//! Disk quota and age sweeps. Replaces iPXQuotaManager.py ("SmartSpace").

use anyhow::Result;

use crate::config::Config;
use crate::db::{Candidate, Db, now};

/// Headroom kept below the quota, as getToQuota()'s `1048576 * 50` did.
pub const PAD_BYTES: u64 = 50 * 1024 * 1024;

#[derive(Debug, Default)]
pub struct Report {
    pub reconciled: usize,
    pub aged_out: Vec<Candidate>,
    pub over_quota: Vec<Candidate>,
    pub entries_pruned: usize,
    pub bytes_freed: u64,
}

/// Oldest-first until enough is freed. Pure, so the ordering rule is testable without a disk.
pub fn pick(candidates: &[Candidate], total: u64, limit: u64) -> Vec<Candidate> {
    let ceiling = limit.saturating_sub(PAD_BYTES);
    if total <= ceiling {
        return vec![];
    }
    let mut need = total - ceiling;
    let mut out = vec![];
    for c in candidates {
        if need == 0 {
            break;
        }
        let size = c.bytes.max(0) as u64;
        out.push(c.clone());
        need = need.saturating_sub(size);
    }
    out
}

/// Files older than the cutoff. Flagged ones are already excluded by the query.
pub fn aged(candidates: &[Candidate], cutoff: i64) -> Vec<Candidate> {
    candidates
        .iter()
        .filter(|c| c.age_key > 0 && c.age_key < cutoff)
        .cloned()
        .collect()
}

pub fn run(cfg: &Config, db: &Db, dry_run: bool) -> Result<Report> {
    let mut report = Report::default();

    // Someone may have deleted a file by hand; the row must stop claiming it exists.
    for (id, path) in db.missing_files()? {
        if !dry_run {
            db.mark_reaped(id)?;
        }
        tracing::debug!(path, "file gone, row reaped");
        report.reconciled += 1;
    }

    let candidates = db.reap_candidates()?;

    if cfg.general.max_age_days > 0 {
        let cutoff = now() - (cfg.general.max_age_days * 86_400) as i64;
        report.aged_out = aged(&candidates, cutoff);
        for c in &report.aged_out {
            report.bytes_freed += remove(db, c, dry_run)?;
        }
        if !dry_run {
            report.entries_pruned = db.prune_entries(cutoff)?;
        }
    }

    if cfg.general.max_total_gb > 0.0 {
        let limit = (cfg.general.max_total_gb * 1_073_741_824.0) as u64;
        // Re-read: the age sweep may already have freed enough.
        let remaining: Vec<Candidate> = candidates
            .iter()
            .filter(|c| !report.aged_out.iter().any(|a| a.id == c.id))
            .cloned()
            .collect();
        let total: u64 = remaining.iter().map(|c| c.bytes.max(0) as u64).sum();
        report.over_quota = pick(&remaining, total, limit);
        for c in &report.over_quota {
            report.bytes_freed += remove(db, c, dry_run)?;
        }
    }

    Ok(report)
}

fn remove(db: &Db, c: &Candidate, dry_run: bool) -> Result<u64> {
    if dry_run {
        return Ok(c.bytes.max(0) as u64);
    }
    let size = std::fs::metadata(&c.path).map(|m| m.len()).unwrap_or(c.bytes.max(0) as u64);
    // Missing is fine: the point is that it is gone.
    if let Err(e) = std::fs::remove_file(&c.path)
        && e.kind() != std::io::ErrorKind::NotFound
    {
        tracing::warn!(path = c.path, error = %e, "could not delete");
        return Ok(0);
    }
    db.mark_reaped(c.id)?;
    Ok(size)
}

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

    fn cand(id: i64, bytes: i64, age_key: i64, read: bool) -> Candidate {
        Candidate {
            id,
            url: format!("https://x/{id}"),
            path: format!("/tmp/{id}"),
            bytes,
            age_key,
            read,
        }
    }

    #[test]
    fn pick_takes_oldest_first_and_stops_once_under() {
        let gb = 1_073_741_824u64;
        // Ten 1 GB files, oldest first as the query would return them.
        let cands: Vec<Candidate> = (1..=10).map(|i| cand(i, gb as i64, i, true)).collect();

        // 10 GB used against a 6 GB quota: need 4 GB back, plus the 50 MB pad.
        let picked = pick(&cands, 10 * gb, 6 * gb);
        assert_eq!(
            picked.iter().map(|c| c.id).collect::<Vec<_>>(),
            vec![1, 2, 3, 4, 5],
            "oldest first, one extra to clear the headroom pad"
        );
    }

    #[test]
    fn pick_deletes_nothing_when_under_quota() {
        let gb = 1_073_741_824u64;
        let cands: Vec<Candidate> = (1..=3).map(|i| cand(i, gb as i64, i, true)).collect();
        assert!(pick(&cands, 3 * gb, 50 * gb).is_empty());
    }

    #[test]
    fn aged_only_takes_files_past_the_cutoff() {
        let cands = vec![cand(1, 10, 100, true), cand(2, 10, 500, true), cand(3, 10, 0, true)];
        let picked = aged(&cands, 200);
        assert_eq!(picked.iter().map(|c| c.id).collect::<Vec<_>>(), vec![1]);
        // age_key 0 means "never recorded" -- not the same as "infinitely old".
    }

    #[test]
    fn query_never_offers_flagged_files_and_prefers_read_ones() {
        let db = Db::memory().unwrap();
        db.exec_for_test(
            "INSERT INTO entries (feed_id, guid, first_seen, read, flagged) VALUES
                ('f', 'keep',   0, 1, 1),
                ('f', 'unread', 0, 0, 0),
                ('f', 'read',   0, 1, 0);
             INSERT INTO enclosures (id, feed_id, guid, url, path, bytes_done, state, downloaded_at) VALUES
                (1, 'f', 'keep',   'u1', '/tmp/keep',   10, 'done', 10),
                (2, 'f', 'unread', 'u2', '/tmp/unread', 10, 'done', 20),
                (3, 'f', 'read',   'u3', '/tmp/read',   10, 'done', 30);",
        )
        .unwrap();

        let got: Vec<i64> = db.reap_candidates().unwrap().iter().map(|c| c.id).collect();
        assert_eq!(got, vec![3, 2], "flagged excluded; read goes before unread");
    }

    #[test]
    fn prune_keeps_entries_that_still_have_a_file() {
        let db = Db::memory().unwrap();
        db.exec_for_test(
            "INSERT INTO entries (feed_id, guid, first_seen, read, flagged) VALUES
                ('f', 'has-file', 100, 1, 0),
                ('f', 'no-file',  100, 1, 0),
                ('f', 'flagged',  100, 1, 1),
                ('f', 'recent',   900, 1, 0);
             INSERT INTO enclosures (id, feed_id, guid, url, path, state) VALUES
                (1, 'f', 'has-file', 'u1', '/tmp/x', 'done');",
        )
        .unwrap();

        assert_eq!(db.prune_entries(500).unwrap(), 1, "only the old, fileless, unflagged one");
    }
}