use std::borrow::Cow;
use std::path::PathBuf;
use std::str::FromStr;
use std::sync::Arc;

use dashmap::DashMap;
use dashmap::mapref::one::Ref;
use fs_err::tokio as fs;
use reqwest_middleware::ClientWithMiddleware;
use tracing::debug;

use uv_cache_key::{RepositoryUrl, cache_digest};
use uv_fs::{LockedFile, LockedFileError, LockedFileMode};
use uv_git_types::{GitHubRepository, GitOid, GitReference, GitUrl};
use uv_static::EnvVars;
use uv_version::version;

use crate::{
    Fetch, GitSource, Reporter,
    rate_limit::{GITHUB_RATE_LIMIT_STATUS, is_github_rate_limited},
};

#[derive(Debug, thiserror::Error)]
pub enum GitResolverError {
    #[error(transparent)]
    Io(#[from] std::io::Error),
    #[error(transparent)]
    LockedFile(#[from] LockedFileError),
    #[error(transparent)]
    Join(#[from] tokio::task::JoinError),
    #[error("Git operation failed")]
    Git(#[source] anyhow::Error),
    #[error(transparent)]
    Reqwest(#[from] reqwest::Error),
    #[error(transparent)]
    ReqwestMiddleware(#[from] reqwest_middleware::Error),
}

/// A resolver for Git repositories.
#[derive(Default, Clone)]
pub struct GitResolver(Arc<DashMap<RepositoryReference, GitOid>>);

impl GitResolver {
    /// Inserts a new [`GitOid`] for the given [`RepositoryReference`].
    pub fn insert(&self, reference: RepositoryReference, sha: GitOid) {
        self.0.insert(reference, sha);
    }

    /// Returns the [`GitOid`] for the given [`RepositoryReference`], if it exists.
    fn get(&self, reference: &RepositoryReference) -> Option<Ref<'_, RepositoryReference, GitOid>> {
        self.0.get(reference)
    }

    /// Return the [`GitOid`] for the given [`GitUrl`], if it is already known.
    pub fn get_precise(&self, url: &GitUrl) -> Option<GitOid> {
        // If the URL is already precise, return it.
        if let Some(precise) = url.precise() {
            return Some(precise);
        }

        // If we know the precise commit already, return it.
        let reference = RepositoryReference::from(url);
        if let Some(precise) = self.get(&reference) {
            return Some(*precise);
        }

        None
    }

    /// Resolve a Git URL to a specific commit without performing any Git operations.
    ///
    /// Returns a [`GitOid`] if the URL has already been resolved (i.e., is available in the cache),
    /// or if it can be fetched via the GitHub API. Otherwise, returns `None`.
    pub async fn github_fast_path(
        &self,
        url: &GitUrl,
        client: &ClientWithMiddleware,
    ) -> Result<Option<GitOid>, GitResolverError> {
        if std::env::var_os(EnvVars::UV_NO_GITHUB_FAST_PATH).is_some() {
            return Ok(None);
        }

        // If the URL is already precise or we know the precise commit, return it.
        if let Some(precise) = self.get_precise(url) {
            return Ok(Some(precise));
        }

        // If the URL is a GitHub URL, attempt to resolve it via the GitHub API.
        let Some(GitHubRepository { owner, repo }) = GitHubRepository::parse(url.repository())
        else {
            return Ok(None);
        };

        // Check if we're rate-limited by GitHub, before determining the Git reference
        if GITHUB_RATE_LIMIT_STATUS.is_active() {
            debug!("Rate-limited by GitHub. Skipping GitHub fast path attempt for: {url}");
            return Ok(None);
        }

        // Determine the Git reference.
        let rev = url.reference().as_rev();

        let github_api_base_url = std::env::var(EnvVars::UV_GITHUB_FAST_PATH_URL)
            .unwrap_or("https://api.github.com/repos".to_owned());
        let github_api_url = format!("{github_api_base_url}/{owner}/{repo}/commits/{rev}");

        debug!("Querying GitHub for commit at: {github_api_url}");
        let mut request = client.get(&github_api_url);
        request = request.header("Accept", "application/vnd.github.3.sha");
        request = request.header(
            "User-Agent",
            format!("uv/{} (+https://github.com/astral-sh/uv)", version()),
        );

        let response = request.send().await?;
        let status = response.status();
        if !status.is_success() {
            // Returns a 404 if the repository does not exist, and a 422 if GitHub is unable to
            // resolve the requested rev.
            debug!(
                "GitHub API request failed for: {github_api_url} ({})",
                response.status()
            );

            if is_github_rate_limited(&response) {
                // Mark that we are being rate-limited by GitHub
                GITHUB_RATE_LIMIT_STATUS.activate();
            }

            return Ok(None);
        }

        // Parse the response as a Git SHA.
        let precise = response.text().await?;
        let precise =
            GitOid::from_str(&precise).map_err(|err| GitResolverError::Git(err.into()))?;

        // Insert the resolved URL into the in-memory cache. This ensures that subsequent fetches
        // resolve to the same precise commit.
        self.insert(RepositoryReference::from(url), precise);

        Ok(Some(precise))
    }

    /// Fetch a remote Git repository.
    pub async fn fetch(
        &self,
        url: &GitUrl,
        disable_ssl: bool,
        offline: bool,
        cache: PathBuf,
        reporter: Option<Arc<dyn Reporter>>,
    ) -> Result<Fetch, GitResolverError> {
        debug!("Fetching source distribution from Git: {url}");

        let reference = RepositoryReference::from(url);

        // If we know the precise commit already, reuse it, to ensure that all fetches within a
        // single process are consistent.
        let url = {
            if let Some(precise) = self.get(&reference) {
                Cow::Owned(url.clone().with_precise(*precise))
            } else {
                Cow::Borrowed(url)
            }
        };

        // Avoid races between different processes, too.
        let lock_dir = cache.join("locks");
        fs::create_dir_all(&lock_dir).await?;
        let repository_url = url.repository().clone();
        let _lock = LockedFile::acquire(
            lock_dir.join(cache_digest(&repository_url)),
            LockedFileMode::Exclusive,
            &repository_url,
        )
        .await?;

        // Fetch the Git repository.
        let source = if let Some(reporter) = reporter {
            GitSource::new(url.as_ref().clone(), cache, offline).with_reporter(reporter)
        } else {
            GitSource::new(url.as_ref().clone(), cache, offline)
        };

        // If necessary, disable SSL.
        let source = if disable_ssl {
            source.dangerous()
        } else {
            source
        };

        let fetch = tokio::task::spawn_blocking(move || source.fetch())
            .await?
            .map_err(GitResolverError::Git)?;

        // Insert the resolved URL into the in-memory cache. This ensures that subsequent fetches
        // resolve to the same precise commit.
        if let Some(precise) = fetch.git().precise() {
            self.insert(reference, precise);
        }

        Ok(fetch)
    }

    /// Given a remote source distribution, return a precise variant, if possible.
    ///
    /// For example, given a Git dependency with a reference to a branch or tag, return a URL
    /// with a precise reference to the current commit of that branch or tag.
    ///
    /// This method takes into account various normalizations that are independent of the Git
    /// layer. For example: removing `#subdirectory=pkg_dir`-like fragments, and removing `git+`
    /// prefix kinds.
    ///
    /// This method will only return precise URLs for URLs that have already been resolved via
    /// [`resolve_precise`], and will return `None` for URLs that have not been resolved _or_
    /// already have a precise reference.
    pub fn precise(&self, url: GitUrl) -> Option<GitUrl> {
        let reference = RepositoryReference::from(&url);
        let precise = self.get(&reference)?;
        Some(url.with_precise(*precise))
    }

    /// Returns `true` if the two Git URLs refer to the same precise commit.
    pub fn same_ref(&self, a: &GitUrl, b: &GitUrl) -> bool {
        // Convert `a` to a repository URL.
        let a_ref = RepositoryReference::from(a);

        // Convert `b` to a repository URL.
        let b_ref = RepositoryReference::from(b);

        // The URLs must refer to the same repository.
        if a_ref.url != b_ref.url {
            return false;
        }

        // If the URLs have the same tag, they refer to the same commit.
        if a_ref.reference == b_ref.reference {
            return true;
        }

        // Otherwise, the URLs must resolve to the same precise commit.
        let Some(a_precise) = a.precise().or_else(|| self.get(&a_ref).map(|sha| *sha)) else {
            return false;
        };

        let Some(b_precise) = b.precise().or_else(|| self.get(&b_ref).map(|sha| *sha)) else {
            return false;
        };

        a_precise == b_precise
    }
}

#[derive(Debug, Clone, PartialEq, Eq, Hash)]
pub struct ResolvedRepositoryReference {
    /// An abstract reference to a Git repository, including the URL and the commit (e.g., a branch,
    /// tag, or revision).
    pub reference: RepositoryReference,
    /// The precise commit SHA of the reference.
    pub sha: GitOid,
}

#[derive(Debug, Clone, PartialEq, Eq, Hash)]
pub struct RepositoryReference {
    /// The URL of the Git repository, with any query parameters and fragments removed.
    pub url: RepositoryUrl,
    /// The reference to the commit to use, which could be a branch, tag, or revision.
    pub reference: GitReference,
}

impl From<&GitUrl> for RepositoryReference {
    fn from(git: &GitUrl) -> Self {
        Self {
            url: git.repository().clone(),
            reference: git.reference().clone(),
        }
    }
}
