use std::collections::{HashMap, HashSet};
use std::path::PathBuf;

use anyhow::Error;

use pbs_api_types::KeepOptions;

use super::BackupInfo;

#[derive(Clone, Copy, PartialEq, Eq)]
pub enum PruneMark {
    Protected,
    Keep,
    KeepPartial,
    Remove,
}

impl PruneMark {
    pub fn keep(self) -> bool {
        self != PruneMark::Remove
    }

    pub fn protected(self) -> bool {
        self == PruneMark::Protected
    }
}

impl std::fmt::Display for PruneMark {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        f.write_str(match self {
            PruneMark::Protected => "protected",
            PruneMark::Keep => "keep",
            PruneMark::KeepPartial => "keep-partial",
            PruneMark::Remove => "remove",
        })
    }
}

fn mark_selections<F: Fn(&BackupInfo) -> Result<String, Error>>(
    mark: &mut HashMap<PathBuf, PruneMark>,
    list: &[BackupInfo],
    keep: usize,
    select_id: F,
) -> Result<(), Error> {
    let mut include_hash = HashSet::new();

    let mut already_included = HashSet::new();
    for info in list {
        let backup_id = info.backup_dir.relative_path();
        if let Some(PruneMark::Keep) = mark.get(&backup_id) {
            let sel_id: String = select_id(info)?;
            already_included.insert(sel_id);
        }
    }

    for info in list {
        let backup_id = info.backup_dir.relative_path();
        if mark.get(&backup_id).is_some() {
            continue;
        }
        if info.protected {
            mark.insert(backup_id, PruneMark::Protected);
            continue;
        }
        let sel_id: String = select_id(info)?;

        if already_included.contains(&sel_id) {
            continue;
        }

        if !include_hash.contains(&sel_id) {
            if include_hash.len() >= keep {
                break;
            }
            include_hash.insert(sel_id);
            mark.insert(backup_id, PruneMark::Keep);
        } else {
            mark.insert(backup_id, PruneMark::Remove);
        }
    }

    Ok(())
}

fn remove_incomplete_snapshots(mark: &mut HashMap<PathBuf, PruneMark>, list: &[BackupInfo]) {
    let mut keep_unfinished = true;
    for info in list.iter() {
        // backup is considered unfinished if there is no manifest
        if info.is_finished() {
            // There is a new finished backup, so there is no need
            // to keep older unfinished backups.
            keep_unfinished = false;
        } else {
            let backup_id = info.backup_dir.relative_path();
            if keep_unfinished {
                // keep first unfinished
                mark.insert(backup_id, PruneMark::KeepPartial);
            } else {
                mark.insert(backup_id, PruneMark::Remove);
            }
            keep_unfinished = false;
        }
    }
}

/// This filters incomplete and kept backups.
pub fn compute_prune_info(
    mut list: Vec<BackupInfo>,
    options: &KeepOptions,
) -> Result<Vec<(BackupInfo, PruneMark)>, Error> {
    let mut mark = HashMap::new();

    BackupInfo::sort_list(&mut list, false);

    remove_incomplete_snapshots(&mut mark, &list);

    if let Some(keep_last) = options.keep_last {
        mark_selections(&mut mark, &list, keep_last as usize, |info| {
            Ok(info.backup_dir.backup_time_string().to_owned())
        })?;
    }

    use proxmox_time::strftime_local;

    if let Some(keep_hourly) = options.keep_hourly {
        mark_selections(&mut mark, &list, keep_hourly as usize, |info| {
            strftime_local("%Y/%m/%d/%H", info.backup_dir.backup_time()).map_err(Error::from)
        })?;
    }

    if let Some(keep_daily) = options.keep_daily {
        mark_selections(&mut mark, &list, keep_daily as usize, |info| {
            strftime_local("%Y/%m/%d", info.backup_dir.backup_time()).map_err(Error::from)
        })?;
    }

    if let Some(keep_weekly) = options.keep_weekly {
        mark_selections(&mut mark, &list, keep_weekly as usize, |info| {
            // Note: Use iso-week year/week here. This year number
            // might not match the calendar year number.
            strftime_local("%G/%V", info.backup_dir.backup_time()).map_err(Error::from)
        })?;
    }

    if let Some(keep_monthly) = options.keep_monthly {
        mark_selections(&mut mark, &list, keep_monthly as usize, |info| {
            strftime_local("%Y/%m", info.backup_dir.backup_time()).map_err(Error::from)
        })?;
    }

    if let Some(keep_yearly) = options.keep_yearly {
        mark_selections(&mut mark, &list, keep_yearly as usize, |info| {
            strftime_local("%Y", info.backup_dir.backup_time()).map_err(Error::from)
        })?;
    }

    let prune_info: Vec<(BackupInfo, PruneMark)> = list
        .into_iter()
        .map(|info| {
            let backup_id = info.backup_dir.relative_path();
            let mark = if info.protected {
                PruneMark::Protected
            } else {
                mark.get(&backup_id).copied().unwrap_or(PruneMark::Remove)
            };

            (info, mark)
        })
        .collect();

    Ok(prune_info)
}