use std::{
    env::current_dir,
    fs,
    io::Write,
    path::{Path, PathBuf},
    process::{Command, Stdio},
};

use anyhow::{Context, Result, bail};
use clap::{Parser, Subcommand};

use crate::parse::{FileDiff, Patch};

mod parse;

#[derive(Parser)]
struct Cli {
    #[command(subcommand)]
    subcommand: Cmd,
}

#[derive(Subcommand)]
enum Cmd {
    /// Apply patches to a rollup target.
    Apply {
        /// The files to pull the patches to rollup from.
        patch_files: Vec<PathBuf>,

        /// Which repository to use as a target for the rollup
        ///
        /// The repository needs to be clean.
        #[arg(short, long)]
        to: PathBuf,

        /// Show debug information related to the parsing of patch files.
        #[arg(short, long)]
        debug_parse: bool,
    },

    /// Create the patch files (based on the given tag)
    Create {
        /// Which tag to use to mark the already applied patches.
        #[arg(default_value = "CONFIG_APPLIED")]
        tag: String,
    },

    /// First create the patches, and then automatically apply them.
    CreateApply {
        /// Which tag to use to mark the already applied patches.
        #[arg(default_value = "CONFIG_APPLIED")]
        tag: String,

        /// Which repository to use as a target for the rollup
        ///
        /// The repository needs to be clean.
        #[arg(short, long)]
        to: PathBuf,

        /// Show debug information related to the parsing of patch files.
        #[arg(short, long)]
        debug_parse: bool,
    },
}

macro_rules! git {
    (@_base for $finalizer:ident in $to:expr; $($args:expr),*) => {
        Command::new("git")
            .args([
                "-C",
                $to.display().to_string().as_str(),
                $($args),*
            ])
            .stdin(Stdio::piped())
            .stdout(Stdio::piped())
            .stderr(Stdio::piped())
            .$finalizer()
            .with_context(|| format!("Failed to run {}", git!(@_fmt_cmd $($args),*)))?
    };
    (@_handle_status $output:expr; $($args:expr),*) => {{
        if !$output.status.success() {
            bail!(
                "{} failed!\n\nStderr was:\n {}",
                git!(@_fmt_cmd $($args),*),
                String::from_utf8($output.stderr).unwrap()
            )
        }
        if !$output.stderr.is_empty() {
            let stderr = String::from_utf8($output.stderr).expect("git should always produce utf8");
            bail!("{} returned some errors:\n{stderr}", git!(@_fmt_cmd $($args),*));
        }
    }};
    (@_fmt_cmd $($args:expr),*) => {{
        let all = ["git", $($args),*].join(" ");
        format!("`{}`", all)
    }};
    (in $to:expr; $($args:expr),*) => {{
        let output = git!(@_base for output in $to; $($args),*);
        git!(@_handle_status output; $($args),*);

        let stdout = String::from_utf8(output.stdout).expect("git should always produce utf8");
        let stderr = String::from_utf8(output.stderr).expect("git should always produce utf8");

        (stdout, stderr)
    }};
    (@set_stdin_to $stdin:expr; in $to:expr; $($args:expr),*) => {{
        let mut child = git!(@_base for spawn in $to; $($args),*);
        let mut stdin = child.stdin.take().expect("is piped");
        write!(stdin, "{}", $stdin)?;
        drop(stdin);
        let output = child.wait_with_output()
            .with_context(|| format!("Failed to run `{}`", git!(@_fmt_cmd $($args),*)))?;
        git!(@_handle_status output; $($args),*);

        let stdout = String::from_utf8(output.stdout).expect("git should always produce utf8");
        let stderr = String::from_utf8(output.stderr).expect("git should always produce utf8");

        (stdout, stderr)
    }};
}

fn main() -> Result<()> {
    let args = Cli::parse();

    match args.subcommand {
        Cmd::Apply {
            patch_files,
            to,
            debug_parse,
        } => {
            check_to(&to)?;
            apply_patches(patch_files, to, debug_parse)?
        }
        Cmd::Create { tag } => {
            create_patches(tag)?;
        }
        Cmd::CreateApply {
            tag,
            to,
            debug_parse,
        } => {
            check_to(&to)?;

            let Some(patches_directory) = create_patches(tag)? else {
                return Ok(());
            };
            let patch_files = {
                let iter = fs::read_dir(patches_directory)?;
                let mut output = vec![];
                for entry in iter {
                    let entry = entry?;
                    if !entry.file_type()?.is_file() {
                        unreachable!("Should not be able to get non-files in patches directory");
                    }
                    output.push(entry.path());
                }
                output
            };
            apply_patches(patch_files, to, debug_parse)?;
        }
    }

    Ok(())
}

fn create_patches(tag: String) -> Result<Option<PathBuf>> {
    let current_dir = current_dir()?;

    let (stdout, _) = git!(in current_dir; "tag", "--contains", "HEAD", tag.as_str());
    if !stdout.is_empty() {
        println!(
            "There are no tags to generate. Tag {} already points to HEAD.",
            tag
        );
        return Ok(None);
    }

    let mktemp = Command::new("mktemp")
        .args(["-t", "rollup_patches_XXXXXX", "-d"])
        .output()
        .context("Failed to run `mktemp -t rollup_patches_XXXXXX -d`")?;
    if !mktemp.status.success() {
        bail!("Failed to generate temp-directory for generated patches.");
    }

    let tempdir = PathBuf::from(String::from_utf8(mktemp.stdout).unwrap().trim());

    git!(in current_dir; "format-patch", format!("{}..", tag).as_str(), "-o", tempdir.display().to_string().as_str());
    git!(in current_dir; "tag", "--delete", tag.as_str());
    git!(in current_dir; "tag", "--annotate", tag.as_str(), "-m", "");

    println!("Patches have been generated here: `{}`", tempdir.display());

    Ok(Some(tempdir))
}

fn apply_patches(patch_files: Vec<PathBuf>, to: PathBuf, debug_parse: bool) -> Result<()> {
    let mut patches = vec![];
    for file in &patch_files {
        patches.push(parse::parse_file(file, debug_parse)?);
    }

    eprintln!("Successfully parsed all {} patch files.", patches.len());

    {
        let (stdout, _) = git!(in to; "status", "--porcelain");
        if !stdout.is_empty() {
            bail!(
                "`--to` (`{}`) workspace is dirty, refusing to continue.",
                to.display()
            );
        }
    }

    for (idx, patch) in patches.iter().enumerate() {
        eprintln!(
            "Applying {}. patch: `{}`... ",
            idx + 1,
            patch_files[idx].display()
        );

        let mut final_diffs = vec![];
        for file_diff in &patch.files {
            match file_diff {
                FileDiff::Add { path, .. } => {
                    if to.join(path).exists() {
                        bail!("A file was added, that already existed. This should be impossible.")
                    }
                    final_diffs.push(file_diff.to_owned());
                    // eprintln!("  > Keeping add of `{}`", path.display());
                }
                FileDiff::Remove { path, .. } => {
                    if to.join(path).exists() {
                        final_diffs.push(file_diff.to_owned());
                        // eprintln!("  > Keeping remove of `{}`", path.display());
                    } else {
                        eprintln!(
                            "  > Dropping remove of `{}`, as the file does not exist in the rollup target.",
                            path.display()
                        );
                    }
                }
                FileDiff::RenameNoChange { from, to, .. }
                | FileDiff::RenameWithChange { from, to, .. } => {
                    if to.join(from).exists() {
                        if to.join(to).exists() {
                            bail!(
                                "A rename (`{}` -> `{}`) tried to rename a path to an already existing path. This should be impossible.",
                                from.display(),
                                to.display()
                            )
                        }
                        final_diffs.push(file_diff.to_owned());
                        // eprintln!("  > Keeping rename of `{}` to `{}`", from.display(), to.display());
                    } else {
                        eprintln!(
                            "  > Dropping rename from `{}` to `{}`, as the from file does not exist in the rollup target.",
                            from.display(),
                            to.display()
                        );
                    }
                }
                FileDiff::Change { path, .. } => {
                    if to.join(path).exists() {
                        final_diffs.push(file_diff.to_owned());
                    } else {
                        eprintln!(
                            "  > Dropping change to `{}`, as the file does not exist in the rollup target.",
                            path.display()
                        );
                    }
                }
            }
        }

        if final_diffs.is_empty() {
            eprintln!("  -> Patch is empty after dropping, skipping it.",);
            continue;
        }

        let filtered_patch = Patch {
            files: final_diffs,
            ..patch.to_owned()
        };

        git!(@set_stdin_to filtered_patch; in to; "apply", "-", "--whitespace=nowarn");
        git!(in to; "add", ".");
        git!(@set_stdin_to filtered_patch.commit_message; in to; "commit", "--file=-", format!("--date={}", filtered_patch.date).as_str(), "--quiet");
    }

    Ok(())
}

fn check_to(to: &Path) -> Result<()> {
    let to = to.join(".git");

    // NOTE: We cannot just try to stat() the path, because landlock might be in use and does not
    // currently deny that (tracked in: https://github.com/landlock-lsm/linux/issues/52) <2026-11-09>
    // So we instead try to list it.
    let is_listable = {
        let dir_entries = fs::read_dir(&to).with_context(|| {
            format!(
                "Failed check regarding `--to` directory (`{}`) readability. Are you in a sandbox?",
                to.display()
            )
        })?;
        dir_entries.count() > 0
    };

    if !is_listable {
        bail!("To directory (`{}`) is not readable", to.display());
    }

    Ok(())
}