use std::fs;
use std::io::{BufRead, BufReader, BufWriter, Write};
use std::path::{Path, PathBuf};

pub struct TestFileInfo {
    pub path: PathBuf,
    pub size_bytes: u64,
    pub line_count: u64,
    pub avg_line_length: f64,
}

/// Check if test file exists and return its info, or generate it
pub fn ensure_test_file(path: &Path) -> std::io::Result<TestFileInfo> {
    if path.exists() {
        return get_file_info(path);
    }
    generate_test_file(path)
}

/// Get info about an existing test file
fn get_file_info(path: &Path) -> std::io::Result<TestFileInfo> {
    let metadata = fs::metadata(path)?;
    let size_bytes = metadata.len();
    let line_count = count_existing_lines(path)?;

    let avg_line_length = if line_count > 0 {
        size_bytes as f64 / line_count as f64
    } else {
        0.0
    };

    Ok(TestFileInfo {
        path: path.to_path_buf(),
        size_bytes,
        line_count,
        avg_line_length,
    })
}

/// Generate a large test file (~5GB / ~74M lines) if it doesn't exist
fn generate_test_file(path: &Path) -> std::io::Result<TestFileInfo> {
    if let Some(parent) = path.parent() {
        fs::create_dir_all(parent)?;
    }

    let mut file = BufWriter::with_capacity(64 * 1024, fs::File::create(path)?);
    let target_lines: u64 = 74_000_000;
    for i in 0..target_lines {
        writeln!(
            file,
            "2024-01-15 10:30:{:02} INFO [thread-{}] Application processing request id={} user_id={}",
            i % 60,
            i % 16,
            i,
            i * 7
        )?;
    }
    file.flush()?;
    drop(file);

    get_file_info(path)
}

/// Generate a smaller file (~10MB / ~150K lines) for growth/rotation tests
pub fn generate_growable_file(dir: &Path) -> std::io::Result<PathBuf> {
    fs::create_dir_all(dir)?;
    let path = dir.join("growable.log");

    let mut file = BufWriter::with_capacity(64 * 1024, fs::File::create(&path)?);
    for i in 0..150_000u64 {
        writeln!(
            file,
            "2024-01-15 10:30:{:02} INFO [thread-{}] Appending test line {}",
            i % 60,
            i % 16,
            i
        )?;
    }
    file.flush()?;

    Ok(path)
}

/// Append `count` lines to the file
pub fn append_lines(path: &Path, count: usize) -> std::io::Result<()> {
    let existing_lines = count_existing_lines(path)?;
    let mut file = BufWriter::with_capacity(
        64 * 1024,
        fs::OpenOptions::new().append(true).open(path)?,
    );
    for i in 0..count {
        writeln!(
            file,
            "2024-01-15 10:30:00 INFO Appended line {}",
            existing_lines + i as u64
        )?;
    }
    file.flush()?;
    Ok(())
}

/// Truncate file to specified size
pub fn truncate_file(path: &Path, size: u64) -> std::io::Result<()> {
    let file = fs::OpenOptions::new().write(true).open(path)?;
    file.set_len(size)
}

/// Rotate file: rename existing file, create new empty file
pub fn rotate_file(path: &Path) -> std::io::Result<PathBuf> {
    let rotated = path.with_extension("log.1");
    fs::rename(path, &rotated)?;
    fs::File::create(path)?;
    Ok(rotated)
}

/// Count lines in a file (helper)
fn count_existing_lines(path: &Path) -> std::io::Result<u64> {
    let file = fs::File::open(path)?;
    let reader = BufReader::new(file);
    let mut count = 0u64;
    for line in reader.lines() {
        line?;
        count += 1;
    }
    Ok(count)
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_generate_growable_file_creates_approximately_correct_size() {
        let dir = tempfile::tempdir().unwrap();
        let path = generate_growable_file(dir.path()).unwrap();

        assert!(path.exists());
        let metadata = fs::metadata(&path).unwrap();
        let size_mb = metadata.len() as f64 / (1024.0 * 1024.0);
        // ~150K lines × ~67 bytes ≈ ~10MB; allow 5MB–15MB range
        assert!(
            (5.0..=15.0).contains(&size_mb),
            "Expected ~10MB, got {size_mb:.1}MB"
        );
    }

    #[test]
    fn test_append_lines_increases_line_count() {
        let dir = tempfile::tempdir().unwrap();
        let path = {
            let mut f = fs::File::create(dir.path().join("test.log")).unwrap();
            for i in 0..10u64 {
                writeln!(f, "line {i}").unwrap();
            }
            dir.path().join("test.log")
        };

        let before = count_existing_lines(&path).unwrap();
        append_lines(&path, 5).unwrap();
        let after = count_existing_lines(&path).unwrap();
        assert_eq!(after, before + 5);
    }

    #[test]
    fn test_truncate_file_reduces_size() {
        let dir = tempfile::tempdir().unwrap();
        let path = dir.path().join("trunc.log");
        {
            let mut f = fs::File::create(&path).unwrap();
            write!(f, "{}", "A".repeat(1024)).unwrap();
        }

        let before = fs::metadata(&path).unwrap().len();
        assert_eq!(before, 1024);

        truncate_file(&path, 512).unwrap();
        let after = fs::metadata(&path).unwrap().len();
        assert_eq!(after, 512);
    }

    #[test]
    fn test_rotate_file_renames_and_creates_empty() {
        let dir = tempfile::tempdir().unwrap();
        let path = dir.path().join("rotate.log");
        {
            let mut f = fs::File::create(&path).unwrap();
            write!(f, "original content").unwrap();
        }

        let rotated = rotate_file(&path).unwrap();

        // Rotated file has the old content
        assert!(rotated.exists());
        assert_eq!(fs::read_to_string(&rotated).unwrap(), "original content");

        // New file is empty
        assert!(path.exists());
        assert_eq!(fs::metadata(&path).unwrap().len(), 0);
    }

    #[test]
    fn test_ensure_test_file_generates_when_missing() {
        let dir = tempfile::tempdir().unwrap();
        let path = dir.path().join("fresh.log");
        assert!(!path.exists());

        // Override the generator to use a small file for test speed:
        // We'll test ensure_test_file indirectly by checking it calls generate_test_file.
        // Since generate_test_file creates 74M lines (too slow for tests), test the logic
        // by directly creating a small file and checking get_file_info works.
        {
            let mut f = fs::File::create(&path).unwrap();
            for i in 0..100u64 {
                writeln!(f, "2024-01-15 10:30:00 INFO line {i}").unwrap();
            }
        }

        let info = ensure_test_file(&path).unwrap();
        assert_eq!(info.line_count, 100);
        assert!(info.size_bytes > 0);
        assert!(info.avg_line_length > 0.0);
    }
}