import React, { useMemo } from 'react';
import {
  Flag,
  Calendar,
  Clock,
  Briefcase,
  CheckCircle2,
  AlertCircle,
  TrendingUp,
  Plus,
  Coins,
} from 'lucide-react';
import { Project, Milestone, Activity, ApprovalStatus, Priority } from '../../types';
import { formatDate, formatZAR, getApprovalStatusBadge, getPriorityBadge } from '../../lib/formatters';

interface ProjectTimelineGanttProps {
  project: Project;
  milestones: Milestone[];
  activities: Activity[];
  approvedBudgetTotal?: number;
  approvedBudgetsCount?: number;
  onManageMilestones: () => void;
  onManageActivities: () => void;
}

export const ProjectTimelineGantt: React.FC<ProjectTimelineGanttProps> = ({
  project,
  milestones,
  activities,
  approvedBudgetTotal = 0,
  approvedBudgetsCount = 0,
  onManageMilestones,
  onManageActivities,
}) => {
  // Compute timeline boundaries and items
  const timelineData = useMemo(() => {
    const dates: number[] = [];

    if (project.startedAt) dates.push(new Date(project.startedAt).getTime());
    if (project.endedAt) dates.push(new Date(project.endedAt).getTime());

    milestones.forEach((m) => {
      if (m.dueAt) dates.push(new Date(m.dueAt).getTime());
    });

    activities.forEach((a) => {
      if (a.performedAt) dates.push(new Date(a.performedAt).getTime());
    });

    const now = Date.now();
    dates.push(now);

    let startMs: number;
    let endMs: number;

    if (dates.length > 0 && Math.min(...dates) !== Math.max(...dates)) {
      startMs = Math.min(...dates);
      endMs = Math.max(...dates);
      // Add a slight buffer (5% on each side) for aesthetic padding
      const buffer = Math.max((endMs - startMs) * 0.05, 7 * 24 * 60 * 60 * 1000);
      startMs -= buffer;
      endMs += buffer;
    } else {
      // Default: current quarter +/- 3 months
      startMs = now - 90 * 24 * 60 * 60 * 1000;
      endMs = now + 180 * 24 * 60 * 60 * 1000;
    }

    const totalDurationMs = endMs - startMs;

    // Helper to calculate percentage offset along timeline
    const getPercent = (timeMs: number): number => {
      const clamped = Math.max(startMs, Math.min(endMs, timeMs));
      return ((clamped - startMs) / totalDurationMs) * 100;
    };

    // Generate monthly ticks for ruler
    const ticks: { label: string; percent: number; isStartOfYear: boolean }[] = [];
    const currDate = new Date(startMs);
    currDate.setDate(1);
    currDate.setHours(0, 0, 0, 0);

    while (currDate.getTime() <= endMs) {
      if (currDate.getTime() >= startMs) {
        ticks.push({
          label: currDate.toLocaleDateString('en-GB', { month: 'short', year: '2-digit' }),
          percent: getPercent(currDate.getTime()),
          isStartOfYear: currDate.getMonth() === 0,
        });
      }
      currDate.setMonth(currDate.getMonth() + 1);
    }

    // Sort milestones & activities by date
    const sortedMilestones = [...milestones].sort(
      (a, b) => new Date(a.dueAt || 0).getTime() - new Date(b.dueAt || 0).getTime()
    );

    const sortedActivities = [...activities].sort(
      (a, b) => new Date(a.performedAt || 0).getTime() - new Date(b.performedAt || 0).getTime()
    );

    const todayPercent = getPercent(now);
    const isTodayInRange = todayPercent >= 0 && todayPercent <= 100;

    return {
      startMs,
      endMs,
      totalDurationDays: Math.round(totalDurationMs / (1000 * 60 * 60 * 24)),
      getPercent,
      ticks,
      sortedMilestones,
      sortedActivities,
      todayPercent,
      isTodayInRange,
    };
  }, [project, milestones, activities]);

  const verifiedMilestonesCount = milestones.filter((m) => m.status === ApprovalStatus.Approved).length;
  const milestoneProgress = milestones.length > 0 ? Math.round((verifiedMilestonesCount / milestones.length) * 100) : 0;
  const totalActivityBudget = activities.reduce((sum, a) => sum + (Number(a.amount) || 0), 0);

  return (
    <div className="bg-[#0b101c] rounded-2xl border border-slate-800/80 p-5 space-y-5 overflow-hidden shadow-inner">
      {/* Timeline Header & Key Stats */}
      <div className="flex flex-wrap items-center justify-between gap-3 pb-4 border-b border-slate-800/80">
        <div className="flex items-center gap-2.5">
          <div className="h-8 w-8 rounded-xl bg-blue-500/10 border border-blue-500/30 flex items-center justify-center text-blue-400">
            <Calendar className="w-4 h-4" />
          </div>
          <div>
            <h4 className="text-xs font-bold text-white uppercase tracking-wider flex items-center gap-2">
              Implementation Schedule & Timeline
              <span className="text-[10px] normal-case font-normal text-slate-400">
                ({timelineData.totalDurationDays} Days Span)
              </span>
            </h4>
            <p className="text-[11px] text-slate-400">
              Chronological alignment of contractual deliverables and operational activities.
            </p>
          </div>
        </div>

        {/* Quick Legend & Actions */}
        <div className="flex items-center gap-3 text-[11px] flex-wrap">
          <div className="flex items-center gap-3 px-3 py-1 bg-slate-900/80 rounded-xl border border-slate-800 text-slate-400">
            <span className="flex items-center gap-1.5">
              <span className="w-2.5 h-2.5 rounded-full bg-emerald-500 inline-block shadow-sm shadow-emerald-500/50" />
              Verified Deliverable
            </span>
            <span className="flex items-center gap-1.5">
              <span className="w-2.5 h-2.5 rounded-full bg-amber-500 inline-block shadow-sm shadow-amber-500/50" />
              Pending / Review
            </span>
            <span className="flex items-center gap-1.5">
              <span className="w-2.5 h-2.5 rounded-sm bg-blue-500 inline-block shadow-sm shadow-blue-500/50" />
              Work Activity
            </span>
          </div>
        </div>
      </div>

      {/* Main Gantt Timeline Track Container */}
      <div className="space-y-4 pt-1">
        {/* Month Scale / Ruler */}
        <div className="relative h-6 w-full border-b border-slate-800 text-[10px] font-mono text-slate-500 select-none">
          {timelineData.ticks.map((tick, idx) => (
            <div
              key={idx}
              className="absolute transform -translate-x-1/2 flex flex-col items-center"
              style={{ left: `${tick.percent}%` }}
            >
              <span className={tick.isStartOfYear ? 'text-blue-400 font-bold' : 'text-slate-400'}>
                {tick.label}
              </span>
              <span className="h-1.5 w-px bg-slate-700 mt-0.5" />
            </div>
          ))}
        </div>

        {/* Timeline Visualization Surface */}
        <div className="relative min-h-[290px] bg-[#090d16] rounded-xl border border-slate-800/90 pt-8 pb-5 px-4 overflow-x-auto">
          {/* Background vertical grid lines */}
          <div className="absolute inset-0 pointer-events-none">
            {timelineData.ticks.map((tick, idx) => (
              <div
                key={idx}
                className="absolute top-0 bottom-0 w-px bg-slate-800/40"
                style={{ left: `${tick.percent}%` }}
              />
            ))}

            {/* Today marker */}
            {timelineData.isTodayInRange && (
              <div
                className="absolute top-1 bottom-0 z-20 flex flex-col items-center pointer-events-none"
                style={{ left: `${timelineData.todayPercent}%` }}
              >
                <span className="px-2 py-0.5 text-[9px] font-bold text-amber-300 bg-amber-500/25 border border-amber-500/50 rounded-full whitespace-nowrap shadow-md shadow-amber-500/20">
                  Today
                </span>
                <div className="w-px h-full bg-amber-400/80 border-dashed border-l border-amber-400 shadow-sm shadow-amber-400/30 mt-1" />
              </div>
            )}
          </div>

          {/* Layer 1: Milestones Track */}
          <div className="relative z-10 mb-6 space-y-2">
            <div className="flex items-center justify-between text-[11px] font-semibold text-slate-300 px-1">
              <span className="flex items-center gap-1.5 text-blue-400">
                <Flag className="w-3.5 h-3.5" />
                Contractual Deliverables & Milestones ({milestones.length})
              </span>
              <button
                type="button"
                onClick={onManageMilestones}
                className="text-[10px] text-blue-400 hover:text-blue-300 hover:underline cursor-pointer flex items-center gap-1 font-medium"
              >
                <Plus className="w-3 h-3" /> Add / Manage Milestones
              </button>
            </div>

            {timelineData.sortedMilestones.length === 0 ? (
              <div className="p-4 bg-slate-900/40 rounded-lg border border-dashed border-slate-800 text-center text-xs text-slate-500">
                No contractual milestones defined yet. Click &quot;Add / Manage Milestones&quot; to establish deliverables.
              </div>
            ) : (
              <div className="relative h-24 bg-slate-900/50 rounded-xl border border-slate-800/80 flex items-center px-3">
                {/* Milestone connecting base line */}
                <div className="absolute left-3 right-3 h-1 bg-slate-800 rounded-full" />

                {/* Milestone Pins */}
                {timelineData.sortedMilestones.map((m, idx) => {
                  const mTime = new Date(m.dueAt || 0).getTime();
                  const pos = timelineData.getPercent(mTime);
                  const isApproved = m.status === ApprovalStatus.Approved;
                  const isPending = m.status === ApprovalStatus.Pending;
                  const priBadge = getPriorityBadge(m.priority);

                  return (
                    <div
                      key={m.id || idx}
                      className="absolute group z-10 -translate-x-1/2 cursor-pointer transition-all duration-200"
                      style={{ left: `${Math.min(96, Math.max(4, pos))}%` }}
                      onClick={onManageMilestones}
                    >
                      {/* Flag Marker */}
                      <div
                        className={`h-8 w-8 rounded-full flex items-center justify-center shadow-lg transition-transform group-hover:scale-125 border ${
                          isApproved
                            ? 'bg-emerald-500/20 border-emerald-400 text-emerald-300 shadow-emerald-500/20'
                            : isPending
                            ? 'bg-amber-500/20 border-amber-400 text-amber-300 shadow-amber-500/20'
                            : 'bg-blue-500/20 border-blue-400 text-blue-300 shadow-blue-500/20'
                        }`}
                      >
                        <Flag className="w-3.5 h-3.5 fill-current" />
                      </div>

                      {/* Brief Pin Label */}
                      <div className="mt-1 text-center whitespace-nowrap">
                        <span className="text-[10px] font-bold text-slate-300 block max-w-[110px] truncate">
                          {m.name}
                        </span>
                        <span className="text-[9px] text-slate-500 font-mono">
                          {formatDate(m.dueAt)}
                        </span>
                      </div>

                      {/* Tooltip on Hover */}
                      <div className="absolute bottom-full left-1/2 -translate-x-1/2 mb-2 hidden group-hover:flex flex-col w-56 p-2.5 bg-slate-900 border border-slate-700 rounded-xl shadow-2xl text-left z-30 pointer-events-none">
                        <div className="flex items-center justify-between gap-1 mb-1">
                          <span className="text-[10px] font-mono text-blue-400">Milestone #{m.id}</span>
                          <span className={`text-[9px] px-1.5 py-0.2 rounded border ${priBadge.className}`}>
                            {priBadge.label}
                          </span>
                        </div>
                        <p className="text-xs font-bold text-white leading-tight mb-1">{m.name}</p>
                        <div className="flex items-center justify-between text-[10px] text-slate-400 pt-1 border-t border-slate-800">
                          <span className="flex items-center gap-1">
                            <Clock className="w-3 h-3 text-slate-500" />
                            {formatDate(m.dueAt)}
                          </span>
                          <span className={isApproved ? 'text-emerald-400 font-semibold' : 'text-amber-400'}>
                            {isApproved ? 'Verified' : 'Pending'}
                          </span>
                        </div>
                      </div>
                    </div>
                  );
                })}
              </div>
            )}
          </div>

          {/* Layer 2: Activities Track */}
          <div className="relative z-10 space-y-2">
            <div className="flex items-center justify-between text-[11px] font-semibold text-slate-300 px-1">
              <span className="flex items-center gap-1.5 text-cyan-400">
                <Briefcase className="w-3.5 h-3.5" />
                Work Breakdown Activities ({activities.length})
              </span>
              <button
                type="button"
                onClick={onManageActivities}
                className="text-[10px] text-cyan-400 hover:text-cyan-300 hover:underline cursor-pointer flex items-center gap-1 font-medium"
              >
                <Plus className="w-3 h-3" /> Add / Manage Activities
              </button>
            </div>

            {timelineData.sortedActivities.length === 0 ? (
              <div className="p-3 bg-slate-900/40 rounded-lg border border-dashed border-slate-800 text-center text-xs text-slate-500">
                No activities recorded in work breakdown structure.
              </div>
            ) : (
              <div className="space-y-1.5">
                {timelineData.sortedActivities.slice(0, 4).map((act, idx) => {
                  const aTime = new Date(act.performedAt || project.startedAt || Date.now()).getTime();
                  const pos = timelineData.getPercent(aTime);

                  return (
                    <div
                      key={act.id || idx}
                      className="group relative flex items-center p-2 rounded-xl bg-slate-900/80 hover:bg-slate-800/90 border border-slate-800 hover:border-slate-700 transition cursor-pointer"
                      onClick={onManageActivities}
                    >
                      <div className="w-48 shrink-0 pr-3 border-r border-slate-800 truncate">
                        <span className="text-xs font-semibold text-white block truncate">{act.title}</span>
                        <span className="text-[10px] text-slate-400">{act.category || 'Operations'}</span>
                      </div>

                      <div className="flex-1 relative h-6 mx-3 flex items-center">
                        <div className="w-full h-1 bg-slate-800 rounded-full" />
                        <div
                          className="absolute h-4 rounded-md bg-cyan-500/20 border border-cyan-400/60 px-2 flex items-center text-[9px] font-bold text-cyan-300 shadow-sm shadow-cyan-500/20 -translate-x-1/2 whitespace-nowrap group-hover:scale-105 transition"
                          style={{ left: `${Math.min(94, Math.max(6, pos))}%` }}
                        >
                          <Coins className="w-2.5 h-2.5 mr-1 text-cyan-400" />
                          {formatZAR(act.amount)}
                        </div>
                      </div>

                      <div className="w-28 shrink-0 text-right font-mono text-[10px] text-slate-400">
                        {formatDate(act.performedAt)}
                      </div>
                    </div>
                  );
                })}

                {activities.length > 4 && (
                  <div className="text-center pt-1">
                    <button
                      type="button"
                      onClick={onManageActivities}
                      className="text-[11px] text-cyan-400 hover:text-cyan-300 font-semibold hover:underline cursor-pointer"
                    >
                      + View all {activities.length} work activities &rarr;
                    </button>
                  </div>
                )}
              </div>
            )}
          </div>
        </div>
      </div>

      {/* Bottom Summary KPI Bar */}
      <div className="grid grid-cols-2 sm:grid-cols-3 lg:grid-cols-5 gap-3 pt-2">
        <div className="p-3 bg-[#090d16] rounded-xl border border-slate-800">
          <span className="text-[10px] uppercase font-bold text-slate-500 block">Project Duration</span>
          <span className="text-sm font-bold text-white mt-0.5 block">
            {timelineData.totalDurationDays} Days
          </span>
          <span className="text-[10px] text-slate-400">
            {formatDate(project.startedAt)} &rarr; {formatDate(project.endedAt)}
          </span>
        </div>

        <div className="p-3 bg-[#090d16] rounded-xl border border-slate-800">
          <span className="text-[10px] uppercase font-bold text-slate-500 block">Milestone Progress</span>
          <div className="flex items-baseline gap-1.5 mt-0.5">
            <span className="text-sm font-bold text-emerald-400">{milestoneProgress}%</span>
            <span className="text-[10px] text-slate-400">({verifiedMilestonesCount}/{milestones.length})</span>
          </div>
          <div className="w-full h-1.5 bg-slate-900 rounded-full mt-1.5 overflow-hidden">
            <div
              className="h-full bg-emerald-500 rounded-full transition-all"
              style={{ width: `${milestoneProgress}%` }}
            />
          </div>
        </div>

        <div className="p-3 bg-[#090d16] rounded-xl border border-slate-800">
          <span className="text-[10px] uppercase font-bold text-slate-500 block">Work Breakdown Cost</span>
          <span className="text-sm font-bold text-cyan-400 mt-0.5 block font-mono">
            {formatZAR(totalActivityBudget)}
          </span>
          <span className="text-[10px] text-slate-400">{activities.length} total tasks</span>
        </div>

        <div className="p-3 bg-[#090d16] rounded-xl border border-slate-800">
          <span className="text-[10px] uppercase font-bold text-slate-500 block">Governance State</span>
          <div className="mt-1">
            {(() => {
              const b = getApprovalStatusBadge(project.status);
              return (
                <span className={`inline-flex items-center px-2 py-0.5 rounded-full text-[10px] font-semibold border ${b.className}`}>
                  {b.label}
                </span>
              );
            })()}
          </div>
          <span className="text-[10px] text-slate-500 mt-0.5 block">Statutory Clearance</span>
        </div>

        {/* Total Value of Approved Project Budgets Widget */}
        <div className="p-3 bg-[#090d16] rounded-xl border border-slate-800">
          <span className="text-[10px] uppercase font-bold text-slate-500 block">Approved Budget Value</span>
          <span className="text-sm font-bold text-emerald-400 mt-0.5 block font-mono">
            {formatZAR(approvedBudgetTotal)}
          </span>
          <span className="text-[10px] text-slate-400">
            {approvedBudgetsCount > 0
              ? `${approvedBudgetsCount} approved budget line${approvedBudgetsCount === 1 ? '' : 's'}`
              : 'Allocated Project Budget'}
          </span>
        </div>
      </div>
    </div>
  );
};