"""Generate one of pi's JSON files from the repo and its fragments.

    pi-merge.py <key> <base|-> <fragment dir> <target>

Run by link/pi.sh, for ~/.pi/agent/models.json (key "providers") and
~/.pi/agent/mcp.json (key "mcpServers"). It lives in a file rather than a
heredoc inside $( ): macOS ships bash 3.2, which does not skip heredoc
content when it scans for the end of a command substitution, so an odd
number of apostrophes in here would stop the whole script parsing -- which
it did, on 2026-09-25.
"""

import glob, json, os, sys

merge_key, base_path, frag_dir, target = sys.argv[1:5]


def load(path):
    with open(path) as f:
        return json.load(f)


# The repo's file, if there is one, then each fragment's. A fragment may add an
# entry under merge_key or replace one of the same name; any other top-level key
# takes the last file's value. Which entry came from where is reported: a
# fragment quietly shadowing one the repo ships would otherwise be invisible.
# With no repo file every entry comes from a fragment, so only a replacement --
# one fragment shadowing another's -- is worth a note.
paths = sorted(glob.glob(os.path.join(frag_dir, "*.json")))
if base_path != "-":
    paths.insert(0, base_path)

# A symlink is the pre-generation state: replace it, even with no fragments, so
# the live file is never a tracked one.
was_link = os.path.islink(target)

# Nothing to generate from, and nothing there: leave it absent rather than
# create an empty file.
if not paths and not was_link and not os.path.exists(target):
    print("unchanged:")
    sys.exit(0)

desired = {}
notes = []
for path in paths:
    try:
        layer = load(path)
    except (OSError, ValueError) as e:
        print("error:cannot read %s: %s" % (path, e))
        sys.exit(0)
    for key, value in layer.items():
        if key == merge_key:
            entries = desired.setdefault(merge_key, {})
            if path != base_path:
                for name in value:
                    if base_path == "-" and name not in entries:
                        continue
                    notes.append("%s %s by %s" % (
                        name,
                        "replaced" if name in entries else "added",
                        os.path.basename(path),
                    ))
            entries.update(value)
        else:
            desired[key] = value

try:
    current = None if was_link else load(target)
except (OSError, ValueError):
    current = None

for note in notes:
    print("note:" + note)

if current == desired:
    print("unchanged:")
elif os.environ.get("DRY_RUN"):
    print("would-write:" + ("replacing the link" if was_link else "merged changes"))
else:
    tmp = target + ".dotfiles-tmp"
    with open(tmp, "w") as f:
        json.dump(desired, f, indent=2)
        f.write("\n")
    os.replace(tmp, target)
    print("wrote:" + ("replaced the link" if was_link else "merged changes"))