use codec::{Decode, Encode};
#[cfg(feature = "std")]
use serde::{Deserialize, Serialize};

/// Length constraint for input validation
#[cfg_attr(feature = "std", derive(Serialize, Deserialize, Debug))]
#[derive(Encode, Decode, Default, Clone, PartialEq, Eq, Copy)]
pub struct InputValidationLengthConstraint {
    /// Minimum length
    pub min: u16,

    /// Difference between minimum length and max length.
    /// While having max would have been more direct, this
    /// way makes max < min unrepresentable semantically,
    /// which is safer.
    pub max_min_diff: u16,
}

impl InputValidationLengthConstraint {
    /// Helper for computing max
    pub fn max(self) -> u16 {
        self.min + self.max_min_diff
    }

    pub fn ensure_valid(
        self,
        len: usize,
        too_short_msg: &'static str,
        too_long_msg: &'static str,
    ) -> Result<(), &'static str> {
        let length = len as u16;
        if length < self.min {
            Err(too_short_msg)
        } else if length > self.max() {
            Err(too_long_msg)
        } else {
            Ok(())
        }
    }

    /// Create default input text constraints.
    pub fn new(min: u16, max_min_diff: u16) -> Self {
        InputValidationLengthConstraint { min, max_min_diff }
    }
}