use std::{fs, path::PathBuf, process::Command, time::Duration};

use anyhow::{anyhow, Context, Result};
use reqwest::blocking::Client;
use serde::{Deserialize, Serialize};
use sha2::{Digest, Sha256};
use uuid::Uuid;

const RELEASE_FEED: &str =
    "https://git.arrowstack.dev/Admin/fieldlens-desktop/raw/branch/main/downloads/release.json";
const LINUX_DEB_URL: &str =
    "https://fieldlens.arrowstack.dev/downloads/fieldlens-print-linux-x64.deb";

#[derive(Debug, Deserialize)]
struct ReleaseFeed {
    version: String,
    downloads: std::collections::HashMap<String, ReleaseDownload>,
}

#[derive(Debug, Deserialize)]
struct ReleaseDownload {
    url: String,
    sha256: String,
}

#[derive(Debug, Serialize)]
#[serde(rename_all = "camelCase")]
pub struct UpdateInstallResult {
    pub status: String,
    pub version: String,
}

fn newer(candidate: &str, current: &str) -> bool {
    let parse = |value: &str| {
        value
            .split('.')
            .map(|part| part.parse::<u64>().unwrap_or(0))
            .collect::<Vec<_>>()
    };
    let left = parse(candidate);
    let right = parse(current);
    let width = left.len().max(right.len());

    for index in 0..width {
        let a = *left.get(index).unwrap_or(&0);
        let b = *right.get(index).unwrap_or(&0);
        if a != b {
            return a > b;
        }
    }
    false
}

#[cfg(target_os = "linux")]
pub fn install_linux_update() -> Result<UpdateInstallResult> {
    let client = Client::builder()
        .timeout(Duration::from_secs(120))
        .build()
        .context("create update HTTP client")?;

    let release: ReleaseFeed = client
        .get(RELEASE_FEED)
        .header("cache-control", "no-cache")
        .send()
        .context("fetch FieldLens release feed")?
        .error_for_status()
        .context("FieldLens release feed returned an error")?
        .json()
        .context("decode FieldLens release feed")?;

    if !newer(&release.version, env!("CARGO_PKG_VERSION")) {
        return Ok(UpdateInstallResult {
            status: "up-to-date".into(),
            version: release.version,
        });
    }

    let download = release
        .downloads
        .get("linux-x86_64-deb")
        .ok_or_else(|| anyhow!("release feed has no Linux DEB"))?;

    if download.url != LINUX_DEB_URL {
        return Err(anyhow!("refusing unexpected Linux update URL"));
    }
    if download.sha256.len() != 64
        || !download.sha256.chars().all(|value| value.is_ascii_hexdigit())
    {
        return Err(anyhow!("release feed contains an invalid SHA-256"));
    }

    let package = client
        .get(&download.url)
        .send()
        .context("download FieldLens update")?
        .error_for_status()
        .context("FieldLens update download returned an error")?
        .bytes()
        .context("read FieldLens update")?;

    let actual = format!("{:x}", Sha256::digest(&package));
    if !actual.eq_ignore_ascii_case(&download.sha256) {
        return Err(anyhow!("FieldLens update checksum verification failed"));
    }

    let path: PathBuf = std::env::temp_dir().join(format!(
        "fieldlens-print-update-{}-{}.deb",
        release.version,
        Uuid::new_v4()
    ));
    fs::write(&path, &package).context("stage FieldLens update")?;

    let installer = if std::path::Path::new("/usr/bin/apt-get").is_file() {
        "/usr/bin/apt-get"
    } else {
        "/usr/bin/dpkg"
    };

    let mut command = Command::new("pkexec");
    command.arg(installer);
    if installer.ends_with("apt-get") {
        command.args(["install", "-y"]).arg(&path);
    } else {
        command.arg("-i").arg(&path);
    }

    let status = command
        .status()
        .context("run elevated FieldLens update installer")?;
    let _ = fs::remove_file(&path);

    if !status.success() {
        return Err(anyhow!(
            "FieldLens update installation was cancelled or failed"
        ));
    }

    Ok(UpdateInstallResult {
        status: "installed".into(),
        version: release.version,
    })
}

#[cfg(not(target_os = "linux"))]
pub fn install_linux_update() -> Result<UpdateInstallResult> {
    Err(anyhow!("Linux DEB updates are only available on Linux"))
}