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

#[derive(Debug, Clone, PartialEq, Eq)]
pub struct GitSpaceMetadata {
    pub key: String,
    pub checkout_key: String,
    pub label: String,
    pub repo_root: PathBuf,
    pub is_linked_worktree: bool,
}

#[derive(Debug, Clone, PartialEq, Eq)]
pub struct GitWorktreeInfo {
    pub repo_root: PathBuf,
    pub git_dir: PathBuf,
    pub git_common_dir: PathBuf,
    pub is_bare: bool,
    pub is_linked_worktree: bool,
}

pub fn derive_label_from_cwd(cwd: &Path) -> String {
    if let Some(repo_root) = git_repo_root(cwd) {
        if let Some(name) = repo_root.file_name().and_then(|n| n.to_str()) {
            return name.to_string();
        }
    }

    if let Ok(home) = std::env::var("HOME") {
        let home = Path::new(&home);
        if cwd == home {
            return "~".to_string();
        }
    }

    cwd.file_name()
        .and_then(|n| n.to_str())
        .filter(|s| !s.is_empty())
        .map(|s| s.to_string())
        .unwrap_or_else(|| cwd.display().to_string())
}

pub fn git_worktree_info(cwd: &Path) -> Option<GitWorktreeInfo> {
    let repo_root = git_repo_root(cwd)?;
    let git_dir = canonicalize_best_effort_path(&git_dir_for_repo_root(&repo_root)?);
    let git_common_dir = canonicalize_best_effort_path(&git_common_dir_for_git_dir(&git_dir));
    let is_linked_worktree = git_dir != git_common_dir;
    let is_bare = git_dir_is_bare(&git_dir);

    Some(GitWorktreeInfo {
        repo_root,
        git_dir,
        git_common_dir,
        is_bare,
        is_linked_worktree,
    })
}

pub fn git_space_metadata(cwd: &Path) -> Option<GitSpaceMetadata> {
    git_repo_root(cwd)?;

    let info = git_worktree_info(cwd)?;
    let key = canonicalize_best_effort_path(&info.git_common_dir)
        .display()
        .to_string();
    let checkout_key = canonicalize_best_effort_path(&info.repo_root)
        .display()
        .to_string();
    let label_path = if info
        .git_common_dir
        .file_name()
        .and_then(|name| name.to_str())
        == Some(".git")
    {
        info.git_common_dir.parent().unwrap_or(&info.repo_root)
    } else {
        &info.repo_root
    };
    let label = label_path
        .file_name()
        .and_then(|name| name.to_str())
        .unwrap_or("repo")
        .to_string();
    Some(GitSpaceMetadata {
        key,
        checkout_key,
        label,
        repo_root: info.repo_root,
        is_linked_worktree: info.is_linked_worktree,
    })
}

pub(super) fn canonicalize_best_effort_path(path: &Path) -> PathBuf {
    std::fs::canonicalize(path).unwrap_or_else(|_| path.to_path_buf())
}

fn git_common_dir_for_git_dir(git_dir: &Path) -> PathBuf {
    let commondir = git_dir.join("commondir");
    let Ok(contents) = std::fs::read_to_string(commondir) else {
        return git_dir.to_path_buf();
    };
    let path = Path::new(contents.trim());
    if path.is_absolute() {
        path.to_path_buf()
    } else {
        git_dir.join(path)
    }
}

pub fn git_branch(cwd: &Path) -> Option<String> {
    let repo_root = git_repo_root(cwd)?;
    let git_dir = git_dir_for_repo_root(&repo_root)?;
    let git_common_dir = git_common_dir_for_git_dir(&git_dir);
    if git_ref_storage_is_reftable(&git_common_dir) {
        return git_symbolic_head_short(&repo_root);
    }

    let head = std::fs::read_to_string(git_dir.join("HEAD")).ok()?;
    parse_git_head_branch(&head)
}

pub(super) fn git_dir_for_repo_root(repo_root: &Path) -> Option<PathBuf> {
    let git_path = repo_root.join(".git");
    if git_path.is_dir() {
        return Some(git_path);
    }

    if let Ok(gitdir) = std::fs::read_to_string(&git_path) {
        if let Some(relative) = gitdir.trim().strip_prefix("gitdir:").map(str::trim) {
            let resolved = Path::new(relative);
            return Some(if resolved.is_absolute() {
                resolved.to_path_buf()
            } else {
                repo_root.join(resolved)
            });
        }
    }

    if path_is_git_dir_layout(repo_root) && git_dir_is_bare(repo_root) {
        return Some(repo_root.to_path_buf());
    }

    None
}

fn path_is_git_dir_layout(path: &Path) -> bool {
    path.join("HEAD").is_file() && path.join("objects").is_dir() && path.join("refs").is_dir()
}

pub(super) fn git_symbolic_head_full(repo_root: &Path) -> Option<String> {
    git_trimmed_stdout(repo_root, &["symbolic-ref", "--quiet", "HEAD"])
}

fn git_symbolic_head_short(repo_root: &Path) -> Option<String> {
    git_trimmed_stdout(repo_root, &["symbolic-ref", "--quiet", "--short", "HEAD"])
}

pub(super) fn git_rev_parse_verify(repo_root: &Path, revision: &str) -> Option<String> {
    git_trimmed_stdout(repo_root, &["rev-parse", "--verify", revision])
}

pub(super) fn git_ref_storage_is_reftable(git_common_dir: &Path) -> bool {
    read_git_config_value(&git_common_dir.join("config"), "extensions", "refstorage")
        .is_some_and(|value| value.eq_ignore_ascii_case("reftable"))
}

fn git_dir_is_bare(git_dir: &Path) -> bool {
    read_git_config_value(&git_dir.join("config"), "core", "bare")
        .is_some_and(|value| value.eq_ignore_ascii_case("true"))
}

fn parse_git_head_branch(head: &str) -> Option<String> {
    let branch = head.trim().strip_prefix("ref: refs/heads/")?;
    (!branch.is_empty()).then(|| branch.to_string())
}

fn read_git_config_value(path: &Path, section: &str, key: &str) -> Option<String> {
    let contents = std::fs::read_to_string(path).ok()?;
    let mut in_section = false;
    for raw_line in contents.lines() {
        let line = raw_line.trim();
        if line.is_empty() || line.starts_with('#') || line.starts_with(';') {
            continue;
        }
        if let Some(section_name) = simple_git_config_section(line) {
            in_section = section_name.eq_ignore_ascii_case(section);
            continue;
        }
        if !in_section {
            continue;
        }
        let Some((name, value)) = line.split_once('=') else {
            continue;
        };
        if name.trim().eq_ignore_ascii_case(key) {
            return Some(strip_git_config_comment(value).trim().to_string());
        }
    }
    None
}

fn simple_git_config_section(line: &str) -> Option<&str> {
    let section = line.strip_prefix('[')?.split_once(']')?.0.trim();
    (!section.contains('"')).then_some(section)
}

fn strip_git_config_comment(value: &str) -> &str {
    let value = value.trim();
    for marker in ['#', ';'] {
        if let Some((prefix, _)) = value.split_once(marker) {
            if prefix.chars().next_back().is_some_and(char::is_whitespace) {
                return prefix;
            }
        }
    }
    value
}

fn git_trimmed_stdout(repo_root: &Path, args: &[&str]) -> Option<String> {
    let output = std::process::Command::new("git")
        .arg("-C")
        .arg(repo_root)
        .args(args)
        .output()
        .ok()?;
    if !output.status.success() {
        return None;
    }

    let stdout = String::from_utf8(output.stdout).ok()?;
    let stdout = stdout.trim();
    (!stdout.is_empty()).then(|| stdout.to_string())
}

pub(super) fn git_repo_root(start: &Path) -> Option<PathBuf> {
    let mut current = if start.is_dir() {
        start.to_path_buf()
    } else {
        start.parent()?.to_path_buf()
    };

    loop {
        if git_dir_for_repo_root(&current)
            .map(|git_dir| git_dir.join("HEAD").is_file())
            .unwrap_or(false)
        {
            return Some(current);
        }
        if !current.pop() {
            return None;
        }
    }
}

pub(super) fn read_ref_oid(common_dir: &Path, full_ref: &str) -> Option<String> {
    let loose_ref = common_dir.join(full_ref);
    if let Ok(contents) = std::fs::read_to_string(loose_ref) {
        let oid = contents.trim();
        if !oid.is_empty() {
            return Some(oid.to_string());
        }
    }

    let packed_refs = std::fs::read_to_string(common_dir.join("packed-refs")).ok()?;
    for line in packed_refs.lines() {
        let line = line.trim();
        if line.is_empty() || line.starts_with('#') || line.starts_with('^') {
            continue;
        }
        let mut parts = line.split_whitespace();
        let oid = parts.next()?;
        let name = parts.next()?;
        if name == full_ref {
            return Some(oid.to_string());
        }
    }
    None
}

#[cfg(test)]
mod tests {
    use std::path::{Path, PathBuf};
    use std::time::{SystemTime, UNIX_EPOCH};

    use super::*;
    use crate::workspace::git::test_support::run_git;

    fn temp_test_dir(name: &str) -> PathBuf {
        let unique = format!(
            "herdr-workspace-tests-{}-{}-{}",
            name,
            std::process::id(),
            SystemTime::now()
                .duration_since(UNIX_EPOCH)
                .unwrap()
                .as_nanos()
        );
        let path = std::env::temp_dir().join(unique);
        std::fs::create_dir_all(&path).unwrap();
        path
    }

    #[test]
    fn git_branch_reads_head_from_standard_repo() {
        let root = temp_test_dir("standard-repo");
        std::fs::create_dir_all(root.join(".git")).unwrap();
        std::fs::write(root.join(".git/HEAD"), "ref: refs/heads/main\n").unwrap();

        assert_eq!(git_branch(&root).as_deref(), Some("main"));

        std::fs::remove_dir_all(root).unwrap();
    }

    #[test]
    fn git_branch_reads_head_from_worktree_gitdir_file() {
        let root = temp_test_dir("worktree");
        let worktree_git_dir = root.join(".bare/worktrees/feature");
        std::fs::create_dir_all(&worktree_git_dir).unwrap();
        std::fs::write(root.join(".git"), "gitdir: .bare/worktrees/feature\n").unwrap();
        std::fs::write(worktree_git_dir.join("HEAD"), "ref: refs/heads/feature\n").unwrap();

        assert_eq!(git_branch(&root).as_deref(), Some("feature"));

        std::fs::remove_dir_all(root).unwrap();
    }

    #[test]
    fn git_branch_returns_none_for_detached_head() {
        let root = temp_test_dir("detached-head");
        std::fs::create_dir_all(root.join(".git")).unwrap();
        std::fs::write(root.join(".git/HEAD"), "3e1b9a8d\n").unwrap();

        assert_eq!(git_branch(&root), None);

        std::fs::remove_dir_all(root).unwrap();
    }

    #[test]
    fn git_branch_reads_symbolic_head_from_reftable_repo() {
        let root = temp_test_dir("reftable-branch");
        let root_arg = root.to_string_lossy().to_string();
        let output = std::process::Command::new("git")
            .args(["init", "--ref-format=reftable", "-b", "main", &root_arg])
            .output()
            .unwrap();
        if !output.status.success() {
            std::fs::remove_dir_all(root).unwrap();
            return;
        }

        assert_eq!(git_branch(&root).as_deref(), Some("main"));

        std::fs::remove_dir_all(root).unwrap();
    }

    #[test]
    fn git_repo_root_ignores_invalid_git_marker() {
        let base = temp_test_dir("invalid-git-root");
        let cwd = base.join("workspace");
        std::fs::create_dir_all(base.join(".git")).unwrap();
        std::fs::create_dir_all(&cwd).unwrap();

        assert_eq!(git_repo_root(&cwd), None);

        std::fs::remove_dir_all(base).unwrap();
    }

    #[test]
    fn git_repo_root_ignores_standalone_non_bare_git_dir_layout() {
        let root = temp_test_dir("standalone-non-bare-git-dir");
        std::fs::write(root.join("HEAD"), "ref: refs/heads/main\n").unwrap();
        std::fs::create_dir_all(root.join("objects")).unwrap();
        std::fs::create_dir_all(root.join("refs")).unwrap();
        std::fs::write(root.join("config"), "[core]\n\tbare = false\n").unwrap();

        assert_eq!(git_repo_root(&root.join("refs")), None);

        std::fs::remove_dir_all(root).unwrap();
    }

    #[test]
    fn git_space_metadata_supports_standalone_bare_repo() {
        let bare = temp_test_dir("bare-space");
        run_git(&bare, &["init", "--bare", "."]);
        let nested = bare.join("refs");

        let info = git_worktree_info(&nested).expect("bare repo should be discovered");
        assert!(info.is_bare);
        assert!(!info.is_linked_worktree);
        assert_eq!(info.git_dir, canonicalize_best_effort_path(&bare));

        let metadata = git_space_metadata(&nested).expect("bare repo should map to a git space");
        assert_eq!(
            canonicalize_best_effort_path(&metadata.repo_root),
            canonicalize_best_effort_path(&bare)
        );
        assert!(!metadata.is_linked_worktree);

        std::fs::remove_dir_all(bare).unwrap();
    }

    #[test]
    fn git_space_metadata_marks_bare_dot_git_repo() {
        let root = temp_test_dir("bare-dot-git");
        run_git(&root, &["init", "--bare", ".git"]);

        let info = git_worktree_info(&root).expect("bare .git repo should be discovered");
        assert!(info.is_bare);
        assert!(!info.is_linked_worktree);
        assert_eq!(
            info.git_dir,
            canonicalize_best_effort_path(&root.join(".git"))
        );

        let metadata = git_space_metadata(&root).expect("bare .git repo should map to a git space");
        assert_eq!(
            canonicalize_best_effort_path(&metadata.repo_root),
            canonicalize_best_effort_path(&root)
        );

        std::fs::remove_dir_all(root).unwrap();
    }

    #[test]
    fn derive_label_prefers_repo_root_name() {
        let root = temp_test_dir("label-repo");
        let nested = root.join("nested");
        std::fs::create_dir_all(root.join(".git")).unwrap();
        std::fs::write(root.join(".git/HEAD"), "ref: refs/heads/main\n").unwrap();
        std::fs::create_dir_all(&nested).unwrap();

        assert_eq!(
            derive_label_from_cwd(&nested),
            root.file_name().and_then(|name| name.to_str()).unwrap()
        );

        std::fs::remove_dir_all(root).unwrap();
    }

    #[test]
    fn derive_label_uses_path_name_outside_git() {
        let root = temp_test_dir("label-plain");
        let label = root.file_name().and_then(|name| name.to_str()).unwrap();

        assert_eq!(derive_label_from_cwd(Path::new(&root)), label);

        std::fs::remove_dir_all(root).unwrap();
    }

    #[test]
    fn git_rev_parse_verify_reads_reftable_refs() {
        let root = temp_test_dir("reftable-ref-oid");
        let root_arg = root.to_string_lossy().to_string();
        let output = std::process::Command::new("git")
            .args(["init", "--ref-format=reftable", "-b", "main", &root_arg])
            .output()
            .unwrap();
        if !output.status.success() {
            std::fs::remove_dir_all(root).unwrap();
            return;
        }

        run_git(&root, &["config", "user.email", "herdr@example.invalid"]);
        run_git(&root, &["config", "user.name", "Herdr Test"]);
        run_git(&root, &["commit", "--allow-empty", "-m", "initial"]);

        let head_oid = git_rev_parse_verify(&root, "HEAD").unwrap();

        assert_eq!(
            git_rev_parse_verify(&root, "refs/heads/main").as_deref(),
            Some(head_oid.as_str())
        );

        std::fs::remove_dir_all(root).unwrap();
    }
}