//! Inspection (spec §27): blame from atom keys, and bisect over
//! dependency-closed prefixes of the candidates between a good and a bad
//! state.

use super::*;

/// One line of `oxy blame`.
#[derive(Clone, Debug)]
pub struct BlameLine {
    pub line: usize,
    pub hash: ChangeHash,
    pub index: u32,
    pub change_id: ChangeId,
    pub author: String,
    pub when_ms: u64,
    pub text: Vec<u8>,
}

/// Where a bisect stands.
#[derive(Clone, Debug, PartialEq, Eq)]
pub enum BisectStep {
    /// More `good`/`bad` marks are needed before the search can start.
    NeedMarks { good: usize, bad: usize },
    /// A state is checked out for testing.
    Testing {
        heads: Vec<ChangeHash>,
        remaining: usize,
        steps_left: u32,
    },
    /// The first change whose inclusion makes the state bad.
    Found { culprit: ChangeHash },
    /// Every remaining candidate was skipped.
    Inconclusive { candidates: Vec<ChangeHash> },
}

#[derive(Clone, Debug, Default)]
struct BisectState {
    start: Vec<ChangeHash>,
    good: Vec<ChangeHash>,
    bad: Vec<ChangeHash>,
    candidates: Vec<ChangeHash>,
    lo: usize,
    hi: usize,
    /// The prefix length currently checked out for testing.
    testing: Option<usize>,
    skipped: Vec<usize>,
}

fn hashes_line(v: &[ChangeHash]) -> String {
    v.iter().map(|h| h.to_hex()).collect::<Vec<_>>().join(" ")
}
fn hashes_from(s: &str) -> Vec<ChangeHash> {
    s.split_whitespace()
        .filter_map(ObjectRef::from_hex)
        .collect()
}

impl Repo {
    /// The introducing change, author, and date of every line of `path` in
    /// the working copy's base state (spec §27).
    pub fn blame(&self, path: &str) -> Result<Vec<BlameLine>> {
        let snap = self.snapshot("oxy blame")?;
        self.blame_state(
            path,
            &snap.base,
            &snap.base_snapshot.tree,
            "the working copy's base state",
        )
    }

    /// Blame `path` in the state with these heads (hosted repositories).
    pub fn blame_in(&self, path: &str, heads: &[ChangeHash]) -> Result<Vec<BlameLine>> {
        let state = self.load_state(heads)?;
        self.blame_of(&state, &state.tree().view(), path)
    }

    /// Blame `path` in a loaded state whose tree view the caller holds; no
    /// file other than `path` is rendered.
    pub fn blame_of(
        &self,
        state: &crate::state::State,
        tree: &crate::tree::TreeView,
        path: &str,
    ) -> Result<Vec<BlameLine>> {
        self.blame_state(path, state, tree, "that state")
    }

    fn blame_state(
        &self,
        path: &str,
        state: &crate::state::State,
        tree: &crate::tree::TreeView,
        what: &str,
    ) -> Result<Vec<BlameLine>> {
        let Some(f) = tree.entries.get(path) else {
            return fail(format!("{path} is not in {what}"));
        };
        if f.kind != crate::objects::NodeKind::File || f.mode.opaque {
            return fail(format!("{path} is not a text file"));
        }
        let mut out = Vec::new();
        for (i, ((hash, index), text)) in state.live_lines(&f.node).into_iter().enumerate() {
            let meta = state.get(&hash);
            let author = match meta {
                Some(m) if !m.author.is_zero() => self
                    .store
                    .get_identity(&m.author)
                    .map(|id| id.name)
                    .unwrap_or_else(|_| m.author.short(12)),
                Some(m) => m
                    .message
                    .lines()
                    .rev()
                    .find_map(|l| l.strip_prefix("Git-Author: "))
                    .map(|a| a.split('<').next().unwrap_or(a).trim().to_string())
                    .unwrap_or_else(|| "unknown".into()),
                None => "unknown".into(),
            };
            out.push(BlameLine {
                line: i + 1,
                hash,
                index,
                change_id: meta.map(|m| m.change_id).unwrap_or(ChangeId([0; 16])),
                author,
                when_ms: meta.map(|m| m.hlc.wall_ms).unwrap_or(0),
                text,
            });
        }
        Ok(out)
    }

    // ------------------------------------------------------------ bisect

    fn bisect_dir(&self) -> PathBuf {
        self.oxy.join("bisect")
    }

    fn bisect_load(&self) -> Result<Option<BisectState>> {
        let dir = self.bisect_dir();
        if !dir.join("start").exists() {
            return Ok(None);
        }
        let read = |name: &str| fs::read_to_string(dir.join(name)).unwrap_or_default();
        let nums: Vec<usize> = read("range")
            .split_whitespace()
            .filter_map(|n| n.parse().ok())
            .collect();
        Ok(Some(BisectState {
            start: hashes_from(&read("start")),
            good: hashes_from(&read("good")),
            bad: hashes_from(&read("bad")),
            candidates: hashes_from(&read("candidates")),
            lo: nums.first().copied().unwrap_or(0),
            hi: nums.get(1).copied().unwrap_or(0),
            testing: nums.get(2).copied().filter(|_| nums.len() > 2),
            skipped: read("skipped")
                .split_whitespace()
                .filter_map(|n| n.parse().ok())
                .collect(),
        }))
    }

    fn bisect_save(&self, st: &BisectState) -> Result<()> {
        let dir = self.bisect_dir();
        fs::create_dir_all(&dir)?;
        write_atomic(&dir.join("start"), hashes_line(&st.start).as_bytes())?;
        write_atomic(&dir.join("good"), hashes_line(&st.good).as_bytes())?;
        write_atomic(&dir.join("bad"), hashes_line(&st.bad).as_bytes())?;
        write_atomic(
            &dir.join("candidates"),
            hashes_line(&st.candidates).as_bytes(),
        )?;
        let mut range = format!("{} {}", st.lo, st.hi);
        if let Some(t) = st.testing {
            range.push_str(&format!(" {t}"));
        }
        write_atomic(&dir.join("range"), range.as_bytes())?;
        write_atomic(
            &dir.join("skipped"),
            st.skipped
                .iter()
                .map(|n| n.to_string())
                .collect::<Vec<_>>()
                .join(" ")
                .as_bytes(),
        )?;
        Ok(())
    }

    /// Begin a bisect: remembers the working copy's base to restore later.
    pub fn bisect_start(&self) -> Result<()> {
        if self.bisect_load()?.is_some() {
            return fail("a bisect is in progress; finish it or run `oxy bisect reset`");
        }
        let (_, wc) = self.working_copy()?;
        let start = self.load_state(&wc.deps)?.maximal(&wc.deps);
        self.bisect_save(&BisectState {
            start,
            ..Default::default()
        })
    }

    pub fn bisect_reset(&self) -> Result<()> {
        let Some(st) = self.bisect_load()? else {
            return fail("no bisect in progress");
        };
        self.checkout(&st.start, false, "oxy bisect reset")?;
        fs::remove_dir_all(self.bisect_dir())?;
        Ok(())
    }

    pub fn bisect_status(&self) -> Result<Option<BisectStep>> {
        let Some(st) = self.bisect_load()? else {
            return Ok(None);
        };
        Ok(Some(self.bisect_step(&st)))
    }

    fn bisect_step(&self, st: &BisectState) -> BisectStep {
        if st.candidates.is_empty() {
            return BisectStep::NeedMarks {
                good: st.good.len(),
                bad: st.bad.len(),
            };
        }
        if st.hi <= st.lo + 1 {
            return BisectStep::Found {
                culprit: st.candidates[st.lo],
            };
        }
        match st.testing {
            Some(_) => {
                let remaining = st.hi - st.lo;
                BisectStep::Testing {
                    heads: self.bisect_heads(st, st.testing.unwrap()),
                    remaining,
                    steps_left: (remaining as f64).log2().ceil() as u32,
                }
            }
            None => BisectStep::Inconclusive {
                candidates: st.candidates[st.lo..st.hi].to_vec(),
            },
        }
    }

    /// `good ∪ candidates[..k]`, as heads.
    fn bisect_heads(&self, st: &BisectState, k: usize) -> Vec<ChangeHash> {
        let mut all = st.good.clone();
        all.extend(st.candidates[..k].iter().copied());
        self.load_state(&all)
            .map(|s| s.maximal(&all))
            .unwrap_or(all)
    }

    /// Check out the midpoint of the open range, skipping indices marked
    /// untestable, and record it as the state under test.
    fn bisect_advance(&self, st: &mut BisectState) -> Result<BisectStep> {
        if st.hi <= st.lo + 1 {
            st.testing = None;
            self.bisect_save(st)?;
            return Ok(BisectStep::Found {
                culprit: st.candidates[st.lo],
            });
        }
        let mid = st.lo + (st.hi - st.lo) / 2;
        // Try mid, then the nearest untried indices on either side.
        let mut order = vec![mid];
        for d in 1..(st.hi - st.lo) {
            if mid + d < st.hi {
                order.push(mid + d);
            }
            if mid > st.lo + d {
                order.push(mid - d);
            }
        }
        let Some(k) = order.into_iter().find(|k| !st.skipped.contains(k)) else {
            st.testing = None;
            self.bisect_save(st)?;
            return Ok(BisectStep::Inconclusive {
                candidates: st.candidates[st.lo..st.hi].to_vec(),
            });
        };
        let heads = self.bisect_heads(st, k);
        self.checkout(
            &heads,
            false,
            &format!("oxy bisect (testing {k} of {})", st.candidates.len()),
        )?;
        st.testing = Some(k);
        self.bisect_save(st)?;
        let remaining = st.hi - st.lo;
        Ok(BisectStep::Testing {
            heads,
            remaining,
            steps_left: (remaining as f64).log2().ceil() as u32,
        })
    }

    /// Mark states good or bad. With `changes`, before the search starts,
    /// they name known-good or known-bad states; without, the state under
    /// test gets the verdict. `None` for `good` means skip (untestable).
    pub fn bisect_mark(&self, good: Option<bool>, changes: &[ChangeHash]) -> Result<BisectStep> {
        let Some(mut st) = self.bisect_load()? else {
            return fail("no bisect in progress; run `oxy bisect start`");
        };
        if !changes.is_empty() {
            if !st.candidates.is_empty() {
                return fail("the search has started; mark the state under test with plain `oxy bisect good|bad`");
            }
            match good {
                Some(true) => st.good.extend(changes.iter().copied()),
                Some(false) => st.bad.extend(changes.iter().copied()),
                None => return fail("skip applies to the state under test"),
            }
            if st.good.is_empty() || st.bad.is_empty() {
                self.bisect_save(&st)?;
                return Ok(BisectStep::NeedMarks {
                    good: st.good.len(),
                    bad: st.bad.len(),
                });
            }
            let good_heads = self.load_state(&st.good)?.maximal(&st.good);
            let bad_heads = self.load_state(&st.bad)?.maximal(&st.bad);
            st.good = good_heads.clone();
            st.bad = bad_heads.clone();
            st.candidates = self.negotiate(&good_heads, &bad_heads)?;
            if st.candidates.is_empty() {
                return fail("the bad state adds nothing to the good state; nothing to bisect");
            }
            st.lo = 0;
            st.hi = st.candidates.len();
            return self.bisect_advance(&mut st);
        }
        let Some(k) = st.testing else {
            return fail("no state is under test; give `oxy bisect good|bad` a change or bookmark to start with");
        };
        match good {
            Some(true) => st.lo = k,
            Some(false) => st.hi = k,
            None => st.skipped.push(k),
        }
        self.bisect_advance(&mut st)
    }

    /// Automate with a command run in the working copy: exit 0 is good, 125
    /// skips, anything else is bad.
    pub fn bisect_run(&self, command: &[String]) -> Result<BisectStep> {
        let Some(st) = self.bisect_load()? else {
            return fail("no bisect in progress; run `oxy bisect start`");
        };
        if st.testing.is_none() {
            return Ok(self.bisect_step(&st));
        }
        loop {
            let status = std::process::Command::new(&command[0])
                .args(&command[1..])
                .current_dir(&self.root)
                .status()
                .map_err(|e| RepoError::Msg(format!("running {}: {e}", command[0])))?;
            let verdict = match status.code() {
                Some(0) => Some(true),
                Some(125) => None,
                _ => Some(false),
            };
            match self.bisect_mark(verdict, &[])? {
                BisectStep::Testing { .. } => continue,
                done => return Ok(done),
            }
        }
    }
}