const std = @import("std");
const Io = std.Io;
const Dir = std.Io.Dir;
const File = std.Io.File;
const process = std.process;

const Version = struct {
    major: u32,
    minor: u32,
    patch: u32,

    fn parse(str: []const u8) ?Version {
        const trimmed = std.mem.trim(u8, str, " \t\n\r\"");
        var parts = std.mem.splitScalar(u8, trimmed, '.');
        const major = std.fmt.parseInt(u32, parts.next() orelse return null, 10) catch return null;
        const minor = std.fmt.parseInt(u32, parts.next() orelse return null, 10) catch return null;
        const patch = std.fmt.parseInt(u32, parts.next() orelse "0", 10) catch return null;
        return Version{ .major = major, .minor = minor, .patch = patch };
    }

    fn isOlderThan(self: Version, other: Version) bool {
        if (self.major != other.major) return self.major < other.major;
        if (self.minor != other.minor) return self.minor < other.minor;
        return self.patch < other.patch;
    }

    fn format(self: Version, allocator: std.mem.Allocator) ![]u8 {
        return std.fmt.allocPrint(allocator, "{d}.{d}.{d}", .{ self.major, self.minor, self.patch });
    }
};

const Stats = struct {
    scanned: u32 = 0,
    updated: u32 = 0,
    errors: u32 = 0,
    skipped: u32 = 0,
};

pub fn main(init: process.Init) !void {
    const allocator = init.gpa;
    const io = init.io;

    // Get stdout/stderr writers
    var stdout_buf: [4096]u8 = undefined;
    var stderr_buf: [4096]u8 = undefined;
    var stdout_writer = File.Writer.initStreaming(.stdout(), io, &stdout_buf);
    var stderr_writer = File.Writer.initStreaming(.stderr(), io, &stderr_buf);
    const stdout = &stdout_writer.interface;
    const stderr = &stderr_writer.interface;

    // Parse CLI arguments
    var args_iter = try process.Args.Iterator.initAllocator(init.minimal.args, allocator);
    defer args_iter.deinit();
    _ = args_iter.skip(); // skip program name

    var dry_run = false;
    while (args_iter.next()) |arg| {
        if (std.mem.eql(u8, arg, "--dry-run")) {
            dry_run = true;
        } else if (std.mem.eql(u8, arg, "--help") or std.mem.eql(u8, arg, "-h")) {
            try stdout.print("Usage: rust-version-updater [--dry-run]\n\n", .{});
            try stdout.print("Recursively updates rust-version in Cargo.toml files to match current rustc.\n\n", .{});
            try stdout.print("Options:\n", .{});
            try stdout.print("  --dry-run  Preview changes without modifying files\n", .{});
            try stdout.print("  --help     Show this help message\n", .{});
            try stdout_writer.flush();
            return;
        }
    }

    // Check for rust-toolchain.toml
    try checkRustToolchain(allocator, io, stdout, &stdout_writer, dry_run);

    // Get current Rust version
    const current_version = getCurrentRustVersion(allocator, io) catch |err| {
        try stderr.print("Error: Failed to get Rust version: {}\n", .{err});
        try stderr_writer.flush();
        std.process.exit(1);
    };
    defer allocator.free(current_version.str);

    try stdout.print("Current Rust version: {d}.{d}.{d}\n", .{ current_version.version.major, current_version.version.minor, current_version.version.patch });
    if (dry_run) {
        try stdout.print("Dry-run mode: no files will be modified\n", .{});
    }
    try stdout.print("\n", .{});

    // Walk directory tree
    var stats = Stats{};
    const cwd = Dir.cwd();

    // Open directory with iterate capability
    const iterable_dir = Dir.openDir(cwd, io, ".", .{ .iterate = true }) catch |err| {
        try stderr.print("Error: Failed to open current directory: {}\n", .{err});
        try stderr_writer.flush();
        std.process.exit(1);
    };
    defer iterable_dir.close(io);

    var walker = Dir.walk(iterable_dir, allocator) catch |err| {
        try stderr.print("Error: Failed to create directory walker: {}\n", .{err});
        try stderr_writer.flush();
        std.process.exit(1);
    };
    defer walker.deinit();

    while (true) {
        const entry = walker.next(io) catch |err| {
            try stderr.print("Warning: Error during directory walk: {}\n", .{err});
            stats.errors += 1;
            continue;
        };
        if (entry == null) break;
        const e = entry.?;

        if (e.kind != .file) continue;
        if (!std.mem.eql(u8, e.basename, "Cargo.toml")) continue;

        stats.scanned += 1;
        processCargoToml(allocator, io, e.path, current_version.version, dry_run, &stats, stdout, stderr) catch |err| {
            try stderr.print("Error processing {s}: {}\n", .{ e.path, err });
            stats.errors += 1;
        };
    }

    // Print summary
    try stdout.print("\n--- Summary ---\n", .{});
    try stdout.print("Files scanned: {d}\n", .{stats.scanned});
    try stdout.print("Files updated: {d}\n", .{stats.updated});
    try stdout.print("Files skipped: {d}\n", .{stats.skipped});
    try stdout.print("Errors: {d}\n", .{stats.errors});
    try stdout_writer.flush();
}

fn checkRustToolchain(
    allocator: std.mem.Allocator,
    io: Io,
    stdout: *Io.Writer,
    stdout_writer: *File.Writer,
    dry_run: bool,
) !void {
    const cwd = Dir.cwd();

    // Try to read the file contents
    const content = blk: {
        const file = Dir.openFile(cwd, io, "rust-toolchain.toml", .{}) catch return;
        defer file.close(io);

        var read_buf: [4096]u8 = undefined;
        var reader = File.Reader.init(file, io, &read_buf);
        break :blk try reader.interface.allocRemaining(allocator, .limited(1024 * 1024));
    };
    defer allocator.free(content);

    try stdout.print("Found rust-toolchain.toml:\n---\n{s}---\n\n", .{content});

    if (dry_run) {
        try stdout.print("Dry-run mode: skipping rust-toolchain.toml deletion prompt\n\n", .{});
        try stdout_writer.flush();
        return;
    }

    try stdout.print("Delete rust-toolchain.toml? [y/N] ", .{});
    try stdout_writer.flush();

    // Read response from stdin
    var stdin_buf: [256]u8 = undefined;
    var stdin_reader = File.Reader.init(.stdin(), io, &stdin_buf);
    const byte = stdin_reader.interface.takeByte() catch return;

    if (byte == 'y' or byte == 'Y') {
        Dir.deleteFile(cwd, io, "rust-toolchain.toml") catch |err| {
            try stdout.print("Warning: Failed to delete rust-toolchain.toml: {}\n", .{err});
            try stdout_writer.flush();
            return;
        };
        try stdout.print("Deleted rust-toolchain.toml\n\n", .{});
    } else {
        try stdout.print("Keeping rust-toolchain.toml, exiting.\n", .{});
        try stdout_writer.flush();
        std.process.exit(0);
    }
    try stdout_writer.flush();
}

const VersionResult = struct {
    version: Version,
    str: []u8,
};

fn getCurrentRustVersion(allocator: std.mem.Allocator, io: Io) !VersionResult {
    const result = try process.run(allocator, io, .{
        .argv = &.{ "rustc", "--version" },
    });
    defer allocator.free(result.stdout);
    defer allocator.free(result.stderr);

    if (result.term != .exited or result.term.exited != 0) {
        return error.RustcFailed;
    }

    // Parse "rustc X.Y.Z (...)" format
    const trimmed = std.mem.trim(u8, result.stdout, " \t\n\r");
    if (!std.mem.startsWith(u8, trimmed, "rustc ")) {
        return error.InvalidRustcOutput;
    }

    const after_rustc = trimmed[6..];
    const space_idx = std.mem.indexOf(u8, after_rustc, " ") orelse after_rustc.len;
    const version_str = after_rustc[0..space_idx];

    const version = Version.parse(version_str) orelse return error.InvalidVersion;
    const str = try allocator.dupe(u8, version_str);

    return VersionResult{ .version = version, .str = str };
}

fn processCargoToml(
    allocator: std.mem.Allocator,
    io: Io,
    path: []const u8,
    current_version: Version,
    dry_run: bool,
    stats: *Stats,
    stdout: *Io.Writer,
    stderr: *Io.Writer,
) !void {
    const cwd = Dir.cwd();
    const file = try Dir.openFile(cwd, io, path, .{});
    defer file.close(io);

    var read_buf: [4096]u8 = undefined;
    var reader = File.Reader.init(file, io, &read_buf);
    const content = try reader.interface.allocRemaining(allocator, .limited(10 * 1024 * 1024));
    defer allocator.free(content);

    // Find and process rust-version line
    const result = try processContent(allocator, content, current_version);
    defer if (result.new_content) |nc| allocator.free(nc);

    switch (result.status) {
        .not_found => {
            stats.skipped += 1;
        },
        .skipped_non_semver => {
            try stdout.print("{s}: skipped (non-semver value)\n", .{path});
            stats.skipped += 1;
        },
        .skipped_not_older => {
            try stdout.print("{s}: skipped (version {s} is not older)\n", .{ path, result.old_version orelse "unknown" });
            stats.skipped += 1;
        },
        .updated => {
            const new_content = result.new_content orelse return error.NoNewContent;
            if (dry_run) {
                try stdout.print("{s}: would update {s} -> {d}.{d}.{d}\n", .{
                    path,
                    result.old_version orelse "unknown",
                    current_version.major,
                    current_version.minor,
                    current_version.patch,
                });
            } else {
                const out_file = try Dir.createFile(cwd, io, path, .{});
                defer out_file.close(io);
                var write_buf: [4096]u8 = undefined;
                var writer = File.Writer.initStreaming(out_file, io, &write_buf);
                try writer.interface.writeAll(new_content);
                try writer.flush();
                try stdout.print("{s}: updated {s} -> {d}.{d}.{d}\n", .{
                    path,
                    result.old_version orelse "unknown",
                    current_version.major,
                    current_version.minor,
                    current_version.patch,
                });
            }
            stats.updated += 1;
        },
    }
    _ = stderr;
}

const ProcessStatus = enum {
    not_found,
    skipped_non_semver,
    skipped_not_older,
    updated,
};

const ProcessResult = struct {
    status: ProcessStatus,
    old_version: ?[]const u8,
    new_content: ?[]u8,
};

fn processContent(allocator: std.mem.Allocator, content: []const u8, current_version: Version) !ProcessResult {
    const rust_version_key = "rust-version";

    // Find rust-version line
    var line_start: usize = 0;
    while (line_start < content.len) {
        const line_end = std.mem.indexOfScalarPos(u8, content, line_start, '\n') orelse content.len;
        const line = content[line_start..line_end];

        // Check if line contains rust-version
        if (std.mem.indexOf(u8, line, rust_version_key)) |key_pos| {
            const after_key = line[key_pos + rust_version_key.len ..];
            const trimmed = std.mem.trimStart(u8, after_key, " \t");

            if (trimmed.len > 0 and trimmed[0] == '=') {
                const after_eq = std.mem.trimStart(u8, trimmed[1..], " \t");

                // Skip non-string values (like { workspace = true })
                if (after_eq.len > 0 and after_eq[0] == '{') {
                    return ProcessResult{ .status = .skipped_non_semver, .old_version = null, .new_content = null };
                }

                // Find quoted version string
                if (std.mem.indexOf(u8, after_eq, "\"")) |quote_start| {
                    const version_start = quote_start + 1;
                    if (std.mem.indexOfScalarPos(u8, after_eq, version_start, '"')) |quote_end| {
                        const old_version_str = after_eq[version_start..quote_end];

                        // Parse the version
                        const old_version = Version.parse(old_version_str) orelse {
                            return ProcessResult{ .status = .skipped_non_semver, .old_version = null, .new_content = null };
                        };

                        // Check if update needed
                        if (!old_version.isOlderThan(current_version)) {
                            return ProcessResult{ .status = .skipped_not_older, .old_version = old_version_str, .new_content = null };
                        }

                        // Build new content
                        const new_version_str = try current_version.format(allocator);
                        defer allocator.free(new_version_str);

                        // Calculate position in full content
                        const abs_version_start = line_start + key_pos + rust_version_key.len + (@intFromPtr(after_eq.ptr) - @intFromPtr(line.ptr) - key_pos - rust_version_key.len) + version_start;
                        const abs_version_end = abs_version_start + old_version_str.len;

                        const new_content = try allocator.alloc(u8, content.len - old_version_str.len + new_version_str.len);
                        @memcpy(new_content[0..abs_version_start], content[0..abs_version_start]);
                        @memcpy(new_content[abs_version_start..][0..new_version_str.len], new_version_str);
                        @memcpy(new_content[abs_version_start + new_version_str.len ..], content[abs_version_end..]);

                        return ProcessResult{ .status = .updated, .old_version = old_version_str, .new_content = new_content };
                    }
                }
            }
        }

        line_start = line_end + 1;
    }

    return ProcessResult{ .status = .not_found, .old_version = null, .new_content = null };
}

// Tests

test "Version.parse valid versions" {
    const v1 = Version.parse("1.70.0").?;
    try std.testing.expectEqual(@as(u32, 1), v1.major);
    try std.testing.expectEqual(@as(u32, 70), v1.minor);
    try std.testing.expectEqual(@as(u32, 0), v1.patch);

    const v2 = Version.parse("1.84.1").?;
    try std.testing.expectEqual(@as(u32, 1), v2.major);
    try std.testing.expectEqual(@as(u32, 84), v2.minor);
    try std.testing.expectEqual(@as(u32, 1), v2.patch);

    // Two-part version (patch defaults to 0)
    const v3 = Version.parse("1.70").?;
    try std.testing.expectEqual(@as(u32, 1), v3.major);
    try std.testing.expectEqual(@as(u32, 70), v3.minor);
    try std.testing.expectEqual(@as(u32, 0), v3.patch);
}

test "Version.parse with whitespace and quotes" {
    const v1 = Version.parse("  1.70.0  ").?;
    try std.testing.expectEqual(@as(u32, 1), v1.major);
    try std.testing.expectEqual(@as(u32, 70), v1.minor);

    const v2 = Version.parse("\"1.84.0\"").?;
    try std.testing.expectEqual(@as(u32, 1), v2.major);
    try std.testing.expectEqual(@as(u32, 84), v2.minor);
}

test "Version.parse invalid versions" {
    try std.testing.expectEqual(@as(?Version, null), Version.parse(""));
    try std.testing.expectEqual(@as(?Version, null), Version.parse("abc"));
    try std.testing.expectEqual(@as(?Version, null), Version.parse("1"));
    try std.testing.expectEqual(@as(?Version, null), Version.parse("1.x.0"));
}

test "Version.isOlderThan" {
    const v1_70 = Version{ .major = 1, .minor = 70, .patch = 0 };
    const v1_84 = Version{ .major = 1, .minor = 84, .patch = 0 };
    const v1_84_1 = Version{ .major = 1, .minor = 84, .patch = 1 };
    const v2_0 = Version{ .major = 2, .minor = 0, .patch = 0 };

    try std.testing.expect(v1_70.isOlderThan(v1_84));
    try std.testing.expect(!v1_84.isOlderThan(v1_70));
    try std.testing.expect(!v1_84.isOlderThan(v1_84)); // equal
    try std.testing.expect(v1_84.isOlderThan(v1_84_1));
    try std.testing.expect(v1_84_1.isOlderThan(v2_0));
}

test "processContent updates older version" {
    const content = "[package]\nrust-version = \"1.70.0\"\n";
    const current = Version{ .major = 1, .minor = 84, .patch = 0 };

    const result = try processContent(std.testing.allocator, content, current);
    defer if (result.new_content) |nc| std.testing.allocator.free(nc);

    try std.testing.expectEqual(ProcessStatus.updated, result.status);
    try std.testing.expectEqualStrings("1.70.0", result.old_version.?);
    try std.testing.expectEqualStrings("[package]\nrust-version = \"1.84.0\"\n", result.new_content.?);
}

test "processContent skips newer version" {
    const content = "[package]\nrust-version = \"1.84.0\"\n";
    const current = Version{ .major = 1, .minor = 70, .patch = 0 };

    const result = try processContent(std.testing.allocator, content, current);

    try std.testing.expectEqual(ProcessStatus.skipped_not_older, result.status);
    try std.testing.expectEqual(@as(?[]u8, null), result.new_content);
}

test "processContent skips equal version" {
    const content = "[package]\nrust-version = \"1.84.0\"\n";
    const current = Version{ .major = 1, .minor = 84, .patch = 0 };

    const result = try processContent(std.testing.allocator, content, current);

    try std.testing.expectEqual(ProcessStatus.skipped_not_older, result.status);
}

test "processContent skips workspace inheritance" {
    const content = "[package]\nrust-version = { workspace = true }\n";
    const current = Version{ .major = 1, .minor = 84, .patch = 0 };

    const result = try processContent(std.testing.allocator, content, current);

    try std.testing.expectEqual(ProcessStatus.skipped_non_semver, result.status);
}

test "processContent not found" {
    const content = "[package]\nname = \"foo\"\nversion = \"0.1.0\"\n";
    const current = Version{ .major = 1, .minor = 84, .patch = 0 };

    const result = try processContent(std.testing.allocator, content, current);

    try std.testing.expectEqual(ProcessStatus.not_found, result.status);
}

test "processContent preserves surrounding content" {
    const content =
        \\[package]
        \\name = "myapp"
        \\version = "0.1.0"
        \\rust-version = "1.70.0"
        \\edition = "2021"
        \\
        \\[dependencies]
        \\serde = "1.0"
        \\
    ;
    const current = Version{ .major = 1, .minor = 84, .patch = 0 };

    const result = try processContent(std.testing.allocator, content, current);
    defer if (result.new_content) |nc| std.testing.allocator.free(nc);

    try std.testing.expectEqual(ProcessStatus.updated, result.status);

    const expected =
        \\[package]
        \\name = "myapp"
        \\version = "0.1.0"
        \\rust-version = "1.84.0"
        \\edition = "2021"
        \\
        \\[dependencies]
        \\serde = "1.0"
        \\
    ;
    try std.testing.expectEqualStrings(expected, result.new_content.?);
}