//! Traits dealing with Postgres data types

use std::collections::HashMap;
use std::error;
use std::fmt;
use std::io::prelude::*;
use std::sync::Arc;
use byteorder::{ReadBytesExt, WriteBytesExt, BigEndian};

pub use self::slice::Slice;
use {Result, SessionInfoNew, InnerConnection, OtherNew, WrongTypeNew, FieldNew};
use error::Error;
use util;

/// Generates a simple implementation of `ToSql::accepts` which accepts the
/// types passed to it.
#[macro_export]
macro_rules! accepts {
    ($($expected:pat),+) => (
        fn accepts(ty: &$crate::types::Type) -> bool {
            match *ty {
                $($expected)|+ => true,
                _ => false
            }
        }
    )
}

/// Generates an implementation of `ToSql::to_sql_checked`.
///
/// All `ToSql` implementations should use this macro.
#[macro_export]
macro_rules! to_sql_checked {
    () => {
        fn to_sql_checked(&self,
                          ty: &$crate::types::Type,
                          out: &mut ::std::io::Write,
                          ctx: &$crate::types::SessionInfo)
                          -> $crate::Result<$crate::types::IsNull> {
            $crate::types::__to_sql_checked(self, ty, out, ctx)
        }
    }
}

// WARNING: this function is not considered part of this crate's public API.
// It is subject to change at any time.
#[doc(hidden)]
pub fn __to_sql_checked<T>(v: &T, ty: &Type, out: &mut Write, ctx: &SessionInfo) -> Result<IsNull>
    where T: ToSql
{
    if !T::accepts(ty) {
        return Err(Error::Conversion(Box::new(WrongType(ty.clone()))));
    }
    v.to_sql(ty, out, ctx)
}

#[cfg(feature = "bit-vec")]
mod bit_vec;
#[cfg(feature = "uuid")]
mod uuid;
#[cfg(feature = "time")]
mod time;
mod slice;
#[cfg(feature = "rustc-serialize")]
mod rustc_serialize;
#[cfg(feature = "serde_json")]
mod serde_json;
#[cfg(feature = "chrono")]
mod chrono;
#[cfg(feature = "eui48")]
mod eui48;

/// A structure providing information for conversion methods.
pub struct SessionInfo<'a> {
    conn: &'a InnerConnection,
}

impl<'a> SessionInfoNew<'a> for SessionInfo<'a> {
    fn new(conn: &'a InnerConnection) -> SessionInfo<'a> {
        SessionInfo { conn: conn }
    }
}

impl<'a> SessionInfo<'a> {
    /// Returns the value of the specified Postgres backend parameter, such
    /// as `timezone` or `server_version`.
    pub fn parameter(&self, param: &str) -> Option<&'a str> {
        self.conn.parameters.get(param).map(|s| &**s)
    }
}

impl<'a> fmt::Debug for SessionInfo<'a> {
    fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
        fmt.debug_struct("SessionInfo")
           .field("parameters", &self.conn.parameters)
           .finish()
    }
}

/// A Postgres OID.
pub type Oid = u32;

/// Represents the kind of a Postgres type.
#[derive(Debug, Clone, PartialEq, Eq)]
pub enum Kind {
    /// A simple type like `VARCHAR` or `INTEGER`.
    Simple,
    /// An enumerated type along with its variants.
    Enum(Vec<String>),
    /// A pseudo-type.
    Pseudo,
    /// An array type along with the type of its elements.
    Array(Type),
    /// A range type along with the type of its elements.
    Range(Type),
    /// A domain type along with its underlying type.
    Domain(Type),
    /// A composite type along with information about its fields.
    Composite(Vec<Field>),
    #[doc(hidden)]
    __PseudoPrivateForExtensibility,
}

/// Information about a field of a composite type.
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct Field {
    name: String,
    type_: Type,
}

impl Field {
    /// Returns the name of the field.
    pub fn name(&self) -> &str {
        &self.name
    }

    /// Returns the type of the field.
    pub fn type_(&self) -> &Type {
        &self.type_
    }
}

impl FieldNew for Field {
    fn new(name: String, type_: Type) -> Field {
        Field {
            name: name,
            type_: type_,
        }
    }
}

macro_rules! as_pat {
    ($p:pat) => ($p)
}

macro_rules! as_expr {
    ($e:expr) => ($e)
}

macro_rules! make_postgres_type {
    ($(#[$doc:meta] $oid:tt: $name:expr => $variant:ident: $kind:expr),+) => (
        /// A Postgres type.
        #[derive(PartialEq, Eq, Clone)]
        pub enum Type {
            $(
                #[$doc]
                $variant,
            )+
            /// An unknown type.
            Other(Other),
        }

        impl fmt::Debug for Type {
            fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
                let s = match *self {
                    $(Type::$variant => stringify!($variant),)+
                    Type::Other(ref u) => return fmt::Debug::fmt(u, fmt),
                };
                fmt.write_str(s)
            }
        }

        impl fmt::Display for Type {
            fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
                match self.schema() {
                    "public" | "pg_catalog" => {}
                    schema => try!(write!(fmt, "{}.", schema)),
                }
                fmt.write_str(self.name())
            }
        }

        impl Type {
            /// Returns the `Type` corresponding to the provided `Oid` if it
            /// corresponds to a built-in type.
            pub fn from_oid(oid: Oid) -> Option<Type> {
                match oid {
                    $(as_pat!($oid) => Some(Type::$variant),)+
                    _ => None
                }
            }

            /// Returns the OID of the `Type`.
            pub fn oid(&self) -> Oid {
                match *self {
                    $(Type::$variant => as_expr!($oid),)+
                    Type::Other(ref u) => u.oid(),
                }
            }

            /// Returns the kind of this type.
            pub fn kind(&self) -> &Kind {
                match *self {
                    $(
                        Type::$variant => {
                            const V: &'static Kind = &$kind;
                            V
                        }
                    )+
                    Type::Other(ref u) => u.kind(),
                }
            }

            /// Returns the schema of this type.
            pub fn schema(&self) -> &str {
                match *self {
                    Type::Other(ref u) => u.schema(),
                    _ => "pg_catalog",
                }
            }

            /// Returns the name of this type.
            pub fn name(&self) -> &str {
                match *self {
                    $(
                        Type::$variant => $name,
                    )+
                    Type::Other(ref u) => u.name(),
                }
            }
        }
    )
}

// Values from pg_type.h
make_postgres_type! {
    /// BOOL - boolean, 'true'/'false'
    16: "bool" => Bool: Kind::Simple,
    /// BYTEA - variable-length string, binary values escaped
    17: "bytea" => Bytea: Kind::Simple,
    /// "char" - single character
    18: "char" => Char: Kind::Simple,
    /// NAME - 63-byte type for storing system identifiers
    19: "name" => Name: Kind::Simple,
    /// INT8/BIGINT - ~18 digit integer, 8-byte storage
    20: "int8" => Int8: Kind::Simple,
    /// INT2/SMALLINT - -32 thousand to 32 thousand, 2-byte storage
    21: "int2" => Int2: Kind::Simple,
    /// INT2VECTOR - array of int2, used in system tables
    22: "int2vector" => Int2Vector: Kind::Array(Type::Int2),
    /// INT4/INT - -2 billion to 2 billion integer, 4-byte storage
    23: "int4" => Int4: Kind::Simple,
    /// REGPROC - registered procedure
    24: "regproc" => Regproc: Kind::Simple,
    /// TEXT - variable-length string, no limit specified
    25: "text" => Text: Kind::Simple,
    /// OID - object identifier(oid), maximum 4 billion
    26: "oid" => Oid: Kind::Simple,
    /// TID - (block, offset), physical location of tuple
    27: "tid" => Tid: Kind::Simple,
    /// XID - transaction id
    28: "xid" => Xid: Kind::Simple,
    /// CID - command identifier type, sequence in transaction id
    29: "cid" => Cid: Kind::Simple,
    /// OIDVECTOR - array of oids, used in system tables
    30: "oidvector" => OidVector: Kind::Array(Type::Oid),
    /// PG_TYPE
    71: "pg_type" => PgType: Kind::Simple,
    /// PG_ATTRIBUTE
    75: "pg_attribute" => PgAttribute: Kind::Simple,
    /// PG_PROC
    81: "pg_proc" => PgProc: Kind::Simple,
    /// PG_CLASS
    83: "pg_class" => PgClass: Kind::Simple,
    /// JSON
    114: "json" => Json: Kind::Simple,
    /// XML - XML content
    142: "xml" => Xml: Kind::Simple,
    /// XML[]
    143: "_xml" => XmlArray: Kind::Array(Type::Xml),
    /// PG_NODE_TREE - string representing an internal node tree
    194: "pg_node_tree" => PgNodeTree: Kind::Simple,
    /// JSON[]
    199: "_json" => JsonArray: Kind::Array(Type::Json),
    /// SMGR - storage manager
    210: "smgr" => Smgr: Kind::Simple,
    /// POINT - geometric point '(x, y)'
    600: "point" => Point: Kind::Simple,
    /// LSEG - geometric line segment '(pt1,pt2)'
    601: "lseg" => Lseg: Kind::Simple,
    /// PATH - geometric path '(pt1,...)'
    602: "path" => Path: Kind::Simple,
    /// BOX - geometric box '(lower left,upper right)'
    603: "box" => Box: Kind::Simple,
    /// POLYGON - geometric polygon '(pt1,...)'
    604: "polygon" => Polygon: Kind::Simple,
    /// LINE - geometric line
    628: "line" => Line: Kind::Simple,
    /// LINE[]
    629: "_line" => LineArray: Kind::Array(Type::Line),
    /// CIDR - network IP address/netmask, network address
    650: "cidr" => Cidr: Kind::Simple,
    /// CIDR[]
    651: "_cidr" => CidrArray: Kind::Array(Type::Cidr),
    /// FLOAT4/REAL - single-precision floating point number, 4-byte storage
    700: "float4" => Float4: Kind::Simple,
    /// FLOAT8/DOUBLE PRECISION - double-precision floating point number, 8-byte storage
    701: "float8" => Float8: Kind::Simple,
    /// ABSTIME - absolute, limited-range date and time (Unix system time)
    702: "abstime" => Abstime: Kind::Simple,
    /// RELTIME - relative, limited-range date and time (Unix delta time)
    703: "reltime" => Reltime: Kind::Simple,
    /// TINTERVAL - (abstime,abstime), time interval
    704: "tinterval" => Tinterval: Kind::Simple,
    /// UNKNOWN
    705: "unknown" => Unknown: Kind::Simple,
    /// CIRCLE - geometric circle '(center,radius)'
    718: "circle" => Circle: Kind::Simple,
    /// CIRCLE[]
    719: "_circle" => CircleArray: Kind::Array(Type::Circle),
    /// MONEY - monetary amounts, $d,ddd.cc
    790: "money" => Money: Kind::Simple,
    /// MONEY[]
    791: "_money" => MoneyArray: Kind::Array(Type::Money),
    /// MACADDR - XX:XX:XX:XX:XX:XX, MAC address
    829: "macaddr" => Macaddr: Kind::Simple,
    /// INET - IP address/netmask, host address, netmask optional
    869: "inet" => Inet: Kind::Simple,
    /// BOOL[]
    1000: "_bool" => BoolArray: Kind::Array(Type::Bool),
    /// BYTEA[]
    1001: "_bytea" => ByteaArray: Kind::Array(Type::Bytea),
    /// "char"[]
    1002: "_char" => CharArray: Kind::Array(Type::Char),
    /// NAME[]
    1003: "_name" => NameArray: Kind::Array(Type::Name),
    /// INT2[]
    1005: "_int2" => Int2Array: Kind::Array(Type::Int2),
    /// INT2VECTOR[]
    1006: "_int2vector" => Int2VectorArray: Kind::Array(Type::Int2Vector),
    /// INT4[]
    1007: "_int4" => Int4Array: Kind::Array(Type::Int4),
    /// REGPROC[]
    1008: "_regproc" => RegprocArray: Kind::Array(Type::Regproc),
    /// TEXT[]
    1009: "_text" => TextArray: Kind::Array(Type::Text),
    /// TID[]
    1010: "_tid" => TidArray: Kind::Array(Type::Tid),
    /// XID[]
    1011: "_xid" => XidArray: Kind::Array(Type::Xid),
    /// CID[]
    1012: "_cid" => CidArray: Kind::Array(Type::Cid),
    /// OIDVECTOR[]
    1013: "_oidvector" => OidVectorArray: Kind::Array(Type::OidVector),
    /// BPCHAR[]
    1014: "_bpchar" => BpcharArray: Kind::Array(Type::Bpchar),
    /// VARCHAR[]
    1015: "_varchar" => VarcharArray: Kind::Array(Type::Varchar),
    /// INT8[]
    1016: "_int8" => Int8Array: Kind::Array(Type::Int8),
    /// POINT[]
    1017: "_point" => PointArray: Kind::Array(Type::Point),
    /// LSEG[]
    1018: "_lseg" => LsegArray: Kind::Array(Type::Lseg),
    /// PATH[]
    1019: "_path" => PathArray: Kind::Array(Type::Path),
    /// BOX[]
    1020: "_box" => BoxArray: Kind::Array(Type::Box),
    /// FLOAT4[]
    1021: "_float4" => Float4Array: Kind::Array(Type::Float4),
    /// FLOAT8[]
    1022: "_float8" => Float8Array: Kind::Array(Type::Float8),
    /// ABSTIME[]
    1023: "_abstime" => AbstimeArray: Kind::Array(Type::Abstime),
    /// RELTIME[]
    1024: "_reltime" => ReltimeArray: Kind::Array(Type::Reltime),
    /// TINTERVAL[]
    1025: "_tinterval" => TintervalArray: Kind::Array(Type::Tinterval),
    /// POLYGON[]
    1027: "_polygon" => PolygonArray: Kind::Array(Type::Polygon),
    /// OID[]
    1028: "_oid" => OidArray: Kind::Array(Type::Oid),
    /// ACLITEM - access control list
    1033: "aclitem" => Aclitem: Kind::Simple,
    /// ACLITEM[]
    1034: "_aclitem" => AclitemArray: Kind::Array(Type::Aclitem),
    /// MACADDR[]
    1040: "_macaddr" => MacaddrArray: Kind::Array(Type::Macaddr),
    /// INET[]
    1041: "_inet" => InetArray: Kind::Array(Type::Inet),
    /// BPCHAR - char(length), blank-padded string, fixed storage length
    1042: "bpchar" => Bpchar: Kind::Simple,
    /// VARCHAR - varchar(length), non-blank-padded string, variable storage length
    1043: "varchar" => Varchar: Kind::Simple,
    /// DATE - date
    1082: "date" => Date: Kind::Simple,
    /// TIME - time of day
    1083: "time" => Time: Kind::Simple,
    /// TIMESTAMP - date and time
    1114: "timestamp" => Timestamp: Kind::Simple,
    /// TIMESTAMP[]
    1115: "_timestamp" => TimestampArray: Kind::Array(Type::Timestamp),
    /// DATE[]
    1182: "_date" => DateArray: Kind::Array(Type::Date),
    /// TIME[]
    1183: "_time" => TimeArray: Kind::Array(Type::Time),
    /// TIMESTAMPTZ - date and time with time zone
    1184: "timestamptz" => TimestampTZ: Kind::Simple,
    /// TIMESTAMPTZ[]
    1185: "_timestamptz" => TimestampTZArray: Kind::Array(Type::TimestampTZ),
    /// INTERVAL - @ &lt;number&gt; &lt;units&gt;, time interval
    1186: "interval" => Interval: Kind::Simple,
    /// INTERVAL[]
    1187: "_interval" => IntervalArray: Kind::Array(Type::Interval),
    /// NUMERIC[]
    1231: "_numeric" => NumericArray: Kind::Array(Type::Numeric),
    /// CSTRING[]
    1263: "_cstring" => CstringArray: Kind::Array(Type::Cstring),
    /// TIMETZ - time of day with time zone
    1266: "timetz" => Timetz: Kind::Simple,
    /// TIMETZ[]
    1270: "_timetz" => TimetzArray: Kind::Array(Type::Timetz),
    /// BIT - fixed-length bit string
    1560: "bit" => Bit: Kind::Simple,
    /// BIT[]
    1561: "_bit" => BitArray: Kind::Array(Type::Bit),
    /// VARBIT - variable-length bit string
    1562: "varbit" => Varbit: Kind::Simple,
    /// VARBIT[]
    1563: "_varbit" => VarbitArray: Kind::Array(Type::Varbit),
    /// NUMERIC - numeric(precision, decimal), arbitrary precision number
    1700: "numeric" => Numeric: Kind::Simple,
    /// REFCURSOR - reference to cursor (portal name)
    1790: "refcursor" => Refcursor: Kind::Simple,
    /// REFCURSOR[]
    2201: "_refcursor" => RefcursorArray: Kind::Array(Type::Refcursor),
    /// REGPROCEDURE - registered procedure (with args)
    2202: "regprocedure" => Regprocedure: Kind::Simple,
    /// REGOPER - registered operator
    2203: "regoper" => Regoper: Kind::Simple,
    /// REGOPERATOR - registered operator (with args)
    2204: "regoperator" => Regoperator: Kind::Simple,
    /// REGCLASS - registered class
    2205: "regclass" => Regclass: Kind::Simple,
    /// REGTYPE - registered type
    2206: "regtype" => Regtype: Kind::Simple,
    /// REGPROCEDURE[]
    2207: "_regprocedure" => RegprocedureArray: Kind::Array(Type::Regprocedure),
    /// REGOPER[]
    2208: "_regoper" => RegoperArray: Kind::Array(Type::Regoper),
    /// REGOPERATOR[]
    2209: "_regoperator" => RegoperatorArray: Kind::Array(Type::Regoperator),
    /// REGCLASS[]
    2210: "_regclass" => RegclassArray: Kind::Array(Type::Regclass),
    /// REGTYPE[]
    2211: "_regtype" => RegtypeArray: Kind::Array(Type::Regtype),
    /// RECORD
    2249: "record" => Record: Kind::Pseudo,
    /// CSTRING
    2275: "cstring" => Cstring: Kind::Pseudo,
    /// ANY
    2276: "any" => Any: Kind::Pseudo,
    /// ANYARRAY
    2277: "anyarray" => AnyArray: Kind::Pseudo,
    /// VOID
    2278: "void" => Void: Kind::Pseudo,
    /// TRIGGER
    2279: "trigger" => Trigger: Kind::Pseudo,
    /// LANGUAGE_HANDLER
    2280: "language_handler" => LanguageHandler: Kind::Pseudo,
    /// INTERNAL
    2281: "internal" => Internal: Kind::Pseudo,
    /// OPAQUE
    2282: "opaque" => Opaque: Kind::Pseudo,
    /// ANYELEMENT
    2283: "anyelement" => Anyelement: Kind::Pseudo,
    /// RECORD[]
    2287: "_record" => RecordArray: Kind::Pseudo,
    /// ANYNONARRAY
    2776: "anynonarray" => Anynonarray: Kind::Pseudo,
    /// TXID_SNAPSHOT[]
    2949: "_txid_snapshot" => TxidSnapshotArray: Kind::Array(Type::TxidSnapshot),
    /// UUID - UUID datatype
    2950: "uuid" => Uuid: Kind::Simple,
    /// TXID_SNAPSHOT - txid snapshot
    2970: "txid_snapshot" => TxidSnapshot: Kind::Simple,
    /// UUID[]
    2951: "_uuid" => UuidArray: Kind::Array(Type::Uuid),
    /// FDW_HANDLER
    3115: "fdw_handler" => FdwHandler: Kind::Pseudo,
    /// PG_LSN - PostgreSQL LSN datatype
    3220: "pg_lsn" => PgLsn: Kind::Simple,
    /// PG_LSN[]
    3221: "_pg_lsn" => PgLsnArray: Kind::Array(Type::PgLsn),
    /// ANYENUM
    3500: "anyenum" => Anyenum: Kind::Pseudo,
    /// TSVECTOR - text representation for text search
    3614: "tsvector" => Tsvector: Kind::Simple,
    /// TSQUERY - query representation for text search
    3615: "tsquery" => Tsquery: Kind::Simple,
    /// GTSVECTOR - GiST index internal text representation for text search
    3642: "gtsvector" => Gtsvector: Kind::Simple,
    /// TSVECTOR[]
    3643: "_tsvector" => TsvectorArray: Kind::Array(Type::Tsvector),
    /// GTSVECTOR[]
    3644: "_gtsvector" => GtsvectorArray: Kind::Array(Type::Gtsvector),
    /// TSQUERY[]
    3645: "_tsquery" => TsqueryArray: Kind::Array(Type::Tsquery),
    /// REGCONFIG - registered text search configuration
    3734: "regconfig" => Regconfig: Kind::Simple,
    /// REGCONFIG[]
    3735: "_regconfig" => RegconfigArray: Kind::Array(Type::Regconfig),
    /// REGDICTIONARY - registered text search dictionary
    3769: "regdictionary" => Regdictionary: Kind::Simple,
    /// REGDICTIONARY[]
    3770: "_regdictionary" => RegdictionaryArray: Kind::Array(Type::Regdictionary),
    /// JSONB
    3802: "jsonb" => Jsonb: Kind::Simple,
    /// ANYRANGE
    3831: "anyrange" => Anyrange: Kind::Pseudo,
    /// JSONB[]
    3807: "_jsonb" => JsonbArray: Kind::Array(Type::Jsonb),
    /// INT4RANGE - range of integers
    3904: "int4range" => Int4Range: Kind::Range(Type::Int4),
    /// INT4RANGE[]
    3905: "_int4range" => Int4RangeArray: Kind::Array(Type::Int4Range),
    /// NUMRANGE - range of numerics
    3906: "numrange" => NumRange: Kind::Range(Type::Numeric),
    /// NUMRANGE[]
    3907: "_numrange" => NumRangeArray: Kind::Array(Type::NumRange),
    /// TSRANGE - range of timestamps without time zone
    3908: "tsrange" => TsRange: Kind::Range(Type::Timestamp),
    /// TSRANGE[]
    3909: "_tsrange" => TsRangeArray: Kind::Array(Type::TsRange),
    /// TSTZRANGE - range of timestamps with time zone
    3910: "tstzrange" => TstzRange: Kind::Range(Type::TimestampTZ),
    /// TSTZRANGE[]
    3911: "_tstzrange" => TstzRangeArray: Kind::Array(Type::TstzRange),
    /// DATERANGE - range of dates
    3912: "daterange" => DateRange: Kind::Range(Type::Date),
    /// DATERANGE[]
    3913: "_daterange" => DateRangeArray: Kind::Array(Type::DateRange),
    /// INT8RANGE - range of bigints
    3926: "int8range" => Int8Range: Kind::Range(Type::Int8),
    /// INT8RANGE[]
    3927: "_int8range" => Int8RangeArray: Kind::Array(Type::Int8Range),
    /// EVENT_TRIGGER
    3838: "event_trigger" => EventTrigger: Kind::Pseudo
}

/// Information about an unknown type.
#[derive(PartialEq, Eq, Clone)]
pub struct Other(Arc<OtherInner>);

impl fmt::Debug for Other {
    fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
        fmt.debug_struct("Other")
           .field("name", &self.0.name)
           .field("oid", &self.0.oid)
           .field("kind", &self.0.kind)
           .field("schema", &self.0.schema)
           .finish()
    }
}

#[derive(PartialEq, Eq)]
struct OtherInner {
    name: String,
    oid: Oid,
    kind: Kind,
    schema: String,
}

impl OtherNew for Other {
    fn new(name: String, oid: Oid, kind: Kind, schema: String) -> Other {
        Other(Arc::new(OtherInner {
            name: name,
            oid: oid,
            kind: kind,
            schema: schema,
        }))
    }
}

impl Other {
    /// The name of the type.
    pub fn name(&self) -> &str {
        &self.0.name
    }

    /// The OID of this type.
    pub fn oid(&self) -> Oid {
        self.0.oid
    }

    /// The kind of this type.
    pub fn kind(&self) -> &Kind {
        &self.0.kind
    }

    /// The schema of this type.
    pub fn schema(&self) -> &str {
        &self.0.schema
    }
}

/// An error indicating that a `NULL` Postgres value was passed to a `FromSql`
/// implementation that does not support `NULL` values.
#[derive(Debug, Clone, Copy)]
pub struct WasNull;

impl fmt::Display for WasNull {
    fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
        fmt.write_str(error::Error::description(self))
    }
}

impl error::Error for WasNull {
    fn description(&self) -> &str {
        "a Postgres value was `NULL`"
    }
}

/// An error indicating that a conversion was attempted between incompatible
/// Rust and Postgres types.
#[derive(Debug)]
pub struct WrongType(Type);

impl fmt::Display for WrongType {
    fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
        write!(fmt,
               "cannot convert to or from a Postgres value of type `{}`",
               self.0)
    }
}

impl error::Error for WrongType {
    fn description(&self) -> &str {
        "cannot convert to or from a Postgres value"
    }
}

impl WrongTypeNew for WrongType {
    fn new(ty: Type) -> WrongType {
        WrongType(ty)
    }
}

/// A trait for types that can be created from a Postgres value.
///
/// # Types
///
/// The following implementations are provided by this crate, along with the
/// corresponding Postgres types:
///
/// | Rust type                                   | Postgres type(s)               |
/// |---------------------------------------------|--------------------------------|
/// | bool                                        | BOOL                           |
/// | i8                                          | "char"                         |
/// | i16                                         | SMALLINT, SMALLSERIAL          |
/// | i32                                         | INT, SERIAL                    |
/// | u32                                         | OID                            |
/// | i64                                         | BIGINT, BIGSERIAL              |
/// | f32                                         | REAL                           |
/// | f64                                         | DOUBLE PRECISION               |
/// | String                                      | VARCHAR, CHAR(n), TEXT, CITEXT |
/// | Vec&lt;u8&gt;                               | BYTEA                          |
/// | HashMap&lt;String, Option&lt;String&gt;&gt; | HSTORE                         |
///
/// In addition, some implementations are provided for types in third party
/// crates. These are disabled by default; to opt into one of these
/// implementations, activate the Cargo feature corresponding to the crate's
/// name. For example, the `serde_json` feature enables the implementation for
/// the `serde_json::Value` type.
///
/// | Rust type                           | Postgres type(s)                    |
/// |-------------------------------------|-------------------------------------|
/// | serialize::json::Json               | JSON, JSONB                         |
/// | serde_json::Value                   | JSON, JSONB                         |
/// | time::Timespec                      | TIMESTAMP, TIMESTAMP WITH TIME ZONE |
/// | chrono::NaiveDateTime               | TIMESTAMP                           |
/// | chrono::DateTime&lt;UTC&gt;         | TIMESTAMP WITH TIME ZONE            |
/// | chrono::DateTime&lt;Local&gt;       | TIMESTAMP WITH TIME ZONE            |
/// | chrono::DateTime&lt;FixedOffset&gt; | TIMESTAMP WITH TIME ZONE            |
/// | chrono::NaiveDate                   | DATE                                |
/// | chrono::NaiveTime                   | TIME                                |
/// | eui48::MacAddress                   | MACADDR                             |
/// | uuid::Uuid                          | UUID                                |
/// | bit_vec::BitVec                     | BIT, VARBIT                         |
///
/// # Nullability
///
/// In addition to the types listed above, `FromSql` is implemented for
/// `Option<T>` where `T` implements `FromSql`. An `Option<T>` represents a
/// nullable Postgres value.
pub trait FromSql: Sized {
    /// Creates a new value of this type from a `Read`er of the binary format
    /// of the specified Postgres `Type`.
    ///
    /// The caller of this method is responsible for ensuring that this type
    /// is compatible with the Postgres `Type`.
    fn from_sql<R: Read>(ty: &Type, raw: &mut R, ctx: &SessionInfo) -> Result<Self>;

    /// Creates a new value of this type from a `NULL` SQL value.
    ///
    /// The caller of this method is responsible for ensuring that this type
    /// is compatible with the Postgres `Type`.
    ///
    /// The default implementation returns
    /// `Err(Error::Conversion(Box::new(WasNull))`.
    #[allow(unused_variables)]
    fn from_sql_null(ty: &Type, ctx: &SessionInfo) -> Result<Self> {
        Err(Error::Conversion(Box::new(WasNull)))
    }

    /// Determines if a value of this type can be created from the specified
    /// Postgres `Type`.
    fn accepts(ty: &Type) -> bool;
}

impl<T: FromSql> FromSql for Option<T> {
    fn from_sql<R: Read>(ty: &Type, raw: &mut R, ctx: &SessionInfo) -> Result<Option<T>> {
        <T as FromSql>::from_sql(ty, raw, ctx).map(Some)
    }

    fn from_sql_null(_: &Type, _: &SessionInfo) -> Result<Option<T>> {
        Ok(None)
    }

    fn accepts(ty: &Type) -> bool {
        <T as FromSql>::accepts(ty)
    }
}

impl FromSql for bool {
    fn from_sql<R: Read>(_: &Type, raw: &mut R, _: &SessionInfo) -> Result<bool> {
        Ok(try!(raw.read_u8()) != 0)
    }

    accepts!(Type::Bool);
}

impl FromSql for Vec<u8> {
    fn from_sql<R: Read>(_: &Type, raw: &mut R, _: &SessionInfo) -> Result<Vec<u8>> {
        let mut buf = vec![];
        try!(raw.read_to_end(&mut buf));
        Ok(buf)
    }

    accepts!(Type::Bytea);
}

impl FromSql for String {
    fn from_sql<R: Read>(_: &Type, raw: &mut R, _: &SessionInfo) -> Result<String> {
        let mut buf = vec![];
        try!(raw.read_to_end(&mut buf));
        String::from_utf8(buf).map_err(|err| Error::Conversion(Box::new(err)))
    }

    fn accepts(ty: &Type) -> bool {
        match *ty {
            Type::Varchar | Type::Text | Type::Bpchar | Type::Name => true,
            Type::Other(ref u) if u.name() == "citext" => true,
            _ => false,
        }
    }
}

impl FromSql for i8 {
    fn from_sql<R: Read>(_: &Type, raw: &mut R, _: &SessionInfo) -> Result<i8> {
        Ok(try!(raw.read_i8()))
    }

    accepts!(Type::Char);
}

macro_rules! primitive_from {
    ($t:ty, $f:ident, $($expected:pat),+) => {
        impl FromSql for $t {
            fn from_sql<R: Read>(_: &Type, raw: &mut R, _: &SessionInfo) -> Result<$t> {
                Ok(try!(raw.$f::<BigEndian>()))
            }

            accepts!($($expected),+);
        }
    }
}

primitive_from!(i16, read_i16, Type::Int2);
primitive_from!(i32, read_i32, Type::Int4);
primitive_from!(u32, read_u32, Type::Oid);
primitive_from!(i64, read_i64, Type::Int8);
primitive_from!(f32, read_f32, Type::Float4);
primitive_from!(f64, read_f64, Type::Float8);

impl FromSql for HashMap<String, Option<String>> {
    fn from_sql<R: Read>(_: &Type,
                         raw: &mut R,
                         _: &SessionInfo)
                         -> Result<HashMap<String, Option<String>>> {
        let mut map = HashMap::new();

        let count = try!(raw.read_i32::<BigEndian>());

        for _ in 0..count {
            let key_len = try!(raw.read_i32::<BigEndian>());
            let mut key = vec![0; key_len as usize];
            try!(util::read_all(raw, &mut key));
            let key = match String::from_utf8(key) {
                Ok(key) => key,
                Err(err) => return Err(Error::Conversion(Box::new(err))),
            };

            let val_len = try!(raw.read_i32::<BigEndian>());
            let val = if val_len < 0 {
                None
            } else {
                let mut val = vec![0; val_len as usize];
                try!(util::read_all(raw, &mut val));
                match String::from_utf8(val) {
                    Ok(val) => Some(val),
                    Err(err) => return Err(Error::Conversion(Box::new(err))),
                }
            };

            map.insert(key, val);
        }

        Ok(map)
    }

    fn accepts(ty: &Type) -> bool {
        match *ty {
            Type::Other(ref u) if u.name() == "hstore" => true,
            _ => false,
        }
    }
}

/// An enum representing the nullability of a Postgres value.
pub enum IsNull {
    /// The value is NULL.
    Yes,
    /// The value is not NULL.
    No,
}

/// A trait for types that can be converted into Postgres values.
///
/// # Types
///
/// The following implementations are provided by this crate, along with the
/// corresponding Postgres types:
///
/// | Rust type                                   | Postgres type(s)               |
/// |---------------------------------------------|--------------------------------|
/// | bool                                        | BOOL                           |
/// | i8                                          | "char"                         |
/// | i16                                         | SMALLINT, SMALLSERIAL          |
/// | i32                                         | INT, SERIAL                    |
/// | u32                                         | OID                            |
/// | i64                                         | BIGINT, BIGSERIAL              |
/// | f32                                         | REAL                           |
/// | f64                                         | DOUBLE PRECISION               |
/// | String                                      | VARCHAR, CHAR(n), TEXT, CITEXT |
/// | &str                                        | VARCHAR, CHAR(n), TEXT, CITEXT |
/// | Vec&lt;u8&gt;                               | BYTEA                          |
/// | &[u8]                                       | BYTEA                          |
/// | HashMap&lt;String, Option&lt;String&gt;&gt; | HSTORE                         |
///
/// In addition, some implementations are provided for types in third party
/// crates. These are disabled by default; to opt into one of these
/// implementations, activate the Cargo feature corresponding to the crate's
/// name. For example, the `serde_json` feature enables the implementation for
/// the `serde_json::Value` type.
///
/// | Rust type                           | Postgres type(s)                    |
/// |-------------------------------------|-------------------------------------|
/// | serialize::json::Json               | JSON, JSONB                         |
/// | serde_json::Value                   | JSON, JSONB                         |
/// | time::Timespec                      | TIMESTAMP, TIMESTAMP WITH TIME ZONE |
/// | chrono::NaiveDateTime               | TIMESTAMP                           |
/// | chrono::DateTime&lt;UTC&gt;         | TIMESTAMP WITH TIME ZONE            |
/// | chrono::DateTime&lt;Local&gt;       | TIMESTAMP WITH TIME ZONE            |
/// | chrono::DateTime&lt;FixedOffset&gt; | TIMESTAMP WITH TIME ZONE            |
/// | chrono::NaiveDate                   | DATE                                |
/// | chrono::NaiveTime                   | TIME                                |
/// | uuid::Uuid                          | UUID                                |
/// | bit_vec::BitVec                     | BIT, VARBIT                         |
///
/// # Nullability
///
/// In addition to the types listed above, `ToSql` is implemented for
/// `Option<T>` where `T` implements `ToSql`. An `Option<T>` represents a
/// nullable Postgres value.
pub trait ToSql: fmt::Debug {
    /// Converts the value of `self` into the binary format of the specified
    /// Postgres `Type`, writing it to `out`.
    ///
    /// The caller of this method is responsible for ensuring that this type
    /// is compatible with the Postgres `Type`.
    ///
    /// The return value indicates if this value should be represented as
    /// `NULL`. If this is the case, implementations **must not** write
    /// anything to `out`.
    fn to_sql<W: ?Sized>(&self, ty: &Type, out: &mut W, ctx: &SessionInfo) -> Result<IsNull>
        where Self: Sized,
              W: Write;

    /// Determines if a value of this type can be converted to the specified
    /// Postgres `Type`.
    fn accepts(ty: &Type) -> bool where Self: Sized;

    /// An adaptor method used internally by Rust-Postgres.
    ///
    /// *All* implementations of this method should be generated by the
    /// `to_sql_checked!()` macro.
    fn to_sql_checked(&self, ty: &Type, out: &mut Write, ctx: &SessionInfo) -> Result<IsNull>;
}

impl<'a, T> ToSql for &'a T
    where T: ToSql
{
    to_sql_checked!();

    fn to_sql<W: Write + ?Sized>(&self,
                                 ty: &Type,
                                 out: &mut W,
                                 ctx: &SessionInfo)
                                 -> Result<IsNull> {
        (*self).to_sql(ty, out, ctx)
    }

    fn accepts(ty: &Type) -> bool {
        T::accepts(ty)
    }
}

impl<T: ToSql> ToSql for Option<T> {
    to_sql_checked!();

    fn to_sql<W: Write + ?Sized>(&self,
                                 ty: &Type,
                                 out: &mut W,
                                 ctx: &SessionInfo)
                                 -> Result<IsNull> {
        match *self {
            Some(ref val) => val.to_sql(ty, out, ctx),
            None => Ok(IsNull::Yes),
        }
    }

    fn accepts(ty: &Type) -> bool {
        <T as ToSql>::accepts(ty)
    }
}

impl ToSql for bool {
    to_sql_checked!();

    fn to_sql<W: Write + ?Sized>(&self,
                                 _: &Type,
                                 mut w: &mut W,
                                 _: &SessionInfo)
                                 -> Result<IsNull> {
        try!(w.write_u8(*self as u8));
        Ok(IsNull::No)
    }

    accepts!(Type::Bool);
}

impl<'a> ToSql for &'a [u8] {
    to_sql_checked!();

    fn to_sql<W: Write + ?Sized>(&self, _: &Type, w: &mut W, _: &SessionInfo) -> Result<IsNull> {
        try!(w.write_all(*self));
        Ok(IsNull::No)
    }

    accepts!(Type::Bytea);
}

impl ToSql for Vec<u8> {
    to_sql_checked!();

    fn to_sql<W: Write + ?Sized>(&self, ty: &Type, w: &mut W, ctx: &SessionInfo) -> Result<IsNull> {
        <&[u8] as ToSql>::to_sql(&&**self, ty, w, ctx)
    }

    fn accepts(ty: &Type) -> bool {
        <&[u8] as ToSql>::accepts(ty)
    }
}

impl<'a> ToSql for &'a str {
    to_sql_checked!();

    fn to_sql<W: Write + ?Sized>(&self, _: &Type, w: &mut W, _: &SessionInfo) -> Result<IsNull> {
        try!(w.write_all(self.as_bytes()));
        Ok(IsNull::No)
    }

    fn accepts(ty: &Type) -> bool {
        match *ty {
            Type::Varchar | Type::Text | Type::Bpchar | Type::Name => true,
            Type::Other(ref u) if u.name() == "citext" => true,
            _ => false,
        }
    }
}

impl ToSql for String {
    to_sql_checked!();

    fn to_sql<W: Write + ?Sized>(&self, ty: &Type, w: &mut W, ctx: &SessionInfo) -> Result<IsNull> {
        <&str as ToSql>::to_sql(&&**self, ty, w, ctx)
    }

    fn accepts(ty: &Type) -> bool {
        <&str as ToSql>::accepts(ty)
    }
}

impl ToSql for i8 {
    to_sql_checked!();

    fn to_sql<W: Write + ?Sized>(&self,
                                 _: &Type,
                                 mut w: &mut W,
                                 _: &SessionInfo)
                                 -> Result<IsNull> {
        try!(w.write_i8(*self));
        Ok(IsNull::No)
    }

    accepts!(Type::Char);
}

macro_rules! to_primitive {
    ($t:ty, $f:ident, $($expected:pat),+) => {
        impl ToSql for $t {
            to_sql_checked!();

            fn to_sql<W: Write+?Sized>(&self, _: &Type, mut w: &mut W, _: &SessionInfo)
                                       -> Result<IsNull> {
                try!(w.$f::<BigEndian>(*self));
                Ok(IsNull::No)
            }

            accepts!($($expected),+);
        }
    }
}

to_primitive!(i16, write_i16, Type::Int2);
to_primitive!(i32, write_i32, Type::Int4);
to_primitive!(u32, write_u32, Type::Oid);
to_primitive!(i64, write_i64, Type::Int8);
to_primitive!(f32, write_f32, Type::Float4);
to_primitive!(f64, write_f64, Type::Float8);

impl ToSql for HashMap<String, Option<String>> {
    to_sql_checked!();

    fn to_sql<W: Write + ?Sized>(&self,
                                 _: &Type,
                                 mut w: &mut W,
                                 _: &SessionInfo)
                                 -> Result<IsNull> {
        try!(w.write_i32::<BigEndian>(try!(downcast(self.len()))));

        for (key, val) in self {
            try!(w.write_i32::<BigEndian>(try!(downcast(key.len()))));
            try!(w.write_all(key.as_bytes()));

            match *val {
                Some(ref val) => {
                    try!(w.write_i32::<BigEndian>(try!(downcast(val.len()))));
                    try!(w.write_all(val.as_bytes()));
                }
                None => try!(w.write_i32::<BigEndian>(-1)),
            }
        }

        Ok(IsNull::No)
    }

    fn accepts(ty: &Type) -> bool {
        match *ty {
            Type::Other(ref u) if u.name() == "hstore" => true,
            _ => false,
        }
    }
}

fn downcast(len: usize) -> Result<i32> {
    if len > i32::max_value() as usize {
        let err: Box<error::Error + Sync + Send> = "value too large to transmit".into();
        Err(Error::Conversion(err))
    } else {
        Ok(len as i32)
    }
}