use std::{
    borrow::{Borrow, Cow},
    convert::{TryFrom, TryInto},
    iter::FromIterator,
    ops::Deref,
};

use serde::{Deserialize, Serialize};

use crate::{
    de::MIN_BSON_DOCUMENT_SIZE,
    spec::BinarySubtype,
    Document,
    RawBinaryRef,
    RawJavaScriptCodeWithScopeRef,
};

use super::{
    bson::RawBson,
    iter::Iter,
    serde::OwnedOrBorrowedRawDocument,
    Error,
    ErrorKind,
    RawBsonRef,
    RawDocument,
    RawIter,
    Result,
};

/// An owned BSON document (akin to [`std::path::PathBuf`]), backed by a buffer of raw BSON bytes.
/// This can be created from a `Vec<u8>` or a [`crate::Document`].
///
/// Accessing elements within a [`RawDocumentBuf`] is similar to element access in
/// [`crate::Document`], but because the contents are parsed during iteration instead of at creation
/// time, format errors can happen at any time during use.
///
/// Iterating over a [`RawDocumentBuf`] yields either an error or a key-value pair that borrows from
/// the original document without making any additional allocations.
///
/// ```
/// # use bson::raw::Error;
/// use bson::raw::RawDocumentBuf;
///
/// let doc = RawDocumentBuf::from_bytes(b"\x13\x00\x00\x00\x02hi\x00\x06\x00\x00\x00y'all\x00\x00".to_vec())?;
/// let mut iter = doc.iter();
/// let (key, value) = iter.next().unwrap()?;
/// assert_eq!(key, "hi");
/// assert_eq!(value.as_str(), Some("y'all"));
/// assert!(iter.next().is_none());
/// # Ok::<(), Error>(())
/// ```
///
/// This type implements [`Deref`] to [`RawDocument`], meaning that all methods on [`RawDocument`]
/// are available on [`RawDocumentBuf`] values as well. This includes [`RawDocument::get`] or any of
/// the type-specific getters, such as [`RawDocument::get_object_id`] or [`RawDocument::get_str`].
/// Note that accessing elements is an O(N) operation, as it requires iterating through the document
/// from the beginning to find the requested key.
///
/// ```
/// use bson::raw::RawDocumentBuf;
///
/// let doc = RawDocumentBuf::from_bytes(b"\x13\x00\x00\x00\x02hi\x00\x06\x00\x00\x00y'all\x00\x00".to_vec())?;
/// assert_eq!(doc.get_str("hi")?, "y'all");
/// # Ok::<(), Box<dyn std::error::Error>>(())
/// ```
#[derive(Clone, PartialEq)]
pub struct RawDocumentBuf {
    data: Vec<u8>,
}

impl RawDocumentBuf {
    /// Creates a new, empty [`RawDocumentBuf`].
    pub fn new() -> RawDocumentBuf {
        let mut data = Vec::new();
        data.extend(MIN_BSON_DOCUMENT_SIZE.to_le_bytes());
        data.push(0);
        Self { data }
    }

    /// Constructs a new [`RawDocumentBuf`], validating _only_ the
    /// following invariants:
    ///   * `data` is at least five bytes long (the minimum for a valid BSON document)
    ///   * the initial four bytes of `data` accurately represent the length of the bytes as
    ///     required by the BSON spec.
    ///   * the last byte of `data` is a 0
    ///
    /// Note that the internal structure of the bytes representing the
    /// BSON elements is _not_ validated at all by this method. If the
    /// bytes do not conform to the BSON spec, then method calls on
    /// the RawDocument will return Errors where appropriate.
    ///
    /// ```
    /// # use bson::raw::{RawDocumentBuf, Error};
    /// let doc = RawDocumentBuf::from_bytes(b"\x05\0\0\0\0".to_vec())?;
    /// # Ok::<(), Error>(())
    /// ```
    pub fn from_bytes(data: Vec<u8>) -> Result<RawDocumentBuf> {
        let _ = RawDocument::from_bytes(data.as_slice())?;
        Ok(Self { data })
    }

    /// Create a [`RawDocumentBuf`] from a [`Document`].
    ///
    /// ```
    /// # use bson::raw::Error;
    /// use bson::{doc, oid::ObjectId, raw::RawDocumentBuf};
    ///
    /// let document = doc! {
    ///     "_id": ObjectId::new(),
    ///     "name": "Herman Melville",
    ///     "title": "Moby-Dick",
    /// };
    /// let doc = RawDocumentBuf::from_document(&document)?;
    /// # Ok::<(), Error>(())
    /// ```
    pub fn from_document(doc: &Document) -> Result<RawDocumentBuf> {
        let mut data = Vec::new();
        doc.to_writer(&mut data).map_err(|e| Error {
            key: None,
            kind: ErrorKind::MalformedValue {
                message: e.to_string(),
            },
        })?;

        Ok(Self { data })
    }

    /// Gets an iterator over the elements in the [`RawDocumentBuf`], which yields
    /// `Result<(&str, RawBson<'_>)>`.
    ///
    /// ```
    /// # use bson::raw::Error;
    /// use bson::{doc, raw::RawDocumentBuf};
    ///
    /// let doc = RawDocumentBuf::from_document(&doc! { "ferris": true })?;
    ///
    /// for element in doc.iter() {
    ///     let (key, value) = element?;
    ///     assert_eq!(key, "ferris");
    ///     assert_eq!(value.as_bool(), Some(true));
    /// }
    /// # Ok::<(), Error>(())
    /// ```
    ///
    /// # Note:
    ///
    /// There is no owning iterator for [`RawDocumentBuf`]. If you need ownership over
    /// elements that might need to allocate, you must explicitly convert
    /// them to owned types yourself.
    pub fn iter(&self) -> Iter<'_> {
        Iter::new(self)
    }

    /// Gets an iterator over the elements in the [`RawDocumentBuf`],
    /// which yields `Result<RawElement<'_>>` values. These hold a
    /// reference to the underlying document but do not explicitly
    /// resolve the values.
    ///
    /// This iterator, which underpins the implementation of the
    /// default iterator, produces `RawElement` objects, which
    /// hold a view onto the document but do not parse out or
    /// construct values until the `.value()` or `.try_into()` methods
    /// are called.
    ///
    /// # Note:
    ///
    /// There is no owning iterator for [`RawDocumentBuf`]. If you
    /// need ownership over elements that might need to allocate, you
    /// must explicitly convert them to owned types yourself.
    pub fn iter_elements(&self) -> RawIter<'_> {
        RawIter::new(self)
    }

    /// Return the contained data as a `Vec<u8>`
    ///
    /// ```
    /// # use bson::raw::Error;
    /// use bson::{doc, raw::RawDocumentBuf};
    ///
    /// let doc = RawDocumentBuf::from_document(&doc!{})?;
    /// assert_eq!(doc.into_bytes(), b"\x05\x00\x00\x00\x00".to_vec());
    /// # Ok::<(), Error>(())
    /// ```
    pub fn into_bytes(self) -> Vec<u8> {
        self.data
    }

    /// Append a key value pair to the end of the document without checking to see if
    /// the key already exists.
    ///
    /// It is a user error to append the same key more than once to the same document, and it may
    /// result in errors when communicating with MongoDB.
    ///
    /// If the provided key contains an interior null byte, this method will panic.
    ///
    /// ```
    /// # use bson::raw::Error;
    /// use bson::{doc, raw::RawDocumentBuf};
    ///
    /// let mut doc = RawDocumentBuf::new();
    /// doc.append("a string", "some string");
    /// doc.append("an integer", 12_i32);
    ///
    /// let mut subdoc = RawDocumentBuf::new();
    /// subdoc.append("a key", true);
    /// doc.append("a document", subdoc);
    ///
    /// let expected = doc! {
    ///     "a string": "some string",
    ///     "an integer": 12_i32,
    ///     "a document": { "a key": true },
    /// };
    ///
    /// assert_eq!(doc.to_document()?, expected);
    /// # Ok::<(), Error>(())
    /// ```
    pub fn append(&mut self, key: impl AsRef<str>, value: impl Into<RawBson>) {
        fn append_string(doc: &mut RawDocumentBuf, value: &str) {
            doc.data
                .extend(((value.as_bytes().len() + 1) as i32).to_le_bytes());
            doc.data.extend(value.as_bytes());
            doc.data.push(0);
        }

        fn append_cstring(doc: &mut RawDocumentBuf, value: &str) {
            if value.contains('\0') {
                panic!("cstr includes interior null byte: {}", value)
            }
            doc.data.extend(value.as_bytes());
            doc.data.push(0);
        }

        let original_len = self.data.len();

        // write the key for the next value to the end
        // the element type will replace the previous null byte terminator of the document
        append_cstring(self, key.as_ref());

        let value = value.into();
        let element_type = value.element_type();

        match value {
            RawBson::Int32(i) => {
                self.data.extend(i.to_le_bytes());
            }
            RawBson::String(s) => {
                append_string(self, s.as_str());
            }
            RawBson::Document(d) => {
                self.data.extend(d.into_bytes());
            }
            RawBson::Array(a) => {
                self.data.extend(a.into_vec());
            }
            RawBson::Binary(b) => {
                let len = RawBinaryRef {
                    bytes: b.bytes.as_slice(),
                    subtype: b.subtype,
                }
                .len();
                self.data.extend(len.to_le_bytes());
                self.data.push(b.subtype.into());
                if let BinarySubtype::BinaryOld = b.subtype {
                    self.data.extend((len - 4).to_le_bytes())
                }
                self.data.extend(b.bytes);
            }
            RawBson::Boolean(b) => {
                self.data.push(b as u8);
            }
            RawBson::DateTime(dt) => {
                self.data.extend(dt.timestamp_millis().to_le_bytes());
            }
            RawBson::DbPointer(dbp) => {
                append_string(self, dbp.namespace.as_str());
                self.data.extend(dbp.id.bytes());
            }
            RawBson::Decimal128(d) => {
                self.data.extend(d.bytes());
            }
            RawBson::Double(d) => {
                self.data.extend(d.to_le_bytes());
            }
            RawBson::Int64(i) => {
                self.data.extend(i.to_le_bytes());
            }
            RawBson::RegularExpression(re) => {
                append_cstring(self, re.pattern.as_str());
                append_cstring(self, re.options.as_str());
            }
            RawBson::JavaScriptCode(js) => {
                append_string(self, js.as_str());
            }
            RawBson::JavaScriptCodeWithScope(code_w_scope) => {
                let len = RawJavaScriptCodeWithScopeRef {
                    code: code_w_scope.code.as_str(),
                    scope: &code_w_scope.scope,
                }
                .len();
                self.data.extend(len.to_le_bytes());
                append_string(self, code_w_scope.code.as_str());
                self.data.extend(code_w_scope.scope.into_bytes());
            }
            RawBson::Timestamp(ts) => {
                self.data.extend(ts.to_le_i64().to_le_bytes());
            }
            RawBson::ObjectId(oid) => {
                self.data.extend(oid.bytes());
            }
            RawBson::Symbol(s) => {
                append_string(self, s.as_str());
            }
            RawBson::Null | RawBson::Undefined | RawBson::MinKey | RawBson::MaxKey => {}
        }
        // update element type
        self.data[original_len - 1] = element_type as u8;
        // append trailing null byte
        self.data.push(0);
        // update length
        let new_len = (self.data.len() as i32).to_le_bytes();
        self.data[0..4].copy_from_slice(&new_len);
    }

    /// Convert this [`RawDocumentBuf`] to a [`Document`], returning an error
    /// if invalid BSON is encountered.
    pub fn to_document(&self) -> Result<Document> {
        self.as_ref().try_into()
    }
}

impl Default for RawDocumentBuf {
    fn default() -> Self {
        Self::new()
    }
}

impl<'de> Deserialize<'de> for RawDocumentBuf {
    fn deserialize<D>(deserializer: D) -> std::result::Result<Self, D::Error>
    where
        D: serde::Deserializer<'de>,
    {
        Ok(OwnedOrBorrowedRawDocument::deserialize(deserializer)?.into_owned())
    }
}

impl Serialize for RawDocumentBuf {
    fn serialize<S>(&self, serializer: S) -> std::result::Result<S::Ok, S::Error>
    where
        S: serde::Serializer,
    {
        let doc: &RawDocument = self.deref();
        doc.serialize(serializer)
    }
}

impl std::fmt::Debug for RawDocumentBuf {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        f.debug_struct("RawDocumentBuf")
            .field("data", &hex::encode(&self.data))
            .finish()
    }
}

impl<'a> From<RawDocumentBuf> for Cow<'a, RawDocument> {
    fn from(rd: RawDocumentBuf) -> Self {
        Cow::Owned(rd)
    }
}

impl<'a> From<&'a RawDocumentBuf> for Cow<'a, RawDocument> {
    fn from(rd: &'a RawDocumentBuf) -> Self {
        Cow::Borrowed(rd.as_ref())
    }
}

impl TryFrom<RawDocumentBuf> for Document {
    type Error = Error;

    fn try_from(raw: RawDocumentBuf) -> Result<Document> {
        Document::try_from(raw.as_ref())
    }
}

impl TryFrom<&Document> for RawDocumentBuf {
    type Error = Error;

    fn try_from(doc: &Document) -> Result<RawDocumentBuf> {
        RawDocumentBuf::from_document(doc)
    }
}

impl<'a> IntoIterator for &'a RawDocumentBuf {
    type IntoIter = Iter<'a>;
    type Item = Result<(&'a str, RawBsonRef<'a>)>;

    fn into_iter(self) -> Iter<'a> {
        Iter::new(self)
    }
}

impl AsRef<RawDocument> for RawDocumentBuf {
    fn as_ref(&self) -> &RawDocument {
        RawDocument::new_unchecked(&self.data)
    }
}

impl Deref for RawDocumentBuf {
    type Target = RawDocument;

    fn deref(&self) -> &Self::Target {
        RawDocument::new_unchecked(&self.data)
    }
}

impl Borrow<RawDocument> for RawDocumentBuf {
    fn borrow(&self) -> &RawDocument {
        self.deref()
    }
}

impl<S: AsRef<str>, T: Into<RawBson>> FromIterator<(S, T)> for RawDocumentBuf {
    fn from_iter<I: IntoIterator<Item = (S, T)>>(iter: I) -> Self {
        let mut buf = RawDocumentBuf::new();
        for (k, v) in iter {
            buf.append(k, v);
        }
        buf
    }
}