#!/bin/bash

# pi's settings.json, generated. Dry run by default; pass `yes` to apply.

set -euo pipefail

# shellcheck source-path=SCRIPTDIR
# shellcheck source=lib.sh
source "$(dirname "$0")/lib.sh" "$@"

# ~/.pi/agent/settings.json is a real file built from config/pi/settings.json
# plus every ~/.config/pi/settings.d/*.json that another layer links in. It
# cannot be a symlink into a repo: pi has no second global settings file to
# layer with, and it writes to this one at runtime (lastChangelogVersion,
# /model, `pi install`), which used to dirty the tracked file.
#
# Merging the sources: list keys (packages, extensions, skills, prompts,
# themes) are concatenated in file order, a package deduplicated by its source
# (an object entry beats a bare string); any other key takes the last file's
# value. Relative paths in a fragment's `extensions`, `skills`, `prompts` and
# `themes` resolve against the fragment's real location, so a layer can point
# at files in its own checkout.
#
# Merging with what is already there is three-way, against what this script
# generated last time (kept in ~/.local/state/dotfiles/pi-settings.json): a key
# -- or a list entry, a package by its source -- that pi or the operator has not
# changed since then takes the new generated value, removal included; one they
# changed keeps their value. With no record of a last run, what is there is kept
# and what is missing is added. So a /model choice or a `pi install` survives
# relinks, and a package dropped from a repo really goes. Keys nothing generates
# (lastChangelogVersion) are simply kept.
#
# Written under pi's own settings lock, via a temporary file and a rename; a run
# that finds the lock held skips and says so, and the next link catches up.
#
# Run after other layers' link.sh, so their fragments are in place.
pi_dir="$HOME/.pi/agent"
if [[ ! -d "$pi_dir" ]]
then
  exit 0
fi

pi_status="$(DRY_RUN="$is_dry_run" python3 - \
  "$config_dir/pi/settings.json" \
  "$xdg_config_dir/pi/settings.d" \
  "$pi_dir/settings.json" \
  "${XDG_STATE_HOME:-$HOME/.local/state}/dotfiles/pi-settings.json" \
  "$config_dir" <<'PY'
import glob, json, os, sys

base_path, frag_dir, target, state_path, config_dir = sys.argv[1:6]
LIST_KEYS = ("packages", "extensions", "skills", "prompts", "themes")
PATH_KEYS = ("extensions", "skills", "prompts", "themes")


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


def source(entry):
    return entry if isinstance(entry, str) else entry.get("source")


def add_packages(into, entries):
    for entry in entries:
        key = source(entry)
        existing = next((i for i, e in enumerate(into) if source(e) == key), None)
        if existing is None:
            into.append(entry)
        elif not isinstance(entry, str):
            into[existing] = entry


# What the repos want now.
desired = {}
for path in [base_path] + sorted(glob.glob(os.path.join(frag_dir, "*.json"))):
    try:
        layer = load(path)
    except (OSError, ValueError) as e:
        print("error:cannot read %s: %s" % (path, e))
        sys.exit(0)
    here = os.path.dirname(os.path.realpath(path))
    for key, value in layer.items():
        if key in PATH_KEYS and path != base_path:
            value = [v if os.path.isabs(os.path.expanduser(v)) else os.path.normpath(os.path.join(here, v))
                     for v in value]
        if key == "packages":
            add_packages(desired.setdefault("packages", []), value)
        elif key in LIST_KEYS:
            merged = desired.setdefault(key, [])
            merged.extend(v for v in value if v not in merged)
        else:
            desired[key] = value

# What is there. A symlink is the pre-generation state: its target is a tracked
# file this repo now owns, so treat it as already matching.
def snapshot():
    """What is on disk now, to notice a write that lands before the lock."""
    try:
        return (os.path.islink(target), open(target).read())
    except OSError:
        return (os.path.islink(target), None)


on_disk = snapshot()
first_run = False
if os.path.islink(target):
    first_run = True
    try:
        local = load(target)
    except (OSError, ValueError):
        local = {}
    local = {k: v for k, v in local.items() if k not in desired and k not in LIST_KEYS and k != "packages"}
    local.update(json.loads(json.dumps(desired)))
    last = desired
else:
    try:
        local = load(target)
    except FileNotFoundError:
        local = {}
    except ValueError as e:
        print("error:%s is not valid JSON, leaving it: %s" % (target, e))
        sys.exit(0)
    # No record of a previous run -- a new machine where pi made its own file
    # first, or lost state: nothing is known to have come from the repos, so
    # keys already there are kept and keys missing arrive.
    try:
        last = load(state_path)
    except (OSError, ValueError):
        last = {}

MISSING = object()


def three_way(ours, before, theirs):
    """ours: on disk; before: generated last time; theirs: generated now."""
    if ours == before:
        return theirs
    return ours


def merge_list(key, identity):
    """Per entry, three-way, in generated order then local-only extras."""
    ours = {identity(e): e for e in local.get(key, [])}
    before = {identity(e): e for e in last.get(key, [])}
    theirs = {identity(e): e for e in desired.get(key, [])}
    merged = []
    for ident in [identity(e) for e in desired.get(key, [])] + \
                 [identity(e) for e in local.get(key, []) if identity(e) not in theirs]:
        value = three_way(ours.get(ident, MISSING), before.get(ident, MISSING), theirs.get(ident, MISSING))
        if value is not MISSING:
            merged.append(value)
    return merged


result = {}
for key in list(local) + [k for k in desired if k not in local]:
    if key in LIST_KEYS:
        merged = merge_list(key, source if key == "packages" else (lambda e: e))
        if merged or key in local:
            result[key] = merged
        continue
    value = three_way(local.get(key, MISSING), last.get(key, MISSING), desired.get(key, MISSING))
    if value is not MISSING:
        result[key] = value

changed = first_run or result != local
lock = target + ".lock"


def take_lock():
    """pi's own lock (proper-lockfile: a directory, stale after 10s), so neither
    side can read, then write over the other's change."""
    import time
    for _ in range(2):
        try:
            os.mkdir(lock)
            return True
        except FileExistsError:
            try:
                if time.time() - os.stat(lock).st_mtime > 10:
                    os.rmdir(lock)
                    continue
            except FileNotFoundError:
                continue
            return False
    return False


def save_state():
    os.makedirs(os.path.dirname(state_path), exist_ok=True)
    with open(state_path + ".tmp", "w") as f:
        json.dump(desired, f, indent=2)
    os.replace(state_path + ".tmp", state_path)


if not changed:
    print("unchanged:")
    if not os.environ.get("DRY_RUN"):
        save_state()
elif os.environ.get("DRY_RUN"):
    print("would-write:" + ("replacing the link" if first_run else "merged changes"))
elif not take_lock():
    print("locked:")
elif snapshot() != on_disk:
    # pi wrote between the read above and taking the lock: merge again next time
    # rather than write over it.
    os.rmdir(lock)
    print("locked:")
else:
    try:
        tmp = target + ".dotfiles-tmp"
        with open(tmp, "w") as f:
            json.dump(result, f, indent=2)
            f.write("\n")
        os.replace(tmp, target)
        save_state()
    finally:
        os.rmdir(lock)
    print("wrote:" + ("replaced the link" if first_run else "merged changes"))
PY
)"

case "${pi_status%%:*}" in
  wrote)       green "pi settings: ${pi_status#*:}" ;;
  unchanged)   green "pi settings: unchanged" ;;
  would-write) yellow "pi settings will be generated: ${pi_status#*:}" ;;
  locked)      yellow "pi settings: pi holds its settings lock; left as is, the next link catches up" ;;
  error)       red "pi settings: ${pi_status#*:}" ;;
esac