//! Traceability gate and matrix generator.
//!
//! ```text
//! traces report          # write docs/traceability.md
//! traces json            # machine-readable, to stdout
//! traces check           # gate: non-zero exit on failure
//! ```
//!
//! The gate fails hard on a *misconfigured run* — zero requirements parsed, or
//! zero source files scanned — rather than reporting a plausible-looking 0%.
//! A gate that cannot distinguish "nothing is tagged" from "I read nothing" is
//! how JellyTau's reported 158% went unnoticed for months.

use std::collections::{BTreeMap, BTreeSet};
use std::path::{Path, PathBuf};

use anyhow::{bail, Context, Result};
use traceability::*;

/// Directories scanned for tags.
///
/// `platform` belongs here as much as the rest: it is where the display-server
/// and secret-store integrations live, so leaving it out made every
/// FR-PLAT-\* and NFR-PORT-\* tag in `dr-plat` invisible and understated the
/// matrix by exactly the requirements the platform layer exists to satisfy.
const SOURCE_ROOTS: &[&str] = &["core", "ui", "platform", "apps", "tools"];

/// Minimum coverage the gate accepts.
///
/// 0 today: the requirements register is written but the code that implements
/// it barely exists. Ratchet upward as tags land; never reset downward.
/// Structural failures below are unconditional and do not depend on this.
const MIN_COVERAGE: f64 = 0.0;

fn main() -> Result<()> {
    let base = repo_root()?;
    let mode = std::env::args().nth(1).unwrap_or_else(|| "report".into());

    let req_path = base.join("docs/requirements.md");
    let markdown = std::fs::read_to_string(&req_path)
        .with_context(|| format!("reading {}", req_path.display()))?;
    let defined = parse_defined_requirements(&markdown);

    let files = collect_sources(&base, SOURCE_ROOTS);
    let mut entries = Vec::new();
    for file in &files {
        let text = std::fs::read_to_string(file).unwrap_or_default();
        let rel = file
            .strip_prefix(&base)
            .unwrap_or(file)
            .to_string_lossy()
            .to_string();
        entries.extend(extract_from_text(&text, &rel));
    }

    let traced: BTreeSet<String> = entries
        .iter()
        .flat_map(|e| e.requirements.iter().cloned())
        .collect();
    let coverage = compute_coverage(&traced, &defined);

    match mode.as_str() {
        "json" => println!(
            "{}",
            serde_json::to_string_pretty(&serde_json::json!({
                "filesScanned": files.len(),
                "tagsFound": entries.len(),
                "defined": defined.total(),
                "coverage": coverage,
            }))?
        ),
        "check" => {
            print_summary(&files, &entries, &defined, &coverage);
            gate(&files, &defined, &coverage)?;
            println!("\ntraceability gate: PASS");
        }
        _ => {
            let out = base.join("docs/traceability.md");
            let md = render(&files, &entries, &defined, &coverage);
            std::fs::write(&out, md)?;
            print_summary(&files, &entries, &defined, &coverage);
            println!("\nwrote {}", out.display());
        }
    }

    Ok(())
}

/// Structural checks that fail regardless of the coverage threshold.
fn gate(files: &[PathBuf], defined: &DefinedRequirements, cov: &Coverage) -> Result<()> {
    // A run that parsed nothing is misconfigured, not passing.
    if defined.total() == 0 {
        bail!("no requirements parsed from docs/requirements.md — misconfigured, not 0% coverage");
    }
    if files.is_empty() {
        bail!("no source files scanned — misconfigured, not 0% coverage");
    }

    // Arithmetic invariant. If this ever trips, the numerator has stopped
    // being an intersection — the exact JellyTau defect.
    if cov.percent > 100.0 {
        bail!(
            "coverage {:.1}% exceeds 100% — numerator is not an intersection of traced and defined",
            cov.percent
        );
    }

    if !cov.orphaned.is_empty() {
        bail!(
            "{} orphan tag(s) naming requirements that do not exist: {}",
            cov.orphaned.len(),
            cov.orphaned.join(", ")
        );
    }

    if cov.percent < MIN_COVERAGE {
        bail!(
            "coverage {:.1}% is below the {:.1}% threshold",
            cov.percent,
            MIN_COVERAGE
        );
    }

    Ok(())
}

fn print_summary(
    files: &[PathBuf],
    entries: &[TraceEntry],
    defined: &DefinedRequirements,
    cov: &Coverage,
) {
    println!("files scanned   {}", files.len());
    println!("tags found      {}", entries.len());
    println!("requirements    {}", defined.total());
    println!(
        "coverage        {:.1}% ({}/{})",
        cov.percent, cov.covered, cov.total
    );
    if !cov.orphaned.is_empty() {
        println!("orphan tags     {}", cov.orphaned.join(", "));
    }
}

fn render(
    files: &[PathBuf],
    entries: &[TraceEntry],
    defined: &DefinedRequirements,
    cov: &Coverage,
) -> String {
    let mut m = String::new();
    m.push_str("# Requirements traceability matrix\n\n");
    m.push_str("<!-- GENERATED FILE — do not edit by hand. -->\n");
    m.push_str("<!-- Regenerate: cargo run -p traceability -- report -->\n\n");
    m.push_str(
        "Denominators are parsed from [`requirements.md`](requirements.md) at run time, \
         never hardcoded. Coverage is the intersection of tagged and defined IDs over \
         defined IDs, so it cannot exceed 100%.\n\n",
    );

    m.push_str("## Summary\n\n| Metric | Value |\n|---|---|\n");
    m.push_str(&format!("| Source files scanned | {} |\n", files.len()));
    m.push_str(&format!("| TRACES tags found | {} |\n", entries.len()));
    m.push_str(&format!("| Requirements defined | {} |\n", defined.total()));
    m.push_str(&format!("| Requirements covered | {} |\n", cov.covered));
    m.push_str(&format!(
        "| **Coverage** | **{:.1}%** ({}/{}) |\n\n",
        cov.percent, cov.covered, cov.total
    ));

    m.push_str("### By type\n\n| Type | Covered | Defined |\n|---|---|---|\n");
    let mut covered_by_type: BTreeMap<&str, usize> = BTreeMap::new();
    for id in &defined.ids {
        if entries.iter().any(|e| e.requirements.contains(id)) {
            *covered_by_type.entry(type_of(id)).or_insert(0) += 1;
        }
    }
    for (ty, count) in &defined.by_type {
        m.push_str(&format!(
            "| {} | {} | {} |\n",
            ty,
            covered_by_type.get(ty.as_str()).copied().unwrap_or(0),
            count
        ));
    }
    m.push('\n');

    m.push_str("## Orphan tags\n\n");
    m.push_str(
        "A tag naming an ID `requirements.md` does not define — what renumbering produces, \
         and what a typo produces.\n\n",
    );
    if cov.orphaned.is_empty() {
        m.push_str("_None._\n\n");
    } else {
        for id in &cov.orphaned {
            m.push_str(&format!("- `{id}`\n"));
        }
        m.push('\n');
    }

    m.push_str("## Tagged requirements\n\n| ID | Tagged in |\n|---|---|\n");
    let mut by_req: BTreeMap<&String, Vec<&TraceEntry>> = BTreeMap::new();
    for e in entries {
        for r in &e.requirements {
            if defined.ids.contains(r) {
                by_req.entry(r).or_default().push(e);
            }
        }
    }
    for (id, es) in &by_req {
        let mut locs: Vec<String> = es
            .iter()
            .map(|e| format!("[`{}:{}`](../{}#L{})", e.file, e.line, e.file, e.line))
            .collect();
        locs.sort();
        locs.dedup();
        m.push_str(&format!("| {} | {} |\n", id, locs.join(", ")));
    }
    m.push('\n');

    m.push_str("## Not yet tagged\n\n");
    m.push_str(&format!(
        "{} of {} requirements have no implementation tag. Expected while the \
         codebase is young; each should gain one as it is built.\n\n",
        cov.untraced.len(),
        defined.total()
    ));
    if !cov.untraced.is_empty() {
        m.push_str("<details><summary>Show untagged requirements</summary>\n\n");
        for id in &cov.untraced {
            m.push_str(&format!("- {id}\n"));
        }
        m.push_str("\n</details>\n");
    }

    m
}

/// The repo root, found by walking up from the executable's manifest dir.
fn repo_root() -> Result<PathBuf> {
    let mut dir = Path::new(env!("CARGO_MANIFEST_DIR")).to_path_buf();
    while !dir.join("docs/requirements.md").exists() {
        if !dir.pop() {
            bail!("could not locate repo root (no docs/requirements.md above the tool)");
        }
    }
    Ok(dir)
}