use anyhow::Result;

use crate::zfs::Snapshot;
use crate::zfs::ZPool;

use crate::zfs::Dataset;

pub enum Todo {
    Absolute(Dataset, Snapshot),
    Incremental(Dataset, Snapshot, Snapshot),
    UpToDate(Dataset, Snapshot),
}

impl Todo {
    pub fn print(&self) {
        match self {
            Todo::Absolute(dataset, snapshot) => {
                println!("  {dataset}@{snapshot} -> [new]")
            }
            Todo::Incremental(dataset, last_common_snapshot, recent_snapshot) => {
                println!("  {dataset}@{last_common_snapshot} -> ...@{recent_snapshot}")
            }
            Todo::UpToDate(dataset, snapshot) => {
                println!("  {dataset}@{snapshot} is already backed up")
            }
        }
    }

    pub fn plan(
        local: &ZPool,
        remote: &ZPool,
        snapshot_tag: String,
        snapshot_interval: String,
    ) -> Result<Vec<Self>> {
        let mut result = vec![];

        for local_dataset in &local.datasets {
            let last_snapshot_with_tag =
                local_dataset.find_last_snapshot_with_tag(&snapshot_tag, &snapshot_interval)?;

            let remote_dataset = local_dataset.change_pool_name(remote);
            if !remote.contains(&remote_dataset) {
                result.push(Todo::Absolute(
                    local_dataset.clone(),
                    last_snapshot_with_tag,
                ));
                continue;
            }

            let remote_dataset = remote.get_matching_dataset(local_dataset).unwrap();

            let last_common_snapshot = Snapshot::find_last_common_snapshot_with_tag(
                local_dataset,
                &remote_dataset,
                &snapshot_tag,
            )
            .unwrap();

            let todo = if last_common_snapshot == last_snapshot_with_tag {
                Todo::UpToDate(local_dataset.clone(), last_common_snapshot)
            } else {
                Todo::Incremental(
                    local_dataset.clone(),
                    last_common_snapshot,
                    last_snapshot_with_tag,
                )
            };

            result.push(todo);
        }
        Ok(result)
    }
}