// Copyright (C) 2009 The Android Open Source Project
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package com.google.gerrit.prettify.common;

import java.util.ArrayList;
import java.util.List;

public class SparseFileContent {
  protected List<Range> ranges;
  protected int size;

  private transient int currentRangeIdx;

  public SparseFileContent() {
    ranges = new ArrayList<>();
  }

  public int size() {
    return size;
  }

  public void setSize(int s) {
    size = s;
  }

  public String get(int idx) {
    final String line = getLine(idx);
    if (line == null) {
      throw new ArrayIndexOutOfBoundsException(idx);
    }
    return line;
  }

  public boolean contains(int idx) {
    return getLine(idx) != null;
  }

  public int first() {
    return ranges.isEmpty() ? size() : ranges.get(0).base;
  }

  public int next(int idx) {
    // Most requests are sequential in nature, fetching the next
    // line from the current range, or the immediate next range.
    //
    int high = ranges.size();
    if (currentRangeIdx < high) {
      Range cur = ranges.get(currentRangeIdx);
      if (cur.contains(idx + 1)) {
        return idx + 1;
      }

      if (++currentRangeIdx < high) {
        // Its not plus one, its the base of the next range.
        //
        return ranges.get(currentRangeIdx).base;
      }
    }

    // Binary search for the current value, since we know its a sorted list.
    //
    int low = 0;
    do {
      final int mid = (low + high) / 2;
      final Range cur = ranges.get(mid);

      if (cur.contains(idx)) {
        if (cur.contains(idx + 1)) {
          // Trivial plus one case above failed due to wrong currentRangeIdx.
          // Reset the cache so we don't miss in the future.
          //
          currentRangeIdx = mid;
          return idx + 1;
        }

        if (mid + 1 < ranges.size()) {
          // Its the base of the next range.
          currentRangeIdx = mid + 1;
          return ranges.get(currentRangeIdx).base;
        }

        // No more lines in the file.
        //
        return size();
      }

      if (idx < cur.base) {
        high = mid;
      } else {
        low = mid + 1;
      }
    } while (low < high);

    return size();
  }

  private String getLine(int idx) {
    // Most requests are sequential in nature, fetching the next
    // line from the current range, or the next range.
    //
    int high = ranges.size();
    if (currentRangeIdx < high) {
      Range cur = ranges.get(currentRangeIdx);
      if (cur.contains(idx)) {
        return cur.get(idx);
      }

      if (++currentRangeIdx < high) {
        final Range next = ranges.get(currentRangeIdx);
        if (next.contains(idx)) {
          return next.get(idx);
        }
      }
    }

    // Binary search for the range, since we know its a sorted list.
    //
    if (ranges.isEmpty()) {
      return null;
    }

    int low = 0;
    do {
      final int mid = (low + high) / 2;
      final Range cur = ranges.get(mid);
      if (cur.contains(idx)) {
        currentRangeIdx = mid;
        return cur.get(idx);
      }
      if (idx < cur.base) {
        high = mid;
      } else {
        low = mid + 1;
      }
    } while (low < high);
    return null;
  }

  public void addLine(int i, String content) {
    final Range r;
    if (!ranges.isEmpty() && i == last().end()) {
      r = last();
    } else {
      r = new Range(i);
      ranges.add(r);
    }
    r.lines.add(content);
  }

  private Range last() {
    return ranges.get(ranges.size() - 1);
  }

  @Override
  public String toString() {
    final StringBuilder b = new StringBuilder();
    b.append("SparseFileContent[\n");
    for (Range r : ranges) {
      b.append("  ");
      b.append(r.toString());
      b.append('\n');
    }
    b.append("]");
    return b.toString();
  }

  static class Range {
    protected int base;
    protected List<String> lines;

    private Range(int b) {
      base = b;
      lines = new ArrayList<>();
    }

    protected Range() {}

    private String get(int i) {
      return lines.get(i - base);
    }

    private int end() {
      return base + lines.size();
    }

    private boolean contains(int i) {
      return base <= i && i < end();
    }

    @Override
    public String toString() {
      // Usage of [ and ) is intentional to denote inclusive/exclusive range
      return "Range[" + base + "," + end() + ")";
    }
  }
}