {
        if (self.match(&[_]TokenType{ TokenType.Bang, TokenType.Minus })) {
            var operator = self.previous();
            var right = try self.unary();
            return ast.mkUnary(operator, &right);
        }

        return try self.primary();
    }

    fn doInt(self: *Parser) !Expr {
        var token = self.previous();

        // try to parse it as an i32 first, if that fails, do i64.

        var num_32 = std.fmt.parseInt(i32, token.lexeme, 10) catch |pi_err| {
            if (pi_err == error.Overflow) {
                var num_64 = std.fmt.parseInt(i64, token.lexeme, 10) catch |pi_err2| {
                    if (pi_err2 == error.Overflow) {
                        try self.tokenError(token, "Failed to parse number: overflow");
                        return Result.CompileError;
                    } else {
                        return pi_err2;
                    }
                };

                return ast.mkNum(i64, num_64);
            } else {
                return pi_err;
            }
        };

        return ast.mkNum(i32, num_32);
    }

    fn primary(self: *Parser) !Expr {
        if (self.matchSingle(TokenType.False)) return ast.Expr{ .Bool = false };
        if (self.matchSingle(TokenType.True)) return ast.Expr{ .Bool = true };
        if (self.matchSingle(TokenType.None)) return ast.Expr{ .Nil = {} };

        if (self.matchSingle(TokenType.Integer)) {
            return try self.doInt();
        }

        if (self.matchSingle(TokenType.String)) {
            var lexeme = self.previous().lexeme;
            var slice = try self.allocator.alloc(u8, lexeme.len);
            std.mem.copy(u8, slice, lexeme);

            return ast.Expr{ .String = slice };
        }

        if (self.matchSingle(TokenType.LeftParen)) {
            var expr = try self.expression();
            _ = try self.consume(.RightParen, "Expect ')' after expression");

            return ast.mkGrouping(&expr);
        }

        try self.tokenError(self.peek(), "Expect expression");
        return Result.CompileError;
    }

    fn expression(self: *Parser) !Expr {
        return try self.equality();
    }

    pub fn parse(self: *Parser) !?*Expr {
        self.tokens = try self.allocator.alloc(Token, 0);
        var i: usize = 0;

        while (true) {
            var tok_opt = try self.scanner.nextToken();
            if (tok_opt) |token| {
                self.tokens = try self.allocator.realloc(self.tokens, i + 1);
                self.tokens[i] = token;
                i += 1;

                if (token.ttype == .EOF) break;
            }
        }

        std.debug.warn("{} tokens\n", i);

        //return Expr{ .Number = ast.Number{ .Integer32 = 69 } };
        //return self.root;
        var expr = self.expression() catch |parse_err| {
            return null;
        };

        return &expr;
    }
};