Imrove base commit detection logic

The previous iteration was imperfect, the question is a lot more
complicated than simply executing git log.

The new solution first tries to see if head matches (as it often will
for recent patches), then if not it looks at the git log of any files
changed in the patch series, and tries to find the latest commit where
the hash of all files matched the expected before values.

Author: dutow

public/scripts/hackorum-patch

@@ -425,51 +425,72 @@ class HackorumPatch
       return base_commit
     end
 
-    # Fall back to index hash detection
-    puts "Detecting base commit from patch index entries..."
-
-    first_patch = all_patch_files.first
-    index_hashes = []
-    new_file_count = 0
-    content = File.read(first_patch)
-    content.scan(/^index ([0-9a-f]+)\.\.([0-9a-f]+)/) do |before_hash, after_hash|
-      if before_hash =~ /^0+$/
-        new_file_count += 1
-      else
-        index_hashes << before_hash
+    # Fall back to index hash detection using file paths
+    puts "Detecting base commit from patch file paths..."
+
+    # Extract file paths and their "before" blob hashes from all patches
+    # Only record the FIRST occurrence of each file - later patches in a series
+    # will have "before" hashes that are the result of earlier patches, not the original state
+    file_info = {}  # path => before_hash
+    all_patch_files.each do |patch_file|
+      content = File.read(patch_file)
+      # Format: diff --git a/path b/path followed by index abc123..def456
+      content.scan(/^diff --git a\/(.+?) b\/\1\n(?:.*?\n)*?index ([0-9a-f]+)\.\.([0-9a-f]+)/m) do |path, before_hash, after_hash|
+        next if before_hash =~ /^0+$/  # Skip new files
+        next if file_info.key?(path)   # Only use first occurrence
+        file_info[path] = before_hash
       end
     end
 
-    if index_hashes.empty?
-      puts "  No index entries found in first patch (#{new_file_count} new files)"
+    if file_info.empty?
+      puts "  No modified files found in patches (all new files?)"
       return detect_default_branch_head
     end
 
-    puts "  Found #{index_hashes.size} index entries in first patch (skipped #{new_file_count} new files)"
-    puts "  Searching for base commit (this may take a moment)..."
+    puts "  Found #{file_info.size} modified files across #{all_patch_files.size} patches"
 
-    candidates = []
-    index_hashes.each_with_index do |hash, idx|
-      puts "  Checking index #{idx + 1}/#{index_hashes.size}..."
+    default_branch = detect_default_branch_head
 
-      output = `git log --all --pretty=format:%H --find-object=#{hash} -n 1 2>/dev/null`.strip
-      if !output.empty? && output =~ /^[0-9a-f]{40}$/
-        candidates << output
-        puts "    Found commit: #{output[0..7]}..."
-      end
+    # Check if the "before" hashes match what's at the default branch HEAD
+    # This confirms HEAD is the correct base
+    default_head = `git rev-parse #{default_branch} 2>/dev/null`.strip
+    all_match = file_info.all? do |path, before_hash|
+      current_hash = `git rev-parse #{default_head}:#{path} 2>/dev/null`.strip
+      current_hash == before_hash || current_hash.start_with?(before_hash) || before_hash.start_with?(current_hash)
     end
 
-    if candidates.empty?
-      puts "  Could not detect base commit from index entries"
-      return detect_default_branch_head
+    if all_match
+      puts "  All file hashes match #{default_branch} HEAD"
+      puts "[OK] Base commit: #{default_head} (#{default_branch})"
+      puts ""
+      return default_head
     end
 
-    base_commit = candidates.first
-    puts "  Using commit: #{base_commit[0..7]}... as base"
-    puts "[OK] Base commit: #{base_commit}"
-    puts ""
+    # Hashes don't match HEAD, search history for a matching commit
+    puts "  File hashes don't match HEAD, searching history..."
+
+    # Find commits on the default branch that touched these files
+    paths = file_info.keys.map { |p| Shellwords.escape(p) }.join(" ")
+    commits = `git log #{default_branch} --pretty=format:%H -n 50 -- #{paths} 2>/dev/null`.strip.split("\n")
+
+    commits.each do |commit|
+      next if commit.empty?
+
+      matches = file_info.all? do |path, before_hash|
+        blob_hash = `git rev-parse #{commit}:#{path} 2>/dev/null`.strip
+        blob_hash == before_hash || blob_hash.start_with?(before_hash) || before_hash.start_with?(blob_hash)
+      end
+
+      if matches
+        puts "  Found matching commit: #{commit[0..11]}..."
+        puts "[OK] Base commit: #{commit}"
+        puts ""
+        return commit
+      end
+    end
 
-    base_commit
+    puts "  Could not find matching commit in history"
+    detect_default_branch_head
   end
 
   def detect_base_commit_from_base_line(patch_files)
@@ -488,7 +509,7 @@ class HackorumPatch
   end
 
   def detect_default_branch_head
-    %w[origin/master master].each do |ref|
+    %w[master origin/master].each do |ref|
       if system("git rev-parse --verify #{ref} > /dev/null 2>&1")
         return ref
       end

public/scripts/hackorum-patch.changelog.json

@@ -7,7 +7,8 @@
       "changes": [
         "Added version check to notify users of updates",
         "Added support for base-commit line from git format-patch --base",
-        "Added support for .diff files (applied with git apply and committed individually)"
+        "Added support for .diff files (applied with git apply and committed individually)",
+        "Fixed base commit detection for --force re-application and multi-patch series"
       ]
     },
     {