using System;
using System.Collections.Generic;
using System.Globalization;
using System.Linq;
using LibGit2Sharp.Core;
using LibGit2Sharp.Core.Handles;

namespace LibGit2Sharp
{
    /// <summary>
    /// Provides helper overloads to a <see cref="ReferenceCollection"/>.
    /// </summary>
    public static class ReferenceCollectionExtensions
    {
        private enum RefState
        {
            Exists,
            DoesNotExistButLooksValid,
            DoesNotLookValid,
        }

        private static RefState TryResolveReference(out Reference reference, ReferenceCollection refsColl, string canonicalName)
        {
            if (!Reference.IsValidName(canonicalName))
            {
                reference = null;
                return RefState.DoesNotLookValid;
            }

            reference = refsColl[canonicalName];

            return reference != null ? RefState.Exists : RefState.DoesNotExistButLooksValid;
        }

        /// <summary>
        /// Creates a direct or symbolic reference with the specified name and target
        /// </summary>
        /// <param name="refsColl">The <see cref="ReferenceCollection"/> being worked with.</param>
        /// <param name="name">The name of the reference to create.</param>
        /// <param name="canonicalRefNameOrObjectish">The target which can be either the canonical name of a reference or a revparse spec.</param>
        /// <param name="logMessage">The optional message to log in the <see cref="ReflogCollection"/> when adding the <see cref="Reference"/></param>
        /// <returns>A new <see cref="Reference"/>.</returns>
        public static Reference Add(this ReferenceCollection refsColl, string name, string canonicalRefNameOrObjectish,
            string logMessage)
        {
            return refsColl.Add(name, canonicalRefNameOrObjectish, logMessage, false);
        }

        /// <summary>
        /// Creates a direct or symbolic reference with the specified name and target
        /// </summary>
        /// <param name="refsColl">The <see cref="ReferenceCollection"/> being worked with.</param>
        /// <param name="name">The name of the reference to create.</param>
        /// <param name="canonicalRefNameOrObjectish">The target which can be either the canonical name of a reference or a revparse spec.</param>
        /// <param name="logMessage">The optional message to log in the <see cref="ReflogCollection"/> when adding the <see cref="Reference"/></param>
        /// <param name="allowOverwrite">True to allow silent overwriting a potentially existing reference, false otherwise.</param>
        /// <returns>A new <see cref="Reference"/>.</returns>
        public static Reference Add(this ReferenceCollection refsColl, string name, string canonicalRefNameOrObjectish, string logMessage, bool allowOverwrite)
        {
            Ensure.ArgumentNotNullOrEmptyString(name, "name");
            Ensure.ArgumentNotNullOrEmptyString(canonicalRefNameOrObjectish, "canonicalRefNameOrObjectish");

            Reference reference;
            RefState refState = TryResolveReference(out reference, refsColl, canonicalRefNameOrObjectish);

            var gitObject = refsColl.repo.Lookup(canonicalRefNameOrObjectish, GitObjectType.Any, LookUpOptions.None);

            if (refState == RefState.Exists)
            {
                return refsColl.Add(name, reference, logMessage, allowOverwrite);
            }

            if (refState == RefState.DoesNotExistButLooksValid && gitObject == null)
            {
                using (ReferenceSafeHandle handle = Proxy.git_reference_symbolic_create(refsColl.repo.Handle, name, canonicalRefNameOrObjectish, allowOverwrite,
                    logMessage))
                {
                    return Reference.BuildFromPtr<Reference>(handle, refsColl.repo);
                }
            }

            Ensure.GitObjectIsNotNull(gitObject, canonicalRefNameOrObjectish);

            if (logMessage == null)
            {
                logMessage = string.Format(CultureInfo.InvariantCulture, "{0}: Created from {1}",
                    name.LooksLikeLocalBranch() ? "branch" : "reference", canonicalRefNameOrObjectish);
            }

            refsColl.EnsureHasLog(name);
            return refsColl.Add(name, gitObject.Id, logMessage, allowOverwrite);
        }


        /// <summary>
        /// Creates a direct or symbolic reference with the specified name and target
        /// </summary>
        /// <param name="refsColl">The <see cref="ReferenceCollection"/> being worked with.</param>
        /// <param name="name">The name of the reference to create.</param>
        /// <param name="canonicalRefNameOrObjectish">The target which can be either the canonical name of a reference or a revparse spec.</param>
        /// <returns>A new <see cref="Reference"/>.</returns>
        public static Reference Add(this ReferenceCollection refsColl, string name, string canonicalRefNameOrObjectish)
        {
            return Add(refsColl, name, canonicalRefNameOrObjectish, null, false);
        }

        /// <summary>
        /// Creates a direct or symbolic reference with the specified name and target
        /// </summary>
        /// <param name="refsColl">The <see cref="ReferenceCollection"/> being worked with.</param>
        /// <param name="name">The name of the reference to create.</param>
        /// <param name="canonicalRefNameOrObjectish">The target which can be either the canonical name of a reference or a revparse spec.</param>
        /// <param name="allowOverwrite">True to allow silent overwriting a potentially existing reference, false otherwise.</param>
        /// <returns>A new <see cref="Reference"/>.</returns>
        public static Reference Add(this ReferenceCollection refsColl, string name, string canonicalRefNameOrObjectish, bool allowOverwrite)
        {
            return Add(refsColl, name, canonicalRefNameOrObjectish, null, allowOverwrite);
        }

        /// <summary>
        /// Updates the target of a direct reference.
        /// </summary>
        /// <param name="refsColl">The <see cref="ReferenceCollection"/> being worked with.</param>
        /// <param name="directRef">The direct reference which target should be updated.</param>
        /// <param name="objectish">The revparse spec of the target.</param>
        /// <param name="logMessage">The optional message to log in the <see cref="ReflogCollection"/></param>
        /// <returns>A new <see cref="Reference"/>.</returns>
        public static Reference UpdateTarget(this ReferenceCollection refsColl, Reference directRef, string objectish, string logMessage)
        {
            Ensure.ArgumentNotNull(directRef, "directRef");
            Ensure.ArgumentNotNull(objectish, "objectish");

            GitObject target = refsColl.repo.Lookup(objectish);

            Ensure.GitObjectIsNotNull(target, objectish);

            return refsColl.UpdateTarget(directRef, target.Id, logMessage);
        }

        /// <summary>
        /// Updates the target of a direct reference
        /// </summary>
        /// <param name="refsColl">The <see cref="ReferenceCollection"/> being worked with.</param>
        /// <param name="directRef">The direct reference which target should be updated.</param>
        /// <param name="objectish">The revparse spec of the target.</param>
        /// <returns>A new <see cref="Reference"/>.</returns>
        public static Reference UpdateTarget(this ReferenceCollection refsColl, Reference directRef, string objectish)
        {
            return UpdateTarget(refsColl, directRef, objectish, null);
        }

        /// <summary>
        /// Rename an existing reference with a new name
        /// </summary>
        /// <param name="currentName">The canonical name of the reference to rename.</param>
        /// <param name="newName">The new canonical name.</param>
        /// <param name="refsColl">The <see cref="ReferenceCollection"/> being worked with.</param>
        /// <returns>A new <see cref="Reference"/>.</returns>
        public static Reference Rename(this ReferenceCollection refsColl, string currentName, string newName)
        {
            return refsColl.Rename(currentName, newName, null, false);
        }

        /// <summary>
        /// Rename an existing reference with a new name
        /// </summary>
        /// <param name="currentName">The canonical name of the reference to rename.</param>
        /// <param name="newName">The new canonical name.</param>
        /// <param name="allowOverwrite">True to allow silent overwriting a potentially existing reference, false otherwise.</param>
        /// <param name="refsColl">The <see cref="ReferenceCollection"/> being worked with.</param>
        /// <returns>A new <see cref="Reference"/>.</returns>
        public static Reference Rename(this ReferenceCollection refsColl, string currentName, string newName,
            bool allowOverwrite)
        {
            return refsColl.Rename(currentName, newName, null, allowOverwrite);
        }

        /// <summary>
        /// Rename an existing reference with a new name
        /// </summary>
        /// <param name="currentName">The canonical name of the reference to rename.</param>
        /// <param name="newName">The new canonical name.</param>
        /// <param name="logMessage">The optional message to log in the <see cref="ReflogCollection"/></param>
        /// <param name="refsColl">The <see cref="ReferenceCollection"/> being worked with.</param>
        /// <returns>A new <see cref="Reference"/>.</returns>
        public static Reference Rename(this ReferenceCollection refsColl, string currentName, string newName,
            string logMessage)
        {
            return refsColl.Rename(currentName, newName, logMessage, false);
        }

        /// <summary>
        /// Rename an existing reference with a new name
        /// </summary>
        /// <param name="currentName">The canonical name of the reference to rename.</param>
        /// <param name="newName">The new canonical name.</param>
        /// <param name="logMessage">The optional message to log in the <see cref="ReflogCollection"/></param>
        /// <param name="allowOverwrite">True to allow silent overwriting a potentially existing reference, false otherwise.</param>
        /// <param name="refsColl">The <see cref="ReferenceCollection"/> being worked with.</param>
        /// <returns>A new <see cref="Reference"/>.</returns>
        public static Reference Rename(this ReferenceCollection refsColl, string currentName, string newName,
            string logMessage, bool allowOverwrite)
        {
            Ensure.ArgumentNotNullOrEmptyString(currentName, "currentName");

            Reference reference = refsColl[currentName];

            if (reference == null)
            {
                throw new LibGit2SharpException(
                    string.Format(CultureInfo.InvariantCulture,
                        "Reference '{0}' doesn't exist. One cannot move a non existing reference.", currentName));
            }

            return refsColl.Rename(reference, newName, logMessage, allowOverwrite);
        }

        /// <summary>
        /// Updates the target of a reference
        /// </summary>
        /// <param name="refsColl">The <see cref="ReferenceCollection"/> being worked with.</param>
        /// <param name="name">The canonical name of the reference.</param>
        /// <param name="canonicalRefNameOrObjectish">The target which can be either the canonical name of a reference or a revparse spec.</param>
        /// <param name="logMessage">The optional message to log in the <see cref="ReflogCollection"/> of the <paramref name="name"/> reference.</param>
        /// <returns>A new <see cref="Reference"/>.</returns>
        public static Reference UpdateTarget(this ReferenceCollection refsColl, string name, string canonicalRefNameOrObjectish, string logMessage)
        {
            Ensure.ArgumentNotNullOrEmptyString(name, "name");
            Ensure.ArgumentNotNullOrEmptyString(canonicalRefNameOrObjectish, "canonicalRefNameOrObjectish");

            if (name == "HEAD")
            {
                return refsColl.UpdateHeadTarget(canonicalRefNameOrObjectish, logMessage);
            }

            Reference reference = refsColl[name];

            var directReference = reference as DirectReference;
            if (directReference != null)
            {
                return refsColl.UpdateTarget(directReference, canonicalRefNameOrObjectish, logMessage);
            }

            var symbolicReference = reference as SymbolicReference;
            if (symbolicReference != null)
            {
                Reference targetRef;

                RefState refState = TryResolveReference(out targetRef, refsColl, canonicalRefNameOrObjectish);

                if (refState == RefState.DoesNotLookValid)
                {
                    throw new ArgumentException(String.Format(CultureInfo.InvariantCulture, "The reference specified by {0} is a Symbolic reference, you must provide a reference canonical name as the target.", name), "canonicalRefNameOrObjectish");
                }

                return refsColl.UpdateTarget(symbolicReference, targetRef, logMessage);
            }

            throw new LibGit2SharpException(string.Format(CultureInfo.InvariantCulture, "Reference '{0}' has an unexpected type ('{1}').", name, reference.GetType()));
        }

        /// <summary>
        /// Updates the target of a reference
        /// </summary>
        /// <param name="refsColl">The <see cref="ReferenceCollection"/> being worked with.</param>
        /// <param name="name">The canonical name of the reference.</param>
        /// <param name="canonicalRefNameOrObjectish">The target which can be either the canonical name of a reference or a revparse spec.</param>
        /// <returns>A new <see cref="Reference"/>.</returns>
        public static Reference UpdateTarget(this ReferenceCollection refsColl, string name, string canonicalRefNameOrObjectish)
        {
            return UpdateTarget(refsColl, name, canonicalRefNameOrObjectish, null);
        }

        /// <summary>
        /// Delete a reference with the specified name
        /// </summary>
        /// <param name="refsColl">The <see cref="ReferenceCollection"/> being worked with.</param>
        /// <param name="name">The canonical name of the reference to delete.</param>
        public static void Remove(this ReferenceCollection refsColl, string name)
        {
            Ensure.ArgumentNotNullOrEmptyString(name, "name");

            Reference reference = refsColl[name];

            if (reference == null)
            {
                return;
            }

            refsColl.Remove(reference);
        }

        /// <summary>
        /// Find the <see cref="Reference"/>s among <paramref name="refSubset"/>
        /// that can reach at least one <see cref="Commit"/> in the specified <paramref name="targets"/>.
        /// </summary>
        /// <param name="refsColl">The <see cref="ReferenceCollection"/> being worked with.</param>
        /// <param name="refSubset">The set of <see cref="Reference"/>s to examine.</param>
        /// <param name="targets">The set of <see cref="Commit"/>s that are interesting.</param>
        /// <returns>A subset of <paramref name="refSubset"/> that can reach at least one <see cref="Commit"/> within <paramref name="targets"/>.</returns>
        public static IEnumerable<Reference> ReachableFrom(
            this ReferenceCollection refsColl,
            IEnumerable<Reference> refSubset,
            IEnumerable<Commit> targets)
        {
            Ensure.ArgumentNotNull(refSubset, "refSubset");
            Ensure.ArgumentNotNull(targets, "targets");

            var refs = new List<Reference>(refSubset);
            if (refs.Count == 0)
            {
                return Enumerable.Empty<Reference>();
            }

            List<ObjectId> targetsSet = targets.Select(c => c.Id).Distinct().ToList();
            if (targetsSet.Count == 0)
            {
                return Enumerable.Empty<Reference>();
            }

            var result = new List<Reference>();

            foreach (var reference in refs)
            {
                var peeledTargetCommit = reference
                                            .ResolveToDirectReference()
                                            .Target.DereferenceToCommit(false);

                if (peeledTargetCommit == null)
                {
                    continue;
                }

                var commitId = peeledTargetCommit.Id;

                foreach (var potentialAncestorId in targetsSet)
                {
                    if (potentialAncestorId == commitId)
                    {
                        result.Add(reference);
                        break;
                    }

                    if (Proxy.git_graph_descendant_of(refsColl.repo.Handle, commitId, potentialAncestorId))
                    {
                        result.Add(reference);
                        break;
                    }
                }
            }

            return result;
        }

        /// <summary>
        /// Find the <see cref="Reference"/>s
        /// that can reach at least one <see cref="Commit"/> in the specified <paramref name="targets"/>.
        /// </summary>
        /// <param name="refsColl">The <see cref="ReferenceCollection"/> being worked with.</param>
        /// <param name="targets">The set of <see cref="Commit"/>s that are interesting.</param>
        /// <returns>The list of <see cref="Reference"/> that can reach at least one <see cref="Commit"/> within <paramref name="targets"/>.</returns>
        public static IEnumerable<Reference> ReachableFrom(
            this ReferenceCollection refsColl,
            IEnumerable<Commit> targets)
        {
            return ReachableFrom(refsColl, refsColl, targets);
        }
    }
}