bake 0.6.0

use crate::bakefile::Bakefile;
use std::{collections::HashSet, convert::AsRef};

// Compute a topological sort of the transitive reflexive closure of a set of
// tasks. The resulting schedule does not depend on the order of the inputs or
// dependencies. We assume the tasks form a DAG [ref:tasks_dag].
pub fn compute<'a>(bakefile: &'a Bakefile, tasks: &[&'a str]) -> Vec<&'a str> {
  // Sort the input tasks to ensure the given order doesn't matter.
  let mut roots: Vec<&'a str> = tasks.to_vec();
  roots.sort();

  // We will use this set to keep track of what tasks have already been
  // seen.
  let mut visited: HashSet<&'a str> = HashSet::new();

  // This vector accumulates the final schedule.
  let mut schedule: Vec<&'a str> = vec![];

  // For each root, compute its transitive reflexive closure, topsort it, and
  // add it to the schedule.
  for root in roots {
    // The frontier is a stack, which means we are doing a depth-first
    // traversal.
    let mut frontier: Vec<(&'a str, bool)> = vec![(root, true)];

    // This vector will accumulate the topsorted tasks.
    let mut topological_sort: Vec<&'a str> = vec![];

    // Keep processing nodes on the frontier until there aren't any more left.
    // [tag:schedule_frontier_nonempty]
    while !frontier.is_empty() {
      // Pop a task from the frontier. [ref:schedule_frontier_nonempty]
      let (task, new) = frontier.pop().unwrap();

      // Check if this is a new task or one that we are coming back to because
      // we finished processing its dependencies.
      if new {
        // If we have already scheduled this root task, skip to the next one.
        if visited.contains(task) {
          continue;
        }

        // Mark this task as seen so we don't process it again.
        visited.insert(task);

        // Come back to this task once all its dependencies have been processed.
        frontier.push((task, false));

        // Add the task's dependencies to the frontier. We sort the
        // dependencies first to ensure their original order doesn't matter.
        // After sorting, we reverse the order of the dependencies before
        // adding them to the frontier so that they will be processed in
        // lexicographical order (since the frontier is a stack rather than a
        // queue). The indexing is safe due to [ref:tasks_valid].
        let mut dependencies: Vec<&'a str> = bakefile.tasks[task]
          .dependencies
          .iter()
          .map(AsRef::as_ref)
          .collect();
        dependencies.sort();
        dependencies.reverse();
        frontier.extend(
          dependencies
            .into_iter()
            .map(|dependency| (dependency, true)),
        );
      } else {
        // Now that the task's dependencies have been processed, schedule it.
        topological_sort.push(task);
      }
    }

    // Add the topsorted tasks to the schedule.
    schedule.extend(topological_sort);
  }

  // Return the final schedule.
  schedule
}

#[cfg(test)]
mod tests {
  use crate::bakefile::{Bakefile, Task, DEFAULT_LOCATION, DEFAULT_USER};
  use crate::schedule::compute;
  use std::{collections::HashMap, path::Path};

  fn task_with_dependencies(dependencies: Vec<String>) -> Task {
    Task {
      dependencies,
      cache: true,
      environment: HashMap::new(),
      input_paths: vec![],
      output_paths: vec![],
      location: Path::new(DEFAULT_LOCATION).to_owned(),
      user: DEFAULT_USER.to_owned(),
      command: None,
    }
  }

  fn empty_task() -> Task {
    task_with_dependencies(vec![])
  }

  #[test]
  fn schedule_empty() {
    let bakefile = Bakefile {
      image: "encom:os-12".to_owned(),
      default: None,
      tasks: HashMap::new(),
    };

    let actual: Vec<&str> = compute(&bakefile, &[]);
    let expected: Vec<&str> = vec![];

    assert_eq!(actual, expected);
  }

  #[test]
  fn schedule_single() {
    let mut tasks = HashMap::new();
    tasks.insert("foo".to_owned(), empty_task());

    let bakefile = Bakefile {
      image: "encom:os-12".to_owned(),
      default: None,
      tasks,
    };

    let actual: Vec<&str> = compute(&bakefile, &["foo"]);
    let expected: Vec<&str> = vec!["foo"];

    assert_eq!(actual, expected);
  }

  #[test]
  fn schedule_linear() {
    let mut tasks = HashMap::new();
    tasks.insert("foo".to_owned(), empty_task());
    tasks.insert(
      "bar".to_owned(),
      task_with_dependencies(vec!["foo".to_owned()]),
    );
    tasks.insert(
      "baz".to_owned(),
      task_with_dependencies(vec!["bar".to_owned()]),
    );

    let bakefile = Bakefile {
      image: "encom:os-12".to_owned(),
      default: None,
      tasks,
    };

    let actual: Vec<&str> = compute(&bakefile, &["baz"]);
    let expected: Vec<&str> = vec!["foo", "bar", "baz"];

    assert_eq!(actual, expected);
  }

  #[test]
  fn schedule_diamond() {
    let mut tasks = HashMap::new();
    tasks.insert("foo".to_owned(), empty_task());
    tasks.insert(
      "bar".to_owned(),
      task_with_dependencies(vec!["foo".to_owned()]),
    );
    tasks.insert(
      "baz".to_owned(),
      task_with_dependencies(vec!["foo".to_owned()]),
    );
    tasks.insert(
      "qux".to_owned(),
      task_with_dependencies(vec!["bar".to_owned(), "baz".to_owned()]),
    );

    let bakefile = Bakefile {
      image: "encom:os-12".to_owned(),
      default: None,
      tasks,
    };

    let actual: Vec<&str> = compute(&bakefile, &["qux"]);
    let expected: Vec<&str> = vec!["foo", "bar", "baz", "qux"];

    assert_eq!(actual, expected);
  }

  #[test]
  fn schedule_lexicographical_tie_breaking() {
    let mut tasks = HashMap::new();
    tasks.insert("foo".to_owned(), empty_task());
    tasks.insert("bar".to_owned(), empty_task());
    tasks.insert("baz".to_owned(), empty_task());

    let bakefile = Bakefile {
      image: "encom:os-12".to_owned(),
      default: None,
      tasks,
    };

    let actual: Vec<&str> = compute(&bakefile, &["foo", "bar", "baz"]);
    let expected: Vec<&str> = vec!["bar", "baz", "foo"];

    assert_eq!(actual, expected);
  }

  #[test]
  fn schedule_dependency_duplicates() {
    let mut tasks1 = HashMap::new();
    tasks1.insert("foo".to_owned(), empty_task());
    tasks1.insert("bar".to_owned(), empty_task());
    tasks1.insert(
      "baz".to_owned(),
      task_with_dependencies(vec![
        "foo".to_owned(),
        "bar".to_owned(),
        "foo".to_owned(),
      ]),
    );

    let mut tasks2 = HashMap::new();
    tasks2.insert("foo".to_owned(), empty_task());
    tasks2.insert("bar".to_owned(), empty_task());
    tasks2.insert(
      "baz".to_owned(),
      task_with_dependencies(vec![
        "bar".to_owned(),
        "foo".to_owned(),
        "bar".to_owned(),
      ]),
    );

    let bakefile1 = Bakefile {
      image: "encom:os-12".to_owned(),
      default: None,
      tasks: tasks1,
    };

    let bakefile2 = Bakefile {
      image: "encom:os-12".to_owned(),
      default: None,
      tasks: tasks2,
    };

    let first: Vec<&str> = compute(&bakefile1, &["baz"]);
    let second: Vec<&str> = compute(&bakefile2, &["baz"]);

    assert_eq!(first, second);
  }

  #[test]
  fn schedule_input_duplicates() {
    let mut tasks = HashMap::new();
    tasks.insert("foo".to_owned(), empty_task());
    tasks.insert("bar".to_owned(), empty_task());
    tasks.insert("baz".to_owned(), empty_task());

    let bakefile = Bakefile {
      image: "encom:os-12".to_owned(),
      default: None,
      tasks,
    };

    let first: Vec<&str> = compute(&bakefile, &["baz", "bar", "baz"]);
    let second: Vec<&str> = compute(&bakefile, &["bar", "baz", "bar"]);

    assert_eq!(first, second);
  }

  #[test]
  fn schedule_dependency_order() {
    let mut tasks1 = HashMap::new();
    tasks1.insert("foo".to_owned(), empty_task());
    tasks1.insert("bar".to_owned(), empty_task());
    tasks1.insert("baz".to_owned(), empty_task());
    tasks1.insert(
      "qux".to_owned(),
      task_with_dependencies(vec![
        "foo".to_owned(),
        "bar".to_owned(),
        "baz".to_owned(),
      ]),
    );

    let mut tasks2 = HashMap::new();
    tasks2.insert("foo".to_owned(), empty_task());
    tasks2.insert("bar".to_owned(), empty_task());
    tasks2.insert("baz".to_owned(), empty_task());
    tasks2.insert(
      "qux".to_owned(),
      task_with_dependencies(vec![
        "baz".to_owned(),
        "bar".to_owned(),
        "foo".to_owned(),
      ]),
    );

    let bakefile1 = Bakefile {
      image: "encom:os-12".to_owned(),
      default: None,
      tasks: tasks1,
    };

    let bakefile2 = Bakefile {
      image: "encom:os-12".to_owned(),
      default: None,
      tasks: tasks2,
    };

    let first: Vec<&str> = compute(&bakefile1, &["baz"]);
    let second: Vec<&str> = compute(&bakefile2, &["baz"]);

    assert_eq!(first, second);
  }

  #[test]
  fn schedule_input_order() {
    let mut tasks = HashMap::new();
    tasks.insert("foo".to_owned(), empty_task());
    tasks.insert("bar".to_owned(), empty_task());
    tasks.insert("baz".to_owned(), empty_task());

    let bakefile = Bakefile {
      image: "encom:os-12".to_owned(),
      default: None,
      tasks,
    };

    let first: Vec<&str> = compute(&bakefile, &["foo", "bar", "baz"]);
    let second: Vec<&str> = compute(&bakefile, &["baz", "bar", "foo"]);

    assert_eq!(first, second);
  }
}