// Copyright 2016 Mozilla
//
// Licensed under the Apache License, Version 2.0 (the "License"); you may not use
// this file except in compliance with the License. You may obtain a copy of the
// License at http://www.apache.org/licenses/LICENSE-2.0
// Unless required by applicable law or agreed to in writing, software distributed
// under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR
// CONDITIONS OF ANY KIND, either express or implied. See the License for the
// specific language governing permissions and limitations under the License.

#![allow(dead_code)]

//! Most transactions can mutate the Mentat metadata by transacting assertions:
//!
//! - they can add (and, eventually, retract and alter) recognized idents using the `:db/ident`
//!   attribute;
//!
//! - they can add (and, eventually, retract and alter) schema attributes using various `:db/*`
//!   attributes;
//!
//! - eventually, they will be able to add (and possibly retract) entid partitions using a Mentat
//!   equivalent (perhaps :db/partition or :db.partition/start) to Datomic's `:db.install/partition`
//!   attribute.
//!
//! This module recognizes, validates, applies, and reports on these mutations.

use std::collections::{BTreeMap, BTreeSet};
use std::collections::btree_map::Entry;

use add_retract_alter_set::{
    AddRetractAlterSet,
};
use edn::symbols;
use entids;
use errors::{
    ErrorKind,
    Result,
    ResultExt,
};
use mentat_core::{
    attribute,
    Entid,
    Schema,
    AttributeMap,
    TypedValue,
    ValueType,
};

use schema::{
    AttributeBuilder,
    AttributeValidation,
};

/// An alteration to an attribute.
#[derive(Clone, Debug, Eq, Hash, Ord, PartialOrd, PartialEq)]
pub enum AttributeAlteration {
    /// From http://blog.datomic.com/2014/01/schema-alteration.html:
    /// - rename attributes
    /// - rename your own programmatic identities (uses of :db/ident)
    /// - add or remove indexes
    Index,
    /// - add or remove uniqueness constraints
    Unique,
    /// - change attribute cardinality
    Cardinality,
    /// - change whether history is retained for an attribute
    NoHistory,
    /// - change whether an attribute is treated as a component
    IsComponent,
}

/// An alteration to an ident.
#[derive(Clone, Debug, Eq, Hash, Ord, PartialOrd, PartialEq)]
pub enum IdentAlteration {
    Ident(symbols::NamespacedKeyword),
}

/// Summarizes changes to metadata such as a a `Schema` and (in the future) a `PartitionMap`.
#[derive(Clone, Debug, Eq, Hash, Ord, PartialOrd, PartialEq)]
pub struct MetadataReport {
    // Entids that were not present in the original `AttributeMap` that was mutated.
    pub attributes_installed: BTreeSet<Entid>,

    // Entids that were present in the original `AttributeMap` that was mutated, together with a
    // representation of the mutations that were applied.
    pub attributes_altered: BTreeMap<Entid, Vec<AttributeAlteration>>,

    // Idents that were installed into the `AttributeMap`.
    pub idents_altered: BTreeMap<Entid, IdentAlteration>,
}

impl MetadataReport {
    pub fn attributes_did_change(&self) -> bool {
        !(self.attributes_installed.is_empty() &&
          self.attributes_altered.is_empty())
    }
}

/// Update a `AttributeMap` in place from the given `[e a typed_value]` triples.
///
/// This is suitable for producing a `AttributeMap` from the `schema` materialized view, which does not
/// contain install and alter markers.
///
/// Returns a report summarizing the mutations that were applied.
pub fn update_attribute_map_from_entid_triples<A, R>(attribute_map: &mut AttributeMap, assertions: A, retractions: R) -> Result<MetadataReport>
    where A: IntoIterator<Item=(Entid, Entid, TypedValue)>,
          R: IntoIterator<Item=(Entid, Entid, TypedValue)> {

    fn attribute_builder_to_modify(attribute_id: Entid, existing: &AttributeMap) -> AttributeBuilder {
        existing.get(&attribute_id)
                .map(AttributeBuilder::to_modify_attribute)
                .unwrap_or_else(AttributeBuilder::default)
    }

    // Group mutations by impacted entid.
    let mut builders: BTreeMap<Entid, AttributeBuilder> = BTreeMap::new();

    // For retractions, we start with an attribute builder that's pre-populated with the existing
    // attribute values. That allows us to check existing values and unset them.
    for (entid, attr, ref value) in retractions.into_iter() {
        let builder = builders.entry(entid).or_insert_with(|| attribute_builder_to_modify(entid, attribute_map));
        match attr {
            // You can only retract :db/unique, :db/doc, :db/isComponent; all others
            // must be altered instead of retracted, or are not allowed to change.
            entids::DB_DOC => {
                // Nothing to do here; we don't keep docstrings inside `Attribute`s.
            },
            entids::DB_IS_COMPONENT => {
                match value {
                    &TypedValue::Boolean(v) if builder.component == Some(v) => {
                        builder.component(false);
                    },
                    v => {
                        bail!(ErrorKind::BadSchemaAssertion(format!("Attempted to retract :db/isComponent with the wrong value {:?}.", v)));
                    },
                }
            },
            entids::DB_UNIQUE => {
                match *value {
                    TypedValue::Ref(u) => {
                        match u {
                            entids::DB_UNIQUE_VALUE if builder.unique == Some(Some(attribute::Unique::Value)) => {
                                builder.non_unique();
                            },
                            entids::DB_UNIQUE_IDENTITY if builder.unique == Some(Some(attribute::Unique::Identity)) => {
                                builder.non_unique();
                            },
                            v => {
                                bail!(ErrorKind::BadSchemaAssertion(format!("Attempted to retract :db/unique with the wrong value {}.", v)));
                            },
                        }
                    },
                    _ => bail!(ErrorKind::BadSchemaAssertion(format!("Expected [:db/retract _ :db/unique :db.unique/_] but got [:db/retract {} :db/unique {:?}]", entid, value)))
                }
            },
            _ => {
                bail!(ErrorKind::BadSchemaAssertion(format!("Retracting attribute {} for entity {} not permitted.", attr, entid)));
            },
        }
    }

    for (entid, attr, ref value) in assertions.into_iter() {
        // For assertions, we can start with an empty attribute builder.
        let builder = builders.entry(entid).or_insert_with(Default::default);

        // TODO: improve error messages throughout.
        match attr {
            entids::DB_DOC => {
                match *value {
                    TypedValue::String(_) => {},
                    _ => bail!(ErrorKind::BadSchemaAssertion(format!("Expected [... :db/doc \"string value\"] but got [... :db/doc {:?}] for entid {} and attribute {}", value, entid, attr)))
                }
            },

            entids::DB_VALUE_TYPE => {
                match *value {
                    TypedValue::Ref(entids::DB_TYPE_BOOLEAN) => { builder.value_type(ValueType::Boolean); },
                    TypedValue::Ref(entids::DB_TYPE_DOUBLE)  => { builder.value_type(ValueType::Double); },
                    TypedValue::Ref(entids::DB_TYPE_INSTANT) => { builder.value_type(ValueType::Instant); },
                    TypedValue::Ref(entids::DB_TYPE_KEYWORD) => { builder.value_type(ValueType::Keyword); },
                    TypedValue::Ref(entids::DB_TYPE_LONG)    => { builder.value_type(ValueType::Long); },
                    TypedValue::Ref(entids::DB_TYPE_REF)     => { builder.value_type(ValueType::Ref); },
                    TypedValue::Ref(entids::DB_TYPE_STRING)  => { builder.value_type(ValueType::String); },
                    TypedValue::Ref(entids::DB_TYPE_UUID)    => { builder.value_type(ValueType::Uuid); },
                    _ => bail!(ErrorKind::BadSchemaAssertion(format!("Expected [... :db/valueType :db.type/*] but got [... :db/valueType {:?}] for entid {} and attribute {}", value, entid, attr)))
                }
            },

            entids::DB_CARDINALITY => {
                match *value {
                    TypedValue::Ref(entids::DB_CARDINALITY_MANY) => { builder.multival(true); },
                    TypedValue::Ref(entids::DB_CARDINALITY_ONE) => { builder.multival(false); },
                    _ => bail!(ErrorKind::BadSchemaAssertion(format!("Expected [... :db/cardinality :db.cardinality/many|:db.cardinality/one] but got [... :db/cardinality {:?}]", value)))
                }
            },

            entids::DB_UNIQUE => {
                match *value {
                    TypedValue::Ref(entids::DB_UNIQUE_VALUE) => { builder.unique(attribute::Unique::Value); },
                    TypedValue::Ref(entids::DB_UNIQUE_IDENTITY) => { builder.unique(attribute::Unique::Identity); },
                    _ => bail!(ErrorKind::BadSchemaAssertion(format!("Expected [... :db/unique :db.unique/value|:db.unique/identity] but got [... :db/unique {:?}]", value)))
                }
            },

            entids::DB_INDEX => {
                match *value {
                    TypedValue::Boolean(x) => { builder.index(x); },
                    _ => bail!(ErrorKind::BadSchemaAssertion(format!("Expected [... :db/index true|false] but got [... :db/index {:?}]", value)))
                }
            },

            entids::DB_FULLTEXT => {
                match *value {
                    TypedValue::Boolean(x) => { builder.fulltext(x); },
                    _ => bail!(ErrorKind::BadSchemaAssertion(format!("Expected [... :db/fulltext true|false] but got [... :db/fulltext {:?}]", value)))
                }
            },

            entids::DB_IS_COMPONENT => {
                match *value {
                    TypedValue::Boolean(x) => { builder.component(x); },
                    _ => bail!(ErrorKind::BadSchemaAssertion(format!("Expected [... :db/isComponent true|false] but got [... :db/isComponent {:?}]", value)))
                }
            },

            entids::DB_NO_HISTORY => {
                match *value {
                    TypedValue::Boolean(x) => { builder.no_history(x); },
                    _ => bail!(ErrorKind::BadSchemaAssertion(format!("Expected [... :db/noHistory true|false] but got [... :db/noHistory {:?}]", value)))
                }
            },

            _ => {
                bail!(ErrorKind::BadSchemaAssertion(format!("Do not recognize attribute {} for entid {}", attr, entid)))
            }
        }
    };

    let mut attributes_installed: BTreeSet<Entid> = BTreeSet::default();
    let mut attributes_altered: BTreeMap<Entid, Vec<AttributeAlteration>> = BTreeMap::default();

    for (entid, builder) in builders.into_iter() {
        match attribute_map.entry(entid) {
            Entry::Vacant(entry) => {
                // Validate once…
                builder.validate_install_attribute()
                       .chain_err(|| ErrorKind::BadSchemaAssertion(format!("Schema alteration for new attribute with entid {} is not valid", entid)))?;

                // … and twice, now we have the Attribute.
                let a = builder.build();
                a.validate(|| entid.to_string())?;
                entry.insert(builder.build());
                attributes_installed.insert(entid);
            },

            Entry::Occupied(mut entry) => {
                builder.validate_alter_attribute()
                       .chain_err(|| ErrorKind::BadSchemaAssertion(format!("Schema alteration for existing attribute with entid {} is not valid", entid)))?;
                let mutations = builder.mutate(entry.get_mut());
                attributes_altered.insert(entid, mutations);
            },
        }
    }

    Ok(MetadataReport {
        attributes_installed: attributes_installed,
        attributes_altered: attributes_altered,
        idents_altered: BTreeMap::default(),
    })
}

/// Update a `Schema` in place from the given `[e a typed_value added]` quadruples.
///
/// This layer enforces that ident assertions of the form [entid :db/ident ...] (as distinct from
/// attribute assertions) are present and correct.
///
/// This is suitable for mutating a `Schema` from an applied transaction.
///
/// Returns a report summarizing the mutations that were applied.
pub fn update_schema_from_entid_quadruples<U>(schema: &mut Schema, assertions: U) -> Result<MetadataReport>
    where U: IntoIterator<Item=(Entid, Entid, TypedValue, bool)> {

    // Group attribute assertions into asserted, retracted, and updated.  We assume all our
    // attribute assertions are :db/cardinality :db.cardinality/one (so they'll only be added or
    // retracted at most once), which means all attribute alterations are simple changes from an old
    // value to a new value.
    let mut attribute_set: AddRetractAlterSet<(Entid, Entid), TypedValue> = AddRetractAlterSet::default();
    let mut ident_set: AddRetractAlterSet<Entid, symbols::NamespacedKeyword> = AddRetractAlterSet::default();

    for (e, a, typed_value, added) in assertions.into_iter() {
        // Here we handle :db/ident assertions.
        if a == entids::DB_IDENT {
            if let TypedValue::Keyword(ref keyword) = typed_value {
                ident_set.witness(e, keyword.as_ref().clone(), added);
                continue
            } else {
                // Something is terribly wrong: the schema ensures we have a keyword.
                unreachable!();
            }
        }

        attribute_set.witness((e, a), typed_value, added);
    }

    // Collect triples.
    let retracted_triples = attribute_set.retracted.into_iter().map(|((e, a), typed_value)| (e, a, typed_value));
    let asserted_triples = attribute_set.asserted.into_iter().map(|((e, a), typed_value)| (e, a, typed_value));
    let altered_triples = attribute_set.altered.into_iter().map(|((e, a), (_old_value, new_value))| (e, a, new_value));

    let report = update_attribute_map_from_entid_triples(&mut schema.attribute_map,
                                                         asserted_triples.chain(altered_triples),
                                                         retracted_triples)?;

    let mut idents_altered: BTreeMap<Entid, IdentAlteration> = BTreeMap::new();

    // Asserted, altered, or retracted :db/idents update the relevant entids.
    for (entid, ident) in ident_set.asserted {
        schema.entid_map.insert(entid, ident.clone());
        schema.ident_map.insert(ident.clone(), entid);
        idents_altered.insert(entid, IdentAlteration::Ident(ident.clone()));
    }

    for (entid, (old_ident, new_ident)) in ident_set.altered {
        schema.entid_map.insert(entid, new_ident.clone()); // Overwrite existing.
        schema.ident_map.remove(&old_ident); // Remove old.
        schema.ident_map.insert(new_ident.clone(), entid); // Insert new.
        idents_altered.insert(entid, IdentAlteration::Ident(new_ident.clone()));
    }

    for (entid, ident) in ident_set.retracted {
        schema.entid_map.remove(&entid);
        schema.ident_map.remove(&ident);
        idents_altered.insert(entid, IdentAlteration::Ident(ident.clone()));
    }

    if report.attributes_did_change() {
        schema.update_component_attributes();
    }

    Ok(MetadataReport {
        idents_altered: idents_altered,
        .. report
    })
}