//! What a continuous mission has already covered.
//!
//! A recurring mission's hard problem is not running the agent — that is 23
//! seconds — it is knowing what it already did last time. A research mission
//! with no memory of prior runs resurfaces the same papers forever and reports
//! success every time.
//!
//! This module keeps that record. It is deliberately small: an index derived
//! from the corpus, never the corpus itself. The vault is the source of truth,
//! the index is rebuildable, and a hand-edited note is never "wrong".
//!
//! # Two kinds, because the real vault forced it
//!
//! The plan assumed notes would carry `arxiv:` / `doi:` / `url:` frontmatter.
//! Measured against the actual vault: **416 notes, 145 with frontmatter, and
//! zero with any of those keys.** The dominant keys are repo-sync metadata
//! (`node`, `org`, `gitea`) and course-note fields (`presenter`, `session`).
//! An ingester keyed only on external identity would have indexed nothing —
//! the same shape of failure as everything else this week.
//!
//! So `note` rows record coverage (what the vault already contains, keyed by
//! path) and `source` rows record consumption (external things a mission
//! read, keyed by natural id). They answer different questions and a
//! continuous mission needs both: "have I already written about this topic?"
//! and "have I already read this paper?".

use sha2::{Digest, Sha256};
use uuid::Uuid;

/// A note parsed out of the vault, ready to be indexed.
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct ParsedNote {
    /// Vault-relative path, used as identity for `kind = 'note'`.
    pub path: String,
    pub title: Option<String>,
    pub content_hash: String,
    /// An external identity the note declares for itself, if any. Nothing in
    /// the vault does this today; missions writing new notes are expected to.
    pub declared_source_id: Option<String>,
}

impl ParsedNote {
    /// `note:<path>` — the `source_id` this note occupies in the index.
    pub fn source_id(&self) -> String {
        format!("note:{}", self.path)
    }
}

/// Hash content for change detection. Not a dedupe key — identity is
/// `source_id`; this only distinguishes "unchanged" from "edited".
pub fn content_hash(body: &str) -> String {
    let mut h = Sha256::new();
    h.update(body.as_bytes());
    format!("{:x}", h.finalize())
}

/// Split YAML frontmatter from the body.
///
/// Returns `(frontmatter, body)`. A note without frontmatter — 271 of the 416
/// in the real vault — yields `("", whole file)` rather than being skipped.
/// Skipping them would drop two thirds of the corpus on the floor.
fn split_frontmatter(text: &str) -> (&str, &str) {
    let Some(rest) = text.strip_prefix("---") else {
        return ("", text);
    };
    let rest = rest.strip_prefix('\n').unwrap_or(rest);
    match rest.find("\n---") {
        Some(end) => {
            let body = &rest[end + 4..];
            (&rest[..end], body.strip_prefix('\n').unwrap_or(body))
        }
        // An opening fence with no close is malformed; treat the whole file as
        // body rather than swallowing it as frontmatter.
        None => ("", text),
    }
}

/// Read one scalar key out of a frontmatter block.
///
/// Deliberately not a YAML parser. The vault's frontmatter is flat
/// `key: value` with occasional quotes and one list (`tags`), and pulling in a
/// YAML dependency to read three keys would be more surface than it is worth.
fn frontmatter_value<'a>(fm: &'a str, key: &str) -> Option<&'a str> {
    for line in fm.lines() {
        let line = line.trim();
        let Some((k, v)) = line.split_once(':') else {
            continue;
        };
        if !k.trim().eq_ignore_ascii_case(key) {
            continue;
        }
        let v = v.trim().trim_matches('"').trim_matches('\'').trim();
        if !v.is_empty() {
            return Some(v);
        }
    }
    None
}

/// Which frontmatter keys may declare an external identity, in priority order.
///
/// None of these appear in the vault today. They are the contract for notes
/// that missions write from here on, and the reason a `source:` key is NOT in
/// the list: the vault already uses `source:` for local filesystem paths of
/// course material (`/Users/quantum/Downloads/...`), which is provenance, not
/// a citable external identity. Treating it as one would fill the seen-set
/// with 25 rows keyed on a laptop path.
const IDENTITY_KEYS: &[&str] = &["source_id", "arxiv", "doi", "url", "permalink"];

/// Parse a note. `path` must be vault-relative.
pub fn parse_note(path: &str, text: &str) -> ParsedNote {
    let (fm, body) = split_frontmatter(text);

    let declared_source_id = IDENTITY_KEYS.iter().find_map(|k| {
        frontmatter_value(fm, k).map(|v| {
            // `source_id` is already qualified; the others name their scheme.
            if *k == "source_id" || v.contains(':') {
                v.to_string()
            } else {
                format!("{k}:{v}")
            }
        })
    });

    // Title: the first markdown H1, else the filename stem. Frontmatter has no
    // consistent title key in this vault.
    let title = body
        .lines()
        .find_map(|l| l.strip_prefix("# ").map(str::trim))
        .filter(|t| !t.is_empty())
        .map(str::to_string)
        .or_else(|| {
            std::path::Path::new(path)
                .file_stem()
                .map(|s| s.to_string_lossy().into_owned())
        });

    ParsedNote {
        path: path.to_string(),
        title,
        // Hash the body, not the whole file: re-syncing a repo note rewrites
        // `updated:`/`size_kb:` in frontmatter without the prose changing, and
        // that should not read as an edit.
        content_hash: content_hash(body),
        declared_source_id,
    }
}

/// What a re-index actually did. `unchanged` is the number that matters: on a
/// vault nobody edited it should equal the note count.
#[derive(Debug, Default, Clone, PartialEq, Eq)]
pub struct IndexStats {
    pub scanned: usize,
    pub inserted: usize,
    pub updated: usize,
    pub unchanged: usize,
}

/// Walk a checkout and index every markdown note.
///
/// Skips `.git` and Obsidian's own `.obsidian` config directory — indexing an
/// editor's workspace state as knowledge would be noise.
pub fn collect_notes(root: &std::path::Path) -> Vec<ParsedNote> {
    fn walk(dir: &std::path::Path, root: &std::path::Path, out: &mut Vec<ParsedNote>) {
        let Ok(entries) = std::fs::read_dir(dir) else {
            return;
        };
        for entry in entries.flatten() {
            let path = entry.path();
            let name = entry.file_name();
            let name = name.to_string_lossy();
            if name.starts_with('.') {
                continue;
            }
            if path.is_dir() {
                walk(&path, root, out);
            } else if path.extension().and_then(|e| e.to_str()) == Some("md") {
                let Ok(text) = std::fs::read_to_string(&path) else {
                    continue;
                };
                let rel = path
                    .strip_prefix(root)
                    .unwrap_or(&path)
                    .to_string_lossy()
                    .into_owned();
                out.push(parse_note(&rel, &text));
            }
        }
    }
    let mut out = Vec::new();
    walk(root, root, &mut out);
    out.sort_by(|a, b| a.path.cmp(&b.path));
    out
}

/// Upsert one item. Returns whether the row was new.
#[allow(clippy::too_many_arguments)]
pub async fn record(
    pool: &sqlx::PgPool,
    workspace_id: Uuid,
    corpus_id: &str,
    kind: &str,
    source_id: &str,
    title: Option<&str>,
    path: Option<&str>,
    url: Option<&str>,
    content_hash: &str,
    mission_id: Option<Uuid>,
) -> Result<bool, String> {
    // `last_seen_at` always moves; `first_seen_at` and `mission_id` never do.
    // The first mission to find a source keeps the credit, which is what makes
    // "did THIS run contribute anything new" answerable.
    let row: (bool,) = sqlx::query_as(
        "INSERT INTO corpus_items
           (id, workspace_id, corpus_id, kind, source_id, title, path, url,
            content_hash, mission_id)
         VALUES ($1,$2,$3,$4,$5,$6,$7,$8,$9,$10)
         ON CONFLICT (workspace_id, corpus_id, source_id) DO UPDATE
           SET last_seen_at = now(),
               title        = COALESCE(EXCLUDED.title, corpus_items.title),
               path         = COALESCE(EXCLUDED.path, corpus_items.path),
               url          = COALESCE(EXCLUDED.url, corpus_items.url),
               content_hash = EXCLUDED.content_hash
         RETURNING (xmax = 0) AS inserted",
    )
    .bind(Uuid::now_v7())
    .bind(workspace_id)
    .bind(corpus_id)
    .bind(kind)
    .bind(source_id)
    .bind(title)
    .bind(path)
    .bind(url)
    .bind(content_hash)
    .bind(mission_id)
    .fetch_one(pool)
    .await
    .map_err(|e| format!("record corpus item {source_id}: {e}"))?;
    Ok(row.0)
}

/// Has this corpus already seen this `source_id`?
pub async fn seen(
    pool: &sqlx::PgPool,
    workspace_id: Uuid,
    corpus_id: &str,
    source_id: &str,
) -> Result<bool, String> {
    // `SELECT 1` is INT4; binding it as i64 fails to decode.
    let row: Option<(i32,)> = sqlx::query_as(
        "SELECT 1 FROM corpus_items
          WHERE workspace_id = $1 AND corpus_id = $2 AND source_id = $3",
    )
    .bind(workspace_id)
    .bind(corpus_id)
    .bind(source_id)
    .fetch_optional(pool)
    .await
    .map_err(|e| format!("seen({source_id}): {e}"))?;
    Ok(row.is_some())
}

/// Of these candidate ids, which has this corpus NOT seen?
///
/// The shape a research agent actually needs: it has ten search hits and wants
/// to know which are worth fetching. One round trip, not ten.
pub async fn unseen(
    pool: &sqlx::PgPool,
    workspace_id: Uuid,
    corpus_id: &str,
    candidates: &[String],
) -> Result<Vec<String>, String> {
    if candidates.is_empty() {
        return Ok(Vec::new());
    }
    let rows: Vec<(String,)> = sqlx::query_as(
        "SELECT source_id FROM corpus_items
          WHERE workspace_id = $1 AND corpus_id = $2 AND source_id = ANY($3)",
    )
    .bind(workspace_id)
    .bind(corpus_id)
    .bind(candidates)
    .fetch_all(pool)
    .await
    .map_err(|e| format!("unseen: {e}"))?;
    let known: std::collections::HashSet<String> = rows.into_iter().map(|r| r.0).collect();
    Ok(candidates
        .iter()
        .filter(|c| !known.contains(*c))
        .cloned()
        .collect())
}

/// How many NEW sources a mission contributed.
///
/// The verification predicate for a continuous research mission. `record`
/// never reassigns `mission_id` on conflict, so the first mission to find a
/// source keeps the credit and a rerun cannot inflate its own count by
/// re-recording what an earlier run already had.
///
/// A mission whose answer is zero produced nothing, whatever its transcript
/// says — which is the check the 0030-0044 generation of this feature lacked.
pub async fn contributed(
    pool: &sqlx::PgPool,
    workspace_id: Uuid,
    corpus_id: &str,
    mission_id: Uuid,
) -> Result<i64, String> {
    let row: (i64,) = sqlx::query_as(
        "SELECT count(*) FROM corpus_items
          WHERE workspace_id = $1 AND corpus_id = $2 AND mission_id = $3
            AND kind = 'source'",
    )
    .bind(workspace_id)
    .bind(corpus_id)
    .bind(mission_id)
    .fetch_one(pool)
    .await
    .map_err(|e| format!("contributed({mission_id}): {e}"))?;
    Ok(row.0)
}

/// Index every note in a checkout. Idempotent by construction.
pub async fn index_vault(
    pool: &sqlx::PgPool,
    workspace_id: Uuid,
    corpus_id: &str,
    root: &std::path::Path,
) -> Result<IndexStats, String> {
    let notes = collect_notes(root);
    let mut stats = IndexStats {
        scanned: notes.len(),
        ..Default::default()
    };

    for note in &notes {
        let existing: Option<(String,)> = sqlx::query_as(
            "SELECT content_hash FROM corpus_items
              WHERE workspace_id = $1 AND corpus_id = $2 AND source_id = $3",
        )
        .bind(workspace_id)
        .bind(corpus_id)
        .bind(note.source_id())
        .fetch_optional(pool)
        .await
        .map_err(|e| format!("lookup {}: {e}", note.path))?;

        match existing {
            Some((hash,)) if hash == note.content_hash => {
                stats.unchanged += 1;
                continue;
            }
            Some(_) => stats.updated += 1,
            None => stats.inserted += 1,
        }

        record(
            pool,
            workspace_id,
            corpus_id,
            "note",
            &note.source_id(),
            note.title.as_deref(),
            Some(&note.path),
            None,
            &note.content_hash,
            None,
        )
        .await?;

        // A note that declares an external identity also registers as a
        // consumed source, so a later mission does not re-read what an
        // earlier one already wrote up.
        if let Some(sid) = &note.declared_source_id {
            record(
                pool,
                workspace_id,
                corpus_id,
                "source",
                sid,
                note.title.as_deref(),
                Some(&note.path),
                None,
                &note.content_hash,
                None,
            )
            .await?;
        }
    }
    Ok(stats)
}

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

    #[test]
    fn frontmatter_is_split_from_body() {
        let (fm, body) = split_frontmatter("---\ntype: lecture\n---\n# Title\n\ntext\n");
        assert_eq!(fm, "type: lecture");
        assert!(body.starts_with("# Title"));
    }

    /// 271 of the vault's 416 notes have no frontmatter. Dropping them would
    /// discard two thirds of the corpus.
    #[test]
    fn a_note_without_frontmatter_is_still_a_note() {
        let (fm, body) = split_frontmatter("# Plain\n\nno frontmatter here\n");
        assert_eq!(fm, "");
        assert!(body.starts_with("# Plain"));
        let n = parse_note("Daily/x.md", "# Plain\n\nbody\n");
        assert_eq!(n.title.as_deref(), Some("Plain"));
        assert_eq!(n.declared_source_id, None);
    }

    /// An unterminated fence must not swallow the file.
    #[test]
    fn malformed_frontmatter_is_treated_as_body() {
        let (fm, body) = split_frontmatter("---\nbroken: yes\nno closing fence\n");
        assert_eq!(fm, "");
        assert!(body.contains("no closing fence"));
    }

    /// The vault's real `source:` values are local filesystem paths of course
    /// material. Treating those as citable identity would fill the seen-set
    /// with 25 rows keyed on a laptop path.
    #[test]
    fn a_local_source_path_is_not_an_external_identity() {
        let note = parse_note(
            "50 APESS 2026/Lectures/talk.md",
            "---\nsource: \"/Users/quantum/Downloads/Material_APESS_2026/x.pdf\"\n\
             date: 2026-07-27\ntype: lecture\n---\n# Agentic Design\n",
        );
        assert_eq!(
            note.declared_source_id, None,
            "a Downloads path is provenance, not a citable source id"
        );
        assert_eq!(note.title.as_deref(), Some("Agentic Design"));
        assert_eq!(note.source_id(), "note:50 APESS 2026/Lectures/talk.md");
    }

    #[test]
    fn declared_identities_are_scheme_qualified() {
        let a = parse_note("p.md", "---\narxiv: 2401.12345\n---\n# T\n");
        assert_eq!(a.declared_source_id.as_deref(), Some("arxiv:2401.12345"));

        let d = parse_note("p.md", "---\ndoi: 10.1000/xyz\n---\n# T\n");
        assert_eq!(d.declared_source_id.as_deref(), Some("doi:10.1000/xyz"));

        // Already-qualified values are not double-prefixed.
        let s = parse_note("p.md", "---\nsource_id: arxiv:2401.99999\n---\n# T\n");
        assert_eq!(s.declared_source_id.as_deref(), Some("arxiv:2401.99999"));

        // A URL carries its own scheme and must not become `url:https:...`.
        let u = parse_note("p.md", "---\nurl: https://example.com/p\n---\n# T\n");
        assert_eq!(
            u.declared_source_id.as_deref(),
            Some("https://example.com/p")
        );
    }

    /// Repo-sync notes rewrite `updated:`/`size_kb:` on every sync without the
    /// prose changing. Hashing the whole file would report 103 phantom edits
    /// per run and make "unchanged" meaningless.
    #[test]
    fn frontmatter_churn_does_not_count_as_an_edit() {
        let a = parse_note("Repos/x.md", "---\nupdated: 2026-08-01\nsize_kb: 12\n---\n# X\n\nbody\n");
        let b = parse_note("Repos/x.md", "---\nupdated: 2026-08-03\nsize_kb: 14\n---\n# X\n\nbody\n");
        assert_eq!(a.content_hash, b.content_hash);

        let c = parse_note("Repos/x.md", "---\nupdated: 2026-08-03\n---\n# X\n\nDIFFERENT\n");
        assert_ne!(a.content_hash, c.content_hash, "real edits must be visible");
    }

    #[test]
    fn note_identity_is_its_path() {
        let n = parse_note("30 Resources/a b.md", "# A\n");
        assert_eq!(n.source_id(), "note:30 Resources/a b.md");
    }

    #[test]
    fn collect_skips_dotfiles_and_non_markdown() {
        let tmp = tempfile::tempdir().unwrap();
        let root = tmp.path();
        std::fs::create_dir_all(root.join(".obsidian")).unwrap();
        std::fs::create_dir_all(root.join("Daily")).unwrap();
        std::fs::write(root.join(".obsidian/workspace.md"), "# editor state\n").unwrap();
        std::fs::write(root.join("Daily/note.md"), "# Real\n").unwrap();
        std::fs::write(root.join("image.png"), "notmd").unwrap();

        let notes = collect_notes(root);
        assert_eq!(notes.len(), 1, "only the real note: {notes:?}");
        assert_eq!(notes[0].path, "Daily/note.md");
    }
}