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// (C) Copyright 2019-2020 Hewlett Packard Enterprise Development LP

use std::fmt;

/// A byte-index tuple representing a span of characters in a string
///
/// Note that spans refer to the position in the input string as read by the
/// parser rather than the output of an expression's `Display` impl.
#[derive(Debug, PartialEq, Eq, Copy, Clone)]
pub struct Span {
  pub start: usize,
  pub end: usize
}

impl From<(usize, usize)> for Span {
  fn from(tup: (usize, usize)) -> Span {
    Span::new(tup.0, tup.1)
  }
}

impl Span {
  pub fn new(start: usize, end: usize) -> Self {
    Span { start, end }
  }

  pub(crate) fn from_node(node: &crate::parser::Node) -> Self {
    let span = node.as_span();
    Span {
      start: span.start(),
      end: span.end()
    }
  }
}

impl fmt::Display for Span {
  fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
    write!(f, "({}, {})", self.start, self.end)
  }
}

/// A Prometheus duration
#[derive(Debug, PartialEq, Eq, Clone, Copy)]
pub enum PromDuration {
  Seconds(u64),
  Minutes(u64),
  Hours(u64),
  Days(u64),
  Weeks(u64),
  Years(u64)
}

type StringResult<T> = std::result::Result<T, String>;

impl PromDuration {
  pub fn from_pair(unit: &str, value: u64) -> StringResult<PromDuration> {
    Ok(match unit {
      "s" => PromDuration::Seconds(value),
      "m" => PromDuration::Minutes(value),
      "h" => PromDuration::Hours(value),
      "d" => PromDuration::Days(value),
      "w" => PromDuration::Weeks(value),
      "y" => PromDuration::Years(value),
      u => return Err(format!("invalid duration unit: {:?}", u))
    })
  }

  pub fn as_char(self) -> char {
    match self {
      PromDuration::Seconds(_) => 's',
      PromDuration::Minutes(_) => 'm',
      PromDuration::Hours(_) => 'h',
      PromDuration::Days(_) => 'd',
      PromDuration::Weeks(_) => 'w',
      PromDuration::Years(_) => 'y'
    }
  }
}

impl fmt::Display for PromDuration {
  fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
    let v = match self {
      PromDuration::Seconds(v) => v,
      PromDuration::Minutes(v) => v,
      PromDuration::Hours(v) => v,
      PromDuration::Days(v) => v,
      PromDuration::Weeks(v) => v,
      PromDuration::Years(v) => v
    };

    write!(f, "{}{}", v, self.as_char())
  }
}

/// A Subquery which converts an instant vector to a range vector by repeatedly
/// evaluating it at set intervals into the relative past
#[derive(Debug, PartialEq, Eq, Clone)]
pub struct Subquery {
  /// Duration back in time to begin the subquery
  pub range: PromDuration,

  /// Optional step size. If unset, uses the global/query default at runtime.
  pub resolution: Option<PromDuration>,

  pub span: Option<Span>
}

impl Subquery {
  pub fn new(range: PromDuration) -> Self {
    Subquery {
      range,
      resolution: None,
      span: None
    }
  }

  pub fn resolution(mut self, res: PromDuration) -> Self {
    self.resolution = Some(res);
    self
  }

  pub fn clear_resolution(mut self) -> Self {
    self.resolution = None;
    self
  }

  pub fn span<S: Into<Span>>(mut self, span: S) -> Self {
    self.span = Some(span.into());
    self
  }
}

impl fmt::Display for Subquery {
  fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
    if let Some(res) = self.resolution {
      write!(f, "[{}:{}]", self.range, res)
    } else {
      write!(f, "[{}:]", self.range)
    }
  }
}