use std::io::Write;
use std::path::{Path, PathBuf};

use hyper::header::IF_MATCH;
use sha2::{Digest, Sha256};

use crate::config::ProxyConfig;

use super::model::ApiFailure;

pub(super) fn parse_if_match(headers: &hyper::HeaderMap) -> Option<String> {
    headers
        .get(IF_MATCH)
        .and_then(|value| value.to_str().ok())
        .map(str::trim)
        .filter(|value| !value.is_empty())
        .map(|value| value.trim_matches('"').to_string())
}

pub(super) async fn ensure_expected_revision(
    config_path: &Path,
    expected_revision: Option<&str>,
) -> Result<(), ApiFailure> {
    let Some(expected) = expected_revision else {
        return Ok(());
    };
    let current = current_revision(config_path).await?;
    if current != expected {
        return Err(ApiFailure::new(
            hyper::StatusCode::CONFLICT,
            "revision_conflict",
            "Config revision mismatch",
        ));
    }
    Ok(())
}

pub(super) async fn current_revision(config_path: &Path) -> Result<String, ApiFailure> {
    let content = tokio::fs::read_to_string(config_path)
        .await
        .map_err(|e| ApiFailure::internal(format!("failed to read config: {}", e)))?;
    Ok(compute_revision(&content))
}

pub(super) fn compute_revision(content: &str) -> String {
    let mut hasher = Sha256::new();
    hasher.update(content.as_bytes());
    hex::encode(hasher.finalize())
}

pub(super) async fn load_config_from_disk(config_path: &Path) -> Result<ProxyConfig, ApiFailure> {
    let config_path = config_path.to_path_buf();
    tokio::task::spawn_blocking(move || ProxyConfig::load(config_path))
        .await
        .map_err(|e| ApiFailure::internal(format!("failed to join config loader: {}", e)))?
        .map_err(|e| ApiFailure::internal(format!("failed to load config: {}", e)))
}

pub(super) async fn save_config_to_disk(
    config_path: &Path,
    cfg: &ProxyConfig,
) -> Result<String, ApiFailure> {
    let serialized = toml::to_string_pretty(cfg)
        .map_err(|e| ApiFailure::internal(format!("failed to serialize config: {}", e)))?;
    write_atomic(config_path.to_path_buf(), serialized.clone()).await?;
    Ok(compute_revision(&serialized))
}

async fn write_atomic(path: PathBuf, contents: String) -> Result<(), ApiFailure> {
    tokio::task::spawn_blocking(move || write_atomic_sync(&path, &contents))
        .await
        .map_err(|e| ApiFailure::internal(format!("failed to join writer: {}", e)))?
        .map_err(|e| ApiFailure::internal(format!("failed to write config: {}", e)))
}

fn write_atomic_sync(path: &Path, contents: &str) -> std::io::Result<()> {
    let parent = path.parent().unwrap_or_else(|| Path::new("."));
    std::fs::create_dir_all(parent)?;

    let tmp_name = format!(
        ".{}.tmp-{}",
        path.file_name()
            .and_then(|s| s.to_str())
            .unwrap_or("config.toml"),
        rand::random::<u64>()
    );
    let tmp_path = parent.join(tmp_name);

    let write_result = (|| {
        let mut file = std::fs::OpenOptions::new()
            .create_new(true)
            .write(true)
            .open(&tmp_path)?;
        file.write_all(contents.as_bytes())?;
        file.sync_all()?;
        std::fs::rename(&tmp_path, path)?;
        if let Ok(dir) = std::fs::File::open(parent) {
            let _ = dir.sync_all();
        }
        Ok(())
    })();

    if write_result.is_err() {
        let _ = std::fs::remove_file(&tmp_path);
    }
    write_result
}