import std/[times, os, strutils, strbasics, strscans, sets, re, tables], parseopt

const VERSION = "0.1"
const MONTHS   = DefaultLocale.MMM.toHashSet + DefaultLocale.MMMM.toHashSet
const WEEKDAYS = DefaultLocale.ddd.toHashSet + DefaultLocale.dddd.toHashSet
const configDir = expandTilde("~/.config/then/")
const defaultConfigFile = configDir & "then.toml"
const defaultCalendarFile = configDir & "calendar.then"

# Forward declarations
proc checkCond(cond: string, date: DateTime): bool

# Creates a default configuration file if it doesn't exist
proc createDefaultConfigFile() =
  if not fileExists(defaultConfigFile):
    if not dirExists(configDir):
      createDir(configDir)
    writeFile(defaultConfigFile, """
    [config]
    directory = "~/.config/then/"
    """)

# Creates a default calendar file if it doesn't exist
proc createDefaultCalendarFile() =
  if not fileExists(defaultCalendarFile):
    if not dirExists(configDir):
      createDir(configDir)
    writeFile(defaultCalendarFile, """
    # Add your events here
    """)

proc printHelp(badCmd: string) =
  if badCmd != "":
    echo badCmd & " is not a valid option\n"
  echo """
Usage:
  then [options] [commands]

OPTIONS
  -h, --help     show list of CLI options
  -v, --version  show then version
  --future=DAYS  set future
  --past=DAYS    set past

COMMANDS
  a              print upcoming agenda (default command)
  e              open default calendar file in $EDITOR
  j              print the modified julian day
  """
  quit()

proc printVersion() =
  echo "then " & VERSION
  quit()

# Check an individual condition (Jan) and return the condition type (month)
proc checkType(c: string): string =
  var cond = c
  if find(cond, re"^\d{4}$") > -1:             return "year"
  if find(cond, re"^\d{1,2}$") > -1:           return "day"
  if find(cond, re"^\dw$") > -1:               return "firstweek"
  if find(cond, re"^\dl$") > -1:               return "lastweek"
  if find(cond, re"^\([A-Za-z0-9 ]+\)$") > -1: return "dategroup"
  if find(cond, re"^\d{4}-\d{4}$") > -1:       return "rangeyear"
  if find(cond, re"^\d{1,2}-\d{1,2}$") > -1:   return "rangeday"
  if find(cond, re"^\d{1,2}:\d{2}(-\d{1,2}:\d{2})?$") > -1:          return "time"
  if find(cond, re"^\(?\s*[Jj]\s*%\s*\d+\s*([-+]\d+)?\s*\)?$") > -1: return "julian"
  cond = cond.toLower.capitalizeAscii
  if cond in MONTHS: return "month"
  if cond in WEEKDAYS: return "dayofweek"

  # Split c on - and check for ranges
  let cs = cond.split("-", maxsplit = 1)
  if cs.len != 2: return "unknown"
  let startRange = cs[0].toLower.capitalizeAscii
  let endRange   = cs[1].toLower.capitalizeAscii
  if (startRange in MONTHS)   and (endRange in MONTHS):   return "rangemonth"
  if (startRange in WEEKDAYS) and (endRange in WEEKDAYS): return "rangedayofweek"
  if find(startRange, re"^\([A-Za-z0-9 ]+\)$") > -1 and find(endRange, re"^\([A-Za-z0-9 ]+\)$") > -1:
    return "rangedategroup"
  return "unknown"

proc getWeekFromEnd(date: DateTime): int =
  let daysInMonth = getDaysInMonth(date.month, date.year)
  return int((daysInMonth - date.monthday) / 7) + 1

proc getWeek(date: DateTime): int =
  return int((date.monthDay - 1) / 7) + 1

# Check each condition in a date group like (Jan 1 2025)
proc checkDateGroup(s: string, date: DateTime): bool =
  var conditions = s
  let cs = conditions[1..conditions.len-2].splitWhitespace
  for c in cs:
    if checkCond(c, date) == false:
      return false
  return true

proc checkRangeYear(s: string, date: DateTime): bool =
  var years = s.split('-')
  return date.year >= years[0] and date.year <= years[1]

proc checkCond(cond: string, date: DateTime): bool =
  var condition = cond
  var invert = false
  var found = false
  if condition[0] == '!':
    condition.delete(0..0)
    invert = true
  case checkType(condition):
    of "time":
      return true
    of "year":
      if parseInt(condition) == date.year:
        found = true
    of "day":
      if condition == date.format("d") or condition == date.format("dd"):
        found = true
    of "month":
      if condition == date.format("MMM") or condition == date.format("MMMM"):
        found = true
    of "dayofweek":
      if condition == date.format("ddd") or condition == date.format("dddd"):
        found = true
    of "firstweek":
      if parseInt(condition[0..1]) == getWeek(date):
        found = true
    of "lastweek":
      if parseInt(condition[0..1]) == getWeekFromEnd(date):
        found = true
    of "dategroup":
      found = checkDateGroup(condition, date)
    of "rangeyear":
      found = checkRangeYear(condition, date)
    of "unknown":
      echo "ERROR: Unknown condition: ", condition
  if invert == true:
    return not found
  return found

# Splits a string on whitespace, but maintains whitespace in date groups
proc splitWhitespaceExceptParens(str:string): seq[string] =
  var result: seq[string] = newSeq[string]()
  var inParens = false
  for token in str.splitWhitespace:
    if inParens:
      result.add(result.pop & ' ' & token)
    else:
      result.add(token)
    for c in token:
      if c == '(': inParens = true
      if c == ')': inParens = false
  return result

# Returns Table[conditionType, seq of conditions]
proc parseDateToTable(date:string): Table[string,seq[string]] =
  var table = initTable[string,seq[string]]()
  let conditions = splitWhitespaceExceptParens(date)
  for c in conditions:
    let condType = checkType(c)
    if not table.hasKey(condType):
      table[condType] = @[]
    table[condType].add(c)
  return table


proc getEvents(cal: seq[string], date: DateTime): seq[string] =
  var events: seq[string] = newSeq[string]()
  for line in cal:
    var (success, dateConditions, event) = scanTuple(line, "$*,$*")
    if success:
      dateConditions.strip
      event.strip
      let conditions  = parseDateToTable(dateConditions)
      var match = true
      # key = Condition Type (e.g. month), cs = Seq of conditions
      for k,cs in conditions:
        var keyMatched = false
        for c in cs:
          #var cond = c.toLower.capitalizeAscii
          if checkCond(c, date) == true:
            keyMatched = true
            break
        if not keyMatched:
          match = false
          break
      if match:
        events.add(event)
    else:
      echo "WARNING: Cannot parse line: ", line
  return events

proc printEvents(cal: seq[string], date: DateTime, format: string) =
  let events = getEvents(cal, date)
  if events.len > 0:
    for e in events:
        echo date.format(format), "  ", e

proc openCal(file: string): seq[string] =
  let f = open(file)
  var cal: seq[string]
  for line in f.lines:
    if line == "": continue
    if line.strip[0] == '#': continue
    cal.add(line)
  f.close()
  return cal

proc printCalendar() =
  let cal = openCal(defaultCalendarFile)
  var past = -3
  var future = 7
  let now = now()

  for i in past..future:
    let curDay = now + i.days
    printEvents(cal, curDay, "ddd  yyyy MMM dd")

proc main() =
  var   past: int = 1
  var future: int = 14
  var  noArg: bool = true
  for kind, key, val in getopt():
    case kind
    of cmdLongOption, cmdShortOption:
      noArg = false
      case key
      of "help", "h":
        printHelp("")
      of "version", "v":
        printVersion()
      else:
        printHelp(key)
    else:
      discard

  if noArg:
    printCalendar()

when isMainModule:
  main()