nmbrs-workload 0.4.0

// Copyright 2024-2026 Jonathan Shook
// SPDX-License-Identifier: Apache-2.0

//! Workload `extends:` resolution and merging (SRD-72).
//!
//! Resolves single-parent workload composition: a child workload
//! YAML may declare `extends: <relative-path>` at the top level
//! to inherit from a parent. The parent is loaded (recursively,
//! if it has its own `extends:`) and merged field-by-field before
//! the resulting workload is fed to `parse::parse_workload`.
//!
//! The merge runs on parsed `serde_json::Value` trees, not on
//! raw YAML text — every merge rule is structural (per-key
//! merge, per-name replace, list union with dedup). The result
//! is re-serialised back to YAML so the existing
//! `parse_workload(&str, …)` entry point can consume it
//! unchanged; template expansion then runs on the merged text
//! with the caller's params, matching the SRD-72 rule that
//! validation and templating run **once**, on the merged whole.

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

use serde_json::Value as JVal;

/// Where a workload in the `extends:` chain came from. SRD-85
/// adds the bundled-catalog source: a bundled parent has no
/// directory context, so its own `extends:` targets resolve
/// through the catalog only.
enum Source {
    /// On-disk file (canonicalised lazily in the loader).
    File(PathBuf),
    /// Catalog entry — name + embedded text.
    Bundled(&'static crate::catalog::BundledWorkload),
}

/// Load a workload YAML from disk, follow its `extends:` chain
/// to completion, and return the merged YAML text ready for
/// `parse::parse_workload`, plus any resolution warnings the
/// chain produced (a target name matching multiple resources —
/// see [`resolve_extends_target`]). Callers surface the warnings
/// on their own channel; dropping them silently is a bug.
///
/// The returned text has every `extends:` directive stripped.
pub fn load_and_merge(path: &Path) -> Result<(String, Vec<String>), String> {
    let mut chain: Vec<String> = Vec::new();
    let mut warnings: Vec<String> = Vec::new();
    let merged_jval = load_recursive(Source::File(path.to_path_buf()), &mut chain, &mut warnings)?;
    let text = serde_yaml::to_string(&merged_jval)
        .map_err(|e| format!("re-serialising merged workload: {e}"))?;
    Ok((text, warnings))
}

/// SRD-85: load a bundled workload from the catalog, follow its
/// `extends:` chain (catalog-resolved — a bundled workload has
/// no directory context), and return the merged YAML text plus
/// any resolution warnings.
pub fn load_and_merge_bundled(
    bundled: &'static crate::catalog::BundledWorkload,
) -> Result<(String, Vec<String>), String> {
    let mut chain: Vec<String> = Vec::new();
    let mut warnings: Vec<String> = Vec::new();
    let merged_jval = load_recursive(Source::Bundled(bundled), &mut chain, &mut warnings)?;
    let text = serde_yaml::to_string(&merged_jval)
        .map_err(|e| format!("re-serialising merged workload: {e}"))?;
    Ok((text, warnings))
}

/// Recursive loader: parses the source, resolves any `extends:`,
/// applies merge rules. `chain` is the parent-chain of sources
/// already being loaded (canonical path or `bundled:<name>`
/// keys), used for cycle detection.
fn load_recursive(
    src: Source,
    chain: &mut Vec<String>,
    warnings: &mut Vec<String>,
) -> Result<JVal, String> {
    // Resolve the source to (cycle key, display name, text,
    // directory context for relative extends targets).
    let (key, display, text, origin_dir): (String, String, String, Option<PathBuf>) = match &src {
        Source::File(path) => {
            let canonical = path
                .canonicalize()
                .map_err(|e| format!("extends: target not found: {} ({e})", path.display()))?;
            let text = std::fs::read_to_string(&canonical)
                .map_err(|e| format!("read {}: {e}", canonical.display()))?;
            let dir = canonical.parent().map(|p| p.to_path_buf());
            (
                canonical.display().to_string(),
                canonical.display().to_string(),
                text,
                dir,
            )
        }
        Source::Bundled(w) => (
            format!("bundled:{}", w.name),
            format!("bundled workload `{}`", w.name),
            w.source.to_string(),
            None,
        ),
    };

    if let Some(idx) = chain.iter().position(|k| k == &key) {
        return Err(format_cycle(chain, idx, &key));
    }
    chain.push(key);

    let mut jval: JVal =
        serde_yaml::from_str(&text).map_err(|e| format!("YAML parse error in {display}: {e}"))?;

    let extends_target = extract_extends_field(&jval, &display)?;

    let result = if let Some(extends_str) = extends_target {
        let bundled_origin = match &src {
            Source::Bundled(w) => Some(w.name),
            Source::File(_) => None,
        };
        let parent_src = resolve_extends_target(
            origin_dir.as_deref(),
            bundled_origin,
            &extends_str,
            &display,
            warnings,
        )?;
        let parent_display = match &parent_src {
            Source::File(p) => p.display().to_string(),
            Source::Bundled(w) => format!("bundled workload `{}`", w.name),
        };
        let parent_jval = load_recursive(parent_src, chain, warnings)
            .map_err(|e| format!("while loading {display}'s parent {parent_display}: {e}"))?;

        // Strip `extends:` from the child before merging so the
        // merge fn doesn't need to special-case it.
        if let Some(obj) = jval.as_object_mut() {
            obj.remove("extends");
        }

        merge(parent_jval, jval)
    } else {
        jval
    };

    chain.pop();
    Ok(result)
}

/// Resolve an `extends:` target per the SRD-85 nearest-first
/// order — the logical filesystem location is always favored:
///
/// 1. A file relative to the including file's directory (when
///    there is one).
/// 2. For a bundled origin: the target inside the origin's
///    namespace (`cql/vector_suite/full_cql_vector_sweep`
///    extending `full_cql_vector.yaml` finds
///    `cql/vector_suite/full_cql_vector`) — the sibling-by-
///    filename idiom works identically on disk and in the
///    catalog.
/// 3. The target as a bare catalog name (extension stripped —
///    files extend siblings by filename, catalog names carry
///    none).
///
/// A target matching MORE THAN ONE of these is a warnable
/// condition, not an error: the nearest candidate wins, and a
/// warning naming every match is pushed for the caller to log —
/// shadowing is allowed but never silent. A `./`-prefixed target
/// that resolves at its pinned location (the local file, or the
/// origin namespace for a bundled origin) is explicit — no
/// warning. Prefer globally unique names to avoid the ambiguity
/// altogether.
fn resolve_extends_target(
    origin_dir: Option<&Path>,
    bundled_origin: Option<&str>,
    target: &str,
    child_display: &str,
    warnings: &mut Vec<String>,
) -> Result<Source, String> {
    let pinned = target.starts_with("./") || target.starts_with("../");

    let local: Option<PathBuf> = origin_dir.map(|d| d.join(target)).filter(|p| p.exists());

    let stem = target
        .strip_suffix(".yaml")
        .or_else(|| target.strip_suffix(".yml"))
        .unwrap_or(target);
    let stem = stem.strip_prefix("./").unwrap_or(stem);
    let ns_hit = bundled_origin
        .and_then(|o| o.rsplit_once('/'))
        .and_then(|(ns, _)| crate::catalog::lookup(&format!("{ns}/{stem}")));
    let bare_hit = crate::catalog::lookup(stem).filter(|b| ns_hit.map(|n| n.name) != Some(b.name));

    // A pinned target that resolves at its pinned location is
    // unambiguous by declaration.
    if pinned && local.is_some() {
        return Ok(Source::File(local.unwrap()));
    }
    if pinned
        && origin_dir.is_none()
        && let Some(w) = ns_hit
    {
        return Ok(Source::Bundled(w));
    }

    // Nearest-first candidate list.
    let mut candidates: Vec<(String, Source)> = Vec::new();
    if let Some(p) = local {
        candidates.push((format!("local file {}", p.display()), Source::File(p)));
    }
    if let Some(w) = ns_hit {
        candidates.push((format!("bundled workload `{}`", w.name), Source::Bundled(w)));
    }
    if let Some(w) = bare_hit {
        candidates.push((format!("bundled workload `{}`", w.name), Source::Bundled(w)));
    }

    if candidates.len() > 1 {
        let names: Vec<&str> = candidates.iter().map(|(n, _)| n.as_str()).collect();
        warnings.push(format!(
            "{child_display}: `extends: {target}` matches multiple resources — {} — \
             using the nearest ({}). Same-named resources in multiple places \
             invite confusion: prefer a unique name, or pin the intent with a \
             `./` path / full catalog name.",
            names.join(" AND "),
            names[0],
        ));
    }

    match candidates.into_iter().next() {
        Some((_, src)) => Ok(src),
        None => {
            let local_hint = origin_dir
                .map(|d| format!("{}", d.join(target).display()))
                .unwrap_or_else(|| {
                    "<no directory context — bundled parents resolve targets \
                     through the catalog>"
                        .to_string()
                });
            Err(format!(
                "{child_display}: `extends: {target}` not found — no file at \
                 {local_hint} and no bundled workload named `{stem}`"
            ))
        }
    }
}

/// Extract `extends:` as a string. Returns `Ok(None)` if absent,
/// `Err` if present but malformed (non-string, empty, or nested
/// inside something other than the top-level mapping).
fn extract_extends_field(jval: &JVal, source: &str) -> Result<Option<String>, String> {
    let Some(obj) = jval.as_object() else {
        return Err(format!("{source} top level must be a YAML mapping"));
    };
    let Some(v) = obj.get("extends") else {
        return Ok(None);
    };
    match v {
        JVal::String(s) if !s.is_empty() => Ok(Some(s.clone())),
        JVal::String(_) => Err(format!("{source}: `extends:` value is empty")),
        _ => Err(format!(
            "{source}: `extends:` must be a single scalar string, got {}",
            describe_kind(v)
        )),
    }
}

fn describe_kind(v: &JVal) -> &'static str {
    match v {
        JVal::Null => "null",
        JVal::Bool(_) => "bool",
        JVal::Number(_) => "number",
        JVal::String(_) => "string",
        JVal::Array(_) => "list",
        JVal::Object(_) => "mapping",
    }
}

fn format_cycle(chain: &[String], cycle_start_idx: usize, repeat: &str) -> String {
    let mut out = String::from("extends: cycle detected\n");
    for (i, p) in chain.iter().enumerate() {
        let arrow = if i == 0 { "  " } else { "  → " };
        out.push_str(&format!("{arrow}{p}\n"));
        let _ = cycle_start_idx; // referenced for clarity below
    }
    out.push_str(&format!("  → {repeat}  (cycle)\n"));
    out
}

/// Merge a child workload onto an already-merged parent per the
/// SRD-72 per-field rules.
fn merge(parent: JVal, child: JVal) -> JVal {
    // Both should be objects in practice (extract_extends_field
    // already validated). Be defensive: a non-object child or
    // parent falls back to whichever is an object.
    let Some(mut merged) = parent.as_object().cloned() else {
        return child;
    };
    let Some(child_obj) = child.as_object() else {
        return JVal::Object(merged);
    };

    for (key, child_val) in child_obj {
        let parent_val = merged.remove(key);
        let new_val = match (key.as_str(), parent_val) {
            ("extends", _) => continue, // defensive — caller should have stripped
            ("description", _) => child_val.clone(),

            ("params", Some(p)) => merge_per_key(p, child_val.clone()),
            ("tags", Some(p)) => merge_per_key(p, child_val.clone()),

            ("bindings", Some(p)) => concat_bindings(p, child_val.clone()),

            ("status_metrics", Some(p)) => union_lists(p, child_val.clone()),

            ("report", Some(p)) => merge_per_name(p, child_val.clone()),
            ("scenarios", Some(p)) => merge_per_name(p, child_val.clone()),
            ("phases", Some(p)) => merge_per_name(p, child_val.clone()),
            ("blocks", Some(p)) => merge_per_name(p, child_val.clone()),
            ("op_templates", Some(p)) => merge_per_name(p, child_val.clone()),

            ("ops", Some(p)) => merge_ops(p, child_val.clone()),

            (_, _) => child_val.clone(),
        };
        merged.insert(key.clone(), new_val);
    }

    JVal::Object(merged)
}

/// Per-key merge: child wins on conflict, new keys added.
fn merge_per_key(parent: JVal, child: JVal) -> JVal {
    let Some(mut p_map) = parent.as_object().cloned() else {
        return child;
    };
    let Some(c_map) = child.as_object() else {
        return JVal::Object(p_map);
    };
    for (k, v) in c_map {
        p_map.insert(k.clone(), v.clone());
    }
    JVal::Object(p_map)
}

/// Per-name merge: child entry replaces parent entry of same
/// name (whole-entry replace). Same shape as `merge_per_key`
/// but kept as a separate fn to make the intent explicit at
/// call sites — the contract differs (whole-entry replace is
/// stricter than per-key merge, even though the operation is
/// identical at this layer).
fn merge_per_name(parent: JVal, child: JVal) -> JVal {
    merge_per_key(parent, child)
}

/// Bindings concat: parent's Polydat source emitted first, child's
/// appended. Handles both the string form (the common case) and
/// the legacy map form. Mixed forms (one string, one map) fall
/// back to child-wins because there's no sensible concatenation.
fn concat_bindings(parent: JVal, child: JVal) -> JVal {
    match (&parent, &child) {
        (JVal::String(p), JVal::String(c)) => {
            let mut out = String::with_capacity(p.len() + c.len() + 1);
            out.push_str(p);
            if !p.ends_with('\n') {
                out.push('\n');
            }
            out.push_str(c);
            JVal::String(out)
        }
        (JVal::Object(_), JVal::Object(_)) => merge_per_key(parent, child),
        _ => child,
    }
}

/// List union with first-occurrence ordering and dedup. Parent's
/// entries come first, child's appended; duplicates suppressed.
fn union_lists(parent: JVal, child: JVal) -> JVal {
    let Some(p_list) = parent.as_array().cloned() else {
        return child;
    };
    let Some(c_list) = child.as_array() else {
        return JVal::Array(p_list);
    };
    let mut seen: HashSet<String> = HashSet::new();
    let mut out: Vec<JVal> = Vec::with_capacity(p_list.len() + c_list.len());
    for v in p_list.into_iter().chain(c_list.iter().cloned()) {
        // dedup by serialised form so non-string list entries
        // (rare in status_metrics, but possible) still compare.
        let key = match &v {
            JVal::String(s) => s.clone(),
            other => other.to_string(),
        };
        if seen.insert(key) {
            out.push(v);
        }
    }
    JVal::Array(out)
}

/// Top-level `ops:` merge. If both forms are map-shaped, do a
/// per-name merge (child entry replaces parent entry of same
/// name). Otherwise (list form, mixed forms) the child wholly
/// replaces the parent — positions are not stable identifiers
/// so by-name override is impossible.
fn merge_ops(parent: JVal, child: JVal) -> JVal {
    match (&parent, &child) {
        (JVal::Object(_), JVal::Object(_)) => merge_per_name(parent, child),
        _ => child,
    }
}

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

    fn vstr(s: &str) -> JVal {
        JVal::String(s.to_string())
    }
    fn arr(items: Vec<JVal>) -> JVal {
        JVal::Array(items)
    }

    fn mp(pairs: &[(&str, JVal)]) -> JVal {
        let mut m = serde_json::Map::new();
        for (k, v) in pairs {
            m.insert((*k).to_string(), v.clone());
        }
        JVal::Object(m)
    }

    #[test]
    fn per_key_merge_child_wins() {
        let p = mp(&[("a", vstr("p")), ("b", vstr("p"))]);
        let c = mp(&[("b", vstr("c")), ("d", vstr("c"))]);
        let merged = merge_per_key(p, c);
        let obj = merged.as_object().unwrap();
        assert_eq!(obj.get("a").unwrap(), &vstr("p"));
        assert_eq!(obj.get("b").unwrap(), &vstr("c"));
        assert_eq!(obj.get("d").unwrap(), &vstr("c"));
    }

    #[test]
    fn concat_bindings_string_form() {
        let merged = concat_bindings(vstr("a := 1"), vstr("b := 2"));
        assert_eq!(merged, vstr("a := 1\nb := 2"));
    }

    #[test]
    fn concat_bindings_preserves_trailing_newline() {
        let merged = concat_bindings(vstr("a := 1\n"), vstr("b := 2"));
        assert_eq!(merged, vstr("a := 1\nb := 2"));
    }

    #[test]
    fn union_lists_dedup_preserves_first_occurrence() {
        let merged = union_lists(
            arr(vec![vstr("a"), vstr("b"), vstr("c")]),
            arr(vec![vstr("b"), vstr("d")]),
        );
        assert_eq!(
            merged,
            arr(vec![vstr("a"), vstr("b"), vstr("c"), vstr("d")])
        );
    }

    #[test]
    fn merge_strips_extends() {
        let parent = mp(&[("description", vstr("parent"))]);
        let child = mp(&[
            ("extends", vstr("./p.yaml")),
            ("description", vstr("child")),
        ]);
        let merged = merge(parent, child);
        let obj = merged.as_object().unwrap();
        assert!(obj.get("extends").is_none());
        assert_eq!(obj.get("description").unwrap(), &vstr("child"));
    }

    #[test]
    fn merge_phases_per_name_replace() {
        let parent = mp(&[(
            "phases",
            mp(&[
                ("a", mp(&[("kind", vstr("p_a"))])),
                ("b", mp(&[("kind", vstr("p_b"))])),
            ]),
        )]);
        let child = mp(&[(
            "phases",
            mp(&[
                ("b", mp(&[("kind", vstr("c_b"))])),
                ("c", mp(&[("kind", vstr("c_c"))])),
            ]),
        )]);
        let merged = merge(parent, child);
        let phases = merged
            .as_object()
            .unwrap()
            .get("phases")
            .unwrap()
            .as_object()
            .unwrap();
        assert_eq!(phases.len(), 3);
        assert_eq!(phases.get("a").unwrap(), &mp(&[("kind", vstr("p_a"))]));
        assert_eq!(phases.get("b").unwrap(), &mp(&[("kind", vstr("c_b"))]));
        assert_eq!(phases.get("c").unwrap(), &mp(&[("kind", vstr("c_c"))]));
    }
}