#!/bin/bash

#
# git-watch: A streaming perspective of git changes and commits.
#
# Monitors the current repository for:
# - New commits (displays 'git show')
# - Working directory & index changes (displays 'git diff HEAD' and untracked files)
#
# Requires 'watchexec' for responsiveness.
#

# Check if we're in a git repo
[ "$(git rev-parse --is-inside-work-tree 2>/dev/null)" = "true" ] || {
  echo "Error: Not a git repository." >&2
  exit 1
}

# Check for dependencies
if ! command -v watchexec >/dev/null 2>&1; then
  echo "Error: 'watchexec' is required for git-watch. Please install it (e.g., 'brew install watchexec')." >&2
  exit 1
fi

if [[ "$1" == "--help" || "$1" == "-h" ]]; then
  echo "git-watch: A streaming perspective of git changes and commits."
  echo
  echo "Usage: git-watch [--debug]"
  echo
  echo "Options:"
  echo "  --debug     Log what would be run instead of running it"
  echo
  echo "Features:"
  echo "  - Shows 'git show' on new commits"
  echo "  - Shows 'git diff HEAD' on working tree/index changes"
  echo "  - Uses 'watchexec' for high-speed responsiveness"
  echo "  - Uses your fancy pager (delta/diff-so-fancy) without blocking"
  exit 0
fi

DEBUG_MODE=false
if [[ "$1" == "--debug" || "$2" == "--debug" ]]; then
  DEBUG_MODE=true
fi

# Pager detection (compatible with delta, diff-so-fancy, etc.)
pager_cmd=$(command -v delta || command -v diff-so-fancy)
if [ -n "$pager_cmd" ]; then
  if [[ "$pager_cmd" == *"delta"* ]]; then
    pager_cmd="$pager_cmd --paging=never"
  fi
  pipe_to_pager=" | $pager_cmd"
fi

git_run() {
  if [ "$DEBUG_MODE" = true ]; then
    echo -e "\033[0;35m[DEBUG] Would run: git --no-pager \"$@\" --color=always$pipe_to_pager\033[0m"
    return
  fi
  eval "git --no-pager \"\$@\" --color=always$pipe_to_pager"
}

# Cross-platform hashing for change detection
hash_cmd=$(command -v shasum || command -v sha1sum || echo "cksum")

update() {
  local mode="$1"
  local git_dir state_file
  git_dir=$(git rev-parse --git-dir 2>/dev/null)
  [ -n "$git_dir" ] || return
  state_file="$git_dir/watch-state"

  local current_head last_head current_state_hash last_state_hash
  current_head=$(git rev-parse HEAD 2>/dev/null)
  
  # Capture status and diff for hashing (ignoring untracked files for now)
  local status_output=$(git status --porcelain --untracked-files=no)
  local diff_output=$(git diff HEAD 2>/dev/null)
  # TODO: Re-evaluate untracked file support later.
  current_state_hash=$( (echo "$status_output"; echo "$diff_output") | $hash_cmd | cut -d' ' -f1)
  
  if [[ -f "$state_file" && "$mode" != "--initial" ]]; then
    read -r last_head last_state_hash < "$state_file"
  fi

  if [ "$DEBUG_MODE" = true ]; then
    echo -e "\033[0;35m[DEBUG] Mode: $mode\033[0m"
    echo -e "\033[0;35m[DEBUG] HEAD: $current_head (Last: ${last_head:-NONE})\033[0m"
    echo -e "\033[0;35m[DEBUG] State Hash: $current_state_hash (Last: ${last_state_hash:-NONE})\033[0m"
  fi

  local did_something=false

  # 1. Commit detection
  if [[ "$current_head" != "$last_head" || "$mode" == "--initial" ]]; then
    echo -e "\n\033[1;34m=== Current Commit: $(git log -1 --format='%h %s' 2>/dev/null) ===\033[0m"
    git_run show --summary --stat -p
    did_something=true
  fi

  # 2. Working directory detection
  if [[ "$current_state_hash" != "$last_state_hash" || "$mode" == "--initial" ]]; then
    if [[ -n "$status_output" ]]; then
      echo -e "\n\033[1;32m=== Changes ===\033[0m"
      
      # Show diff of tracked changes
      if [[ -n "$diff_output" ]]; then
        git_run diff HEAD
      fi
      
      # TODO: Implement surgical untracked file support here if needed.
      did_something=true
    fi
  fi

  # Update state so we don't repeat this in the next --step
  if [[ "$did_something" == "true" ]]; then
    if [ "$DEBUG_MODE" = true ]; then
      echo -e "\033[0;35m[DEBUG] Would update state file: $current_head $current_state_hash\033[0m"
    else
      echo "$current_head $current_state_hash" > "$state_file"
    fi
  fi
}

# Internal flag for watchexec to call back into the script
if [[ "$1" == "--step" ]]; then
  update "--step"
  exit 0
fi

# Main execution loop
update "--initial"

pass_debug=""
if [ "$DEBUG_MODE" = true ]; then
  pass_debug="--debug"
fi

echo -e "\033[0;32mWatching with watchexec...\033[0m"
# --postpone: don't run immediately on start (we already did update --initial)
# --quiet: suppress watchexec status messages
# exec is used so that Ctrl-C goes directly to watchexec and terminates the session
exec watchexec --quiet --postpone -i .git -w . -w "$(git rev-parse --git-dir)/HEAD" -- "$0" --step $pass_debug