convertis/src/pathfinder.rs

// Copyright (C) 2026 Elias Wendland <eliaswendland@pm.me>
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, version 3 exclusively.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program.  If not, see <https://www.gnu.org/licenses/>.

use crate::plugin::Plugin;
use std::collections::{HashMap, VecDeque};
use std::rc::Rc;

#[derive(Clone)]
pub struct PathNode<'a> {
    pub plugin: &'a dyn Plugin,
    pub from_format: &'a str,
    pub to_format: &'a str,
    pub prev: Option<Rc<PathNode<'a>>>,
}

impl<'a> PathNode<'a> {
    pub fn get_path(&self) -> Vec<(&'a dyn Plugin, &'a str, &'a str)> {
        let mut path = Vec::new();
        path.push((self.plugin, self.from_format, self.to_format));

        let mut curr = self.prev.clone();
        while let Some(node) = curr {
            path.push((node.plugin, node.from_format, node.to_format));
            curr = node.prev.clone();
        }

        path.reverse();
        path
    }
}

#[tracing::instrument(skip(plugins))]
pub fn find_best_path<'a>(
    plugins: &'a [Box<dyn Plugin>],
    from_format: &'a str,
    to_format: &str,
    priority: &str,
    banned_plugins: &[&str],
) -> Option<Vec<(&'a dyn Plugin, &'a str, &'a str)>> {
    let mut adj_list: HashMap<&str, Vec<&'a dyn Plugin>> = HashMap::new();
    for p in plugins {
        if banned_plugins.contains(&p.name()) {
            tracing::trace!("Skipping banned plugin: {}", p.name());
            continue;
        }
        if !p.is_available() {
            tracing::trace!("Skipping unavailable plugin: {}", p.name());
            continue;
        }
        for &from in &p.from_formats() {
            adj_list.entry(from).or_default().push(p.as_ref());
        }
    }

    // BFS to find paths with least amount of conversions
    let mut queue = VecDeque::new();
    queue.push_back((from_format, None::<Rc<PathNode<'a>>>));

    let mut min_length = None;
    let mut best_paths: Vec<Vec<(&'a dyn Plugin, &'a str, &'a str)>> = Vec::new();

    let mut visited_depth = HashMap::new();
    visited_depth.insert(from_format, 0);

    while let Some((curr_format, prev_node)) = queue.pop_front() {
        let current_depth = visited_depth.get(curr_format).copied().unwrap_or(0);
        tracing::trace!("Visiting format node: {} at depth {}", curr_format, current_depth);

        if let Some(min_len) = min_length {
            if current_depth > min_len {
                tracing::trace!("Pruning path exploration at depth {} (min_len={})", current_depth, min_len);
                break; // We've moved beyond the shortest paths
            }
        }

        if curr_format == to_format && prev_node.is_some() {
            if min_length.is_none() {
                min_length = Some(current_depth);
            }
            if min_length == Some(current_depth) {
                best_paths.push(prev_node.unwrap().get_path());
            }
            continue;
        }

        if let Some(neighbors) = adj_list.get(curr_format) {
            for plugin in neighbors {
                for &next_format in &plugin.to_formats() {
                    let next_depth = current_depth + 1;

                    let prev_depth = visited_depth
                        .get(next_format)
                        .copied()
                        .unwrap_or(usize::MAX);

                    if next_depth <= prev_depth {
                        visited_depth.insert(next_format, next_depth);

                        let new_node = Rc::new(PathNode {
                            plugin: *plugin,
                            from_format: curr_format,
                            to_format: next_format,
                            prev: prev_node.clone(),
                        });

                        queue.push_back((next_format, Some(new_node)));
                    }
                }
            }
        }
    }

    if best_paths.is_empty() {
        tracing::debug!("No valid paths found from {} to {}.", from_format, to_format);
        return None;
    }

    tracing::debug!("Found {} path(s) of minimum length {}. Evaluating priority: '{}'", best_paths.len(), min_length.unwrap_or(0), priority);

    // Evaluate based on priority (maximize score)
    let best = best_paths
        .into_iter()
        .max_by(|path_a, path_b| compare_paths(path_a, path_b, priority));

    if let Some(ref path) = best {
        tracing::debug!("Selected path with length {}: {:?}", path.len(), path.iter().map(|p| p.0.name()).collect::<Vec<_>>());
    }
    best
}

fn compare_paths(
    path_a: &[(&dyn Plugin, &str, &str)],
    path_b: &[(&dyn Plugin, &str, &str)],
    priority: &str,
) -> std::cmp::Ordering {
    for ch in priority.chars() {
        match ch {
            'f' | 'F' => {
                let score_a: u32 = path_a
                    .iter()
                    .map(|(p, from, to)| p.familiarity(*from, *to) as u32)
                    .sum();
                let score_b: u32 = path_b
                    .iter()
                    .map(|(p, from, to)| p.familiarity(*from, *to) as u32)
                    .sum();
                if score_a != score_b {
                    return score_a.cmp(&score_b);
                }
            }
            'q' | 'Q' => {
                let score_a: u32 = path_a
                    .iter()
                    .map(|(p, from, to)| p.quality(*from, *to) as u32)
                    .sum();
                let score_b: u32 = path_b
                    .iter()
                    .map(|(p, from, to)| p.quality(*from, *to) as u32)
                    .sum();
                if score_a != score_b {
                    return score_a.cmp(&score_b);
                }
            }
            's' | 'S' => {
                let score_a: u32 = path_a
                    .iter()
                    .map(|(p, from, to)| p.speed(*from, *to) as u32)
                    .sum();
                let score_b: u32 = path_b
                    .iter()
                    .map(|(p, from, to)| p.speed(*from, *to) as u32)
                    .sum();
                if score_a != score_b {
                    return score_a.cmp(&score_b);
                }
            }
            _ => {}
        }
    }
    std::cmp::Ordering::Equal
}

#[cfg(test)]
mod tests {
    use super::*;

    struct MockPlugin {
        name: &'static str,
        from: Vec<&'static str>,
        to: Vec<&'static str>,
        f: u8,
        q: u8,
        s: u8,
    }

    impl Plugin for MockPlugin {
        fn name(&self) -> &'static str {
            self.name
        }
        fn from_formats(&self) -> Vec<&'static str> {
            self.from.clone()
        }
        fn to_formats(&self) -> Vec<&'static str> {
            self.to.clone()
        }
        fn familiarity(&self, _from: &str, _to: &str) -> u8 {
            self.f
        }
        fn quality(&self, _from: &str, _to: &str) -> u8 {
            self.q
        }
        fn speed(&self, _from: &str, _to: &str) -> u8 {
            self.s
        }
        fn convert(
            &self,
            _input: &[u8],
            _from: &str,
            _to: &str,
            _temp_dir: &std::path::Path,
        ) -> Result<Vec<u8>, String> {
            Ok(vec![])
        }
    }

    #[test]
    fn test_shortest_path() {
        let plugins: Vec<Box<dyn Plugin>> = vec![
            Box::new(MockPlugin {
                name: "A",
                from: vec!["jpeg"],
                to: vec!["png"],
                f: 10,
                q: 10,
                s: 10,
            }),
            Box::new(MockPlugin {
                name: "B",
                from: vec!["jpeg"],
                to: vec!["bmp"],
                f: 10,
                q: 10,
                s: 10,
            }),
            Box::new(MockPlugin {
                name: "C",
                from: vec!["bmp"],
                to: vec!["png"],
                f: 10,
                q: 10,
                s: 10,
            }),
        ];

        let path = find_best_path(&plugins, "jpeg", "png", "fqs", &[]).unwrap();
        assert_eq!(path.len(), 1);
        assert_eq!(path[0].0.name(), "A");
    }

    #[test]
    fn test_priority_tie_break() {
        let plugins: Vec<Box<dyn Plugin>> = vec![
            Box::new(MockPlugin {
                name: "A",
                from: vec!["jpeg"],
                to: vec!["png"],
                f: 10,
                q: 50,
                s: 10,
            }),
            Box::new(MockPlugin {
                name: "B",
                from: vec!["jpeg"],
                to: vec!["png"],
                f: 50,
                q: 10,
                s: 10,
            }),
        ];

        let path = find_best_path(&plugins, "jpeg", "png", "fqs", &[]).unwrap();
        assert_eq!(path[0].0.name(), "B");

        let path = find_best_path(&plugins, "jpeg", "png", "qfs", &[]).unwrap();
        assert_eq!(path[0].0.name(), "A");
    }

    macro_rules! test_pathfinder {
        ($name:ident, $from:expr, $to:expr, $priority:expr, $expected_len:expr, $expected_first:expr) => {
            #[test]
            fn $name() {
                let plugins: Vec<Box<dyn Plugin>> = vec![
                    Box::new(MockPlugin {
                        name: "A",
                        from: vec!["a"],
                        to: vec!["b"],
                        f: 10,
                        q: 10,
                        s: 10,
                    }),
                    Box::new(MockPlugin {
                        name: "B",
                        from: vec!["b"],
                        to: vec!["c"],
                        f: 20,
                        q: 10,
                        s: 10,
                    }),
                    Box::new(MockPlugin {
                        name: "C",
                        from: vec!["a"],
                        to: vec!["c"],
                        f: 5,
                        q: 10,
                        s: 10,
                    }),
                    Box::new(MockPlugin {
                        name: "D",
                        from: vec!["a"],
                        to: vec!["d"],
                        f: 10,
                        q: 20,
                        s: 10,
                    }),
                    Box::new(MockPlugin {
                        name: "E",
                        from: vec!["d"],
                        to: vec!["c"],
                        f: 10,
                        q: 20,
                        s: 10,
                    }),
                    Box::new(MockPlugin {
                        name: "F",
                        from: vec!["a"],
                        to: vec!["b"],
                        f: 50,
                        q: 5,
                        s: 5,
                    }), // High familiarity, low q/s
                    Box::new(MockPlugin {
                        name: "G",
                        from: vec!["c"],
                        to: vec!["e"],
                        f: 10,
                        q: 10,
                        s: 50,
                    }),
                ];

                let path = find_best_path(&plugins, $from, $to, $priority, &[]);
                if $expected_len == 0 {
                    assert!(path.is_none());
                } else {
                    let p = path.unwrap();
                    assert_eq!(p.len(), $expected_len);
                    assert_eq!(p[0].0.name(), $expected_first);
                }
            }
        };
    }

    test_pathfinder!(test_path_1, "a", "b", "fqs", 1, "F"); // F has higher f
    test_pathfinder!(test_path_2, "a", "b", "qfs", 1, "A"); // A has higher q
    test_pathfinder!(test_path_3, "a", "c", "fqs", 1, "C"); // Shortest path is length 1 (C)
    test_pathfinder!(test_path_4, "a", "d", "fqs", 1, "D");
    test_pathfinder!(test_path_5, "d", "c", "fqs", 1, "E");
    test_pathfinder!(test_path_6, "a", "e", "fqs", 2, "C"); // Shortest path to e goes through c. So a->c (C), c->e (G)
    test_pathfinder!(test_path_7, "b", "e", "fqs", 2, "B");
    test_pathfinder!(test_path_8, "e", "a", "fqs", 0, ""); // No path
    test_pathfinder!(test_path_9, "c", "b", "fqs", 0, ""); // No path
    test_pathfinder!(test_path_10, "x", "y", "fqs", 0, ""); // No path

    macro_rules! test_pathfinder_2 {
        ($name:ident, $from:expr, $to:expr, $priority:expr, $expected_len:expr) => {
            #[test]
            fn $name() {
                let plugins: Vec<Box<dyn Plugin>> = vec![
                    Box::new(MockPlugin {
                        name: "1",
                        from: vec!["1"],
                        to: vec!["2"],
                        f: 10,
                        q: 10,
                        s: 10,
                    }),
                    Box::new(MockPlugin {
                        name: "2",
                        from: vec!["2"],
                        to: vec!["3"],
                        f: 10,
                        q: 10,
                        s: 10,
                    }),
                    Box::new(MockPlugin {
                        name: "3",
                        from: vec!["3"],
                        to: vec!["4"],
                        f: 10,
                        q: 10,
                        s: 10,
                    }),
                    Box::new(MockPlugin {
                        name: "4",
                        from: vec!["4"],
                        to: vec!["5"],
                        f: 10,
                        q: 10,
                        s: 10,
                    }),
                    Box::new(MockPlugin {
                        name: "5",
                        from: vec!["5"],
                        to: vec!["6"],
                        f: 10,
                        q: 10,
                        s: 10,
                    }),
                ];
                let path = find_best_path(&plugins, $from, $to, $priority, &[]);
                if $expected_len == 0 {
                    assert!(path.is_none());
                } else {
                    assert_eq!(path.unwrap().len(), $expected_len);
                }
            }
        };
    }

    test_pathfinder_2!(test_p2_1, "1", "2", "f", 1);
    test_pathfinder_2!(test_p2_2, "1", "3", "f", 2);
    test_pathfinder_2!(test_p2_3, "1", "4", "f", 3);
    test_pathfinder_2!(test_p2_4, "1", "5", "f", 4);
    test_pathfinder_2!(test_p2_5, "1", "6", "f", 5);
    test_pathfinder_2!(test_p2_6, "2", "6", "f", 4);
    test_pathfinder_2!(test_p2_7, "3", "6", "f", 3);
    test_pathfinder_2!(test_p2_8, "4", "6", "f", 2);
    test_pathfinder_2!(test_p2_9, "5", "6", "f", 1);
    test_pathfinder_2!(test_p2_10, "6", "1", "f", 0);
}