use std::cmp::max;
use std::collections::BTreeMap;
use std::path::{Path, PathBuf};

use serde::Deserialize;
use tracing::{debug, warn};

use crate::git_info::{Commit, Tags};
use crate::timestamp::Timestamp;

#[derive(Debug, thiserror::Error)]
pub enum CacheInfoError {
    #[error("Failed to parse glob patterns for `cache-keys`: {0}")]
    Glob(#[from] globwalk::GlobError),
    #[error(transparent)]
    Io(#[from] std::io::Error),
}

/// The information used to determine whether a built distribution is up-to-date, based on the
/// timestamps of relevant files, the current commit of a repository, etc.
#[derive(Default, Debug, Clone, Hash, PartialEq, Eq, serde::Deserialize, serde::Serialize)]
#[serde(rename_all = "kebab-case")]
pub struct CacheInfo {
    /// The timestamp of the most recent `ctime` of any relevant files, at the time of the build.
    /// The timestamp will typically be the maximum of the `ctime` values of the `pyproject.toml`,
    /// `setup.py`, and `setup.cfg` files, if they exist; however, users can provide additional
    /// files to timestamp via the `cache-keys` field.
    timestamp: Option<Timestamp>,
    /// The commit at which the distribution was built.
    commit: Option<Commit>,
    /// The Git tags present at the time of the build.
    tags: Option<Tags>,
    /// Environment variables to include in the cache key.
    #[serde(default, skip_serializing_if = "BTreeMap::is_empty")]
    env: BTreeMap<String, Option<String>>,
}

impl CacheInfo {
    /// Return the [`CacheInfo`] for a given timestamp.
    pub fn from_timestamp(timestamp: Timestamp) -> Self {
        Self {
            timestamp: Some(timestamp),
            ..Self::default()
        }
    }

    /// Compute the cache info for a given path, which may be a file or a directory.
    pub fn from_path(path: &Path) -> Result<Self, CacheInfoError> {
        let metadata = fs_err::metadata(path)?;
        if metadata.is_file() {
            Ok(Self::from_file(path)?)
        } else {
            Self::from_directory(path)
        }
    }

    /// Compute the cache info for a given directory.
    pub fn from_directory(directory: &Path) -> Result<Self, CacheInfoError> {
        let mut commit = None;
        let mut tags = None;
        let mut timestamp = None;
        let mut env = BTreeMap::new();

        // Read the cache keys.
        let cache_keys =
            if let Ok(contents) = fs_err::read_to_string(directory.join("pyproject.toml")) {
                if let Ok(pyproject_toml) = toml::from_str::<PyProjectToml>(&contents) {
                    pyproject_toml
                        .tool
                        .and_then(|tool| tool.uv)
                        .and_then(|tool_uv| tool_uv.cache_keys)
                } else {
                    None
                }
            } else {
                None
            };

        // If no cache keys were defined, use the defaults.
        let cache_keys = cache_keys.unwrap_or_else(|| {
            vec![
                CacheKey::Path("pyproject.toml".to_string()),
                CacheKey::Path("setup.py".to_string()),
                CacheKey::Path("setup.cfg".to_string()),
            ]
        });

        // Incorporate timestamps from any direct filepaths.
        let mut globs = vec![];
        for cache_key in cache_keys {
            match cache_key {
                CacheKey::Path(file) | CacheKey::File { file } => {
                    if file.chars().any(|c| matches!(c, '*' | '?' | '[' | '{')) {
                        // Defer globs to a separate pass.
                        globs.push(file);
                        continue;
                    }

                    // Treat the path as a file.
                    let path = directory.join(&file);
                    let metadata = match path.metadata() {
                        Ok(metadata) => metadata,
                        Err(err) if err.kind() == std::io::ErrorKind::NotFound => {
                            continue;
                        }
                        Err(err) => {
                            warn!("Failed to read metadata for file: {err}");
                            continue;
                        }
                    };
                    if !metadata.is_file() {
                        warn!(
                            "Expected file for cache key, but found directory: `{}`",
                            path.display()
                        );
                        continue;
                    }
                    timestamp = max(timestamp, Some(Timestamp::from_metadata(&metadata)));
                }
                CacheKey::Git {
                    git: GitPattern::Bool(true),
                } => match Commit::from_repository(directory) {
                    Ok(commit_info) => commit = Some(commit_info),
                    Err(err) => {
                        debug!("Failed to read the current commit: {err}");
                    }
                },
                CacheKey::Git {
                    git: GitPattern::Set(set),
                } => {
                    if set.commit.unwrap_or(false) {
                        match Commit::from_repository(directory) {
                            Ok(commit_info) => commit = Some(commit_info),
                            Err(err) => {
                                debug!("Failed to read the current commit: {err}");
                            }
                        }
                    }
                    if set.tags.unwrap_or(false) {
                        match Tags::from_repository(directory) {
                            Ok(tags_info) => tags = Some(tags_info),
                            Err(err) => {
                                debug!("Failed to read the current tags: {err}");
                            }
                        }
                    }
                }
                CacheKey::Git {
                    git: GitPattern::Bool(false),
                } => {}
                CacheKey::Environment { env: var } => {
                    let value = std::env::var(&var).ok();
                    env.insert(var, value);
                }
            }
        }

        // If we have any globs, process them in a single pass.
        if !globs.is_empty() {
            let walker = globwalk::GlobWalkerBuilder::from_patterns(directory, &globs)
                .file_type(globwalk::FileType::FILE | globwalk::FileType::SYMLINK)
                .build()?;
            for entry in walker {
                let entry = match entry {
                    Ok(entry) => entry,
                    Err(err) => {
                        warn!("Failed to read glob entry: {err}");
                        continue;
                    }
                };
                let metadata = match entry.metadata() {
                    Ok(metadata) => metadata,
                    Err(err) => {
                        warn!("Failed to read metadata for glob entry: {err}");
                        continue;
                    }
                };
                if !metadata.is_file() {
                    warn!(
                        "Expected file for cache key, but found directory: `{}`",
                        entry.path().display()
                    );
                    continue;
                }
                timestamp = max(timestamp, Some(Timestamp::from_metadata(&metadata)));
            }
        }

        Ok(Self {
            timestamp,
            commit,
            tags,
            env,
        })
    }

    /// Compute the cache info for a given file, assumed to be a binary or source distribution
    /// represented as (e.g.) a `.whl` or `.tar.gz` archive.
    pub fn from_file(path: impl AsRef<Path>) -> std::io::Result<Self> {
        let metadata = fs_err::metadata(path.as_ref())?;
        let timestamp = Timestamp::from_metadata(&metadata);
        Ok(Self {
            timestamp: Some(timestamp),
            ..Self::default()
        })
    }

    /// Returns `true` if the cache info is empty.
    pub fn is_empty(&self) -> bool {
        self.timestamp.is_none()
            && self.commit.is_none()
            && self.tags.is_none()
            && self.env.is_empty()
    }
}

/// A `pyproject.toml` with an (optional) `[tool.uv]` section.
#[derive(Debug, Deserialize)]
#[serde(rename_all = "kebab-case")]
struct PyProjectToml {
    tool: Option<Tool>,
}

#[derive(Debug, Deserialize)]
#[serde(rename_all = "kebab-case")]
struct Tool {
    uv: Option<ToolUv>,
}

#[derive(Debug, Deserialize)]
#[serde(rename_all = "kebab-case")]
struct ToolUv {
    cache_keys: Option<Vec<CacheKey>>,
}

#[derive(Debug, Clone, serde::Deserialize)]
#[cfg_attr(feature = "schemars", derive(schemars::JsonSchema))]
#[serde(untagged, rename_all = "kebab-case", deny_unknown_fields)]
pub enum CacheKey {
    /// Ex) `"Cargo.lock"` or `"**/*.toml"`
    Path(String),
    /// Ex) `{ file = "Cargo.lock" }` or `{ file = "**/*.toml" }`
    File { file: String },
    /// Ex) `{ git = true }` or `{ git = { commit = true, tags = false } }`
    Git { git: GitPattern },
    /// Ex) `{ env = "UV_CACHE_INFO" }`
    Environment { env: String },
}

#[derive(Debug, Clone, serde::Deserialize)]
#[cfg_attr(feature = "schemars", derive(schemars::JsonSchema))]
#[serde(untagged, rename_all = "kebab-case", deny_unknown_fields)]
pub enum GitPattern {
    Bool(bool),
    Set(GitSet),
}

#[derive(Debug, Clone, serde::Deserialize)]
#[cfg_attr(feature = "schemars", derive(schemars::JsonSchema))]
#[serde(rename_all = "kebab-case", deny_unknown_fields)]
pub struct GitSet {
    commit: Option<bool>,
    tags: Option<bool>,
}

pub enum FilePattern {
    Glob(String),
    Path(PathBuf),
}