From b5d37721c4bddc82129e411d67503938433b4acf Mon Sep 17 00:00:00 2001
From: "@permadeath.com" <did:plc:nlzmjyfv6loqtxyzvdcznwgf>
Date: Wed, 19 Aug 2026 19:43:53 -0400
Subject: [PATCH] feat(unit-rules): helm wear

Prints what was taken off and what the machine came to, as a repair list read
the other way round.
---
 README.md                   |  5 +++
 crates/helm-cli/src/main.rs | 75 +++++++++++++++++++++++++++++++++++++
 2 files changed, 80 insertions(+)

diff --git a/README.md b/README.md
index 9b14152..001e016 100644
--- a/README.md
+++ b/README.md
@@ -82,6 +82,11 @@ equipment shot out and the magazines to fill, location by location:
 
     helm repairs <file.mul> --megamek <dir> --bridge-dir <dir> --why
 
+The other direction, for fitting a machine that has already been in a fight
+into a scenario's budget - damage a design until it is worth a given figure:
+
+    helm wear "Atlas AS7-D" --to 1500 --megamek <dir> --bridge-dir <dir>
+
 `--clusters` is the one that matters. A ranked list of the worst disagreements
 shows whichever design is strangest; grouping them by what they have in common
 shows which *rule* is missing, and its second section ranks the failures by how
diff --git a/crates/helm-cli/src/main.rs b/crates/helm-cli/src/main.rs
index ae63a2f..edabf4f 100644
--- a/crates/helm-cli/src/main.rs
+++ b/crates/helm-cli/src/main.rs
@@ -25,6 +25,7 @@ fn main() -> ExitCode {
         Some("force") => force(&args[1..]),
         Some("check") => check(&args[1..]),
         Some("repairs") => repairs(&args[1..]),
+        Some("wear") => wear(&args[1..]),
         Some("-h") | Some("--help") | Some("help") | None => {
             usage();
             return ExitCode::SUCCESS;
@@ -52,6 +53,7 @@ USAGE
   helm force <force.mul> --megamek <dir> --bridge-dir <dir>
   helm check <force.mul> --megamek <dir> --bridge-dir <dir>
   helm repairs <force.mul> --megamek <dir> --bridge-dir <dir>
+  helm wear <design> --to <bv> --megamek <dir> --bridge-dir <dir>
 
 BUILD
   --megamek <dir>     A MegaMek install. Reads data/mekfiles/unit_files.zip,
@@ -88,6 +90,12 @@ CHECK
   more plate or frame than a design was built with. Exits non-zero when a
   file has something wrong with it.
 
+WEAR
+  Damage a design until it is worth a given battle value, for fitting a
+  machine that has already been in a fight into a scenario's budget. Plate
+  first, then the frame under it, spread evenly across the locations.
+  --to <bv>           The figure to aim for. Required.
+
 REPAIRS
   What a force needs putting right, location by location: points of plate,
   points of frame, the equipment shot out and the magazines to fill.
@@ -114,6 +122,7 @@ struct Opts {
     rules: bool,
     bench: bool,
     why: bool,
+    to: Option<i64>,
 }
 
 fn parse_opts(args: &[String]) -> Result<Opts, String> {
@@ -128,6 +137,7 @@ fn parse_opts(args: &[String]) -> Result<Opts, String> {
         rules: false,
         bench: false,
         why: false,
+        to: None,
     };
     let mut i = 0;
     while i < args.len() {
@@ -170,6 +180,14 @@ fn parse_opts(args: &[String]) -> Result<Opts, String> {
                 o.bench = true;
                 i += 1;
             }
+            "--to" => {
+                o.to = Some(
+                    need(i)?
+                        .parse()
+                        .map_err(|_| "--to takes a battle value".to_string())?,
+                );
+                i += 2;
+            }
             "--why" => {
                 o.why = true;
                 i += 1;
@@ -597,6 +615,63 @@ fn check(args: &[String]) -> Result<(), String> {
     ))
 }
 
+/// Wear a design down to a battle value.
+fn wear(args: &[String]) -> Result<(), String> {
+    let name = args.first().filter(|a| !a.starts_with("--")).ok_or(
+        "name a design: helm wear \"Atlas AS7-D\" --to 1500 --megamek <dir> --bridge-dir <dir>",
+    )?;
+    let opts = parse_opts(&args[1..])?;
+    let target = opts
+        .to
+        .ok_or("--to <bv> is required: there is nothing to aim at without it")?;
+    let megamek = opts.megamek.ok_or("--megamek is required")?;
+    let bridge = opts
+        .bridge_dir
+        .ok_or("--bridge-dir is required: the catalogue lives there")?;
+
+    let library = read_library(&megamek)?;
+    let catalogue =
+        helm_bridge::read_catalogue(&bridge.join("equipment.jsonl")).map_err(|e| e.to_string())?;
+    let unit = library
+        .units
+        .iter()
+        .find(|u| u.display_name().eq_ignore_ascii_case(name))
+        .ok_or_else(|| format!("no design called {name}"))?;
+
+    let worn = helm_bv::wear_to(unit, &catalogue, target).map_err(|e| e.to_string())?;
+    println!(
+        "{} is {} whole, {} worn{}",
+        unit.display_name(),
+        worn.whole,
+        worn.value,
+        if worn.is_exact() {
+            String::new()
+        } else {
+            format!(" - {} off {target}", worn.missed_by)
+        }
+    );
+    let repairs = helm_bv::repairs(unit, &worn.condition);
+    for repair in &repairs {
+        let mut parts = Vec::new();
+        if repair.armor > 0 {
+            parts.push(format!("{} armour", repair.armor));
+        }
+        if repair.rear_armor > 0 {
+            parts.push(format!("{} rear armour", repair.rear_armor));
+        }
+        if repair.structure > 0 {
+            parts.push(format!("{} structure", repair.structure));
+        }
+        println!("  {:<16} {}", repair.location, parts.join(", "));
+    }
+    let total = helm_bv::Total::of(&repairs);
+    println!(
+        "  {:<16} {} armour and {} structure gone",
+        "", total.armor, total.structure
+    );
+    Ok(())
+}
+
 /// What a post-match `.mul` would take to put right.
 ///
 /// The other half of reading a file that came back from a battle: `--why` says
-- 
2.51.2