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

namespace LibGit2Sharp
{
    /// <summary>
    /// Provides access to configuration variables for a repository.
    /// </summary>
    public class Configuration : IDisposable,
        IEnumerable<ConfigurationEntry<string>>
    {
        private readonly FilePath globalConfigPath;
        private readonly FilePath xdgConfigPath;
        private readonly FilePath systemConfigPath;

        private readonly Repository repository;

        private ConfigurationSafeHandle configHandle;

        /// <summary>
        /// Needed for mocking purposes.
        /// </summary>
        protected Configuration()
        { }

        internal Configuration(Repository repository, string globalConfigurationFileLocation,
            string xdgConfigurationFileLocation, string systemConfigurationFileLocation)
        {
            this.repository = repository;

            globalConfigPath = globalConfigurationFileLocation ?? Proxy.git_config_find_global();
            xdgConfigPath = xdgConfigurationFileLocation ?? Proxy.git_config_find_xdg();
            systemConfigPath = systemConfigurationFileLocation ?? Proxy.git_config_find_system();

            Init();
        }

        private void Init()
        {
            configHandle = Proxy.git_config_new();

            if (repository != null)
            {
                //TODO: push back this logic into libgit2.
                // As stated by @carlosmn "having a helper function to load the defaults and then allowing you
                // to modify it before giving it to git_repository_open_ext() would be a good addition, I think."
                //  -- Agreed :)
                string repoConfigLocation = Path.Combine(repository.Info.Path, "config");
                Proxy.git_config_add_file_ondisk(configHandle, repoConfigLocation, ConfigurationLevel.Local);

                Proxy.git_repository_set_config(repository.Handle, configHandle);
            }

            if (globalConfigPath != null)
            {
                Proxy.git_config_add_file_ondisk(configHandle, globalConfigPath, ConfigurationLevel.Global);
            }

            if (xdgConfigPath != null)
            {
                Proxy.git_config_add_file_ondisk(configHandle, xdgConfigPath, ConfigurationLevel.Xdg);
            }

            if (systemConfigPath != null)
            {
                Proxy.git_config_add_file_ondisk(configHandle, systemConfigPath, ConfigurationLevel.System);
            }
        }

        /// <summary>
        /// Access configuration values without a repository. Generally you want to access configuration via an instance of <see cref="Repository"/> instead.
        /// </summary>
        /// <param name="globalConfigurationFileLocation">Path to a Global configuration file. If null, the default path for a global configuration file will be probed.</param>
        /// <param name="xdgConfigurationFileLocation">Path to a XDG configuration file. If null, the default path for a XDG configuration file will be probed.</param>
        /// <param name="systemConfigurationFileLocation">Path to a System configuration file. If null, the default path for a system configuration file will be probed.</param>
        public Configuration(string globalConfigurationFileLocation = null, string xdgConfigurationFileLocation = null, string systemConfigurationFileLocation = null)
            : this(null, globalConfigurationFileLocation, xdgConfigurationFileLocation, systemConfigurationFileLocation)
        {
        }

        /// <summary>
        /// Determines which configuration file has been found.
        /// </summary>
        public virtual bool HasConfig(ConfigurationLevel level)
        {
            using (ConfigurationSafeHandle handle = RetrieveConfigurationHandle(level, false))
            {
                return handle != null;
            }
        }

        #region IDisposable Members

        /// <summary>
        /// Performs application-defined tasks associated with freeing, releasing, or resetting unmanaged resources.
        /// Saves any open configuration files.
        /// </summary>
        public void Dispose()
        {
            Dispose(true);
            GC.SuppressFinalize(this);
        }

        #endregion

        /// <summary>
        /// Unset a configuration variable (key and value).
        /// </summary>
        /// <param name="key">The key to unset.</param>
        /// <param name="level">The configuration file which should be considered as the target of this operation</param>
        public virtual void Unset(string key, ConfigurationLevel level = ConfigurationLevel.Local)
        {
            Ensure.ArgumentNotNullOrEmptyString(key, "key");

            using (ConfigurationSafeHandle h = RetrieveConfigurationHandle(level, true))
            {
                Proxy.git_config_delete(h, key);
            }
        }

        /// <summary>
        /// Performs application-defined tasks associated with freeing, releasing, or resetting unmanaged resources.
        /// </summary>
        protected virtual void Dispose(bool disposing)
        {
            configHandle.SafeDispose();
        }

        /// <summary>
        /// Get a configuration value for a key. Keys are in the form 'section.name'.
        /// <para>
        ///    The same escalation logic than in git.git will be used when looking for the key in the config files:
        ///       - local: the Git file in the current repository
        ///       - global: the Git file specific to the current interactive user (usually in `$HOME/.gitconfig`)
        ///       - xdg: another Git file specific to the current interactive user (usually in `$HOME/.config/git/config`)
        ///       - system: the system-wide Git file
        ///
        ///   The first occurence of the key will be returned.
        /// </para>
        /// <para>
        ///   For example in order to get the value for this in a .git\config file:
        ///
        ///   <code>
        ///   [core]
        ///   bare = true
        ///   </code>
        ///
        ///   You would call:
        ///
        ///   <code>
        ///   bool isBare = repo.Config.Get&lt;bool&gt;("core.bare").Value;
        ///   </code>
        /// </para>
        /// </summary>
        /// <typeparam name="T">The configuration value type</typeparam>
        /// <param name="key">The key</param>
        /// <returns>The <see cref="ConfigurationEntry{T}"/>, or null if not set</returns>
        public virtual ConfigurationEntry<T> Get<T>(string key)
        {
            Ensure.ArgumentNotNullOrEmptyString(key, "key");

            return Proxy.git_config_get_entry<T>(configHandle, key);
        }

        /// <summary>
        /// Get a configuration value for a key. Keys are in the form 'section.name'.
        /// <para>
        ///   For example in order to get the value for this in a .git\config file:
        ///
        ///   <code>
        ///   [core]
        ///   bare = true
        ///   </code>
        ///
        ///   You would call:
        ///
        ///   <code>
        ///   bool isBare = repo.Config.Get&lt;bool&gt;("core.bare").Value;
        ///   </code>
        /// </para>
        /// </summary>
        /// <typeparam name="T">The configuration value type</typeparam>
        /// <param name="key">The key</param>
        /// <param name="level">The configuration file into which the key should be searched for</param>
        /// <returns>The <see cref="ConfigurationEntry{T}"/>, or null if not set</returns>
        public virtual ConfigurationEntry<T> Get<T>(string key, ConfigurationLevel level)
        {
            Ensure.ArgumentNotNullOrEmptyString(key, "key");

            using (ConfigurationSafeHandle handle = RetrieveConfigurationHandle(level, false))
            {
                if (handle == null)
                {
                    return null;
                }

                return Proxy.git_config_get_entry<T>(handle, key);
            }
        }

        /// <summary>
        /// Set a configuration value for a key. Keys are in the form 'section.name'.
        /// <para>
        ///   For example in order to set the value for this in a .git\config file:
        ///
        ///   [test]
        ///   boolsetting = true
        ///
        ///   You would call:
        ///
        ///   repo.Config.Set("test.boolsetting", true);
        /// </para>
        /// </summary>
        /// <typeparam name="T">The configuration value type</typeparam>
        /// <param name="key">The key parts</param>
        /// <param name="value">The value</param>
        /// <param name="level">The configuration file which should be considered as the target of this operation</param>
        public virtual void Set<T>(string key, T value, ConfigurationLevel level = ConfigurationLevel.Local)
        {
            Ensure.ArgumentNotNullOrEmptyString(key, "key");

            using (ConfigurationSafeHandle h = RetrieveConfigurationHandle(level, true))
            {
                if (!configurationTypedUpdater.ContainsKey(typeof(T)))
                {
                    throw new ArgumentException(string.Format(CultureInfo.InvariantCulture, "Generic Argument of type '{0}' is not supported.", typeof(T).FullName));
                }

                configurationTypedUpdater[typeof(T)](key, value, h);
            }
        }

        /// <summary>
        /// Find configuration entries matching <paramref name="regexp"/>.
        /// </summary>
        /// <param name="regexp">A regular expression.</param>
        /// <param name="level">The configuration file into which the key should be searched for.</param>
        /// <returns>Matching entries.</returns>
        public virtual IEnumerable<ConfigurationEntry<string>> Find(string regexp,
                                                                     ConfigurationLevel level = ConfigurationLevel.Local)
        {
            Ensure.ArgumentNotNullOrEmptyString(regexp, "regexp");

            using (ConfigurationSafeHandle h = RetrieveConfigurationHandle(level, true))
            {
                return Proxy.git_config_iterator_glob(h, regexp, BuildConfigEntry).ToList();
            }
        }

        private ConfigurationSafeHandle RetrieveConfigurationHandle(ConfigurationLevel level, bool throwIfStoreHasNotBeenFound)
        {
            ConfigurationSafeHandle handle = null;
            if (configHandle != null)
            {
                handle = Proxy.git_config_open_level(configHandle, level);
            }

            if (handle == null && throwIfStoreHasNotBeenFound)
            {
                throw new LibGit2SharpException(
                    string.Format(CultureInfo.InvariantCulture, "No {0} configuration file has been found.",
                    Enum.GetName(typeof(ConfigurationLevel), level)));
            }

            return handle;
        }

        private static Action<string, object, ConfigurationSafeHandle> GetUpdater<T>(Action<ConfigurationSafeHandle, string, T> setter)
        {
            return (key, val, handle) => setter(handle, key, (T)val);
        }

        private readonly static IDictionary<Type, Action<string, object, ConfigurationSafeHandle>> configurationTypedUpdater = new Dictionary<Type, Action<string, object, ConfigurationSafeHandle>>
        {
            { typeof(int), GetUpdater<int>(Proxy.git_config_set_int32) },
            { typeof(long), GetUpdater<long>(Proxy.git_config_set_int64) },
            { typeof(bool), GetUpdater<bool>(Proxy.git_config_set_bool) },
            { typeof(string), GetUpdater<string>(Proxy.git_config_set_string) },
        };

        /// <summary>
        /// Returns an enumerator that iterates through the configuration entries.
        /// </summary>
        /// <returns>An <see cref="IEnumerator{T}"/> object that can be used to iterate through the configuration entries.</returns>
        public virtual IEnumerator<ConfigurationEntry<string>> GetEnumerator()
        {
            return BuildConfigEntries().GetEnumerator();
        }

        System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator()
        {
            return ((IEnumerable<ConfigurationEntry<string>>)this).GetEnumerator();
        }

        private IEnumerable<ConfigurationEntry<string>> BuildConfigEntries()
        {
            return Proxy.git_config_foreach(configHandle, BuildConfigEntry);
        }

        private static ConfigurationEntry<string> BuildConfigEntry(IntPtr entryPtr)
        {
            var entry = entryPtr.MarshalAs<GitConfigEntry>();

            return new ConfigurationEntry<string>(LaxUtf8Marshaler.FromNative(entry.namePtr),
                                                  LaxUtf8Marshaler.FromNative(entry.valuePtr),
                                                  (ConfigurationLevel)entry.level);
        }

        /// <summary>
        /// Builds a <see cref="Signature"/> based on current configuration.
        /// <para>
        ///    Name is populated from the user.name setting, and is "unknown" if unspecified.
        ///    Email is populated from the user.email setting, and is built from
        ///    <see cref="Environment.UserName"/> and <see cref="Environment.UserDomainName"/> if unspecified.
        /// </para>
        /// <para>
        ///    The same escalation logic than in git.git will be used when looking for the key in the config files:
        ///       - local: the Git file in the current repository
        ///       - global: the Git file specific to the current interactive user (usually in `$HOME/.gitconfig`)
        ///       - xdg: another Git file specific to the current interactive user (usually in `$HOME/.config/git/config`)
        ///       - system: the system-wide Git file
        /// </para>
        /// </summary>
        /// <param name="now">The timestamp to use for the <see cref="Signature"/>.</param>
        /// <returns>The signature.</returns>
        public virtual Signature BuildSignature(DateTimeOffset now)
        {
            return BuildSignature(now, false);
        }

        internal Signature BuildSignature(DateTimeOffset now, bool shouldThrowIfNotFound)
        {
            var name = Get<string>("user.name");
            var email = Get<string>("user.email");

            if (shouldThrowIfNotFound && ((name == null) || (email == null)))
            {
                throw new LibGit2SharpException("Can not find Name or Email setting of the current user in Git configuration.");
            }

            return new Signature(
                name != null ? name.Value : "unknown",
                email != null ? email.Value : string.Format(
                        CultureInfo.InvariantCulture, "{0}@{1}", Environment.UserName, Environment.UserDomainName),
                now);
        }
    }
}