const Tokenizer = @This();

const std = @import("std");
const Io = std.Io;
const testing = std.testing;
const assert = std.debug.assert;
const Allocator = std.mem.Allocator;

index: usize = 0,
bytes: []const u8,
state: State = .lhs,

pub fn next(self: *Tokenizer) ?Token {
    var start = self.index;
    var must_resolve = false;
    while (self.index < self.bytes.len) {
        const char = self.bytes[self.index];
        switch (self.state) {
            .lhs => switch (char) {
                '\t', '\n', '\r', ' ' => self.index += 1, // Ignore whitespace.
                else => {
                    start = self.index;
                    self.state = .target;
                },
            },
            .target => switch (char) {
                '\n', '\r' => {
                    return errorIllegalChar(.invalid_target, self.index, char);
                },
                '$' => {
                    self.state = .target_dollar_sign;
                    self.index += 1;
                },
                '\\' => {
                    self.state = .target_reverse_solidus;
                    self.index += 1;
                },
                ':' => {
                    self.state = .target_colon;
                    self.index += 1;
                },
                '\t', ' ' => {
                    self.state = .target_space;

                    const bytes = self.bytes[start..self.index];
                    std.debug.assert(bytes.len != 0);
                    self.index += 1;

                    return finishTarget(must_resolve, bytes);
                },
                else => {
                    self.index += 1;
                },
            },
            .target_reverse_solidus => switch (char) {
                '\t', '\n', '\r' => {
                    return errorIllegalChar(.bad_target_escape, self.index, char);
                },
                ' ', '#', '\\' => {
                    must_resolve = true;
                    self.state = .target;
                    self.index += 1;
                },
                '$' => {
                    self.state = .target_dollar_sign;
                    self.index += 1;
                },
                else => {
                    self.state = .target;
                    self.index += 1;
                },
            },
            .target_dollar_sign => switch (char) {
                '$' => {
                    must_resolve = true;
                    self.state = .target;
                    self.index += 1;
                },
                else => {
                    return errorIllegalChar(.expected_dollar, self.index, char);
                },
            },
            .target_colon => switch (char) {
                '\n', '\r' => {
                    const bytes = self.bytes[start .. self.index - 1];
                    if (bytes.len != 0) {
                        self.state = .lhs;
                        return finishTarget(must_resolve, bytes);
                    }
                    // silently ignore null target
                    self.state = .lhs;
                },
                '/', '\\' => {
                    self.state = .target_colon_reverse_solidus;
                    self.index += 1;
                },
                else => {
                    const bytes = self.bytes[start .. self.index - 1];
                    if (bytes.len != 0) {
                        self.state = .rhs;
                        return finishTarget(must_resolve, bytes);
                    }
                    // silently ignore null target
                    self.state = .lhs;
                },
            },
            .target_colon_reverse_solidus => switch (char) {
                '\n', '\r' => {
                    const bytes = self.bytes[start .. self.index - 2];
                    if (bytes.len != 0) {
                        self.state = .lhs;
                        return finishTarget(must_resolve, bytes);
                    }
                    // silently ignore null target
                    self.state = .lhs;
                },
                else => {
                    self.state = .target;
                },
            },
            .target_space => switch (char) {
                '\t', ' ' => {
                    // silently ignore additional horizontal whitespace
                    self.index += 1;
                },
                ':' => {
                    self.state = .rhs;
                    self.index += 1;
                },
                else => {
                    return errorIllegalChar(.expected_colon, self.index, char);
                },
            },
            .rhs => switch (char) {
                '\t', ' ' => {
                    // silently ignore horizontal whitespace
                    self.index += 1;
                },
                '\n', '\r' => {
                    self.state = .lhs;
                },
                '\\' => {
                    self.state = .rhs_continuation;
                    self.index += 1;
                },
                '"' => {
                    self.state = .prereq_quote;
                    self.index += 1;
                    start = self.index;
                },
                else => {
                    start = self.index;
                    self.state = .prereq;
                },
            },
            .rhs_continuation => switch (char) {
                '\n' => {
                    self.state = .rhs;
                    self.index += 1;
                },
                '\r' => {
                    self.state = .rhs_continuation_linefeed;
                    self.index += 1;
                },
                else => {
                    return errorIllegalChar(.continuation_eol, self.index, char);
                },
            },
            .rhs_continuation_linefeed => switch (char) {
                '\n' => {
                    self.state = .rhs;
                    self.index += 1;
                },
                else => {
                    return errorIllegalChar(.continuation_eol, self.index, char);
                },
            },
            .prereq_quote => switch (char) {
                '"' => {
                    self.index += 1;
                    self.state = .rhs;
                    return finishPrereq(must_resolve, self.bytes[start .. self.index - 1]);
                },
                else => {
                    self.index += 1;
                },
            },
            .prereq => switch (char) {
                '\t', ' ' => {
                    self.state = .rhs;
                    return finishPrereq(must_resolve, self.bytes[start..self.index]);
                },
                '\n', '\r' => {
                    self.state = .lhs;
                    return finishPrereq(must_resolve, self.bytes[start..self.index]);
                },
                '\\' => {
                    self.state = .prereq_continuation;
                    self.index += 1;
                },
                else => {
                    self.index += 1;
                },
            },
            .prereq_continuation => switch (char) {
                '\n' => {
                    self.index += 1;
                    self.state = .rhs;
                    return finishPrereq(must_resolve, self.bytes[start .. self.index - 2]);
                },
                '\r' => {
                    self.state = .prereq_continuation_linefeed;
                    self.index += 1;
                },
                '\\' => {
                    // The previous \ wasn't a continuation, but this one might be.
                    self.index += 1;
                },
                ' ' => {
                    // not continuation, but escaped space must be resolved
                    must_resolve = true;
                    self.state = .prereq;
                    self.index += 1;
                },
                else => {
                    // not continuation
                    self.state = .prereq;
                    self.index += 1;
                },
            },
            .prereq_continuation_linefeed => switch (char) {
                '\n' => {
                    self.index += 1;
                    self.state = .rhs;
                    return finishPrereq(must_resolve, self.bytes[start .. self.index - 3]);
                },
                else => {
                    return errorIllegalChar(.continuation_eol, self.index, char);
                },
            },
        }
    } else {
        switch (self.state) {
            .lhs,
            .rhs,
            .rhs_continuation,
            .rhs_continuation_linefeed,
            => return null,
            .target => {
                return errorPosition(.incomplete_target, start, self.bytes[start..]);
            },
            .target_reverse_solidus,
            .target_dollar_sign,
            => {
                const idx = self.index - 1;
                return errorIllegalChar(.incomplete_escape, idx, self.bytes[idx]);
            },
            .target_colon => {
                const bytes = self.bytes[start .. self.index - 1];
                if (bytes.len != 0) {
                    self.index += 1;
                    self.state = .rhs;
                    return finishTarget(must_resolve, bytes);
                }
                // silently ignore null target
                self.state = .lhs;
                return null;
            },
            .target_colon_reverse_solidus => {
                const bytes = self.bytes[start .. self.index - 2];
                if (bytes.len != 0) {
                    self.index += 1;
                    self.state = .rhs;
                    return finishTarget(must_resolve, bytes);
                }
                // silently ignore null target
                self.state = .lhs;
                return null;
            },
            .target_space => {
                const idx = self.index - 1;
                return errorIllegalChar(.expected_colon, idx, self.bytes[idx]);
            },
            .prereq_quote => {
                return errorPosition(.incomplete_quoted_prerequisite, start, self.bytes[start..]);
            },
            .prereq => {
                self.state = .lhs;
                return finishPrereq(must_resolve, self.bytes[start..]);
            },
            .prereq_continuation => {
                self.state = .lhs;
                return finishPrereq(must_resolve, self.bytes[start .. self.index - 1]);
            },
            .prereq_continuation_linefeed => {
                self.state = .lhs;
                return finishPrereq(must_resolve, self.bytes[start .. self.index - 2]);
            },
        }
    }
    unreachable;
}

fn errorPosition(comptime id: std.meta.Tag(Token), index: usize, bytes: []const u8) Token {
    return @unionInit(Token, @tagName(id), .{ .index = index, .bytes = bytes });
}

fn errorIllegalChar(comptime id: std.meta.Tag(Token), index: usize, char: u8) Token {
    return @unionInit(Token, @tagName(id), .{ .index = index, .char = char });
}

fn finishTarget(must_resolve: bool, bytes: []const u8) Token {
    return if (must_resolve) .{ .target_must_resolve = bytes } else .{ .target = bytes };
}

fn finishPrereq(must_resolve: bool, bytes: []const u8) Token {
    return if (must_resolve) .{ .prereq_must_resolve = bytes } else .{ .prereq = bytes };
}

const State = enum {
    lhs,
    target,
    target_reverse_solidus,
    target_dollar_sign,
    target_colon,
    target_colon_reverse_solidus,
    target_space,
    rhs,
    rhs_continuation,
    rhs_continuation_linefeed,
    prereq_quote,
    prereq,
    prereq_continuation,
    prereq_continuation_linefeed,
};

pub const Token = union(enum) {
    target: []const u8,
    target_must_resolve: []const u8,
    prereq: []const u8,
    prereq_must_resolve: []const u8,

    incomplete_quoted_prerequisite: IndexAndBytes,
    incomplete_target: IndexAndBytes,

    invalid_target: IndexAndChar,
    bad_target_escape: IndexAndChar,
    expected_dollar: IndexAndChar,
    continuation_eol: IndexAndChar,
    incomplete_escape: IndexAndChar,
    expected_colon: IndexAndChar,

    pub const IndexAndChar = struct {
        index: usize,
        char: u8,
    };

    pub const IndexAndBytes = struct {
        index: usize,
        bytes: []const u8,
    };

    /// Resolve escapes in target or prereq. Only valid with .target_must_resolve or .prereq_must_resolve.
    pub fn resolve(self: Token, gpa: Allocator, list: *std.ArrayList(u8)) error{OutOfMemory}!void {
        switch (self) {
            .target_must_resolve => |bytes| {
                var state: enum { start, escape, dollar } = .start;
                for (bytes) |c| {
                    switch (state) {
                        .start => {
                            switch (c) {
                                '\\' => state = .escape,
                                '$' => state = .dollar,
                                else => try list.append(gpa, c),
                            }
                        },
                        .escape => {
                            switch (c) {
                                ' ', '#', '\\' => {},
                                '$' => {
                                    try list.append(gpa, '\\');
                                    state = .dollar;
                                    continue;
                                },
                                else => try list.append(gpa, '\\'),
                            }
                            try list.append(gpa, c);
                            state = .start;
                        },
                        .dollar => {
                            try list.append(gpa, '$');
                            switch (c) {
                                '$' => {},
                                else => try list.append(gpa, c),
                            }
                            state = .start;
                        },
                    }
                }
            },
            .prereq_must_resolve => |bytes| {
                var state: enum { start, escape } = .start;
                for (bytes) |c| {
                    switch (state) {
                        .start => {
                            switch (c) {
                                '\\' => state = .escape,
                                else => try list.append(gpa, c),
                            }
                        },
                        .escape => {
                            switch (c) {
                                ' ' => {},
                                '\\' => {
                                    try list.append(gpa, c);
                                    continue;
                                },
                                else => try list.append(gpa, '\\'),
                            }
                            try list.append(gpa, c);
                            state = .start;
                        },
                    }
                }
            },
            else => unreachable,
        }
    }

    pub fn format(token: Token, w: *Io.Writer) Io.Writer.Error!void {
        switch (token) {
            .target, .target_must_resolve, .prereq, .prereq_must_resolve => return w.writeAll(@tagName(token)),
            .incomplete_quoted_prerequisite, .incomplete_target => |info| return w.print("{t} {q} at position {d}", .{
                token, info.bytes, info.index,
            }),
            .invalid_target,
            .bad_target_escape,
            .expected_dollar,
            .continuation_eol,
            .incomplete_escape,
            .expected_colon,
            => |info| return w.print("illegal char '{f}' at position {d}: {t}", .{
                std.zig.fmtChar(info.char), info.index, token,
            }),
        }
    }
};

test "empty file" {
    try depTokenizer("", "");
}

test "empty whitespace" {
    try depTokenizer("\n", "");
    try depTokenizer("\r", "");
    try depTokenizer("\r\n", "");
    try depTokenizer(" ", "");
}

test "empty colon" {
    try depTokenizer(":", "");
    try depTokenizer("\n:", "");
    try depTokenizer("\r:", "");
    try depTokenizer("\r\n:", "");
    try depTokenizer(" :", "");
}

test "empty target" {
    try depTokenizer("foo.o:", "target = {\"foo.o\"}");
    try depTokenizer(
        \\foo.o:
        \\bar.o:
        \\abcd.o:
    ,
        \\target = {"foo.o"}
        \\target = {"bar.o"}
        \\target = {"abcd.o"}
    );
}

test "whitespace empty target" {
    try depTokenizer("\nfoo.o:", "target = {\"foo.o\"}");
    try depTokenizer("\rfoo.o:", "target = {\"foo.o\"}");
    try depTokenizer("\r\nfoo.o:", "target = {\"foo.o\"}");
    try depTokenizer(" foo.o:", "target = {\"foo.o\"}");
}

test "escape empty target" {
    try depTokenizer("\\ foo.o:", "target = {\" foo.o\"}");
    try depTokenizer("\\#foo.o:", "target = {\"#foo.o\"}");
    try depTokenizer("\\\\foo.o:", "target = {\"\\\\foo.o\"}");
    try depTokenizer("$$foo.o:", "target = {\"$foo.o\"}");
}

test "empty target linefeeds" {
    try depTokenizer("\n", "");
    try depTokenizer("\r\n", "");

    const expect = "target = {\"foo.o\"}";
    try depTokenizer(
        \\foo.o:
    , expect);
    try depTokenizer(
        \\foo.o:
        \\
    , expect);
    try depTokenizer(
        \\foo.o:
    , expect);
    try depTokenizer(
        \\foo.o:
        \\
    , expect);
}

test "empty target linefeeds + continuations" {
    const expect = "target = {\"foo.o\"}";
    try depTokenizer(
        \\foo.o:\
    , expect);
    try depTokenizer(
        \\foo.o:\
        \\
    , expect);
    try depTokenizer(
        \\foo.o:\
    , expect);
    try depTokenizer(
        \\foo.o:\
        \\
    , expect);
}

test "empty target linefeeds + hspace + continuations" {
    const expect = "target = {\"foo.o\"}";
    try depTokenizer(
        \\foo.o: \
    , expect);
    try depTokenizer(
        \\foo.o: \
        \\
    , expect);
    try depTokenizer(
        \\foo.o: \
    , expect);
    try depTokenizer(
        \\foo.o: \
        \\
    , expect);
}

test "empty target + hspace + colon" {
    const expect = "target = {\"foo.o\"}";

    try depTokenizer("foo.o :", expect);
    try depTokenizer("foo.o\t\t\t:", expect);
    try depTokenizer("foo.o \t \t :", expect);
    try depTokenizer("\r\nfoo.o :", expect);
    try depTokenizer(" foo.o :", expect);
}

test "prereq" {
    const expect =
        \\target = {"foo.o"}
        \\prereq = {"foo.c"}
    ;
    try depTokenizer("foo.o: foo.c", expect);
    try depTokenizer(
        \\foo.o: \
        \\foo.c
    , expect);
    try depTokenizer(
        \\foo.o: \
        \\ foo.c
    , expect);
    try depTokenizer(
        \\foo.o:    \
        \\    foo.c
    , expect);
}

test "prereq continuation" {
    const expect =
        \\target = {"foo.o"}
        \\prereq = {"foo.h"}
        \\prereq = {"bar.h"}
    ;
    try depTokenizer(
        \\foo.o: foo.h\
        \\bar.h
    , expect);
    try depTokenizer(
        \\foo.o: foo.h\
        \\bar.h
    , expect);
}

test "prereq continuation (CRLF)" {
    const expect =
        \\target = {"foo.o"}
        \\prereq = {"foo.h"}
        \\prereq = {"bar.h"}
    ;
    try depTokenizer("foo.o: foo.h\\\r\nbar.h", expect);
}

test "multiple prereqs" {
    const expect =
        \\target = {"foo.o"}
        \\prereq = {"foo.c"}
        \\prereq = {"foo.h"}
        \\prereq = {"bar.h"}
    ;
    try depTokenizer("foo.o: foo.c foo.h bar.h", expect);
    try depTokenizer(
        \\foo.o: \
        \\foo.c foo.h bar.h
    , expect);
    try depTokenizer(
        \\foo.o: foo.c foo.h bar.h\
    , expect);
    try depTokenizer(
        \\foo.o: foo.c foo.h bar.h\
        \\
    , expect);
    try depTokenizer(
        \\foo.o: \
        \\foo.c       \
        \\     foo.h\
        \\bar.h
        \\
    , expect);
    try depTokenizer(
        \\foo.o: \
        \\foo.c       \
        \\     foo.h\
        \\bar.h\
        \\
    , expect);
    try depTokenizer(
        \\foo.o: \
        \\foo.c       \
        \\     foo.h\
        \\bar.h\
    , expect);
}

test "multiple targets and prereqs" {
    try depTokenizer(
        \\foo.o: foo.c
        \\bar.o: bar.c a.h b.h c.h
        \\abc.o: abc.c \
        \\  one.h two.h \
        \\  three.h four.h
    ,
        \\target = {"foo.o"}
        \\prereq = {"foo.c"}
        \\target = {"bar.o"}
        \\prereq = {"bar.c"}
        \\prereq = {"a.h"}
        \\prereq = {"b.h"}
        \\prereq = {"c.h"}
        \\target = {"abc.o"}
        \\prereq = {"abc.c"}
        \\prereq = {"one.h"}
        \\prereq = {"two.h"}
        \\prereq = {"three.h"}
        \\prereq = {"four.h"}
    );
    try depTokenizer(
        \\ascii.o: ascii.c
        \\base64.o: base64.c stdio.h
        \\elf.o: elf.c a.h b.h c.h
        \\macho.o: \
        \\  macho.c\
        \\  a.h b.h c.h
    ,
        \\target = {"ascii.o"}
        \\prereq = {"ascii.c"}
        \\target = {"base64.o"}
        \\prereq = {"base64.c"}
        \\prereq = {"stdio.h"}
        \\target = {"elf.o"}
        \\prereq = {"elf.c"}
        \\prereq = {"a.h"}
        \\prereq = {"b.h"}
        \\prereq = {"c.h"}
        \\target = {"macho.o"}
        \\prereq = {"macho.c"}
        \\prereq = {"a.h"}
        \\prereq = {"b.h"}
        \\prereq = {"c.h"}
    );
    try depTokenizer(
        \\a$$scii.o: ascii.c
        \\\\base64.o: "\base64.c" "s t#dio.h"
        \\e\\lf.o: "e\lf.c" "a.h$$" "$$b.h c.h$$"
        \\macho.o: \
        \\  "macho!.c" \
        \\  a.h b.h c.h
    ,
        \\target = {"a$scii.o"}
        \\prereq = {"ascii.c"}
        \\target = {"\\base64.o"}
        \\prereq = {"\\base64.c"}
        \\prereq = {"s t#dio.h"}
        \\target = {"e\\lf.o"}
        \\prereq = {"e\\lf.c"}
        \\prereq = {"a.h$$"}
        \\prereq = {"$$b.h c.h$$"}
        \\target = {"macho.o"}
        \\prereq = {"macho!.c"}
        \\prereq = {"a.h"}
        \\prereq = {"b.h"}
        \\prereq = {"c.h"}
    );
}

test "windows quoted prereqs" {
    try depTokenizer(
        \\c:\foo.o: "C:\Program Files (x86)\Microsoft Visual Studio\foo.c"
        \\c:\foo2.o: "C:\Program Files (x86)\Microsoft Visual Studio\foo2.c" \
        \\  "C:\Program Files (x86)\Microsoft Visual Studio\foo1.h" \
        \\  "C:\Program Files (x86)\Microsoft Visual Studio\foo2.h"
    ,
        \\target = {"c:\\foo.o"}
        \\prereq = {"C:\\Program Files (x86)\\Microsoft Visual Studio\\foo.c"}
        \\target = {"c:\\foo2.o"}
        \\prereq = {"C:\\Program Files (x86)\\Microsoft Visual Studio\\foo2.c"}
        \\prereq = {"C:\\Program Files (x86)\\Microsoft Visual Studio\\foo1.h"}
        \\prereq = {"C:\\Program Files (x86)\\Microsoft Visual Studio\\foo2.h"}
    );
}

test "windows mixed prereqs" {
    try depTokenizer(
        \\cimport.o: \
        \\  C:\msys64\home\anon\project\zig\master\zig-cache\o\qhvhbUo7GU5iKyQ5mpA8TcQpncCYaQu0wwvr3ybiSTj_Dtqi1Nmcb70kfODJ2Qlg\cimport.h \
        \\  "C:\Program Files (x86)\Windows Kits\10\\Include\10.0.17763.0\ucrt\stdio.h" \
        \\  "C:\Program Files (x86)\Windows Kits\10\\Include\10.0.17763.0\ucrt\corecrt.h" \
        \\  "C:\Program Files (x86)\Microsoft Visual Studio\2019\BuildTools\VC\Tools\MSVC\14.21.27702\lib\x64\\..\..\include\vcruntime.h" \
        \\  "C:\Program Files (x86)\Microsoft Visual Studio\2019\BuildTools\VC\Tools\MSVC\14.21.27702\lib\x64\\..\..\include\sal.h" \
        \\  "C:\Program Files (x86)\Microsoft Visual Studio\2019\BuildTools\VC\Tools\MSVC\14.21.27702\lib\x64\\..\..\include\concurrencysal.h" \
        \\  C:\msys64\opt\zig\lib\zig\include\vadefs.h \
        \\  "C:\Program Files (x86)\Microsoft Visual Studio\2019\BuildTools\VC\Tools\MSVC\14.21.27702\lib\x64\\..\..\include\vadefs.h" \
        \\  "C:\Program Files (x86)\Windows Kits\10\\Include\10.0.17763.0\ucrt\corecrt_wstdio.h" \
        \\  "C:\Program Files (x86)\Windows Kits\10\\Include\10.0.17763.0\ucrt\corecrt_stdio_config.h" \
        \\  "C:\Program Files (x86)\Windows Kits\10\\Include\10.0.17763.0\ucrt\string.h" \
        \\  "C:\Program Files (x86)\Windows Kits\10\\Include\10.0.17763.0\ucrt\corecrt_memory.h" \
        \\  "C:\Program Files (x86)\Windows Kits\10\\Include\10.0.17763.0\ucrt\corecrt_memcpy_s.h" \
        \\  "C:\Program Files (x86)\Windows Kits\10\\Include\10.0.17763.0\ucrt\errno.h" \
        \\  "C:\Program Files (x86)\Microsoft Visual Studio\2019\BuildTools\VC\Tools\MSVC\14.21.27702\lib\x64\\..\..\include\vcruntime_string.h" \
        \\  "C:\Program Files (x86)\Windows Kits\10\\Include\10.0.17763.0\ucrt\corecrt_wstring.h"
    ,
        \\target = {"cimport.o"}
        \\prereq = {"C:\\msys64\\home\\anon\\project\\zig\\master\\zig-cache\\o\\qhvhbUo7GU5iKyQ5mpA8TcQpncCYaQu0wwvr3ybiSTj_Dtqi1Nmcb70kfODJ2Qlg\\cimport.h"}
        \\prereq = {"C:\\Program Files (x86)\\Windows Kits\\10\\\\Include\\10.0.17763.0\\ucrt\\stdio.h"}
        \\prereq = {"C:\\Program Files (x86)\\Windows Kits\\10\\\\Include\\10.0.17763.0\\ucrt\\corecrt.h"}
        \\prereq = {"C:\\Program Files (x86)\\Microsoft Visual Studio\\2019\\BuildTools\\VC\\Tools\\MSVC\\14.21.27702\\lib\\x64\\\\..\\..\\include\\vcruntime.h"}
        \\prereq = {"C:\\Program Files (x86)\\Microsoft Visual Studio\\2019\\BuildTools\\VC\\Tools\\MSVC\\14.21.27702\\lib\\x64\\\\..\\..\\include\\sal.h"}
        \\prereq = {"C:\\Program Files (x86)\\Microsoft Visual Studio\\2019\\BuildTools\\VC\\Tools\\MSVC\\14.21.27702\\lib\\x64\\\\..\\..\\include\\concurrencysal.h"}
        \\prereq = {"C:\\msys64\\opt\\zig\\lib\\zig\\include\\vadefs.h"}
        \\prereq = {"C:\\Program Files (x86)\\Microsoft Visual Studio\\2019\\BuildTools\\VC\\Tools\\MSVC\\14.21.27702\\lib\\x64\\\\..\\..\\include\\vadefs.h"}
        \\prereq = {"C:\\Program Files (x86)\\Windows Kits\\10\\\\Include\\10.0.17763.0\\ucrt\\corecrt_wstdio.h"}
        \\prereq = {"C:\\Program Files (x86)\\Windows Kits\\10\\\\Include\\10.0.17763.0\\ucrt\\corecrt_stdio_config.h"}
        \\prereq = {"C:\\Program Files (x86)\\Windows Kits\\10\\\\Include\\10.0.17763.0\\ucrt\\string.h"}
        \\prereq = {"C:\\Program Files (x86)\\Windows Kits\\10\\\\Include\\10.0.17763.0\\ucrt\\corecrt_memory.h"}
        \\prereq = {"C:\\Program Files (x86)\\Windows Kits\\10\\\\Include\\10.0.17763.0\\ucrt\\corecrt_memcpy_s.h"}
        \\prereq = {"C:\\Program Files (x86)\\Windows Kits\\10\\\\Include\\10.0.17763.0\\ucrt\\errno.h"}
        \\prereq = {"C:\\Program Files (x86)\\Microsoft Visual Studio\\2019\\BuildTools\\VC\\Tools\\MSVC\\14.21.27702\\lib\\x64\\\\..\\..\\include\\vcruntime_string.h"}
        \\prereq = {"C:\\Program Files (x86)\\Windows Kits\\10\\\\Include\\10.0.17763.0\\ucrt\\corecrt_wstring.h"}
    );
}

test "windows funky targets" {
    try depTokenizer(
        \\C:\Users\anon\foo.o:
        \\C:\Users\anon\foo\ .o:
        \\C:\Users\anon\foo\#.o:
        \\C:\Users\anon\foo$$.o:
        \\C:\Users\anon\\\ foo.o:
        \\C:\Users\anon\\#foo.o:
        \\C:\Users\anon\$$foo.o:
        \\C:\Users\anon\\\ \ \ \ \ foo.o:
    ,
        \\target = {"C:\\Users\\anon\\foo.o"}
        \\target = {"C:\\Users\\anon\\foo .o"}
        \\target = {"C:\\Users\\anon\\foo#.o"}
        \\target = {"C:\\Users\\anon\\foo$.o"}
        \\target = {"C:\\Users\\anon\\ foo.o"}
        \\target = {"C:\\Users\\anon\\#foo.o"}
        \\target = {"C:\\Users\\anon\\$foo.o"}
        \\target = {"C:\\Users\\anon\\     foo.o"}
    );
}

test "windows funky prereqs" {
    // Note we don't support unquoted escaped spaces at the very beginning of a relative path
    // e.g. `\ SpaceAtTheBeginning.c`
    // This typically wouldn't be seen in the wild, since depfiles usually use absolute paths
    // and supporting it would degrade error messages for cases where it was meant to be a
    // continuation, but the line ending is missing.
    try depTokenizer(
        \\cimport.o: \
        \\  trailingbackslash\\
        \\  C:\Users\John\ Smith\AppData\Local\zig\p\1220d14057af1a9d6dde4643293527bd5ee5099517d655251a066666a4320737ea7c\cimport.c \
        \\  somedir\\ a.c\
        \\  somedir/\ a.c\
        \\  somedir\\ \ \ b.c\
        \\  somedir\\ \\ \c.c\
        \\
    ,
        \\target = {"cimport.o"}
        \\prereq = {"trailingbackslash\\"}
        \\prereq = {"C:\\Users\\John Smith\\AppData\\Local\\zig\\p\\1220d14057af1a9d6dde4643293527bd5ee5099517d655251a066666a4320737ea7c\\cimport.c"}
        \\prereq = {"somedir\\ a.c"}
        \\prereq = {"somedir/ a.c"}
        \\prereq = {"somedir\\   b.c"}
        \\prereq = {"somedir\\ \\ \\c.c"}
    );
}

test "windows drive and forward slashes" {
    try depTokenizer(
        \\C:/msys64/what/zig-cache\tmp\48ac4d78dd531abd-cxa_thread_atexit.obj: \
        \\  C:/msys64/opt/zig3/lib/zig/libc/mingw/crt/cxa_thread_atexit.c
    ,
        \\target = {"C:/msys64/what/zig-cache\\tmp\\48ac4d78dd531abd-cxa_thread_atexit.obj"}
        \\prereq = {"C:/msys64/opt/zig3/lib/zig/libc/mingw/crt/cxa_thread_atexit.c"}
    );
}

test "error incomplete escape - reverse_solidus" {
    try depTokenizer("\\",
        \\ERROR: illegal char '\\' at position 0: incomplete_escape
    );
    try depTokenizer("\t\\",
        \\ERROR: illegal char '\\' at position 1: incomplete_escape
    );
    try depTokenizer("\n\\",
        \\ERROR: illegal char '\\' at position 1: incomplete_escape
    );
    try depTokenizer("\r\\",
        \\ERROR: illegal char '\\' at position 1: incomplete_escape
    );
    try depTokenizer("\r\n\\",
        \\ERROR: illegal char '\\' at position 2: incomplete_escape
    );
    try depTokenizer(" \\",
        \\ERROR: illegal char '\\' at position 1: incomplete_escape
    );
}

test "error incomplete escape - dollar_sign" {
    try depTokenizer("$",
        \\ERROR: illegal char '$' at position 0: incomplete_escape
    );
    try depTokenizer("\t$",
        \\ERROR: illegal char '$' at position 1: incomplete_escape
    );
    try depTokenizer("\n$",
        \\ERROR: illegal char '$' at position 1: incomplete_escape
    );
    try depTokenizer("\r$",
        \\ERROR: illegal char '$' at position 1: incomplete_escape
    );
    try depTokenizer("\r\n$",
        \\ERROR: illegal char '$' at position 2: incomplete_escape
    );
    try depTokenizer(" $",
        \\ERROR: illegal char '$' at position 1: incomplete_escape
    );
}

test "error incomplete target" {
    try depTokenizer("foo.o",
        \\ERROR: incomplete_target "foo.o" at position 0
    );
    try depTokenizer("\tfoo.o",
        \\ERROR: incomplete_target "foo.o" at position 1
    );
    try depTokenizer("\nfoo.o",
        \\ERROR: incomplete_target "foo.o" at position 1
    );
    try depTokenizer("\rfoo.o",
        \\ERROR: incomplete_target "foo.o" at position 1
    );
    try depTokenizer("\r\nfoo.o",
        \\ERROR: incomplete_target "foo.o" at position 2
    );
    try depTokenizer(" foo.o",
        \\ERROR: incomplete_target "foo.o" at position 1
    );

    try depTokenizer("\\ foo.o",
        \\ERROR: incomplete_target "\\ foo.o" at position 0
    );
    try depTokenizer("\\#foo.o",
        \\ERROR: incomplete_target "\\#foo.o" at position 0
    );
    try depTokenizer("\\\\foo.o",
        \\ERROR: incomplete_target "\\\\foo.o" at position 0
    );
    try depTokenizer("$$foo.o",
        \\ERROR: incomplete_target "$$foo.o" at position 0
    );
}

test "error illegal char at position - bad target escape" {
    try depTokenizer("\\\t",
        \\ERROR: illegal char '\t' at position 1: bad_target_escape
    );
    try depTokenizer("\\\n",
        \\ERROR: illegal char '\n' at position 1: bad_target_escape
    );
    try depTokenizer("\\\r",
        \\ERROR: illegal char '\r' at position 1: bad_target_escape
    );
    try depTokenizer("\\\r\n",
        \\ERROR: illegal char '\r' at position 1: bad_target_escape
    );
}

test "error illegal char at position - expecting dollar_sign" {
    try depTokenizer("$\t",
        \\ERROR: illegal char '\t' at position 1: expected_dollar
    );
    try depTokenizer("$\n",
        \\ERROR: illegal char '\n' at position 1: expected_dollar
    );
    try depTokenizer("$\r",
        \\ERROR: illegal char '\r' at position 1: expected_dollar
    );
    try depTokenizer("$\r\n",
        \\ERROR: illegal char '\r' at position 1: expected_dollar
    );
}

test "error illegal char at position - invalid target" {
    try depTokenizer("foo\n.o",
        \\ERROR: illegal char '\n' at position 3: invalid_target
    );
    try depTokenizer("foo\r.o",
        \\ERROR: illegal char '\r' at position 3: invalid_target
    );
    try depTokenizer("foo\r\n.o",
        \\ERROR: illegal char '\r' at position 3: invalid_target
    );
}

test "error target - continuation expecting end-of-line" {
    try depTokenizer("foo.o: \\\t",
        \\target = {"foo.o"}
        \\ERROR: illegal char '\t' at position 8: continuation_eol
    );
    try depTokenizer("foo.o: \\ ",
        \\target = {"foo.o"}
        \\ERROR: illegal char ' ' at position 8: continuation_eol
    );
    try depTokenizer("foo.o: \\x",
        \\target = {"foo.o"}
        \\ERROR: illegal char 'x' at position 8: continuation_eol
    );
    try depTokenizer("foo.o: \\\x0dx",
        \\target = {"foo.o"}
        \\ERROR: illegal char 'x' at position 9: continuation_eol
    );
}

test "error prereq - continuation expecting end-of-line" {
    try depTokenizer("foo.o: foo.h\\\x0dx",
        \\target = {"foo.o"}
        \\ERROR: illegal char 'x' at position 14: continuation_eol
    );
}

test "error illegal char at position - expecting colon" {
    try depTokenizer("foo\t.o:",
        \\target = {"foo"}
        \\ERROR: illegal char '.' at position 4: expected_colon
    );
    try depTokenizer("foo .o:",
        \\target = {"foo"}
        \\ERROR: illegal char '.' at position 4: expected_colon
    );
    try depTokenizer("foo \n.o:",
        \\target = {"foo"}
        \\ERROR: illegal char '\n' at position 4: expected_colon
    );
    try depTokenizer("foo.o\t\n:",
        \\target = {"foo.o"}
        \\ERROR: illegal char '\n' at position 6: expected_colon
    );
}

// - tokenize input, emit textual representation, and compare to expect
fn depTokenizer(input: []const u8, expect: []const u8) !void {
    var arena_allocator = std.heap.ArenaAllocator.init(std.testing.allocator);
    const arena = arena_allocator.allocator();
    defer arena_allocator.deinit();

    var it: Tokenizer = .{ .bytes = input };
    var buffer: std.ArrayList(u8) = .empty;
    var aux: std.ArrayList(u8) = .empty;
    var i: usize = 0;
    while (it.next()) |token| {
        if (i != 0) try buffer.appendSlice(arena, "\n");
        switch (token) {
            .target, .prereq => |bytes| {
                try buffer.print(arena, "{t} = {{{q}}}", .{ token, bytes });
            },
            .target_must_resolve => {
                try buffer.appendSlice(arena, "target = {");
                aux.clearRetainingCapacity();
                try token.resolve(arena, &aux);
                try buffer.print(arena, "{q}", .{aux.items});
                try buffer.appendSlice(arena, "}");
            },
            .prereq_must_resolve => {
                try buffer.appendSlice(arena, "prereq = {");
                aux.clearRetainingCapacity();
                try token.resolve(arena, &aux);
                try buffer.print(arena, "{q}", .{aux.items});
                try buffer.appendSlice(arena, "}");
            },
            else => {
                try buffer.print(arena, "ERROR: {f}", .{token});
                break;
            },
        }
        i += 1;
    }

    try testing.expectEqualStrings(expect, buffer.items);
}