#!/usr/bin/env python3

import argparse
import os
import re
import sys

arg_parser = argparse.ArgumentParser(
    description="""
Reports time consumed for one or more task in a format similar to the standard
Bash 'time' builtin. Optionally sorts tasks by real (wall-clock), user (user
space CPU), or sys (kernel CPU) time.
""")

arg_parser.add_argument(
    "paths",
    metavar="path",
    nargs="+",
    help="""
A path containing task buildstats. If the path is a directory, e.g.
build/tmp/buildstats, then all task found (recursively) in it will be
processed. If the path is a single task buildstat, e.g.
build/tmp/buildstats/20161018083535/foo-1.0-r0/do_compile, then just that
buildstat will be processed. Multiple paths can be specified to process all of
them. Files whose names do not start with "do_" are ignored.
""")

arg_parser.add_argument(
    "--sort",
    choices=("none", "real", "user", "sys"),
    default="none",
    help="""
The measurement to sort the output by. Defaults to 'none', which means to sort
by the order paths were given on the command line. For other options, tasks are
sorted in descending order from the highest value.
""")

args = arg_parser.parse_args()

# Field names and regexes for parsing out their values from buildstat files
field_regexes = (("elapsed",    ".*Elapsed time: ([0-9.]+)"),
                 ("user",       "rusage ru_utime: ([0-9.]+)"),
                 ("sys",        "rusage ru_stime: ([0-9.]+)"),
                 ("child user", "Child rusage ru_utime: ([0-9.]+)"),
                 ("child sys",  "Child rusage ru_stime: ([0-9.]+)"))

# A list of (<path>, <dict>) tuples, where <path> is the path of a do_* task
# buildstat file and <dict> maps fields from the file to their values
task_infos = []

def save_times_for_task(path):
    """Saves information for the buildstat file 'path' in 'task_infos'."""

    if not os.path.basename(path).startswith("do_"):
        return

    with open(path) as f:
        fields = {}

        for line in f:
            for name, regex in field_regexes:
                match = re.match(regex, line)
                if match:
                    fields[name] = float(match.group(1))
                    break

        # Check that all expected fields were present
        for name, regex in field_regexes:
            if name not in fields:
                print("Warning: Skipping '{}' because no field matching '{}' could be found"
                      .format(path, regex),
                      file=sys.stderr)
                return

        task_infos.append((path, fields))

def save_times_for_dir(path):
    """Runs save_times_for_task() for each file in path and its subdirs, recursively."""

    # Raise an exception for os.walk() errors instead of ignoring them
    def walk_onerror(e):
        raise e

    for root, _, files in os.walk(path, onerror=walk_onerror):
        for fname in files:
            save_times_for_task(os.path.join(root, fname))

for path in args.paths:
    if os.path.isfile(path):
        save_times_for_task(path)
    else:
        save_times_for_dir(path)

def elapsed_time(task_info):
    return task_info[1]["elapsed"]

def tot_user_time(task_info):
    return task_info[1]["user"] + task_info[1]["child user"]

def tot_sys_time(task_info):
    return task_info[1]["sys"] + task_info[1]["child sys"]

if args.sort != "none":
    sort_fn = {"real": elapsed_time, "user": tot_user_time, "sys": tot_sys_time}
    task_infos.sort(key=sort_fn[args.sort], reverse=True)

first_entry = True

# Catching BrokenPipeError avoids annoying errors when the output is piped into
# e.g. 'less' or 'head' and not completely read
try:
    for task_info in task_infos:
        real = elapsed_time(task_info)
        user = tot_user_time(task_info)
        sys = tot_sys_time(task_info)

        if not first_entry:
            print()
        first_entry = False

        # Mimic Bash's 'time' builtin
        print("{}:\n"
              "real\t{}m{:.3f}s\n"
              "user\t{}m{:.3f}s\n"
              "sys\t{}m{:.3f}s"
              .format(task_info[0],
                      int(real//60), real%60,
                      int(user//60), user%60,
                      int(sys//60), sys%60))

except BrokenPipeError:
    pass
