using System;
using System.Collections.Generic;
using System.Linq;

namespace Jovian.EncounterSystem {
    /// <summary>Tag for a quest log entry.</summary>
    public enum QuestLogEventType {
        Started,
        Advanced,
        Completed
    }

    /// <summary>
    /// One chronological entry in the quest log. Names are cached alongside ids so a loaded save
    /// can display the log even if the underlying encounter has since been renamed or removed.
    /// </summary>
    [Serializable]
    public class QuestLogEntry {
        public QuestLogEventType type;
        public string encounterInternalId;
        public string encounterName;
        public string fromEncounterName;
    }

    /// <summary>
    /// Chronological, serializable record of quest events. Subscribes to <see cref="QuestProgress"/>
    /// events at construction time — build it before any encounter fires so nothing is missed.
    /// </summary>
    /// <remarks>
    /// This is the save payload for quest progression. On load, call <see cref="Restore"/> with the
    /// saved entries and then <see cref="QuestProgress.LoadResolvedIds"/> with
    /// <see cref="ResolvedEncounterIds"/> to rehydrate the gating set.
    /// </remarks>
    public class QuestLog {
        private readonly List<QuestLogEntry> entries = new();

        /// <summary>The log in chronological order.</summary>
        public IReadOnlyList<QuestLogEntry> Entries => entries;

        /// <summary>Subscribe to <paramref name="progress"/>'s quest events; every fire appends an entry.</summary>
        public QuestLog(QuestProgress progress) {
            progress.QuestStarted += quest => Record(QuestLogEventType.Started, null, quest);
            progress.QuestAdvanced += (from, to) => Record(QuestLogEventType.Advanced, from, to);
            progress.QuestCompleted += quest => Record(QuestLogEventType.Completed, null, quest);
        }

        /// <summary>Return a copy of the current entries suitable for serialization.</summary>
        public List<QuestLogEntry> CreateSnapshot() {
            return new List<QuestLogEntry>(entries);
        }

        /// <summary>Replace the current entries with those from a save. Pass the list straight from
        /// the save payload.</summary>
        public void Restore(IEnumerable<QuestLogEntry> saved) {
            entries.Clear();
            if(saved == null) {
                return;
            }

            entries.AddRange(saved);
        }

        /// <summary>Enumerate the distinct encounter ids present in the log — what
        /// <see cref="QuestProgress.LoadResolvedIds"/> needs on load.</summary>
        public IEnumerable<string> ResolvedEncounterIds() {
            return entries
                .Select(entry => entry.encounterInternalId)
                .Where(id => !string.IsNullOrEmpty(id));
        }

        private void Record(QuestLogEventType type, IEncounter from, IEncounter to) {
            entries.Add(new QuestLogEntry {
                type = type,
                encounterInternalId = to?.EncounterDefinition?.internalId,
                encounterName = to?.EncounterDefinition?.name,
                fromEncounterName = from?.EncounterDefinition?.name
            });
        }
    }
}