// nixos-config - My current NixOS configuration
//
// Copyright (C) 2025 Benedikt Peetz <benedikt.peetz@b-peetz.de>
// SPDX-License-Identifier: GPL-3.0-or-later
//
// This file is part of my nixos-config.
//
// You should have received a copy of the License along with this program.
// If not, see <https://www.gnu.org/licenses/gpl-3.0.txt>.

use std::fmt::Write;

use anyhow::bail;
use log::debug;

#[derive(Clone, Debug)]
pub struct MapKey {
    pub key: char,

    pub(crate) resolution: usize,

    /// Part of the path, used to derive the key
    pub(crate) part_path: String,
}

impl std::hash::Hash for MapKey {
    fn hash<H: std::hash::Hasher>(&self, state: &mut H) {
        self.key.hash(state)
    }
}

impl Eq for MapKey {}
impl PartialEq for MapKey {
    fn eq(&self, other: &Self) -> bool {
        self.key == other.key
    }
}

impl Ord for MapKey {
    fn cmp(&self, other: &Self) -> std::cmp::Ordering {
        self.key.cmp(&other.key)
    }
}
impl PartialOrd for MapKey {
    fn partial_cmp(&self, other: &Self) -> Option<std::cmp::Ordering> {
        Some(self.cmp(other))
    }
}

impl MapKey {
    pub fn new_from_part_path(part_path: &str, resolution: usize) -> Vec<Self> {
        let key = Self::part_path_to_key(part_path, resolution);

        key.chars()
            .map(|ch| Self {
                key: ch,
                resolution,
                part_path: part_path.to_owned(),
            })
            .collect()
    }

    pub fn new_ones_from_path(path: &str, number_of_chars: usize) -> Vec<Self> {
        let key: Vec<MapKey> = path
            .split('/')
            .flat_map(|part| Self::new_from_part_path(part, number_of_chars))
            .collect();

        debug!(
            "Generated full MapKeys: '{}' -> '{}'",
            path,
            MapKey::display(&key)
        );
        key
    }

    pub fn increment(&self, target_resolution: usize) -> Vec<Self> {
        let new_resolution = target_resolution;

        // debug!("Incrementing: '{}' ('{}')", &self, &self.part_path);

        let added_chars = if new_resolution < self.part_path.len() {
            MapKey::part_path_to_key(&self.part_path, new_resolution)
        } else {
            let mut generated_chars =
                MapKey::part_path_to_key(&self.part_path, self.part_path.len());

            generated_chars.extend(
                (0..(new_resolution - self.part_path.len()))
                    .into_iter()
                    .map(|_| self.part_path.chars().last().expect("This will exists")),
            );

            generated_chars
        };

        let part_path = self.part_path.clone();
        let output: Vec<Self> = added_chars
            .chars()
            .enumerate()
            .map(|(res, ch)| MapKey {
                key: ch,
                resolution: res + 1,
                part_path: part_path.clone(),
            })
            .collect();

        // debug!("Finished increment: '{}' ('{}')", MapKey::display(&output), output[0].part_path);
        output
    }

    pub fn display(values: &[Self]) -> String {
        values.iter().map(|value| value.key.clone()).collect()
    }

    fn part_path_to_key(part: &str, number_of_chars: usize) -> String {
        fn make(pat: char, part: &str, number_of_chars: usize) -> String {
            let mut acc = String::new();

            if !part.split(pat).all(|part| part.len() > 0) {
                panic!(
                    "\
Can't turn this path '{}' to a mapping.
This should not happen, please report the bug!",
                    part
                )
            }

            let mut last_working = None;
            for i in 0..number_of_chars {
                for str in part.split(pat) {
                    if acc.len() != number_of_chars {
                        acc.push(match str.chars().nth(i) {
                            Some(ch) => ch,
                            None => {
                                if let Some(last) = last_working {
                                    str.chars().nth(last).expect("This should always exist")
                                } else {
                                    last_working = Some(i - 1);
                                    str.chars().nth(i - 1).expect("This should always exist")
                                }
                            }
                        })
                    }
                }
            }

            acc
        }

        let value = if part.contains('_') && !part.starts_with('_') && !part.ends_with('_') {
            make('_', part, number_of_chars)
        } else if part.contains('-') && !part.starts_with('-') && !part.ends_with('-') {
            make('-', part, number_of_chars)
        } else {
            part.chars().take(number_of_chars).collect::<String>()
        };

        assert_eq!(
            value.len(),
            number_of_chars,
            "'{}' does not have expected length of: {}",
            value,
            number_of_chars
        );
        value
    }

    /// Checks whether a tiebreak via the [`Self::increment`] function can result in unique keys.
    pub fn can_tiebreak_with(&self, other: &Self) -> anyhow::Result<()> {
        /// Check whether the `input` &str is composed of only one character.
        /// If so, returns this character, otherwise returns None.
        fn reduce_string(input: &str) -> Option<char> {
            let first_char = input
                .chars()
                .take(1)
                .last()
                .expect("Should contain one char");

            if input.chars().all(|ch| ch == first_char) {
                Some(first_char)
            } else {
                None
            }
        }

        /// Check whether `a` is a subset of `b` or `b` is a subset of `a`.
        fn is_subset_either(a: &str, b: &str) -> bool {
            /// Checks if `subset` is a subset of `set`.
            ///
            /// # Examples
            /// ```
            /// let a = "a";
            /// let b = "aa";
            /// assert!(is_subset(a, b))
            /// ```
            ///
            /// ```
            /// let a = "abc";
            /// let b = "def";
            /// assert!(!is_subset(a, b))
            /// ```
            fn is_subset(subset: &str, set: &str) -> bool {
                let prefix: String = set.chars().take(subset.len()).collect();
                let suffix: String = set.chars().skip(subset.len()).collect();

                if prefix == subset {
                    let clean_suffix = reduce_string(&suffix);
                    if let Some(ch) = clean_suffix {
                        ch == subset.chars().last().expect("Will exists")
                    } else {
                        false
                    }
                } else {
                    false
                }
            }

            match a.len().cmp(&b.len()) {
                std::cmp::Ordering::Less => {
                    // `b` is the longer string. As such we need to check if `a` is a subset of `b`.
                    is_subset(a, b)
                }
                std::cmp::Ordering::Greater => {
                    // `a` is the longer string. As such we need to check if `b` is a subset of `a`.
                    is_subset(b, a)
                }
                std::cmp::Ordering::Equal => a == b,
            }
        }

        if reduce_string(&other.part_path)
            .is_some_and(|a| Some(a) == reduce_string(&self.part_path))
        {
            bail!(
                "\
The foreign_key ('{}', path_part: '{}' -> '{}') and our_key ('{}', path_part: '{}' -> '{}') \
have an identical path_part (when duplicated chars are removed)!
I cannot extended them via incrementation.
Please rename the paths to fix this.
                        ",
                other,
                &other.part_path,
                reduce_string(&other.part_path).expect("Is some here"),
                self,
                &self.part_path,
                reduce_string(&self.part_path).expect("Is some here"),
            );
        }

        if is_subset_either(&other.part_path, &self.part_path) {
            bail!(
                "\
The foreign_key ('{}', path_part: '{}') and our_key ('{}', path_part: '{}') \
are subsets of one another!
A discrimination through incrementation will not work!
Please rename the paths to fix this.
                        ",
                other,
                &other.part_path,
                self,
                &self.part_path,
            );
        }

        Ok(())
    }
}

impl std::fmt::Display for MapKey {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        f.write_char(self.key)
    }
}