use crate::{
    autobatcher::BatchKind,
    task::{Details, Kind, KindWithContent, Status, Task},
    Error, IndexScheduler, Result, TaskId,
};
use index::apply_settings_to_builder;
use index::error::{IndexError, MilliError};
use index::{Settings, Unchecked};
use log::{debug, info};
use milli::documents::DocumentsBatchReader;
use milli::heed::{RoTxn, RwTxn};
use milli::update::IndexDocumentsConfig;
use milli::update::{DocumentAdditionResult, DocumentDeletionResult, IndexDocumentsMethod};
use uuid::Uuid;

pub(crate) enum Batch {
    Cancel(Task),
    Snapshot(Vec<Task>),
    Dump(Vec<Task>),
    IndexOperation(IndexOperation),
    IndexCreation {
        index_uid: String,
        primary_key: Option<String>,
        task: Task,
    },
    IndexUpdate {
        index_uid: String,
        primary_key: Option<String>,
        task: Task,
    },
    IndexDeletion {
        index_uid: String,
        tasks: Vec<Task>,
    },
}

pub(crate) enum IndexOperation {
    DocumentImport {
        index_uid: String,
        primary_key: Option<String>,
        method: IndexDocumentsMethod,
        content_files: Vec<Uuid>,
        tasks: Vec<Task>,
    },
    DocumentDeletion {
        index_uid: String,
        documents: Vec<String>,
        tasks: Vec<Task>,
    },
    DocumentClear {
        index_uid: String,
        tasks: Vec<Task>,
    },
    Settings {
        index_uid: String,
        // TODO what's that boolean, does it mean that it removes things or what?
        settings: Vec<(bool, Settings<Unchecked>)>,
        tasks: Vec<Task>,
    },
    DocumentClearAndSetting {
        index_uid: String,
        cleared_tasks: Vec<Task>,

        // TODO what's that boolean, does it mean that it removes things or what?
        settings: Vec<(bool, Settings<Unchecked>)>,
        settings_tasks: Vec<Task>,
    },
    SettingsAndDocumentImport {
        index_uid: String,

        primary_key: Option<String>,
        method: IndexDocumentsMethod,
        content_files: Vec<Uuid>,
        document_import_tasks: Vec<Task>,

        // TODO what's that boolean, does it mean that it removes things or what?
        settings: Vec<(bool, Settings<Unchecked>)>,
        settings_tasks: Vec<Task>,
    },
}

impl Batch {
    pub fn ids(&self) -> Vec<TaskId> {
        match self {
            Batch::Cancel(task)
            | Batch::IndexCreation { task, .. }
            | Batch::IndexUpdate { task, .. } => vec![task.uid],
            Batch::Snapshot(tasks) | Batch::Dump(tasks) | Batch::IndexDeletion { tasks, .. } => {
                tasks.iter().map(|task| task.uid).collect()
            }
            Batch::IndexOperation(operation) => match operation {
                IndexOperation::DocumentImport { tasks, .. }
                | IndexOperation::DocumentDeletion { tasks, .. }
                | IndexOperation::Settings { tasks, .. }
                | IndexOperation::DocumentClear { tasks, .. } => {
                    tasks.iter().map(|task| task.uid).collect()
                }
                IndexOperation::SettingsAndDocumentImport {
                    document_import_tasks: tasks,
                    settings_tasks: other,
                    ..
                }
                | IndexOperation::DocumentClearAndSetting {
                    cleared_tasks: tasks,
                    settings_tasks: other,
                    ..
                } => tasks.iter().chain(other).map(|task| task.uid).collect(),
            },
        }
    }
}

impl IndexScheduler {
    pub(crate) fn create_next_batch_index(
        &self,
        rtxn: &RoTxn,
        index_uid: String,
        batch: BatchKind,
    ) -> Result<Option<Batch>> {
        match batch {
            BatchKind::DocumentClear { ids } => {
                Ok(Some(Batch::IndexOperation(IndexOperation::DocumentClear {
                    tasks: self.get_existing_tasks(rtxn, ids)?,
                    index_uid,
                })))
            }
            BatchKind::DocumentImport { method, import_ids } => {
                let tasks = self.get_existing_tasks(rtxn, import_ids)?;
                let primary_key = match &tasks[0].kind {
                    KindWithContent::DocumentImport { primary_key, .. } => primary_key.clone(),
                    _ => unreachable!(),
                };
                let content_files = tasks
                    .iter()
                    .map(|task| match task.kind {
                        KindWithContent::DocumentImport { content_file, .. } => content_file,
                        _ => unreachable!(),
                    })
                    .collect();

                Ok(Some(Batch::IndexOperation(
                    IndexOperation::DocumentImport {
                        index_uid,
                        primary_key,
                        method,
                        content_files,
                        tasks,
                    },
                )))
            }
            BatchKind::DocumentDeletion { deletion_ids } => {
                let tasks = self.get_existing_tasks(rtxn, deletion_ids)?;

                let mut documents = Vec::new();
                for task in &tasks {
                    match task.kind {
                        KindWithContent::DocumentDeletion {
                            ref documents_ids, ..
                        } => documents.extend_from_slice(documents_ids),
                        _ => unreachable!(),
                    }
                }

                Ok(Some(Batch::IndexOperation(
                    IndexOperation::DocumentDeletion {
                        index_uid,
                        documents,
                        tasks,
                    },
                )))
            }
            BatchKind::Settings { settings_ids } => {
                let tasks = self.get_existing_tasks(rtxn, settings_ids)?;

                let mut settings = Vec::new();
                for task in &tasks {
                    match task.kind {
                        KindWithContent::Settings {
                            ref new_settings,
                            is_deletion,
                            ..
                        } => settings.push((is_deletion, new_settings.clone())),
                        _ => unreachable!(),
                    }
                }

                Ok(Some(Batch::IndexOperation(IndexOperation::Settings {
                    index_uid,
                    settings,
                    tasks,
                })))
            }
            BatchKind::ClearAndSettings {
                other,
                settings_ids,
            } => {
                let (index_uid, settings, settings_tasks) = match self
                    .create_next_batch_index(rtxn, index_uid, BatchKind::Settings { settings_ids })?
                    .unwrap()
                {
                    Batch::IndexOperation(IndexOperation::Settings {
                        index_uid,
                        settings,
                        tasks,
                    }) => (index_uid, settings, tasks),
                    _ => unreachable!(),
                };
                let (index_uid, cleared_tasks) = match self
                    .create_next_batch_index(
                        rtxn,
                        index_uid,
                        BatchKind::DocumentClear { ids: other },
                    )?
                    .unwrap()
                {
                    Batch::IndexOperation(IndexOperation::DocumentClear { index_uid, tasks }) => {
                        (index_uid, tasks)
                    }
                    _ => unreachable!(),
                };

                Ok(Some(Batch::IndexOperation(
                    IndexOperation::DocumentClearAndSetting {
                        index_uid,
                        cleared_tasks,
                        settings,
                        settings_tasks,
                    },
                )))
            }
            BatchKind::SettingsAndDocumentImport {
                settings_ids,
                method,
                import_ids,
            } => {
                let settings = self.create_next_batch_index(
                    rtxn,
                    index_uid.clone(),
                    BatchKind::Settings { settings_ids },
                )?;

                let document_import = self.create_next_batch_index(
                    rtxn,
                    index_uid.clone(),
                    BatchKind::DocumentImport { method, import_ids },
                )?;

                match (document_import, settings) {
                    (
                        Some(Batch::IndexOperation(IndexOperation::DocumentImport {
                            primary_key,
                            content_files,
                            tasks: document_import_tasks,
                            ..
                        })),
                        Some(Batch::IndexOperation(IndexOperation::Settings {
                            settings,
                            tasks: settings_tasks,
                            ..
                        })),
                    ) => Ok(Some(Batch::IndexOperation(
                        IndexOperation::SettingsAndDocumentImport {
                            index_uid,
                            primary_key,
                            method,
                            content_files,
                            document_import_tasks,
                            settings,
                            settings_tasks,
                        },
                    ))),
                    _ => unreachable!(),
                }
            }
            BatchKind::IndexCreation { id } => {
                let task = self.get_task(rtxn, id)?.ok_or(Error::CorruptedTaskQueue)?;
                let (index_uid, primary_key) = match &task.kind {
                    KindWithContent::IndexCreation {
                        index_uid,
                        primary_key,
                    } => (index_uid.clone(), primary_key.clone()),
                    _ => unreachable!(),
                };
                Ok(Some(Batch::IndexCreation {
                    index_uid,
                    primary_key,
                    task,
                }))
            }
            BatchKind::IndexUpdate { id } => {
                let task = self.get_task(rtxn, id)?.ok_or(Error::CorruptedTaskQueue)?;
                let primary_key = match &task.kind {
                    KindWithContent::IndexUpdate { primary_key, .. } => primary_key.clone(),
                    _ => unreachable!(),
                };
                Ok(Some(Batch::IndexUpdate {
                    index_uid,
                    primary_key,
                    task,
                }))
            }
            BatchKind::IndexDeletion { ids } => Ok(Some(Batch::IndexDeletion {
                index_uid,
                tasks: self.get_existing_tasks(rtxn, ids)?,
            })),
            BatchKind::IndexSwap { id: _ } => todo!(),
        }
    }

    /// Create the next batch to be processed;
    /// 1. We get the *last* task to cancel.
    /// 2. We get the *next* snapshot to process.
    /// 3. We get the *next* dump to process.
    /// 4. We get the *next* tasks to process for a specific index.
    pub(crate) fn create_next_batch(&self, rtxn: &RoTxn) -> Result<Option<Batch>> {
        let enqueued = &self.get_status(rtxn, Status::Enqueued)?;
        let to_cancel = self.get_kind(rtxn, Kind::CancelTask)? & enqueued;

        // 1. we get the last task to cancel.
        if let Some(task_id) = to_cancel.max() {
            return Ok(Some(Batch::Cancel(
                self.get_task(rtxn, task_id)?
                    .ok_or(Error::CorruptedTaskQueue)?,
            )));
        }

        // 2. we batch the snapshot.
        let to_snapshot = self.get_kind(rtxn, Kind::Snapshot)? & enqueued;
        if !to_snapshot.is_empty() {
            return Ok(Some(Batch::Snapshot(
                self.get_existing_tasks(rtxn, to_snapshot)?,
            )));
        }

        // 3. we batch the dumps.
        let to_dump = self.get_kind(rtxn, Kind::DumpExport)? & enqueued;
        if !to_dump.is_empty() {
            return Ok(Some(Batch::Dump(self.get_existing_tasks(rtxn, to_dump)?)));
        }

        // 4. We take the next task and try to batch all the tasks associated with this index.
        if let Some(task_id) = enqueued.min() {
            let task = self
                .get_task(rtxn, task_id)?
                .ok_or(Error::CorruptedTaskQueue)?;

            // This is safe because all the remaining task are associated with
            // AT LEAST one index. We can use the right or left one it doesn't
            // matter.
            let index_name = task.indexes().unwrap()[0];

            let _index = self.get_index(rtxn, index_name)? & enqueued;

            let enqueued = enqueued
                .into_iter()
                .map(|task_id| {
                    self.get_task(rtxn, task_id)
                        .and_then(|task| task.ok_or(Error::CorruptedTaskQueue))
                        .map(|task| (task.uid, task.kind.as_kind()))
                })
                .collect::<Result<Vec<_>>>()?;

            if let Some(batchkind) = crate::autobatcher::autobatch(enqueued) {
                return self.create_next_batch_index(rtxn, index_name.to_string(), batchkind);
            }
        }

        // If we found no tasks then we were notified for something that got autobatched
        // somehow and there is nothing to do.
        Ok(None)
    }

    pub(crate) fn process_batch(&self, batch: Batch) -> Result<Vec<Task>> {
        match batch {
            Batch::Cancel(_) => todo!(),
            Batch::Snapshot(_) => todo!(),
            Batch::Dump(_) => todo!(),
            Batch::IndexOperation(operation) => {
                let index = match operation {
                    IndexOperation::DocumentDeletion { ref index_uid, .. }
                    | IndexOperation::DocumentClear { ref index_uid, .. } => {
                        // only get the index, don't create it
                        let rtxn = self.env.read_txn()?;
                        self.index_mapper.index(&rtxn, index_uid)?
                    }
                    IndexOperation::DocumentImport { ref index_uid, .. }
                    | IndexOperation::Settings { ref index_uid, .. }
                    | IndexOperation::DocumentClearAndSetting { ref index_uid, .. }
                    | IndexOperation::SettingsAndDocumentImport { ref index_uid, .. } => {
                        // TODO check if the user was allowed to create an index.

                        // create the index if it doesn't already exist
                        let mut wtxn = self.env.write_txn()?;
                        let index = self.index_mapper.create_index(&mut wtxn, index_uid)?;
                        wtxn.commit()?;
                        index
                    }
                };

                let mut index_wtxn = index.write_txn()?;
                let tasks = self.apply_index_operation(&mut index_wtxn, &index, operation)?;
                index_wtxn.commit()?;

                Ok(tasks)
            }
            Batch::IndexCreation {
                index_uid,
                primary_key,
                task,
            } => todo!(),
            Batch::IndexUpdate {
                index_uid,
                primary_key,
                task,
            } => todo!(),
            Batch::IndexDeletion { index_uid, tasks } => todo!(),
        }
    }

    fn apply_index_operation<'txn, 'i>(
        &self,
        index_wtxn: &'txn mut RwTxn<'i, '_>,
        index: &'i milli::Index,
        operation: IndexOperation,
    ) -> Result<Vec<Task>> {
        match operation {
            IndexOperation::DocumentClear {
                index_uid,
                mut tasks,
            } => {
                let result = milli::update::ClearDocuments::new(index_wtxn, index).execute();
                for task in &mut tasks {
                    match result {
                        Ok(deleted_documents) => {
                            task.details = Some(Details::ClearAll {
                                deleted_documents: Some(deleted_documents),
                            })
                        }
                        Err(ref error) => task.error = Some(MilliError(error).into()),
                    }
                }

                Ok(tasks)
            }
            IndexOperation::DocumentImport {
                index_uid,
                primary_key,
                method,
                content_files,
                mut tasks,
            } => {
                let indexer_config = self.index_mapper.indexer_config();
                if let Some(primary_key) = primary_key {
                    if index.primary_key(index_wtxn)?.is_none() {
                        let mut builder =
                            milli::update::Settings::new(index_wtxn, index, indexer_config);
                        builder.set_primary_key(primary_key);
                        builder.execute(|_| ())?;
                    }
                }

                let config = IndexDocumentsConfig {
                    update_method: method,
                    ..Default::default()
                };

                let mut builder = milli::update::IndexDocuments::new(
                    index_wtxn,
                    index,
                    indexer_config,
                    config,
                    |indexing_step| debug!("update: {:?}", indexing_step),
                )?;

                let mut results = Vec::new();
                for content_uuid in content_files.into_iter() {
                    let content_file = self.file_store.get_update(content_uuid)?;
                    let reader = DocumentsBatchReader::from_reader(content_file)
                        .map_err(IndexError::from)?;
                    let (new_builder, user_result) = builder.add_documents(reader)?;
                    builder = new_builder;

                    let user_result = match user_result {
                        Ok(count) => {
                            let addition = DocumentAdditionResult {
                                indexed_documents: count,
                                number_of_documents: count,
                            };
                            Ok(addition)
                        }
                        Err(e) => Err(IndexError::from(e)),
                    };

                    results.push(user_result);
                }

                if results.iter().any(|res| res.is_ok()) {
                    let addition = builder.execute()?;
                    info!("document addition done: {:?}", addition);
                }

                for (task, ret) in tasks.iter_mut().zip(results) {
                    match ret {
                        Ok(DocumentAdditionResult {
                            indexed_documents,
                            number_of_documents,
                        }) => {
                            task.details = Some(Details::DocumentAddition {
                                received_documents: number_of_documents,
                                indexed_documents,
                            })
                        }
                        Err(error) => task.error = Some(error.into()),
                    }
                }

                Ok(tasks)
            }
            IndexOperation::DocumentDeletion {
                index_uid,
                documents,
                mut tasks,
            } => {
                let mut builder = milli::update::DeleteDocuments::new(index_wtxn, index)?;
                documents.iter().for_each(|id| {
                    builder.delete_external_id(id);
                });
                let result = builder.execute();

                for (task, documents) in tasks.iter_mut().zip(documents) {
                    match result {
                        Ok(DocumentDeletionResult {
                            deleted_documents,
                            remaining_documents: _,
                        }) => {
                            task.details = Some(Details::DocumentDeletion {
                                received_document_ids: documents.len(),
                                deleted_documents: Some(deleted_documents),
                            });
                        }
                        Err(ref error) => task.error = Some(MilliError(error).into()),
                    }
                }

                Ok(tasks)
            }
            IndexOperation::Settings {
                index_uid,
                settings,
                mut tasks,
            } => {
                let indexer_config = self.index_mapper.indexer_config();
                // TODO merge the settings to only do *one* reindexation.
                for (task, (_, settings)) in tasks.iter_mut().zip(settings) {
                    let checked_settings = settings.clone().check();
                    task.details = Some(Details::Settings { settings });

                    let mut builder =
                        milli::update::Settings::new(index_wtxn, index, indexer_config);
                    apply_settings_to_builder(&checked_settings, &mut builder);
                    let result = builder.execute(|indexing_step| {
                        debug!("update: {:?}", indexing_step);
                    });

                    if let Err(ref error) = result {
                        task.error = Some(MilliError(error).into());
                    }
                }

                Ok(tasks)
            }
            IndexOperation::SettingsAndDocumentImport {
                index_uid,
                primary_key,
                method,
                content_files,
                document_import_tasks,
                settings,
                settings_tasks,
            } => {
                let settings_tasks = self.apply_index_operation(
                    index_wtxn,
                    index,
                    IndexOperation::Settings {
                        index_uid: index_uid.clone(),
                        settings,
                        tasks: settings_tasks,
                    },
                )?;

                let mut import_tasks = self.apply_index_operation(
                    index_wtxn,
                    index,
                    IndexOperation::DocumentImport {
                        index_uid,
                        primary_key,
                        method,
                        content_files,
                        tasks: document_import_tasks,
                    },
                )?;

                let mut tasks = settings_tasks;
                tasks.append(&mut import_tasks);
                Ok(tasks)
            }
            IndexOperation::DocumentClearAndSetting {
                index_uid,
                cleared_tasks,
                settings,
                settings_tasks,
            } => {
                let mut import_tasks = self.apply_index_operation(
                    index_wtxn,
                    index,
                    IndexOperation::DocumentClear {
                        index_uid: index_uid.clone(),
                        tasks: cleared_tasks,
                    },
                )?;

                let settings_tasks = self.apply_index_operation(
                    index_wtxn,
                    index,
                    IndexOperation::Settings {
                        index_uid,
                        settings,
                        tasks: settings_tasks,
                    },
                )?;

                let mut tasks = settings_tasks;
                tasks.append(&mut import_tasks);
                Ok(tasks)
            }
        }
    }
}