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

use crate::error::{AppError, AppResult};

#[derive(Debug, Clone)]
pub struct CompareCommit {
    pub id: String,
    pub summary: String,
    pub author_name: String,
    pub author_email: String,
}

#[derive(Debug, Clone)]
pub struct CompareFile {
    pub path: String,
    pub additions: i64,
    pub deletions: i64,
}

#[derive(Debug, Clone)]
pub struct CompareResult {
    pub merge_base: String,
    pub head_commit_id: String,
    pub commits: Vec<CompareCommit>,
    pub files: Vec<CompareFile>,
}

pub fn init_bare_repo_with_binary(
    git_binary: &str,
    repo_path: &Path,
    default_branch: &str,
) -> AppResult<()> {
    if let Some(parent) = repo_path.parent() {
        fs::create_dir_all(parent)?;
    }

    run(Command::new(git_binary)
        .arg("init")
        .arg("--bare")
        .arg(repo_path))?;
    run(Command::new(git_binary)
        .arg("--git-dir")
        .arg(repo_path)
        .arg("symbolic-ref")
        .arg("HEAD")
        .arg(format!("refs/heads/{default_branch}")))?;
    run(Command::new(git_binary)
        .arg("--git-dir")
        .arg(repo_path)
        .arg("update-server-info"))?;
    Ok(())
}

pub fn create_initial_commit_with_binary(
    git_binary: &str,
    repo_path: &Path,
    default_branch: &str,
    readme: &str,
    author_name: &str,
    author_email: &str,
) -> AppResult<()> {
    let worktree = repo_path.with_extension("work");
    if worktree.exists() {
        fs::remove_dir_all(&worktree)?;
    }
    fs::create_dir_all(&worktree)?;

    fs::write(worktree.join("README.md"), readme)?;

    run(Command::new(git_binary)
        .arg("init")
        .arg("--initial-branch")
        .arg(default_branch)
        .arg(&worktree))?;
    run(Command::new(git_binary)
        .current_dir(&worktree)
        .env("GIT_AUTHOR_NAME", author_name)
        .env("GIT_AUTHOR_EMAIL", author_email)
        .env("GIT_COMMITTER_NAME", author_name)
        .env("GIT_COMMITTER_EMAIL", author_email)
        .arg("add")
        .arg("README.md"))?;
    run(Command::new(git_binary)
        .current_dir(&worktree)
        .env("GIT_AUTHOR_NAME", author_name)
        .env("GIT_AUTHOR_EMAIL", author_email)
        .env("GIT_COMMITTER_NAME", author_name)
        .env("GIT_COMMITTER_EMAIL", author_email)
        .arg("commit")
        .arg("-m")
        .arg("Initial commit"))?;
    run(Command::new(git_binary)
        .current_dir(&worktree)
        .arg("remote")
        .arg("add")
        .arg("origin")
        .arg(repo_path))?;
    run(Command::new(git_binary)
        .current_dir(&worktree)
        .arg("push")
        .arg("origin")
        .arg(default_branch))?;

    fs::remove_dir_all(&worktree)?;
    Ok(())
}

pub fn clone_bare_repo_with_binary(
    git_binary: &str,
    source_repo_path: &Path,
    target_repo_path: &Path,
) -> AppResult<()> {
    if let Some(parent) = target_repo_path.parent() {
        fs::create_dir_all(parent)?;
    }

    run(Command::new(git_binary)
        .arg("clone")
        .arg("--bare")
        .arg(source_repo_path)
        .arg(target_repo_path))?;
    run(Command::new(git_binary)
        .arg("--git-dir")
        .arg(target_repo_path)
        .arg("update-server-info"))?;
    Ok(())
}

pub fn list_branches_with_binary(git_binary: &str, repo_path: &Path) -> AppResult<Vec<String>> {
    let output = Command::new(git_binary)
        .arg("--git-dir")
        .arg(repo_path)
        .arg("for-each-ref")
        .arg("--format=%(refname:short)")
        .arg("refs/heads")
        .output()
        .map_err(|err| AppError::Git(err.to_string()))?;
    if !output.status.success() {
        let stderr = String::from_utf8_lossy(&output.stderr).trim().to_string();
        return Err(AppError::Git(stderr));
    }

    let stdout = String::from_utf8_lossy(&output.stdout);
    Ok(stdout
        .lines()
        .map(str::trim)
        .filter(|line| !line.is_empty())
        .map(ToOwned::to_owned)
        .collect())
}

pub fn branch_exists_with_binary(
    git_binary: &str,
    repo_path: &Path,
    branch: &str,
) -> AppResult<bool> {
    let branches = list_branches_with_binary(git_binary, repo_path)?;
    Ok(branches.iter().any(|name| name == branch))
}

pub fn merge_base_with_binary(
    git_binary: &str,
    base_repo_path: &Path,
    base_branch: &str,
    head_repo_path: &Path,
    head_branch: &str,
) -> AppResult<String> {
    let temp = std::env::temp_dir().join(format!(
        "gitr-merge-base-{}",
        std::time::SystemTime::now()
            .duration_since(std::time::UNIX_EPOCH)
            .unwrap_or_default()
            .as_nanos()
    ));
    run(Command::new(git_binary)
        .arg("clone")
        .arg("--bare")
        .arg(base_repo_path)
        .arg(&temp))?;
    let result = (|| -> AppResult<String> {
        run(Command::new(git_binary)
            .arg("--git-dir")
            .arg(&temp)
            .arg("remote")
            .arg("add")
            .arg("head_repo")
            .arg(head_repo_path))?;
        run(Command::new(git_binary)
            .arg("--git-dir")
            .arg(&temp)
            .arg("fetch")
            .arg("head_repo")
            .arg(head_branch))?;
        let output = Command::new(git_binary)
            .arg("--git-dir")
            .arg(&temp)
            .arg("merge-base")
            .arg(format!("refs/heads/{base_branch}"))
            .arg("FETCH_HEAD")
            .output()
            .map_err(|err| AppError::Git(err.to_string()))?;
        if !output.status.success() {
            let stderr = String::from_utf8_lossy(&output.stderr).trim().to_string();
            return Err(AppError::Git(stderr));
        }
        Ok(String::from_utf8_lossy(&output.stdout).trim().to_string())
    })();
    let _ = fs::remove_dir_all(&temp);
    result
}

pub fn test_merge_with_binary(
    git_binary: &str,
    base_repo_path: &Path,
    base_branch: &str,
    head_repo_path: &Path,
    head_branch: &str,
) -> AppResult<bool> {
    let temp = temp_git_path("gitr-test-merge");
    run(Command::new(git_binary)
        .arg("clone")
        .arg("-b")
        .arg(base_branch)
        .arg(base_repo_path)
        .arg(&temp))?;
    let result = (|| -> AppResult<bool> {
    run(Command::new(git_binary)
        .current_dir(&temp)
        .arg("remote")
            .arg("add")
            .arg("head_repo")
            .arg(head_repo_path))?;
        run(Command::new(git_binary)
            .current_dir(&temp)
            .arg("fetch")
            .arg("head_repo")
            .arg(head_branch))?;

        let output = Command::new(git_binary)
            .current_dir(&temp)
            .arg("merge")
            .arg("--no-ff")
            .arg("--no-commit")
            .arg("FETCH_HEAD")
            .output()
            .map_err(|err| AppError::Git(err.to_string()))?;
        Ok(output.status.success())
    })();
    let _ = fs::remove_dir_all(&temp);
    result
}

pub fn merge_pull_request_with_binary(
    git_binary: &str,
    base_repo_path: &Path,
    base_branch: &str,
    head_repo_path: &Path,
    head_branch: &str,
    author_name: &str,
    author_email: &str,
    message: &str,
) -> AppResult<String> {
    let temp = temp_git_path("gitr-merge-pr");
    run(Command::new(git_binary)
        .arg("clone")
        .arg("-b")
        .arg(base_branch)
        .arg(base_repo_path)
        .arg(&temp))?;
    let result = (|| -> AppResult<String> {
        run(Command::new(git_binary)
            .current_dir(&temp)
            .arg("remote")
            .arg("add")
            .arg("head_repo")
            .arg(head_repo_path))?;
        run(Command::new(git_binary)
            .current_dir(&temp)
            .arg("fetch")
            .arg("head_repo")
            .arg(head_branch))?;
        let head_commit_id = rev_parse_with_binary(git_binary, &temp.join(".git"), "FETCH_HEAD")?;

        let merge = Command::new(git_binary)
            .current_dir(&temp)
            .arg("merge")
            .arg("--no-ff")
            .arg("--no-commit")
            .arg("FETCH_HEAD")
            .output()
            .map_err(|err| AppError::Git(err.to_string()))?;
        if !merge.status.success() {
            let stderr = String::from_utf8_lossy(&merge.stderr).trim().to_string();
            let stdout = String::from_utf8_lossy(&merge.stdout).trim().to_string();
            let detail = if !stderr.is_empty() { stderr } else { stdout };
            return Err(AppError::Conflict(format!(
                "pull request cannot be merged automatically: {detail}"
            )));
        }

        run(Command::new(git_binary)
            .current_dir(&temp)
            .env("GIT_AUTHOR_NAME", author_name)
            .env("GIT_AUTHOR_EMAIL", author_email)
            .env("GIT_COMMITTER_NAME", author_name)
            .env("GIT_COMMITTER_EMAIL", author_email)
            .arg("commit")
            .arg("-m")
            .arg(message))?;
        run(Command::new(git_binary)
            .current_dir(&temp)
            .arg("push")
            .arg("origin")
            .arg(base_branch))?;
        run(Command::new(git_binary)
            .arg("--git-dir")
            .arg(base_repo_path)
            .arg("update-server-info"))?;
        Ok(head_commit_id)
    })();
    let _ = fs::remove_dir_all(&temp);
    result
}

pub fn compare_refs_with_binary(
    git_binary: &str,
    base_repo_path: &Path,
    base_branch: &str,
    head_repo_path: &Path,
    head_branch: &str,
) -> AppResult<CompareResult> {
    let temp = temp_git_path("gitr-compare-refs");
    run(Command::new(git_binary)
        .arg("clone")
        .arg("--bare")
        .arg(base_repo_path)
        .arg(&temp))?;
    let result = (|| -> AppResult<CompareResult> {
        run(Command::new(git_binary)
            .arg("--git-dir")
            .arg(&temp)
            .arg("remote")
            .arg("add")
            .arg("head_repo")
            .arg(head_repo_path))?;
        run(Command::new(git_binary)
            .arg("--git-dir")
            .arg(&temp)
            .arg("fetch")
            .arg("head_repo")
            .arg(head_branch))?;

        let merge_base = merge_base_for_repo(git_binary, &temp, base_branch, "FETCH_HEAD")?;
        let head_commit_id = rev_parse_with_binary(git_binary, &temp, "FETCH_HEAD")?;
        compare_rev_range_with_binary(git_binary, &temp, &merge_base, &head_commit_id)
    })();
    let _ = fs::remove_dir_all(&temp);
    result
}

pub fn compare_rev_range_with_binary(
    git_binary: &str,
    repo_path: &Path,
    merge_base: &str,
    head_commit_id: &str,
) -> AppResult<CompareResult> {
    let commits =
        list_commits_between_with_binary(git_binary, repo_path, merge_base, head_commit_id)?;
    let files = if merge_base == head_commit_id {
        Vec::new()
    } else {
        diff_numstat_with_binary(git_binary, repo_path, merge_base, head_commit_id)?
    };
    Ok(CompareResult {
        merge_base: merge_base.to_string(),
        head_commit_id: head_commit_id.to_string(),
        commits,
        files,
    })
}

pub fn rev_parse_with_binary(git_binary: &str, repo_path: &Path, rev: &str) -> AppResult<String> {
    let output = Command::new(git_binary)
        .arg("--git-dir")
        .arg(repo_path)
        .arg("rev-parse")
        .arg(rev)
        .output()
        .map_err(|err| AppError::Git(err.to_string()))?;
    if !output.status.success() {
        let stderr = String::from_utf8_lossy(&output.stderr).trim().to_string();
        return Err(AppError::Git(stderr));
    }
    Ok(String::from_utf8_lossy(&output.stdout).trim().to_string())
}

fn run(command: &mut Command) -> AppResult<()> {
    let output = command
        .output()
        .map_err(|err| AppError::Git(err.to_string()))?;
    if output.status.success() {
        return Ok(());
    }

    let stderr = String::from_utf8_lossy(&output.stderr).trim().to_string();
    let stdout = String::from_utf8_lossy(&output.stdout).trim().to_string();
    let message = if !stderr.is_empty() { stderr } else { stdout };
    Err(AppError::Git(message))
}

fn temp_git_path(prefix: &str) -> std::path::PathBuf {
    std::env::temp_dir().join(format!(
        "{prefix}-{}",
        std::time::SystemTime::now()
            .duration_since(std::time::UNIX_EPOCH)
            .unwrap_or_default()
            .as_nanos()
    ))
}

fn merge_base_for_repo(
    git_binary: &str,
    repo_path: &Path,
    base_branch: &str,
    head_rev: &str,
) -> AppResult<String> {
    let output = Command::new(git_binary)
        .arg("--git-dir")
        .arg(repo_path)
        .arg("merge-base")
        .arg(format!("refs/heads/{base_branch}"))
        .arg(head_rev)
        .output()
        .map_err(|err| AppError::Git(err.to_string()))?;
    if !output.status.success() {
        let stderr = String::from_utf8_lossy(&output.stderr).trim().to_string();
        return Err(AppError::Git(stderr));
    }
    Ok(String::from_utf8_lossy(&output.stdout).trim().to_string())
}

fn list_commits_between_with_binary(
    git_binary: &str,
    repo_path: &Path,
    merge_base: &str,
    head_commit_id: &str,
) -> AppResult<Vec<CompareCommit>> {
    if merge_base == head_commit_id {
        return Ok(Vec::new());
    }

    let output = Command::new(git_binary)
        .arg("--git-dir")
        .arg(repo_path)
        .arg("log")
        .arg("--reverse")
        .arg("--format=%H%x1f%s%x1f%an%x1f%ae%x1e")
        .arg(format!("{merge_base}..{head_commit_id}"))
        .output()
        .map_err(|err| AppError::Git(err.to_string()))?;
    if !output.status.success() {
        let stderr = String::from_utf8_lossy(&output.stderr).trim().to_string();
        return Err(AppError::Git(stderr));
    }

    let stdout = String::from_utf8_lossy(&output.stdout);
    let mut commits = Vec::new();
    for record in stdout.split('\x1e') {
        let record = record.trim();
        if record.is_empty() {
            continue;
        }
        let mut fields = record.split('\x1f');
        let id = fields.next().unwrap_or_default().to_string();
        let summary = fields.next().unwrap_or_default().to_string();
        let author_name = fields.next().unwrap_or_default().to_string();
        let author_email = fields.next().unwrap_or_default().to_string();
        commits.push(CompareCommit {
            id,
            summary,
            author_name,
            author_email,
        });
    }
    Ok(commits)
}

fn diff_numstat_with_binary(
    git_binary: &str,
    repo_path: &Path,
    merge_base: &str,
    head_commit_id: &str,
) -> AppResult<Vec<CompareFile>> {
    let output = Command::new(git_binary)
        .arg("--git-dir")
        .arg(repo_path)
        .arg("diff")
        .arg("--numstat")
        .arg(merge_base)
        .arg(head_commit_id)
        .output()
        .map_err(|err| AppError::Git(err.to_string()))?;
    if !output.status.success() {
        let stderr = String::from_utf8_lossy(&output.stderr).trim().to_string();
        return Err(AppError::Git(stderr));
    }

    let stdout = String::from_utf8_lossy(&output.stdout);
    let mut files = Vec::new();
    for line in stdout.lines() {
        if line.trim().is_empty() {
            continue;
        }
        let mut parts = line.splitn(3, '\t');
        let additions = parse_numstat_value(parts.next().unwrap_or_default());
        let deletions = parse_numstat_value(parts.next().unwrap_or_default());
        let path = parts.next().unwrap_or_default().to_string();
        files.push(CompareFile {
            path,
            additions,
            deletions,
        });
    }
    Ok(files)
}

fn parse_numstat_value(value: &str) -> i64 {
    value.parse::<i64>().unwrap_or(0)
}

pub struct GitHttpBackendRequest<'a> {
    pub git_binary: &'a str,
    pub project_root: &'a Path,
    pub path_info: &'a str,
    pub method: &'a str,
    pub query_string: &'a str,
    pub content_type: Option<&'a str>,
    pub remote_user: Option<&'a str>,
    pub body: &'a [u8],
}

pub struct GitHttpBackendResponse {
    pub status_code: u16,
    pub headers: Vec<(String, String)>,
    pub body: Vec<u8>,
}

pub fn run_git_http_backend(req: GitHttpBackendRequest<'_>) -> AppResult<GitHttpBackendResponse> {
    let mut command = Command::new(req.git_binary);
    command
        .arg("http-backend")
        .env("GIT_PROJECT_ROOT", req.project_root)
        .env("GIT_HTTP_EXPORT_ALL", "1")
        .env("PATH_INFO", req.path_info)
        .env("REQUEST_METHOD", req.method)
        .env("QUERY_STRING", req.query_string)
        .env("CONTENT_LENGTH", req.body.len().to_string())
        .stdin(Stdio::piped())
        .stdout(Stdio::piped())
        .stderr(Stdio::piped());
    if let Some(content_type) = req.content_type {
        command.env("CONTENT_TYPE", content_type);
    }
    if let Some(remote_user) = req.remote_user {
        command.env("REMOTE_USER", remote_user);
    }
    let mut child = command
        .spawn()
        .map_err(|err| AppError::Git(err.to_string()))?;

    if let Some(mut stdin) = child.stdin.take() {
        stdin.write_all(req.body)?;
    }

    let output = child
        .wait_with_output()
        .map_err(|err| AppError::Git(err.to_string()))?;
    if !output.status.success() {
        let stderr = String::from_utf8_lossy(&output.stderr).trim().to_string();
        return Err(AppError::Git(stderr));
    }

    parse_git_http_backend_output(&output.stdout)
}

fn parse_git_http_backend_output(stdout: &[u8]) -> AppResult<GitHttpBackendResponse> {
    let split = stdout
        .windows(4)
        .position(|w| w == b"\r\n\r\n")
        .map(|i| (i, 4))
        .or_else(|| stdout.windows(2).position(|w| w == b"\n\n").map(|i| (i, 2)))
        .ok_or_else(|| AppError::Git("invalid git-http-backend response".to_string()))?;

    let header_bytes = &stdout[..split.0];
    let body = stdout[split.0 + split.1..].to_vec();
    let header_text = String::from_utf8_lossy(header_bytes);

    let mut status_code = 200;
    let mut headers = Vec::new();
    for line in header_text.lines() {
        if line.is_empty() {
            continue;
        }
        if let Some(value) = line.strip_prefix("Status:") {
            let code = value
                .split_whitespace()
                .next()
                .and_then(|v| v.parse::<u16>().ok())
                .ok_or_else(|| AppError::Git(format!("invalid status line: {line}")))?;
            status_code = code;
            continue;
        }

        let (name, value) = line
            .split_once(':')
            .ok_or_else(|| AppError::Git(format!("invalid header line: {line}")))?;
        headers.push((name.trim().to_string(), value.trim().to_string()));
    }

    Ok(GitHttpBackendResponse {
        status_code,
        headers,
        body,
    })
}