use std::{
    ops::Deref,
    sync::atomic::{AtomicBool, Ordering},
    time::Instant,
};

use git_features::progress::{MessageLevel, Progress};

use crate::{
    pack,
    store::verify::integrity::{IndexStatistics, SingleOrMultiStatistics},
    types::IndexAndPacks,
};

///
pub mod integrity {
    use std::{marker::PhantomData, path::PathBuf};

    use crate::pack;

    /// Options for use in [`Store::verify_integrity()`][crate::Store::verify_integrity()].
    pub type Options<F> = pack::index::verify::integrity::Options<F>;

    /// Returned by [`Store::verify_integrity()`][crate::Store::verify_integrity()].
    #[derive(Debug, thiserror::Error)]
    #[allow(missing_docs)]
    pub enum Error {
        #[error(transparent)]
        MultiIndexIntegrity(#[from] pack::index::traverse::Error<pack::multi_index::verify::integrity::Error>),
        #[error(transparent)]
        IndexIntegrity(#[from] pack::index::traverse::Error<pack::index::verify::integrity::Error>),
        #[error(transparent)]
        IndexOpen(#[from] pack::index::init::Error),
        #[error(transparent)]
        LooseObjectStoreIntegrity(#[from] crate::loose::verify::integrity::Error),
        #[error(transparent)]
        MultiIndexOpen(#[from] pack::multi_index::init::Error),
        #[error(transparent)]
        PackOpen(#[from] pack::data::init::Error),
        #[error(transparent)]
        InitializeODB(#[from] crate::store::load_index::Error),
        #[error("The disk on state changed while performing the operation, and we observed the change.")]
        NeedsRetryDueToChangeOnDisk,
    }

    #[derive(Debug, PartialEq, Eq, Hash, Ord, PartialOrd, Clone)]
    #[cfg_attr(feature = "serde1", derive(serde::Serialize, serde::Deserialize))]
    /// Integrity information about loose object databases
    pub struct LooseObjectStatistics {
        /// The path to the root directory of the loose objects database
        pub path: PathBuf,
        /// The statistics created after verifying the loose object database.
        pub statistics: crate::loose::verify::integrity::Statistics,
    }

    #[derive(Debug, PartialEq, Eq, Hash, Ord, PartialOrd, Clone)]
    #[cfg_attr(feature = "serde1", derive(serde::Serialize, serde::Deserialize))]
    /// Traversal statistics of packs governed by single indices or multi-pack indices.
    #[allow(missing_docs)]
    pub enum SingleOrMultiStatistics {
        Single(pack::index::traverse::Statistics),
        Multi(Vec<(PathBuf, pack::index::traverse::Statistics)>),
    }

    /// Statistics gathered when traversing packs of various kinds of indices.
    #[derive(Debug, PartialEq, Eq, Hash, Ord, PartialOrd, Clone)]
    #[cfg_attr(feature = "serde1", derive(serde::Serialize, serde::Deserialize))]
    pub struct IndexStatistics {
        /// The path to the index or multi-pack index for which statics were gathered.
        pub path: PathBuf,
        /// The actual statistics for the index at `path`.
        pub statistics: SingleOrMultiStatistics,
    }

    /// Returned by [`Store::verify_integrity()`][crate::Store::verify_integrity()].
    pub struct Outcome<P> {
        /// Statistics for validated loose object stores.
        pub loose_object_stores: Vec<LooseObjectStatistics>,
        /// Pack traversal statistics for each index and their pack(s)
        pub index_statistics: Vec<IndexStatistics>,
        /// The provided progress instance.
        pub progress: P,
    }

    /// The progress ids used in [`Store::verify_integrity()`][crate::Store::verify_integrity()].
    ///
    /// Use this information to selectively extract the progress of interest in case the parent application has custom visualization.
    #[derive(Debug, Copy, Clone)]
    pub enum ProgressId {
        /// Contains the path of the currently validated loose object database.
        VerifyLooseObjectDbPath,
        /// The root progress for all verification of an index. It doesn't contain any useful information itself.
        VerifyIndex(PhantomData<git_pack::index::verify::integrity::ProgressId>),
        /// The root progress for all verification of a multi-index. It doesn't contain any useful information itself.
        VerifyMultiIndex(PhantomData<git_pack::multi_index::verify::integrity::ProgressId>),
    }

    impl From<ProgressId> for git_features::progress::Id {
        fn from(v: ProgressId) -> Self {
            match v {
                ProgressId::VerifyLooseObjectDbPath => *b"VISP",
                ProgressId::VerifyMultiIndex(_) => *b"VIMI",
                ProgressId::VerifyIndex(_) => *b"VISI",
            }
        }
    }
}

impl super::Store {
    /// Check the integrity of all objects as per the given `options`.
    ///
    /// Note that this will not not force loading all indices or packs permanently, as we will only use the momentarily loaded disk state.
    /// This does, however, include all alternates.
    pub fn verify_integrity<C, P, F>(
        &self,
        mut progress: P,
        should_interrupt: &AtomicBool,
        options: integrity::Options<F>,
    ) -> Result<integrity::Outcome<P>, integrity::Error>
    where
        P: Progress,
        C: pack::cache::DecodeEntry,
        F: Fn() -> C + Send + Clone,
    {
        let mut index = self.index.load();
        if !index.is_initialized() {
            self.consolidate_with_disk_state(true, false)?;
            index = self.index.load();
            assert!(
                index.is_initialized(),
                "BUG: after consolidating successfully, we have an initialized index"
            )
        }

        progress.init(
            Some(index.slot_indices.len()),
            git_features::progress::count("pack indices"),
        );
        let mut statistics = Vec::new();
        let index_check_message = |path: &std::path::Path| {
            format!(
                "Checking integrity: {}",
                path.file_name()
                    .map(|f| f.to_string_lossy())
                    .unwrap_or_else(std::borrow::Cow::default)
            )
        };
        for slot_index in &index.slot_indices {
            let slot = &self.files[*slot_index];
            if slot.generation.load(Ordering::SeqCst) != index.generation {
                return Err(integrity::Error::NeedsRetryDueToChangeOnDisk);
            }
            let files = slot.files.load();
            let files = Option::as_ref(&files).ok_or(integrity::Error::NeedsRetryDueToChangeOnDisk)?;

            let start = Instant::now();
            let (mut child_progress, num_objects, index_path) = match files {
                IndexAndPacks::Index(bundle) => {
                    let index;
                    let index = match bundle.index.loaded() {
                        Some(index) => index.deref(),
                        None => {
                            index = pack::index::File::at(bundle.index.path(), self.object_hash)?;
                            &index
                        }
                    };
                    let pack;
                    let data = match bundle.data.loaded() {
                        Some(pack) => pack.deref(),
                        None => {
                            pack = pack::data::File::at(bundle.data.path(), self.object_hash)?;
                            &pack
                        }
                    };
                    let outcome = index.verify_integrity(
                        Some(pack::index::verify::PackContext {
                            data,
                            options: options.clone(),
                        }),
                        progress.add_child_with_id(
                            "verify index",
                            integrity::ProgressId::VerifyIndex(Default::default()).into(),
                        ),
                        should_interrupt,
                    )?;
                    statistics.push(IndexStatistics {
                        path: bundle.index.path().to_owned(),
                        statistics: SingleOrMultiStatistics::Single(
                            outcome
                                .pack_traverse_statistics
                                .expect("pack provided so there are stats"),
                        ),
                    });
                    (outcome.progress, index.num_objects(), index.path().to_owned())
                }
                IndexAndPacks::MultiIndex(bundle) => {
                    let index;
                    let index = match bundle.multi_index.loaded() {
                        Some(index) => index.deref(),
                        None => {
                            index = pack::multi_index::File::at(bundle.multi_index.path())?;
                            &index
                        }
                    };
                    let outcome = index.verify_integrity(
                        progress.add_child_with_id(
                            "verify multi-index",
                            integrity::ProgressId::VerifyMultiIndex(Default::default()).into(),
                        ),
                        should_interrupt,
                        options.clone(),
                    )?;

                    let index_dir = bundle.multi_index.path().parent().expect("file in a directory");
                    statistics.push(IndexStatistics {
                        path: Default::default(),
                        statistics: SingleOrMultiStatistics::Multi(
                            outcome
                                .pack_traverse_statistics
                                .into_iter()
                                .zip(index.index_names())
                                .map(|(statistics, index_name)| (index_dir.join(index_name), statistics))
                                .collect(),
                        ),
                    });
                    (outcome.progress, index.num_objects(), index.path().to_owned())
                }
            };

            child_progress.set_name(index_check_message(&index_path));
            child_progress.show_throughput_with(
                start,
                num_objects as usize,
                git_features::progress::count("objects").expect("set"),
                MessageLevel::Success,
            );
            progress.inc();
        }

        progress.init(
            Some(index.loose_dbs.len()),
            git_features::progress::count("loose object stores"),
        );
        let mut loose_object_stores = Vec::new();
        for loose_db in &*index.loose_dbs {
            let out = loose_db
                .verify_integrity(
                    progress.add_child_with_id(
                        loose_db.path().display().to_string(),
                        integrity::ProgressId::VerifyLooseObjectDbPath.into(),
                    ),
                    should_interrupt,
                )
                .map(|statistics| integrity::LooseObjectStatistics {
                    path: loose_db.path().to_owned(),
                    statistics,
                })?;
            loose_object_stores.push(out);
        }

        Ok(integrity::Outcome {
            loose_object_stores,
            index_statistics: statistics,
            progress,
        })
    }
}