///////////////////////////////////////////////////////////////////////////////
//
//  Microsoft Research Singularity
//
//  Copyright (c) Microsoft Corporation.  All rights reserved.
//
//  File:   PathUtils.sg
//
//  Note:
//
//       Character vector utilities.
//

using Microsoft.Singularity.Channels;
using Microsoft.Singularity.Directory;
using Microsoft.SingSharp;

using System;

namespace Microsoft.Singularity.Services.Fat.Fs
{
    public class PathUtils
    {
        public const char Separator = '/';

        /// <summary> Remove duplicate and trailing separators
        /// from character vector representing a path. A leading
        /// separator is preserved. </summary>
        public static char[]! in ExHeap
        CleanSeparators([Claims] char[]! in ExHeap path)
        {
            int src = 0;
            int dst = 0;
            while (src < path.Length) {
                bool skip = (path[src] == Separator);
                path[dst++] = path[src++];
                if (skip) {
                    while (src < path.Length && path[src] == Separator) {
                        src++;
                    }
                }
            }

            if (dst > 1 && path[dst - 1] == Separator) {
                // Chop trailing separator if not root separator
                dst--;
            }
            if (dst != src) {
                Bitter.Truncate(ref path, dst);
            }
            return path;
        }

        private static char[]! in ExHeap
        DropTrailingSeparator([Claims] char[]! in ExHeap path)
        {
            if (path.Length > 1 && path[path.Length - 1] == Separator) {
                Bitter.Truncate(ref path, path.Length - 1);
            }
            return path;
        }

        private static int
        GetLastSeparator(char[]! in ExHeap path)
        {
            int i = path.Length - 1;
            while (i >= 0 && path[i] != Separator) {
                i--;
            }
            return i;
        }

        private static int
        GetNextSeparator(char[]! in ExHeap path, int start)
        {
            while (start < path.Length) {
                if (path[start] == Separator) {
                    return start;
                }
                start++;
            }
            return -1;
        }

        /// <summary>
        /// Splits path into top most path component and remainder.
        ///
        ///   path         top       remainder
        /// ---------- ------------------------
        /// "/a/b/c"       "/"          "a/b/c"
        /// "a/b/c"        "a"          "b/c"
        /// "/a"           "/"          "a"
        /// "a"            "a"          null
        /// "/"            "/"          null
        /// "//"           "/"          null
        /// "///a/b//"     "/"          "a/b"
        /// </summary>
        public static void
        SplitPathTopDown([Claims] char[]! in ExHeap path,
                         out char[] in ExHeap       top,
                         out char[] in ExHeap       remainder)
            requires path.Length >= 1;
        {
            path = CleanSeparators(path);
            if (path[0] == Separator) {
                if (path.Length == 1) {
                    top       = path;
                    remainder = null;
                }
                else {
                    remainder = Bitter.SplitOff(ref path, 1);
                    top       = path;
                    if (remainder.Length == 0) {
                        delete remainder;
                        remainder = null;
                    }
                }
            }
            else {
                int nextSep = GetNextSeparator(path, 0);
                if (nextSep < 0) {
                    top       = path;
                    remainder = null;
                }
                else {
                    // nextSep must be less than path.Length as
                    // CleanSeparators removes trailing
                    // separators.
                    assert ((path.Length >= 3) &&
                            (nextSep < path.Length - 1));
                    remainder = Bitter.SplitOff(ref path, nextSep + 1);
                    top       = DropTrailingSeparator(path);
                }
            }
        }

        /// <summary>
        /// Split path into directory name and base name components.
        ///
        /// "/a/b/c" -> "/a/b"  "c"
        /// "/a"     -> "/"     "a"
        /// "a//"    -> null    "a"
        /// "a"      -> null    "a"
        /// "/"      -> "/"     null
        /// </summary>
        public static void
        SplitPathBottomUp([Claims] char[]! in ExHeap path,
                          out char[] in ExHeap dirname,
                          out char[] in ExHeap basename)
        {
            path = CleanSeparators(path);

            int lastSep = GetLastSeparator(path);
            if (lastSep >= 0) {
                basename = Bitter.SplitOff(ref path, lastSep + 1);
                if (basename.Length == 0) {
                    delete basename;
                    basename = null;
                }
                dirname  = DropTrailingSeparator(path);
            }
            else {
                dirname  = null;
                basename = path;
            }
        }

        private static char[]! in ExHeap
        TrimInternal(
            [Claims] char[]! in ExHeap vector,
            bool                       trimStart,
            bool                       trimEnd
            )
        {
            int lower = 0;
            int upper = vector.Length - 1;

            if (trimEnd) {
                while (upper > 0 && Char.IsWhiteSpace(vector[upper])) {
                    upper--;
                }
            }

            if (trimStart) {
                while (lower <= upper && Char.IsWhiteSpace(vector[lower])) {
                    lower++;
                }
            }

            int newLength = upper - lower + 1;
            if (newLength != vector.Length) {
                Bitter.Copy(vector, 0, newLength, vector, lower);
                Bitter.Truncate(ref vector, newLength);
            }
            return vector;
        }

        private static char[]! in ExHeap
        TrimInternal(
            [Claims] char[]! in ExHeap vector,
            char []!                   trimChars,
            bool                       trimStart,
            bool                       trimEnd
            )
        {
            int lower = 0;
            int upper = vector.Length - 1;

            if (trimEnd) {
                while (upper > 0 &&
                       Array.IndexOf(trimChars, vector[upper]) >= 0) {
                    upper--;
                }
            }

            if (trimStart) {
                while (lower <= upper &&
                       Array.IndexOf(trimChars, vector[lower]) >= 0) {
                    lower++;
                }
            }

            int newLength = upper - lower + 1;
            if (newLength != vector.Length) {
                Bitter.Copy(vector, 0, newLength, vector, lower);
                Bitter.Truncate(ref vector, newLength);
            }
            return vector;
        }

        public static char[]! in ExHeap
        Trim([Claims] char[]! in ExHeap vector)
        {
            return TrimInternal(vector, true, true);
        }

        public static char[]! in ExHeap
        TrimStart([Claims] char[]! in ExHeap vector)
        {
            return TrimInternal(vector, true, false);
        }

        public static char[]! in ExHeap
        TrimEnd([Claims] char[]! in ExHeap vector)
        {
            return TrimInternal(vector, false, true);
        }

        public static char[]! in ExHeap
        Trim([Claims] char[]! in ExHeap vector, char[]! trimChars)
        {
            return TrimInternal(vector, trimChars, true, true);
        }

        public static char[]! in ExHeap
        TrimStart([Claims] char[]! in ExHeap vector, char[]! trimChars)
        {
            return TrimInternal(vector, trimChars, true, false);
        }

        public static char[]! in ExHeap
        TrimEnd([Claims] char[]! in ExHeap vector, char[]! trimChars)
        {
            return TrimInternal(vector, trimChars, false, true);
        }

        // --------------------------------------------------------------------
        // Self-test routines

        private static bool CompareChars(string expected,
                                         [Claims] char[] in ExHeap received)
        {
            string other = null;
            if (received != null) {
                other = Bitter.ToString2(received);
                delete received;
            }
            DebugStub.Assert(expected == other);
            return (expected == other);
        }

        private static void TestSplitPathBottomUp()
        {
            string [][] tests = new string [][] {
                new string [] { "/",            "/",    null },
                new string [] { "/abra/cadabra", "/abra", "cadabra" },
                new string [] { "/the///cat//sat/on//the/mat",
                                "/the/cat/sat/on/the",
                                "mat" },
                new string [] { "/a",           "/",    "a" },
                new string [] { "a//",          null,   "a" },
                new string [] { "a",            null,   "a" },
                new string [] { "////",         "/",    null },
                new string [] { "////a",        "/",    "a" },
                new string [] { "////a/b///",   "/a",    "b" },
            };

            for (int i = 0; i < tests.Length; i++) {
                string[]! values = (!)tests[i];
                DebugStub.Print("Testing {0}\n",
                                __arglist((!)values[0]));
                string! spath = (!)(values[0]);
                char[]! in ExHeap path = Bitter.FromString2(spath);
                char [] in ExHeap dirname;
                char [] in ExHeap basename;
                PathUtils.SplitPathBottomUp(path, out dirname, out basename);

                DebugStub.Assert(CompareChars(values[1], dirname));
                DebugStub.Assert(CompareChars(values[2], basename));
            }
        }

        private static void TestSplitPathTopDown()
        {
            string [][] tests = new string [][] {
                new string [] { "/abra/cadabra", "/", "abra/cadabra" },
                new string [] { "abra/cadabra", "abra", "cadabra" },
                new string [] { "/the///cat//sat/on//the/mat",
                                "/", "the/cat/sat/on/the/mat" },
                new string [] { "the///cat//sat/on//the/mat",
                                "the", "cat/sat/on/the/mat" },
                new string [] { "/a",           "/",    "a" },
                new string [] { "a",            "a",    null },
                new string [] { "/",            "/",    null },
                new string [] { "////",         "/",    null },
                new string [] { "////a/b///",   "/",    "a/b" },
            };

            for (int i = 0; i < tests.Length; i++) {
                string[]! values = (!)tests[i];
                DebugStub.Print("Testing {0}\n",
                                __arglist((!)values[0]));
                string! spath = (!)(values[0]);
                char[]! in ExHeap path = Bitter.FromString2(spath);
                char [] in ExHeap top;
                char [] in ExHeap remainder;
                PathUtils.SplitPathTopDown(path, out top, out remainder);

                DebugStub.Assert(CompareChars(values[1], top));
                DebugStub.Assert(CompareChars(values[2], remainder));
            }
        }

        internal static void SelfTest()
        {
            TestSplitPathTopDown();
            TestSplitPathBottomUp();
        }
    }
}