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use std::str::FromStr;
use std::fmt;
use std::collections::BTreeMap;

use bson::{Bson, Document};
use error::Error::{self, ArgumentError};
use error::Result;

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum ReadMode {
    Primary,
    PrimaryPreferred,
    Secondary,
    SecondaryPreferred,
    Nearest,
}

impl FromStr for ReadMode {
    type Err = Error;
    fn from_str(s: &str) -> Result<Self> {
        Ok(match s {
            "Primary" => ReadMode::Primary,
            "PrimaryPreferred" => ReadMode::PrimaryPreferred,
            "Secondary" => ReadMode::Secondary,
            "SecondaryPreferred" => ReadMode::SecondaryPreferred,
            "Nearest" => ReadMode::Nearest,
            _ => return Err(ArgumentError(format!("Could not convert '{}' to ReadMode.", s))),
        })
    }
}

impl fmt::Display for ReadMode {
    fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
        let string = match *self {
            ReadMode::Primary => "primary",
            ReadMode::PrimaryPreferred => "primaryPreferred",
            ReadMode::Secondary => "secondary",
            ReadMode::SecondaryPreferred => "secondaryPreferred",
            ReadMode::Nearest => "nearest"
        };

        fmt.write_str(string)
    }
}

#[derive(Debug, Clone)]
pub struct ReadPreference {
    /// Indicates how a server should be selected during read operations.
    pub mode: ReadMode,
    /// The read preference maxStalenessSeconds option lets you specify a maximum replication lag, or “staleness”, for reads from secondaries.
    pub max_staleness_seconds: Option<i32>,
    /// Filters servers based on the first tag set that matches at least one server.
    pub tag_sets: Vec<BTreeMap<String, String>>,
}

impl ReadPreference {
    pub fn new(mode: ReadMode, max_staleness_seconds: Option<i32>, tag_sets: Option<Vec<BTreeMap<String, String>>>) -> ReadPreference {
        ReadPreference {
            mode,
            max_staleness_seconds,
            tag_sets: tag_sets.unwrap_or_else(Vec::new),
        }
    }

    pub fn to_document(&self) -> Document {
        let mut doc = doc!{ "mode": self.mode.to_string() };
        let bson_tag_sets: Vec<_> = self.tag_sets
            .iter()
            .map(|map| {
                let mut bson_map = Document::new();
                for (key, val) in map.iter() {
                    bson_map.insert(&**key, Bson::String(val.to_string()));
                }
                Bson::Document(bson_map)
            })
            .collect();

        if let Some(seconds) = self.max_staleness_seconds {
            doc.insert("maxStalenessSeconds", seconds);
        }

        if bson_tag_sets.len() > 0 {
            doc.insert("tags", Bson::Array(bson_tag_sets));
        }

        doc
    }
}