use crate::{Error, Result};
use serde::{Deserialize, Serialize};
use std::fmt;

/// A scenario step.
///
/// The scenario parser creates these kinds of data structures to
/// represent the parsed scenario step. The step consists of a kind
/// (expressed as a StepKind), and the text of the step.
///
/// This is just the step as it appears in the scenario in the input
/// text. It has not been matched with a binding. See MatchedStep for
/// that.
#[derive(Clone, Debug, Eq, PartialEq, Serialize, Deserialize)]
pub struct ScenarioStep {
    kind: StepKind,
    text: String,
}

impl ScenarioStep {
    /// Construct a new step.
    pub fn new(kind: StepKind, text: &str) -> ScenarioStep {
        ScenarioStep {
            kind,
            text: text.to_owned(),
        }
    }

    /// Return the kind of a step.
    pub fn kind(&self) -> StepKind {
        self.kind
    }

    /// Return the text of a step.
    pub fn text(&self) -> &str {
        &self.text
    }

    /// Construct a step from a line in a scenario.
    ///
    /// If the step uses the "and" or "but" keyword, use the default
    /// step kind instead.
    pub fn new_from_str(text: &str, default: StepKind) -> Result<ScenarioStep> {
        let mut words = text.split_whitespace();

        let kind = match words.next() {
            Some("given") => StepKind::Given,
            Some("when") => StepKind::When,
            Some("then") => StepKind::Then,
            Some("and") => default,
            Some("but") => default,
            _ => return Err(Error::UnknownStepKind),
        };

        let mut joined = String::new();
        for word in words {
            joined.push_str(word);
            joined.push_str(" ");
        }
        if joined.len() > 1 {
            joined.pop();
        }
        Ok(ScenarioStep::new(kind, &joined))
    }
}

impl fmt::Display for ScenarioStep {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "{} {}", self.kind(), self.text())
    }
}

/// The kind of scenario step we have: given, when, or then.
///
/// This needs to be extended if the Subplot language gets extended with other
/// kinds of steps. However, note that the scenario parser will hide aliases,
/// such as "and" to mean the same kind as the previous step.
#[derive(Clone, Copy, Debug, Eq, PartialEq, Serialize, Deserialize)]
pub enum StepKind {
    /// A "given some precondition" step.
    Given,

    /// A "when something happens" step.
    When,

    /// A "then some condition" step.
    Then,
}

impl fmt::Display for StepKind {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        let s = match self {
            StepKind::Given => "given",
            StepKind::When => "when",
            StepKind::Then => "then",
        };
        write!(f, "{}", s)
    }
}

#[cfg(test)]
mod test {
    use super::{ScenarioStep, StepKind};

    #[test]
    fn parses_given() {
        let step = ScenarioStep::new_from_str("given I am Tomjon", StepKind::Then).unwrap();
        assert_eq!(step.kind(), StepKind::Given);
        assert_eq!(step.text(), "I am Tomjon");
    }

    #[test]
    fn parses_given_with_extra_spaces() {
        let step =
            ScenarioStep::new_from_str("   given     I   am   Tomjon   ", StepKind::When).unwrap();
        assert_eq!(step.kind(), StepKind::Given);
        assert_eq!(step.text(), "I am Tomjon");
    }

    #[test]
    fn parses_when() {
        let step =
            ScenarioStep::new_from_str("when I declare myself king", StepKind::Given).unwrap();
        assert_eq!(step.kind(), StepKind::When);
        assert_eq!(step.text(), "I declare myself king");
    }

    #[test]
    fn parses_then() {
        let step = ScenarioStep::new_from_str("then everyone accepts it", StepKind::Given).unwrap();
        assert_eq!(step.kind(), StepKind::Then);
        assert_eq!(step.text(), "everyone accepts it");
    }

    #[test]
    fn parses_and() {
        let step = ScenarioStep::new_from_str("and everyone accepts it", StepKind::Then).unwrap();
        assert_eq!(step.kind(), StepKind::Then);
        assert_eq!(step.text(), "everyone accepts it");
    }
}