// 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.

extern crate chrono;
extern crate enum_set;
extern crate ordered_float;
extern crate uuid;

#[macro_use]
extern crate lazy_static;

extern crate edn;

pub mod values;

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

use std::fmt;
use std::rc::Rc;

use enum_set::EnumSet;

use self::ordered_float::OrderedFloat;

pub use uuid::Uuid;

pub use chrono::{
    DateTime,
    Timelike,       // For truncation.
};

pub use edn::{
    FromMicros,
    NamespacedKeyword,
    ToMicros,
    Utc,
};

/// Core types defining a Mentat knowledge base.

/// Represents one entid in the entid space.
///
/// Per https://www.sqlite.org/datatype3.html (see also http://stackoverflow.com/a/8499544), SQLite
/// stores signed integers up to 64 bits in size.  Since u32 is not appropriate for our use case, we
/// use i64 rather than manually truncating u64 to u63 and casting to i64 throughout the codebase.
pub type Entid = i64;

/// An entid that's either already in the store, or newly allocated to a tempid.
/// TODO: we'd like to link this in some way to the lifetime of a particular PartitionMap.
#[derive(Clone, Copy, Debug, Hash, Eq, PartialEq, Ord, PartialOrd)]
pub struct KnownEntid(pub Entid);

impl From<KnownEntid> for Entid {
    fn from(k: KnownEntid) -> Entid {
        k.0
    }
}

impl From<KnownEntid> for TypedValue {
    fn from(k: KnownEntid) -> TypedValue {
        TypedValue::Ref(k.0)
    }
}

/// The attribute of each Mentat assertion has a :db/valueType constraining the value to a
/// particular set.  Mentat recognizes the following :db/valueType values.
#[derive(Clone, Copy, Debug, Eq, Hash, Ord, PartialOrd, PartialEq)]
#[repr(u32)]
pub enum ValueType {
    Ref,
    Boolean,
    Instant,
    Long,
    Double,
    String,
    Keyword,
    Uuid,
}

pub type ValueTypeTag = i32;

impl ValueType {
    pub fn all_enums() -> EnumSet<ValueType> {
        // TODO: lazy_static.
        let mut s = EnumSet::new();
        s.insert(ValueType::Ref);
        s.insert(ValueType::Boolean);
        s.insert(ValueType::Instant);
        s.insert(ValueType::Long);
        s.insert(ValueType::Double);
        s.insert(ValueType::String);
        s.insert(ValueType::Keyword);
        s.insert(ValueType::Uuid);
        s
    }
}


impl enum_set::CLike for ValueType {
    fn to_u32(&self) -> u32 {
        *self as u32
    }

    unsafe fn from_u32(v: u32) -> ValueType {
        std::mem::transmute(v)
    }
}

impl ValueType {
    pub fn into_keyword(self) -> NamespacedKeyword {
        NamespacedKeyword::new("db.type", match self {
            ValueType::Ref => "ref",
            ValueType::Boolean => "boolean",
            ValueType::Instant => "instant",
            ValueType::Long => "long",
            ValueType::Double => "double",
            ValueType::String => "string",
            ValueType::Keyword => "keyword",
            ValueType::Uuid => "uuid",
        })
    }

    pub fn into_typed_value(self) -> TypedValue {
        TypedValue::typed_ns_keyword("db.type", match self {
            ValueType::Ref => "ref",
            ValueType::Boolean => "boolean",
            ValueType::Instant => "instant",
            ValueType::Long => "long",
            ValueType::Double => "double",
            ValueType::String => "string",
            ValueType::Keyword => "keyword",
            ValueType::Uuid => "uuid",
        })
    }

    pub fn into_edn_value(self) -> edn::Value {
        match self {
            ValueType::Ref => values::DB_TYPE_REF.clone(),
            ValueType::Boolean => values::DB_TYPE_BOOLEAN.clone(),
            ValueType::Instant => values::DB_TYPE_INSTANT.clone(),
            ValueType::Long => values::DB_TYPE_LONG.clone(),
            ValueType::Double => values::DB_TYPE_DOUBLE.clone(),
            ValueType::String => values::DB_TYPE_STRING.clone(),
            ValueType::Keyword => values::DB_TYPE_KEYWORD.clone(),
            ValueType::Uuid => values::DB_TYPE_UUID.clone(),
        }
    }
}

impl fmt::Display for ValueType {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "{}", match *self {
            ValueType::Ref =>     ":db.type/ref",
            ValueType::Boolean => ":db.type/boolean",
            ValueType::Instant => ":db.type/instant",
            ValueType::Long =>    ":db.type/long",
            ValueType::Double =>  ":db.type/double",
            ValueType::String =>  ":db.type/string",
            ValueType::Keyword => ":db.type/keyword",
            ValueType::Uuid =>    ":db.type/uuid",
        })
    }
}

/// Represents a Mentat value in a particular value set.
// TODO: expand to include :db.type/{instant,url,uuid}.
// TODO: BigInt?
#[derive(Clone,Debug,Eq,Hash,Ord,PartialOrd,PartialEq)]
pub enum TypedValue {
    Ref(Entid),
    Boolean(bool),
    Long(i64),
    Double(OrderedFloat<f64>),
    Instant(DateTime<Utc>),               // Use `into()` to ensure truncation.
    // TODO: &str throughout?
    String(Rc<String>),
    Keyword(Rc<NamespacedKeyword>),
    Uuid(Uuid),                        // It's only 128 bits, so this should be acceptable to clone.
}

impl TypedValue {
    /// Returns true if the provided type is `Some` and matches this value's type, or if the
    /// provided type is `None`.
    #[inline]
    pub fn is_congruent_with<T: Into<Option<ValueType>>>(&self, t: T) -> bool {
        t.into().map_or(true, |x| self.matches_type(x))
    }

    #[inline]
    pub fn matches_type(&self, t: ValueType) -> bool {
        self.value_type() == t
    }

    pub fn value_type(&self) -> ValueType {
        match self {
            &TypedValue::Ref(_) => ValueType::Ref,
            &TypedValue::Boolean(_) => ValueType::Boolean,
            &TypedValue::Long(_) => ValueType::Long,
            &TypedValue::Instant(_) => ValueType::Instant,
            &TypedValue::Double(_) => ValueType::Double,
            &TypedValue::String(_) => ValueType::String,
            &TypedValue::Keyword(_) => ValueType::Keyword,
            &TypedValue::Uuid(_) => ValueType::Uuid,
        }
    }

    /// Construct a new `TypedValue::Keyword` instance by cloning the provided
    /// values and wrapping them in a new `Rc`. This is expensive, so this might
    /// be best limited to tests.
    pub fn typed_ns_keyword(ns: &str, name: &str) -> TypedValue {
        TypedValue::Keyword(Rc::new(NamespacedKeyword::new(ns, name)))
    }

    /// Construct a new `TypedValue::String` instance by cloning the provided
    /// value and wrapping it in a new `Rc`. This is expensive, so this might
    /// be best limited to tests.
    pub fn typed_string(s: &str) -> TypedValue {
        TypedValue::String(Rc::new(s.to_string()))
    }

    pub fn current_instant() -> TypedValue {
        Utc::now().into()
    }

    /// Construct a new `TypedValue::Instant` instance from the provided
    /// microsecond timestamp.
    pub fn instant(micros: i64) -> TypedValue {
        DateTime::<Utc>::from_micros(micros).into()
    }
}

trait MicrosecondPrecision {
    /// Truncate the provided `DateTime` to microsecond precision.
    fn microsecond_precision(self) -> Self;
}

impl MicrosecondPrecision for DateTime<Utc> {
    fn microsecond_precision(self) -> DateTime<Utc> {
        let nanoseconds = self.nanosecond();
        if nanoseconds % 1000 == 0 {
            return self;
        }
        let microseconds = nanoseconds / 1000;
        let truncated = microseconds * 1000;
        self.with_nanosecond(truncated).expect("valid timestamp")
    }
}

/// Return the current time as a UTC `DateTime` instance with microsecond precision.
pub fn now() -> DateTime<Utc> {
    Utc::now().microsecond_precision()
}

// We don't do From<i64> or From<Entid> 'cos it's ambiguous.

impl From<bool> for TypedValue {
    fn from(value: bool) -> TypedValue {
        TypedValue::Boolean(value)
    }
}

/// Truncate the provided `DateTime` to microsecond precision, and return the corresponding
/// `TypedValue::Instant`.
impl From<DateTime<Utc>> for TypedValue {
    fn from(value: DateTime<Utc>) -> TypedValue {
        TypedValue::Instant(value.microsecond_precision())
    }
}

impl From<Uuid> for TypedValue {
    fn from(value: Uuid) -> TypedValue {
        TypedValue::Uuid(value)
    }
}

impl From<String> for TypedValue {
    fn from(value: String) -> TypedValue {
        TypedValue::String(Rc::new(value))
    }
}

impl From<NamespacedKeyword> for TypedValue {
    fn from(value: NamespacedKeyword) -> TypedValue {
        TypedValue::Keyword(Rc::new(value))
    }
}

impl From<u32> for TypedValue {
    fn from(value: u32) -> TypedValue {
        TypedValue::Long(value as i64)
    }
}

impl From<i32> for TypedValue {
    fn from(value: i32) -> TypedValue {
        TypedValue::Long(value as i64)
    }
}

impl From<f64> for TypedValue {
    fn from(value: f64) -> TypedValue {
        TypedValue::Double(OrderedFloat(value))
    }
}

/// Type safe representation of the possible return values from SQLite's `typeof`
#[derive(Clone, Copy, Debug, Eq, Hash, Ord, PartialOrd, PartialEq)]
pub enum SQLTypeAffinity {
    Null,    // "null"
    Integer, // "integer"
    Real,    // "real"
    Text,    // "text"
    Blob,    // "blob"
}

// Put this here rather than in `db` simply because it's widely needed.
pub trait SQLValueType {
    fn value_type_tag(&self) -> ValueTypeTag;
    fn accommodates_integer(&self, int: i64) -> bool;

    /// Return a pair of the ValueTypeTag for this value type, and the SQLTypeAffinity required
    /// to distinguish it from any other types that share the same tag.
    ///
    /// Background: The tag alone is not enough to determine the type of a value, since multiple
    /// ValueTypes may share the same tag (for example, ValueType::Long and ValueType::Double).
    /// However, each ValueType can be determined by checking both the tag and the type's affinity.
    fn sql_representation(&self) -> (ValueTypeTag, Option<SQLTypeAffinity>);
}

impl SQLValueType for ValueType {
    fn sql_representation(&self) -> (ValueTypeTag, Option<SQLTypeAffinity>) {
        match *self {
            ValueType::Ref     => (0, None),
            ValueType::Boolean => (1, None),
            ValueType::Instant => (4, None),

            // SQLite distinguishes integral from decimal types, allowing long and double to share a tag.
            ValueType::Long    => (5, Some(SQLTypeAffinity::Integer)),
            ValueType::Double  => (5, Some(SQLTypeAffinity::Real)),
            ValueType::String  => (10, None),
            ValueType::Uuid    => (11, None),
            ValueType::Keyword => (13, None),
        }
    }

    #[inline]
    fn value_type_tag(&self) -> ValueTypeTag {
        self.sql_representation().0
    }

    /// Returns true if the provided integer is in the SQLite value space of this type. For
    /// example, `1` is how we encode `true`.
    ///
    /// ```
    /// use mentat_core::{ValueType, SQLValueType};
    /// assert!(!ValueType::Instant.accommodates_integer(1493399581314));
    /// assert!(!ValueType::Instant.accommodates_integer(1493399581314000));
    /// assert!(ValueType::Boolean.accommodates_integer(1));
    /// assert!(!ValueType::Boolean.accommodates_integer(-1));
    /// assert!(!ValueType::Boolean.accommodates_integer(10));
    /// assert!(!ValueType::String.accommodates_integer(10));
    /// ```
    fn accommodates_integer(&self, int: i64) -> bool {
        use ValueType::*;
        match *self {
            Instant                 => false,          // Always use #inst.
            Long | Double           => true,
            Ref                     => int >= 0,
            Boolean                 => (int == 0) || (int == 1),
            ValueType::String       => false,
            Keyword                 => false,
            Uuid                    => false,
        }
    }
}

trait EnumSetExtensions<T: enum_set::CLike + Clone> {
    /// Return a set containing both `x` and `y`.
    fn of_both(x: T, y: T) -> EnumSet<T>;

    /// Return a clone of `self` with `y` added.
    fn with(&self, y: T) -> EnumSet<T>;
}

impl<T: enum_set::CLike + Clone> EnumSetExtensions<T> for EnumSet<T> {
    /// Return a set containing both `x` and `y`.
    fn of_both(x: T, y: T) -> Self {
        let mut o = EnumSet::new();
        o.insert(x);
        o.insert(y);
        o
    }

    /// Return a clone of `self` with `y` added.
    fn with(&self, y: T) -> EnumSet<T> {
        let mut o = self.clone();
        o.insert(y);
        o
    }
}

#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub struct ValueTypeSet(pub EnumSet<ValueType>);

impl Default for ValueTypeSet {
    fn default() -> ValueTypeSet {
        ValueTypeSet::any()
    }
}

impl ValueTypeSet {
    pub fn any() -> ValueTypeSet {
        ValueTypeSet(ValueType::all_enums())
    }

    pub fn none() -> ValueTypeSet {
        ValueTypeSet(EnumSet::new())
    }

    /// Return a set containing only `t`.
    pub fn of_one(t: ValueType) -> ValueTypeSet {
        let mut s = EnumSet::new();
        s.insert(t);
        ValueTypeSet(s)
    }

    /// Return a set containing `Double` and `Long`.
    pub fn of_numeric_types() -> ValueTypeSet {
        ValueTypeSet(EnumSet::of_both(ValueType::Double, ValueType::Long))
    }

    /// Return a set containing `Ref` and `Keyword`.
    pub fn of_keywords() -> ValueTypeSet {
        ValueTypeSet(EnumSet::of_both(ValueType::Ref, ValueType::Keyword))
    }

    /// Return a set containing `Ref` and `Long`.
    pub fn of_longs() -> ValueTypeSet {
        ValueTypeSet(EnumSet::of_both(ValueType::Ref, ValueType::Long))
    }
}

impl ValueTypeSet {
    pub fn insert(&mut self, vt: ValueType) -> bool {
        self.0.insert(vt)
    }

    pub fn len(&self) -> usize {
        self.0.len()
    }

    /// Returns a set containing all the types in this set and `other`.
    pub fn union(&self, other: &ValueTypeSet) -> ValueTypeSet {
        ValueTypeSet(self.0.union(other.0))
    }

    pub fn intersection(&self, other: &ValueTypeSet) -> ValueTypeSet {
        ValueTypeSet(self.0.intersection(other.0))
    }

    /// Returns the set difference between `self` and `other`, which is the
    /// set of items in `self` that are not in `other`.
    pub fn difference(&self, other: &ValueTypeSet) -> ValueTypeSet {
        ValueTypeSet(self.0 - other.0)
    }

    /// Return an arbitrary type that's part of this set.
    /// For a set containing a single type, this will be that type.
    pub fn exemplar(&self) -> Option<ValueType> {
        self.0.iter().next()
    }

    pub fn is_subset(&self, other: &ValueTypeSet) -> bool {
        self.0.is_subset(&other.0)
    }

    /// Returns true if `self` and `other` contain no items in common.
    pub fn is_disjoint(&self, other: &ValueTypeSet) -> bool {
        self.0.is_disjoint(&other.0)
    }

    pub fn contains(&self, vt: ValueType) -> bool {
        self.0.contains(&vt)
    }

    pub fn is_empty(&self) -> bool {
        self.0.is_empty()
    }

    pub fn is_unit(&self) -> bool {
        self.0.len() == 1
    }

    pub fn iter(&self) -> ::enum_set::Iter<ValueType> {
        self.0.iter()
    }
}

impl IntoIterator for ValueTypeSet {
    type Item = ValueType;
    type IntoIter = ::enum_set::Iter<ValueType>;

    fn into_iter(self) -> Self::IntoIter {
        self.0.into_iter()
    }
}

impl ::std::iter::FromIterator<ValueType> for ValueTypeSet {
    fn from_iter<I: IntoIterator<Item = ValueType>>(iterator: I) -> Self {
        let mut ret = Self::none();
        ret.0.extend(iterator);
        ret
    }
}

impl ::std::iter::Extend<ValueType> for ValueTypeSet {
    fn extend<I: IntoIterator<Item = ValueType>>(&mut self, iter: I) {
        for element in iter {
            self.0.insert(element);
        }
    }
}

pub trait SQLValueTypeSet {
    fn value_type_tags(&self) -> BTreeSet<ValueTypeTag>;
    fn has_unique_type_code(&self) -> bool;
    fn unique_type_code(&self) -> Option<ValueTypeTag>;
}

impl SQLValueTypeSet for ValueTypeSet {
    // This is inefficient, but it'll do for now.
    fn value_type_tags(&self) -> BTreeSet<ValueTypeTag> {
        let mut out = BTreeSet::new();
        for t in self.0.iter() {
            out.insert(t.value_type_tag());
        }
        out
    }

    fn unique_type_code(&self) -> Option<ValueTypeTag> {
        if self.is_unit() || self.has_unique_type_code() {
            self.exemplar().map(|t| t.value_type_tag())
        } else {
            None
        }
    }

    fn has_unique_type_code(&self) -> bool {
        if self.is_unit() {
            return true;
        }

        let mut acc = BTreeSet::new();
        for t in self.0.iter() {
            if acc.insert(t.value_type_tag()) && acc.len() > 1 {
                // We inserted a second or subsequent value.
                return false;
            }
        }
        !acc.is_empty()
    }
}

#[test]
fn test_typed_value() {
    assert!(TypedValue::Boolean(false).is_congruent_with(None));
    assert!(TypedValue::Boolean(false).is_congruent_with(ValueType::Boolean));
    assert!(!TypedValue::typed_string("foo").is_congruent_with(ValueType::Boolean));
    assert!(TypedValue::typed_string("foo").is_congruent_with(ValueType::String));
    assert!(TypedValue::typed_string("foo").is_congruent_with(None));
}

/// Bit flags used in `flags0` column in temporary tables created during search,
/// such as the `search_results`, `inexact_searches` and `exact_searches` tables.
/// When moving to a more concrete table, such as `datoms`, they are expanded out
/// via these flags and put into their own column rather than a bit field.
pub enum AttributeBitFlags {
    IndexAVET     = 1 << 0,
    IndexVAET     = 1 << 1,
    IndexFulltext = 1 << 2,
    UniqueValue   = 1 << 3,
}

pub mod attribute {
    use TypedValue;

    #[derive(Clone, Copy, Debug, Eq, Hash, Ord, PartialOrd, PartialEq)]
    pub enum Unique {
        Value,
        Identity,
    }

    impl Unique {
        // This is easier than rejigging DB_UNIQUE_VALUE to not be EDN.
        pub fn into_typed_value(self) -> TypedValue {
            match self {
                Unique::Value => TypedValue::typed_ns_keyword("db.unique", "value"),
                Unique::Identity => TypedValue::typed_ns_keyword("db.unique", "identity"),
            }
        }
    }
}

/// A Mentat schema attribute has a value type and several other flags determining how assertions
/// with the attribute are interpreted.
///
/// TODO: consider packing this into a bitfield or similar.
#[derive(Clone,Debug,Eq,Hash,Ord,PartialOrd,PartialEq)]
pub struct Attribute {
    /// The associated value type, i.e., `:db/valueType`?
    pub value_type: ValueType,

    /// `true` if this attribute is multi-valued, i.e., it is `:db/cardinality
    /// :db.cardinality/many`.  `false` if this attribute is single-valued (the default), i.e., it
    /// is `:db/cardinality :db.cardinality/one`.
    pub multival: bool,

    /// `None` if this attribute is neither unique-value nor unique-identity.
    ///
    /// `Some(attribute::Unique::Value)` if this attribute is unique-value, i.e., it is `:db/unique
    /// :db.unique/value`.
    ///
    /// *Unique-value* means that there is at most one assertion with the attribute and a
    /// particular value in the datom store.  Unique-value attributes can be used in lookup-refs.
    ///
    /// `Some(attribute::Unique::Identity)` if this attribute is unique-identity, i.e., it is `:db/unique
    /// :db.unique/identity`.
    ///
    /// Unique-identity attributes always have value type `Ref`.
    ///
    /// *Unique-identity* means that the attribute is *unique-value* and that they can be used in
    /// lookup-refs and will automatically upsert where appropriate.
    pub unique: Option<attribute::Unique>,

    /// `true` if this attribute is automatically indexed, i.e., it is `:db/indexing true`.
    pub index: bool,

    /// `true` if this attribute is automatically fulltext indexed, i.e., it is `:db/fulltext true`.
    ///
    /// Fulltext attributes always have string values.
    pub fulltext: bool,

    /// `true` if this attribute is a component, i.e., it is `:db/isComponent true`.
    ///
    /// Component attributes always have value type `Ref`.
    ///
    /// They are used to compose entities from component sub-entities: they are fetched recursively
    /// by pull expressions, and they are automatically recursively deleted where appropriate.
    pub component: bool,
}

impl Attribute {
    /// Combine several attribute flags into a bitfield used in temporary search tables.
    pub fn flags(&self) -> u8 {
        let mut flags: u8 = 0;

        if self.index {
            flags |= AttributeBitFlags::IndexAVET as u8;
        }
        if self.value_type == ValueType::Ref {
            flags |= AttributeBitFlags::IndexVAET as u8;
        }
        if self.fulltext {
            flags |= AttributeBitFlags::IndexFulltext as u8;
        }
        if self.unique.is_some() {
            flags |= AttributeBitFlags::UniqueValue as u8;
        }
        flags
    }

    pub fn to_edn_value(&self, ident: Option<NamespacedKeyword>) -> edn::Value {
        let mut attribute_map: BTreeMap<edn::Value, edn::Value> = BTreeMap::default();
        if let Some(ident) = ident {
            attribute_map.insert(values::DB_IDENT.clone(), edn::Value::NamespacedKeyword(ident));
        }

        attribute_map.insert(values::DB_VALUE_TYPE.clone(), self.value_type.into_edn_value());

        attribute_map.insert(values::DB_CARDINALITY.clone(), if self.multival { values::DB_CARDINALITY_MANY.clone() } else { values::DB_CARDINALITY_ONE.clone() });

        match self.unique {
            Some(attribute::Unique::Value) => { attribute_map.insert(values::DB_UNIQUE.clone(), values::DB_UNIQUE_VALUE.clone()); },
            Some(attribute::Unique::Identity) => { attribute_map.insert(values::DB_UNIQUE.clone(), values::DB_UNIQUE_IDENTITY.clone()); },
            None => (),
        }

        if self.index {
            attribute_map.insert(values::DB_INDEX.clone(), edn::Value::Boolean(true));
        }

        if self.fulltext {
            attribute_map.insert(values::DB_FULLTEXT.clone(), edn::Value::Boolean(true));
        }

        if self.component {
            attribute_map.insert(values::DB_IS_COMPONENT.clone(), edn::Value::Boolean(true));
        }

        edn::Value::Map(attribute_map)
    }
}

impl Default for Attribute {
    fn default() -> Attribute {
        Attribute {
            // There's no particular reason to favour one value type, so Ref it is.
            value_type: ValueType::Ref,
            fulltext: false,
            index: false,
            multival: false,
            unique: None,
            component: false,
        }
    }
}

/// Map `NamespacedKeyword` idents (`:db/ident`) to positive integer entids (`1`).
pub type IdentMap = BTreeMap<NamespacedKeyword, Entid>;

/// Map positive integer entids (`1`) to `NamespacedKeyword` idents (`:db/ident`).
pub type EntidMap = BTreeMap<Entid, NamespacedKeyword>;

/// Map attribute entids to `Attribute` instances.
pub type AttributeMap = BTreeMap<Entid, Attribute>;

/// Represents a Mentat schema.
///
/// Maintains the mapping between string idents and positive integer entids; and exposes the schema
/// flags associated to a given entid (equivalently, ident).
///
/// TODO: consider a single bi-directional map instead of separate ident->entid and entid->ident
/// maps.
#[derive(Clone, Debug, Default, Eq, Hash, Ord, PartialOrd, PartialEq)]
pub struct Schema {
    /// Map entid->ident.
    ///
    /// Invariant: is the inverse map of `ident_map`.
    pub entid_map: EntidMap,

    /// Map ident->entid.
    ///
    /// Invariant: is the inverse map of `entid_map`.
    pub ident_map: IdentMap,

    /// Map entid->attribute flags.
    ///
    /// Invariant: key-set is the same as the key-set of `entid_map` (equivalently, the value-set of
    /// `ident_map`).
    pub attribute_map: AttributeMap,
}

pub trait HasSchema {
    fn entid_for_type(&self, t: ValueType) -> Option<KnownEntid>;

    fn get_ident<T>(&self, x: T) -> Option<&NamespacedKeyword> where T: Into<Entid>;
    fn get_entid(&self, x: &NamespacedKeyword) -> Option<KnownEntid>;
    fn attribute_for_entid<T>(&self, x: T) -> Option<&Attribute> where T: Into<Entid>;

    // Returns the attribute and the entid named by the provided ident.
    fn attribute_for_ident(&self, ident: &NamespacedKeyword) -> Option<(&Attribute, KnownEntid)>;

    /// Return true if the provided entid identifies an attribute in this schema.
    fn is_attribute<T>(&self, x: T) -> bool where T: Into<Entid>;

    /// Return true if the provided ident identifies an attribute in this schema.
    fn identifies_attribute(&self, x: &NamespacedKeyword) -> bool;
}

impl Schema {
    /// Returns an symbolic representation of the schema suitable for applying across Mentat stores.
    pub fn to_edn_value(&self) -> edn::Value {
        edn::Value::Vector((&self.attribute_map).iter()
            .map(|(entid, attribute)|
                attribute.to_edn_value(self.get_ident(*entid).cloned()))
            .collect())
    }

    fn get_raw_entid(&self, x: &NamespacedKeyword) -> Option<Entid> {
        self.ident_map.get(x).map(|x| *x)
    }
}

impl HasSchema for Schema {
    fn entid_for_type(&self, t: ValueType) -> Option<KnownEntid> {
        // TODO: this can be made more efficient.
        self.get_entid(&t.into_keyword())
    }

    fn get_ident<T>(&self, x: T) -> Option<&NamespacedKeyword> where T: Into<Entid> {
        self.entid_map.get(&x.into())
    }

    fn get_entid(&self, x: &NamespacedKeyword) -> Option<KnownEntid> {
        self.get_raw_entid(x).map(KnownEntid)
    }

    fn attribute_for_entid<T>(&self, x: T) -> Option<&Attribute> where T: Into<Entid> {
        self.attribute_map.get(&x.into())
    }

    fn attribute_for_ident(&self, ident: &NamespacedKeyword) -> Option<(&Attribute, KnownEntid)> {
        self.get_raw_entid(&ident)
            .and_then(|entid| {
                self.attribute_for_entid(entid).map(|a| (a, KnownEntid(entid)))
            })
    }

    /// Return true if the provided entid identifies an attribute in this schema.
    fn is_attribute<T>(&self, x: T) -> bool where T: Into<Entid> {
        self.attribute_map.contains_key(&x.into())
    }

    /// Return true if the provided ident identifies an attribute in this schema.
    fn identifies_attribute(&self, x: &NamespacedKeyword) -> bool {
        self.get_raw_entid(x).map(|e| self.is_attribute(e)).unwrap_or(false)
    }
}

#[cfg(test)]
mod test {
    use super::*;

    use std::str::FromStr;

    fn associate_ident(schema: &mut Schema, i: NamespacedKeyword, e: Entid) {
        schema.entid_map.insert(e, i.clone());
        schema.ident_map.insert(i, e);
    }

    fn add_attribute(schema: &mut Schema, e: Entid, a: Attribute) {
        schema.attribute_map.insert(e, a);
    }

    #[test]
    fn test_attribute_flags() {
        let attr1 = Attribute {
            index: true,
            value_type: ValueType::Ref,
            fulltext: false,
            unique: None,
            multival: false,
            component: false,
        };

        assert!(attr1.flags() & AttributeBitFlags::IndexAVET as u8 != 0);
        assert!(attr1.flags() & AttributeBitFlags::IndexVAET as u8 != 0);
        assert!(attr1.flags() & AttributeBitFlags::IndexFulltext as u8 == 0);
        assert!(attr1.flags() & AttributeBitFlags::UniqueValue as u8 == 0);

        let attr2 = Attribute {
            index: false,
            value_type: ValueType::Boolean,
            fulltext: true,
            unique: Some(attribute::Unique::Value),
            multival: false,
            component: false,
        };

        assert!(attr2.flags() & AttributeBitFlags::IndexAVET as u8 == 0);
        assert!(attr2.flags() & AttributeBitFlags::IndexVAET as u8 == 0);
        assert!(attr2.flags() & AttributeBitFlags::IndexFulltext as u8 != 0);
        assert!(attr2.flags() & AttributeBitFlags::UniqueValue as u8 != 0);

        let attr3 = Attribute {
            index: false,
            value_type: ValueType::Boolean,
            fulltext: true,
            unique: Some(attribute::Unique::Identity),
            multival: false,
            component: false,
        };

        assert!(attr3.flags() & AttributeBitFlags::IndexAVET as u8 == 0);
        assert!(attr3.flags() & AttributeBitFlags::IndexVAET as u8 == 0);
        assert!(attr3.flags() & AttributeBitFlags::IndexFulltext as u8 != 0);
        assert!(attr3.flags() & AttributeBitFlags::UniqueValue as u8 != 0);
    }

    #[test]
    fn test_datetime_truncation() {
        let dt: DateTime<Utc> = DateTime::from_str("2018-01-11T00:34:09.273457004Z").expect("parsed");
        let expected: DateTime<Utc> = DateTime::from_str("2018-01-11T00:34:09.273457Z").expect("parsed");

        let tv: TypedValue = dt.into();
        if let TypedValue::Instant(roundtripped) = tv {
            assert_eq!(roundtripped, expected);
        } else {
            panic!();
        }
    }

    #[test]
    fn test_as_edn_value() {
        let mut schema = Schema::default();

        let attr1 = Attribute {
            index: true,
            value_type: ValueType::Ref,
            fulltext: false,
            unique: None,
            multival: false,
            component: false,
        };
        associate_ident(&mut schema, NamespacedKeyword::new("foo", "bar"), 97);
        add_attribute(&mut schema, 97, attr1);

        let attr2 = Attribute {
            index: false,
            value_type: ValueType::String,
            fulltext: true,
            unique: Some(attribute::Unique::Value),
            multival: true,
            component: false,
        };
        associate_ident(&mut schema, NamespacedKeyword::new("foo", "bas"), 98);
        add_attribute(&mut schema, 98, attr2);

        let attr3 = Attribute {
            index: false,
            value_type: ValueType::Boolean,
            fulltext: false,
            unique: Some(attribute::Unique::Identity),
            multival: false,
            component: true,
        };

        associate_ident(&mut schema, NamespacedKeyword::new("foo", "bat"), 99);
        add_attribute(&mut schema, 99, attr3);

        let value = schema.to_edn_value();

        let expected_output = r#"[ {   :db/ident     :foo/bar
    :db/valueType :db.type/ref
    :db/cardinality :db.cardinality/one
    :db/index true },
{   :db/ident     :foo/bas
    :db/valueType :db.type/string
    :db/cardinality :db.cardinality/many
    :db/unique :db.unique/value
    :db/fulltext true },
{   :db/ident     :foo/bat
    :db/valueType :db.type/boolean
    :db/cardinality :db.cardinality/one
    :db/unique :db.unique/identity
    :db/component true }, ]"#;
        let expected_value = edn::parse::value(&expected_output).expect("to be able to parse").without_spans();
        assert_eq!(expected_value, value);

        // let's compare the whole thing again, just to make sure we are not changing anything when we convert to edn.
        let value2 = schema.to_edn_value();
        assert_eq!(expected_value, value2);
    }
}

pub mod intern_set;
pub mod counter;
pub mod util;