denet 0.4.1

//! Build script for denet
//!
//! When the 'ebpf' feature is enabled, this script:
//! 1. Checks for clang availability
//! 2. Compiles eBPF C programs to bytecode
//! 3. Makes bytecode available for embedding in the binary

use std::env;
use std::path::PathBuf;
use std::process::Command;

fn main() {
    println!("cargo:rerun-if-changed=build.rs");

    // Only compile eBPF when the feature is enabled
    if env::var("CARGO_FEATURE_EBPF").is_ok() {
        println!("cargo:warning=Building with eBPF support - checking for clang...");

        // Check if clang is available
        if !check_clang_available() {
            panic!(
                "\n\n🚫 ERROR: clang is required to build eBPF programs!\n\n\
                Please install clang:\n\
                - Ubuntu/Debian: sudo apt install clang llvm libbpf-dev\n\
                - CentOS/RHEL: sudo yum install clang llvm-devel libbpf-devel\n\
                - macOS: brew install llvm\n\n\
                Or build without eBPF: cargo build (without --features ebpf)\n"
            );
        }

        println!("cargo:warning=✓ clang found - compiling eBPF programs...");

        // Compile eBPF programs
        compile_ebpf_programs();

        println!("cargo:warning=✓ eBPF programs compiled successfully");
    } else {
        println!("cargo:warning=Building without eBPF support (no --features ebpf)");
    }
}

/// Check if clang is available and supports BPF target
fn check_clang_available() -> bool {
    // Check if clang command exists
    let clang_check = Command::new("clang").arg("--version").output();

    if clang_check.is_err() {
        return false;
    }

    // Check if clang supports BPF target
    let bpf_target_check = Command::new("clang")
        .arg("-target")
        .arg("bpf")
        .arg("--print-supported-cpus")
        .output();

    bpf_target_check.is_ok()
}

/// Compile eBPF C programs to bytecode
fn compile_ebpf_programs() {
    let out_dir = env::var("OUT_DIR").unwrap();
    let ebpf_src_dir = "src/ebpf/programs";

    // Create eBPF programs directory in OUT_DIR
    let ebpf_out_dir = PathBuf::from(&out_dir).join("ebpf");
    std::fs::create_dir_all(&ebpf_out_dir).unwrap();

    // List of eBPF programs to compile
    let ebpf_programs = vec!["syscall_tracer.c", "simple_test.c"];

    for program in ebpf_programs {
        let src_path = PathBuf::from(ebpf_src_dir).join(program);
        let obj_name = program.replace(".c", ".o");
        let obj_path = ebpf_out_dir.join(&obj_name);

        println!("cargo:rerun-if-changed={}", src_path.display());

        // Only compile if source file exists
        if !src_path.exists() {
            println!("cargo:warning=Creating placeholder for {program}");
            create_placeholder_ebpf_program(&src_path);
        }

        // Compile eBPF C program to bytecode
        let compilation = Command::new("clang")
            .arg("-target")
            .arg("bpf")
            .arg("-O2")
            .arg("-g")
            .arg("-c")
            .arg(&src_path)
            .arg("-o")
            .arg(&obj_path)
            .arg("-I/usr/include")
            .arg("-I/usr/include/x86_64-linux-gnu")
            .arg("-D__TARGET_ARCH_x86")
            .arg("-Wno-unused-value")
            .arg("-Wno-pointer-sign")
            .arg("-Wno-compare-distinct-pointer-types")
            .arg("-Wunused")
            .arg("-Wall")
            .arg("-Werror")
            .output();

        match compilation {
            Ok(output) => {
                if !output.status.success() {
                    let stderr = String::from_utf8_lossy(&output.stderr);
                    panic!("Failed to compile {program}: {stderr}");
                }
                println!("cargo:warning=✓ Compiled {program} -> {obj_name}");
            }
            Err(e) => {
                panic!("Failed to run clang for {program}: {e}");
            }
        }

        // Tell Rust where to find the compiled object file
        println!(
            "cargo:rustc-env=EBPF_{}_PATH={}",
            obj_name.replace(".o", "").to_uppercase(),
            obj_path.display()
        );
    }
}

/// Create a placeholder eBPF program if it doesn't exist
fn create_placeholder_ebpf_program(path: &PathBuf) {
    let program_name = path.file_stem().unwrap().to_str().unwrap();

    let placeholder_content = match program_name {
        "simple_test" => {
            r#"//! Simple eBPF program for testing tracepoints
//! This is a minimal program that should be easy to load

#include <linux/bpf.h>
#include <bpf/bpf_helpers.h>
#include <bpf/bpf_tracing.h>

// Simple array map for testing
struct {
    __uint(type, BPF_MAP_TYPE_ARRAY);
    __type(key, __u32);
    __type(value, __u64);
    __uint(max_entries, 10);
} test_map SEC(".maps");

// Simple tracepoint for openat syscall
SEC("tracepoint/syscalls/sys_enter_openat")
int trace_openat_enter(void *ctx) {
    __u32 key = 0;
    __u64 *value = bpf_map_lookup_elem(&test_map, &key);
    if (value) {
        (*value)++;
    }
    return 0;
}

char LICENSE[] SEC("license") = "GPL";
"#
        }
        "syscall_tracer" => {
            r#"//! Syscall tracing eBPF program
//! This program attaches to syscall tracepoints and counts syscall frequency

#include <linux/bpf.h>
#include <bpf/bpf_helpers.h>
#include <bpf/bpf_tracing.h>

// BPF map to store syscall counts per PID
struct {
    __uint(type, BPF_MAP_TYPE_HASH);
    __type(key, __u32);   // PID
    __type(value, __u64); // syscall count
    __uint(max_entries, 10240);
} syscall_counts SEC(".maps");

// Tracepoint for syscall entry
SEC("tracepoint/syscalls/sys_enter_openat")
int trace_openat_enter(void *ctx) {
    __u32 pid = bpf_get_current_pid_tgid() >> 32;

    // Get current count for this PID
    __u64 *count = bpf_map_lookup_elem(&syscall_counts, &pid);
    if (count) {
        __sync_fetch_and_add(count, 1);
    } else {
        __u64 initial_count = 1;
        bpf_map_update_elem(&syscall_counts, &pid, &initial_count, BPF_ANY);
    }

    return 0;
}

// Additional tracepoints for common syscalls
SEC("tracepoint/syscalls/sys_enter_read")
int trace_read_enter(void *ctx) {
    __u32 pid = bpf_get_current_pid_tgid() >> 32;

    __u64 *count = bpf_map_lookup_elem(&syscall_counts, &pid);
    if (count) {
        __sync_fetch_and_add(count, 1);
    } else {
        __u64 initial_count = 1;
        bpf_map_update_elem(&syscall_counts, &pid, &initial_count, BPF_ANY);
    }

    return 0;
}

SEC("tracepoint/syscalls/sys_enter_write")
int trace_write_enter(void *ctx) {
    __u32 pid = bpf_get_current_pid_tgid() >> 32;

    __u64 *count = bpf_map_lookup_elem(&syscall_counts, &pid);
    if (count) {
        __sync_fetch_and_add(count, 1);
    } else {
        __u64 initial_count = 1;
        bpf_map_update_elem(&syscall_counts, &pid, &initial_count, BPF_ANY);
    }

    return 0;
}

char LICENSE[] SEC("license") = "GPL";
"#
        }
        _ => "// Placeholder eBPF program\n",
    };

    // Create directory if it doesn't exist
    if let Some(parent) = path.parent() {
        std::fs::create_dir_all(parent).unwrap();
    }

    std::fs::write(path, placeholder_content).unwrap();
}