//! File-backed TruthRule loader (Phase 42 PRD).
//!
//! PRD: "truth/ dir at repo root — rule files, versioned in git."
//! This module walks a directory, parses every `*.toml` file it finds,
//! and registers the rules into a caller-supplied store. Rule IDs must
//! be unique across the combined set — duplicate-ID collisions are
//! load-time errors.
//!
//! The TOML format matches the shape at `truth/README.md`. The same
//! `RuleCondition` + `RuleAction` enums used by the in-code registrars
//! deserialize directly from `condition = { type = "FieldEquals", ... }`
//! thanks to `#[serde(tag = "type")]`.

use std::fs;
use std::path::Path;
use serde::Deserialize;

use crate::{TruthRule, TruthStore};

/// Deserialization wrapper — a TOML file is a list of [[rule]] blocks.
#[derive(Deserialize)]
struct RuleFile {
    #[serde(default)]
    rule: Vec<TruthRule>,
}

/// Load every `*.toml` file in `dir` and add its rules to `store`.
/// Returns the number of rules loaded across all files.
///
/// Errors:
///   - directory doesn't exist or can't be read
///   - any `.toml` file fails to parse
///   - any rule ID collides with an existing rule (same ID already
///     registered in the store)
///
/// Non-goals: recursive walk (flat dir only), hot reload (one-shot load).
pub fn load_from_dir(store: &mut TruthStore, dir: impl AsRef<Path>) -> Result<usize, String> {
    let dir = dir.as_ref();
    let entries = fs::read_dir(dir)
        .map_err(|e| format!("read_dir {}: {e}", dir.display()))?;

    let mut loaded_ids = store.all_rule_ids();
    let mut count = 0usize;

    let mut paths: Vec<_> = entries
        .filter_map(|e| e.ok())
        .map(|e| e.path())
        .filter(|p| p.extension().and_then(|s| s.to_str()) == Some("toml"))
        .collect();
    // Deterministic order — alphabetical by filename. Matters when a
    // cross-file ID collision happens; the earlier filename wins
    // nothing (both error), but the error message is reproducible.
    paths.sort();

    for path in paths {
        let raw = fs::read_to_string(&path)
            .map_err(|e| format!("read {}: {e}", path.display()))?;
        let file: RuleFile = toml::from_str(&raw)
            .map_err(|e| format!("parse {}: {e}", path.display()))?;
        for rule in file.rule {
            if !loaded_ids.insert(rule.id.clone()) {
                return Err(format!(
                    "duplicate rule id '{}' from {}",
                    rule.id,
                    path.display()
                ));
            }
            store.add_rule(rule);
            count += 1;
        }
    }

    Ok(count)
}

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

    fn write_file(dir: &Path, name: &str, content: &str) {
        let path = dir.join(name);
        let mut f = fs::File::create(&path).unwrap();
        f.write_all(content.as_bytes()).unwrap();
    }

    #[test]
    fn loads_rules_from_toml_files() {
        let tmp = tempdir_for("loader_test");
        write_file(&tmp, "a.toml", r#"
[[rule]]
id = "a-rule"
task_class = "test"
description = "test rule"
action = { type = "Pass" }

[rule.condition]
type = "Always"
"#);
        let mut store = TruthStore::new();
        let n = load_from_dir(&mut store, &tmp).unwrap();
        assert_eq!(n, 1);
        assert_eq!(store.get_rules("test").len(), 1);
        let _ = fs::remove_dir_all(&tmp);
    }

    #[test]
    fn rejects_duplicate_rule_ids() {
        let tmp = tempdir_for("dup_ids");
        write_file(&tmp, "a.toml", r#"
[[rule]]
id = "same"
task_class = "t"
description = ""
action = { type = "Pass" }
[rule.condition]
type = "Always"
"#);
        write_file(&tmp, "b.toml", r#"
[[rule]]
id = "same"
task_class = "t"
description = ""
action = { type = "Pass" }
[rule.condition]
type = "Always"
"#);
        let mut store = TruthStore::new();
        let err = load_from_dir(&mut store, &tmp).unwrap_err();
        assert!(err.contains("duplicate"), "got: {err}");
        let _ = fs::remove_dir_all(&tmp);
    }

    #[test]
    fn duplicate_with_in_code_rule_is_rejected() {
        // Existing in-store IDs count as "already registered." Operator
        // can't shadow an in-code rule by file without changing the ID.
        let tmp = tempdir_for("dup_in_code");
        write_file(&tmp, "conflict.toml", r#"
[[rule]]
id = "worker-active"
task_class = "staffing.fill"
description = "file attempt"
action = { type = "Pass" }
[rule.condition]
type = "Always"
"#);
        // staffing_rules registers "worker-active"
        let mut store = crate::staffing::staffing_rules(TruthStore::new());
        let err = load_from_dir(&mut store, &tmp).unwrap_err();
        assert!(err.contains("duplicate") && err.contains("worker-active"));
        let _ = fs::remove_dir_all(&tmp);
    }

    #[test]
    fn skips_non_toml_files() {
        let tmp = tempdir_for("skip_non_toml");
        write_file(&tmp, "a.toml", r#"
[[rule]]
id = "x"
task_class = "t"
description = ""
action = { type = "Pass" }
[rule.condition]
type = "Always"
"#);
        write_file(&tmp, "README.md", "not a toml file");
        let mut store = TruthStore::new();
        let n = load_from_dir(&mut store, &tmp).unwrap();
        assert_eq!(n, 1); // README.md ignored
        let _ = fs::remove_dir_all(&tmp);
    }

    #[test]
    fn missing_dir_returns_error() {
        let mut store = TruthStore::new();
        let err = load_from_dir(&mut store, "/nonexistent/path/here").unwrap_err();
        assert!(err.contains("read_dir"));
    }

    fn tempdir_for(tag: &str) -> std::path::PathBuf {
        let dir = std::env::temp_dir().join(format!("truth_loader_{}_{}", tag,
            std::process::id()));
        fs::create_dir_all(&dir).unwrap();
        dir
    }
}