// FlexVer - Flexible Version Comparison
//
// This implementation is based on the original implementation of the
// `flexver-rs` crate, which no longer appears to be maintained.
//
// See:
//  <https://git.sleeping.town/exa/FlexVer/src/branch/trunk/rust/src/lib.rs>
//
// This implementation provides semver-like version comparison with support for:
//
// - Flexible version string parsing (not strict semver)
// - Pre-release handling (parts starting with `-`)
// - Build metadata stripping (parts after `+`)
// - Numerical vs lexical comparison

use std::{
  cmp::Ordering::{self, Equal, Greater, Less},
  collections::VecDeque,
};

/// Type of version component for sorting purposes
#[derive(Debug, Clone, PartialEq)]
enum SortingType {
  /// A numeric component with both i64 value and string representation
  Numerical(i64, String),

  /// A lexical string component
  Lexical(String),

  /// A semver pre-release component (starting with `-`)
  SemverPrerelease(String),
}

impl SortingType {
  fn into_string(self) -> String {
    match self {
      Self::Numerical(_, s) | Self::Lexical(s) | Self::SemverPrerelease(s) => s,
    }
  }
}

fn is_semver_prerelease(s: &str) -> bool {
  s.len() > 1 && s.starts_with('-')
}

/// Decompose a version string into its component parts
fn decompose(str_in: &str) -> VecDeque<SortingType> {
  if str_in.is_empty() {
    return VecDeque::new();
  }

  // Strip build metadata (after `+`)
  let s = if let Some((left, _)) = str_in.split_once('+') {
    left
  } else {
    str_in
  };

  let mut out: VecDeque<SortingType> = VecDeque::new();
  let mut current = String::new();

  let mut currently_numeric = s.starts_with(|c: char| c.is_ascii_digit());
  let mut skip = s.starts_with('-');

  fn handle_split(
    current: &str,
    c: Option<&char>,
    currently_numeric: bool,
  ) -> Option<SortingType> {
    let numeric = if let Some(c) = c {
      c.is_ascii_digit()
    } else {
      false
    };

    use SortingType::*;

    if currently_numeric {
      if numeric {
        return None;
      } else {
        return Some(Numerical(
          current.parse::<i64>().unwrap(),
          current.to_owned(),
        ));
      }
    }

    if !(numeric || c == Some(&'-') || c.is_none()) {
      return None;
    }

    if is_semver_prerelease(current) {
      if c == Some(&'-') {
        // Pre-releases can have multiple dashes
        None
      } else {
        Some(SemverPrerelease(current.to_owned()))
      }
    } else {
      Some(Lexical(current.to_owned()))
    }
  }

  for c in s.chars() {
    if let Some(part) = handle_split(&current, Some(&c), currently_numeric) {
      if skip {
        skip = false;
      } else {
        out.push_back(part);
        current.clear();
        currently_numeric = c.is_ascii_digit();
      }
    }
    current.push(c);
  }

  if let Some(part) = handle_split(&current, None, currently_numeric) {
    out.push_back(part);
  }

  out
}

/// Compare two version strings using FlexVer rules.
///
/// Returns:
/// - `Ordering::Less` if `a` < `b`
/// - `Ordering::Equal` if `a` == `b`
/// - `Ordering::Greater` if `a` > `b`
///
/// This matches the behavior of flexver-java:
/// - "1.0.0" > "1.0.0-beta" (release > pre-release)
/// - "1.0.0-beta" < "1.0.0+build123" (pre-release < build metadata)
pub fn compare(left: &str, right: &str) -> Ordering {
  let iter = VersionComparisonIterator {
    left:  decompose(left),
    right: decompose(right),
  };

  for next in iter {
    use SortingType::*;

    let current = match next {
      // Left ran out first
      (Some(l), None) => {
        if let SemverPrerelease(_) = l {
          Less
        } else {
          Greater
        }
      },
      // Right ran out first
      (None, Some(r)) => {
        if let SemverPrerelease(_) = r {
          Greater
        } else {
          Less
        }
      },
      // Both have components
      (Some(l), Some(r)) => {
        match (l, r) {
          (Numerical(l, _), Numerical(r, _)) => l.cmp(&r),
          (l, r) => l.into_string().cmp(&r.into_string()),
        }
      },
      (None, None) => unreachable!(),
    };

    if current != Equal {
      return current;
    }
  }

  Equal
}

/// Version comparison iterator that yields pairs of components
#[derive(Debug)]
struct VersionComparisonIterator {
  left:  VecDeque<SortingType>,
  right: VecDeque<SortingType>,
}

impl Iterator for VersionComparisonIterator {
  type Item = (Option<SortingType>, Option<SortingType>);

  fn next(&mut self) -> Option<Self::Item> {
    let item = (self.left.pop_front(), self.right.pop_front());
    if let (None, None) = item {
      None
    } else {
      Some(item)
    }
  }
}

/// FlexVer type for use with standard library traits
#[derive(Debug, Copy, Clone)]
pub struct FlexVer<'a>(pub &'a str);

impl PartialEq for FlexVer<'_> {
  fn eq(&self, other: &Self) -> bool {
    compare(self.0, other.0) == Equal
  }
}

impl Eq for FlexVer<'_> {}

impl PartialOrd for FlexVer<'_> {
  fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
    Some(self.cmp(other))
  }
}

impl Ord for FlexVer<'_> {
  fn cmp(&self, other: &Self) -> Ordering {
    compare(self.0, other.0)
  }
}

#[cfg(test)]
mod tests {
  use std::cmp::Ordering;

  use super::*;

  fn cmp(a: &str, b: &str) -> Ordering {
    compare(a, b)
  }

  #[test]
  fn test_basic_release_comparison() {
    assert_eq!(cmp("1.0.0", "1.0.0"), Ordering::Equal);
    assert_eq!(cmp("1.0.0", "1.0.1"), Ordering::Less);
    assert_eq!(cmp("1.0.1", "1.0.0"), Ordering::Greater);
    assert_eq!(cmp("1.0.0", "1.1.0"), Ordering::Less);
    assert_eq!(cmp("1.1.0", "1.0.0"), Ordering::Greater);
    assert_eq!(cmp("2.0.0", "1.9.9"), Ordering::Greater);
  }

  #[test]
  fn test_prerelease_comparison() {
    // Release > pre-release
    assert_eq!(cmp("1.0.0", "1.0.0-beta"), Ordering::Greater);
    assert_eq!(cmp("1.0.0-beta", "1.0.0"), Ordering::Less);

    // Pre-release with tilde
    assert_eq!(cmp("1.0.0~1", "1.0.0~2"), Ordering::Less);
    assert_eq!(cmp("1.0.0~2", "1.0.0~1"), Ordering::Greater);
    assert_eq!(cmp("1.0.0~1", "1.0.0~1"), Ordering::Equal);
  }

  #[test]
  fn test_prerelease_with_tilde_vs_alpha() {
    // In FlexVer, "~" is not treated as a pre-release marker
    // Only "-" followed by text marks a pre-release
    // So "1.0.0~1" is compared lexicographically vs "1.0.0-beta"
    // Since '~' (ASCII 126) > '-' (ASCII 45), "~1" > "-beta"
    assert_eq!(cmp("1.0.0~1", "1.0.0-beta"), Ordering::Greater);
    assert_eq!(cmp("1.0.0-beta", "1.0.0~1"), Ordering::Less);
  }

  #[test]
  fn test_build_metadata() {
    // Build metadata with + is stripped for comparison
    assert_eq!(cmp("1.0.0+build", "1.0.0"), Ordering::Equal);
    assert_eq!(cmp("1.0.0+build", "1.0.0-alpha"), Ordering::Greater);
  }

  #[test]
  fn test_with_file_extensions() {
    // File extensions should be handled by string comparison
    assert_eq!(cmp("mod-1.0.0.jar", "mod-1.0.0.jar"), Ordering::Equal);
    assert!(cmp("mod-1.0.0.jar", "mod-1.0.1.jar").is_lt());
    assert!(cmp("mod-1.0.1.jar", "mod-1.0.0.jar").is_gt());
  }

  #[test]
  fn test_complex_versions() {
    // Simple version comparison
    assert!(cmp("sodium-1.0.0", "sodium-1.0.1").is_lt());
    assert!(cmp("sodium-1.0.1", "sodium-1.0.0").is_gt());

    // File extensions are NOT stripped - they're part of the version string
    // "sodium-1.0.0.jar" < "sodium-1.0.0~1.jar" because '.' (48) < '~' (126)
    assert!(cmp("sodium-1.0.0.jar", "sodium-1.0.0~1.jar").is_lt());
    assert!(cmp("sodium-1.0.0~1.jar", "sodium-1.0.0.jar").is_gt());

    assert!(cmp("fabric-0.15.0.1", "fabric-0.15.0.2").is_lt());
  }

  #[test]
  fn test_min_max() {
    assert_eq!(FlexVer("1.0.0").min(FlexVer("1.0.0")), FlexVer("1.0.0"));
    assert_eq!(FlexVer("a1.2.6").min(FlexVer("b1.7.3")), FlexVer("a1.2.6"));
    assert_eq!(FlexVer("b1.7.3").max(FlexVer("a1.2.6")), FlexVer("b1.7.3"));
  }

  #[test]
  fn test_commutative() {
    // If a > b, then b < a
    let pairs = vec![
      ("1.0.0", "1.0.1"),
      ("1.0.0-beta", "1.0.0"),
      ("1.0.0~1", "1.0.0~2"),
    ];

    for (a, b) in pairs {
      let ordering = compare(a, b);
      let inverse = match ordering {
        Ordering::Less => Ordering::Greater,
        Ordering::Greater => Ordering::Less,
        Ordering::Equal => Ordering::Equal,
      };
      assert_eq!(
        compare(b, a),
        inverse,
        "Commutativity violation: {} vs {}",
        a,
        b
      );
    }
  }
}